ENCYCLOPEDIA OF DAIRY SCIENCES SECOND EDITION
ENCYCLOPEDIA OF DAIRY SCIENCES SECOND EDITION Editor-in-Chief John W. Fuquay Mississippi State University, Mississippi State, MS, USA
Editors Patrick F. Fox University College, Cork, Ireland
Paul L. H. McSweeney University College, Cork, Ireland
AMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK OXFORD PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO Academic Press is an imprint of Elsevier
Academic Press is an imprint of Elsevier 32 Jamestown Road, London NW1 7BY, UK The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK 525 B Street, Suite 1900, San Diego, CA 92101-4495, USA Copyright Ó 2011 Elsevier Ltd. All rights reserved The following articles are US Government works in the public domain and are not subject to copyright: ANALYTICAL METHODS: DNA-Based Assays DISEASES OF DAIRY ANIMALS: Infectious Diseases: Johne’s Disease FEED INGREDIENTS: Feed Concentrates: Co-Product Feeds GENETICS: Selection: Evaluation and Methods; International Flow of Genes LACTATION: Galactopoiesis, Effects of Hormones and Growth Factors; Galactopoiesis, Effect of Treatment with Bovine Somatotropin No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the publisher. Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone (+44) (0) 1865 843830; fax (+44) (0) 1865 853333; email:
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EDITORS’ BIOGRAPHIES
John W. Fuquay, Professor Emeritus of Dairy Science at Mississippi State University, served on the faculty there from 1969 to 1999. His areas of emphasis in teaching and research were environmental physiology and reproductive physiology. He received his BS and MS degrees from North Carolina State University and his PhD degree from Pennsylvania State University, all in the area of dairy science. After completing the PhD degree in 1969, he accepted a teaching and research position at Mississippi State University, where he progressed through the ranks from assistant professor to professor before retiring in 1999. Professor Fuquay served as Coordinator for the Graduate Program in Animal Physiology from 1986 to 1999. He was a Visiting Professor in the Animal Sciences Department, University of California-Davis in 1979 and in 1985–86. Professor Fuquay was active in his professional society, The American Dairy Science Association. He was a member of the editorial board of Journal of Dairy Science for seven years, an editor for four years, and served as the first Editor-in-Chief for six years (1997–2002). For his professional contributions and service to the Association, Professor Fuquay was recognized as a Fellow in the American Dairy Science Association in 2001 and received the Association’s Award of Honor in 2002. Other recognitions include the World Association of Animal Production Jean Boyazoglu Award in 2003, the Distinguished Dairy Science Alumnus Award from Pennsylvania State University in 2003, and several teaching and research awards from his university. Professor Fuquay has participated in a variety of international activities. He has presented short courses and lectures as well as provided consultations in a number of countries, primarily in Asia and Latin America. In addition to his research publications, he is the coauthor of a textbook, Applied Animal Reproduction (Prentice Hall), that has been widely used by universities in the United States and internationally. The first edition was published in 1980 and the last (sixth) edition in 2004. In 2010, he published a memoir, Musings of a Depression-Era Southern Farm Boy (Vantage Press), which reflects on how the experience of growing up on a farm in the southern United States during the great depression instills one with an understanding of the importance of strong family bonds and a sound work ethic in meeting the challenges of the adult world.
Patrick F. Fox was Professor and Head of the Department of Food Chemistry at University College, Cork (UCC), Ireland, from 1969 to 1997; he retired in December 1997 and is now Emeritus Professor of Food Chemistry at UCC. Prof. Fox received his BSc degree in Dairy Science from UCC in 1959 and PhD degree in Food Chemistry from Cornell University in 1964. After postdoctoral periods in Biochemistry at Michigan State University and in Food Biochemistry at the University of California, Davis, he returned to Ireland in 1967 to take up a research position at the Dairy Products Research Centre at Moorepark before moving to UCC in 1969. Prof. Fox’s research has focused on the biochemistry of cheese, the heat stability of milk, physicochemical properties of milk proteins, and food enzymology. He has authored or coauthored about 520 research and review papers, and authored or edited 25 text books on Dairy Chemistry. He was one of the founding editors of the International Dairy Journal. In recognition of his work, Prof. Fox has received the Research & Innovation Award of the (Irish) National Board for Science and Technology (1983), the Miles-Marschall Award of the American Dairy Science Association (1987), Medal of Honour, University of Helsinki (1991), the DSc degree of the National University of Ireland (1993), the Senior Medal for Agricultural & Food Chemistry of the Royal Society for Chemistry (2000), the ISI Highly Cited Award in Agricultural Science (2002), the International Dairy Federation Award (2002), Gold Medal of the UK Society of Dairy Technology (2007), and an autobiography published in Annual Review of Food Science & Technology (2011). Prof. Fox has been invited to lecture in various countries around the world. He has served in various capacities with the International Dairy Federation, including President of Commission F (Science, Nutrition and Education) from 1980 to 1983.
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Editors’ Biographies
Paul McSweeney is Professor of Food Chemistry in the School of Food and Nutritional Sciences, University College, Cork, Ireland (UCC). He graduated with a BSc degree in Food Science and Technology in 1990 and a PhD degree in Food Chemistry from UCC in 1993 and also has an MA in Ancient Classics. He worked for a year in the University of Wisconsin (1991–92) as part of his PhD and as a postdoctoral research scientist in UCC (1993–94). He was appointed to the academic staff of UCC in 1995. The overall theme of his research is dairy biochemistry with particular reference to factors affecting cheese flavor and proteolysis during cheese maturation including the role of non-starter lactic acid bacteria and smear microorganisms, the ripening of hybrid and non-Cheddar varieties, the specificity of proteinases on the caseins, proteolysis and lipolysis in cheese during ripening, and characterization of enzymes important to cheese ripening (proteinases, peptidases, amino acid catabolic enzymes). He is the coauthor or coeditor of eight books, including the third edition of Cheese: Chemistry, Physics and Microbiology (Amsterdam, 2004) and the Advanced Dairy Chemistry Series (New York, 2003, 2006, 2009), and has published numerous research papers and reviews. Prof. McSweeney is an experienced lecturer and researcher and has successfully managed research projects funded through the Food Industry Research Measure and its predecessors administered by the Irish Department of Agriculture and Food, the EU Framework Programmes, the US–Ireland Co-operative Programme in Agriculture/Food Science and Technology, and Bioresearch Ireland and Industry. He was awarded the Marschall Danisco International Dairy Science Award of the American Dairy Science Association in 2004 and in 2009 a higher doctorate (DSc) on published work by the National University of Ireland.
EDITORIAL ADVISORY BOARD
Ryozo Akuzawa Nippon Veterinary and Life Sciences University, Tokyo, Japan Arie Brand Utrecht University, Utrecht, The Netherlands Hilton Deeth University of Queensland, Brisbane, QLD, Australia Cathy Donnelly University of Vermont, Burlington, VT, USA Nana Farkye California Polytechnic State University, San Luis Obispo, CA, USA Harsharn Gill Department of Primary Industries, Melbourne, VIC, Australia Marco Gobbetti University of Bari, Bari, Italy Mansel Griffiths University of Guelph, Guelph, ON, Canada T P Guinee Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland
Michael Keane University College, Cork, Ireland Hannu Korhonen MTT Agrifood Research Finland, Jokioinen, Finland Sylvie Lortal INRA Rennes, Rennes, France John P McNamara Washington State University, Pullman, WA, USA Vikram Mistry South Dakota State University, Brookings, SD, USA Stephen C Nickerson University of Georgia, Athens, GA, USA Donatus Nohr University of Hohenheim, Stuttgart, Germany Jorge C Oliveira University College, Cork, Ireland Robert R Peters University of Maryland, College Park, MD, USA Morten D Rasmussen Aarhus University, Tjele, Denmark Geoffrey E. Robards Glenbrook, NSW, Australia
George F W Haenlein University of Delaware, Newark, DE, USA
John Roche DairyNZ Ltd, Hamilton, New Zealand
Peter Hansen University of Florida, Gainesville, FL, USA
Hubert Roginski University of Melbourne, Melbourne, VIC, Australia
Claus Heggum Danish Agriculture & Food Council, Aarhus, Denmark
Harald Rohm Technical University of Dresden, Dresden, Germany
Thom Huppertz NIZO Food Research, Ede, The Netherlands
Harjinder Singh Massey University, Palmerston North, New Zealand
Erica Hynes Universidad Nacional del Litoral, Santa Fe, Argentina
George R Wiggans United States Department of Agriculture, Beltsville, MD, USA
Paul Jelen University of Alberta, Edmonton, AB, Canada
Andrew Wilbey University of Reading, Reading, UK
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CONTRIBUTORS A Abbas University College, Cork, Ireland M H Abd El-Salam National Research Center, Cairo, Egypt C F Afonso University of Porto, Porto, Portugal S A Aherne University College, Cork, Ireland A Ahmadzadeh University of Idaho, Moscow, ID, USA S L Aitken Michigan State University, East Lansing, MI, USA R M Akers Virginia Polytechnic Institute and State University, Blacksburg, VA, USA R Akuzawa Nippon Veterinary and Life Science University, Tokyo, Japan G A Alhadrami UAE University, Al-Ain, United Arab Emirates R A Almeida The University of Tennessee, Knoxville, TN, USA V B Alvarez The Ohio State University, Columbus, OH, USA L Amigo ´ en Ciencias de Alimentacion ´ Instituto de Investigacion (CIAL, CSIC-UAM), Madrid, Spain S K Anand South Dakota State University, Brookings, SD, USA ´ A Andren Swedish University of Agricultural Sciences, Uppsala, Sweden
J Andrews Department of Primary Industries, Mutdapilly, QLD, Australia and Dairy Research and Development Corporation, Melbourne, VIC, Australia K Antelli Technical University of Crete, Chania, Greece Y Ardo¨ University of Copenhagen, Frederiksberg C, Denmark S Arora National Dairy Research Institute, Karnal, Haryana, India A M Arve Danish Dairy Board, Aarhus, Denmark S Asakuma National Agricultural Research Center for Hokkaido Region, Sapporo, Hokkaido, Japan H Asperger Veterinary University, Vienna, Austria Z Atamer University of Hohenheim, Stuttgart, Germany M Auldist Department of Primary Industries, Ellinbank, VIC, Australia P Aureli Istituto Superiore di Sanita`, Rome, Italy M Auty Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland ˜ L Avendano-Reyes ´ Universidad Autonoma de Baja California, Mexico G Averdunk Landesanstalt fu¨r Landwirtschaft, Mu¨nchen, Germany S Awad Alexandria University, Alexandria, Egypt ix
x Contributors V Azaı¨s-Braesco VAB-Nutrition, Clermont–Ferrand, France H-P Bachmann Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland E I Back Novartis Pharma GmbH, Nu¨rnberg, Germany R L Baldwin University of California, Davis, CA, USA J M Banks NIZO Food Research, Ede, The Netherlands
Z Bercovich Institute for Animal Science and Health, Lelystad, The Netherlands T P Beresford Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland J K Bernard University of Georgia, Tifton, GA, USA D P Berry Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland
N Bansal The University of Queensland, Brisbane, QLD, Australia
E Beuvier Institut National de la Recherche Agronomique, Poligny, France
J Bao Heilongjiang Bayi Agricultural University, Heilongjiang, PR China
V Bhandari Massey University, Palmerston North, New Zealand
E Barrio Cavanilles of Biodiversity and Evolutionary Biology, University of Valencia, Valencia, Spain
W G Bickert Michigan State University, East Lansing, MI, USA
M D Barton University of South Australia, Adelaide, SA, Australia D E Bauman Cornell University, Ithaca, NY, USA
H K Biesalski Universita¨t Hohenheim, Stuttgart, Germany P Billon Institut de l’Elevage, Le Rheu, France
L H Baumgard University of Arizona, Tucson, AZ, USA
A G Binetti Instituto de Lactelogı´a Industrial (Universidad Nacional del Litoral–CONICET), Santa Fe, Argentina
C R Baumrucker The Pennsylvania State University, University Park, PA, USA
M Bionaz University of Illinois, Urbana, IL, USA
H J Bearden Mississippi State University, Mississippi State, MS, USA
W Bisig Agroscope Liebefeld-Posieux Research Station ALP, Bern, Switzerland
S T Beckett Formerly Nestle´ Product Technology Centre York, York, UK
J Bjo¨rkroth University of Helsinki, Helsinki, Finland
C J M Beeren Leatherhead Food Research, Leatherhead, UK
A Blais AgroParisTech, Paris, France
C Belloch Institute of Agrochemistry and Food Technology (IATA), CSIC, Valencia, Spain
W Bockelmann Federal Research Institute of Nutrition and Food (Max Rubner Institute), Kiel, Germany
R J Bennett Massey University, Palmerston North, New Zealand
M J Boland Riddet Institute, Palmerston North, New Zealand
G A Benson North Carolina State University, Raleigh, NC, USA
M P Boland University College, Dublin, Ireland
Contributors
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U Bolmstedt Tetra Pak Processing Components AB, Lund, Sweden
M F Budinich University of Wisconsin, Madison, WI, USA
J Bonke GEA Process Engineering – Niro, Søborg, Denmark
J Burger BurgerMetrics SIA, Jelgava, Latvia
A Borghese Animal Production Research Institute, Monterotondo, Italy
S Burgess Fonterra Research Centre, Palmerston North, New Zealand
F H M Borgsteede Central Veterinary Institute of Wageningen UR, Lelystad, The Netherlands
A M Burgher Pfizer Nutrition, Collegeville, PA, USA
R Boston University of Pennsylvania, Kennett Square, PA, USA J S Bowen Bowen Mobile Veterinary Practice, Wellington, CO, USA J Boyazoglu Aristotle University of Thessaloniki, Greece
H Burling Arla Foods amba, Lund, Sweden E M Buys University of Pretoria, Pretoria, South Africa E Byrne University College, Cork, Ireland
R L Bradley, Jr. University of Wisconsin–Madison, Madison, WI, USA
R J Byrne Jacobs Engineering, Mahon Industrial Estate, Blackrock, Cork, Ireland
P Bremer University of Otago, Dunedin, New Zealand
C Caddick Fonterra Research Centre, Palmerston North, New Zealand
K Brew Florida Atlantic University, Boca Raton, FL, USA
R Di Cagno University of Bari, Bari, Italy
J R Broadbent Utah State University, Logan, UT, USA
M Calasso DIBCA, University of Bari, Bari, Italy
C Brockman Leatherhead Food Research, Leatherhead, UK
C Cantoni University of Milan, Milan, Italy
J Brooks AUT University, Auckland, New Zealand
A V Capuco US Department of Agriculture, ARS, Beltsville, MD, USA
M C Broome Dairy Innovation Australia, Werribee, VIC, Australia
B Carnat World Organisation for Animal Health (OIE), Paris, France
N Brunton Ashtown Food Research Centre, Dublin, Ireland
K D Cashman University College, Cork, Ireland
N R Bu¨chl Technische Universita¨t, Mu¨nchen, Germany
B G Cassell Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
U Bu¨tikofer Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland D S Buchanan Oklahoma State University, Stillwater, OK, USA S Buchin Institut National de la Recherche Agronomique, Poligny, France
S Cattaneo Universita` degli Studi di Milano, Milan, Italy C Cebo Institut National de la Recherche Agronomique, Jouy-en-Josas, France W Chalupa University of Pennsylvania, Kennett Square, PA, USA
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Contributors
D Champion ENSBANA–Universite´ de Bourgogne, Dijon, France
´ A Correa-Calderon ´ Universidad Autonoma de Baja California, Mexico
J Charlier Ghent University, Merelbeke, Belgium
M Corredig University of Guelph, Guelph, ON, Canada
L E Chase Cornell University, Ithaca, NY, USA
A Corsetti Universita` degli Studi di Teramo, Mosciano S. Angelo (TE), Italy
D E W Chatterton University of Copenhagen, Frederiksberg C, Denmark F Chevalier ´ Institut de Radiobiologie Cellulaire et Moleculaire, Fontenay aux Roses, France A Christiansson Swedish Dairy Association, Lund, Sweden C J Cifelli The Council, Rosemont, IL, USA E Claerebout Ghent University, Merelbeke, Belgium S Claps Consiglio per la Ricerca e la sperimentazione in Agricoltura, Muro Lucano, Italy R Cocker Ayndo Tree Farm, County Cork, Ireland B Cocks Biosciences Research Division, Melbourne, VIC, Australia A Coffey Cork Institute of Technology, Bishopstown, Cork, Ireland T M Cogan Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland R J Collier University of Arizona, Tucson, AZ, USA M T Collins University of Wisconsin–Madison, Madison, WI, USA G Comi University of Udine, Udine, Italy
P D Cotter Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland L K Creamer Riddet Institute, Massey University, Palmerston North, New Zealand K Cronin University College, Cork, Ireland V Crow Formerly at Fonterra Research Centre, Palmerston North, New Zealand M A Crowe University College, Dublin, Ireland B Curry Formerly at Fonterra Research Centre, Palmerston North, New Zealand S E Curtis University of Illinois–Urbana, Urbana, IL, USA C B G Daamen DSM Food-Specialties, Delft, The Netherlands J Dalton University College, Cork, Ireland A Darragh Massey University, Palmerston North, New Zealand N Datta Victoria University, Melbourne, VIC, Australia G Davey Fonterra Research Centre, Palmerston North, New Zealand
T Coolbear Fonterra Research Centre, Palmerston North, New Zealand
T Davison Department of Primary Industries, Mutdapilly, QLD, Australia and Dairy Research and Development Corporation, Melbourne, VIC, Australia
S Cooney University College, Dublin, Ireland
M De Angelis University of Bari, Bari, Italy
S Coppola Universit`a degli Studi di Napoli Federico II, Portici NA, Italy
L C P M G de Groot Wageningen University, Wageningen, The Netherlands
Contributors C J A M de Koning Wageningen UR Livestock Research, AB Lelystad, The Netherlands
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M A Drake North Carolina State University, Raleigh, NC, USA
I De Noni Universita` degli Studi di Milano, Milan, Italy
D Dupont INRA Agrocampus Ouest, UMR Science et Technologie du Lait et de l’Œuf, Rennes, France
H C Deeth University of Queensland, Brisbane, QLD, Australia
E M Du¨sterho¨ft NIZO Food Research, Ede, The Netherlands
P J T Dekker DSM Food-Specialties, Delft, The Netherlands
M L Eastridge The Ohio State University, Columbus, OH, USA
C M Delahunty CSIRO, North Ryde, Sydney, NSW, Australia
E I El-Agamy Qassim University, Qassim, Saudi Arabia
C Delaney University of Vermont, Burlington, VT, USA
F Eliskases-Lechner Federal Institute of Alpine Dairying, Jenbach, Austria
P Desmarchelier Consultant, Pullenvale, QLD, Australia
H Engelhardt University of Waterloo, Waterloo, ON, Canada
S M Deutsch INRA, Agrocampus, Ouest, Rennes, France
W Engels NIZO Food Research, Ede, The Netherlands
C Devendra Jalan Awan Jwa, Kuala Lumpur, Malaysia
T E Engle Colorado State University, Fort Collins, CO, USA
R Di Cagno University of Bari, Bari, Italy
I Eppert Chr. Hansen A/S, Hørsholm, Denmark
J Dijkstra Wageningen University, Wageningen, The Netherlands
D Ercolini Universita` degli Studi di Napoli Federico II, Portici NA, Italy
M G Diskin Teagasc, Animal & Grassland Research and Innovation Centre, Mellows Campus, County Galway, Ireland
B L Erven Ohio State University, Columbus, OH, USA
A D W Dobson University College, Cork, Ireland W Dominguez University of Minnesota, St Paul, MN, USA
C T Estill Oregon State University, Corvallis, OR, USA K G Evans Cornell University, Ithaca, NY, USA
S S Donkin Purdue University, West Lafayette, IN, USA
M H Fahmy International Genetics Consulting Service, Ottawa, Canada
I A Doolan University of Limerick, Limerick, Ireland
H Falentin INRA, Agrocampus, Ouest, Rennes, France
M Doreau Institut National de la Recherche Agronomique, Saint` Champanelle, France Genes
S Fanning University College, Dublin, Ireland
Z Dou University of Pennsylvania, Kennett Square, PA, USA P T Doyle Future Farming Systems Research, Tatura, VIC, Australia
Z Farah Swiss Federal Institute of Technology, Zu¨rich, Switzerland N Y Farkye California Polytechnic State University, San Luis Obispo, CA, USA
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Contributors
H M Farrell Jr., USDA, Eastern Regional Research Center, Wyndmoor, PA, USA N Fegan Food Science Australia, Brisbane, QLD, Australia C Ferris Agri-Food and Biosciences Institute, Hillsborough, County Down, UK S Feyo de Azevedo University of Porto, Portugal J L Firkins The Ohio State University, Columbus, OH, USA
J France University of Guelph, Guelph, ON, Canada G Franciosa Istituto Superiore di Sanita`, Rome, Italy J F Frank South Dakota State University, Brookings, SD, USA and University of Georgia, Athens, GA, USA S T Franklin University of Kentucky, Lexington, KY, USA E Frede Federal Dairy Research Centre, Kiel, Germany
W J Fischer Syngenta International AG, Basel, Switzerland
M-T Fro¨hlich-Wyder Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland
R J FitzGerald University of Limerick, Limerick, Ireland
H Fujimoto Teikyo Heisei University, Chiba, Japan
D Fitzpatrick University College, Cork Ireland
W J Fulkerson Formerly at the University of Sydney, Sydney, NSW, Australia
J J Fitzpatrick University College, Cork, Ireland S Flint Massey, University Palmerston North, New Zealand A Flynn University College, Cork, Ireland E A Foegeding North Carolina State University, Raleigh, NC, USA
D A Funk ABS Global, Inc., DeForest, WI, USA J W Fuquay Mississippi State University, Mississippi State, MS, USA ¨ M G Ganzle University of Alberta, Edmonton, AB, Canada G Garcı´a de Fernando Universidad Complutense, Madrid, Spain
J Fontecha ´ en Ciencias de Alimentacion ´ Instituto de Investigacion (CIAL, CSIC-UAM), Madrid, Spain
B Garin-Bastuji French Agency for Food, Environmental & Occupational Health Safety (ANSES), Maisons-Alfort, France
R H Foote Cornell University, Ithaca, NY, USA
D L Garner GametoBiology Consulting, Graeagle, CA, USA
I A Forsyth The Babraham Institute, Cambridge, UK
H A Garverick University of Missouri, Columbia, MO, USA
S Fosset Institut National Agronomique de Paris–Grignon, Paris, France
F Gaucheron INRA Science et Technologie du Lait et de l’Œuf, Rennes, France
T J Foster Trinity College, Dublin, Ireland
J M Gay Washington State University, Pullman, WA, USA
P D Fox Ballincollig, 90 Old Quarter, Cork, Ireland
V Gekas Cyprus University of Technology, Limassol, Cyprus
P F Fox University College, Cork, Ireland
N Gengler Gembloux Agricultural University, Gembloux, Belgium
Contributors P Georgieva University of Aveiro, Aveiro, Portugal
M Guo University of Vermont, Burlington, VT, USA
J B German The University of California, Davis, CA, USA
M Gue´guen University of Caen Basse–Normandie, Caen, France
G Gernigon UMR 1253 INRA-Agrocampus Ouest, Rennes, France
G F W Haenlein University of Delaware, Newark, DE, USA
J Gibbs Lincoln University, Canterbury, New Zealand
D Haisman Massey University, Palmerston North, New Zealand
M B Gilsenan Leatherhead Food Research, Leatherhead, UK
M B Hall US Dairy Forage Research Center, Madison, WI, USA
H Gjøstein ˚ Norway Norwegian University of Life Sciences, As,
H O Hansen University of Copenhagen, Copenhagen, Denmark
J D Glennon University College, Cork, Ireland
P J Hansen University of Florida, Gainesville, FL, USA
M Gobbetti University of Bari, Bari, Italy
J Harnett Fonterra Research Centre, Palmerston North, New Zealand
M E Goddard University of Melbourne, Parkville, VIC, Australia H D Goff University of Guelph, Guelph, ON, Canada E Gootwine The Volcani Center, Bet Dagan, Israel P K Gopal Fonterra Research Centre, Palmerston North, New Zealand A A Gowen University College, Dublin, Ireland
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W J Harper The Ohio State University, Columbus, OH, USA R Harrison University of Bath, Bath, UK S P Hart Langston University, Langston, OK, USA R W Hartel University of Wisconsin-Madison, Madison, WI, USA K J Harvatine Pennsylvania State University, University Park, PA, USA
R Grappin Formerly at Institut National de la Recherche Agronomique, Poligny, France
J F Hasler Bonner Creek Ranch, Laporte, CO, USA
B Graulet INRA, Unite´ de Recherche sur les Herbivores, Saint Gene`s Champanelle, France
A N Hassan South Dakota State University, Brookings, SD, USA and University of Georgia, Athens, GA, USA
M W Griffiths University of Guelph, Guelph, ON, Canada
J Hatziminaoglou Aristotle University of Thessaloniki, Greece
P Grolier INRA, Laboratoire PsyNuGen, Universite´ Bordeaux 2, Bordeaux, France
P Haughton University College, Dublin, Ireland
T P Guinee Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland
E J Havilah Formerly New South Wales Primary Industries and New South Wales Agriculture, Berry, NSW, Australia
H D Guither University of Illinois–Urbana, Urbana, IL, USA
A A Hayaloglu Inonu University, Malatya, Turkey
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Contributors
B J Hayes Biosciences Research Division, Melbourne, VIC, Australia
A Hosono Japan Dairy Technical Association, Tokyo, Japan
B Healy University College, Dublin, Ireland
J T Huber University of Arizona, Tucson, AZ, USA
C Heggum Danish Agricultural & Food Council, Aarhus, Denmark
D E Hume Grasslands Research Centre, Palmerston North, New Zealand
K E Herold University of Maryland, College Park, MD, USA B Herr Leatherhead Food Research, Leatherhead, UK C Heydel Justus Liebig University, Giessen, Germany B Heymann GEA Westfalia Separator Process GmbH, Oelde, Germany M Hickey Michael Hickey Associates, Charleville, County Cork, Ireland C Hill University College, Cork, Ireland J P Hill Fonterra Research Centre, Palmerston North, New Zealand T R Hill University College, Cork, Ireland J Hinrichs University of Hohenheim, Stuttgart, Germany W Hoffmann Max Rubner-Institut, Kiel, Germany H Hogeveen Wageningen University, Wageningen, The Netherlands
T Huppertz NIZO Food Research, Ede, The Netherlands W L Hurley University of Illinois, Urbana, IL, USA M F Hutjens University of Illinois, Urbana, IL, USA N Hyatt Dyadem International Ltd, Toronto, ON, Canada H E Indyk Fonterra Co–operative Group Ltd., Waitoa, New Zealand B Ismail University of Minnesota, St. Paul, MN, USA D Isolini Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland C Iversen University College, Dublin, Ireland J A Jackson University of Kentucky, Lexington, KY, USA E Jakob Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland
Ø Holand ˚ Norway Norwegian University of Life Sciences, As,
R E James Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
R Holland Fonterra Research Centre, Palmerston North, New Zealand
G Jan INRA, Agrocampus, Ouest, Rennes, France
C Holt University of Glasgow, Scotland, UK
D Jaros ¨ Dresden, Dresden, Germany Technische Universitat
R M Hopper Mississippi State University, MS, USA
R Jeantet UMR 1253 INRA-Agrocampus Ouest, Rennes, France
D S Horne Formerly at Hannah Research Institute, Ayr, UK
P Jelen University of Alberta, Edmonton, AB, Canada
Contributors xvii T C Jenkins Clemson University, Clemson, SC, USA
A Kilara Nutri + Food Business Consulting, Chapel Hill, NC, USA
E Jesse University of Wisconsin–Madison, Madison, WI, USA
K N Kilcawley Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland
T Ji The Ohio State University, Columbus, OH, USA M E Johnson Wisconsin Center for Dairy Research, Madison, WI, USA K A Johnston Fonterra Research Centre, Palmerston North, New Zealand C M Jones Virginia Polytechnic Institute and State University, Blacksburg, VA, USA M Jones Centre for Food Technology, Toowoomba, QLD, Australia
G J King University of Guelph, Guelph, ON, Canada M Kitaoka National Food Research Institute, Tsukuba, Ibaraki, Japan P J Kononoff University of Nebraska-Lincoln, Lincoln, NE, USA J Koort University of Helsinki, Helsinki, Finland H Korhonen MTT, Agrifood Research Finland, Biotechnology and Food Research, Jokioinen, Finland
M Juarez Instituto de Investigatio´n en Ciencias de la Alimentac´ion (CSIC-UAM), Madrid, Spain
N Krog Danisco, Brabrand, Denmark
M T Kaproth Genex Cooperative, Ithaca, NY, USA
D Krogmeier Landesanstalt fu¨r Landwirtschaft, Mu¨nchen, Germany
Y Kato Kinki University, Nakamachi, Nara, Japan
T P Labuza University of Minnesota, St. Paul, MN, USA
M Keane University College, Cork, Ireland
R H Laby Ellinbank Centre, Ellinbank, VIC, Australia
K M Keener Purdue University, West Lafayette, IN, USA
G Laible Ruakura Research Centre, Hamilton, New Zealand
E B Kegley University of Arkansas, Fayetteville, AR, USA
K A Lampel Food and Drug Administration, College Park, MD, USA
D W Kellogg University of Arkansas, Fayetteville, AR, USA
S Landau The Volcani Center, Bet Dagan, Israel
A L Kelly University College, Cork, Ireland
V A Landells Fonterra, Melbourne, VIC, Australia
P M Kelly Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland
I J Lean SBScibus and University of Sydney, Camden, NSW, Australia
W Kenifel ¨ Bodenkultur, Vienna, Austria Universitat
M-N Leclercq-Perlat INRA – GMPA, Thiverval-Grignon, France
R S Kensinger Oklahoma State University, Stillwater, OK, USA
J-H Lee University of Minnesota, St Paul, MN, USA
M S Khan University of Agriculture, Faisalabad, Pakistan
C Lefevre Deakin University, Geelong, VIC, Australia
xviii
Contributors
D Lefier Institut National de la Recherche Agronomique, Poligny, France G Leitner Kimron Veterinary Institute, Bet Dagan, Israel ´ e´ J-L Le Quer UMR Flavour, Vision and Consumer Behaviour, INRA, Dijon, France Z Libudzisz ´ z, Poland Technical University of Łod´ G K Y Limsowtin Formerly at Australian Starter Culture Research Centre, Werribee, VIC, Australia D Lindsay Fonterra Research Centre, Palmerston North, New Zealand S-Q Liu National University of Singapore, Kent Ridge, Singapore A L Lock Michigan State University, East Lansing, MI, USA P Lonergan University College, Dublin, Ireland B Lo¨nnerdal University of California, Davis, CA, USA J J Loor University of Illinois, Urbana, IL, USA A Lopez-Hernandez University of Wisconsin–Madison, Madison, WI, USA L Lopez-Kleine Institut National de la Recherche Agronomique (INRA), Jouy-en-Josas, France S M Loveday Riddet Institute, Massey University, Palmerston North, New Zealand K F Lowe Formerly Queensland Primary Industries and Fisheries, Peak Crossing, QLD, Australia
J Lyne Chr Hansen Inc, Milwaukee, WI, USA C Macaldowie Moredun Research Institute, Penicuik, Midlothian, UK A K H MacGibbon Fonterra Research Centre, Palmerston North, New Zealand F E Madalena Federal University of Minas Gerais, Brazil A L Magliaro-Macrina Pennsylvania State University, University Park, PA, USA A Malet AgroParisTech, Paris, France J Malmo Maffra Veterinary Centre, Maffra, VIC, Australia A G Marangoni University of Guelph, Guelph, ON, Canada F Mariette Cemagref, UR TERE, Rennes, France, Universite´ ´ Europeenne de Bretagne, Rennes, France P Marnila MTT, Agrifood Research Finland, Biotechnology and Food Research, Jokioinen, Finland R Marsili Rockford College, Rockford, IL, USA H Martens ¨ Berlin, Berlin, Germany Freie Universitat B Martin INRA, Unite´ de Recherche sur les Herbivores, Saint Gene`s Champanelle, France D Martin Max Rubner-Institute, Federal Research Institute of Nutrition and Food, Kiel, Germany P Martin Institut National de la Recherche Agronomique, Jouy-en-Josas, France
J A Lucey University of Wisconsin–Madison, Madison, WI, USA
W Martin-Rosset Institut National de la Recherche Agronomique, Saint-Gen`es Champanelle, France
P Luck North Carolina State University, Raleigh, NC, USA
I H Mather University of Maryland, College Park, MD, USA
M C Lucy University of Missouri, Columbia, MO, USA
J-L Maubois INRA Dairy Research Laboratory, Rennes, France
Contributors S Mayne Agri-Food and Biosciences Institute, Hillsborough, County Down, UK O J McCarthy Massey University, Palmerston North, New Zealand J McCaughey Agri-Food and Biosciences Institute, Hillsborough, County Down, UK M E McCormick Louisiana State University Agricultural Center, Franklinton, LA, USA B T McDaniel North Carolina State University, Raleigh, NC, USA
M Messer University of Sydney, Sydney, NSW, Australia L Meunier-Goddik Oregon State University, Corvallis, OR, USA O Mills British Sheep Dairying Association, Alresford, Hants, UK S Mills Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland F Minervini Universita` degli Studi di Bari, Bari, Italy
R K McGuffey Formerly at Elanco Animal Health, Indianapolis, IN, USA
G Miranda Institut National de la Recherche Agronomique, Jouy-en-Josas, France
M A McGuire University of Idaho, Moscow, ID, USA
V V Mistry South Dakota State University, Brookings, SD, USA
R McLaughlin Seattle University, Seattle, WA, USA
T Miura Nippon Veterinary and Life Science University, Tokyo, Japan
P McLoughlin Ashtown Food Research Centre, Dublin, Ireland D J McMahon Utah State University, Logan, UT, USA J P McNamara Washington State University, Pullman, WA, USA J D McPhee Guelph University, Guelph, ON, Canada P L H McSweeney University College, Cork, Ireland M Medina National Institute for Agricultural and Food Research and Technology (INIA), Madrid, Spain P Melendez University of Florida, Gainesville, FL, USA M Mellado University Autonoma Agraria Antonio Narro, Saltillo, Mexico K Menzies Deakin University, Geelong, VIC, Australia U Merin The Volcani Centre, Bet Dagan, Israel P Mermillod INRA, Physiologie de la Reproduction et des Comportements, Nouzilly, France
xix
P J Moate Ellinbank Centre, Ellinbank, VIC, Australia B Moioli Animal Production Research Institute, Monterotondo, Italy G Molle Istituto Zootecnico e Caseario per la Sardegna, Olmedo, Italy E M Molloy University College, Cork, Ireland D R Monke Select Sires, Inc., Plain City, OH, USA V Monnet Institut National de la Recherche Agronomique (INRA), Jouy-en-Josas, France A J Morgan Centenary Institute of Cancer Medicine and Cell Biology, Camperdown, NSW, Australia P A Morrissey University College Cork, Ireland B K Mortensen Tikøb, Denmark O S Mota University of Porto, Porto, Portugal
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Contributors
L D Muller The Pennsylvania State University, University Park, PA, USA
C J Oberg Weber State University, Ogden, UT, USA
D M Mulvihill University College, Cork, Ireland
B O’Brien Animal & Grassland Research and Innovation Centre, Moorepark, Fermoy, County Cork, Ireland
M Murphy Cork County Council, County Cork, Ireland
N M O’Brien University College, Cork, Ireland
M R Murphy University of Illinois at Urbana-Champaign, Champaign, IL, USA
S O’Brien University College, Dublin, Ireland
M Naum Food and Drug Administration, College Park, MD, USA
D J O’Callaghan Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland
R L Nebel Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
D M O’Callaghan Wyeth Nutritionals Ireland, Askeaton, County Limerick, Ireland
F Neijenhuis Livestock Research, Lelystad, The Netherlands K F Ng-Kwai-Hang McGill University, Montreal, QC, Canada K R Nicholas Deakin University, Geelong, VIC, Australia S C Nickerson LSU Agricultural Center, Homer, LA, USA and University of Georgia, Athens, GA, USA S S Nielsen Purdue University, West Lafayette, IN, USA
J E O’Connell University College, Cork, Ireland M J O’Connell Chr. Hansen (UK) Ltd., Hungerford, Berkshire, UK D O’Connor Institute of Technology, Cork, Ireland T P O’Connor University College, Cork, Ireland A M O’Donnell Cornell University, Ithaca, NY, USA C P O’Donnell University College, Dublin, Ireland
M Nieminen Finnish Game and Fisheries Research Institute, Kaamanen, Finland
J A O’Donnell California Dairy Research Foundation, Davis, CA, USA
J A Nieuwenhuijse Friesland Campina Research, Deventer, The Netherlands
G R Oetzel University of Wisconsin–Madison, Madison, WI, USA
D Nohr Universita¨t Hohenheim, Stuttgart, Germany
O T Oftedal Smithsonian Environmental Research Center, Edgewater, MD, USA
A B Nongonierma University of Limerick, Limerick, Ireland J P Noordhuizen University of Utrecht, The Netherlands
A C Oliveira University of Porto, Porto, Portugal J C Oliveira University College, Cork, Ireland
˜ M Nunez National Institute for Agricultural and Food Research and Technology (INIA), Madrid, Spain
R Oliveira New University of Lisbon, Portugal
H Nursten University of Reading, Reading, UK
S P Oliver The University of Tennessee, Knoxville, TN, USA
Contributors E O’Mahony Cork County Council, Cork, Ireland
A Patrick Fonterra Research Centre, Palmerston North, New Zealand
J A O’Mahony Wyeth Nutritionals Ireland, Askeaton, County Limerick, Ireland
S Patton La Jolla, CA, USA
J O’Regan University College, Cork, Ireland
L Pearce Fonterra Research Centre, Palmerston North, New Zealand
N O’Shea University College, Cork, Ireland G Osthoff University of the Orange Free State, Bloemfontein, South Africa D J O’Sullivan University of Minnesota, St Paul, MN, USA M O’Sullivan University College, Dublin, Ireland A C Ouwehand Danisco, Enteromix, Kantvik, Finland W E Owens LSU Agricultural Center, Homer, LA, USA J Palmer Massey University, Palmerston North, New Zealand J M Panoff University of Caen Basse–Normandie, Caen, France E Parente Universita` degli Studi della Basilicata, Potenza, Italy S M Parish Washington State University, Pullman, WA, USA Y W Park Fort Valley State University, Fort Valley, GA, USA J E Parks Cornell University, Ithaca, NY, USA P W Parodi Dairy Australia, Melbourne, VIC, Australia M A Pascall The Ohio State University, Columbus, OH, USA A H J Paterson Massey University, Palmerston North, New Zealand
xxi
L Pellegrino Universita` degli Studi di Milano, Milan, Italy M C Perotti Universidad Nacional del Litoral (UNL) – Consejo Nacional de Investigaciones Cientı´ficas y Tecnolo¨gicas (CONICET), Santa Fe, Argentina G M Pighetti The University of Tennessee, Knoxville, TN, USA A Pihlanto MTT Agrifood Research Finland, Jokioinen, Finland M Pizzillo Consiglio per la Ricerca e la Sperimentazione in Agricoltura, Muro Lucano, Italy H W Ploeger Utrecht University, Utrecht, The Netherlands S Pochet Institut National de la Recherche Agronomique, Poligny, France C Poppe Public Health Agency of Canada, Guelph, ON, Canada I B Powell Dairy Innovation Australia, Werribee, VIC, Australia R L Powell USDA Beltsville Agricultural Research Center, Beltsville, MD, USA V Prabhakar The Ohio State University, Columbus, OH, USA M Pravda University College, Cork, Ireland A Querol Institute of Agrochemistry and Food Technology (IATA), CSIC, Valencia, Spain A Quiberoni Instituto de Lactelogı´a Industrial (Universidad Nacional del Litoral–CONICET), Santa Fe, Argentina
xxii
Contributors
E M M Quigley University College, Cork, Ireland
J R Roche DairyNZ, Hamilton, New Zealand
K S Ramanujam Pfizer Nutrition, Collegeville, PA, USA
L Rodriguez-Saona The Ohio State University, Columbus, OH, USA
M Ramos Instituto de Investigatio´n en Ciencias de la Alimentac´ion (CSIC-UAM), Madrid, Spain
H Roginski The University of Melbourne, VIC, Australia
A R Rankin University of Wisconsin–Madison, Madison, WI, USA
H Rohm ¨ Dresden, Dresden, Technische Universitat Germany
S A Rankin University of Wisconsin–Madison, Madison, WI, USA
D Romagnolo University of Arizona, Tucson, AZ, USA
M D Rasmussen University of Aarhus, Horsens, Denmark
Y H Roos University College, Cork, Ireland
A Rasooly National Institutes of Health, Rockville, MD, USA
M Rosenberg University of California–Davis, Davis, CA, USA
F P Rattray Chr. Hansen A/S, Hørsholm, Denmark E Refstrup GEA Process Engineering – Niro, Søborg, Denmark D J Reinemann University of Wisconsin-Madison, Madison, WI, USA J A Reinheimer Universidad Nacional del Litoral–CONICET, Santa Fe, Argentina C K Reynolds The University of Reading, Reading, UK M A Reynolds Fonterra Research Centre, Palmerston North, New Zealand F Riedewald CEL-International, Cork, Ireland C A Risco University of Florida, Gainesville, FL, USA C G Rizzello University of Bari, Bari, Italy G L Robertson University of Queensland, Brisbane, QLD, Australia A-L Robin Leatherhead Food Research, Leatherhead, UK R K Robinson Formerly at University of Reading, Reading, UK
Y Rosnina Universiti Putra Malaysia, Selangor, Malaysia R P Ross Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland E Roth Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland Z Roth The Hebrew University of Jerusalem, Rehovot, Israel G Roudaut ENSBANA–Universite´ de Bourgogne, Dijon, France J-P Roy ´ St-Hyacinthe, QC, Canada Universite´ de Montreal, R Rubino Consiglio per la Ricerca e la Sperimentazione in Agricoltura, Muro Lucano, Italy E O Rukke ˚ Norway Norwegian University of Life Sciences, As, P L Ryan Mississippi State University, MS, USA E T Ryser Michigan State University, East Lansing, MI, USA T Sako Yakult Central Institute for Microbiological Research, Kunitachi, Tokyo, Japan
Contributors xxiii E Salimei Universita` degli Studi del Molise, Campobasso, Italy
B Seale University of Otago, Dunedin, New Zealand
S Salminen University of Turku, Turku, Finland
K M Seamans University College, Cork, Ireland
S Sandra University of Massachusetts, Amherst, MA, USA
H Seiler Technische Universita¨t, Mu¨nchen, Germany
O Santos Mota University of Porto, Porto, Portugal
N P Shah Victoria University, Melbourne, VIC, Australia
J E P Santos University of Florida, Gainesville, FL, USA
Shakeel-Ur-Rehman California Polytechnic State University, San Luis Obispo, CA, USA
L D Satter University of Wisconsin, Madison, WI, USA A B Saunders Fonterra Research Centre, Palmerston North, New Zealand P Sauvant ENITA de Bordeaux, Unite´ de Formation QENS, Gradignan, France L Sawyer The University of Edinburgh, Edinburgh, Scotland C Scalfaro Istituto Superiore di Sanita`, Rome, Italy K K Schillo University of Kentucky, Lexington, KY, USA B Schilter Nestle´ Research Center, Lausanne, Switzerland E Schlimme Max Rubner-Institute, Federal Research Institute of Nutrition and Food, Kiel, Germany B Schobinger Rehberger Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland D T Scholl ´ St-Hyacinthe, QC, Canada Universite´ de Montreal,
M Shamsuddin Bangladesh Agricultural University, Mymensingh, Bangladesh J A Sharp Deakin University, Geelong, VIC, Australia K Shea Horizon Organic, Longmont, CO, USA J J Sheehan Teagasc Food Research Centre, Moorepark, Fermoy, County Cork, Ireland P A Sheehy University of Sydney, Sydney, NSW, Australia M Shelton Texas A & M University, San Angelo, TX, USA J E Shirley Kansas State University, Tompkinsville, KY, USA J N B Shrestha Agriculture and Agri-Food Canada, Sherbrooke, QC, Canada R Sieber Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland D Simatos ENSBANA–Universite´ de Bourgogne, Dijon, France
R S Schrijver Veteffect Veterinary and Public Health, Bilthoven, The Netherlands
J S Sindhu National Dairy Research Institute, Karnal, Haryana, India
P Schuck INRA Agrocampus Ouest, Rennes, France
R P Singh University of California-Davis, Davis, CA, USA
C G Schwab University of New Hampshire, Durham, NH, USA
H Singh Massey University, Palmerston North, New Zealand
xxiv Contributors M Skanderby GEA Niro A/S, Soeborg, Denmark
´ V B Suarez Instituto de Lactelogı´a Industrial (Universidad Nacional del Litoral–CONICET), Santa Fe, Argentina
B Slaghuis Research Institute for Animal Husbandry, Lelystad, The Netherlands
A Subramanian The Ohio State University, Columbus, OH, USA
T R Smith Mississippi State University, MS, USA
I S Surono University of Indonesia, Jakarta, Indonesia
M El Soda Alexandria University, Alexandria, Egypt N Sommerer INRA UMR, Montpellier, France L M Sordillo Michigan State University, East Lansing, MI, USA T Sørhaug ˚ Norway Norwegian University of Life Sciences, As, J W Spears North Carolina State University, Raleigh, NC, USA S B Spencer Pennsylvania State University, University Park, PA, USA
B J Sutherland Sutherland Dairy Consulting, Melbourne, VIC, Australia N Suttle Moredun Foundation, Penicuik, UK J D Sutton The University of Reading, Earley Gate, Reading, UK K Svendsen Danish Agriculture and Food Council, Arhus, Denmark D M Swallow University College London, London, UK S Tabata Tokyo Metropolitan Institute of Public Health, Tokyo, Japan
D E Spiers University of Missouri, Columbia, MO, USA
D Tait Max Rubner-Institute, Federal Research Institute of Nutrition and Food, Kiel, Germany
J R Stabel National Animal Disease Center, Ames, IA, USA
T Takano Calpis Co. Ltd, Kanagawa, Japan
R H Stadler Nestle´ Product Technology Center, Orbe, Switzerland
R Tanaka Yakult Central Institute for Microbiological Research, Kunitachi, Tokyo, Japan
C R Staples University of Florida, Gainesville, FL, USA J L Steele University of Wisconsin, Madison, WI, USA K Stelwagen Hamilton, New Zealand
M W Taylor Massey University, Palmerston North, New Zealand W W Thatcher University of Florida, Gainesville, FL, USA A Thierry INRA, Agrocampus, Ouest, Rennes, France
L Stepaniak ˚ Norway Agricultural University, As,
´ Thiry E ` ` University of Liege, Liege, Belgium
J S Stevenson Kansas State University, Manhattan, KS, USA
D L Thomas University of Wisconsin–Madison, Madison, WI, USA
R J E Stewart University of Zimbabwe, Harare, Zimbabwe
D Tome´ AgroParisTech, Paris, France
C R Stockdale Future Farming Systems Research, Tatura, VIC, Australia
P S Tong California Polytechnic State University, San Luis Obispo, CA, USA
Contributors xxv A M Tritscher World Health Organization, Geneva, Switzerland
M Walton Society of Dairy Technology, Appleby in Westmorland, UK
Y Tsunoda Kinki University, Nakamachi, Nara, Japan
G M Wani Sher-e-Kashmir University of Agricultural Sciences and Technology, Srinagar, Kashmir, India
C Tyburczy Cornell University, Ithaca, NY, USA T Uniacke-Lowe University College, Cork, Ireland T Urashima Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido, Japan L Vaccaro Universidad Central de Venezuela, Maracay, Venezuela B Vallat World Organisation for Animal Health (OIE), Paris, France S Valmorri Universita` degli Studi di Teramo, Mosciano S. Angelo (TE), Italy G van den Berg NIZO Food Research, Ede, The Netherlands H H Van Horn University of Florida, Gainesville, FL, USA W A van Staveren Wageningen University, Wageningen, The Netherlands
D Wechsler Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland B C Weimer University of California, Davis, CA, USA W P Weiss The Ohio State University, Wooster, OH, USA H Whelton University College Cork, Ireland C H White Mississippi State University, Starkville, MS, USA, Randolph Associates, Inc., Birmingham, AL, USA P Whyte University College, Dublin, Ireland M Wiedmann Cornell University, Ithaca, NY, USA G Wiener Roslin Institute, Edinburgh, UK
B Vardhanabhuti University of Missouri, Columbia, MO, USA
G R Wiggans United States Department of Agriculture, Beltsville, MD, USA
C Varming University of Copenhagen, Frederiksberg C, Denmark
L Wiking Aarhus University, Tjele, Denmark
P Vavra OECD, Paris, France
R A Wilbey The University of Reading, Reading, UK
J Vercruysse Ghent University, Merelbeke, Belgium E Villalobo Universidad de Sevilla, Seville, Spain W Vosloo Australian Animal Health Laboratory, Geelong, VIC, Australia H Wahid Universiti Putra Malaysia, Selangor, Malaysia B Walther Agroscope Liebefeld-Posieux Research Station ALP, Berne, Switzerland
G Wildbrett Technical University of Munich, Weihenstephan, Germany M G Wilkinson University of Limerick, Limerick, Ireland S T Willard Mississippi State University, Mississippi State, MS, USA H Willems Justus Liebig University, Giessen, Germany M Wilson University of Georgia, Athens, GA, USA
xxvi Contributors C M Wittho¨ft Swedish University of Agricultural Sciences, Uppsala, Sweden G Wolters Research Institute for Animal Husbandry, Lelystad, The Netherlands
R Yacamini Formerly at University College, Cork, Ireland N Yamamoto Calpis Co. Ltd, Kanagawa, Japan
D C Woollard NZ Laboratory Services, Auckland, New Zealand
C A Zalazar Universidad Nacional del Litoral (UNL) – Consejo Nacional de Investigaciones Cientı´ficas y Tecnolo¨gicas (CONICET), Santa Fe, Argentina
J Worley University of Georgia, Athens, GA, USA
R Zanabria Eyzaguirre University of Guelph, Guelph, ON, Canada
A J Wright University of Guelph, Guelph, ON, Canada
P Zangerl Federal Institute of Alpine Dairying BAM, Rotholz, Austria
W M D Wright University College, Cork, Ireland P C Wynn E H Graham Centre for Agricultural Innovation (NSW Department of Primary Industries and Charles Sturt University), Wagga Wagga, NSW, Australia Z Z Xu Livestock Improvement Corporation Ltd., Hamilton, New Zealand
P Zhou Jiangnan University, Wuxi, Jiangsu Province, People’s Republic of China A Zittermann University of Bochum, Bad Oeynhausen, Germany S E Zorrilla Instituto de Desarrollo Tecnolo´gico para la Industria Quı´mica (INTEC), Santa Fe, Argentina
GUIDE TO USE OF THE ENCYCLOPEDIA STRUCTURE OF THE ENCYCLOPEDIA The material in the Encyclopedia is arranged as a series of entries in alphabetical order. Some entries comprise a single article, whilst entries on more diverse subjects consist of several articles that deal with various aspects of the topic. In the latter case the articles are arranged in a logical sequence within an entry. To help you realize the full potential of the material in the Encyclopedia we have provided three features to help you find the topic of your choice.
1. CONTENTS LISTS Your first point of reference will probably be the contents list. The complete contents list appearing in each volume will provide you with both the volume number and the page number of the entry. On the opening page of an entry a contents list is provided so that the full details of the articles within the entry are immediately available. Alternatively you may choose to browse through a volume using the alphabetical order of the entries as your guide. To assist you in identifying your location within the Encyclopedia a running headline indicates the current entry and the current article within that entry.
2. CROSS REFERENCES All of the articles in the Encyclopedia have been extensively cross referenced. The cross references, which appear at the end of an article, have been provided at three levels: i. To indicate if a topic is discussed in greater detail elsewhere. ii. To draw the reader’s attention to parallel discussions in other articles. iii. To indicate material that broadens the discussion. Example The following list of cross references appear at the end of the entry entitled Bacteria, Beneficial|Lactic Acid Bacteria: An Overview See also: Bacteria, Beneficial: Bifidobacterium spp.: Applications in Fermented Milks; Bifidobacterium spp.: Morphology and Physiology. Lactic Acid Bacteria: Citrate Fermentation by Lactic Acid Bacteria; Lactic Acid Bacteria in Flavor Development; Lactobacillus spp.: General Characteristics; Lactobacillus spp.: Lactobacillus acidophilus; Lactobacillus spp.: Lactobacillus casei Group; Lactobacillus spp.: Lactobacillus delbrueckii Group; Lactobacillus spp.: Lactobacillus helveticus; Lactobacillus spp.: Lactobacillus plantarum; Lactobacillus spp.: Other Species; Lactococcus lactis; Leuconostoc spp.; Pediococcus spp.; Physiology and Stress Resistance; Proteolytic Systems; Streptococcus thermophilus; Taxonomy and Biodiversity. Pathogens in Milk: Enterobacteriaceae.
3. INDEX The index will provide you with the volume number and page number of where the material is to be located, and the index entries differentiate between material that is a whole article, is part of an article, or is data presented in a table or figure. Detailed notes are provided on the opening page of the index.
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Guide to Use of the Encyclopedia
4. COLOR PLATES The color figures for each volume have been grouped together in a plate section. The location of this section is cited in the contents list. Color versions of black and white figures are cited in figure captions within individual articles.
5. CONTRIBUTORS A full list of contributors appears at the beginning of each volume.
6. GLOSSARY A glossary of terms used within the work is provided in Volume Four before the Index.
PREFACE
W
e are pleased to present the second edition of the Encyclopedia of Dairy Sciences. The first edition was published in 2003 by the Major Reference Works Division of Academic Press, now part of Elsevier Sciences, and it comprised 427 articles. The objective was to satisfy the need for an authoritative source of information for people involved in the integrated system of production, manufacture, and distribution of dairy foods. It was realized from the beginning that a program of revision would be needed to keep the Encyclopedia up to date. This goal has been met in the second edition through 503 articles, of which 121 are new articles and 382 are revised articles. We express appreciation to the Editorial Advisory Board for its role in evaluating articles for needed revision, reviewing new and revised articles, and for help in identifying new topics to be included along with appropriate authors. Likewise, we are grateful for the contributions of the many authors who have either revised their articles or prepared new articles. The main topics related to milk production and dairy technology are addressed in addition to providing information on nutrition, public health, and dairy industry economics including aspects of trade in milk and dairy products. All species that produce milk for human consumption have been included in this work. Some of these species are of regional significance only, but they have been included because of the essential role that their milk plays in the nutrition of people inhabiting various regions of the world. A significant addition to the second edition is four introductory articles addressing the history of Dairy Science and Technology. A synopsis has been prepared for each article in the second edition and will appear with the online listing of the articles in this publication. The primary aim of the Encyclopedia is to provide a complete resource for researchers, students, and practitioners involved in all aspects of the dairy sciences as well as those involved with economic and nutritional policy and members of the media. We have tried to do this with a writing style that is easily comprehended by persons who are not highly trained in the technical aspects of the Dairy Sciences. Users should be able to access information on topics that are peripheral to their areas of expertise. We express appreciation to the staff of the Major Reference Works Division, responsible for this Encyclopedia, for their timely responsiveness to the needs of the editors and their essential administrative role in keeping this major reference work on-track toward a satisfactory completion within the desired time schedule. We remember Nancy Maragioglio, Senior Life Sciences Editor, who initiated the work and was ever responsive to queries by the editors, as well as Sera Relton, Esmond Collins, Milo Perkins, and Claire Byrne, Development Editors, and Charlotte (Charlie) Kent, Publishing Administrator, who kept things moving through their communication with editors, authors, and reviewers and who exhibited almost flawless administrative skills. Sera Relton was particularly helpful as she assisted us in moving through the final submission and review stages. Laura Jackson is recognized for her contributions as Production Manager of the Encyclopedia. Special recognition is due to Ms Anne Cahalane, Senior Executive Assistant, School of Food & Nutritional Sciences, University College, Cork, whose stylized representation of a cow, a milk can, and a wedge of cheese adorns the cover of the first and second editions of the Encyclopedia of Dairy Sciences. John W. Fuquay Patrick F. Fox and Paul L. H. McSweeney
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FOREWORD
The cow is the foster mother of the human race. From the days of the ancient Hindoo to this time have the thoughts of men turned to this kindly and beneficent creature as one of the chief sustaining forces of human life. William Dempster Hoard (1836-1918) Former governor, state of Wisconsin, USA (1889-1891) Founder of Hoard’s Dairyman (1885)
W
e must never forget that milk and milk products are and will always be important sources of basic food nutrients for humans both young and old. The more scientific facts we can discover, understand, and apply related to producing, processing, and marketing milk and milk products, the better we will serve the nutritional needs of humanity throughout the world. More than 2000 years ago Aristotle noted, Everyone honors the wise and excellent. We are indebted to those wise enough to conceptualize and envision the favorable global impact that is certain to follow by bringing together this exhaustive, rich collection of 503 pertinent articles written and reviewed by more than 700 world-renowned disciplinary experts representing 50 countries – persons each of whom bears the mark of excellence. Happily these timely topics are now recorded in four informative, important, engaging volumes. We thank, commend, and salute the prodigious efforts of the wise and excellent authors who generated, compiled, and put the spotlight on the useful information and data, and who now share them through their well-written articles. One noteworthy value and enduring virtue of these articles is bringing into clear perspective the context of both the state-of-the-art and the future of dairy sciences. When the history and contributions of scholarly publications related to the all-important global dairy industry are recorded, the second edition of the Encyclopedia of Dairy Sciences will be cited often and with great respect and appreciation. Fundamental to continued progress and success in the dairy industry have been the signal service, cooperation, and collective contributions of dedicated scientists, teachers, agricultural advisors/extension workers, and representatives of governments and industries. Additional exciting breakthroughs in applying new findings and developments in research and technology to the production and processing of milk are sure to follow as we move surefootedly through the twentyfirst century. This continued growth and success will be aided immensely by the vast and extraordinarily useful knowledge base made available by the idea-rich, insightful authors, editorial advisory board members, editors, and publisher of the second edition of the Encyclopedia of Dairy Sciences. Indeed, by perusing the comprehensive and authoritative articles of this greatly needed and monumental encyclopedia, readers will be made even more aware of the tremendous progress that has occurred in the basic and applied sciences underpinning the global dairy industry. Ours is an internationally competitive and incredibly technological world. And unless talented, creative scientists continue to work together in researching and applying the most effective and economical ways and means of providing
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Foreword
an abundant, safe supply of milk and milk products for an ever-increasing world population, we will never reach our noble goal of adequately feeding all the earth’s people. May we utilize the comprehensive scientific knowledge base made available through this second edition of the Encyclopedia of Dairy Sciences as we pledge to realize advances in the health and well-being of the undernourished millions – including many who need and deserve to be rescued from the ugly grip of hunger – by increasing the availability of nature’s most nearly perfect food – milk! Pure milk from healthy animals is a luxury of the rich, whereas it ought to be the common food of the poor. Mohandas Gandhi (1869-1948) Indian nationalist leader
John R. Campbell, Ph.D., D.Sc. (Hon.) President Emeritus and Professor of Animal Science Oklahoma State University Dean Emeritus and Professor Emeritus of Animal Sciences College of Agriculture, University of Illinois Professor Emeritus of Animal Sciences University of Missouri Past President, ADSA (1980-81) April 2010
CONTENTS VOLUME 1 INTRODUCTION History of Dairy Science and Technology History of Dairy Farming
P F Fox, R K McGuffey, J E Shirley and T M Cogan
R K McGuffey and J E Shirley
History of Dairy Products and Processes History of Dairy Chemistry
P F Fox
2 12
P F Fox
History of Dairy Bacteriology
1
18
T M Cogan
26
A ADDITIVES IN DAIRY FOODS Types and Functions of Additives in Dairy Products
B Herr
Consumer Perceptions of Additives in Dairy Products Legislation Safety
C Brockman and C J M Beeren
A-L Robin
41 49
M B Gilsenan
Emulsifiers
34
55
N Krog
61
ANALYTICAL METHODS Sampling
R L Bradley, Jr.
72
Proximate and Other Chemical Analyses
M O’Sullivan
Statistical Methods for Assessing Analytical Data Multivariate Statistical Tools for Chemometrics Spectroscopy, Overview
E Parente E Parente
R McLaughlin and J D Glennon
Infrared Spectroscopy in Dairy Analysis
A Subramanian, V Prabhakar and L Rodriguez-Saona
Hyperspectral Imaging for Dairy Products Light Scattering Techniques
A A Gowen, C P O’Donnell, J Burger and D O’Callaghan
D S Horne
Atomic Spectrometric Techniques
Nuclear Magnetic Resonance: Principles
83 93 109 115 125 133
D Fitzpatrick and J D Glennon
Nuclear Magnetic Resonance: An Introduction
76
P McLoughlin and N Brunton F Mariette
141 146 153
Chromatographic Methods
Y Ardo¨, D E W Chatterton and C Varming
169
Immunochemical Methods
D Dupont
177
Electrophoresis
F Chevalier
Electrochemical Analysis
M Pravda
185 193
xxxiii
xxxiv
Contents
Mass Spectrometric Methods Ultrasonic Techniques Microbiological
F Chevalier and N Sommerer
198
W M D Wright
206
S K Anand
DNA-Based Assays
215
M Naum and K A Lampel
221
Microscopy (Microstructure of Milk Constituents and Products) Biosensors
M Auty
A Rasooly and K E Herold
Physical Methods
235
V Bhandari and H Singh
Differential Scanning Calorimetry
226
248
P Zhou and T P Labuza
256
Principles and Significance in Assessing Rheological and Textural Properties H Rohm and D Jaros
264
Rheological Methods: Instrumentation
272
Sensory Evaluation
H Rohm and D Jaros
M A Drake and C M Delahunty
279
ANIMALS THAT PRODUCE DAIRY FOODS Major Bos taurus Breeds
D S Buchanan
284
Minor and Dual-Purpose Bos taurus Breeds
G Averdunk and D Krogmeier
Bos indicus Breeds and Bos indicus Bos taurus Crosses Goat Breeds
F E Madalena
293 300
C Devendra and G F W Haenlein
310
Sheep Breeds
M H Fahmy and J N B Shrestha
325
Water Buffalo
M S Khan
340
Yak
G Wiener
343
Camel
G A Alhadrami
351
Horse
M Doreau and W Martin-Rosset
358
Donkey Reindeer
E Salimei
365
Ø Holand, H Gjøstein and M Nieminen
374
B BACTERIA, BENEFICIAL Bifidobacterium spp.: Morphology and Physiology
N P Shah
Bifidobacterium spp.: Applications in Fermented Milks
N P Shah
381 388
Brevibacterium linens, Brevibacterium aurantiacum and Other Smear Microorganisms T M Cogan
395
Lactic Acid Bacteria: An Overview
401
Propionibacterium spp.
P F Fox
A Thierry, H Falentin, S M Deutsch and G Jan
Probiotics, Applications in Dairy Products BACTERIOCINS
S Salminen, W Kenifel and A C Ouwehand
E M Molloy, C Hill, P D Cotter and R P Ross
403 412 420
BACTERIOPHAGE Biological Aspects
A Quiberoni, V B Sua´rez, A G Binetti and J A Reinheimer
Technological Importance in the Diary Industry
J Lyne
430 439
BIOFILM FORMATION S Flint, J Palmer, P Bremer, B Seale, J Brooks, D Lindsay and S Burgess
445
M Nun˜ez and M Medina
451
BIOGENIC AMINES
Contents
xxxv
BODY CONDITION Measurement Techniques and Data Processing
J P McNamara
Effects on Health, Milk Production, and Reproduction
J P McNamara
457 463
BULL MANAGEMENT Artificial Insemination Centers Dairy Farms
D R Monke
468
J Malmo
475
BUSINESS MANAGEMENT Roles and Responsibilities of the Manager Management Records and Analysis
G A Benson G A Benson
481 486
BUTTER AND OTHER MILKFAT PRODUCTS The Product and Its Manufacture Modified Butters
B K Mortensen
B K Mortensen
Properties and Analysis
500
E Frede
506
Anhydrous Milk Fat/Butter Oil and Ghee Milk Fat-Based Spreads Fat Replacers
492
B K Mortensen
B K Mortensen
515 522
T P O’Connor and N M O’Brien
528
C CHEESE Overview
P F Fox
534
Preparation of Cheese Milk
M E Johnson
Starter Cultures: General Aspects
I B Powell, M C Broome and G K Y Limsowtin
Starter Cultures: Specific Properties Secondary Cultures
M C Broome, I B Powell and G K Y Limsowtin
F P Rattray and I Eppert
Rennet-Induced Coagulation of Milk
D J O’Callaghan
T P Guinee and B J Sutherland R J Bennett and K A Johnston
Membrane Processing in Cheese Manufacture Microbiology of Cheese
Non-Starter Lactic Acid Bacteria
J R Broadbent, M F Budinich and J L Steele
Cheese Rheology
607 618
632 639 645
H-P Bachmann, M-T Fro¨hlich-Wyder, E Jakob, E Roth, D Wechsler, E Beuvier and S Buchin J J Sheehan
Biochemistry of Cheese Ripening
595
625 D Ercolini and S Coppola
T M Cogan
Avoidance of Gas Blowing
Cheese Flavor
V V Mistry
T M Cogan
Use of Microbial DNA Fingerprinting
Public Health Aspects
585 591
Mechanization of Cheesemaking
Raw Milk Cheeses
579
J A Lucey
Salting of Cheese
559
574 J A Lucey
Gel Firmness and Its Measurement
552
567
A Andre´n
Rennets and Coagulants
Curd Syneresis
544
661
P L H McSweeney
J-L Le Que´re´
667 675
T P Guinee
Acid- and Acid/Heat Coagulated Cheese
652
685 J A Lucey
698
xxxvi
Contents
Cheddar-Type Cheeses
J M Banks
706
Swiss-Type Cheeses
H-P Bachmann, U Bu¨tikofer, M-T Fro¨hlich-Wyder, D Isolini and E Jakob
712
Dutch-Type Cheeses
E M Du¨sterho¨ft, W Engels and G van den Berg
721
Hard Italian Cheeses
R Di Cagno and M Gobbetti
728
Pasta-Filata Cheeses: Low-Moisture Part-Skim Mozzarella (Pizza Cheese) Pasta-Filata Cheeses: Traditional Pasta-Filata Cheese Smear-Ripened Cheeses
D J McMahon and C J Oberg
M De Angelis and M Gobbetti
W Bockelmann
767
Camembert, Brie, and Related Varieties
M-N Leclercq-Perlat
Cheese with Added Herbs, Spices and Condiments Cheeses Matured in Brine
M El Soda and S Awad
T P Guinee
790
799
814
T P Guinee
Low-Fat and Reduced-Fat Cheese
822
M E Johnson
Current Legislation for Cheeses
783
805
T P Guinee
Cheese as a Food Ingredient
773
795
M G Wilkinson, I A Doolan and K N Kilcawley
Pasteurized Processed Cheese Products Cheese Analogues
A A Hayaloglu and N Y Farkye
M El Soda, S Awad and M H Abd El-Salam
Accelerated Cheese Ripening Enzyme-Modified Cheese
745 753
Y Ardo¨
Blue Mold Cheese
737
833
M Hickey
843
CHOCOLATE Milk Chocolate
S T Beckett
856
CONCENTRATED DAIRY PRODUCTS Evaporated Milk
J A Nieuwenhuijse
Sweetened Condensed Milk Dulce de Leche Khoa
862
J A Nieuwenhuijse
869
C A Zalazar and M C Perotti
874
N Bansal
881
CONTAMINANTS OF MILK AND DAIRY PRODUCTS Contamination Resulting from Farm and Dairy Practices A M Tritscher and R H Stadler Environmental Contaminants
W J Fischer, B Schilter,
W J Fischer, B Schilter, A M Tritscher and R H Stadler
Nitrates and Nitrites as Contaminants
H E Indyk and D C Woollard
887 898 906
CREAM Manufacture Products
W Hoffmann
912
W Hoffmann
920
VOLUME 2
D DAIRY EDUCATION Dairy Production
L D Muller
1
Dairy Technology
P Jelen
6
Contents
xxxvii
DAIRY FARM LAYOUT AND DESIGN Building and Yard Design, Warm Climates
J Andrews and T Davison
13
DAIRY FARM MANAGEMENT SYSTEMS Seasonal, Pasture-Based, Dairy Cow Breeds
P T Doyle and C R Stockdale
Non-Seasonal, Pasture Optimized, Dairy Cow Breeds in the United States
M E McCormick
Non-Seasonal, Pasture-Based Milk Production Systems in Western Europe Dry Lot Dairy Cow Breeds
29
S Mayne, J McCaughey and C Ferris
M F Hutjens
38 44 52
Goats
R Rubino, M Pizzillo, S Claps and J Boyazoglu
59
Sheep
J N B Shrestha
67
DAIRY PRODUCTION IN DIVERSE REGIONS Africa
R J E Stewart
77
China
J Bao
83
Latin America
L Vaccaro
88
Southern Asia
M Shamsuddin
94
DAIRY SCIENCE SOCIETIES, AND ASSOCIATIONS
P F Fox
101
DEHYDRATED DAIRY PRODUCTS Milk Powder: Types and Manufacture
P Schuck
108
Milk Powder: Physical and Functional Properties of Milk Powders Dairy Ingredients in Non-Dairy Foods Infant Formulae
P Schuck
W J Harper
117 125
D M O’Callaghan, J A O’Mahony, K S Ramanujam and A M Burgher
135
DISEASES OF DAIRY ANIMALS Infectious Diseases: Bluetongue
J-P Roy, D T Scholl and E´ Thiry
146
Infectious Diseases: Brucellosis
J Gibbs and Z Bercovich
153
Infectious Diseases: Foot-and-Mouth Disease
R S Schrijver and W Vosloo
160
Infectious Diseases: Hairy Heel Warts
C T Estill
168
Infectious Diseases: Johne’s Disease
M T Collins and J R Stabel
174
Infectious Diseases: Leptospirosis Infectious Diseases: Listeriosis
H J Bearden
181
M Wiedmann and K G Evans
184
Infectious Diseases: Salmonellosis
C Poppe
190
Infectious Diseases: Tuberculosis
M T Collins
195
Non-Infectious Diseases: Acidosis/Laminitis Non-Infectious Diseases: Bloat
J P McNamara and J M Gay
P J Moate and R H Laby
Non-Infectious Diseases: Displaced Abomasum Non-Infectious Diseases: Fatty Liver
S S Donkin
Non-Infectious Diseases: Grass Tetany Non-Infectious Diseases: Ketosis Non-Infectious Diseases: Milk Fever
S M Parish
230
G R Oetzel
239
I J Lean
246 R M Hopper
L Avendan˜o-Reyes and A Correa-Caldero´n
Parasites, Internal: Gastrointestinal Nematodes
212
224
I J Lean
Parasites, External: Mange, Dermatitis and Dermatosis Parasites, External: Tick Infestations
206
217
H Martens
Non-Infectious Diseases: Pregnancy Toxemia
199
J Charlier, E Claerebout and J Vercruysse
250 253 258
xxxviii
Contents
Parasites, Internal: Liver Flukes
F H M Borgsteede
264
Parasites, Internal: Lungworms
H W Ploeger
270
E ENZYMES EXOGENOUS TO MILK IN DAIRY TECHNOLOGY -D-Galactosidase Lipases
P J T Dekker and C B G Daamen
276
A Kilara
Proteinases
284
A B Nongonierma and R J FitzGerald
Transglutaminase
289
D Jaros and H Rohm
297
Catalase, Glucose Oxidase, Glucose Isomerase and Hexose Oxidase
P L H McSweeney
301
ENZYMES INDIGENOUS TO MILK Lipases and Esterases
H C Deeth
304
Plasmin System in Milk
B Ismail and S S Nielsen
308
Phosphatases Lactoperoxidase
Shakeel-Ur-Rehman and N Y Farkye E M Buys
Xanthine Oxidoreductase Other Enzymes
314 319
R Harrison
324
N Y Farkye and N Bansal
327
F FEED INGREDIENTS Feed Concentrates: Cereal Grains
M L Eastridge and J L Firkins
Feed Concentrates: Co-Product Feeds
M B Hall and P J Kononoff
Feed Concentrates: Oilseed and Oilseed Meals Feed Supplements: Anionic Salts
J K Bernard
342 349
G R Oetzel
Feed Supplements: Fats and Protected Fats
335
356 T C Jenkins
363
Feed Supplements: Macrominerals
L D Satter and J R Roche
371
Feed Supplements: Microminerals
J W Spears and T E Engle
378
Feed Supplements: Organic-Chelated Minerals
D W Kellogg and E B Kegley
Feed Supplements: Ruminally Protected Amino Acids Feed Supplements: Vitamins
C G Schwab
W P Weiss
384 389 396
FEEDS, PREDICTION OF ENERGY AND PROTEINS Feed Energy Feed Proteins
W P Weiss
403
J E P Santos and J T Huber
409
FEEDS, RATION FORMULATION Systems Describing Nutritional Requirements of Dairy Cows Models in Nutritional Research Models in Nutritional Management Dry Period Rations in Cattle
I J Lean
418
J France, J Dijkstra and R L Baldwin
429
R Boston, Z Dou and W Chalupa
436
T R Smith
Lactation Rations in Cows on Grazing Systems Lactation Rations for Dairy Cattle on Dry Lot Systems
448 J R Roche
453
L E Chase
Transition Cow Feeding and Management on Pasture Systems
J R Roche
458 464
Contents
xxxix
FERMENTED MILKS Types and Standards of Identity Starter Cultures
I S Surono and A Hosono
I S Surono and A Hosono
Health Effects of Fermented Milks Buttermilk
T Takano and N Yamamoto
483 489
H Roginski
Middle Eastern Fermented Milks Asian Fermented Milks
Kefir
477
Z Libudzisz and L Stepaniak
Nordic Fermented Milks
Koumiss
470
496
M H Abd El-Salam
503
R Akuzawa, T Miura and I S Surono
507
T Uniacke-Lowe
512
F P Rattray and M J O’Connell
Yogurt: Types and Manufacture
518
R K Robinson
Yogurt: Role of Starter Culture
525
R K Robinson
FLAVORS AND OFF-FLAVORS IN DAIRY FOODS
529 R Marsili
533
FORAGES AND PASTURES Annual Forage and Pasture Crops – Species and Varieties
E J Havilah
Annual Forage and Pasture Crops – Establishment and Management Perennial Forage and Pasture Crops – Species and Varieties
E J Havilah
K F Lowe, D E Hume and W J Fulkerson
Perennial Forage and Pasture Crops – Establishment and Maintenance K F Lowe and D E Hume Grazing Management
552 563 576
W J Fulkerson,
W J Fulkerson and K F Lowe
586 594
G GAMETE AND EMBRYO TECHNOLOGY Artificial Insemination Cloning
R H Foote and J E Parks
602
Y Kato and Y Tsunoda
In Vitro Fertilization
610
P Mermillod
616
Multiple Ovulation and Embryo Transfer Sexed Offspring Transgenic Animals
P Lonergan and M P Boland
J F Hasler and D L Garner
623 631
G Laible
637
B T McDaniel
646
GENETICS Selection: Concepts
Selection: Evaluation and Methods
G R Wiggans and N Gengler
Selection: Economic Indices for Genetic Evaluation Cattle Genomics
B G Cassell
B J Hayes, B Cocks and M E Goddard
International Flow of Genes GENETIC DEFECTS IN CATTLE
649 656 663
R L Powell
669
D A Funk
675
H HAZARD ANALYSIS AND CRITICAL CONTROL POINTS HACCP Total Quality Management and Dairy Herd Health Processing Plants
M Jones
J P Noordhuizen
679 687
xl
Contents
HEAT TREATMENT OF MILK Thermization of Milk
E O Rukke, T Sørhaug and L Stepaniak
Ultra-High Temperature Treatment (UHT): Heating Systems
693 H C Deeth and N Datta
Ultra-High Temperature Treatment (UHT): Aseptic Packaging
G L Robertson
699 708
Sterilization of Milk and Other Products
J Hinrichs and Z Atamer
714
Non-Thermal Technologies: Introduction
H C Deeth and N Datta
725
Non-Thermal Technologies: High Pressure Processing
N Datta and H C Deeth
732
Non-Thermal Technologies: Pulsed Electric Field Technology and Ultrasonication H C Deeth and N Datta
738
Heat Stability of Milk
744
J E O’Connell and P F Fox
HOMOGENIZATION OF MILK Principles and Mechanism of Homogenization, Effects and Assessment of Efficiency: Valve Homogenizers R A Wilbey
750
High-Pressure Homogenizers
755
T Huppertz
Other Types of Homogenizer (High-Speed Mixing, Ultrasonics, Microfluidizers, Membrane Emulsification) T Huppertz HORMONES IN MILK
C R Baumrucker and A L Magliaro-Macrina
761 765
HUSBANDRY OF DAIRY ANIMALS Buffalo: Asia
H Wahid and Y Rosnina
Buffalo: Mediterranean Region
772
A Borghese and B Moioli
Goat: Feeding Management
780
S P Hart
785
Goat: Health Management
J S Bowen
797
Goat: Milking Management
P Billon
804
Goat: Multipurpose Management
G M Wani
814
Goat: Replacement Management
S P Hart and C Delaney
825
Goat: Reproductive Management
M Mellado
834
Predator Control in Goats and Sheep Sheep: Feeding Management
M Shelton
841
G Molle and S Landau
848
Sheep: Health Management
C Macaldowie
857
Sheep: Milking Management
O Mills
865
Sheep: Multipurpose Management
J Hatziminaoglou and J Boyazoglu
875
Sheep: Replacement Management
D L Thomas
882
Sheep: Reproductive Management
E Gootwine
887
I ICE CREAM AND DESSERTS Ice Cream and Frozen Desserts: Product Types Ice Cream and Frozen Desserts: Manufacture Dairy Desserts
A B Saunders
IMITATION DAIRY PRODUCTS
H D Goff H D Goff
893 899 905
D Haisman
913
Contents xli
VOLUME 3 L LABELING OF DAIRY PRODUCTS
C Heggum
LABOR MANAGEMENT ON DAIRY FARMS
1
B L Erven
9
LACTATION Lactogenesis
R M Akers and A V Capuco
Induced Lactation
15
R S Kensinger and A L Magliaro-Macrina
Galactopoiesis, Effects of Hormones and Growth Factors
A V Capuco and R M Akers
Galactopoiesis, Effect of Treatment with Bovine Somatotropin Galactopoiesis, Seasonal Effects
20
A V Capuco and R M Akers
R J Collier, D Romagnolo and L H Baumgard
26 32 38
LACTIC ACID BACTERIA J Bjo¨rkroth and J Koort
Taxonomy and Biodiversity Proteolytic Systems
45
L Lopez-Kleine and V Monnet
Physiology and Stress Resistance
49
B C Weimer
Genomics, Genetic Engineering
56
D J O’Sullivan, J-H Lee and W Dominguez
Lactobacillus spp.: General Characteristics
M De Angelis and M Gobbetti
Lactobacillus spp.: Lactobacillus acidophilus
P K Gopal
Lactobacillus spp.: Lactobacillus casei Group
F Minervini
67 78 91 96
Lactobacillus spp.: Lactobacillus helveticus
R Di Cagno and M Gobbetti
105
Lactobacillus spp.: Lactobacillus plantarum
A Corsetti and S Valmorri
111
Lactobacillus spp.: Lactobacillus delbrueckii Group Lactobacillus spp.: Other Species
C G Rizzello and M De Angelis
M Calasso and M Gobbetti
119 125
Lactococcus lactis
S Mills, R P Ross and A Coffey
132
Leuconostoc spp.
R Holland and S-Q Liu
138
Streptococcus thermophilus Pediococcus spp.
J Harnett, G Davey, A Patrick, C Caddick and L Pearce
R Holland, V Crow and B Curry
Enterococcus in Milk and Dairy Products
G Garcı´a de Fernando
Lactic Acid Bacteria in Flavor Development
T Coolbear, B Weimer and M G Wilkinson
Citrate Fermentation by Lactic Acid Bacteria
T P Beresford
143 149 153 160 166
LACTOSE AND OLIGOSACCHARIDES Lactose: Chemistry, Properties Lactose: Crystallization
P F Fox
P Schuck
Lactose: Production, Applications Lactose: Derivatives
Maillard Reaction Lactose Intolerance
182 A H J Paterson
M G Ga¨nzle
Lactose: Galacto-Oligosaccharides
196 202
M G Ga¨nzle
H Nursten
209 217
D M Swallow
Indigenous Oligosaccharides in Milk
173
236 T Urashima, S Asakuma, M Kitaoka and M Messer
241
LIQUID MILK PRODUCTS Liquid Milk Products: Pasteurized Milk
L Meunier-Goddik and S Sandra
274
xlii
Contents
Liquid Milk Products: Super-Pasteurized Milk (Extended Shelf-Life Milk) A Lopez-Hernandez and A R Rankin Liquid Milk Products: UHT Sterilized Milks
S A Rankin, 281
M Rosenberg
288
Liquid Milk Products: Modified Milks
M Guo
297
Liquid Milk Products: Flavored Milks
W Bisig
301
Liquid Milk Products: Membrane-Processed Liquid Milk
J-L Maubois
Pasteurization of Liquid Milk Products: Principles, Public Health Aspects Recombined and Reconstituted Products
307 E T Ryser
P S Tong
310 316
M MAMMALS
I A Forsyth
320
MAMMARY GLAND Anatomy
S C Nickerson and R M Akers
Growth, Development and Involution
328
W L Hurley and J J Loor
Gene Networks Controlling Development and Involution
J J Loor, M Bionaz and W L Hurley
338 346
MAMMARY GLAND, MILK BIOSYNTHESIS AND SECRETION Milk Fat
D E Bauman, M A McGuire and K J Harvatine
Milk Protein Lactose
K Stelwagen
352 359
K Stelwagen
367
Secretion of Milk Constituents
I H Mather
373
MAMMARY RESISTANCE MECHANISMS Anatomical
S C Nickerson
Endogenous
381
L M Sordillo and S L Aitken
386
MANURE / EFFLUENT MANAGEMENT Systems Design and Government Regulations Nutrient Recycling
J Worley and M Wilson
H H Van Horn
392 399
MASTITIS PATHOGENS Contagious Pathogens
S C Nickerson
Environmental Pathogens
408
S P Oliver, G M Pighetti and R A Almeida
415
MASTITIS THERAPY AND CONTROL Automated Online Detection of Abnormal Milk Management Control Options Medical Therapy Options
H Hogeveen
S C Nickerson
429
W E Owens and S C Nickerson
Role of Milking Machines in Control of Mastitis MICROORGANISMS ASSOCIATED WITH MILK
422
F Neijenhuis A N Hassan and J F Frank
435 440 447
MILK Introduction
P F Fox
Physical and Physico-Chemical Properties of Milk Bovine Milk Goat Milk Sheep Milk
P F Fox L Amigo and J Fontecha M Ramos and M Juarez
458 O J McCarthy
467 478 484 494
Contents xliii Buffalo Milk
J S Sindhu and S Arora
503
Camel Milk
Z Farah
512
Equid Milk
T Uniacke-Lowe and P F Fox
518
Milks of Other Domesticated Mammals (Pigs, Yaks, Reindeer, etc.) Milks of Non-Dairy Mammals
G Osthoff
Milk of Monotremes and Marsupials Milk of Marine Mammals Human Milk Colostrum
Y W Park
538
J A Sharp, K Menzies, C Lefevre and K R Nicholas
O T Oftedal
581
P Marnila and H Korhonen
591
Seasonal Effects on Processing Properties of Cows’ Milk
Milk of Primates
553 563
A Darragh and B Lo¨nnerdal
Milk in Human Health and Nutrition
530
B O’Brien and T P Guinee
S Patton
598 607
T Uniacke-Lowe and P F Fox
613
MILKING AND HANDLING OF RAW MILK Milking Hygiene
B Slaghuis, G Wolters and D J Reinemann
Influence on Free Fatty Acids
632
L Wiking
638
Effect of Storage and Transport on Milk Quality
C H White
642
MILK LIPIDS General Characteristics Fatty Acids
M W Taylor and A K H MacGibbon
649
M W Taylor and A K H MacGibbon
Conjugated Linoleic Acid Triacylglycerols
655
D E Bauman, C Tyburczy, A M O’Donnell and A L Lock
M W Taylor and A K H MacGibbon
Phospholipids
665
A K H MacGibbon and M W Taylor
Fat Globules in Milk
675 I H Mather
680
Buttermilk and Milk Fat Globule Membrane Fractions Analytical Methods
R Zanabria Eyzaguirre and M Corredig
A K M MacGibbon and M A Reynolds
Rheological Properties and Their Modification Nutritional Significance Lipid Oxidation
670
P F Fox
Milk Fat Globule Membrane
A J Wright, A G Marangoni and R W Hartel
716
H C Deeth
721 S A Aherne
Removal of Cholesterol from Dairy Products
704 711
N M O’Brien and T P O’Connor
Cholesterol: Factors Determining Levels in Blood
691 698
N M O’Brien and T P O’Connor
Lipolysis and Hydrolytic Rancidity
660
727
R Sieber, B Schobinger Rehberger and B Walther
734
MILK PROTEINS Analytical Methods
D Dupont, R Grappin, S Pochet and D Lefier
Heterogeneity, Fractionation, and Isolation
K F Ng-Kwai-Hang
Casein Nomenclature, Structure, and Association Casein, Micellar Structure -Lactalbumin -Lactoglobulin
751
H M Farrell, Jr.
765
D S Horne
772
K Brew
780
L K Creamer, S M Loveday and L Sawyer
Minor Proteins, Bovine Serum Albumin, Vitamin-Binding Proteins Lactoferrin
741
H Korhonen and P Marnila
787 P C Wynn, A J Morgan and P A Sheehy
795 801
xliv
Contents
Immunoglobulins
P Marnila and H Korhonen
807
A Malet, A Blais and D Tome´
Nutritional Quality of Milk Proteins
816
Inter-Species Comparison of Milk Proteins: Quantitative Variability and Molecular Diversity P Martin, C Cebo and G Miranda
821
Proteomics
843
F Chevalier
MILK PROTEIN PRODUCTS Milk Protein Concentrate
P M Kelly
848
Caseins and Caseinates, Industrial Production, Compositional Standards, Specifications, and Regulatory Aspects J O’Regan and D M Mulvihill
855
Membrane-Based Fractionation
864
Whey Protein Products
P M Kelly
E A Foegeding, P Luck and B Vardhanabhuti
Bioactive Peptides
873
A Pihlanto
879
Functional Properties of Milk Proteins
H Singh
887
MILK QUALITY AND UDDER HEALTH Test Methods and Standards
A L Kelly, G Leitner and U Merin
Effect on Processing Characteristics
894
M Auldist
902
MILK SALTS Distribution and Analysis
F Gaucheron
908
Interaction with Caseins
C Holt
917
Macroelements, Nutritional Significance
K D Cashman
925
Trace Elements, Nutritional Significance
K D Cashman
933
MILKING MACHINES Principles and Design Robotic Milking
S B Spencer
941
C J A M de Koning
952
MILKING PARLORS
D J Reinemann and M D Rasmussen
MOLECULAR GENETICS AND DAIRY FOODS
959
S Mills, R P Ross and D P Berry
965
D Martin, E Schlimme and D Tait
971
N NUCLEOSIDES AND NUCLEOTIDES IN MILK NUTRIENTS, DIGESTION AND ABSORPTION Fermentation in the Rumen
M R Murphy
Fiber Digestion in Pasture-Based Cows Small Intestine of Lactating Ruminants Absorption of Minerals and Vitamins
980
J Gibbs and J R Roche
985
J D Sutton and C K Reynolds
989
N Suttle
996
NUTRITION AND HEALTH Nutritional and Health-Promoting Properties of Dairy Products: Contribution of Dairy Foods to Nutrient Intake C J Cifelli, J B German and J A O’Donnell Nutritional and Health-Promoting Properties of Dairy Products: Bone Health
1003 A Zittermann
Nutritional and Health-Promoting Properties of Dairy Products: Colon Cancer Prevention
E M M Quigley
1009 1016
Nutritional and Health-Promoting Properties of Dairy Products: Fatty Acids of Milk and Cardiovascular Disease P W Parodi
1023
Nutritional and Oral Health-Promoting Properties of Dairy Products: Caries Prevention and Oral Health H Whelton
1034
Contents Milk Allergy
E I El-Agamy
1041
Diabetes Mellitus and Consumption of Milk and Dairy Products Galactosemia
xlv
J P Hill, M J Boland and V A Landells
A Flynn
1046 1051
Nutrigenomics and Nutrigenetics
K M Seamans and K D Cashman
1056
S Fosset and D Tome´
Nutraceuticals from Milk
1062
Effects of Processing on Protein Quality of Milk and Milk Products S Cattaneo and I De Noni
L Pellegrino, 1067
VOLUME 4 O OFFICE OF INTERNATIONAL EPIZOOTIES Mission, Organization and Animal Health Code ORGANIC DAIRY PRODUCTION
B Vallat and B Carnat
K Shea
1 9
P PACKAGING
V B Alvarez and M A Pascall
16
PATHOGENS IN MILK Bacillus cereus Brucella spp.
A Christiansson
24
B Garin-Bastuji
Campylobacter spp.
31
P Whyte, P Haughton, S O’Brien, S Fanning, E O’Mahony and M Murphy
40
Clostridium spp.
P Aureli, G Franciosa and C Scalfaro
47
Coxiella burnetii
C Heydel and H Willems
54
Escherichia coli
P Desmarchelier and N Fegan
60
Enterobacteriaceae
S K Anand and M W Griffiths
Enterobacter spp.
S Cooney, C Iversen, B Healy, S O’Brien and S Fanning
Listeria monocytogenes Mycobacterium spp. Salmonella spp. Shigella spp.
67
E T Ryser
81
J Dalton and C Hill
87
C Poppe
93
E Villalobo
99
Staphylococcus aureus – Molecular Staphylococcus aureus – Dairy Yersinia enterocolitica
72
T J Foster
104
H Asperger and P Zangerl
111
M D Barton
117
PLANT AND EQUIPMENT Process and Plant Design
R P Singh and S E Zorrilla
Materials and Finishes for Plant and Equipment
124
K Cronin and R Cocker
Flow Equipment: Principles of Pump and Piping Calculations
J C Oliveira
134 139
Flow Equipment: Pumps
J C Oliveira
145
Flow Equipment: Valves
K Cronin and E Byrne
152
Agitators in Milk Processing Plants
K Cronin and J J Fitzpatrick
160
xlvi
Contents
Centrifuges and Separators: Types and Design
B Heymann
Centrifuges and Separators: Applications in the Dairy Industry Heat Exchangers
O J McCarthy
175
U Bolmstedt
Pasteurizers, Design and Operation Evaporators
166
184 A L Kelly and N O’Shea
193
V Gekas and K Antelli
Milk Dryers: Drying Principles Milk Dryers: Dryer Design
200
E Refstrup and J Bonke
208
M Skanderby
216
Instrumentation and Process Control: Instrumentation
R Oliveira, P Georgieva and S Feyo de Azevedo
234
Instrumentation and Process Control: Process Control
P Georgieva
242
Robots
J C Oliveira
Corrosion
252
P D Fox
257
Continuous Process Improvement and Optimization Quality Engineering
J C Oliveira
263
J C Oliveira
Safety Analysis and Risk Assessment In-Place Cleaning
273 N Hyatt
277
M Walton
283
POLICY SCHEMES AND TRADE IN DAIRY PRODUCTS Agricultural Policy Schemes: Price and Support Systems in Agricultural Policy
H O Hansen
286
Agricultural Policy Schemes: European Union’s Common Agricultural Policy M Keane and D O’Connor
295
Agricultural Policy Schemes: United States’ Agricultural System
300
Agricultural Policy Schemes: Other Systems Codex Alimentarius
E Jesse
P Vavra
306
C Heggum
Standards of Identity of Milk and Milk Products
312 C Heggum
Trade in Milk and Dairy Products, International Standards: Harmonized Systems
322 K Svendsen
331
Trade in Milk and Dairy Products, International Standards: World Trade Organization
A M Arve
338
World Trade Organization and Other Factors Shaping the Dairy Industry in the Future
P Vavra
345
PREBIOTICS Types
T Sako and R Tanaka
Functions
354
T Sako and R Tanaka
365
PSYCHROTROPHIC BACTERIA Arthrobacter spp.
G Comi and C Cantoni
Pseudomonas spp.
372
J D McPhee and M W Griffiths
Other Psychrotrophs
L Stepaniak
379 384
R REPLACEMENT MANAGEMENT IN CATTLE Growth Standards and Nutrient Requirements Pre-Ruminant Diets and Weaning Practices Growth Diets
R E James R E James
R E James
Breeding Standards and Pregnancy Management Health Management
S T Franklin and J A Jackson
390 396 403
J S Stevenson and A Ahmadzadeh
410 417
Contents
xlvii
REPRODUCTION, EVENTS AND MANAGEMENT Estrous Cycles: Puberty
K K Schillo
Estrous Cycles: Characteristics
421
M A Crowe
Estrous Cycles: Postpartum Cyclicity
428
H A Garverick and M C Lucy
Estrous Cycles: Seasonal Breeders
434
S T Willard
Control of Estrous Cycles: Synchronization of Estrus
440 Z Z Xu
448
Control of Estrous Cycles: Synchronization of Ovulation and Insemination Mating Management: Detection of Estrus
R L Nebel, C M Jones and Z Roth
Mating Management: Artificial Insemination, Utilization Mating Management: Fertility
W W Thatcher and J E P Santos
M T Kaproth and R H Foote
M G Diskin
Pregnancy: Characteristics
454 461 467 475
H Engelhardt and G J King
485
Pregnancy: Physiology
P J Hansen
493
Pregnancy: Parturition
P L Ryan
503
Pregnancy: Periparturient Disorders
C A Risco and P Melendez
RHEOLOGY OF LIQUID AND SEMI-SOLID MILK PRODUCTS RISK ANALYSIS
514
O J McCarthy
520
C Heggum
RODENTS, BIRDS, AND INSECTS
532 K M Keener
540
S STANDARDIZATION OF FAT AND PROTEIN CONTENT
P Jelen
545
STRESS IN DAIRY ANIMALS Cold Stress: Effects on Nutritional Requirements, Health and Performance Cold Stress: Management Considerations
W G Bickert
Heat Stress: Effects on Milk Production and Composition Heat Stress: Effects on Reproduction
L E Chase
550 555
C R Staples and W W Thatcher
P J Hansen and J W Fuquay
Management Induced Stress in Dairy Cattle: Effects on Reproduction and D E Spiers
561 567
M C Lucy, H A Garverick 575
U UTILITIES AND EFFLUENT TREATMENT Water Supply Heat Generation Refrigeration
582
O S Mota
589
A C Oliveira and C F Afonso
Compressed Air Electricity
F Riedewald
596
O Santos Mota
602
R Yacamini
Dairy Plant Effluents
610
G Wildbrett
Design and Operation of Dairy Effluent Treatment Plants
613 R J Byrne
Reducing the Negative Impact of the Dairy Industry on the Environment V B Alvarez, M Eastridge and T Ji
619 631
xlviii
Contents
V VITAMINS General Introduction
D Nohr
636
Vitamin A
P Sauvant, B Graulet, B Martin, P Grolier and V Azaı¨s-Braesco
639
Vitamin D
W A van Staveren and L C P M G de Groot
646
Vitamin E
P A Morrissey and T R Hill
652
Vitamin K
T R Hill and P A Morrissey
661
Vitamin C
P A Morrissey and T R Hill
667
D Nohr, H K Biesalski and E I Back
Vitamin B12 Folates
C M Wittho¨ft
Biotin (Vitamin B7) Niacin
D Nohr, H K Biesalski and E I Back
687 690
D Nohr, H K Biesalski and E I Back
694
D Nohr, H K Biesalski and E I Back
Vitamin B6
Riboflavin
678
D Nohr, H K Biesalski and E I Back
Pantothenic Acid
Thiamine
675
697
D Nohr, H K Biesalski and E I Back
701
D Nohr, H K Biesalski and E I Back
704
W WATER IN DAIRY PRODUCTS Water in Dairy Products: Significance
Y H Roos
Analysis and Measurement of Water Activity
707
D Simatos, G Roudaut and D Champion
WELFARE OF ANIMALS, POLITICAL AND MANAGEMENT ISSUES
H D Guither and S E Curtis
715 727
WHEY PROCESSING Utilization and Products Demineralization
P Jelen
731
G Gernigon, P Schuck, R Jeantet and H Burling
738
Y YEASTS AND MOLDS Yeasts in Milk and Dairy Products Kluyveromyces spp.
744
C Belloch, A Querol and E Barrio
754
F Eliskases-Lechner, M Gue´guen and J M Panoff
Geotrichum candidum Penicillium roqueforti
A Abbas and A D W Dobson
Penicillium camemberti
776
T Sørhaug
780
A D W Dobson
785
Mycotoxins: Classification, Occurrence and Determination Mycotoxins: Aflatoxins and Related Compounds
765 772
A Abbas and A D W Dobson
Spoilage Molds in Dairy Products Aspergillus flavus
N R Bu¨chl and H Seiler
S Tabata
H Fujimoto
792 801
Glossary
813
Index
833
COLOR PLATE SECTIONS At end of each volume
O OFFICE OF INTERNATIONAL EPIZOOTIES
Mission, Organization and Animal Health Code B Vallat and B Carnat, World Organisation for Animal Health (OIE), Paris, France ª 2011 Elsevier Ltd. All rights reserved.
Introduction The need for a global approach in the fight against animal diseases is now very clear. The World Organisation for Animal Health (which is also known by its historical acronym OIE (Office International des Epizooties)) is leading this fight worldwide. The OIE is the international standard-setting organization for animal disease control, the safety of international trade of animals and animal products, animal disease prevention, surveillance, control, and information, animal welfare, animal production, and food safety. The purpose of this article is to describe the OIE and its efforts and importance in improving animal health in the world, thereby improving human health. In order to better understand the organization, its history, structure, mandate and activities, and its major publications such as the Animal Health Codes for Terrestrial and Aquatic Animals will be examined.
A Brief History of the OIE In 1920, rinderpest, a devastating plague of cattle, was introduced to Belgium, through the port of Antwerp by zebu cattle that were en route by boat to Brazil from India. This was the impetus for an international conference to examine the animal health situation in the world, to discuss the exchange of animal health information, and to consider export health measures and disease control methods. This so-called ‘Paris Conference’ expressed the wish that an ‘international office of epizootics for the control of infectious animal diseases’ be
set up in Paris. Thus, in 1924, more than 20 years before the creation of the United Nations, an agreement was signed by the veterinary authorities of 28 countries from Europe, North and South America, Africa, and Asia to establish the OIE in Paris – where it remains to this day. In 1995, the World Trade Organisation (WTO) recognized the OIE as the international standard-setting organization for trade in animals and animal products under the agreement on the application of sanitary and phytosanitary (SPS) measures. The WTO’s SPS agreement states that ‘‘to harmonize sanitary and phytosanitary measures on as wide a basis as possible, Members shall base their sanitary or phytosanitary measures on international standards, guidelines or recommendations’’. The agreement names the OIE as the relevant international standard-setting organization for animal health, including diseases transmissible to humans. In May 2003, the representatives of all OIE members agreed to change the name of the organization from ‘Office International des Epizooties’ to ‘World Organisation for Animal Health’ but decided to keep its historical acronym ‘OIE’. As of 2009, the organization has 175 member countries and territories and more than 200 reference laboratories and collaborating centers. It has formal agreements with 35 international and regional organizations such as FAO, WHO, the World Bank, Codex Alimentarius, and non-governmental organizations representing producers and animal welfare groups. The OIE’s financial resources are derived principally from regular annual contributions, backed up by voluntary contributions from members. The amount of the annual budget of the organization makes the OIE one of the most cost-efficient international organizations.
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2 Office of International Epizooties | Mission, Organization and Animal Health Code
In 2004, the OIE established the World Animal Health and Welfare Fund, for the purpose of projects of international public utility relating to the control of animal diseases, including those transmissible to humans, and the promotion of animal welfare and animal production food safety. This effort was funded initially by international donors, including the World Bank, the United States Department of Agriculture, Switzerland, Japan, France, Canada, and Australia.
Structure of the OIE The World Assembly of Delegates The General Assembly of Delegates is the highest authority and the governing body of the OIE. It is comprised of one delegate per country, who is usually the chief veterinary officer (CVO), and is officially nominated by the Government of the member country. It meets every year at the annual general session in May in Paris. The main functions of the General Assembly of Delegates are to adopt international standards in the field of animal health and the control of animal diseases; to elect the members of the governing bodies (President and Vice President of the general assembly, members of the council, members of the regional and specialist commissions); to appoint the Director General (by secret ballot); and to examine and approve the annual report of activities, the financial report of the Director General, the annual budget, and the strategic plans of the OIE. Voting by delegates within the World Assembly of Delegates respects the democratic principle of ‘one country, one vote’. All resolutions voted by the World Assembly must be implemented by the Director General. Council The Council represents the World Assembly of Delegates during the interval between the assemblies. It meets at least twice a year to examine technical and administrative matters and, in particular, the working program and the proposed budget to be presented to the members. There are six elected members in addition to the President, Vice President, and past president of the World Assembly. The members are elected to reflect the regional balance. Headquarters The OIE headquarters is based in Paris, France. Under the authority of the Director General, the headquarters implements and coordinates disease information, and the scientific and administrative activities that the members have decided upon, as well as the World Fund for Animal Health and Welfare.
Furthermore, it provides the secretariat for the annual World Assembly of Delegates and for the meetings of the specialized commissions and other technical meetings. Assistance is also given by the headquarters to the secretariat of the OIE regional and technical conferences. Regional Commissions There are five regional commissions, for Africa; the Americas; Asia, the Far East, and Oceania; Europe; and the Middle East, whose objective is to promote cooperation and organize regional activities in the field of prevention and control of animal diseases and animal welfare promotion. The President and three other members of each regional commission are elected by countries of each region for a 3-year term. A regional commission conference is organized once every 2 years in one of the countries of the region. These conferences are devoted mainly to technical items and to regional cooperation in the control of animal diseases. Regional Representations The OIE maintains representations in Africa, the Americas, Asia and the Pacific, eastern Europe, and the Middle East, and maintains close links with the relevant regional commissions. The goal of these representations is mainly to provide regionally adapted capacity building programs to relevant policy makers of OIE members. There are also currently sub-regional representations for the Southern African Development Community (SADC) in Botswana, in Tunis for northern Africa, in Brussels for western Europe, in Panama for Central America, and in Thailand for southeast Asia. Specialized Commissions and Companion Groups and Supports There are four specialized commissions. Their role is to use current scientific information to study the problems of epidemiology and the prevention and control of animal diseases, to develop and revise OIE’s international standards, and to address scientific and technical issues raised by member countries. The members of these commissions are elected at the World Assembly for a 3-year term. Terrestrial Animal Health Standards Commission and Aquatic Animal Health Standards Commission (Code Commission)
Founded in 1960, these commissions are responsible for the preparation of standards adopted by members contained in the Terrestrial Animal Health Code and the Aquatic Animal Health Code (Terrestrial and Aquatic
Office of International Epizooties | Mission, Organization and Animal Health Code
Code) to ensure that they reflect current scientific information on the protection of international trade and surveillance methods for terrestrial and aquatic animal diseases. They work with internationally renowned specialists in ad hoc and permanent working groups to prepare proposed standards in light of advances in veterinary science. The Aquatic Animal Health Standards Commission is also responsible for the Manual of Diagnostic Tests and Vaccines for Aquatic Animals. The Scientific Commission for Animal Diseases
The Scientific Commission for Animal Diseases, founded in 1946, assists in identifying strategies and measures for animal disease control. It also examines member country submissions for requests to be certified free of the four diseases for which the OIE can officially certify country freedom: foot-and-mouth disease, bovine spongiform encephalopathy, rinderpest, and contagious bovine pleuropneumonia. The Biological Standards Commission
The Biological Standards Commission, founded in 1949, also referred to as the Laboratories Commission, is responsible for the preparation of the Manual of Diagnostic Tests and Vaccines for Terrestrial Animals. It establishes standards for methods of diagnosing diseases of animals and for testing biological products, such as vaccines. Permanent and ad hoc working groups
Comprising leading specialists from all OIE members, these expert groups are brought together to support specialist commissions for the preparation of draft standards and guidelines. There are currently three permanent working groups: on wildlife disease, on animal production food safety, and on animal welfare. Ad hoc groups are not permanent. Recently, they have been convened on a wide range of topics including biotechnology, brucellosis, communication, diseases of camels, epidemiology, and the evaluation of veterinary services (VSs). OIE reference laboratories and collaborating centers
OIE reference laboratories are centers of expertise designated to pursue all the scientific and technical problems relating to a disease on the OIE list. The reference (leading) expert, responsible to the OIE and its member countries with regard to these issues, is an active researcher helping the reference laboratory to provide scientific and technical assistance and expert advice to the OIE and its member countries on diagnostics and topics linked to surveillance and control of the disease for which the reference laboratory is responsible. The laboratories also provide and
3
coordinate scientific and technical studies in collaboration with other laboratories or relevant stakeholders. By the end of 2009, the OIE had a global network of 187 reference laboratories with 161 experts covering 100 diseases/topics in 36 countries. The network brings together experts from many fields. This is an incalculable resource for the OIE headquarters and developed and developing countries, promoting research and encouraging development of laboratory standards. The laboratories provide members with confirmation of diagnostics, current methods for diagnosis, vaccine production, disease surveillance for animal diseases and zoonoses, and safe trade in animals and animal products. OIE collaborating centers are centers of expertise in a specific designated sphere of competence relating to the management of general questions on animal health issues such as epidemiology, risk analysis, veterinary training, or validation of diagnostic tests. Twenty-nine collaborating centers are currently involved in the network covering 27 topics in 18 countries. In its designated field of competence, an OIE collaborating center provides its expertise internationally, and operates as a center of research, standardization, capacity building, and dissemination of techniques. Laboratory twinning
Since a large majority of OIE member countries are developing countries and have variable scientific capacity or access to scientific expertise within their national veterinary laboratories, a project of laboratory twinning was developed, the main objective of which is to assist laboratories in developing or in-transition countries to build their capacity and scientific expertise with the eventual aim that some of them could become OIE reference laboratories in their own right. To apply this concept, a direct link between an existing OIE reference laboratory or collaborating center and another laboratory or institution in a developing or in-transition country is established on a strictly voluntary basis for exchange of scientific expertise and capacity building.
OIE Mandate The core mandate of the OIE is to improve animal health in the world. Under this overarching mandate, the OIE is dedicated – to guarantee the transparency of animal disease status worldwide, – to collect, analyze, and disseminate veterinary scientific information, – to provide expertise and promote international solidarity for the control of animal diseases,
4 Office of International Epizooties | Mission, Organization and Animal Health Code
– to guarantee the sanitary safety of world trade by developing sanitary rules for international trade in animals and animal products, – to improve food safety from the farm to the abattoir, – to develop standards for animal welfare, and – to improve the legal framework and resources of national VSs.
Disease Information Obligations of member countries
Information on the presence of disease is essential for controlling it. With the goal of minimizing the spread of disease comes the obligation to share information about disease outbreaks. Member countries of the OIE are therefore obligated to report disease outbreaks of the OIE-listed diseases, as well as any new relevant epidemiological event. The OIE list of diseases: There are almost 100 OIE-listed diseases included in the first chapter of the Terrestrial Animal Health Code. The criteria used to determine whether a disease appears on the list are as follows: – Is there international spread of disease, that is, has it spread internationally in the past, or is it currently affecting three or more countries? – Does it have zoonotic potential, that is, can this animal disease affect people? – If not, is it spreading in the native population with important morbidity (infecting a high percentage of animals) or mortality (killing an important percentage of the animals that are infected)? – Is it an emerging disease with rapid spread or zoonotic potential? A positive answer to any of these – international spread, zoonosis or high morbidity or mortality or an emerging disease – means that the disease is included on the OIE list. Member countries are committed to report as follows. Immediate notification is required for the first occurrence of a listed disease or infection, the reoccurrence following a report, the first occurrence of a new strain of a pathogen, a sudden and unexpected increase in the morbidity, mortality, or distribution of a disease, or a change in the epidemiology of a disease. The immediate notification is to be by e-mail, fax, telephone, or telegraph. These are to be followed by weekly updates. Members are further committed to semi-annual reports describing the situation regarding OIE-listed diseases in each country and annual reports, which also include information on diseases that are not on the OIE list and diseases of wildlife, the impact of zoonoses on the human population, animal population statistics, the structure of the VSs, national reference laboratories and the diagnostic
tests they can perform, and, where appropriate, vaccine manufacturers and the vaccines they produce. Tools for transparency
WAHIS is the World Animal Health Information System. It is the web interface that is available to member countries for disease notification, allowing countries to notify electronically in a rapid and simple manner. However, when the capacity for electronic reporting is not available, submission of paper reports is acceptable. Many countries have nominated a focal point for specific diseases, or species, whose responsibility is to report disease information to the OIE. This focal point receives specific training from the OIE. WAHID – World Animal Health Information Database – is openly available on the OIE website. With the capacity to search by country or by disease, it provides a rapid, clear, and evident overview of the disease status of a country, the presence or absence of a disease, disease outbreaks or timelines, and the populations of animals in a country, even allowing a comparison of the animal health status of two countries. The OIE publishes ‘World Animal Health’ every year, which is a compilation of all the information listed above. This publication is unique worldwide. Disease tracking
OIE is also engaged in active search and verification of disease outbreaks. Seeking unofficial information from the reference laboratories, the regional representations, collaborating centers, internet resources, or the press, the OIE gathers information, analyzes it, and asks the member for verification where relevant. This is an extremely effective tool. The OIE does not work alone. The Global Early Warning System for Animal Disease including Zoonoses (GLEWS) is a joint OIE/FAO/WHO initiative that synergistically builds on combining and coordinating the disease tracking and alert and response mechanisms of the three organizations. Through sharing of information on animal disease outbreaks and epidemiological analysis, the GLEWS initiative aims at improving global early warning as well as transparency among countries for controlling animal disease as well as zoonoses including food-borne diseases. Veterinary Scientific Information Reference laboratories, collaborating centers, and the four specialist commissions develop and gather scientific information on animal disease prevention and control methods, including zoonoses and food-borne diseases, and on animal welfare. The OIE provides this information through various channels including
Office of International Epizooties | Mission, Organization and Animal Health Code
5
– – – –
global and regional scientific conferences, web site, The Bulletin, the yearly publication of the World Animal Health Situation, – The Scientific and Technical Review, and – other publications (handbooks).
while contributing to help free countries safeguard their free status. OIE offers to developing countries independent evaluation of their animal health policies and infrastructures, gap analysis, and donor opportunities if needed (see ‘Strengthening Veterinary Services’).
The Bulletin is published 4 times yearly. Each issue is focused on a specific topic (e.g., animal welfare, wildlife diseases, or food safety). It also provides member countries with an update on current issues, on activities of headquarters and regional offices, and upcoming events and notifications of self-declarations of the disease status of member countries on a voluntary basis. The World Animal Health is a yearly publication on the occurrences of animal disease throughout the world. It also contains information on the most important control, prevention, and prophylaxis measures adopted and the number of animals slaughtered, destroyed, or vaccinated. Figures on animal population are also provided. Other sections provide detailed information on human cases of the OIE-listed zoonotic diseases, veterinary personnel, national reference laboratories, and vaccine production. This publication is unique in the world. The Scientific and Technical Review is a peer-reviewed journal that contains in-depth studies devoted to current scientific and technical developments in animal health and veterinary public health worldwide. The particular distinction of this publication lies in relating specialized research to practical problems encountered in safeguarding animal health and veterinary public health, an essential aspect for the improvement of animal production and the protection of public health. It appears 3 times per year. Other technical publications include technical series on a variety of topics such as assessment and management of pain in animals, or epidemiology, and global or regional scientific conference proceedings.
International Trade in Animal and Animal Products
International Solidarity More than 120 members are developing countries or countries in transition. These countries often find it difficult to free themselves from epizootics, including zoonoses. This leaves a reservoir of pathogens that threatens the status of countries that have attained disease freedom, often at great expense. The OIE influences the wealthier countries to help developing countries and offers its expertise and that of the networks as well as its own resources to help them meet the OIE standards. This results in a ‘win-win’ situation because the control of diseases in developing countries also results in reduction of poverty and increases food security, market access, and public health
As described above, the OIE is the international organization given the responsibility by the WTO for establishing standards in animal diseases and zoonoses. The standards contained in the Terrestrial and Aquatic Code are intended to prevent and control the spread of animal disease while avoiding unjustified sanitary barriers to the international trade of animals and animal products. The OIE certifies countries free of four diseases (rinderpest, foot-and-mouth disease, contagious bovine pleuropneumonia, and bovine spongiform encephalopathy) according to specific guidelines by which a country can demonstrate that the disease is not present in its animal population. This allows importing countries to take decisions without having to control the situation in the exporting country directly in the field. For other diseases, such as avian influenza, there are specified criteria by which a country can certify itself as free from a disease. The OIE can also play a role in mediating trade disputes between countries by offering a voluntary dispute settlement mechanism. This is a science-based approach to finding alternative solutions and resolving differences, as distinct from the legalistic approach used in the formal WTO system. The mechanism is voluntary and the agreement of both parties is needed before the OIE can initiate the process. Animal Production Food safety Preventing or eliminating hazards at their source, at the farm level, is clearly more effective than trying to detect and eliminate them downstream. A permanent working group on food safety was established in 2002, sharing membership with Codex Alimentarius, FAO, and WHO, to establish standards for food safety from the farm to the abattoir in order to eliminate hazards existing during production at the farm and prior to the slaughter of animals or the primary processing of animal products (meat, milk, eggs, etc.) that could pose a risk to consumers. This group is also working to prevent gaps and duplications between Codex Alimentarius and the OIE standards. Veterinarians have an established role at the farm level. Under OIE guidelines, veterinarians working at the abattoir screen for diseases particularly during anteand post-mortem inspection. They verify that animal
6 Office of International Epizooties | Mission, Organization and Animal Health Code
welfare standards are met, and assure the humane slaughter. VSs are well placed as part of a multidisciplinary team of professionals, to work for the safe production of food, including dairy products from the farm to the fork. As part of the effort to ensure the safety of food of animal origin, and indeed for the purpose of controlling animal disease outbreaks, there must be a reliable and effective way to trace the animal back to the farm of origin. This should be based on the identification of farms, individual animal identification, or identification of groups of homogeneous animals, the ability to track movement of animals, and a record-keeping system. Traceability has important implications for trade as well as for animal health, disease control, and food safety. Therefore, the OIE developed standards for animal traceability. In addition, the OIE organized a world conference in 2009 bringing together governments, international organizations, industry, and primary producers with the purpose of supporting the implementation of the relevant international standards for identification and traceability of live animals and facilitating the bridge of traceability between animals and animal food products globally. Animal Welfare Animal welfare was identified as a priority when OIE member countries mandated the organization to take the lead internationally on animal welfare and to elaborate recommendations and guidelines covering animal welfare practices. This is all the more relevant to the OIE since animal health is a key component of animal welfare. The Permanent Animal Welfare Working Group was inaugurated at the 70th World Assembly of Delegates in May 2002. To date, the OIE has developed guidelines for the transport of animals by land, sea, and air, for the slaughter of animals, and for killing animals for disease control purposes. The next standards to be developed are on the control of stray dog populations, livestock production systems, and laboratory animal welfare. To further progress on animal welfare standards, the OIE has held two global conferences, in 2004 and 2008, in order to promote the worldwide implementation of OIE animal welfare standards, to raise the profile of animal welfare, and to encourage veterinarians and VSs to take greater responsibility for animal welfare. Strengthening Veterinary Services In order to adequately implement OIE standards, a country requires a VS with adequate human, physical, and financial resources, technical authority and capacity, interaction with stakeholders, and access to markets. However, more than 120 of the 175 OIE
members are developing countries where VSs may not always comply with international OIE standards on the quality and performance of VS. The OIE sees VSs as a global public good and their compliance with international standards as a priority for public investment. The OIE is therefore actively engaged in the evaluation and improvements of the capacities of national VS. The process chosen by the OIE consists of the democratic adoption of quality standards contained in the Terrestrial Animal Health Code, and the creation of a tool to analyze the conformity of the countries to the standards. The OIE’s tool for the evaluation of the performance of VSs, the PVS tool, is designed to assist VSs to establish their current level of performance, to identify gaps and weaknesses regarding their ability to comply with standards described above, and to establish priorities and carry out strategic initiatives. This tool is the principal lever of the OIE to bring compliance with quality standards in the governance of VSs of all countries. The PVS establishes a diagnostic. The OIE also offers a gap analysis in collaboration with FAO and various key funding agencies, permitting members to define detailed priorities for investment in order to be able to comply using their national budget and priorities and, if needed, soliciting aid from the international community. For member countries requesting assistance with capacity building, the OIE also provides expertise and training for national senior officials, both to improve sanitary governance and to help prepare and implement animal disease control and eradication programs.
Standard Setting Procedures and Publication of International Animal Health Codes The Terrestrial Animal Health Code, now in its 17th edition (2008), and the Aquatic Animal Health Code, in its 10th edition, are intended to assure the sanitary safety of international trade in terrestrial and aquatic animals and their products and to provide surveillance methods for important animal diseases. This is achieved through the detailing of health measures to be used by veterinary authorities to avoid the transfer of agents pathogenic to animals or humans, while avoiding unjustified sanitary barriers and while implementing surveillance of major diseases. They are written in two sections: the first contains recommendations that apply to a wide range of topics, production sectors, and/or diseases (so-called ‘horizontal standards’) and the second contains recommendations on specific diseases (so-called ‘vertical standards’) including
Office of International Epizooties | Mission, Organization and Animal Health Code
recommendations on agent inactivation and on surveillance and risk assessment. The horizontal standards include most notably the general and ethical obligations for importing and exporting countries, methodologies for risk analysis, and the criteria by which diseases are included on the list and by which countries are to report disease outbreaks to the OIE. Other horizontal standards are animal welfare standards, veterinary public health measures such as the role of VSs in food safety, and the responsible use of antimicrobials in veterinary medicine. The second section of the Codes consists of recommendations applicable to specific diseases on the OIE list. The diseases selected for inclusion in this list affect fish, shellfish, mammals, birds, or bees. These include diseases that are considered the most serious due to their potential for rapid spread beyond national borders, or for transmission to humans, as well as diseases that are less highly contagious but whose economic or health importance justifies their being taken into consideration in international trade. Each disease is dealt with in a separate chapter. Diseases are grouped as those that affect multiple species and those that affect a single species. There are more than 100 terrestrial and aquatic animal diseases for which standards have been developed. These standards are related to the risks of transmission of the diseases or disease-causing agents linked to animal and animal products. But certainly it should be noted that certain products or commodities subjected to specific treatments may in fact pose no risk, no matter the sanitary status of the country. The recommendations contained in the OIE Animal Health Codes are developed with the active participation of member countries, knowing that these will apply equally to themselves and to others. They are the fruit of a consensus of very senior veterinary authorities of member countries, thus accounting for their value and their very wide practical application. Procedures for Updating the Codes All standards are prepared and submitted by the elected specialized commissions to the World Assembly of National Delegates. They are adopted following the rule of ‘one country – one vote’.
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laboratories. Their purpose is to contribute to the international harmonization of methods for the surveillance and control of the most important animal diseases. Standards are described for laboratory diagnostic tests and the production and control of biological products (principally vaccines) for veterinary use across the globe, providing internationally agreed diagnostic laboratory methods. The Manuals set laboratory standards for all OIE-listed diseases as well as several other diseases of global importance. In particular, they specify those ‘prescribed tests’ that are recommended for use in health screening for international trade or movement of animals.
Other OIE Activities Communication In recognition of the centrality of communication for the VSs, which underpins everything they do, including disease surveillance, prevention, control and response, animal welfare, public health, and food safety, guidelines on communication useful for national VSs are being developed for inclusion in the Code. Veterinary Education In line with OIE’s efforts to strengthen VSs is the recognition that veterinary education is basic to an effective VS. Society has placed increasing demands on veterinarians in the fields of food security, food safety, public health, and animal welfare. The OIE recognizes these, seeing them as integral to veterinary education. The harmonization and quality of veterinary curricula are a crucial component of sound national animal health systems. A principal mandate of the regional representations and the subregional representations is to develop programs for capacity building in the members for the benefit of the delegates, and their national focal points, the people officially identified as national contacts with the OIE in specific areas. As part of its multifaceted approach to improve VSs, the OIE has organized a meeting of all the world’s veterinary schools with the aim of helping them incorporate into their curricula the concepts with the international public good principles expected from veterinary missions and activities.
Other OIE Standards and Guidelines While the Codes are highly important documents, it should be noted that they must be used with the companion documents, the Manual of Diagnostic Tests and Vaccines for Terrestrial Animals (Terrestrial Manual) and the Manual of Diagnostic Tests and Vaccines for Aquatic Animals, the reference standards for veterinary
Conclusion A Global Public Good Among the many challenges facing the world, the dramatic increase of human and domestic animal populations, globalization and the unprecedented movement
8 Office of International Epizooties | Mission, Organization and Animal Health Code
of people and commodities worldwide, and the increasing encroachment on natural ecosystems are leading to increasing disease threats. As the interrelationships between animal and human health and the health of the ecosystem are better understood, it becomes clear that the consequence of an effective VS is a healthier animal and human population, less afflicted by zoonotic diseases, better nourished, and participating in an improved world economy. This entails prevention and control of emerging diseases at the human–animal interface. The concept of ‘One World, One Health’ has been developed jointly by the WHO, FAO, UNICEF, World Bank, and OIE, and accepted by most other international health organizations. It is based on more preventative actions, increased cooperation between VSs and public health authorities, and on strengthening emergency response capabilities while helping the poorest nations and strengthening animal and public health systems. The result should be a better capacity to respond to emerging disease situations. All countries must be prepared in face of these new disease threats and it is widely accepted that the work of the VSs is a global public good.
Since its inception in 1924, the OIE has been the global leader in animal disease prevention and control, has served as a focal point for international cooperation on animal health issues, has promoted global safe trade in animal products, has promoted transparency on the global situation of animal diseases including zoonoses, and has shared veterinary expertise among member countries. With increasing trade, growing demand for foods of animal origin, growing disease threats, unprecedented movements of people and animals, and a changing climate, the role of the OIE has increasing importance. The larger vision of the OIE of contributing to improving public health, food safety and security, and the livelihoods of poor farming communities can only be achieved if governments agree to foster closer cooperation between all the sectors in the health system, to support VSs, and to share information.
Relevant Websites http://www.oie.int – World Organisation for Animal Health.
ORGANIC DAIRY PRODUCTION K Shea, Horizon Organic, Longmont, CO, USA ª 2002 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2193–2199, ª 2002, Elsevier Ltd.
History In the early days of organic agriculture, products were sold at farmers’ markets, cooperatives and directly from the farm. The definition of ‘organic’ and the actual methods for raising the products as organic varied from place to place and farm to farm. Gradually private and public institutions began emerging to set organic farming standards and provide third-party verification of label claims. Many producers turn to organic farming systems in order to take advantage of the high-value niche market and improve farm income, thereby enabling themselves to compete in today’s vertically integrated agriculture system. Organic producers have an intense belief that their farming system is superior in its ability to care properly for the land and its finite resources. Today, organic production is well defined and has matured into a significant market segment.
Market Trends According to the US Department of Agriculture, the amount of farmland managed under certified organic practices has expanded dramatically, as has consumer demand for organically grown food. In the United States, organic farming became one of the fas test-growing trends in agriculture during the 1990s. Certified organic cropland more than doubled from 1992 to 1997, and two organic livestock sectors – eggs and dairy – grew even faster. Organic foods are one of the top consumer trends today, accounting for more than US$7.8 billion in annual sales, and doubling every 4 years since 1990. The Western Agricultural Economics Association published information on sales of organic milk in mainstream supermarkets showing a growth over the last 8 years, reaching US$75.7 million in 1999. Organic dairy products can be found in conventional supermarkets and natural-food stores across the United States and in the
United Kingdom, where the demand for organic milk and dairy produce is now growing strongly. One leading retailer is predicting a 10-fold increase in its sales over the next 5 years. The Soil Association shows the United Kingdom organic food market currently growing at around 40% year 1 and by 2002 it is expected to top £1 billion. The organic sector in Canada is small but growing rapidly. According to industry sources, farm cash receipts from this industry reached about Can$500 million in 1999, with an estimated retail value of Can$1 billion, including processed and nonprocessed products. Canadian organic retail sales growth is expected to rise from Can$0.7 billion in 1997 to Can$3.1 billion in 2005, which equates to an average growth of 20% annually. The industry anticipates that its market share will increase to 10% of the Canadian retail market by 2010. Worldwide, growth in organic retail sales is between 20% and 30% per annum. At this rate, 30% of the land in Europe is predicted to be in organic production or in conversion to organic by 2010. In Europe, organic retail sales are estimated at approximately US$7.5 billion, in the United States at US$6.5 billion and in Japan at US$1.5 billion. It is predicted that, by 2005, the industry in Japan will hit the US$10 billion mark. Although still fledgling in Australia, the organic industry turns over US$250 million per year in retail sales of organic food and it exports approximately US$25–30 million worth of organic produce. The Organic Products Exporters of NZ Inc. (OPENZ) was formed to encourage and support companies and organizations, which have an interest in the New Zealand organic export industry. OPENZ reported a significant increase in the value of organic exports to June 2000. Survey results showed that New Zealand certified organic exports reached over NZ$60 million for the year 1999–2000. This was an increase of 77% on the previous year’s figure of NZ$34.08 million. The survey was administered by Trade New Zealand and received responses from 34 out of the 40 exporter members of OPENZ.
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Organic Dairy Production
A report suggesting organic dairy products will become a profitable, long-term niche market worth up to NZ$200 million a year within a decade has convinced the Dairy Board to foster organic farming in New Zealand. New Zealand currently exports about NZ$60 million-worth of organic products, mostly fruit and vegetables. It has been estimated that the organic market will be unlikely to exceed 5% of the board’s NZ$7.6 billion business, but it is a niche that the board wishes to exploit.
International Organic Standards Comparisons There have been organic standards in the European Union (EU), and EU regulation 2092/91 has been in force since 1991. In many European countries, organic agriculture is known as ecological agriculture, reflecting the reliance on ecosystem management rather than external inputs. According to the Codex Alimentarius Commission: Organic agriculture’s increased momentum is due to consumer demand and to positive environmental impact. Many aspects of organic farming are important elements of a systems approach to sustainable food production, including in developing countries, both for domestic consumption and export. The Committee on Food Labeling of the Codex Alimentarius Commission has developed Guidelines for the Production, Processing, Labelling, and Marketing of Organically Produced Foods (Table 1). The International Federation of Organic Agriculture Movements (IFOAM) represents, internationally, the organic movement in parliamentary, administrative and policy-making forums. IFOAM has consultative status with the UNO and FAO. It sets and regularly revises the international IFOAM Basic Standards of Organic Agriculture and Food Processing, which are translated into 19 languages. IFOAM also operates the International Organic Accreditation Services, Inc. (IOAS), in order to administrate the IFOAM Accreditation Program to ensure equivalency of certification programs worldwide. In the United Kingdom, the integrity of organic food is safeguarded by international legislation. Organic livestock production is regulated by EU Regulation 804/ 1999. The United Kingdom Register of Organic Food Standards (UKROFS) is the British control body for the organic sector. Food sold as organic anywhere in the EU must be certified as produced under an approved system authorized by an official inspection and certification service. The Soil Association is the best known of the UKROFS validating bodies.
Canadian organic dairy products have been widely distributed since 1995 and, in Canada, there is more information available on organic dairy farming, than on other types of livestock farming. The Canadian Organic Advisory Board Inc. (COAB) was established in 1992 as a national, nonprofit advisory body to represent the interests of organic production and certification groups across Canada. The Board is a vehicle for collaboration of stakeholders within the organic industry and, notably, agencies within the federal and provincial government that have been involved in the development of organic standards. The Certified Organic Associations of British Columbia (COABC) works on a voluntary basis to maintain a credible set of organic production and processing standards. COABC ensures compliance with the standards by administrating the accreditation and auditing process in partnership with the British Columbia Ministry of Agriculture, Fisheries and Food (BCMAFF). The United States signed into law the Organic Foods Production Act (OFPA) in 1990. The final rule implementing OFPA was published in the Federal Register in December of 2000. This final rule establishes the National Organic Program (NOP) under the direction of the Agricultural Marketing Service (AMS), an arm of the US Department of Agriculture. The goal of this national program is to facilitate domestic and international marketing of fresh and processed food that is organically produced and to assure consumers that such products meet consistent, uniform standards. To ensure that access of New Zealand organic products into the EU is maintained, the Organic Products Exporters Group Inc. (OPEG) has requested that the Ministry of Agriculture and Forestry (MAF) Food establish an Official Organic Assurance Program for organic products exported to the EU. The objective of this program is to provide an official assurance to the EU that organic products exported from New Zealand comply with the requirements of Council Regulation 2092/91. Japan’s Ministry of Agriculture, Forestry and Fisheries (MAFF) have completed the development of their own national standard for organic production using the Codex Guidelines for the Production, Processing, Labelling, and Marketing of Organically Produced Foods as a base. The Japan standard covers plant products only and Japan’s MAFF have advised that imported products labeled as organic will need to comply with the standard by April 2001. A comparison of standards around the world shows that they are mostly consistent but do vary in a few areas. These areas are pasture requirements, percent of total feed which must be organic and the use of antibiotics.
Table 1 Standards for organic dairying International Federation of Organic Agricultural Movements
Codex (1999 Draft only, not agreed upon)
Living conditions as related to access to pasture or free range
Access to open air and/ or grazing appropriate to type of animals and season
Herbivores must have access to pasture. May allow exceptions in certain circumstances
Conversion: dairy herds
Not less than 30 days
Still under discussion
Feed
Health care
12 months organic feed, 90 days health and living conditions 100% organically grown feed, with 50% coming from farm or produced within the region. If impossible, allowance for 15% of feed from nonorganic sources Natural medicines and methods emphasized. Use of conventional veterinary medicines allowed when no alternatives are available
Should be 100% organically grown. If operator can demonstrate such feed is not available, livestock will maintain status with 85% organic feed Use of veterinary drugs prohibited in absence of an illness. If no alternative permitted treatment or management, vaccinations and therapeutic uses permitted. Should not withhold necessary treatment to maintain organic status
Canada June 1999 Environment suited to their needs that provides regular access to pasture, free-range open-air runways or other areas subject to weather and ground conditions In accordance with the standards for at least 12 months
Certified Organic Associations of British Columbia 1997 Free access to pastures, paddocks or runways. Access to grazing land 120 days of the year
12 months incorporating all required practices. Replacements 90-day transition if certified livestock not available but must be heifers or 120-day dry-treated cows
US Department of Agriculture NOP 2000
Soil Association UK 1998
Access to outdoors and direct sunlight. Access to pasture for ruminants. Allows temporary exemptions in case of certain circumstances or to protect soil 12 months incorporating all required practices. New herd conversion, 80% organic feed for first 10 months
All stock must have access to pasture during grazing season unless specifically exempted
12 weeks
100% from organic sources. May be 85% for ruminants in the short term only
Certified organic required, certified transitional feed is regulated
Certified organically produced feed and pasture required
Livestock systems should be planned to provide 100% in accordance with standards. Allowed 90% on a daily basis, or 85% dairy stock
Vaccination and use of veterinary drugs allowed only when disease cannot be combated by other means. Withholding of necessary treatments to maintain organic status is not permitted
Vaccinations allowed as appropriate to each bioregion. Withholding of necessary medical treatment that would disqualify organic status is prohibited
Vaccinations allowed. Administrations of medications in absence of illness prohibited. Withholding treatment to maintain organic status causing suffering or death shall be grounds for decertification
Use of veterinary medical products where no known problem exists prohibited. Medications must never be withheld where it will result in unnecessary suffering. Vaccines restricted to known disease risk that cannot be controlled by other means (Continued )
Table 1 (Continued) International Federation of Organic Agricultural Movements
Codex (1999 Draft only, not agreed upon)
Use of antibiotics
When conventional veterinary medicines are used the withholding period shall be at least double
Withdrawal periods double that required by legislation. After 2005 antibiotics not allowed
If veterinary drugs used, withdrawal period at least double
Use of parasiticides
When conventional veterinary medicines are used the withholding period shall be at least double
Withdrawal periods double that required by legislation
If veterinary drugs used withdrawal at least double
Canada June 1999
Certified Organic Associations of British Columbia 1997 Not permitted for slaughter animals. Allowed for breeding animals but not in a subtherapeutic manner. Use on animals in 3rd trimester or during lactating will disqualify offspring for slaughter. Milk to be withheld for 30 days or twice withdrawal period if longer Not permitted for slaughter animals. Allowed for breeding herd use but use in 3rd trimester or during lactation disqualifies offspring as organic for slaughter purposes
US Department of Agriculture NOP 2000
Soil Association UK 1998
Not permitted
Permitted in clinical cases where no other remedy is effective. Withdrawal at least three times that permitted on product license and not less than 14 days
Not permitted for slaughter stock. Allowed in breeder stock if sickness or infection present; routine use not allowed. Progeny can be sold as organic but not if used during 3rd trimester of gestation or during lactation. 90day withdrawal or dairy animals
Permitted when used therapeutically when clinical symptoms appear. Restricted use on routine basis over a specific time period as part of the disease reduction program. Ivermectin-based products prohibited
Organic Dairy Production
Before the NOP rule was published, certification agency standards in the United States varied in regards to antibiotics. Some allowed none; other allowed their use with a 30–90-day withdrawal period. During this withdrawal period, the milk or milk products could not be sold as organic, and the meat could never be used as organic. Today under the NOP, antibiotics are never allowed on organic cattle. Under COABC regulations, cows can be brought back into the milking string after 30 days. Though the particulars of organic livestock production may vary between nations, around the world the standards emphasize proactive health care, the principle of prevention versus treatment. Healthy cow care and early sick-cow recognition are crucial. By doing the utmost to control the animals’ environment, and thereby prevent illness and lower stress, the animals remain healthier than similar cows where these preventative practices are not performed. Standards usually require access to the outdoors, fresh air, sunlight and shelter, and they recognize species-appropriate behavior and make allowances for it. Using the NOP as a model, here is a glimpse into organic certification requirements: The farmland itself must have no prohibited materials applied to it for at least 36 months before the harvest of organic crops. It must have distinct, defined boundaries and buffer zones such as runoff diversions to prevent the unintended application of a prohibited substance to the crop or contact with a prohibited substance applied to adjoining land that is not under organic management. The producer must select and implement tillage and cultivation practices that maintain or improve the physical, chemical and biological condition of soil and minimize soil erosion. The producer must manage crop nutrients and soil fertility through rotations, cover crops, and the application of plant and animal materials. Milk or milk products must be from animals that have been under continuous organic management beginning no later than 1 year prior to the production of such products, except for the conversion of an entire, distinct herd to organic production. For the first 9 months of the year of conversion, the producer may provide the herd with a minimum of 80% feed that is either organic or produced from land included in the organic system plan and managed in compliance with organic crop requirements. During the final 3 months of the year of conversion, the producer must provide the herd with 100% organic feed. The producer of an organic livestock operation must maintain records sufficient to preserve the identity of all organically managed livestock and all edible and nonedible organic livestock products produced on his or her operation. The producer must not use animal drugs, including hormones, to promote growth in an animal or provide feed supplements or additives in amounts above those
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needed for adequate growth and health maintenance for the species at its specific stage of life. The producer of an organic livestock operation must establish and maintain preventive animal health care practices. The producer must establish appropriate housing, pasture conditions and sanitation practices to minimize the occurrence and spread of diseases and parasites. Animals in an organic livestock operation must be maintained under conditions that provide for exercise, freedom of movement and reduction of stress appropriate to the species. Additionally, all physical alterations performed on animals in an organic livestock operation must be conducted to promote the animals’ welfare and in a manner that minimizes stress and pain. The producer of an organic livestock operation must administer vaccines and other veterinary biologics as needed to protect the well-being of animals in his or her care. When preventive practices and veterinary biologics are inadequate to prevent sickness, the producer may administer medications included on the National List of synthetic substances allowed for use in livestock operations. The producer may not administer synthetic parasiticides to breeder stock during the last third of gestation or during lactation if the progeny is to be sold, labeled, or represented as organically produced. After administering synthetic parasiticides to dairy stock, the producer must observe a 90-day withdrawal period before selling the milk or milk products produced from the treated animal as organically produced. Every use of a synthetic medication or parasiticides must be incorporated into the livestock operation’s organic system plan subject to approval by the certifying agent. The producer of an organic livestock operation must not treat an animal in that operation with antibiotics, any synthetic substance not included on the National List of synthetic substances allowed for use in livestock production, or any substance that contains a nonsynthetic substance included on the National List of nonsynthetic substances prohibited for use in organic livestock production. The producer must not administer any animal drug, other than vaccinations, in the absence of illness. The use of hormones for growth promotion is prohibited in organic livestock production, as is the use of synthetic parasiticides on a routine basis. The producer must not administer synthetic parasiticides to slaughter stock or administer any animal drug in violation of the Federal Food, Drug, and Cosmetic Act. The producer must not withhold medical treatment from a sick animal to maintain its organic status. All appropriate medications and treatments must be used to restore an animal to health when methods acceptable to organic production standards fail. Livestock that are treated with prohibited materials must be clearly identified and shall not be sold, labeled or represented as organic.
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Organic Dairy Production
A livestock producer must document in his or her organic system plan the preventative measures he or she has in place to deter illness, the allowed practices he or she will employ if illness occurs, and his or her protocol for determining when a sick animal must receive a prohibited animal drug. These standards will not allow an organic system plan that envisions an acceptable level of chronic illness or proposes to deal with disease by sending infected animals to slaughter. The organic system plan must reflect a proactive approach to health management, drawing upon allowable practices and materials. Animals with conditions that do not respond to this approach must be treated appropriately and diverted to nonorganic markets. The producer of an organic livestock operation must establish and maintain livestock living conditions for the animals under his or her care which accommodate the health and natural behavior of the livestock. The producer must provide access to the outdoors, shade, shelter, exercise areas, fresh air and direct sunlight suitable to the species, its stage of production, the climate, and the environment. This requirement includes access to pasture for ruminant animals. The producer must also provide appropriate clean, dry bedding, and, if the bedding is typically consumed by the species, it must comply with applicable organic feed requirements. The producer must provide shelter designed to allow for the natural maintenance, comfort level, and opportunity to exercise appropriate to the species. The shelter must also provide the temperature level, ventilation and air circulation suitable to the species and reduce the potential for livestock injury. The producer may provide temporary confinement of an animal because of inclement weather; the animal’s stage of production; conditions under which the health, safety, or well-being of the animal could be jeopardized; or risk to soil or water quality. The producer of an organic livestock operation is required to manage manure in a manner that does not contribute to contamination of crops, soil or water by plant nutrients, heavy metals or pathogenic organisms and optimizes nutrient recycling.
Future of Organic Dairying Nitrogen self-sufficiency through the use of legumes and biological nitrogen fixation, as well as effective recycling of organic materials, including crop residues and livestock manure, will positively affect the impact of the farming system on the wider environment. These practices, coupled with conservation of wildlife and natural habitats, are some of the many benefits of organic production practices. Livestock manures are one of the most valued resources on an organic farm or ranch. Conservation of manure and its proper application are a key means of
recycling nutrients, building soil and improving the sustainability of an organic operation. Ideally, manures for organic crop production are composted. However, uncomposted manures are allowed with restrictions. Raw, uncomposted livestock manures may not be applied to crops destined for human consumption unless incorporated into the soil a minimum of 120 days prior to harvest. At the same time, water resources must be protected. Fertilizers and manures must be applied to prevent runoff and leaching, fields must be managed to prevent erosion, and ‘catch crops’ must be used where necessary to soak up excess nitrogen. Riparian zones must be stabilized and protected, natural wetlands must be maintained and protected, and waterways must be protected from livestock and livestock waste through the use of fencing and water tanks to prevent fouling natural streams. Fliebach, Mader, Pfiffner, Dubois and Gunst recently released results of a 21-year field trial in Switzerland, comparing organic and nonorganic farming systems. The study shows dramatic differences in soil health. It was reported that there were more microorganisms (which play a role in soil fertility and delivering nutrients to roots) in the organically managed field than in the conventionally managed field. Consumers have become increasingly aware of these environmental issues. The alleged liberal use of pesticides by farmers and the purported suffering of livestock have been highlighted in the press over recent years, and caused rising numbers of consumers to turn to organic products. The organic sector is growing with sales projected to increase from $US1.31 billion in 1995 to $US4.37 billion in 2005. At present highest demand in the market is for single ingredients in the form of organic milk, cheese or yogurt. An increase in unit shipments of organic dairy desserts and organic ready-made meals is expected and should increase revenues over the rest of the forecast period. See also: Manure/Effluent Management: Nutrient Recycling; Systems Design and Government Regulations. Office of International Epizooties: Mission, Organization and Animal Health Code. Policy Schemes and Trade in Dairy Products: Codex Alimentarius; Trade in Milk and Dairy Products, International Standards: Harmonized Systems.
Further Reading Canford P (2001) The Origins of the Organic Movement. Edinburgh: Floris Books. Fliebach A and Mader P (2000) Microbial mass and size-density actions differ between soils of organic and conventional agricultural systems. Soil Biology and Biochemistry 32, pp. 757–768. Lampkin N, Foster C, and Padel S (1999) Organic Farming in Europe: Economics and Policy. Germany: Hohenheim, Stuttgart.
Organic Dairy Production Macey A (ed.) (2000) Organic Livestock Handbook. Ottawa, Canada: Canadian Organic Growers Inc. Willer H and Yussefi M (2001). Organic Agriculture Worldwide: Statistics and Future Prospects. http://www/soel.de/inhalte.publikationen/ s74ges.pdf /.
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Information on organic farming is available for the following countries at the website addresses below: Canada: http://www.cog.ca Europe: http://www.organic-europe.net New Zealand: http:// www.organicsnewzealnd.org.nz/index.htm United States: http:// www/ams.usda.gov/nop.
P PACKAGING
V B Alvarez and M A Pascall, The Ohio State University, Columbus, OH, USA ª 2011 Elsevier Ltd. All rights reserved.
Introduction The packaging of food can be traced to ancient times although its early beginning was with crude materials. Early reports document wine being stored in animal skin and various liquids including water being packaged and stored in earthen vessels. Increases in the complexity of human civilization also saw the development and use of diverse types of packages made from varying types of materials. The Industrial Revolution, which started during the 1700s, also had an effect on food packaging because the new industrial workers demanded a more convenient manner for transporting and storing meals. Beginning in the 1950s and within modern times, the growth of the fast-food industry has significantly influenced the food-packaging industry. Examples of foods in this category include gravy preparations, dry cake mixes, boil-in-bag foods, and TV dinners. These developments created a demand for new types of packages. The packaging of fluid milk started prior to the 1950s when Gail Borden discovered and patented the process for condensed milk. This occurred in 1856 and was followed by the development of the glass milk bottle in 1884, the invention of the automatic bottle filler and capper in 1886, and the introduction of the first plastic-coated paper milk carton in 1932. Due to the properties of milk and dairy products, packaging is considered to be a critical step in the processing operations. The reason is that packaging is the last link in the processing chain. If the choice of packaging is inappropriate or its failure occurs during handling, transportation, and storage of milk products, the processing steps would be useless, even if they were properly executed. In an attempt to minimize food
16
safety hazards associated with inadequately processed and/or packaged milk products, the Pasteurized Milk Ordinance (PMO) enacted by the US government mandates regulatory guidelines for the dairy industry. Figure 1 shows a typical fluid milk filling room that complies with the PMO’s requirements. The filling room is separated from other processing operations, and the equipment and facilities have the infrastructure to prevent any contamination of milk.
Purpose of Packaging of Dairy Products The systems and requirements for packaging of dairy products are similar to those of other foods. Milk and dairy products are packed in various types of packaging materials depending on the specific product properties, processing conditions, storage, handling, and end use. The primary purposes of packaging are to preserve and protect dairy products against spoilage and harmful factors in the outside environment, to contain specific amounts of the product in units that are easy to handle during production, storage, transportation, and consumption, and to provide information about the product to the consumer and regulators. Important considerations about materials used to package dairy products are toxicity and compatibility with the product, resistance to impact, maintenance of sanitation, odor and light protection, tamper resistance, size specifications, shape and weight requirements, marketing appeal, printability, and cost. Examples of packaging types used for dairy products include glass and plastic bottles, gable-top and bricktype cartons, bags, pouches, two- and three-piece cans, aerosol containers, plastic tubs, and other containers.
Packaging 17
Figure 1 Traditional milk filler room that meets the Pasteurized Milk Ordinance requirements to prevent milk contamination. Courtesy of Seiberling Inc.
Table 1 lists the common packaging materials, their properties, advantages, and disadvantages, and dairy products that are packaged in containers fabricated from them.
Packaging of Dairy Products Fluid Milk This is currently marketed as standardized low-fat milk with 0.5, 1.0, 1.5, or 2.0% fat content. It is also marketed as skim milk with > :
k¼1
; PRþ u
1 PHp k ¼ 1 e ðt þ kÞ ;eðt þ kÞ ¼ ref ðt þ kÞ – Hp yp ðt þ kÞ;uðt þ kÞ ¼ uðt þ k – 1Þ – uðt þ k – 2Þ; is the prediction model response. The prediction horizon Hp is the number of time steps over which the prediction errors are minimized, and the control horizon Hc is the number of time steps over which the control increments are minimized. u ðt þ kÞ; u ðt þ k þ 1Þ; . . . u ðt þ Hc Þ are tentative values of the future control signal, which are limited by umin and umax . The controller is denoted as an ET MPC formulation because the optimization is performed only when the error function EP is bigger than a predefined real positive value . To reduce the computational burden when the error is less than , the control action is equal to u , which is the last value of u, computed before the error enters the strip. Note that EP in eqn [17] is defined as the mean value of the future errors, between the predicted output and its reference along the next Hp steps. where EP ¼
Conclusion In new integrated dairy plants, each process is carried out in multiple phases, and there exists strong nonlinear and dynamic effects between the variables. Therefore, modern process control systems have usually a hierarchical architecture including decentralized controllers, remote input and output (I/O) modules, fieldbus systems, local area networks (LANs), and smart sensors and other devices. The huge amount of information flows are stored and used online or off-line for executing the IC alternatives like FLC, ANN MPC, or SPC, all methods described in this article. Interested readers are advised to consult not only the references in the ‘Further Reading’ section but also to
½17
; if EP <
follow publications in the Journal of Food Engineering, Journal of Biotechnology and Bioengineering, and the International Dairy Journal.
Acknowledgment This work was financially supported by the Portuguese Foundation for Science and Technology within the activity of the Institute of Electronic Engineering and Telematics of Aveiro (IEETA). See also: Plant and Equipment: Instrumentation and Process Control: Instrumentation.
Further Reading Braha D (2001) Data Mining for Design and Manufacturing: Methods and Applications (Massive Computing). Dordrecht, Netherlands: Kluwer Academic Publishers. Burns RS (2001) Advanced Control Engineering. Linare House, Jordan Hill, Oxford: Butterworth-Heinemann. Camacho EF and Bordons C (2004) Model Predictive Control in the Process Industry. London: Springer-Verlag. Haykin S (1999) Neural Networks: A Comprehensive Foundation. Upper Saddle River, NJ: Prentice Hall. Nagy ZK and Braatz RD (2003) Robust nonlinear model predictive control of batch processes. AIChE Journal 49: 1776–1786. Norgaard M, Ravn O, Poulsen NK, and Hansen LK (2000) Neural Networks for Modelling and Control of Dynamic Systems. London: Springer-Verlag. Oliveira C, Georgieva P, Rocha F, Ferreira A, and Feyo de Azevedo S (2007) Dynamical model of brushite precipitation. Journal of Crystal Growth 305: 201–210. Oliveira C, Georgieva P, Rocha F, and Feyo de Azevedo S (2008) Artificial neural networks for modeling in reaction process systems. Neural Computing & Applications 18: 15–24.
Plant and Equipment | Instrumentation and Process Control: Process Control Petermeier H, Benning R, Delgado A, and Becker T (2002) Hybrid model of the fouling process in tubular heat exchangers for the dairy industry. Journal of Food Engineering 55: 9–17. Rossiter JA (2003) Model Based Predictive Control. A Practical Approach. New York: CRC Press. Simoglou A, Georgieva P, Martin EB, Morris J, and Feyo de Azevedo S (2005) online monitoring of a sugar crystallization process. Computers & Chemical Engineering 29: 1411–1422.
251
Simoglou A, Martin EB, and Morris AJ (2002) Statistical performance monitoring of dynamic multivariate processes using state space modelling. Computers & Chemical Engineering 26: 909–920. Sua´rez LAP, Georgieva P, and Feyo de Azevedo S (2009) Computationally efficient process control with neural network-based predictive models. International Joint Conference on Neural Networks (IJCNN), Atlanta, GA, USA, 14– 9 June. Wang XZ (1999) Data Mining and Knowledge Discovery for Process Monitoring and Control (Advances in Industrial Control). London: Springer.
Robots J C Oliveira, University College Cork, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction Robots are electromechanical devices that perform repetitive operations otherwise carried out by humans. In a modern dairy factory, human handling is rare in processing equipment; from liquid milk to packaged product, there are few, if any, manual operations. Even packaging lines have been highly automated, and operators in a modern dairy plant are needed mostly to load/unload some machines, check the controls, and react to production problems. The interest in robots in dairy lies mostly in the two extremes of the process: (1) milking and herd management; (2) final palletizing and stock management. Robots rarely look like humans, as they only need to have the parts that perform the specific action. In essence, an industrial robot must have sensors to detect positions, shapes, and forms, a program that allows it to identify what it will be handling, moving parts with grippers for grabbing and handling, and other sensors directing the moving parts to place what it is handling in the correct position. They may also have valves, pumps, and other devices, depending on the nature of the action they need to perform. Robots must be programmable, so that the actions can be set up by the operator with the required flexibility. This is the main reason why robots are a solution where automation is otherwise not possible. Usually, a period of training of the program will be necessary, so the accuracy of the action can be adjusted to the inputs from the sensors. Dairy offers a good example of the difference between automation and robotics. The latter implies the former, but not the reverse. It is possible to milk a cow using automated systems that collect the milk and even detach the cups from the teats automatically, once they detect that milking should cease. However, it takes a human to place that automated milking device on a cow, because individual animals have their own size and anatomy and teats may be affected by some illness or defect and cannot be handled as if they were all the same. Furthermore, mastitis or any problem with teats or the udder needs to be assessed, and individual animals may need individual attention in feeding or medication. Using robots means that humans are no longer needed for these actions. Simple automation can work only for standardized situations, while robotics can provide the flexibility that the human analysis gives, by mimicking what that analysis does.
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Robots can have several advantages. The most obvious are that they can have much higher productivity and consistency than humans, and that they minimize labor costs. In the food industry, in general, they also have the advantage of high hygienic conditions and ease of sanitizing, compared to humans, therefore ensuring more aseptic conditions. Whether they are a valuable investment or not depends, therefore, on their costs versus labor costs, productivity gains, and lower quality rejection costs. There are other benefits that may accrue in some specific cases, and milking is one of those.
Milking Robots Milking robots have been one of the most popular applications of robotics in agriculture. The first farm to implement such a system in Europe did so in 1992; the first installation in North America was in 1999 (Canada). Interest in the subject rose steadily in the 1990s. In 1997, Computers and Electronics in Agriculture devoted a special issue to robotic milking. In 2000, the European Union commissioned a project on the introduction of automatic milking on dairy farms, under its R&D Framework Programme, which also produced substantial information and analysis (completed in 2003, but the website is still accessible). The Future Dairy project run in Australia also provides comprehensive information and details to assist farmers in evaluating the interest these systems may have for them. In 2006, there were over 4000 farms worldwide reported to use robotic milking. The need to lower farming costs, and particularly labor costs, in developed countries is the most obvious driver for investment. Lack of human resources for farming is also a growing problem in these countries, as the average age of farmers continues to increase, and less people are willing to work as salaried peasants. Robots that facilitate strenuous farm activities have also been claimed to permit farmers to work to a later retirement age, and to be able to take care of themselves better (e.g., cows need to be milked daily even if the farmer needs to be in hospital for a couple of days). Labor issues are therefore a primary reason for a dairy farmer to decide investing in robotic milking, but it should be noted that in farming that is more than just costs. Furthermore, a fully automated milking system (AMS) has other advantages:
Plant and Equipment | Robots
1. The increased sanitization and hygienic conditions from the absence of humans minimize crosscontamination of mastitis and health problems in general (not only between animals, but also between animals and humans), which improves well-being and minimizes health costs. 2. Milking can take place at any time throughout the day, therefore avoiding that animals may need to wait for long times, thus improving their general wellbeing. 3. Animals can be milked more than the conventional 2 times daily. It has been found that increases in milk production of 5 up to 25% typically result from increasing milking from 2 times daily to 3 times daily. 4. Each animal can set the regime that suits it best, instead of a ‘one-size-fits-all’ scheduling of conventional milking (with robotic milking, the animal decides when to be milked). As a result, well-being and production are improved. 5. Feed regimes can be individualized. Typically, animals are attracted to the milking robot by feeding, and so milking robots can also control the feed and nutrient intake, as well as any medication needed. 6. Milking robots can also detect illnesses, such as mastitis, and presence of blood or contaminants in the milk with sensors, besides knowing if the specific animal is going through some medication regime, and automatically divert contaminated milk, thus allowing for an easy management of health-related issues in milk collection. Milking robots cannot be confused with automatic milking systems operated by people, where the animal traffic is controlled by farmers, the animals are placed in position, and automated milking cups are then placed by farmers on the teats for automatic pumping and collection in vats, such as in a rotary dairy parlor. Relatively new dairies may have quite some automation already, such as in-shed computer-managed feeding, automatic cup removal (ACR), teat spraying, and drafting. In fact, one could consider that the only new element of the robot is automatic cup attachment (ACA), so why not add just that one element in an already fairly automated process? Unfortunately, retrofitting a rotary dairy for robotics is not feasible, and in general, any previous automations are made redundant if a farmer invests in milking robots. Typically, robotic milking goes together with free animal traffic, and the animal is motivated to go to the robot, rather than being pushed or forced in some way. Feeding is the usual attraction. As an animal approaches an available robot, its entrance gate opens, the animal goes in to feed, and the gate then closes. The robot detects the individual animal from its collar or tag (if fitted with a relevant device, such as a small radio frequency tag), and may therefore dispense a tailored feed (with eventual
253
medication or supplementation needed). The sensors detect the position and size of the animal, and activate an electromechanical arm that reaches under the udder and puts the automated milking cups in place. Teats are brushed first and cups attached one at a time. The robot will also have sensors to detect the flow rate of milk, so it controls the milking amount (thus avoiding overmilking), as well as color, conductivity, and presence of blood. It can therefore divert the milk collection in case of contamination. It may also decide not to collect milk from one of the cups and hence not handle a teat, if there is any reason for the system to do so, such as a health issue. The cups are removed in sequence; as the milk flow rate falls below a given threshold, it removes the quarter teat cup, and so on, until all quarters are milked. Milk collection management by quarter instead of overall udder mix is one of the advantages of AMS, especially if one of the teats has any particular problem. A teat spray is then applied to improve hygiene. All information regarding each individual animal is stored in the system. The animal is released through the exit gate, and the entry gate can then open for the next one. Animal traffic management can be designed to optimize the performance. New animals are trained relatively fast (2–6 milking days have been reported in the literature, with heifers being trained more easily than cows), and adjust their daily cycles to distribute themselves regularly throughout the whole day (and night). Studies showed that cows visit robots an average of 3–4 times a day, and that the number of cows that do not attend a robot for milking over a day, for no apparent reason (thus called ‘lazy cows’), can reach a figure as high as 10%. This was found to relate quite strongly to the palatability of the pelleted concentrate added to the feed, so feed composition plays an important role in motivating the animals to the robot. Ideally, the barn itself should be designed with the implementation of the robots and animal traffic in mind, rather than retrofitting. The design of the infrastructure, farm layout, laneways, ramp, automatic control gates, and strip grazing layouts are very important. Both management and facilities need to be redesigned to integrate AMS successfully. It is not surprising that the herd manager will spend more time servicing the equipment and reading and interpreting the information collected in the system about each individual animal than in actual attending to the animals themselves. The data collected by the sensors will detect estrus, as well as mastitis and other illnesses, and the farmer can plan medication and feeding in the robot, so the health care seems to take place by proxy. On the other hand, the farmer has more time to devote to analyzing the detailed information, which allows for more informed and speedy decisions to maximize efficiency and profitability. The economics of robotic milking are not straightforward. Some analyses indicate that the financial benefits
254 Plant and Equipment | Robots
are clearer for smaller producers, while others point to a break-even level of investment that is about twice that of a conventional parlor milking system and hence a greater financial clout than that of small farms. Cost factors vary from year to year and location to location, and which benefits are more important to individual farmers also vary substantially, depending on various factors such as size of herd, type of management, lifestyle, age, and availability of human resources on the farm. Each farm therefore needs to consider its specific situation to evaluate the feasibility of implementing AMS properly. There may be various reasons for robotic milking to be attractive to one farmer and not to the neighbor. It should be noted that milking robot costs are not just investment. Running costs of a milking robot include maintenance of a sophisticated system and electrical power supply. Typically, a robot will require between 15 and 25 kW per tonne of milk, while being capable of harvesting 2–2.5 tonnes of milk per day. The most important factor to bear in mind is the need for a strategic approach to the whole milking and farming process. The use of electronic tagging and automated gates permits a full herd management approach based on the individuality of each animal, thus including health management to the detail of medication and feeding of individuals, which maximizes the well-being and the benefits. Personalized feeding may prove financially more beneficial than saving labor costs, as the former account typically for 45–50% of the dairy farm costs, compared to 8–15% for labor (approximately half the labor costs are due to milking). The better hygienic handling and more precise health management can also lower health costs. Robotic milking is not only a cost analysis, as gains need to be factored as well, namely the increased milk production resulting from more efficient health and feed management and more frequent milking. The main manufacturers of milking robots are Lely and DeLaval. The former has been on the market for longer and is the market leader. The latter reported selling its 5000th unit in April 2009. Supplier support and training has been considered crucial and therefore a good working relationship between farmers and manufacturers is essential.
several layers in warehouses. All these operations can be robotized. Figures 1–3 show a robotic palletizing solution for 1 l containers. Robots are fed from two fully automated packaging lines for the 1 l containers that begin by forming them out of reels of the packaging material, and fill them volumetrically in one machine. Both lines can then send them individually to the next room, or group them in packs of 10 (or 12) with plastic wrapping in another machine. Conveyors then transport the individual 1 l containers or the packs of 10 or 12 in separate lines from the packaging to the palletizing room, one conveyor line for each robot. Figure 1 shows one of the conveyors delivering the packs of 10 or 12 to robot 1 for palletizing. This robot moves a double gripper that can pick up and then place two packs at a time on one of two palettes. This is the most usual type of palletizing robot, which can also handle other types of boxes, such as yogurt and butter containers. Note in Figure 1 that the packs of 10 were moved so they are not aligned, and that 3 were placed at the base. This will not be a problem for the robot, as its sensors allow it to know exactly where the packs are, when to close the gripper, and to what strength, so that two packs are picked up and placed gently in place. Figure 2 shows the whole palletizing room, and gives a different view of this first robot. It is placing two packs of 10 packages of 1 l at a time on two palettes. In order to improve stability, the stacking patterns are changed from layer to layer. The robot stacks the layers on the palettes
Gripper
Palette 1
Robotic arm
Palette bases
Palette 2
Packs of 1 l
Conveyor 1
Palletizing Robots Once individual containers of any dairy product are bundled in secondary packages (carton boxes, or simple plastic wrapping of individual containers, as with many liquid milk cartons), these must be piled on palettes at the end of the packaging line. These will be stored in warehouses and later loaded onto trucks for sale. The palettes are moved around with forklifts, and often piled on
Figure 1 Palletizing robot with a double gripper. It is picking up two packs of ten 1 l containers at a time and stacking them with varying patterns on two palettes, alternately. The palette (wooden) bases are moved by the robot itself from the stack at the commencement of each palletizing. A conveyor brings the packs to the robot from the packaging room. Photographed by the author, courtesy of Ernesto Morgado S.A.
Plant and Equipment | Robots
2nd robot
255
Robotic arm
Gripper
Conveyor 2 Palette 1
Palette 2
Packs of 10 1 l
Conveyor 1
Figure 2 Example of a robotic palletizing room implemented in a tight space. The robot in Figure 1 is on the right, behind a column. One of the roller conveyors that slide palettes away when ready can be seen at the center. A train line then transports the palettes to the next room. A second robot is on the top left of the figure. Each of the robots in this room is handling over 1000 containers per hour, a rate that is actually controlled by the rate at which conveyors move packs and packages rather than by rate constraints of the robot itself, and could thus be increased further to about 2500 per hour. Photographed by the author, courtesy of Ernesto Morgado S.A.
Robotic arm
Suction line Gripper Carton container
Suction cups Loading tray
Figure 3 Palletizing robot with suction cups. One-liter packages are transported by a conveyor from the packaging room and accumulated as a 6 8 layer of 1 l packs at the bottom plate. The gripper plate, with 48 suction cups, picks up the layer and stacks it on the carton container seen on the right of the picture. When ready, it is slided out to the train line by a roller conveyor, and then moved to the next room. Photographed by the author, courtesy of Ernesto Morgado S.A.
so they will be ready to move on alternately (when one is ready, the other is about half done). When ready, each palette slides with roller conveyors to a train line (near the wall) that will carry the palettes to another room, where they will be automatically wrapped with plastic for extra rigidity, and are then ready for forklifts to carry them to the warehouse. A second robot is also seen on the
left of Figure 2. Note also in this example how robots can be operated in a very tight space, and work around the constraints of an awkward building. Each of the robots in this example is handling over thousand 1 l containers per hour, working at less than 50% of its maximum achievable rate (this is because in these lines the rates are constrained by the rates of the packaging machines).
256 Plant and Equipment | Robots
Achieving these productivities with human handling would require a much bigger room. The second robot can be seen in more detail in Figure 3. It has a different gripping system, so it can handle a whole layer composed of individual 1 l packages into a big carton container. This robot uses a plate with suction cups to pick up a 6 8 layer of individual 1 l packages from the bottom plate, which is fed by the other conveyor coming from the packaging room. These two robotic solutions reflect the client requirements of this particular company. Some clients wish to have packs of 10 or 12 to place on shelves at the point of sale; others prefer to receive a big carton container that is placed like that at the shop floor. From the beginning of forming the 1 l containers to the fully wrapped palettes, the only human intervention in this case is placing the reels of packaging material in the packaging machines and the base of the palettes in the robot stack. In addition to increased productivity and reliability, this has eliminated human intervention, which can be strenuous and prone to employee absence for health reasons, such as ‘bad back’. There are many manufacturers of such systems, such as Robomatic, Robotworx, Kuka, and Yaskawa (Motoman make). The example shown has no more robotic solution, so the forklifts to handle the palettes are still operated by humans. It is however possible to robotize that step also and actually run an entire automated warehouse, with robotic vehicles forklifting and moving the palettes to the warehouse, placing them in locations that its own management program defines, and retrieve them when necessary also according to the store management program of the automated system. Instead of small vehicles, it is also possible to operate the system with hoists and cranes moving around the ceiling, although this would be rather expensive for handling palettes the size of those in Figures 1–3. A robotic warehouse for palettes is rarer, though, because the economic advantages are less significant than those of palletizing. Replacing one or two persons operating forklifts (which is not a strenuous task) by an expensive robotic system likely results in investment costs that are difficult to recoup. Automated warehouses can be found in retailing, where a high turnover of small
items is needed, or in assembly lines using a large amount of small components (as in electronic manufacturing). Some manufacturers who offer these solutions include RMT Robotics and Kiva Systems.
Further Reading Bower-Spence K (2002) Robotic economics: Robots can be profitable for smaller herds, but there are caveats. Dairy Today 18(9): 17–19. Devir S, Maltz E, and Metz J (1997) Strategic management planning and implementation at the milking robot dairy farm. Computers and Electronics in Agriculture 17: 95–110. Dijkhuizen A, Huirne R, Harsh S, and Gardner R (1997) Economics of robot application. Computers and Electronics in Agriculture 17: 111–121. Halachmi I, Adan I, van der Wal J, Heesterbeek J, and van Beek P (2000) The design of robotic dairy barns using closed queuing networks. European Journal of Operational Research 124: 437–446. Hogeveen H (2001) Robotic milking. In: Hogeveen H and Meijering H (eds.) Proceedings of the International Symposium on Robotic Milking. Lelystad, The Netherlands. Wageningen, NL: Wageningen Press. Ipema AH (1997) Integration of robotic milking in dairy housing systems. Review of cow traffic and milking capacity aspects. Computers and Electronics in Agriculture 17: 79–94. Meijering A, van der Vorst Y, and de Koning K (2002) Implications of the introduction of automatic milking on dairy farms: An extended integrated EU project.Proceedings of the First North American Conference on Robotic Milking. Toronto, Canada, March. Wageningen, NL: Wageningen Press. Rodenburg J (2002) Strategies for incorporating robotic milking into North American herd management. Proceedings of the First North American Conference on Robotic Milking. Toronto, Canada, March. Wageningen, NL: Wageningen press. Spahr S and Maltz E (1997) Herd management for robot milking. Computers and Electronics in Agriculture 17: 53–62.
Relevant Websites http://www.automaticmilking.nl – EU-Project Automatic Milking. Website of the EU integrated project on automatic milking. It contains several articles and project results. http://www.lely.com and www.delaval.com – Lely and DeLaval. Websites of the main manufacturers of milking robots. They contain several illustrative pictures of their equipment. http://www.roboticdairy.com – Robotic Dairy. Website of an Australian dairy farm. It has four live cameras at different parts of the farm where the operations can be seen in real time. http://www.futuredairy.com.au – Website of an Australian Project. It covers more than robotic milking, and also contains several articles and analysis on this subject.
Corrosion P D Fox, 90 Old Quarter, Ballincollig, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction
E ¼ E0 –
Corrosion is the deterioration of metals by an oxidation– reduction reaction, usually with loss of the metal to solution. Metals are generally found in their natural state in the Earth as metal oxides or ores. Most metals are more thermodynamically stable as oxides rather than as pure metals, with perhaps the exception of the noble metals, for example, gold and platinum. Mining and refining a metal is therefore an energy-intensive process, that is, there is an input of energy, and corrosion can be seen as the return of the metal to a more thermodynamically stable state. Corrosion causes the loss of billions of dollars per annum, and in industrial nations constitutes a large fraction of the gross national product. These losses are due to replacement of materials and labor costs, as well as plant downtime. Losses due to leaking or contamination of product and heat transfer problems are also significant. Conservation of natural resources is enhanced by the prevention of corrosion. In order to understand corrosion, one needs to be familiar with the basic principles of thermodynamics and electrochemistry.
Thermodynamics and Electrochemistry The change in the Gibbs free energy, G, of a reaction indicates whether or not the reaction will proceed. A reaction is said to be spontaneous if G is negative. At constant temperature and pressure, the maximum amount of work, !max, a system can perform is given by the Gibbs free energy, that is, rG = !max. The Gibbs free energy of a reaction under non-standard conditions can be related to the equilibrium quotient, Q, by the following equation: r G ¼ r G o þ RT ln Q
½1
j ajuj
where Q ¼ and u is the stoichiometric number of the species j. Terms that make up the equilibrium quotient include the activities of metal ions, protons, and gases. In an electric cell, work is due to transfer of charge in the form of electrons across an electrochemical potential, E, between two electrodes. Therefore, the product of charge and potential results in work: r G ¼ !e max ¼ uFE
½2
The Gibbs free energy can be related to electrochemical potential using the Nernst equation:
RT lnQ uF
½3
This equilibrium relates potential to standard potential and the equilibrium under non-standard conditions.
Standard Reduction Potential Electrochemical reactions involve the transfer of electrons resulting in a change of oxidation state: Cu2þ ðaqÞ þ Zn ! Cu þ Zn2þ ðaqÞ
½I
Reaction [I] can be broken down into a combination of two half-cell components, one for reduction (IIa) and one for oxidation (IIb): Cu2þ ðaqÞ þ 2e – ! Cu
½IIa
Zn ! Zn2þ ðaqÞ þ 2e –
½IIb
Half-cell reactions occur at specific potentials. The overall potential of a reaction is the difference between the individual half-cell potentials. However, it is not possible to measure the absolute potential of an electrochemical process; so it is necessary to define a standard half-cell reaction relative to which the potential of all others is measured. For this purpose, by convention, a hydrogen electrode, also known as the standard hydrogen electrode (SHE), was chosen and arbitrarily assigned a value of 0 V: 1 Hþ ðaqÞ þ e – ! H2 ðg Þ; E ðHþ ; H2 Þ ¼ 0V 2
½4
The standard reduction potential of a test electrode is defined by whether it is oxidized or reduced when connected to a standard hydrogen electrode. If electrons flow from the hydrogen electrode to the test electrode, causing reduction of the test electrode, the measured potential is positive. The standard reduction potential is negative if the electrons flow in the opposite direction, that is, from the test electrode to the hydrogen electrode, thus oxidizing the test electrode. Using the standard hydrogen electrode as reference, tables have been constructed for all other electrodes, the reduction potential of which is either positive or negative relative to hydrogen. A partial list is given in Table 1. The same principle applies to any two electrodes when constructing an electrochemical cell. The electrode with the lower standard reduction potential is the
257
258 Plant and Equipment | Corrosion
The exact form of the water/oxygen electrode half-cell depends on the chemical environment, which can be acidic or alkaline. In acidic solution:
Table 1 Standard reduction potentials for selected half-cells
Electrode
E V
Au+ + e ! Au O2 + 4H+ + 4e ! 2H2O Ag+ + e ! Ag Fe3+ + e ! Fe2+ Hg2Cl2 + 2e ! 2Hg + 2Cl Cu2+ + 2e ! Cu Co2+ + 2e ! Co 2H+ + 2e ! H2 Fe3+ + 3e ! Fe Fe2+ + 2e ! Fe Zn2+ + 2e ! Zn 2H2O + 2e ! H2 + 2OH Al3+ + 3e ! Al Mg2+ + 2e ! Mg
+1.83 +1.23 +0.80 +0.77 +0.27 +0.34 0.28 0.00 0.04 0.44 0.76 0.83 1.68 2.37
The basic concepts of electrochemistry and half-cells can also be applied to corrosion. In fact, corrosion is the combination of a metal electrode (IIIa) with a water/ oxygen electrode (IIIb). In this section, iron and various grades of stainless steel, due to their extensive use in the dairy industry, will be used to illustrate thermodynamic and kinetic data regarding corrosion: ½IIIa –
2H2 OðlÞ þ O2 ðgÞ þ 4e ! 4OH ðaqÞ
½IIIb
2FeðsÞ þ 2H2 OðlÞ þ O2 ðgÞ ! 2FeðOHÞ2 ðsÞ
½IIIc
V, VI. or VII, therefore as in the previous example, the reaction can be broken down into its individual half-cell components and their corresponding standard reduction potentials as in Table 1: Fe2þ ðaqÞ þ 2e – ! FeðsÞ;E ¼ – 0:44V
4Hþ ðaqÞ þ O2 þ 4e – ! 2H2 OðlÞ;E ¼ þ1:23V
½VI
2H2 Oð1Þ þ O2 þ e – ! 4OH – ðaqÞ;E ¼ þ0:40V
Thermodynamics of Corrosion
–
½V
In alkaline solution:
anode, where oxidation occurs, and that with the higher potential is the cathode, where reduction occurs. The difference in the standard reduction potentials of the two electrodes, that is, cathode potential minus anode potential, is the overall cell potential. Using Table 1 the potential of the cell in eqn [I] is found to be 1.1 V and when substituted into eqn [2], gives a negative Gibbs free energy. The current generated by this cell arises from the spontaneous flow of electrons from the zinc anode to the copper electrode. The flow of electrons from copper to zinc is a non-spontaneous process and requires external energy, as in the recharging of a battery by the electric mains.
2FeðsÞ ! 2Fe2þ ðaqÞ þ 4e –
2Hþ ðaqÞ þ 2e – ! H2 ðgÞ;E ¼ 0V
½IV
½VII
As shown in the previous section, when two electrodes are combined, the electrode with the lower standard reduction potential is the anode and undergoes oxidation. The electrode with the higher standard reduction potential is the cathode and is reduced. Since iron has a lower standard potential (IV) than the half-cells , V, VI or VII, therefore it undergoes oxidation when in contact with water/oxygen. This leads to an overall positive potential and a negative Gibbs free energy, showing that oxidation, that is, corrosion of iron, is a thermodynamically favorable process. A common method for illustrating the thermodynamic data of a metal involves the use of a Pourbaix diagram, which is shown for iron in Figure 1(a). It shows the most stable species of iron as a function of potential and pH. The activities of iron and other ions in solution determine at which pH and potential the transitions between different metal phases occur. Water is stable between the lines a and b (reactions [V] and [VI], respectively). A potential below line a causes the reduction of water to hydrogen, while above line b, water is oxidized and oxygen is evolved. However, the activity of protons in solution is pH dependent. Substitution of a or b into the Nernst equation [3] allows potential to be expressed as a function of proton activity or, more conveniently, as a function of pH: E ¼ 0:00 – 0:059 pH
½5
E ¼ 1:23 – 0:059 pH
½6
The potential for the oxidation and reduction of water, lines a and b, respectively, decreases by 59 mV for every increase of 1 pH unit. In the Pourbaix diagram of iron (Figure 1(a)), the horizontal lines represent equilibrium reactions that are independent of pH, while the vertical lines represent reactions that do not involve the transfer of electrons. Diagonal lines are reactions that involve electron transfer and are pH dependent. The exact position of these lines is determined by the concentration of iron ions or by the presence of other ions in solution. All these reactions can be substituted into the Nernst equation [3] to derive expressions relating potential to standard potential, pH, and ion concentration. For a more complete description of the phase diagrams of
Plant and Equipment | Corrosion
259
(b)
(a) Fe3+ O2, H+/H2O, b E
E
Corrosion Passivation
H+/H2, a Fe2+
Fe2O3
Corrosion
Fe3O4 Fe 0
Immunity
Fe(OH)–3 7
14
0
7
14
pH
pH
Figure 1 (a) Pourbaix diagram for most stable species of iron in pure water. (b) Pourbaix diagram showing regions of immunity, passivation, and corrosion.
iron, as well as many other electrodes, the reader is referred to the Further Reading section. Figure 1(a) shows that at low pH and potential, iron is stable. Increasing the potential at low pH results in hydrated Fe2+ and Fe3+ and so corrosion occurs. At high pH, iron exists as oxides or hydroxides, with the oxidation number increasing with potential. If the oxide is soluble, further corrosion occurs. However, if the iron oxide is insoluble in water, a thin layer of oxide builds up on the surface. This oxide then protects iron from further oxidation and the metal is said to be ‘passivated’. A similar effect is seen in the formation of green copper oxide, for example, on rooftops where the initial oxidation of copper forms a protective film and prevents further oxidation. Figure 1(b) shows the regions of immunity, corrosion, and passivation for iron.
Kinetics of Corrosion Potential measurements and Pourbaix diagrams indicate whether or not corrosion is thermodynamically favorable. However, thermodynamic data provide no information about the rate of corrosion. Therefore, it is necessary to develop kinetic methods to measure the rate of corrosion. Kinetic information in electrochemistry is usually represented by a Tafel plot. When an electrode is at equilibrium, oxidation and reduction currents of equal magnitude but opposing direction result in zero net current. This equilibrium current is known as the exchange current, i0, and the potential at equilibrium is Eeq. In order to measure i0, a positive or negative polarizing current is applied resulting in an overpotential, . Overpotential is defined as the deviation of potential from Eeq, that is, = EeqE. At high overpotential, a plot of lnji j as a
function of is linear(see Figure 2). Extrapolation back to Eeq gives the value of exchange current: lnji j ¼ lni0 þ
nF RT
½7
The slope gives information about the symmetry, , of the reaction, which relates the reactant and the product to the activated complex along the reaction coordinate. A value of 0.5 means that the structure of the activation complex resembles that of the reactant and product equally. Corrosion is a two-electrode system at equilibrium. The combination of two electrodes results in a mixed potential, known as corrosion potential, Ecorr. Corrosion current, Icorr, is equal to the absolute values of the opposing oxidation and reduction currents. When the Tafel
ln|i |
Eeq
E
Figure 2 Tafel plot for the measurement of exchange current, i0. Transfer coefficient, , is measured from the slope and has a typical value of 0.5.
260 Plant and Equipment | Corrosion
and Equipment). The most popular steel in use in austenitic stainless steel, which contains 18% chromium and 8% nickel and is more commonly known as 18-8 austenitic steel. The carbon content is kept low (0.08%) to ensure that chromium, which is necessary for the prevention of corrosion, is not precipitated as chromium carbide.
+ − i0 (H2 / H +) H2 → 2H + 2e
E
Eeq (H2 /H+)
M → M n+ + ne–
Icorr Ecorr
Eeq (M /M n+)
2H + + 2e– → H2
Types of Corrosion
i0 (M /M n+) M n+ + ne– → M In|i | Figure 3 Tafel plot for corrosion of a metal in water showing equilibrium potential, Eeq, and exchange current, i0, of hydrogen and metal electrodes. Extrapolation of both slopes yields corrosion potential, Ecorr, and corrosion current, Icorr.
plots for both hydrogen and metal are combined (see Figure 3), the point of intersection gives the corrosion potential and corrosion current. The exchange current and equilibrium potential for the individual hydrogen and metal electrodes are also shown in the figure. Stern and Geary derived a simplified version of the Tafel relationship, using empirical values of b, which does not require knowledge of the surface: Icorr ¼
1 ba – jbc j Iappl 2:3 ba þ bc E
½8
where b = 2.3RT/nF. When the potential is varied by not more than 10 mV of Ecorr, it varies linearly with applied current, Iappl. The slope, Iappl/E, is known as polarization conductance, Kcorr. The rate of corrosion, Rcorr, can be related to the corrosion current by Faraday’s law: Rcorr ¼
Icorr Mt nF A
½9
where M is the molecular mass (g mol1), the density (g cm1), A the area (cm2), and n the number of electrons transferred. Integration of this equation for t = 1 year gives the more common expression for corrosion, cm yr1.
Properties and Types of Steel Alloying of iron is an effective approach to increasing mechanical strength and resistance against corrosion. Stainless steel is a chromium–iron–nickel alloy, with a low carbon content, which has good mechanical properties and is resistant to corrosion. There are three different types of steel, martensitic, ferritic, and austenitic, which differ in their crystal structure (see article Plant and Equipment: Materials and Finishes for Plant
There are many types of corrosion. A plant engineer should know the rate of corrosion but should also be aware of the various modes of attack. This information has to be taken into account for plant design. Corrosion of iron or steel is always a result of exposure to air and water. The time span for corrosion can vary dramatically, from hours to years. The amount of damage also depends on the exact form of the corrosion process, which can be influenced by the chemical environment, mechanical stresses, or metallurgical properties. The exact reason for corrosion can be due to any one or a combination of these factors. Pitting and Crevice Corrosion Uniform corrosion of a metal results in an easily measurable loss of metal. However, metal surfaces are rarely homogeneous and are usually covered with a protective layer of oxide or hydroxide. Pitting and crevice corrosion are two forms of localized corrosion where anodic and cathodic areas, that is, regions where oxidation and reduction occur, develop on the metal surface. The anodic area undergoes severe corrosion, whereas the cathodic area is unaffected. Environments containing aggressive species often result in the formation of deep pits on the surface of the metal. This is known as pitting corrosion. The most common cause of pitting is the chloride ion, which is able to penetrate the porous oxide layer (see Figure 4). Pitting generally occurs locally, due to variations in the structure and thickness of the oxide film or due to surface defects, rather than over the entire surface. Chlorides compete with oxygen for adsorption onto metal sites. Once adsorbed on the metal, chloride ions encourage hydration of metal ions and removal from the surface rather than the buildup of a passive oxide layer. Due to a difference in oxygen concentration, a large potential gradient of up to 0.5 V builds up between the anodic area within the developing pit and the cathodic bulk steel, which allows for a considerable current flow between the anodic and cathodic sites. More highly mobile chloride is then attracted into the pitting site in order to balance the charge built up by iron ions. Iron chloride undergoes hydrolysis, further decreasing pH,
Plant and Equipment | Corrosion
O2
Cl–
OH–
Air Solution
Air
Oxide
Oxide
261
Solution O2
OH–
Bolt M n+
ne–
Mn+
Metal
ne– Metal
Figure 4 Schematic illustration of pitting corrosion. Pitting corrosion occurs when the protective oxide layer is breached by chloride. It is an example of localized corrosion on a metal surface, which arises from concentration gradients.
and so pitting corrosion continues in an autocatalytic manner. Therefore, corrosion continues in areas where pitting has been initiated rather than starting at new sites. In this way, the pit can grow very quickly. A Pourbaix diagram for iron modified for a chloride solution shows a region where pitting occurs in addition to areas of passivity, immunity, and corrosion (see Figure 5). Crevice corrosion occurs in areas where movement of electrolyte is likely to be confined, such as between bolts, washers, or gaskets (see Figure 6). The electrolyte within the crevice is stagnant and has different oxygen and metal ion concentrations from bulk surface metal causing a potential gradient. Metal ions released within the crevice cause the local pH to be lowered by up to 6 units. As in pitting corrosion, chloride ions migrate into the crevice to balance the charge. As a result, passivity within the crevice is broken and the potential gradient is increased further, accelerating the rate of corrosion. Another cause of crevice corrosion arises if the protective oxide layer is breached due to a scratch, thereby exposing the metal. A
Pitting E
Corrosion
Passivation
Figure 6 Schematic illustration of crevice corrosion. Crevice corrosion occurs when the electrolyte is stagnant, such as under a bolt. Differing electrolyte composition within the crevice compared to the bulk results in a potential difference and localized corrosion.
potential is again built up between the two sites and crevice corrosion is initiated. The main difference between pitting and crevice corrosion is that pitting starts only when a critical pitting potential is reached, as shown in Figure 5. Crevice corrosion depends on whether passivity due to the oxide layer can be breached within the crevice and can also proceed with ions other than chloride, such as sulfates, nitrates, or acetates.
Intergranular Corrosion Intergranular corrosion is a localized attack at metal grain boundaries, which form during the cooling process in steel production where several nucleation points for crystal growth exist. The orientation of each crystal is random and so when two crystals meet they are often out of phase and a grain boundary is formed. The Gibbs free energy at the boundary is higher than that of the bulk metal and the boundary is preferentially corroded. It is thought that the intergranular corrosion results from improper, or sensitizing, heat treatments of the metal during production or welding. Sensitizing heat treatment of stainless steel depletes the grain boundary of chromium, which precipitates as chromium carbide; chromium is necessary for corrosion protection. Corrosion of this type penetrates the whole boundary, reducing mechanical strength and resulting in failure, even though actual loss of metal is low.
Stress Corrosion Cracking Immunity 0
7
14
pH Figure 5 Pourbaix diagram for iron in salt solution showing four regions: immunity, passivation, corrosion, and pitting.
Stress corrosion cracking results from tensile or residual stress on a metal in a corrosive environment. Without the corrosive environment, the stress would not induce cracking. Stress corrosion cracking can be initiated at metal discontinuities, pits, or intergranular boundaries. Whether propagation of the crack is intergranular or
262 Plant and Equipment | Corrosion
transgranular depends on the exact chemical environment and pretreatment of the metal.
Corrosion Fatigue When subjected to a repeated alternating stress, a metal will fail after a number of cycles; this is known as metal fatigue. In a corrosive environment, the number of cycles required to cause failure is reduced; this is known as corrosion fatigue and is usually generally transgranular and branched. The damage caused by corrosion fatigue is greater than the sum of the individual effects of corrosion and fatigue due to branching.
Cavitation Cavitation occurs under conditions of rapid fluid velocity, where repetitive high- and low-pressure areas are developed and bubbles are formed, which then collapse at the metal–liquid interface. The metal becomes deeply pitted due to mechanical damage and chemical removal of the protective oxide film. Cavitation often occurs on rotors and turbine blades. This is a physical process, not chemical, and it is therefore a form of erosion rather than corrosion proper. It is appropriate, however, to list it as well.
Galvanic/Bimetallic Corrosion Galvanic corrosion occurs when two metals separated by an electrolyte are in close contact. The metal with a lower standard reduction potential is oxidized, whereas the other is reduced. A common source of galvanic corrosion are bolts used to attach a fixture to steel; corrosion then occurs at the joint. Another cause is the welding together of two different grades of steel. Cathodic protection refers to the preferential oxidation of the metal with a lower standard reduction potential over another when two different metals or alloys are in contact with oxygen; the second of the two metals remains unaffected by corrosion. This approach to protection against corrosion is a common practice on ships where a zinc block, which has a lower standard potential than steel, is attached to the hull and is preferentially corroded by seawater while the steel hull remains uncorroded.
Environmental Factors Affecting Corrosion The availability of oxygen is critical for the corrosion process and its availability is affected by a number of interrelated factors. This is the basis of corrosion prevention methods, such as painting, where oxygen availability is suppressed. Steady-state corrosion is dependent on the diffusion rate of oxygen to the metal surface. Therefore, at low oxygen concentrations, corrosion is proportional to the concentration of oxygen. However, above a certain critical concentration, corrosion decreases with increasing oxygen level due to oxide passivation of steel. The critical concentration is increased by increasing salt concentration and/or temperature but is reduced by increasing fluid velocity and pH. Since corrosion is controlled by diffusion of oxygen, its rate increases with temperature. However, at high temperatures, oxygen availability is reduced and the rate of corrosion decreases. Moving liquids supply oxygen to the surface and hence increase the rate of corrosion. At higher flow rates, partial passivity occurs. However, at very high flow rates, mechanical removal of the oxide layer or the prevention of passive oxide layer formation increases the rate of corrosion. Also, in the presence of chlorides, as in brines, oxide layers are not formed and corrosion will continue to increase with flow rate. Increasing the NaCl concentration reduces the solubility of oxygen. However, corrosion increases to a maximum at 3% NaCl, due to Cl, and then declines; this is due to breaching in the passive oxide layer. See also: Plant and Equipment: Materials and Finishes for Plant and Equipment.
Further Reading Evans UR (1960) The Corrosion and Oxidation of Metals: Scientific Principles and Practical Applications. London: Arnold. Korb LJ (1987) Metals Handbook, Vol. 13: Corrosion. Metals Park, OH: ASM International. Lide DR (2000) Handbook of Chemistry and Physics, 81st edn. Boca Raton, FL: CRC Press. MacDonald DD (1978) An impedance interpretation of small amplitude cyclic voltammetry. 1. Theoretical analyses for a resistive–capacitive system. Journal of the Electrochemical Society 125: 1443–1449. Pourbaix M (1966) Atlas of Electrochemical Equilibria in Aqueous Solutions. Oxford: Pergamon Press. Stern M and Geary J (1957) Electrochemical polarization. 1. A theoretical analysis of the shape of polarization curves. Journal of the Electrochemical Society 104: 56. Uhlig H and Revie R (1985) Corrosion and Corrosion Control. New York: Wiley-Interscience.
Continuous Process Improvement and Optimization J C Oliveira, University College Cork, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction Origin of the Concept ‘Continuous process improvement’ is a term that emerged from the studies undertaken in American business science on the manufacturing strategies used by the Japanese industries. As such, it is often known by its Japanese term ‘kaizen’. There are many other terms that became popular and are related to managerial and operational strategies from Japanese practice, of which continuous process improvement is one element, such as quality engineering, lean manufacturing, value engineering, manufacturing excellence, and world-class manufacturing, and even six sigma can be related to it. Six sigma is discussed further in the article Plant and Equipment: Quality Engineering. The methodologies developed for continuous process improvement are now regarded as crucial for ensuring competitiveness in a global market, and as such, have been permeating across all sectors of the manufacturing industry. It is worthwhile to understand the origins of the concept. Following World War II, Japanese industry was devastated. In the 1950s, products made were of generally poor quality and the lack of economies of scale and of investment capacity seemed to condemn Japanese industry to a secondary role for a long time, compared to the paradigms of the day, the US industry. However, by the 1970s, American companies began recognizing that the Japanese products were of superior quality and lower price, beating them in their own markets. One of the industrial sectors more strongly affected by the giant leaps of quality and efficiency of the Japanese industry was car manufacturing. It was obvious by then that some time during the 1950s and 1960s Japanese manufacturing was able to find methods to produce high-quality products at a cheaper rate, even though it did not avail (at that time) of the economies of scale that the ‘Detroit giants’ (Ford, Chrysler, and General Motors) had. As the Toyota Motor Company was at the forefront of these developments, and it practiced a notable open philosophy about itself, it became the most widely studied by American business science researchers. Toyota was not the only company developing these approaches in Japan, nor the creator of all the methodologies used, but was one of the pioneers, and became the best
known. In a sense, the fact that various people analyzed various aspects of what was later called the ‘Toyota Production System’ (TPS) and then added their own perspectives and interpretations has ultimately led to the emergence of several ‘westernized’ concepts, such as just-in-time, total quality management, continuous process improvement, and lean manufacturing. However, the Japanese, and Toyota in particular, would not consider any of these concepts as an independent methodology, but as part of a whole. The first studies of TPS brought to global attention a completely different way of organizing production, with just-in-time stock management, a production pull system rather than push system, and a revolutionary approach to the role and intervention of operators in the process, which in itself sparked a new philosophy about teamwork. Studies of the TPS became known as the first paradox (how can quality be achieved with low cost when there are few economies of scale?) after another influential work addressed what it called the second Toyota paradox, which deals with the new product development approach of Toyota (how can a new product development cycle be faster and cheaper by delaying decisions as much as possible?). Another landmark in the dissemination of these practices was the seminal work on lean manufacturing, The Machine That Changed the World.
From Car Manufacturing to Dairy There is a very important conclusion to bear in mind from the historical backgrounds of continuous process improvement and all the TPS-related paraphernalia of modern management best practices and fads: they were not developed and implemented by Toyota, the biggest car manufacturer in the world (that is not what Toyota was then). They were developed and implemented by Toyota, a small company producing low-quality products at a high cost because it had no economies of scale, and therefore had very little financial capacity for investments. What it had was the belief that it could do better, that it could solve the paradox ‘high quality and low cost even without economies of scale’. Toyota did not develop its famous TPS by hiring expensive consultants to design optimum solutions by applying bestin-class principles. It had no financial or human
263
264 Plant and Equipment | Continuous Process Improvement and Optimization
resources to do so. It started with months of observation of what happened in the reality of the factory floor, what operators really did and how. Then, considering what was the best in class, how could those efficiencies be emulated? And finally, finding out that they could actually be bettered. It is very informative to know what really happened: Liker provides a historical account that is well worth a read. The relevance of this to modern industries is obvious, as emulating means that abstract principles can be applied across industrial sectors, and there is none that has been immune to the application of the principles of continuous process improvement, lean manufacturing, six sigma, and other improvement programs (see for instance, the list of main clients of the Kaizen Institute – one of the many consultancy groups providing services in this area – at its website). For the dairy industry, see the cover story by Markgraf on an American dairy. It is however crucial to bear in mind the main lesson of Toyota’s origins: if deploying continuous process improvement (or any associated principles) requires an expensive engagement of external experts who will propose an optimum solution from their analysis, then the proposition negates the philosophy right from the start. Continuous process improvement (1) must be a transformation that comes from within (albeit guidance by external experts facilitates commencement, cuts corners, and can thus save time and money), (2) must be ardently desired by the most senior management, and (3) should require few, if any, costs.
United States (and Europe) had been to design an optimum process. This implies defining what the optimum target is, often accepting that the multicriteria nature of ‘optimum’ will require some compromise or trade-off, and from that conceptual definition of what the optimum should be, the process is then designed in one single go to reach that optimum, using sophisticated methods. As the design is complex, it needs advanced knowledge, so the designer is an expert in designing, does so expensively, and is unlikely to be engaged in the actual daily operation of that design. On the other hand, the operators are typically not involved in the design, and are supposed to do exactly as told and exactly as planned in the design. This is, of course, a gross generalization, but the underlying nature of the approach can lead to such extreme dichotomy between the optimum abstract ideal of the design and the practical reality on the factory floor. Therefore, continuous process improvement (kaizen) experts often like to boast of the improvements they were able to extract out of what was supposedly an ‘optimum’ process. Notwithstanding, process optimization methodologies are not to be discarded, some kaizen engineering design methods over rely on simplified approaches, and ‘western’ engineering design has developed some more consistent and comprehensive ones. From a practical point of view, of course, semantics are irrelevant, and what matters is the efficacy of the methods deployed to improve competitiveness.
Continuous Process Improvement or Process Optimization?
Operational Improvements
As the name suggests, continuous process improvement uses methodologies to improve a manufacturing process, so the first question should be what is the target of improvement – costs? productivity? quality? This is a methodology to improve what? The answer is simple: everything. That is one of the reasons for using the word ‘paradox’ in relation to the TPS: How can everything be made better, when reality usually requires compromises and trade-offs? How can costs be reduced and quality improved? The second feature of the term is the word ‘continuous’: process improvement is a neverending journey, the process is to be made better all the time, one improvement after another, because optimum is an ideal, and as such, unreachable. Semantics, therefore, show that the concept implies an incremental approach (one step at a time), where no improvement is too small (summing enough small improvements leads to a big improvement). This, therefore, reveals a fundamental difference between continuous process improvement and the ‘western’ counterpart, process optimization. The practice in the
The first step for improving a manufacturing process is to analyze its operations, from procurement to sales, and not only on the factory floor. Starting with purchase orders (when are ingredients purchased and how, where are they stored and for how long?) and ending with sales (manufacture-to-stock, or manufacture-toorder?) means that stock management strategies are an integral part of process improvement. In relation to the manufacturing process itself, the whole sequence of operations needs to be considered, including not only the actual processing functions, but also its associated functions, such as quality control. In essence, a factory organizes a series of operations, generically, buy ! make ! test ! sell (not necessarily linearly). The first core principle of kaizen is to analyze the operations from the point of view of the flow of the product itself, which already brings in a difference from ‘western’ conventions, where processes tend to be described from the managerial perspective. In order for a process to be improved, this combination of operations must be the most efficient. Redesigning the
Plant and Equipment | Continuous Process Improvement and Optimization
entire set can be associated to the concept of business process reengineering (BPR), a management concept that gave mixed results and was therefore more popular in the 1990s than it is today. BPR considers the ‘western’ approach: that an optimum can be designed from scratch by best principles applications, using sophisticated methods if necessary, and isolated from real practice if need be. A BPR proposes a giant leap to an ideal world. It is not a useless concept, and it can give very good results (and has in reported literature), but obviously, the more reality deviates from ideality, the greater the chance that the giant leap may be toward a big hole. Literature also reports negative experiences of companies with BPR. Incremental approaches therefore have this big advantage: they may be more modest but will always lead to a better situation, and over several incremental steps, the gains will become significant. Critics will contest that incremental solutions may not explore areas of the solution space beyond convention, while advocates prefer to explore without excessive risk in the explorations, and point to practical end results that are equally enviable. It is noted that BPR often shows up associated to the introduction of novel solutions from information technologies (IT) to reorganize business processes. This is a special case of BPR, where it comes associated with the digestion of new IT procedures by company and staff, which in itself (with BPR or not) has its own success and failure factors. Introducing IT may facilitate process improvement, or it may not, and it is not a concern here. IT is a tool; it should be recognized that in fact IT always facilitates kaizen from a conceptual (theoretical) perspective – but how will it work in practice? kaizen in itself is not about a better business concept, it is about a better business reality. Continuous process improvement will suggest starting more modestly than reinventing from scratch, by analyzing all operations and apply what is also known to some extent as value engineering. Of all the business operations involved in manufacturing, some add value to the product and thus to the end client, but some do not. They may well be necessary for some reason, or they would not be there, but if they do not add value, then they are a waste from the point of view of the product and of the client. The Japanese word for wasteful activity (‘muda’) is often cited in this context. A better process will be one where waste is nonexistent, so these operations should, ideally, be eliminated. Therefore, it is logical to start improving a process by eliminating non-value operations (why spend time and resources improving those that are best eliminated altogether?). This analysis is not as straightforward as it looks, because company executives and operators are not used to think from the point of view of the client or of
265
the product. A typical example is quality control: from the point of view of the product or the client, it is a wasteful operation. This might seem an excessive comment, but a more detailed analysis shows the philosophy at play here. Quality control is a problem of the manufacturing company, not of the client. The client expects that quality, indeed, he paid for it. If the company is not able to deliver that quality, that is the company’s problem that becomes a client’s waste. From the point of view of the product, being stored somewhere waiting for the results of a quality control test is a waste of time. The product should have quality unless the process is faulty. An improved process should not be faulty, so the product should have quality all the time. This would lead to the concept of quality by design, which is discussed in detail in the article Plant and Equipment: Quality Engineering. A second principle is that the flow of the product must be continuous. From entering the raw materials storehouse to leaving for sale, the product (ingredients/ components, etc.) must not stop; if it does, it is lying idle, and so there is a waste. Hence, storage is a waste, and so the concept of just-in-time, one of the first that was immediately grasped for its financial advantages. The best way to ensure this continuous flow is to pull the product from the end, that is, the last operation sends an order to the before last, and so forth, so the product is pulled from the end. A pull operation (request for a product or part needed) was originally sent with a card in Toyota, or ‘kanban’ in Japanese, a term that endures as synonym of just-in-time operations by a production pull strategy. A good starting point for analysis of the improvements that can be made by eliminating wasteful operations (and hence become ‘lean’) is to apply the lean questionnaire developed by MIT (LESAT – Lean Self Assessment Tool), available for free at the website of the Lean Advancement Initiative of MIT (this site contains plenty of other free tools and studies under the ‘products’ menu). It may help to give a different perspective on what can be classified as waste, and how much waste there is in a normal business operation when it is analyzed from the perspective of the value to the client, or of the product flow. Waste is not confined to operations that should be eliminated because they do not add value; TPS deals with two other types of waste. An obvious waste comes from product variability and consequent loss of quality, which is addressed in the article Plant and Equipment: Quality Engineering, and often referred to by its Japanese term ‘mura’. The third is waste resulting from overcomplexity (‘muri’ in Japanese). This means that every operation and sequence of operations should be as simple and direct as possible. Standardization of simple operations and their straightforward combination
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are the ideal basis to eliminate this type of waste and hence maximize productivity. In some industrial sectors where operations involve manual handling, eliminating muri requires appropriate ergonomic design of the workplace and workstations (the operation should be easy and simple to perform, thus minimizing energy, effort, and time).
Process Engineering Improvements General Approach The operational and managerial implications of kaizen leave a highly flexible, efficient, and productive factory floor, alongside an entire lean supply chain. Operations on the factory floor involve a series of equipment units where the product components are progressively incorporated and turned into the final product. Each of these operations must now be improved. In the context of a process industry such as dairy, the raw materials undergo transformations toward a product of a different nature (e.g., fermentation in yogurts, coagulation in cheese) or that hinder microbial activity to provide shelf life (e.g., ultra-high temperature (UHT) processing, drying). These operations are controlled by a number of variables or control factors, such as temperatures, flow rates, amounts of ingredients, and time of operation. The company decides on the settings (values) of these factors from its knowledge of the system, characteristics of the equipment, recipes, and other things. Each of these control factors can be set at any value within a range of physical interest, and there is an infinite number of combinations of settings of these factors that result in a final product, although not all combinations are possible. Some, however, result in products that are better than others, or in processes that are cheaper, or more productive, or use less energy, and so on (for instance, the objective of reaching a given microbial lethality in the thermal treatment of liquid milk can be achieved equally at a higher or lower temperature, with the processing time being longer the lower the temperature, but the quality characteristics of the product, such as nutrient retention and taste, are better at higher temperature-short time than at low temperature-long time). In this context, process improvement will deploy methods to find a combination of settings of the control factors that will result in a better performance. It may be possible to estimate better combinations of these settings by developing mathematical models that mimic the operation of the equipment by applying first principle equations (laws of conservation of mass, energy and momentum, thermodynamics, kinetics, heat and mass transfer, etc.). However, such models will need to make assumptions that may or may not be good images of
reality, and may also be too complex. The continuous process improvement concept prefers to ‘let the system speak by itself’, and obtain process data from which to infer improvements. Process optimization does the same, only that it assumes that a single giant leap is possible, and that the absolute optimum is identifiable. Kaizen is prepared to move stepwise. The need for process data to infer directions of improvement is an issue in some industrial sectors, such as dairy. If the equipment operates with large quantities of product at any given time, and the business margins are small, there is little room to perform tests with the equipment, each of which could cost many kilograms of product that run the risk of being unsuitable for sale (when the test happens to try settings of the control factors that do not lead to a suitable product). However, process data can also be collected simply from the historical records of the process. This has the huge disadvantages of providing data that have not been planned, with many data points around the same settings, with uncontrolled variabilities, and a scan of the solution space decided by chance and the inaccuracies of the control systems. However, it is ‘free’ data and may reveal useful information about the system, if handled properly. Design of Experiments Kaizen recommends an experimental plan, and as such it starts by giving great importance to the planning of the tests. It is obvious that if each test involves the actual process and equipment, the most information needs to be obtained from the least amount of data, and therefore, it is not surprising that the area of statistics dealing with design of experiments (DoE) must be brought in. The most widely used approach in Japan is due to Genichi Taguchi, and is generally known as the Taguchi method of robust engineering design. The method seeks to achieve improvement of performance and also consistency of performance, and as such it is the foundation of quality engineering too, discussed in the article Plant and Equipment: Quality Engineering. In the context of performance improvement or optimization, it is noted that in order to minimize experimental requirements and take as much information as possible from the data, Taguchi chose designs based on orthogonal arrays (aka Latin squares). They are usually designated as L-4, L-8, L-9, L-12, L-16, L-27, and so on, where L stands for ‘Latin squares’, and the number indicates the number of rows of the array, which is also the number of tests that needs to be performed. When consistency of performance is to be considered as well, the whole set must be repeated a number of times, and therefore, using arrays with as few rows as possible is important. Each array will allow testing
Plant and Equipment | Continuous Process Improvement and Optimization
a number of control factors, which depends on the array, with one factor associated to a column of the array. That column will contain the settings to be used for the factor. Some arrays have only two different settings (two-level design), others have three (three-level design), and other commonly used arrays have four by combining columns of two-level factors (for instance, M-16 or L-16M refers to the L-16 array modified, which tests four different settings of factors, but it can be used for much less factors than the original L-16). There are also some mixed level designs. Table 1 shows an example, the L-8 array, which can be used to test up to seven factors with only two settings used for each. These experimental designs are very good for limiting the number of tests that need to be performed, but come at a cost: the design generates an intricate set of confoundings that may be difficult to separate. ‘Confounding’ is the statistical name given to a combination of terms or factors in the design that results in their effect being indistinguishable. It does not mean that the confounded factors are confounded by nature, it is a consequence of the experimental design that their impact is confounded (pooled together). For instance, if a design tests a system at 20 and 30 C, and also considers a flow rate of 1 or 2 l s1, but in all tests performed the flow rate of 1 l s1 was always used with 20 C and the flow rate of 2 l s1 was used only with 30 C, then when analyzing the data it is not possible to know if the differences were due to (1) the temperature increase, with flow rate change being irrelevant, or (2) the flow rate increase, with the change in temperature being irrelevant, or (3) both changes. Orthogonal arrays do not produce confoundings between factors, but they do between the effects of factors and the effects of their interactions. An ‘interaction’ is a basic feature of nonlinearity in a system. It means that the way that a factor influences a system depends on the actual value of another factor. For instance, if increasing the flow rate has no effect at lower temperature but is important at higher Table 1 L-8 orthogonal array Test no.
1
2
3
4
5
6
7
1 2 3 4 5 6 7 8
1 1 1 1 2 2 2 2
1 1 2 2 1 1 2 2
1 1 2 2 21 2 1 1
1 2 1 2 2 2 1 2
1 2 1 2 1 1 2 1
1 2 2 1 2 2 2 1
1 2 2 1 1 1 2
Control factors are assigned to columns, and the rows indicate the settings of each factor for each of the eight tests that need to be performed. Each factor is tested with only one of two settings. Designs should be replicated, if possible.
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temperature, there is an interaction between flow rate and temperature. For this reason, ‘western’ statisticians prefer other experimental designs that provide a better differentiation between different effects, such as the ‘central composite design’. This design uses five settings for each factor, and tests some combinations of those settings that conform to a particularly well-balanced view of the solution space, which minimizes error regions of mathematical models then used to interpret the data. However, it requires a large amount of data than the orthogonal arrays. Whatever DoE is chosen, it is noted that it can be considered as a plan for tests that will be done (the ideal scenario), or as a filter to be used to collect data from historical records in order to ensure minimum bias of the analysis of those data (even if only a small subset of data are thus collected; this is preferable to overweighing parts of the solution space). Stepwise Approach The Taguchi method advocates a comprehensive approach including meetings, brain-storming, and teamwork, that is not detailed in this text, but it is noted that the first step must be to consider how many factors may influence the system. Usually, this analysis compiles a large number of factors that may be interesting to analyze. If the system should ‘speak for itself’, then one should not curtail the list by rational thought; instead, it is better to rely on Vilfredo Pareto’s famous principle, the 80/20 rule, and use a first experimental plan to zoom in on the 20% of factors that may be causing 80% of the consequences. This is also where analyzing historical records could be helpful, and provide ‘free’ information. A simple twolevel orthogonal array design can be used for this purpose. An L-8 can test up to 7 factors with 8 runs, an L-16 allows one to consider up to 15 factors with only 16 runs, and an L-32 would allow for up to 31 factors with just 32 runs (can, and should, be repeated), and so on, so that the selection can be done quite efficiently. It is noted that the consequences of the confoundings of this design are that some factors that may be considered important in the data analysis could actually be negligible (and this would be because one of the confounded interactive effects was relevant), but if a factor is judged to be negligible, then it is, and so are all effects confounded with it. That means that nothing of importance is lost by analyzing in this way which factors are more crucial for improving the performance. There are possibilities for overlooking important issues with these two-level designs, though: if a factor has an influence that shows a maximum or minimum of its average impact on the performance, it is possible that by a stroke of bad luck the averages at the two extremes used for the settings (low and high, 1 and 2) are similar, and the
268 Plant and Equipment | Continuous Process Improvement and Optimization
data analysis will then infer that the factor was negligible, while data from a design with three levels would conclude otherwise. Continuous process improvement is however prepared to be incremental – there will always be time to go back into more analysis and improvements. Once two, three, or at most four control factors are chosen for being the most crucial ones, then a design with more levels (three, four, or a central composite design) can be used and the solution space explored in more detail to reveal regions of improved performance. Data Analysis: Identifying Crucial Factors The Taguchi method does not need to fit mathematical models to the data obtained with the orthogonal array design. Instead, it applies an analysis of variance (ANOVA), a statistical method that quantifies the variability of the data collected by its variance, and then determines how much of it can be explained by the fact that each of the factors changed its settings. If the amount of data is sufficient to have enough degrees of freedom with the DoE used, a significance test can also be applied to ascertain which factors have a statistically significant effect. Results can be shown in the form of a pie chart, which gives a very good image of what is more important and what might be neglected in a first approach. A typical result from ANOVA, with the most relevant outcomes in the form of a table and pie chart for a situation where the relevance of seven factors was tested with an L-8, is shown in Figure 1 (case study regarding a particle coating process). In this example, the design was replicated (2 runs for each condition, totaling 16 data points), which gives enough degrees of freedom to test for significance. The pie chart shows not only the relative importance of each factor, but also how much of the variability of the data is unexplained. The unexplained amount of the variance may be due to (1) the relevance of interactions and the consequences of the intricate confounding of the design, (2) the influence of other factors that were not controlled and not considered in the design, and (3) the natural variability, or white noise, which may come from variability in control factors, in the characteristics of the materials or process, and also of the method of analysis of the performance, which is similar to random experimental error. The example shown suggests that changing the settings of three of the factors accounts for a large proportion of the changes that can be achieved in the performance. Data Analysis: Identifying Settings for Improved Performance with the Taguchi Method The estimate of which is the combination of settings of the control factors that gives the best performance is done in the Taguchi method by simply choosing for
each factor the setting that had the best average performance. This has the advantage of not relying on any model fitting, and the disadvantages are that it will suggest settings for all factors from only among those that were used in the experimental design (even if the best combination is not one of those tested), and that it does not account for interactive effects. It is possible to include a correction for the effect of some interactive effects if the DoE has enough degrees of freedom for that, but it is a matter of interpretation which interactive effects are being tested because of the intricate nature of the confoundings. Taguchi recommends the calculation of a severity index to at least evaluate the relative potential importance of all interactions between pairs of control factors, but the extent to which this effectively gives unique results is not clear. Furthermore, when searching for a region of optimum performance, the designs usually have at least three (if not more) settings, and in this case it is virtually impossible to properly account for any interaction, unless one is effectively using a full factorial design (e.g., only two factors in an L-9). Therefore, the best combination of settings obtained by the Taguchi method assumes in practice that interactions between factors are negligible. Taguchi recommends validation tests for the new settings, of course. Figure 2 gives an example of the graphs showing the averages of the data for each setting of each factor, known as the ‘means plots’, for a system where three factors were changed with four levels, according to a modified L-16. The maximum performance in that case is suggested for the combination of settings 3-4-2 of the three factors. The estimated performance of the system for that combination of settings is 99.08, obtained simply by adding to the global average of the data (81.29 in that case) the incremental benefit of choosing the respective setting of each factor, as per the means plots. Estimating performance in this way may lead to physically inconsistent values in some cases (for instance, performance above 100% or losses below 0%), which can be improved by a logarithmic transformation, such as the omega transformation. Data Analysis: Identifying Settings for Improved Performance with Response Surface Method An alternative that has been widely applied in Europe and the United States is the response surface method (RSM; or response surface analysis (RSA)). It can be applied to any design, including the central composite design, and is based on postulating a mathematical model to describe the influence of the factors (and interactions) on the performance. It has the advantage that designs such as the central composite design that have much less confounding issues can be handled, but
Plant and Equipment | Continuous Process Improvement and Optimization
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ANOVA table for data FACTORS Torque Rotational speed Temperature Oil viscosity Drip feed rate Drip concentration Coating Error Total
SS 0.000 798 0.001 58 9.51E-05 0.008 145 0.037 733 0.021 098 0.037 153 0.008 633 0.115 234
df 1 1 1 1 1 1 1 8 15 16
Total no. of data points:
VARIENCE 0.000 798 0.001 58 9.51E-05 0.008 145 0.037 733 0.021 098 0.037 153 0.001 079 0.007 682
F 0.739 589 1.464 292 0.088 097 7.548 277 34.96 838 19.551 75 34.430 41
F-limit: 3.457 919 Ne: 2
(a)
Torque 1%
Rotational speed 1%
Error 7%
Temperature 0% Oil viscosity 7%
Coating 32%
Drip feed rate 34%
Drip concentration 18% Figure 1 Example of an analysis of variance (ANOVA) table (a) and pie chart of the corrected sums of squares (b) for a system potentially influenced by seven factors, tested with an L-8 design replicated once. Factors in bold in the ANOVA table have statistical significance at a 90% confidence level. Ne is the effective number of data points, which is equal to the actual number of data points divided by 1+ the sum of degrees of freedom of the factors used to produce the estimate. The table and graph were produced in MS Excel.
the disadvantage is that the results will assume the validity of the mathematical model, and so the lack of fit is added to the overall amount of unexplained variance. The simplest model is a quadratic multifactorial polynomial, that is, the sum of linear, interactive, and quadratic terms. A linear term is proportional to the value of the factor, an interactive term is proportional to the product of the value of one factor and the other, and a quadratic term is proportional to the square of the value of the factor. All values must be normalized between maximum and minimum, which is called ‘coding’ (numerically, 1 and 1 are common, but can also be 0 and 1, or 0 and 100%). While being
useful in terms of all parameters of the model having a very clear meaning, it assumes parabolic curves for all effects, which tends to suggest points of minimum or maximum that do not really exist. Once a model is fitted to the data and its goodness of fit accepted, it can be used to pinpoint the location of the best combination of settings (searching for the point of maximum or minimum within the constraints of the solution space). The goodness of fit is typically quantified by the coefficient of determination (designated R2), which quantifies the percentage of the variance of the data that is explained by the model, and values over 90% are usually desired.
270 Plant and Equipment | Continuous Process Improvement and Optimization Drip feed rate
Drip concentration
Coating
95 90 Best
85
Best
Best 80 75
4
3
tti ng Se
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tti ng Se
1
tti ng Se
4
tti ng Se
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tti ng Se
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tti ng Se
tti ng Se
Se
tti ng
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3 Se
tti ng
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tti ng Se
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Figure 2 Example of means plots of the performance of a system affected by three factors changed with four settings each, according to a modified L-16 array. The dotted line indicates the average of all data. For each factor, the data are divided in four subsets according to the setting of that factor and the dots show the four averages. Calculations and plots were produced in MS Excel.
There are two useful plots, Pareto charts and surface plots. The Pareto chart represents the standardized effects as horizontal bars, and as such the limit of statistical significance can also be represented as a vertical line. The bigger the bar, the more important the effect. Standardized effects are the effects divided by the standard errors, and when using a model they are also equal to the parameters of the model divided by their confidence
intervals. An example is shown in Figure 3 (case study of loss of an active ingredient in a pasteurization process, as affected by flow rate, inlet temperature, and length of holding section). Surface plots can only be made for a pair of factors at a time, and they can be represented in three dimension (3D) or two dimension (2D) (Figure 4) to help visualizing the regions of improved performance, as predicted by the model.
P1
9.35 5.98
P11 P2
5.27 4.82
P12 2.89
P22 P3
1.81 0.95
P13 P33
0.71
P23
0.63 0
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6
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10
Standardized effects
Figure 3 Example of a Pareto chart for a system affected by three factors, which was tested with a central composite design, fitted with a quadratic model. The vertical line represents the limit of significance at a 95% confidence level. The notation 1, 2, or 3 refers to the linear effects (linear terms of the model), 11, 22, and 33 to the quadratic effects, and 12, 13, and 23 to the interactive effects, where 1, 2, and 3 are the generic names of the factors. In this example, factor 3 and all its interactions are not statistically significant. Factor 1 is the most important, and its effect is strongly nonlinear, showing a significant curvature (quadratic effect very relevant) and an influence affected by the settings of factor 2 (interactive effect 1 2 significant). In this case study, the factors were inlet temperature, flow rate, and length of holding section in a pasteurizer. The calculations and graph were produced in MS Excel.
Plant and Equipment | Continuous Process Improvement and Optimization
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(a) 46 44 42 40
80 70 60 50 40 30 20 10 0 0 –1 2 3 0 3 8 2 6 2 4 Tb 2 22
38 36 34 32 30 28 26 24 22 20 18
1 1 .2 1.1 .20 5 1 1 .1 5 1.0 .05 0 0 0 20 8 0 .9 0. .90 5 1 8 1 4 0 0.80 85 1 .75
16 14 12 10 8 6 4 2
(b) 32 30 28 26 24 22 20 18 16 14 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25
50 48 46 44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2
Figure 4 (see color plate 89) Examples of three-dimensional (a) and two-dimensional (b) plots of the influence of two factors on the performance of a system predicted by a model (other influential factors are kept at a constant setting). In the example, optimum performance means minimum losses of a valuable active ingredient, and the two factors shown are inlet temperature and flow rate. The plots were made using the Statistica software (Statsoft).
See also: Plant and Equipment: Quality Engineering.
Further Reading Bashein B, Markus M, and Riley P (1994) Preconditions for BPR success – and how to prevent failures. Information System Management 11(2): 7–13. Womack J, Jones D, and Roos D (1990) The Machine That Changed the World – The Story of Lean Manufacturing. New York: McMillan Pub. Co. Liker J (2004) The Toyota Way – Fourteen Management Principles from the World’s Greatest Manufacturer. New York: McGraw-Hill. Markgraf S (1997) Fortified with kaizen: Superior Dairy celebrates its 75th anniversary with a ‘different’ approach to doing business – kaizen business concept. Dairy Foods 1 September 1997.
Monden Y (1981a) What makes the Toyota production system really tick? Industrial Engineering 13(1): 36. Monden Y (1981b) Adaptable kanban system helps Toyota maintain just-in-time production. Industrial Engineering 13(5): 29. Monden Y (1981c) Smoothed production lets Toyota adapt to demand changes and reduce inventory. Industrial Engineering 13(8): 42. Monden Y (1981d) Toyota production smoothing. 2. How Toyota shortened supply lot production time, waiting time and conveyance time. Industrial Engineering 13(9): 22–30. Montgomery D (2009) Design and Analysis of Experiments, 7th edn. Hoboken, NJ: John Wiley & Sons. Ross P (1988) Taguchi Techniques for Quality Engineering. New York: McGraw-Hill. Roy R (2001) Design of Experiments Using the Taguchi Approach – 16 Steps to Product and Process Improvement. New York: Wiley Interscience.
272 Plant and Equipment | Continuous Process Improvement and Optimization Shigeo S and Dillon AP (1989) A Study of the Toyota Production System from an Industrial Engineering Viewpoint. Norwalk, CT: Productivity Press. Sugimori Y, Kusunoki K, Cho F, and Uchikawa S (1977) Toyota production system and kanban system materialization of just-in-time and respect-for-human system. International Journal of Production Research 15(6): 553–564. Taguchi G, Chowdhury S, and Taguchi S (2000) Robust engineering implementation strategy. In: Robust Engineering – Learn How to Boost Quality While Reducing Costs and Time to Market, ch. 2, pp. 10–15. New York: McGraw-Hill.
Ward A, Liker JK, Cristiano JJ, and Sobek DK (1995) The second Toyota paradox: How delaying decisions can make better cars faster. Sloan Management Review 36(3): 43–61.
Relevant Websites http://kaizen.com – Kaizen Institute. http://lean.mit.edu – Lean Advancement Initiative of MIT.
Quality Engineering J C Oliveira, University College Cork, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Quality Engineering and Quality by Design Engineering is the application of scientific and empirical knowledge to create a new good or service. To ‘engineer’ something means to design what it should be, how it should be made, and how the process of making it should operate. ‘Quality engineering’ therefore means that the quality of a product (or service) can be engineered in its production process itself, so that it becomes a characteristic inherent to the product every time it is manufactured in the process. Quality not being a characteristic that is measured, but a consequence of the design of the process and of the way that it operates, leads to the term ‘quality by design’ (QbD) alternatively used to express this concept. Conventional quality control systems act on the end result: products are tested for quality and compared to the desired specifications. Non-conformity of a product to the specifications results in a waste: the product must be discarded or reprocessed, depending on whether something can be done to ensure conformity. Quality control is therefore a waste-generating activity. On the other hand, having no quality control can result in a worse consequence, from simple loss of market image to more serious impact, such as that resulting from inadequately processed foods unsafe for consumption. Quality control therefore implies a lack of trust on the capacity of the process to perform consistently and provide quality products all the time. As the process will certainly have been developed properly, this means that it is subjected to variability in its conditions and/or materials it uses, and that variability may result in non-conformities. Not knowing how these sources of variability can present themselves and what can be done to compensate for them, the only option is to check the result at the end, and pray that it is on target most of the time. Achieving QbD, therefore, implies one of two things: (1) eliminate all sources of variability, controlling obsessively everything so that there is no variation and the system repeats itself exactly the same, time after time; (2) analyze the variabilities of the system inputs, know what their impact will be, and operate the system so that it dampens those variabilities to oscillations within conformity. The first case requires good control systems, and the second needs good process intelligence. The first concept would be hopeless in most food industries because of the natural variability of biological
materials: for instance, in dairy, the composition of milk varies throughout the year, with the lactating cycles of the animals. However, there are sectors where such variability in raw materials does not occur, and one could then envisage that tight control systems would suffice. One should consider, though, whether the cost of such tight control would be an acceptable proposition. In the pharmaceutical industry, there has been a growing deployment of process analytical technologies (PATs), one feature of which may be that more sophisticated sensors measure better aspects of the process so that it may ensure better consistency. Some companies have acquired mass spectrometers for applications such as these. However, some simple calculations should be considered: How much does a mass spectrometer cost to buy and to run? What is the value of the quality gains from the better control? How long does it take for the investment to be recovered? In the pharmaceutical industry, it may well be that the product margins are such that expensive equipment is paid for in some years; in the case of the dairy industry, those margins might point to a few centuries. This has led to a much less interest of the food industry in general for PAT, as deployed in the pharmaceutical sector, which is a pity, because in fact PAT does not necessarily imply that very expensive analytical technologies are used to monitor the process and enable a proactive approach to quality control. It is therefore useful to focus on the second option described above, go back to basics, and work out a better system by using process intelligence to achieve QbD, independent of whether acquiring that intelligence requires expensive analytical technologies or not.
The Principles of the Taguchi Method The pioneering work of Genichi Taguchi was a very influential basis of the modern QbD approach. Appointed to lead the Electronic Communications Laboratory (Nippon Telephone and Telegraph Co.) of Japan in 1950, he was faced with ensuring consistently good communications on resources devastated by war. The problem required solutions to be found fast and there were few resources to help and little money to invest. Taguchi spent the best part of the next 12 years developing methods to improve quality and reliability. One of the companies that took up his concepts early on
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274 Plant and Equipment | Quality Engineering
was Toyota, and through it and the Toyota Production System (see Plant and Equipment: Continuous Process Improvement and Optimization), the Taguchi method began permeating US and then European industrial practice in the late 1980s. That such a story is at the origin of QbD is very relevant, as it shows that the essence of the system is all about being able to solve problems without throwing money at them. There are two important concepts at the basis: differentiating between control factors and noise factors, and the loss of quality function. The performance of a system is influenced by factors that are controlled by the operator, probably within tight margins, such as temperatures, flow rates, and pressures. It is, however, also influenced by factors that are not controlled, and these may vary more or less significantly depending on random or non-random effects. For instance, milk composition varies throughout the year and also from producer to producer, as it is influenced by animal feed too, not to mention the genetics of the animals. Although control factors may have a bigger influence on the performance, as they are controlled tightly, the variability of performance may be due more to noise factors than to improper control of the control factors. Therefore, more sophisticated control systems for the control factors may be almost pointless. First and foremost, the sources of variability, and how they influence product variability, must be understood. For instance, a pasteurizer may be set to work at 92 C, and the control system does not give better than 1 C. On the other hand, the pasteurizer was designed considering that ambient temperature was a given constant figure (e.g., 15 C). However, depending on the location, this may vary during the year from anywhere between 20 and 40 C. Even though ambient temperature in itself may be less important than the operating temperature for the design of the equipment, in the operation of the pasteurizer its variability may cause more fluctuations than that of the process temperature. However, it is obvious that controlling ambient temperature tightly is a preposterous idea, so controlling variability may not be an option, and the only possibility may be to find a way to live with it. As an engineer, Taguchi knew that changing the settings of a system influences its inertia and so the way that it amplifies, or dampens, the input oscillations. Therefore, one should look for the settings of the control factors that lead to a system that dampens the input oscillations as much as possible: hence the term robust design. A system has a robust design when it performs consistently in spite of the variability of the inputs. The concept of loss of quality function was another original contribution of Taguchi. Previously, the norm was to consider that a product was either acceptable (within the range of specifications defined) or not acceptable, so there was full acceptance or full loss of a product.
Taguchi considered that every time that the product is not exactly on target, there is a loss, which is bigger the further the result is from the target. Taguchi used a simple parabolic function to quantify the loss of quality as the quality indicator deviates from the target value. In fact, if quality is below expectations, there is loss to the client, which over time becomes loss to the company in terms of market image, market share, and so on. If quality is above expectations, there is loss of opportunity for the company, which could have made use of that better quality to get a better price or greater market share. Furthermore, if that higher quality is presented to a client once, that client will then expect the same higher quality next time, and therefore there can be a greater loss of quality by underperforming to expectations the next time. Therefore, the quality loss function should be minimized, and the process should be steered to the quality indicator value that can be delivered more consistently. This means that one would even prefer a business where the product has a lower average quality but that can be delivered consistently, to one with a greater variability even though on average it may be better. In the long term, the second case is going to pile up client dissatisfaction for one reason or another and hurt the business. It can be argued that the evolution of the world wine markets between French producers and New World producers offers a case in point. In order to improve both average quality and its consistency, Taguchi defined the signal-to-noise ratio (S/N) as the objective of an optimization approach: search for the combination of settings of the control factors that gives the maximum S/N. S/N integrates the two objectives: best average quality and best quality consistency. There are three mathematical definitions of S/N, depending on the type of problem, known as ‘bigger is best’ (the higher the average of the quality indicator, the better), ‘smaller is best’ (the lower the average of the quality indicator, the better), and ‘nominal is best’ (the closest the average of the quality indicator is to a nominal target, the better). In essence, the Taguchi method for robust engineering design consists in deploying an experimental plan and statistical data analysis procedure to identify the combination of settings of the control factors that maximizes S/N (for the methods that Taguchi selected for experimental design and data analysis, see Plant and Equipment: Continuous Process Improvement and Optimization). The Taguchi method does not consist solely of applying statistics to plan and then analyzing a set of tests, but it considers the entire framework of operation, teamwork, and other things. See articles in Further Reading for more information. It is noted that once the ‘process intelligence’ has been gathered in terms of availing of a simple model that relates input variability, control factor settings, and
Plant and Equipment | Quality Engineering
output variability (S/N), it is possible to develop a proactive approach to process control (also known as feed forward; see Plant and Equipment: Instrumentation and Process Control: Process Control). By measuring the input factors and their variability (even if they are not controlled, as noise factors), the model can predict what the outcome will be, and hence correct the settings of the control factors to ensure the robustness of the operation (see Plant and Equipment: Instrumentation and Process Control: Process Control). Recently, Charteris advocated the use of experimental design methods and the Taguchi method in particular for competitive quality systems in the food, and specially dairy, industry. The increasingly extensive application of the method in various companies across industrial sectors is its greatest selling point. Theoretically, the Taguchi approach has been contested, mostly for two reasons: it relies on orthogonal arrays in the experimental design, which leads to intricate confoundings (see Plant and Equipment: Continuous Process Improvement and Optimization), and the S/N ratio concept integrates average and standard deviation, and therefore model predictions bundle them together. It may also be noted that in practice maximizing S/N assumes no interactions between factors (see Plant and Equipment: Continuous Process Improvement and Optimization). However, by giving more and due importance to variability and repeatability, it often leads to good results from a limited amount of data.
Statistical Process Control As Taguchi was beginning his work in Japan, ‘western’ statisticians were also assisting industry to develop methods for improving quality consistency. That a proactive approach to quality control was needed was also concluded early. The process should be monitored at several key moments, the variability must be addressed then, and actions must be taken immediately, as needed. The concepts of statistical process control (SPC) were thus developed (for more details, see Plant and Equipment: Instrumentation and Process Control: Process Control). In this case, the type of variability is categorized between common and special causes. The former are identified primarily due to the randomness of variability, while the latter are pinpointed by a clear pattern in the data that cannot be due to chance. The original practice involved using process charts to identify the sources of variability and progressively eliminate or squeeze them, which an enthusiast of the Taguchi method might regard as too laborious and hence not pro-active enough. It also has the obvious disadvantage of relying on process data, which means that the range of
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values considered for the control factors may be too small and the data excessively biased. SPC is basically very good for ensuring that the oscillations in a given process are minimized, but is not really designed to establish best conditions of operation that offer a more robust operation. It may also lead to the over-zealousness of controlling factors with increasingly expensive methods even if such control results in savings that do not justify the costs. Quality engineers deploying SPC may need to resist the temptation for expensive applications of information technologies (IT) or PAT, unless the benefits are clear upfront. For further details, see articles in Further Reading.
Six Sigma The best practice of modern manufacturing industries is generally regarded to be the six-sigma system, although there is some controversy on this. Its name reveals its primary focus on maximizing consistency and thus eliminating waste, as sigma is the Greek letter used in statistics to denote the standard deviation, a quantitative measure of the spread of a series of data. If the data are normally distributed, then the band defined by the average 6 contains 99.999 998 1% of the data. Bringing some element of reality of process operations, the six-sigma creators discounted 1.5 from this, saying that over time a process becomes more ‘sloppy’ than the original design by this much, that is, a process is said to be 6 when the range of average 4.5 is within the specification range: thus, one would be out of spec only 3.4 times in one million (99.999 66% of the data of a normal distribution within 4.5). In practice, it really means that the process is designed/operated to deliver consistency all the time, or as sometimes stated in business science literature, ‘first time right, every time right’. It is generally accepted that the origin of the system lies in Motorola in the early 1980s, and that it was particularly disseminated by Jack Welch, a charismatic former CEO of General Electric (who famously stated that ‘variation is evil’). In broader terms, six sigma results from giving an American managerial approach and organization to projects aimed at eliminating variation that apply much of the concepts and methods of Japanese manufacturing, with the Taguchi concepts being particularly eminent. Six sigma is a method, or work system, not a tool, and therefore it collects and deploys whatever tools can assist to achieve its objective better. Just like the Taguchi method, it involves a comprehensive approach including teamwork, planning, and other things, and it is data driven, that is, it relies on obtaining and analyzing actual process data. In that respect, six sigma is more an American version of the Taguchi approach than the Taguchi method is a part of six sigma. There is some
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confusion in the literature as to what is a tool and what is a system, and often the Taguchi method is taken as the distillation of its statistical approaches – that, however, is only a part of the whole. Just like Taguchi did, six sigma picks up the tools it finds more useful. Among these are the tools used in the Taguchi method (e.g., design of experiment (DoE), analysis of variance (ANOVA), S/N), but many others as well, such as SPC and lean analysis. When lean thinking is added, it is often denoted as the lean six-sigma approach. As it incorporates both operational and process improvements, it is a proper approach to achieve manufacturing excellence in an organized and systematic manner. Critics contest its novelty, as almost everything it uses existed before, and so are the aspects of its implementation. For someone experienced in the Taguchi method, it also seems to be overcomplex, and could lead to the deployment of different approaches that yield the same end result, with no particular benefit in the redundancy. It is common to summarize the overall approach with acronyms: a project to achieve optimum consistency in an existing process applies a series of steps known broadly as DMAIC (define, measure, analyze, improve, and control), while a project geared at developing a new process or product is composed of a series of steps represented by
DMADV (define, measure, analyze, design and validate, or verify). The latter is also known as DFSS, from design for six sigma, that is, design the new process or product so that it will deliver a six-sigma consistency, which is therefore the same as QbD. See also: Plant and Equipment: Continuous Process Improvement and Optimization; Instrumentation and Process Control: Process Control.
Further Reading Chambers D and Wheeler D (1992) Understanding Statistical Process Control. Knoxville, TN: SPC Press. Charteris W (2007) Taguchi’s system of experimental design and data analysis: A quality engineering technology for the food industry. International Journal of Dairy Technology 45(2): 33–49. Ross P (1988) Taguchi Techniques for Quality Engineering. New York: McGraw-Hill. Roy R (2001) Design of Experiments Using the Taguchi Approach – 16 Steps to Product and Process Improvement. New York: Wiley Interscience. Taguchi G, Chowdhury S, and Taguchi S (2000) Robust Engineering – Learn How to Boost Quality While Reducing Costs and Time to Market. New York: McGraw-Hill. Taguchi G, Chowdhury S, and Yuin W (2004) Taguchi’s Quality Engineering Handbook. New York: Wiley Interscience. Welch J and Welch S (2005) Winning. New York: Harper Collins Publication.
Safety Analysis and Risk Assessment N Hyatt, Dyadem International Ltd, Toronto, ON, Canada ª 2011 Elsevier Ltd. All rights reserved.
Importance of Plant Safety in the Dairy Industry Safety is important in both milk production and dairy processing facilities. Both people and animals can be exposed to a diverse range of hazards. These need to be identified and managed. As an example, people who handle chemicals, antibiotics, vaccines, and veterinary drugs need to be familiar not only with their benefits but also with their potentially hazardous properties. To ensure that these substances are handled safely, the use and distribution of Material Safety Data Sheets (MSDSs) to all involved personnel are a prerequisite. Chemicals, fertilizers, and pesticides can cause environmental damage and possible contamination problems if improperly used or incorrectly handled. Contamination and pollution can also be caused by incorrect handling and storage of manure and dairy wastes. In some instances, asbestos insulation may be present in older farm buildings, which carries the risk of mesothelioma and necessitates a careful and organized program for removal of such insulation by qualified asbestos removal contractors. Dust can also become a health hazard and, if combustible, could lead to fire and/or explosion. Typical job safety hazards are also posed by effluent ponds where drowning can occur and with electrical equipment, often of a temporary and makeshift nature, where electrocution through use of ungrounded electrical equipment, in an aqueous environment, can occur. The use of unguarded prime movers, the temporary removal of guards, and the failure to isolate machinery during maintenance are all sources of hazard and risk: the use of lockout/tagout procedures is essential if maintenance of equipment with moving parts is involved. Also, personnel who work at heights may risk falling and those who engage in manual lifting may sustain injuries. The dairy industry, when compared with many other industries, is not normally associated with high-risk activities. However, large dairy facilities may use a number of hazardous materials that can still pose high risks to both plant personnel and the neighboring communities. As an example, the following substances can present significant risk: 1. Anhydrous ammonia which may be used in refrigeration systems. Release of anhydrous ammonia to the environment, which is normally stored as a liquid
under pressure, can result in a highly toxic subcooled aerosol mist that can hug the ground until it heats up and disperses. Such releases can have quite devastating effects in the path of release. 2. Liquid chlorine which may be stored under pressure and normally used for sanitization purposes. Chlorine gas is heavier than air and is highly toxic: it can cause death even in relatively small amounts. 3. Propane which is stored as a liquefied gas in bullets under pressure. Propane may be used as a heating medium for boilers and heating systems. A number of dangerous incidents have arisen as a result of propane bullets becoming overheated, due to external fires impinging on them and causing Boiling Liquid Expanding Vapor Explosions (BLEVEs). Overall, many different types of hazards are often present at a dairy facility and the failure to be aware of these can lead to accidents and injuries. It therefore follows that potential hazards, in the first instance, need to be formally identified in order for them to be managed. The key steps in safety analysis are (1) the systematic identification of hazards that are present, whether obvious or latent, (2) the prioritization of hazards using a risk matrix approach, and (3) the management of hazards through the introduction of risk control or risk mitigation measures. Usually, these three steps are adequate for the majority of in-plant safety issues. Where greater issues that could pose significant risks not only to in-plant personnel but also to the neighboring communities exist, it may be necessary, in addition, to perform a Quantitative Risk Assessment (QRA).
Formal Safety Analysis A formal safety analysis can be performed using a number of alternative methodologies. These are known collectively as Process Hazards Analysis (PHA). Typically, they proceed as shown in the following six steps: Step 1: Collect engineering drawings such as Process Flow Diagrams (PFDs), Piping and Instrument Diagrams (P&IDs), and documents that specify the nature and operation of the facility in question. In addition, MSDS for all hazardous substances stored or used at the facility should be available for the analysis.
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Step 2: Break down the facility into definable and specific subunits that provide a common function. This is a form of itemizing and is sometimes known as creating ‘nodes’. Step 3: List questions for each subunit or node that can explore and investigate design or operational deviations that might reveal undesirable or possibly hazardous conditions outside the normal range. Step 4: For each question listed in Step 3, record the causes for the deviations and the consequences that might occur or result from such deviations. In addition, the safeguards that may already be in place to either prevent the cause of the deviation or to protect or mitigate the consequences should be recorded. Furthermore, any recommendations should be considered to reduce the risk by providing additional safeguards that are not currently available. Step 5: Proceed throughout the facility so that all subunits or nodes are covered. Step 6: Prepare a detailed report that includes both documentation on the facility as well as details of the PHA. When this stage is reached, it is possible to create a risk management plan to determine what needs to be done to reduce the risk in order to make the facility safer. Also, when the PHA is being undertaken, it is often best to assemble a team of personnel responsible for the design and operation of the facility so that all possible concerns are systematically investigated. There are four different types of PHA that are typically used: 1. Hazard and Operability (HAZOP) analysis, where deviations are created by applying guidewords such as High, Low, Reverse, As Well As, Part Of, and Other Than to properties such as Flow, Level, Pressure, Temperature, Concentration, and pH. This is a popular methodology within the process industries but is really applicable only where the systems involve flowing fluids, often on a continuous basis. HAZOP may also be applied to batch operations where the guidewords also include Sooner and Later to account for time aspects. 2. ‘What if. . .’ analysis, where deviations are created by listing questions that pose design and/or operational problems. This is a relatively simple technique that, although less structured than HAZOP, is applicable to almost any facility or part of any facility regardless of design, function, or operation. Furthermore, it is easy to learn and apply. 3. Failure Mode and Effects Analysis (FMEA), where items of equipment are broken down into components. For each component, the deviations are different possible failure modes for that component. The consequences are the effects of the various types of failure that are identified. FMEA is normally recommended for analyzing equipment failures as opposed to fluid system failures. It can typically be applied to prime movers, instrumentation, and control equipment, and,
in addition, is a useful method for improving reliability through the identification of possible failure modes. 4. Checklist analysis, where a list of questions and concerns is created from either preexisting data or information or based upon previous experience. This technique is less structured than the other three methods described above but is useful prior to commissioning a new system where there are concerns over any residual issues that might have been created or overlooked by construction teams. In addition to these above four methodologies, ‘What if . . .’ analysis and Checklist analysis are often combined as ‘What if/Checklist’. This ensures that an adequate list of questions (i.e., possible deviations) is created. Furthermore, when applying these types of methodologies to occupational safety, the form of analysis used is Job Safety Analysis (JSA) where people’s jobs are specifically analyzed for hazards. All of the above methods are oriented toward the identification of potential hazards and hazardous situations, whether obvious or latent. These analyses normally identify single jeopardy hazards as opposed to double or multiple jeopardy situations. From the standpoint of likelihood, single jeopardy is the most likely and double or multiple jeopardy is far more unlikely.
Definition of Risk While the identification of hazards, including potential hazards, is of paramount importance, the quantification of risk can, in some instances, be desirable. Risk is a measure of the importance of hazards posed and is a function of both the severity of the hazard and the likelihood, or frequency, of the hazard occurring. The technical definition of risk is the product of the consequence, that is, the severity of the hazard and the frequency, that is, the likelihood of the hazard ever occurring. In other words Risk ðRÞ ¼ Consequence ðCÞ Frequency ðF Þ
The consequence may be expressed as the chance of mortality, as financial damage that may be incurred or the loss of revenue that may result from an incident. Typically, when consequence is expressed in terms of mortality or, more specifically, in terms of the probability of fatality, the values provided in Table 1 can be useful. The frequency is often expressed as the number of times per annum that the incident may occur. Hence, for example, if the incident were likely to occur once every year or so, this would be deemed as ‘very likely’ but if it occurred only once in a 1000 years it would be deemed as ‘very unlikely’. It can seem difficult to envision individual risk levels without comparison to known risks experienced on a day-to-day basis. Table 2 provides this comparison.
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Table 1 Value of fatality probability and associated effects Value of fatality probability
Associated effects
1.0 0.1 0.01 0.001
Effects would be fatal for any individual exposed to the hazard With 10 persons exposed to the hazard there would be one fatality With 100 persons exposed to the hazard there would be one fatality With 1000 persons exposed to the hazard there would be one fatality
Table 2 Example of comparative mortality statistics Hazard
Total number of deaths
Individual chance of death per year
Heart disease Cancer Work accidents All accidents Motor vehicles Homicides Falls Drowning Fires, burns Poisoning by solids or liquids Suffocation, ingested objects Firearms, sporting Railroads Civil aviation Water transport Poisoning by gases Pleasure boating Lightning Hurricanes Tornadoes Bites and stings
757 075 351 055 13 400 105 000 46 200 20 465 16 300 8100 6500 3800 2900 2400 1989 1757 1725 1700 1446 124 93 91 48
3.4 103 1.6 103 1.5 104 4.8 104 2.1 104 9.3 105 7.4 105 3.7 105 3.0 105 1.7 105 1.3 105 1.1 105 9.0 106 8.0 106 7.8 106 7.7 106 6.6 106 5.6 107 4.1 107 4.1 107 2.2 107
Data on Mortality Statistics for USA, 1974, and revised, 2000: Chemical Manufacturer’s Association.
In Figure 1, an example of a risk matrix is shown that can be used in conjunction with a PHA to enable members of a risk analysis team to assess first-order estimates of risk associated with an activity or item of plant. When values are in excess of 103 deaths per annum then some additional risk control measures or additional risk mitigation should be considered. Every activity normally carries some level of risk, however small it may be, and most people accept this as part of the day-to-day reality of life. Zero risk for an activity is not usually possible unless the activity ceases altogether.
incidents are high-enough risk to warrant full risk quantification and assessment. Step 2: Model the consequence of the incident as a function of distance from the hazard source. This is done using mathematical models as typically listed in Table 3. Step 3: Model the frequency of the potential incidents. A variety of methods can be used as shown in Table 4. Step 4: Having numerically determined both the consequences, in terms of probability of death per occurrence and frequency of occurrence in times per annum per event, individual risk can be computed as R i ¼ C i Fi
Risk Assessment When incidents involving hazardous materials could cause significant in-plant damage and also threaten neighboring communities, it may be in order to consider performing a QRA for the facility. The following steps are usually undertaken: Step 1: From the PHA already performed and by applying the risk matrix methodology, determine which
where Ri ¼ individual risk, in deaths per annum for a single event, i; Ci ¼ probability of death, dimensionless from the consequence of event, i; and Fi ¼ frequency of single event, expressed in events per annum. The idea behind individual risk is the risk that might be posed to an individual who is in the vicinity and exposed to the hazard in question. Individual risk is also a function of distance from the hazard, which, although not affecting the frequency,
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Figure 1 Matrix showing individual risk in deaths per annum.
Table 3 Listing of consequence models used for risk assessment Hazard
Consequence model
Effects and modeling
Fire
Pool fire Jet fire Fireball Flash fire Vapor Cloud Explosion (VCE) Missiles and shrapnel generation Boiling Liquid Expanding Vapor Explosion (BLEVE)
Thermal radiation generated by fire can cause burns that can be lethal and models can predict exposure levels as a function of distance from source. Probit analysis can predict probability of death as a result of radiation dosage and exposure time. Overpressure and momentum forces can result in lung and ear-drum damage and cause the collapse of buildings leading to death. Probit analysis can predict likely effects and probability of death as a function of overpressure. Simple models for missiles and shrapnel generation exist that indicate likely size, number, and range. BLEVEs are also modeled as fireballs. Vapor dispersion and dilution occur in the atmosphere and can be modeled as a function of distance from the source of the release for both neutrally buoyant and dense gases taking into account meteorological conditions, wind direction, and wind speeds. Probit analysis for specific gases can predict probability of death with dosage and time elapsed.
Explosion
Toxic vapor releases
Vapor dispersion
could increase the consequence if the exposure to the hazard is increased. Since there is often more than one source of risk, it is also relevant to consider total or integrated risk. Thus, the overall integrated risk, considering n events and each event having its own specific consequences and frequency, can be expressed as Roverall ¼
n X ðCi Fi Þ
Step 5: Determine the basis for benchmarking or judging what levels of risk can be considered as acceptable. In judging individual risk criteria, the criteria shown in Table 5 may be considered. Societal risk, as opposed to individual risk, represents the integrated risk that may be posed to a group or multiple individuals located within a specific area or zone. Societal risk may thus be expressed mathematically as
i¼l
where Roverall ¼ integrated individual risk, in deaths per annum for n events in total.
Rsocietal ¼ N
n X ðCi Fi Þ i¼l
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Table 4 Modeling of frequency or likelihood of incidents Method
Basis
Data used
Fault trees
Fault trees model events using a top-down approach to show top event as the undesirable event and all contributory factors and subevents that lead to the top event. Proceeds from left to right starting with initial cause of incident and considers optional outcomes that can be assigned probabilities of occurring or failing to occur. A range of possible final outcomes is the end result.
Available failure rate data, reliability data, and contingent factors analysis where no data are readily available. Original causal event frequency is assigned based on failure rates of piping, gaskets, etc. Subsequent events likelihood use assigned probabilities based on available data, best judgments, and estimates. Recorded data from same, similar facilities and recorded data available on a global basis.
Event trees
Historical data
Use of available databases to provide frequencies of specific types of events.
Table 5 Risk tolerance criteria Individual risk level in deaths/annum >1 103 1 103 1 104 106
Tolerance level Exceeding 1 103 deaths per annum is deemed intolerable Should not exceed 1 103 deaths per annum maximum for workers provided that As Low As Reasonably Practicable (ALARP) measures are in place Should not exceed 1 104 deaths per annum maximum for the public provided that ALARP measures are in place Individual risk criteria are broadly acceptable at 1 106 deaths per annum
Data from ALARP – Guidance on as low as reasonably practicable decisions in COMAH: Health & Safety Executive (HSE), UK.
where N ¼ total number of persons exposed to the individual total risk and where risks vary depending on the numbers in different communities and their locations: Rsocietal overall ¼ Rsocietal overall;1 þ Rsocietal overall;2 þRsocietal overall;3 þ
Although societal risk may be evaluated, the acceptability of criteria is more complex than that of individual risk. FN curves may be used for societal risk where the ordinate represents the cumulative frequency distribution of N or more fatalities and the abscissa represents the consequence (N fatalities). Although there are published data on FN curves, their acceptability has not been widely adopted. Currently of greater interest is the ALARP (As Low As Reasonably Practicable) criteria. This recognizes three regions. The first of these is the ‘unacceptable region’ where the activity is of such a high risk as to render it unacceptable. The second region is the ‘broadly acceptable region’ where the activity has a very low risk and no further measures are needed for risk reduction. The third region is the ‘tolerable region’ where the level of risk falls between ‘unacceptable’ and ‘broadly acceptable’ and has been reduced to the lowest level of risk as considered to be practicable. Step 6: Apply risk management principles. Risk may be managed once the hazards have been identified. If the QRA route has been undertaken, then the calculated overall risk, Roverall or Rsocietal overall should be compared
to what may be deemed as tolerable. Depending on the level of tolerable risk, the decision to accept the risk or take remedial action(s) must be made. If the level of risk is within accepted margins, then no further action may be necessary. If the level of risk is excessive, then actions requiring remediation and costing plant modifications, procedural changes, as well as emergency response planning may be needed.
Risk Reduction and Risk Mitigation Risk reduction is possible only if hazards are identified and then measures are taken to reduce these risks. Although it may be possible to reduce the risk to a level that is considered acceptable, it is rarely possible to eliminate risk altogether. When facilities are designed originally, there may be good opportunities to introduce design features that can minimize risk whereas if safety is addressed as an issue only late in the design it may be extremely costly to incorporate such features. Safety in design is sometimes considered in terms of ‘active’ and ‘passive’ safety features. A passive safety feature requires no form of activation or initiation for the feature to be protective. For example, increased distance and spacing is valuable as a passive safety feature as would also improved road access, dikes around tanks containing flammable materials, and reduced
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inventories of hazardous materials. An active safety feature would be instruments, controls and automated trips, and most safety devices operated electrically, electronically, hydraulically, pneumatically, or even mechanically. Although both active and passive safety features are needed at a facility, passive safety features are much more dependable. On existing facilities, it may be difficult or impossible to add passive safety features and very often only additional active safety features can be incorporated where risk reduction is required.
Qualitative Risk Analysis versus Quantitative Risk Assessment Risk may be analyzed either qualitatively or quantitatively. For the majority of cases where no significant risk is posed to adjoining communities, the qualitative analysis should be adequate. However, where the potential for encroachment by new housing communities is an issue, the quantitative assessment has merit for establishing recommended buffer zones around the facility. It is often difficult to say where an assessment of risks ends and risk control begins or to assess risks without making a number of assumptions; at best, a risk assessment is an order of magnitude estimate and is directional as opposed to being absolute. Unless inputs and assumptions are very similar, the repeatability of risk assessment is hard to achieve. Risk assessment is a tool for extrapolating from statistical, engineering, and scientific data, a value that people will accept as an estimate of the risk attached to a particular facility. There are many techniques for risk estimation, tailored to different applications that cover a wide range of different disciplines, such as toxicology, engineering, statistics, economics, and demography. The true value of risk assessment, through the QRA, lies mainly in comparing overall risk levels both before and after risk remediation is incorporated. For example, suppose an overall level of individual risk is determined to be 104 deaths per annum for a facility and that after remediation it is reduced to 106 deaths per annum. This means that remediation has made the facility 100 times safer. This improvement may be considered to be more important than trying to determine exact levels of risk.
Risk Assessment and Emergency Response Planning A QRA can identify situations where an Emergency Response Plan (ERP) or buffer zones or restrictions should be considered. The output of an analysis, of risk
versus distance from the hazard source, can indicate hazard zones. Depending on these findings, a detailed ERP may be needed. This will also address the Emergency Response Planning Guideline (ERPG) levels 1, 2, and 3 distances. The distance to the ERPG-3 level corresponds to the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for 1 h without experiencing or developing life-threatening health effects. The distance to the ERPG-2 level corresponds to the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for 1 h without experiencing irreversible or other serious health effects or symptoms that could impair their abilities to take protective action. The distance to the ERPG-1 level corresponds to the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for 1 h without experiencing other than mild transient adverse health effects or perceiving a clearly objectionable odor.
See also: Risk Analysis.
Further Reading Center for Chemical Process Safety (CCPS) (1989) Guidelines for Process Equipment Reliability Data, with Data Table. New York, NY: American Institute of Chemical Engineers. Center for Chemical Process Safety (CCPS) (1994) Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires and BLEVE’s. New York, NY: American Institute of Chemical Engineers. Center for Chemical Process Safety (CCPS) (2000) Guidelines for Chemical Process Quantitative Risk Analysis. New York, NY: American Institute of Chemical Engineers. Center for Chemical Process Safety (CCPS) (2008) Guidelines for Hazard Evaluation Procedures. New York, NY: American Institute of Chemical Engineers. Cox AW, Lees FP, and Ang ML (1990) Classification of Hazardous Locations. Rugby, UK: Institution of Chemical Engineers. Hyatt N (2004) Guidelines for Process Hazards Analysis, Hazards Identification & Risk Analysis. Boca Raton, FL: CRC Press. Hyatt N (2006) Incident Investigation and Accident Prevention in the Process and Allied Industries. Boca Raton, FL: CRC Press. Kletz TA (1992) HAZOP and HAZAN. Rugby, UK: Institution of Chemical Engineers. Lees FP (1996) Loss Prevention in the Process Industries, Vol. 1, ch. 2, pp. 10–25. Oxford: Butterworth-Heinemann. Pape RP and Nussey C (1985) A basic approach for the analysis of risks from major toxic hazards. IChemE Symposium Series No.93, pp. 367–388. Rugby, UK: Institution of Chemical Engineers. Parry ST (1986) A Review of Hazard Identification Techniques and Their Application to Major Accident Hazards. SRD R 379. United Kingdom Atomic Energy Authority. SRD R 379. Rijnmond Public Authority (1982) Risk Analysis of Six Potentially Hazardous Industrial Objects in the Rijnmond Area: A Pilot Study. Springer, Hardcover-02-1982, ISBN 90-277-1393–6. Sutton I (2002) Process Hazards Analysis. SW/Sutton & Associates. UK Health & Safety Executive (1980) Quantified Risk Assessment: Its Input to Decision Making. UK Health & Safety Executive (UK HSE).
In-Place Cleaning M Walton, Society of Dairy Technology, Appleby in Westmorland, UK ª 2011 Elsevier Ltd. All rights reserved.
Introduction Cleaning in place (CIP) is a vital discipline within the modern food, dairy, and beverage processing industry. Dairy and beverage have tended to lead the way due to the major products being liquid and the process equipment lending itself to CIP. However, many food or pharmaceutical operations now incorporate CIP and the technology is therefore much more common. In the 1990 edition of the Society of Dairy Technology (SDT) Manual Cleaning In Place, CIP was defined as ‘‘The cleaning of complete items of plant or pipeline circuits without dismantling or opening of the equipment and with little or no manual involvement on the part of the operator. The process involves the jetting or spraying of surfaces or circulation of cleaning solutions through the plant under conditions of increased turbulence and flow velocity.’’ This was taken from the National Dairymens Association (NDA) Chemical Safety Code, 1985, and while the NDA has been superseded, their definition of CIP is still felt to be quite appropriate.
Practice in the Dairy Industry The modern dairy plant, be it for liquid milk or the multitude of other dairy products, will have at least two CIP sets at its heart; it is generally accepted as best practice that raw and finished product should be segregated to avoid cross-contamination. The raw milk CIP set will be responsible for cleaning the raw milk silos and associated milk intake pipe-work along with any in-line coolers and filters including transfer lines to the pasteurizer. It is at this point that the segregation between raw and finished (pasteurized) products is maintained. In many cases the pasteurizer with its associated items of processing equipment such as homogenizer, separator, and standardization unit will be cleaned together. The cleaning operation can be single-stage or two-stage, but the principle of single use remains. In a few sites, a partial recovery system may be used. There are benefits and drawbacks in each type of system and these will be discussed in more detail later. The finished milk CIP set will clean all items of plant that are used to store, process, and pack finished or pasteurized product. It is vital that this cleaning equipment be maintained to the highest
standards in order to ensure good plant hygiene and to avoid product contamination, either physical or microbiological, that would have an adverse effect on final product quality or shelf-life.
Outline of a CIP System The main stages of CIP are similar to any other standard cleaning routine: removal of gross debris (product purge); pre-rinse; detergent (normally acid- or caustic-based); intermediate rinse; second detergent if applicable; intermediate rinse; disinfectant; and final rinse with potable water. The diluted detergents are generally stored in tanks as part of the CIP unit or CIP set and will be built up into a fully operational CIP set with valves, manifolds, and interconnecting pipe-work, including an automated control system. The design of the CIP set will depend on the duty required. Other considerations such as available space and budget constraints do influence the design but making compromises at the design stage is not recommended, as poor CIP performance can have a significant impact on product quality. Figure 1 shows a four-tank partial recovery system with a single channel or CIP route operation. On larger sets, there can be five or six separate channels linked by common inlet and outlet manifolds. Other configurations are possible, with or without a rinse recovery tank. It is quite unusual to find recovered disinfectant storage tanks as these require very close management and can easily become contaminated leading to potentially serious consequences; hence, the tank denoted as ‘utility’ in Figure 1 when used for disinfection is likely to be of single use. Most CIP sets have some degree of automation, the most basic being a set of timers to open and close automatic valves in a particular programmed sequence at specific times. More sophisticated sets incorporate significant levels of field instrumentation with sensors, usually mounted in-line to monitor flow, temperature, pressure, conductivity, turbidity, etc. Control of detergent concentration is usually automated and the most common configuration is a control conductivity probe situated in a recirculation loop to ensure good mixing when extra detergent is added to the solution.
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Alkali Acid Water T
F
Other C
CIP ret
CIP out
Acid
Alkali
Recovered water
T
Steam
Utility tank P
PT
PT
PT
PT
F
Filter
FD
Sanitizer FD
Figure 1 Single-channel, four-tank partial recovery CIP system.
Detergents and Disinfectants In the dairy industry, the most common type of detergent is a caustic soda-based product, quite often containing a blend of sequestrants, surfactants, and other additives to assist with the cleaning task. The detergent also needs to be compatible with the prevailing water hardness conditions in order to prevent scale deposition, especially during rinsing. The selection of the correct detergent is a specialist activity and needs to take into account factors such as materials of construction, soiling type and levels, and product safety. The effectiveness of the caustic sodabased material is heavily influenced by the specific blend of additives and these are designed to remove dairy soils such as fat, protein, and more complex molecules and structures that are created by the process or simply by heat such as calcium carbonate. In certain circumstances, acidic detergents are used; these are often based on phosphoric or nitric acid or blends of the two and are found to be effective at removing inorganic deposits in dairy processing plants. Disinfectant solutions can generally be divided into oxidizing and non-oxidizing products, the former being more common for CIP use as they tend to be more efficacious and have a lower tendency to foaming that can lead to rinsing difficulties. The traditional dairy disinfectant was sodium hypochlorite, a very cost-effective product for CIP disinfection but with the major drawback for dairy CIP of
being corrosive to stainless steel. It is now more common to utilize an equilibrium mixture of hydrogen peroxide and acetic acid – peracetic acid – and this is commercially available, often supplied at 5 or 15% activity.
Application in Dairy Equipment The four main types of equipment encountered in a typical dairy situation are pipelines, vessels, fillers, and cheesemaking equipment. These are all normally cleaned using CIP and it is important to ensure that each is cleaned in the correct manner, for example, to clean a pipe effectively, turbulent flow should be achieved. As a generally accepted ‘rule of thumb’ the flow rate required to achieve turbulent flow and therefore provide optimal cleaning is around 1.8 ms 1. Fillers and complex items such as cheesemaking equipment will require purpose-built cleaning and spray systems installed within the plant to ensure good coverage. In some cases, there is a requirement to clean internal surfaces via CIP and also to include external surfaces, such as on a liquid milk filler, and utilize a specific, permanently installed foam cleaning system. All tanks and process vessels will include a spray device of some description. Traditionally this was a simple spray ball, which is now being superseded by the use of rotating spray heads that provide a much
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more effective clean and have the added benefit of lower water consumption. See also: Biogenic Amines. Hazard Analysis and Critical Control Points: Processing Plants. Utilities and Effluent Treatment: Design and Operation of Dairy Effluent Treatment Plants.
Further Reading Seiberling DA (ed.) (2007) Clean-in-Place for Biopharmaceutical Processes (Drugs and the Pharmaceutical Sciences), 1st edn. Informa HealthCare. ISBN-13: 978-0849340697. Tamime AY (ed.) (2008) Cleaning-in-Place: Dairy, Food and Beverage Operations, 3rd edn. Wiley-Blackwell in association with the Society of Dairy Technology. ISBN-13:978-14051-5503-8.
POLICY SCHEMES AND TRADE IN DAIRY PRODUCTS
Contents Agricultural Policy Schemes: Price and Support Systems in Agricultural Policy Agricultural Policy Schemes: European Union’s Common Agricultural Policy Agricultural Policy Schemes: United States’ Agricultural System Agricultural Policy Schemes: Other Systems Codex Alimentarius Standards of Identity of Milk and Milk Products Trade in Milk and Dairy Products, International Standards: Harmonized Systems Trade in Milk and Dairy Products, International Standards: World Trade Organization World Trade Organization and Other Factors Shaping the Dairy industry in the Future
Agricultural Policy Schemes: Price and Support Systems in Agricultural Policy H O Hansen, University of Copenhagen, Copenhagen, Denmark ª 2011 Elsevier Ltd. All rights reserved.
Introduction Agricultural support is a very important element in agricultural policy in many countries. Agricultural support is basically an instrument to meet the overall objectives of the agricultural policy – objectives set by society. There are a great number of instruments and ways of intervention in agricultural policy and they have different functions and consequences. Often, price mechanisms are used as support instruments, while direct income support is used in other cases. Choice of support system is of major importance and may have far-reaching consequences.
Objectives and Instruments in Agricultural Policy Intervention through agricultural policy is a very important phenomenon in the agricultural sector in many countries. Often, the intervention takes place through the market, and the aim is to improve or stabilize the economic conditions. Intervention itself is not an objective, but it is an instrument to achieve the overall objectives and aims set by society.
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Before the examination of the different instruments, it will be valuable to expose the underlying factors that legitimize those instruments, including support and price policy, of agricultural policy. There is a close correlation between the objectives and the instruments in agricultural policy. Basically, society has set up a number of objectives, which lay down guidelines and directions for the development of agricultural policy. These objectives, which to a large degree are similar from country to country, explain and set the grounds for the instruments in agricultural policy. There are a number of common features in the objectives that are found in agricultural policy in developed countries. In general, agricultural policy in developed countries aims at improving in agriculture, • income income distribution among farmers, • productivity in agriculture, • efficiency in the and marketing chain, • supply and price processing stability, • demographic situation, • environmental status, and • export, employment, production, added value, and so on. •
Policy Schemes and Trade in Dairy Products | Price and Support Systems in Agricultural Policy
Many different types of instruments can be used to achieve the given objectives, and it is a very complicated relationship. Some instruments can be used to achieve several different objectives, whereas other instruments benefit the achievement of some and limit the achievement of others. Finally, important differences with respect to financing, effect on production and trade, transparency, and other elements are observed. The instruments in agricultural policy can be divided into different groups:
Price Support Support in the form of higher market prices than, for example, on the world market.
Deficiency Payments Transfers from taxpayers to farmers corresponding to the production multiplied by the difference between the world market price and a given target price on the domestic market.
Support Coupled to Input Factors premiums • Area Headage • Financial premiums support • Other supports to reduce costs • Direct Support Coupled with Other Factors
• Extensification of landscape • Protection Support to enhance structural change • Economic development in rural areas • Support Fully Decoupled from Production for the effects of drought and other • Compensation calamities support, lump sum payments • Income Early retirement schemes • Furthermore, one finds a number of other instruments that should not directly be used to achieve the objectives, but should be used to reduce supply and/or costs related to agricultural policy. Quotas and set-aside are examples of such instruments. Price support and deficiency payments are the most important instruments in the agricultural policy of industrialized countries and account for about 75% of the total agricultural support.
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High and Low Price Systems Market price support and deficiency payments are two very important instruments in agricultural policy; however, they belong to two different support regimes or support systems. Market price support operates in the so-called high price system and is financed by consumers, while deficiency payments operate in the so-called low price system and are financed by taxpayers. In the high price system, support is given mainly by means of import regulations, etc., which ensure a relatively high domestic price. In the low price system, support is given by means of direct support, while market prices are left undistorted at, or close to, world market level. The two different support systems have very different implications for agricultural production, financing, markets, and aspects; still, there is an income transfer to agriculture in both systems in the short run. The balance between market price support and direct payments varies greatly from country to country (Figure 1). In countries like the United States, Ukraine, and Australia, agricultural support is granted mainly as direct payments financed by taxpayers, while market price policy, financed mainly by consumers, is predominant in countries like Japan, Korea, and Russia. Figure 1 also shows the total level of agricultural support. Agricultural support includes transfers from consumers and taxpayers to agricultural producers arising from policy measures that support agriculture – producer support estimate (PSE). PSE is here measured as a percentage of gross farm income including support. The figure illustrates that countries like Iceland, Japan, Korea, Norway, and Switzerland have a high agricultural support level. On the other hand, countries like New Zealand, Chile, Brazil, South Africa, and Ukraine have an almost liberalized agriculture. During the recent decades, agricultural support has changed significantly. The level of support has decreased – protectionism has weakened and liberalization has strengthened. At the same time, the composition of agricultural support has changed significantly. Consumer-financed market price support has decreased, and taxpayer-financed direct support has increased (Figure 2).
Structure and Function As shown in Figure 1, countries like Korea and Japan use mainly the high price system in agricultural policy. In this system, support to farmers is given through high market prices maintained by different instruments like import tariffs (variable or fixed) or other import restrictions, export subsidies, and so on. These instruments ensure an artificially high price level compared to the price level that would result from the interaction of supply and demand in an undistorted market.
288 Policy Schemes and Trade in Dairy Products | Price and Support Systems in Agricultural Policy Consumers’ and taxpayers’ share of cost from agricultural support Consumers
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Figure 1 Level and composition of agricultural support (2007). From OECD (2009) producer and consumer support estimates, OECD database 1986–2008.
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Figure 2 Level and composition of agricultural support in OECD (1986–2007). From OECD (2009) producer and consumer support estimates, OECD database 1986–2008.
Support in high price systems is financed by consumers through high consumer prices. Depending on the self-sufficiency rate, public costs and income are also affected. If the country is a net importer, the country will receive a revenue from the import tariff. On the contrary, a net exporting country will have to
pay export subsidies to ensure the price level on the domestic market. The low price system has for decades been the predominant support system in the agricultural policy in the United States. As a result of the recent reforms of the Common Agricultural Policy (CAP) in the European
Policy Schemes and Trade in Dairy Products | Price and Support Systems in Agricultural Policy
Union and as a result of more focus on decoupled support in the World Trade Organization (WTO) negotiations, the European Union has moved toward more low price support and less high price support. Low price support system is now the most important support system in the European Union. In low price systems, market prices are more or less unaffected, and farmers receive prices which in principle correspond to world market prices. Instead, market support payments are given directly to the farmers. These payments can be coupled with production or they can be fully decoupled. Coupled support means that a farmer will receive a payment corresponding to the production multiplied by the difference between the world market price and a given target price on the domestic market. In this case, there is no major difference between a high and a low price system from a farmer’s point of view. If support is more or less decoupled from production, the economic transfer to farmers may have an element of income or social aid. Support can be coupled with the agricultural area or the number of animals belonging to the farm. In this case, support is still decoupled from production. Low price systems are financed by the public budget, indicating that the taxpayers finance this kind of agricultural support in the end. High and low price systems may have different modifications, individual structures, and so on. The income transfer can have various nuances giving different consequences in each case. However, the general structure of high and low price systems is shown in Figure 3. It does not make sense – a priori – to determine whether one system is superior to the other. Support level is independent of the support system, and both systems have advantages and disadvantages. Therefore, it is necessary to compare these pros and cons with the objectives in the agricultural policy. It is evident that the choice of high and low price systems may have profound consequences within and outside the agricultural sector.
High price system
Low price system
Market price
Target price
Price support
World market
World Direct market payments
Figure 3 General structure of high and low price systems.
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Consequences of High and Low Price Systems Conditions and Competition in the (Processing) Food Industry High price systems necessitate border protection of commodities traded internationally. This means that the border protection must comprise processed commodities and not the basic agricultural raw materials. This is the case for milk where border protection must cover the processed and traded goods like butter, cheese, and condensed milk. In this way, the high price system will influence a major part of the food industry and not only the primary agricultural sector. This must be seen in relation to the fact that it is normally only the conditions in the primary agricultural sector that should be improved through the agricultural policy. Especially if the food industry is very concentrated and having great market power, the farmers may not achieve the intended advantages of the high price system. In other fields, a high price policy can be negative for the food industry. At first, the raw materials of the food industry will become more expensive, and unless this cost increase will be fully compensated through other systems, it will lead to worsening of the competitive power. Such distortions of competition conditions in the food industry will not occur in a low price system. Here, a free world market price exists and is created by supply and demand without market intervention, and the food industry will automatically adjust correspondingly to the international comparative advantage of the sector.
Competition Conditions in the Agricultural Sector Another problem with the high price system is that it is often difficult to grant the same subsidies to all products. It is most difficult to implement a uniform subsidy if it is a question about high and low processed products, and also, for some products there is only import protection and for others there may also be supply restrictions. Furthermore, a general price increase for all agricultural products of, for instance, 10% will primarily benefit the crop production whereas gains for animal production will be lower. The explanation is that a major part of the production factors in animal farming consist of crop production, and in this way a general price increase will not have total trenchancy in these production areas. For all industrial countries, there is a clear negative correlation between the grade of self-sufficiency and agricultural subsidy. This means, the higher the grade of self-sufficiency, the lower the agricultural subsidy.
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It is characteristic that some countries often reduce the subsidy level for the products where the degree of selfsufficiency increases considerably to over 100%. With an increasing net export, the nationally financed agricultural subsidy increases, and therefore there will be a distinct incentive to reduce the subsidy. Apart from this, the self-sufficiency objective determines that one in particular protects the products where the grade of self-sufficiency is low. In both cases, there are signs that one in particular protects the products that the agricultural trade already has poor possibilities to produce. On the other hand, the subsidy for the products that have the best natural conditions will be relatively low. It is assumed that a relatively high degree of self-sufficiency all in all is a sign of a comparative advantage. Seen in a global perspective, the subsidy is highest in countries where the degree of self-sufficiency is low. Seen in a national perspective, it applies correspondingly that the subsidy is relatively the highest on products where the grade of self-sufficiency is relatively low. Both factors are part of a blurring of the comparative advantages and the result is welfare economic losses. In the low price system, it can also be difficult to grant the same subsidy to all products; however, it is less complicated than in the high price system. One explanation is that the subsidy is granted directly and past the processing sector and in this way the real agricultural subsidy in the individual production areas is easier to calculate. Apart from that, it is not seen in a low price system that price subsidy for one product has the effect as extra costs in another product area. On the other hand, in a low price system, it can be very difficult to distribute a ‘fair’ subsidy independent of production among the farmers. Historic, structural, or social criteria are often necessary; however, they are rarely logical and they can be very static and not least they can be very difficult to control.
It should also be considered that the above-mentioned costs are calculated with the actual world market prices as reference basis. After both a one-sided and general liberalization, these prices will increase and thereby the consumers’ gains will be smaller than the actual costs calculations show. Even though the prices of agricultural products in a high price system are forced high, it will have far from full trenchancy on the food prices. This is due to the fact that only approximately 25–30% of the consumer price on food in highly developed countries traces back to the agricultural trade. The rest of the costs are wages in the processing industry, transport costs, and so on, and these costs are really independent of the subsidy level in the primary production.
Income Distribution in the Society The choice between the high and low price systems will also influence the income distribution in the society. A high price system, which will cause an increase in the food prices, will after all be the largest burden to the lowest income groups in the society. People with low incomes use a relatively large part of their earnings on food, which means that an increase on these products will limit their consumption possibilities relatively much. Higher prices on food and other necessary products as a result of political or economical measures will in this way have the same effect as a degressive tax. On the other hand, the low price system builds on low prices to producers as well as consumers and that is why this form of protection will be the cheapest solution for the part of the population that have the lowest incomes. The financing of public expenses for income support, supplementary payments, and other supports is normally done by means of income tax, which in most cases is progressive. Contrary to the high price system, the costs of the agricultural policy in this case will be placed on citizens with higher incomes.
The Composition of Consumption The composition of consumption is also affected by the choice between the high and low price systems. In the high price system, the consumers will, through higher food prices, primarily finance the agricultural policy. This means that food prices will increase compared to other products, and in this way the consumption of food will decrease compared to the consumption of other products. The result will be that the consumers’ purchasing power will decrease. At first, the consumers’ loss as a result of the high price policy can seem great, approximately 25% of the agricultural production value is subsidy, and for the European Union 33% of the subsidy is consumer financed.
The State Expenses High and low price systems have a significant impact on public costs and expenses. Market intervention often implies economic support, taxes, levies, and revenues, which means that public expenses will be affected. For a net import country, the revenue of the state will at first increase by imposing a high price system based upon import tax. The state receives customs receipts, and at the domestic market the consumers finance the price subsidy to the agricultural sector. On the other hand, there can be large costs for the state finances with the low price system where direct support to the farmers is a major instrument.
Policy Schemes and Trade in Dairy Products | Price and Support Systems in Agricultural Policy
Finally, any intervention and protection measure will have a negative impact on resource allocation and economic welfare in society. Different measures have different consequences, but in general, coupled price support tends to be the most distorting measure imposing the highest loss of economic welfare in society. The change in agricultural policy during the last decades in OECD countries – decreasing support and increasing role of taxpayer cost – has reduced the total cost, but the taxpayer cost has increased in relative and nominal terms. Direct or Indirect Subsidy The choice between the high and low price systems can also be of great importance as to how direct the subsidy systems are. In a high price system, the agricultural subsidy is given ‘through the market’, and therefore the subsidy is more indirect and invisible. In a low price system, where by means of tax collection the money is directly transferred to the agricultural sector, the transfer is much more obvious. The low price system contains in this way a very direct subsidy to the farmer; however, the effect on international trade is more indirect and invisible. However, in most cases, the effect is the same for agricultural trade, and therefore it is only a pedagogical and comprehension problem. Still, it is certain that a low price subsidy is so visible that there will be a natural pressure from the surroundings (the taxpayers) to reduce the subsidy. Production and Productivity Development The choice between the high and low price systems can also be of great importance to agricultural production and productivity. The high price system gives, at first, the farmers better sales prices, thus better terms of trade, and it will undoubtedly stimulate production. The size of the productivity increase will depend on the size of the supply elasticity. In general, the agricultural production responds relatively weakly to price changes. In the long term – and especially in case of price increases – it is characteristic that the agricultural production to a great extent adjusts itself to the changed price relations. Normally, productivity will be improved through structural and political instruments, where through research, development, education, advising, and other means one can make the production more rational. However, the high price policy will also be able to affect productivity. On the one hand, there will be an incentive to increase production in relation to, for instance, the acreage effort. In this way, there will be an increased yield, and also the yield of the livestock production will increase. This will increase productivity.
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On the other hand, the agricultural policy will also attract input factors which under normal conditions would be used in other sectors or which would not be used at all. For instance, poor soil will be cultivated and this will reduce the average yield. This will also be the case for other input factors, for instance, fertilizers, pesticides, capital, and labor. The low price system has in principle the same consequences for production and productivity development provided that it concerns fully production-coupled subsidies. If, on the other hand, the payments to the farmers are partly or fully decoupled from the size of production, the consequences are crucially different. A totally independent income subsidy means that the farmers receive a relatively low price for their products, and that they have no incentives to increase production. It is only economically optimal to increase production as long as the marginal earnings are larger than the marginal costs, and this point is reached relatively fast with the low market prices. At the same time, the income subsidy is assigned to the farmer regardless of the size of production, which means that production does not increase considerably. However, it must be expected that even a decoupled production income subsidy in a low price system can seem encouraging to production. All agro-political measures will affect the resource allocation in the society, and in this way an income subsidy will maintain resources in the agricultural sector. In this way also the production will be affected to a larger or smaller extent. Decoupled income subsidy will very much limit production development in the agricultural sector. Farmers will not be sufficiently urged (or forced) to introduce new technology or new production methods. At the same time, the more efficient farmers do not benefit sufficiently from the extra effort or risk which they undertake. The high and low price systems can, in this way, have different consequences for production and productivity development in the agricultural sector. One cannot in advance say that one consequence is better than the other.
Market Price Subsidy The market price subsidy – where the market price is kept higher than on the world market – is still a common subsidy measure in the agricultural policies of the Western world (Figure 1). Among others, the European Union has through decades used the market price subsidy as an important instrument in the agricultural policy. The use of the market price subsidy in a high price system demands, naturally, a considerable regulation of the markets. To secure the high price level, the markets are more or less isolated from the surrounding world, as
292 Policy Schemes and Trade in Dairy Products | Price and Support Systems in Agricultural Policy
Target price Market price Import duty Intervention price
Export subsidy
Expenditure Intervention Revenue World market price
World market price
Domestic market
Figure 4 Instruments in a market price system (high price system).
free import or export will make the system collapse. Furthermore, there can be a need for public buying (intervention) or export support, dependent on the degree of self-sufficiency. There are different types of market price subsidies but the most important one is a price system, where the state in different ways is adjusting the market with the purpose to ensure that the farmers on the market itself are able to obtain the aimed prices. This type of market systems can be schematically illustrated as shown in Figure 4. The target price is the price aimed at for the producers to obtain on the market. The intervention price forms a safety net for the price formation on the market as the product can be sold within the European Union at this price. The actual market price will often be between the target price and the intervention price. If the market price levels drop below the intervention price, some suppliers begin to sell to intervention. This will reduce the supply on the market as the bought-up products will be stocked. This will normally lead to recovery of the market price. The intervention price and the intervention system are, in other words, a central part of the internal regulation of a high price market. However, intervention alone is not enough to secure the price, as there must also be a regulation by import and export. When importing, an import duty is collected, which, in principle, is the difference between the price on the world market and the threshold price. In principle, it can be both a variable and a firm import duty. If the import duty varies, it can continuously be changed according to the world market price, and it therefore increases when the world market price is low and vice versa. In this way, the variable import duty can be a part of securing a constant price level on the internal market. Previously, the variable import duty was often used, but as a result of the WTO agreements a gradual change in the tariffs has taken place. This means that the import
barriers have changed to more firm tariff rates. When exporting, an export restitution (subsidy) is paid, which in principle is the difference between the price on the world market and domestic market price. In the European Union, the market price subsidy works in such a way that the EU farmers have secure higher prices than on the world market. This is still the case for some products where reforms have not yet changed the original support system. This is naturally especially true for products where the market price subsidy is the most important measure and where the subsidy level is high. This applies for, among others, milk, whereas the market price subsidy on the cereal area has decreased considerably as a result of reforms in the EU agricultural policy (Figure 5).
Future Developments Several conditions will influence the future development with regard to the agro-political instruments. The choice between the high and low price systems must not be seen from an economic and social point of view alone. The international negotiations in WTO are also of great importance. The explanation is that the high and low price policy influences the international trade in different ways. First, it is important that the consequences for the size of production are different. All influences on the size of the production will directly influence the foreign trade, as for instance an increase in the production will make the import decrease or the export increase. In this way, these trade-influencing instruments are made objects of negotiations in, for instance, WTO. As mentioned before, all agro-political measures will always influence the resource allocation and production,
Policy Schemes and Trade in Dairy Products | Price and Support Systems in Agricultural Policy Wheat
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Figure 5 EU market prices and world market prices for agricultural products. In general, the intervention price system in the European Union has stopped or is diminishing.
and with this, also the foreign trade to a larger or smaller extent. Still, in the international trade negotiations, there is talk about ‘non-trade distortions’, which are instruments with no influence on the trade. It is implied that some agro-political instruments have a less harmful influence on the international trade and that they in this way are more or less legitimate to use. Second, it is important that in a high price system one is forced to introduce trade barriers, which in a very obvious way illustrate protection. The trade barriers can of course be of the same magnitude in a low price system, but here the trade protection is less transparent. Politically seen, the relationship to the trade partners can therefore favor the low price system. The use of import duty, import tax, and especially export subsidy is normally necessary in a high price system, but they very clearly state that one wishes to protect the domestic producers against the surrounding world. This is probably also one of the explanations why the EU agricultural policy was so heavily attacked during the WTO negotiation rounds. It is certain that the WTO rounds were a defeat for the high price system and a victory for the low price system. This fact must be seen in spite of the fact that the low price system does not necessarily create more free trade or greater economical welfare than the high price system.
On the other hand, the results of the WTO rounds, until now, mean that more countries in the future will be prompted to operate an agricultural policy based upon the low price system. Also, more independent experts argue for a gradual change from the high price system to the low price system. The arguments are, for instance, that the subsidy rates will be more transparent and sometimes more trading neutral as well. Also, the instruments and the subsidy level in a low price system can easily be gradually removed and even completely replaced by pure social support arrangements. See also: Policy Schemes and Trade in Dairy Products: Agricultural Policy Schemes: European Union’s Common Agricultural Policy; Agricultural Policy Schemes: Other Systems; Agricultural Policy Schemes: United States’ Agricultural System.
Further Reading European Commission (2009) Agriculture in the European Union – Statistical and Economic Information 2007. http://ec.europa.eu/ agriculture/agrista/2007/table_en/index.htm (accessed 27 March) Hansen HO (2001) Landbrug i et moderne samfund, 438pp. þ XXVIII. Copenhagen, Denmark: Business School Press. Knutson RD, Penn JB, and Boehm WT (1990) Agricultural and Food Policy, 2nd edn., 437pp. Englewood Cliffs, NJ: Prentice-Hall.
294 Policy Schemes and Trade in Dairy Products | Price and Support Systems in Agricultural Policy Nedergaard P, Hansen HO, and Mikkelsen P (1993) EF’s landbrugspolitik og Danmark. Udviklingen frem til a˚r 2000, 398pp. Copenhagen, Denmark: Copenhagen Business School Press. OECD (2008) Agricultural Policies in OECD Countries: At a Glance 2008. Paris: OECD. OECD (2009) Producer and consumer support estimates, OECD database 1986–2008.
Ritson C (1977) Agricultural Economics. Principles and Policy, 409pp. London: Crosby Lockwood Staples. Tracy M (1993) Food and Agriculture in a Market Economy. La Hutte, Belgium: APS Agricultural Policy Studies. Shane M, Roe T, and Gopinath M (1998) U.S. Agricultural Growth and Productivity: An Economy-wide perspective (Agricultural Economic Report No. 758). Washington, Dc: USDA.
Agricultural Policy Schemes: European Union’s Common Agricultural Policy M Keane, University College, Cork, Ireland D O’Connor, Institute of Technology, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by K. W. Rasmussen, Volume 1, pp 15–20, ª 2002, Elsevier Ltd.
Background The Common Agricultural Policy (CAP) was established on the basis of the Treaty of Rome, with effect from 1 January 1958. Article 39 stipulates five fundamental objectives: 1. to increase agricultural productivity by stimulating technical progress and ensuring the rational development of agricultural production and the optimum utilization of factors of production, in particular labor; 2. to ensure a fair standard of living for the farming population, in particular by increasing the earnings of the persons engaged in agriculture; 3. to stabilize markets; 4. to assure the availability of food supplies; and 5. to ensure that supplies reach consumers at reasonable prices. In the following years, the CAP gradually firmed up. It was based initially on the idea of a dual agricultural policy, consisting of structural measures on the one hand and price and market-related measures on the other hand. Eventually, the price and market policy became the overall dominating element of the CAP. The price and market system comprises all the major agricultural products, including milk. In the original form, the policy was based on the following principles: movement of goods within the European Union • free and common prices for the same good; preferences in relation to third countries • common (common import duty system); and financial responsibility for market and price • common policies of the European Community Fund via the European Agricultural Guidance and Guarantee Fund (EAGGF). These principles were adopted at the Stresa Conference in 1958 and meant that the politically fixed prices became the central element of the CAP and the annual price negotiations of the EU Council of Ministers, which took place in April, started attracting great interest. Up to the implementation of the General Agreement on Tariffs and Trade (GATT) in 1995, three prices of
the principal products were fixed at the price negotiations: target prices, intervention prices, and threshold prices. The target price was the price aimed at in the market, but with no guarantee for the producers. The intervention prices for butter and skim milk powder, however, formed the safety net of the price formation in the market, as at worst the products – with various modifications – could be sold to the EU Commission at this price. As dairy produce consists mainly of fat and protein, the safety net really covers all products. Originally, the threshold price was the lowest acceptable import price for third-country products. The threshold price was used to calculate the variable import taxes, which, in principle, formed the difference between the world market price and the threshold price. However, the GATT agreement signed in 1994 meant that import taxes were frozen on 30 June 1995, which is why threshold prices are no longer fixed. The fourth fundamental principle of the EU price and market system is export refunds. Refunds are paid on exports and in principle they form the difference between world market prices and the EU market price. The size of the fixed refunds is the same for all EU Member States, but may be differentiated by destination, if special conditions apply. In connection with the reform of the EU CAP in 1992 (the MacSharry reform), far-reaching changes in price and market policies were introduced, particularly regarding cereals and beef. However, in the milk sector, the old system still applied (Figure 1) as the proposed reform was unacceptable to the EU Council of Ministers. Thus, there were no major changes in the milk regime until the implementation of the CAP Reform in 2003, as discussed later.
Financing of the CAP The CAP system was financed by the EAGGF, which is divided into a guarantee section, financing the price and market policies, and a development section, financing the structural policies. From the start of the European Union, the CAP consumed by far the largest
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296 Policy Schemes and Trade in Dairy Products | Agricultural Policy Schemes Target price
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Intervention price income World market price
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Figure 1 The EU market scheme.
share of the total EU budget. Relatively speaking, the expenses for the agricultural policies have been declining gradually since the 1970s, and now total about 40% of the total EU budget. This decline must be seen in the context of other EU policies and a growing request to stabilize farm expenses. Concurrent with restrictions on farm expenditure, larger funds have gradually been transferred to finance the development of other structural funds, with particular emphasis in recent years on energy, the environment, and new Member States. The EU revenues are based on based on gross national income, • contributions contributions from • tax (VAT) basis, all Member States on a value-added receipts, and • customs various production levies. •
The Price and Intervention Scheme for Milk and Dairy Products The EU basic regulation on milk and dairy products was finally adopted in 1968 (EEC 804/68). The institutional prices for milk and dairy products were fixed for a whole dairy year, running from 1 July to 30 June. The target price was fixed for milk, with 3.7% fat carriage paid at any processing factory. The intervention prices were fixed for skim milk powder and butter and formed a safety net under the milk prices. In this way, the main ingredients, protein and fat, were safeguarded and stored in a form that could be controlled by intervention buying. While intervention prices continue to be fixed as in the past, the levels are now considerably lower following CAP Reform as discussed later. Up to 1987, the
Intervention Boards of the individual Member States were obliged to purchase any product for sale at the fixed intervention price. Subsequently, various modifications have been made.
The System prior to CAP Reform 2003 Skim milk powder and skim milk (EC 1255/99 art. 7, 11, and 12)
During the winter season, from 1 September to 28 February, intervention with regard to skim milk powder is suspended. From 1 March to 31 August, intervention may be suspended; however, private storage of skim milk powder may be subsidized. Only first-class produce meeting the set requirements on age and packaging may be the subject of intervention. As of the market year 1995–96, a minimum protein content of 30% in skim milk powder for intervention was introduced. At a protein content of 34% and above, maximum subsidy is paid, whereas contents between 30 and 34% have 1.75% deducted from the intervention price for each percentage point below 34%. Products subject to intervention, which cannot be sold on normal market terms, may be subject to special stock disposal measures and sold at reduced prices. As for skim milk powder, its use in mixed feedstuffs for calves is subsidized (the most important scheme) as well as its use in mixed feedstuffs for pigs and poultry. Skim milk for processing into casein and caseinates is also subsidized. These products are used as the primary material for processing of various industrial products and foodstuffs, such as processed cheese. Subsidies for casein and caseinates are a production subsidy, as distinct from the price subsidy schemes.
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The intervention system for butter (EC 1255 art. 6 and 13)
From 1987, the intervention system for butter has been a tender procedure. Tenders are submitted every 2 weeks, as the EU Commission fixes a maximum buying-in price. All bids below this price are purchased. Since 1987, the buying-in price has been steady at 90% of the formally fixed intervention price. Like skim milk powder, butter for intervention must meet certain requirements on quality, age, and packaging. When the market situation allows, subsidized butter pursuant to regulations is remarketed on terms that do not damage the competitive position of butter in the market. Butter subject to intervention is remarketed within the European Union under the special scheme for sale of butter at reduced prices, for use in the food industry and for the manufacture of pastry products, ice cream, and other foodstuffs. Analogous to the sale of subsidized butter for food manufacturers, similar subsidies are paid for the use of fresh butter and cream in the food industry. Butter for social institutions and hospitals is also subsidized, as well as for the armed forces. To safeguard the normal market supply and price of butter during winter months, private storage of butter and cream is financially supported. The storage period, fixed by the EU Commission, usually starts on 1 April and ends on 15 August. The stock disposal period is from 16 August to 28 February the following year. The storage period must be a minimum of 4 months. The intervention system for cheese (EC 1255/99 art. 8)
In addition to the general intervention schemes for butter and skim milk powder, private storage of the cheese types Grana Padano, Parmigiano Reggiano, and Provolone may be subsidized in Italy. The special scheme was established as the production of these particular cheese types is a staple element of the Italian dairy industry. Subsidies for sale of liquid milk (EC 1255 art. 14)
To stimulate liquid milk consumption, the European Union contributes to the implementation of the Member States’ special aid schemes to supply milk and selected dairy products for schoolchildren at reduced prices.
the basic period from 1986 to 1988. Moreover, the GATT/ WTO agreement imposes minimum import access quotas at reduced tariff rates, equal to 5% of consumption in the basic period. In addition, the European Union is obliged to give access to butter from New Zealand at a special low rate. This amount represents the average amount exported annually to the United Kingdom by New Zealand under bilateral agreements during the GATT/WTO basic period. Further to GATT/WTO obligations, the European Union has entered a number of bilateral agreements aimed at facilitating market access on a mutual basis. For instance, there are special quotas for the United States, Canada, Norway, Switzerland, South Africa, and others.
Export Schemes for Milk and Dairy Products As a matter of principle, the European Union subsidizes most dairy products for export to balance the price gap between the European Union and the world market, except when this price gap disappears as in the 2007/ 2008 period. Non-Annex I products are subsidized as well; these are processed products containing agricultural produce, such as cereals, sugar, eggs, and milk. After the implementation of the GATT/WTO agreement, the refund system was somewhat restricted. Compared to the basic period of 1986–90, subsidized exports were reduced by 21%, in parallel with a 36% reduction of the refund budgets. The budget restrictions apply only to non-Annex I products. In order to ensure that the restrictions are met, all exports qualifying for refunds are subject to presentation of an export license, prefixing the refund. Export licenses are limited to the permitted quantity, which implies that it is a scarce commodity in times of great demand. The limited opportunity to use refunds means that export refunds for cheese no longer exist for a number of destinations. This generally applies to areas such as the United States, Canada, Australia, Switzerland, and Norway. In other areas, refunds for only selected products have been abolished.
The Milk Quota Scheme The Import System for Milk and Dairy Products Before the introduction of the GATT/World Trade Organization (WTO) agreement on 1 July 1995, thirdcountry imports were subject to variable import levies. Now these levies are tariffed, that is, converted into a fixed tariff rate, payable in Euro per tonne or as a percentage of the import price. Pursuant to the agreement, the rates have been reduced by an average of 36% compared to
As a result of the increasing imbalance between production and demand, the milk quota scheme was introduced in 1984. The purpose of Article 39 of the Treaty of Rome had long been accomplished and the choice was between a reduction of prices and limiting production. Production was chosen and the measures proved effective in limiting surplus production. Each Member State was allocated a national quota (reference quantity) for the quota year 1984–85, which as a rule equaled the total national milk production in 1981 plus 1%. Ireland, Italy, and Northern
298 Policy Schemes and Trade in Dairy Products | Agricultural Policy Schemes
Ireland got a somewhat larger quantity. The Member States were allowed certain latitude to implement the quota scheme in one of two ways, either as direct sales quotas or as dairy quotas. Under the direct sales quota scheme, the national reference quantity was reallocated to individual milk producers. Under the dairy quota scheme, the quota was reallocated to the dairies, which subsequently had to fix quotas for individual producers. In the event of milk production in excess of the quota, a superlevy was collected, totaling 115% of the target price. Regardless of the choice of management scheme, the producers who exceed their quota must pay the superlevy. The dairy quota scheme provides the option to use a net principle, allowing the underuse of quota by some producers to be converted into a deduction for producers who have exceeded their quota. In this way, the quota is fully utilized and the payment of a superlevy reduced.
3. In addition, each Member State would receive financial support by the so-called ‘national envelopes’, which may be allocated according to nationally determined criteria. 4. The total quantity eligible for direct payments in each Member State would be equal to the sum of all individual reference quantities for the 12-month period 1999–2000. 5. A total increase of milk quotas of 2.8 Million tonne (2.4%): in the years 2000–01 to 2001–02, the national quotas were increased for Spain (10%), Italy (6%), Northern Ireland and Ireland (3%) as well as Greece (11%). The increase for the remaining countries was to be 1.5% in the years 2005–06 to 2007–08. 6. The milk quota scheme would continue up to 2008. In 2003, a ‘mid-term review’ would be initiated.
Agenda 2000
CAP Reform (Mid-Term Review) 2003
Following nearly 2 years of discussion, the EU Heads of State finally made the decision to reform the EU CAP, entitled Agenda 2000, at the summit meeting in Berlin in March 1999. Agenda 2000 also embraced the budgetary framework of the European Union for the period 2000–06 and the plans for enlargement by the inclusion of central and east European countries as well as a reform of the structural policy. The fundamental element of the agricultural reform was a reduction of refunds for the most essential agricultural products, as opposed to extended financial aid to producers by premium schemes, only partly related to production. For agricultural produce and beef, the 1992 reform was further expanded, whereas in the case of the milk and dairy sector it is a profound breach of previous policies. The purpose of the reform was to
In 2002, the Mid-Term Review of Agenda 2000 commenced. It concluded in June 2003 with a fundamental reform which provided for the decoupling of direct payments from production in the case of livestock production, milk production, and arable crops, with partial decoupling options for Member States that did not wish to decouple fully. Direct payments (coupled or decoupled) were made conditional on compliance by farmers with a range of food safety, environmental, and animal welfare measures. With regard to the dairy sector specifically, the most important elements were as follows:
the competitiveness of EU agriculture on both • improve domestic and external markets, the progressive integration of new Member • facilitate States, the European Union for the next WTO round, • prepare ensure continuously stable farm incomes, and • integrate environmental goals into the CAP. • The original intention was to implement the reform of the dairy sector in the period 2000–03. However, the final agreement between the Heads of State in Berlin postponed the implementation to 2005–08. The principal elements of the reform that was agreed were as follows: 1. A total 15% reduction in intervention prices for butter and skim milk powder, in three stages from 2005–06 to 2007–08. 2. To compensate for the price cut, milk producers were to be allocated a direct payment per tonne milk quota, fixed at E5.75 in 2005, E11.49 in 2006, and E17.24 in 2007.
1. An asymmetric reduction in intervention price: 25% for butter (from E328.20 to 246.39 per 100 kg) and 15% (from E205.52 to 174.69 per 100 kg) for skim milk powder. The reduction was brought forward to 2004–05, with the butter price reduction spread over 4 years (7, 7, 7, and 4%) and the skim milk powder price reduction in three equal annual steps. 2. Partial compensation for the intervention price cut for dairy farmers: a direct payment of E24.49 per 100 kg of quota and a supplementary payment per Member State equivalent to approximately E11 per 100 kg. Such compensation is paid for the total of national quota as at 1999/2000. Originally, the coupled payments had been programmed in Agenda 2000 at a lower level. The payments were to be decoupled at the latest in 2007. 3. Discouragement of butter intervention: by introducing the possibility to open a tender for intervention buying-in after 30 000 tonnes at fixed prices have been bought in. 4. Expiration of production quotas on 1 April 2015. 5. Postponement by 1 year of the gradual quota increase of 1.5% in three steps of 0.5% for 11 Member States, as
Policy Schemes and Trade in Dairy Products | Agricultural Policy Schemes 299
already foreseen in Agenda 2000. The increase corresponds to 1.4 million tonnes of milk. 6. Reduction of the superlevy: in four steps from E35.63 per 100 kg in 2003/2004 to E27.83 per 100 kg from 2007/2008 onward. Coinciding with the start of the dairy reform in 2004, 10 new Member States joined the European Union. This increased the EU base quota by 18.5 million tonnes and added 80 million consumers. Furthermore, in accordance with the accession agreements, a restructuring reserve of 0.67 million tonnes was established for eight of the new Member States. This additional reserve was added to their national quotas on 1 April 2006. In 2007, a further two new Member States with a total quota of 4 million tonnes joined the European Union, bringing the total amount of quota for the EU-27 to 142 million tonnes. Thus, by 1 April 2008, further to 103 million consumers, 24.5 million tonnes of additional quota will have been added to the EU total since 2003. The aim of the 2003 dairy reform was to increase competitiveness and market orientation. It was intended that by reducing the guaranteed price for butter and SMP, these products would be less attractive to produce and this would give the industry an incentive to produce more value-added products like cheese and fresh dairy products. Increasing the quota at the same time would encourage additional production, facilitate restructuring of the sector, and encourage entrance into the sector of young farmers. It will be recalled that the European Commission’s proposal for the CAP Reform 2003 was to increase quota by 2% on top of the 1.5% increase already agreed in Agenda 2000. In the June 2003 compromise, however, the Council declared that ‘‘No additional quota increase in 2007 and 2008 will be decided now. The Commission will present a market outlook report once the reform is fully implemented on the basis of which a decision will be taken.’’
CAP Health Check 2008 As part of CAP Reform 2003, a mid-term review of policy was completed in 2008, which became known as the CAP Health Check. Agreement was reached among farm ministers in November 2008. The main points related to dairying were as follows: 1. Five annual milk quota increases of 1% each with effect from April 2009, prior to total abolition of the quota system as from 1 April 2015. As is now traditional, when it comes to milk quota, Italy will receive a special derogation that allows it to increase its quota by the full 5% in the first year.
2. The rate of modulation (shifting funds from direct aids to rural development aids) will be raised from 5% at present to 10% by 2012. The increase will be made gradually: 7% in 2009, 8% in 2010, and 9% in 2011. The progressive modulation concept has been watered down; only recipients of more than E300 000 will face a higher modulation rate: 4 percentage points higher than the standard rate. The resulting money will be allocated for ‘new challenges’ – climate change, energy, biodiversity, and water management – but it will also have to fund ‘accompanying measures’ for the dairy sector.
Conclusion The EU CAP is and will remain a fundamental basis of EU cooperation. Financial problems, disputes about GATT/WTO principles as well as problems regarding the enlargement of the European Union have permanently placed reforms of the agricultural system on the EU political agenda. For the first time, the market scheme for milk and dairy products underwent fundamental change in 2003 and further changes may be anticipated in the decade ahead, particularly when milk quotas are finally abolished in April 2015. See also: Policy Schemes and Trade in Dairy Products: Agricultural Policy Schemes: Other Systems; Agricultural Policy Schemes: Price and Support Systems in Agricultural Policy; Agricultural Policy Schemes: United States’ Agricultural System; Trade in Milk and Dairy Products, International Standards: World Trade Organization.
Further Reading EU Commission (1997a) Agenda 2000, Vol. 1: For a Stronger and Wider Union. Brussels, Belgium: EU Commission. EU Commission (1997b) Agenda 2000, Vol. 2: The Challenge of Enlargement. Brussels, Belgium: EU Commission. EU Commission (2009) Dairy Market Situation 2009, SEC (2009) 1050. Brussels, Belgium: EU Commission. http://caphealthcheck.eu/ health-check-deal (accessed July 2008). European Council Regulations (1999) EEC 804/1968. EC 1255/1999. EC 1256/1999. Brussels, Belgium: EU Council. European Economic Community (1958) Treaty of Rome. Brussels, Belgium: EEC. Nedergaard P (1988) EF’s Landbrugspolitik under Omstilling. Copenhagen, Denmark: DJØF. Organization for Economic Cooperation and Development (2000) Agricultural Policies in OECD Countries: Monitoring and Evaluation 2000. Paris: OECD. Williams RE (1997) The Political Economy of the Common Market in Milk and Dairy Products in the European Union. Rome, Italy: FAO. ZMP (2000) Marktbilanz Milch. Bonn, Germany: ZMP.
Agricultural Policy Schemes: United States’ Agricultural System E Jesse, University of Wisconsin–Madison, Madison, WI, USA ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by D. A. Sumner, J. V. Balagtas, Volume 1, pp 20–25, ª 2002, Elsevier Ltd.
Introduction An active agricultural commodity policy was developed in the United States in the 1930s in response to economic conditions of the Great Depression. Major commodity programs for grains, oilseeds, cotton, peanuts, sugar, tobacco, and dairy that are in place today have their origins in the programs that began nearly 70 years ago. Dairy policy in the United States comprises the following major components: 1. Border measures that create import barriers for most dairy products and export subsidies for a few manufactured dairy products. 2. Federal and state marketing orders that regulate milk prices at the processor and farm levels. 3. Government purchases of manufactured dairy products to support the farm price of milk. 4. Income support to dairy farmers through deficiency payments. Federal, state, and local governments also have longstanding food safety and sanitation regulations for milk and dairy products. In addition, there are myriads of more recent environmental, land use zoning, labor, and other regulations or incentives that influence the dairy industry. This article provides an overview of the key elements of US dairy policy, and provides some statistics to illustrate the economic effects of these programs.
Border Measures for Dairy Products Trade barriers for many dairy products have limited US imports of these products to less than 5% of US consumption (Table 1). Import barriers have traditionally kept the domestic price of dairy products above the price for traded products in world markets, although the gap has narrowed recently (Figure 1). By insulating the domestic dairy economy from foreign supplies of dairy products, the import barriers also make possible the key domestic elements of the dairy program – milk marketing order pricing rules and the price support program (described in the following sections).
300
As a part of the Uruguay Round trade agreement that took effect on 1 July 1995, a system of absolute import quotas gave way to a system of tariff rate quotas (TRQs) that set a relatively low tariff on imports up to a determined quantity (the quota) and a relatively high tariff on overquota quantities. Although the quantity of access expanded with the Uruguay Round agreement, the second-tier tariffs applied to over-quota imports remain prohibitively high; therefore, for the present, the effects of the TRQs remain the same as the absolute quotas that were replaced, although at expanded import quantities. Imports of fluid milk, cream, butter, cheese, milk powders, and many other dairy products are subject to TRQs. For those products subject to TRQs, imports accounted for 5% or less of domestic consumption, but for other products, including casein, milk protein concentrate, and some cheeses, imports are not restricted. Not surprisingly, imports of partly or fully unrestricted dairy products represent the bulk of US dairy imports – caseins, milk protein concentrates, and cheeses represented nearly 80% of total import value in 2009. Overall, the United States imports more than $2 billion worth of dairy products each year, and is a substantial importer as well as exporter in the world dairy market. In addition to limiting import access to the domestic market for most dairy products, the US government continues to provide small amounts of direct financial subsidy for US exporters of dairy products. Subsidized exports, along with donations to domestic food programs and international food aid, have long been used to dispose of stocks of dairy products acquired under the price support program. Subsidized exports have been considered a market for US dairy products that does not disrupt domestic commercial sales. In addition to the disposal of government stocks, the Dairy Export Incentive Program (DEIP) has provided explicit price subsidies for commercial dairy product exports since the 1980s. Commodities eligible for DEIP (and annual Uruguay Round WTO maximum subsidized export volumes) are skim milk powder (68 000 tonnes), butter (21 000 tonnes), and cheese (3000 tonnes). With high world market prices for dairy products in recent years, DEIP subsidies have been infrequent. But very low world prices in 2009 triggered DEIP subsidization of 37 200 tonnes of milk powder, 17 400 tonnes of butter, and 1800 tonnes of cheese.
Policy Schemes and Trade in Dairy Products | Agricultural Policy Schemes 301 Table 1 US production, trade, and consumption of select dairy products, 2006–09
All cheese US production (1000 tonnes) US exports (1000 tonnes) US imports (1000 tonnes) Consumptiona (1000 tonnes) Imports/consumption (%) Butter US production (1000 tonnes) US exports (1000 tonnes) US imports (1000 tonnes) Consumptiona (1000 tonnes) Imports/consumption (%) Skim milk powder/nonfat dry milk US production (1000 tonnes) US exports (1000 tonnes) US imports (1000 tonnes) Consumptiona (1000 tonnes) Imports/consumption (%)
2006
2007
2008
2009
4320 71 206 4500 4.6
4433 100 198 4545 4.4
4505 131 170 4600 3.7
4583 108 162 4682 3.5
657 11 32 651
695 41 29 687
746 91 16 778
711 29 19 697
4.9
4.2
2.1
2.7
676 287 2 397 0.5
669 258 2 386 0.5
845 391 1 399 0.2
775 258 1 518 0.2
a Due to storage, consumption does not equal production plus imports minus exports. Government intervention purchases are not included in consumption. Data compiled from US Department of Agriculture, National Agricultural Statistics Service and Foreign Agricultural Service.
3.6 3.4
Butter Cheese Skim milk powder
3.2 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2
9
9
-0 Ju l
-0
8 -0
8 -0
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6 Ja n
6 -0
5
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-0
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1
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-0
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Figure 1 Ratio of US market price to Oceania export price for primary dairy export products, 2000–09. Data from the US Department of Agriculture as reported at http://future.aae.wisc.edu/tab/prices.htm#13.
302 Policy Schemes and Trade in Dairy Products | Agricultural Policy Schemes
Regional Milk Marketing Orders The pricing of nearly all of the milk produced in the United States is regulated by milk marketing orders. In 2010, 10 federal marketing orders regulated the sale of about two-thirds of all milk produced in the country. California, which operates its own marketing order, regulates the sale of another 20% of the country’s milk. Some of the remainder is regulated by other state marketing orders (Maine, Montana, Nevada, Virginia) and some (notably Idaho with 6% of US milk production) is not regulated by any marketing order. State and municipal governments set separate sanitary standards for milk that may be used in fluid products and milk that may be used only in manufactured dairy products. Grade A milk is milk that meets sanitary standards for use in fluid products. Of all milk produced in the United States, 99% is grade A. Grade B milk is eligible for use in only manufactured dairy products and is not regulated by milk marketing orders. Both federal and California milk marketing orders use price discrimination to raise the average price received by producers, setting minimum prices that processors must pay for grade A milk according to its end use (classified pricing). Federal orders distinguish between four end-use classes: fluid products, fresh and frozen products, hard cheeses, and butter and dry milk powder. Each month, federal orders set the minimum prices for milk used in cheese and milk used in butter and dry milk according to formulae that take into account the wholesale prices of these products. The minimum prices for milk used in fluid products (Class I) and soft and frozen products (Class II) are set as a specified differential over the manufacturing-use minimum prices. The differential for Class II is the same across all federal orders, but Class I differentials vary by order. Although the details of the Federal Milk Marketing Order (FMMO) pricing rules have changed over time, the key element of price discrimination remains; the minimum price for milk used in fluid products is set at a premium over the minimum price set for milk used in manufactured dairy products. The California state order distinguishes among five end-use classes, and uses similar formulae to set minimum prices for each class. In addition, each federal marketing order administers a revenue-sharing or ‘pooling’ scheme that distributes revenues from relatively high-priced Class I milk across all grade A milk. Each month, each federal order pools revenues from all end-use classes and announces a uniform, order-wide average price to individual farmers delivering milk to that order, regardless of how any individual producer’s milk was actually used. The weighted average or pool price in any order depends not only on the class prices but also on the utilization rates of milk in the
various end-use classes, which also vary from order to order. California’s revenue-sharing scheme differs from that used in the federal system. In California, a quota program determines how milk revenues from the various end-use classes are distributed among producers. The milk quota program in California does not restrict production or marketing. Rather, for each 100 kg of milk quota owned by an individual producer, the producer receives a fixed payment of $3.75 from the statewide pool of total milk revenues in a month. The remainder of total regulated milk revenues (i.e., what is left over after subtracting total quota payments) is distributed uniformly among all producers in the same way as federal orders. Overall, quotas cover about 22% of all the milk produced in the state. To the extent they raise the average price of milk above what it would be in their absence, both federal and state milk marketing orders encourage milk production. By setting relatively high prices for milk used in fluid products, marketing orders reduce sales of fluid milk. As a result, marketing orders encourage production of manufactured dairy products such as cheese, butter, and milk powder. Each marketing order regulates milk within a geographically defined marketing area. Figure 2 is a map of the 10 federal marketing areas. The relationship of prices among federal orders is determined, in part, by the formulae used to set minimum prices in each order. By formula, the minimum prices for milk used in manufactured dairy products are the same across orders. However, the fluid differentials, and thus the minimum price for milk in fluid uses, are different for each order. Differentials range from a high of $13.23 per 100 kg in parts of Florida, to a low of $3.53 per 100 kg in parts of the Upper Midwest. Table 2 lists the fluid differentials, Class I milk prices, and pool prices that were in effect for the 10 federal orders in 2009. In order to maintain different minimum prices in each marketing order, regulations are in place to discourage the transport of milk across regions. Milk transported freely across marketing order borders would undermine the maintenance of separate fluid milk markets in different orders. Regulations on inter-order milk shipments ensure that there is little economic advantage to arbitrage across prices in different orders. Because marketing orders create separate fluid milk markets in different regions, the benefits and costs of milk marketing orders vary regionally.
Federal Price Supports for Dairy Industry As early as 1935, the federal government was purchasing manufactured dairy products in order to support the farm price of milk. The Agricultural Act of 1949 required the
Policy Schemes and Trade in Dairy Products | Agricultural Policy Schemes 303
Pacific Northwest
Upper Midwest Northeast Mideast
Central
Appalachian Arizona Southeast
Southwest
Florida
Figure 2 Map of the Federal Milk Marketing Order areas as of 1 January 2010. Differences in shading merely serve to differentiate between marketing areas. Reproduced from US Department of Agriculture, Agricultural Marketing Service, Dairy Programs.
Table 2 Federal Milk Marketing Order annual average prices,a 2009 Marketing areaa
Class I differential ($ per 100 kg)
Class I milk price ($ per 100 kg)
Pool priceb ($ per 100 kg)
Northeast (Boston) Appalachian (Charlotte) Southeast (Atlanta) Florida (Tampa) Mideast (Cleveland) Upper Midwest (Chicago) Central (Kansas City) Southwest (Dallas) Arizona (Phoenix) Pacific Northwest (Seattle) Weighted average
7.17 7.50 8.38 11.91 4.41 3.97 4.41 6.62 5.18 4.19 6.34
32.48 32.81 33.69 37.22 29.72 29.28 29.72 31.93 30.50 29.50 31.66
28.62 30.87 31.38 35.61 26.66 25.51 25.75 28.05 26.61 25.91 27.41
a
Prices quoted at ‘principal pricing points’ (in parentheses) within each marketing area. Pool price is the market-wide weighted average of all minimum end-use class prices. Data reproduced from US Department of Agriculture, Agricultural Marketing Service, Dairy Programs. b
US Department of Agriculture (USDA) to continue to support the farm price of milk. Since that time, the USDA has purchased butter, non-fat dry milk, and cheese from processors at administratively determined intervention prices calculated to help ensure that the farm prices of manufacturing milk remain above the legislated support price. In 2008, the dairy price support program was modified to remove the requirement that USDA support a specific milk price, but intervention prices for eligible dairy products remained the same. The name of the support program was changed from the ‘milk’ price support program to the ‘dairy product’ price support program. Table 3 lists the support price for milk and the government purchase prices for eligible dairy products from 2000 through 2009. Note that, on average, market prices exceeded intervention prices, but occasionally fell far
enough below during the year to trigger government purchases. Annual purchases of butter, cheese, and nonfat dry milk are shown in Table 4. Since 1990, dairy price supports have played a minor role and government purchases have been relatively small compared to the 1980s. The 1996 FAIR Act lowered dairy price supports by 33 cents per 100 kg to $21.83 per 100 kg through 1999, at which time the program was scheduled to be terminated. However, the price support program was extended and subsequently reinstated in omnibus farm legislation passed in 2002. While the support price program plays a potentially important role in flooring prices for manufactured dairy products, the current intervention prices provide only the lowest of safety nets. Moreover, added costs of selling to the government (nonstandard packaging, mandatory federal inspection) mean that market prices for cheese often
304 Policy Schemes and Trade in Dairy Products | Agricultural Policy Schemes Table 3 US market prices and US Department of Agriculture price support and purchase prices, 2000–09 Milk Support
Butter Class III pricea
Support
Year
($ per 100 kg)
($ per kg)
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
21.83 21.83 21.83 21.83 21.83 21.83 21.83 21.83 NA NA
1.45 1.70 1.96 2.32 2.32 2.32 2.32 2.32 2.32 2.32
21.48 28.89 22.97 25.18 33.94 30.97 26.21 39.78 38.45 25.04
Cheese
Nonfat dry milk
Marketb
Support
Marketb
Support
Marketc
2.76 3.86 2.31 2.58 4.05 3.39 2.73 3.10 3.38 2.82
2.45 2.49 2.49 2.49 2.49 2.49 2.49 2.49 2.49 2.59
2.53 3.17 2.61 2.90 3.64 3.29 2.73 3.88 4.09 2.86
2.23 2.08 1.95 1.76 1.76 1.76 1.76 1.76 1.76 1.83
2.30 2.27 2.08 1.85 1.96 2.15 2.04 4.03 3.00 2.26
a
Federal Milk Marketing Order price for milk used to make cheese. Chicago Mercantile cash market prices. Market and support prices for cheese price are for Cheddar in 40-pound (18.14 kg) blocks. c Wholesale price for western high-heat non-fat dry milk. b
Table 4 US government net purchases of dairy products
Butter Year
(tonnes)
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
4017 0 0 13 182 2971 0 0 0 0 4535
Cheese
Non-fat dry milk
12 711 1749 7179 18 712 2692 907 0 0 0 13 605
328 994 224 878 372 683 301 185 47 816 36 281 31 293 12 245 52 154 62 585
Negative values denote net sales from government stocks. Values include DEIP subsidies in the form of product.
fall below the intervention price without triggering government sales. This further diminishes the ability of the program to provide a price floor.
An annual cap on the amount of milk per farm eligible for payment was initially set at 1.1 million kg, which represented the annual production of about 120 cows. The payment rate was reduced from 45 to 34% on 1 October 2005, but reinstated at 45% in the 2008 Farm Bill. That legislation also provided for an upward adjustment in the MILC target price if dairy feed costs exceed a base level and raised the annual farm production cap to 1.35 million kg. MILC payments since the retroactive inception of the program through 2009 are shown in Figure 3. Payments closely follow milk prices. No payments were made during 2007 and 2008. The crash in milk prices in 2009 combined with a higher target price from the feed price adjuster led to record high payments during the first half of the year. The MILC program has been controversial among producers, mainly because the production cap favors regions with a smaller average herd size. Large western dairies can exceed the production cap in a single month. Their owners argue that they have been forced to bear the brunt of adjusting milk supply to low prices because MILC payments insulate smaller producers.
Direct Deficiency Payments – The Milk Income Loss Contract Program
Final Remarks
The 2002 US ‘Farm Bill’ introduced another dairy subsidy scheme in the form of the Milk Income Loss Contract (MILC) program. MILC is a target price-deficiency payment program that makes payments to all dairy farmers (subject to a production cap) in any month when milk prices fall below a target level. The initial base target price was $37.35 per 100 kg in reference to the Class I milk price announced for Boston. If the Boston Class I price in any month fell below $37.35, then all US milk producers were eligible to receive 45% of the difference.
In the United States, the federal government and several state governments directly and indirectly subsidize milk producers and regulate dairy prices. These programs stimulate additional milk output, raise the price of beverage milk, and shift income from taxpayers and consumers to the dairy industry. Economic research has documented that costs to taxpayers and consumers are significantly larger than gains to producers as a group, but of course, any individual producer gains much more than the system costs a typical dairy consumer or taxpayer.
Policy Schemes and Trade in Dairy Products | Agricultural Policy Schemes 305 0.60 0.55 0.50 Market price
0.45 0.40 Target price $ per kg
0.35 0.30 0.25 0.20 0.15 0.10 0.05
MILC payment
p
ay
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Se Ja p n '0 9
ay M
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ay
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ay
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ay
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M
Se Ja p n '0 4
ay M
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ay
Se
M
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0.00
Figure 3 Milk Income Loss Contract (MILC) payments. Reproduced from US Department of Agriculture as reported at http:// future.aae.wisc.edu/milc.html.
See also: Policy Schemes and Trade in Dairy Products: Agricultural Policy Schemes: European Union’s Common Agricultural Policy; Agricultural Policy Schemes: Other Systems; Agricultural Policy Schemes: Price and Support Systems in Agricultural Policy.
Further Reading Benedict MR (1953) The Farm Policies of the United States 1790–1950. New York: Twentieth Century Fund. California Department of Food and Agriculture (2010) Dairy Programs web page. http://www.cdfa.ca.gov/dairy (accessed 19 February 2010). Chite RM and Shields DA (2008) Dairy policy and the 2008 farm bill. Congressional Research Service, report no. RL34036, 22 January 2009. Washington, DC: Library of Congress. Cox TL and Chavas J-P (2001) An interregional analysis of price discrimination and domestic policy reform in the US dairy sector. American Journal of Agricultural Economics 83: 89–106. FAPRI–UW Alliance (2006) Dairy policy briefs. Food and Agricultural Policy Research Institute and University of Wisconsin–Madison.
http://future.aae.wisc.edu/alliance/DPAA_wCover.pdf (accessed 19 February 2010). Ippolito RA and Masson RT (1978) The social cost of government regulation of milk. Journal of Law Economy 21: 33–65. Jesse EV and Cropp RA (2008) Milk pricing concepts for dairy farmers. Cooperative Extension, University of Wisconsin-Extension, bulletin no. 3738. Jesse EV, Cropp RA, and Gould B (2008) Dairy subtitle: Food, Conservation, and Energy Act of 2008, Marketing and Policy Briefing Paper No. 94. Department of Agricultural and Applied Economics, University of Wisconsin–Madison, and Cooperative Extension, University of Wisconsin-Extension. http://future.aae.wisc.edu/ publications/farm_bill/M&P_Dairy_6-1.pdf (accessed 22 February 2010). Manchester AC (1983) The Public Role in the Dairy Economy: Why and How Governments Intervene in the Milk Business. Boulder, CO: Westview Press. Sumner DA and Wilson N (2000) Creation and distribution of economic rents by regulation: Development and evolution of milk marketing orders in California. Agricultural History 74: 198–210. Sumner DA and Wolf C (2000) Quotas without supply control: Effects of dairy quota policy in California. American Journal of Agricultural Economics 78: 354–366.
Agricultural Policy Schemes: Other Systems P Vavra1, OECD, Paris, France ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by L. Boonekamp, Volume 1, pp 25–31, ª 2002, Elsevier Ltd.
Introduction Milk producers in many countries benefit from government interventions that increase the prices they receive for their raw milk production. In some countries, a system of milk production quota was established to control the growth of surplus production while maintaining the market price support. Below are reviewed the current dairy policies in Canada, Japan, Australia, and New Zealand. The review illustrates the very different policy approaches and the degree of dairy policy interventions. The Organisation for Economic Co-operation and Development (OECD) collects and analyzes information regarding the level of support provided to producers through agricultural policies and calculates some measures of the monetary transfers caused by such policies – the producer support estimate (PSE). Since 2005, the total PSE is no longer broken down for individual commodities, which reflects the gradual shift (in many countries) away from direct commodity-linked supports. Figure 1 shows the change in %PSE for selected countries and the OECD average during the periods 1986–88 and 2002–04. The %PSE expresses the monetary value of the support as a share of gross farm receipts. A notable feature of the %PSE for milk is the reduction in support since the early 1990s, although the reduction varies considerably among countries. Since 2005, a new commodity-based indicator is calculated by the OECD, the so-called single commodity transfers (SCTs), which shows the annual monetary value of gross transfers from policies linked to the production of a single commodity such that the producer must produce the designated commodity in order to receive the transfer. For the countries reviewed below, the change from the commodity-specific PSE to the SCT indicator does not make much difference for New Zealand and Australia, where milk producers are supported either very little or not at all, while in Canada and Japan, a majority of the 1
The author is an agricultural markets and policy analyst at the OECD, Paris. The opinions expressed in this article are those of the author and do not necessarily represent those of the OECD or its member countries.
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support (more then 90%) has been based on market price support (MPS), which continues to be reported in SCTs. The evolution of the SCT for milk production in the reviewed countries is illustrated in Figure 2 for the period 1986–2008.
Canada Background Since the first dominion dairy commissioner was appointed in 1890, the Canadian Federal Government has played an active role in policymaking for the dairy sector. A milk supply management system was introduced in the early 1970s, and it remains the cornerstone of Canada’s current dairy policy. Import restrictions at the border and milk production quotas are the main instruments allowing for a high level of support to the dairy sector, which continues to be the most heavily supported sector within Canada’s agriculture. In 2004, around 35% of all support to Canadian agriculture (as measured by PSE) went to the dairy sector. Figure 1 also illustrates that Canada’s support to dairy farmers is higher than that in OECD countries on average. When considering the SCT, 33% of the total SCT was attributable to the dairy sector in 2008. Figure 2 shows the relatively stable levels of SCT support, which declined notably after 2006 as international reference prices soared. (In 2009, the SCT level increased significantly following the dramatic price fall on the international dairy markets which has not been transmitted to the domestic market in Canada. The preliminary figures estimated by the OECD indicate an increase of % SCT to a level of 60%.) Canada and Its Milk Supply Management System The milk supply management system, introduced in the early 1970s, is the essence of Canada’s dairy policy. The system is governed by the Canadian Milk Supply Management Committee (CMSMC). The committee is responsible for policy determination and supervision of the national milk marketing plan. The CMSMC annually sets a national production target, the market sharing quota
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OECD United States 2002–04 New Zealand
1986–88
Japan European Union Canada Australia 0
20
40
60
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100 90 80 70 60 %
50 40 30 20 10 0 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 Japan
Canada
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Figure 2 Single commodity transfers (SCTs) for milk over the period 1986–2008 in various countries. Source: OECD.
(MSQ), for industrial milk. The MSQ is set with the goal to achieve a domestic market balance in terms of butterfat, and is assigned to provinces largely on the basis of historical shares. In addition to the MSQ, each province controls its own production quota for fluid milk, and the entire milk quota – industrial and fluid together – is allocated to producers. For the supply management to be effective there is a need to continue the policies of substantial border measures. In other words, a quota system allows a domestic market to be managed only if that market is isolated from external sources of supply. Under the 1994 Uruguay Round Agreement on Agriculture (URAA), the diverse forms of trade measures were converted to tariffs, and market access for sensitive products was provided through a system of tariff rate quotas (TRQs). Under the TRQ system, exporting countries have access to the Canadian dairy market to the tune of 5% of the
domestic consumption. For most products, the final access quota quantities remain below 1000 tonnes (i.e., 1kt), but are 3.2 kt for butter and dry whey, 20.4 kt for cheese, and 64.5 kt for fluid milk. While the in-quota duties are generally low, tariff rates applicable to overquota imports are prohibitively high, ranging from 202% for skim milk powder to 246% for cheese and 299% for butter. A strict control of supplies from domestic production and imports allows prices paid to producers to be supported at levels marginally above the costs of production. The Canadian Dairy Commission annually reviews and establishes a target price for industrial milk. This target price is supported by market intervention for butter and skim milk powder (SMP) at support prices set similarly on an annual basis. The support prices have been increasing steadily over the last decades. In 2009, the support prices for butter and SMP were raised to Can$7102.4 and
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Can$6178.3 per tonne, respectively. For a comparison, the respective prices in 2000 stood at 5540.7 and Can$4684.2 per tonne, which translates to a 28 and 32% increase in the support prices over the 2000–09 period. (Over the same period, 2000–09, in the European Union the butter and SMP intervention prices declined by 25 and 15%, respectively. Using the October 2009 Can$/Euro exchange rate of 0.65, the butter and SMP support prices of Canada in 2009 would amount to E4611 and E4011 per tonne, respectively. The corresponding intervention prices for butter and SMP in the European Union were E2462 and E1764 per tonne, respectively.) In 1995, a supplementary scheme was introduced that provided for the pricing of five classes of milk by virtue of a new permit system. The change allowed dairy processors to purchase surplus milk (over the quota milk) at a discount rate, determined by the government, for the production of dairy products for exports. The United States, joined by New Zealand, claimed that this in fact constituted an export subsidy, that it was in violation of Canada’s commitments under the Uruguay Round, and requested investigation by a World Trade Organization (WTO) compliance panel. In December 2002, the WTO confirmed that Canada’s approach to the export of dairy products constituted an export subsidy. On 9 May 2003, Canada announced that it had entered into an agreement with the United States and New Zealand, and eliminated the subsidies that violated the WTO rules. The supply management system in Canada is sometimes used as an example of a functioning stable system that enables milk producers to receive good prices. Supply management might be considered the second best option in a narrow sense as it alleviates surplus accumulation resulting from a high market price support, but it is unlikely to be the long-term solution in the face of rapid technological and structural developments throughout the world. The problems linked to supply management include the inefficiencies that the system may create, the costs that it imposes on consumers, the difficulties and costs of administration that may arise for governments, the difficulty in setting the quota at a level that would match consumption, the vested interests that it generates (quota rent), and importantly the need to continue the policies of high border measures.
Japan Background Japanese domestic dairy policy focuses mainly on supporting milk destined for the production of dairy products, which procures a lower price than drinking milk and is subject to international competition. Up until 2001, government support was provided mainly
Agricultural Policy Schemes: Other Systems
through three programs: price support, voluntary program to limit supply, and import tariff rate quotas. Price support was administered via a system of deficiency payments on manufacturing-milk introduced in 1966. The deficiency payments, defined as the difference between a guaranteed price and the price paid by dairy plants for milk used in processing (standard transaction price), were limited to an annually fixed quota volume and to designated products such as butter, SMP, and condensed milk. A voluntary production quota for liquid milk was initiated in 1979 in an effort to regulate shipments from Hokkaido – the low-cost production region with over 80% of milk used for manufacturing – to higher-cost production regions. This quota is determined by the Central Council of Dairy Cooperatives and allocated between prefectural cooperatives, who in turn allocate a quota to each farmer. The allocation between prefectures takes into account production of the previous year and planned production for the coming year. Since the voluntary production planning system has no legal binding power, some 5% of dairy farmers choose to operate outside the production guidelines. As measured by the PSE, total transfers to dairy farmers relative to total gross receipts amounted to 73% in the period 2002–04. The support has declined from the levels calculated in the mid-1980s although the Japanese dairy sector remains among the most heavily supported in the world. A Change in Dairy Domestic Policy in 2001 In April 2001, a policy change was introduced to deal with the rigidity of the guaranteed price system, increased budgetary cost, and the additional pressures to reduce domestic support resulting from Japan’s commitments under the Uruguay Round. The policy abolished the guaranteed price and the standard transaction price along with the deficiency payment scheme, and a new direct-payment program was introduced instead; but the annually determined manufacturing-grade milk quotas were kept in place. The move away from a marketintervention system to a payment-based system was designed to improve the market orientation of dairy farms. Producers’ direct payments were to be set annually in light of the unit rate paid in the previous year and the changes in cost of raw milk production. In 2001, in order to ensure a smooth adjustment to the new policy, the direct payments were set equal to deficiency payments of 2000 at ¥10.3 per kg. The amount of manufacturingmilk eligible for payment was set at 2.27 mt. The evolution of deficiency payments and, from 2001, direct payments together with the eligible quantities is illustrated in Figure 3. The move to a more marketoriented system was compensated for by the introduction of emergency measures to protect farmers from
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12
3
Yen Kg–1
2 11 1.5 10.5 1 10
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2.5
11.5
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9.5
0 1993
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1999
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Figure 3 The evolution of deficiency and direct payments for milk together with eligible quantities, in Japan. Source: MAFF, Japan. Deficiency payments until 2000; direct payments afterward.
unforeseen fluctuations in the price of manufacturing milk. If the average market price falls, then 80% of the difference between the average market price and the base price (the average transaction price during the previous 3 years) is to be compensated from an income stabilization fund to which producers and the state contribute at the ratio of 1:3. An additional system of direct payments was introduced to provide incentives for environmental conservation under the land using-type dairy farming promotion project and the direct payment system in hilly and mountainous districts. Japan manages imports of dairy products under TRQs by import licensing and state trading. Quantities under import license are allocated by the Ministry of Agriculture, Forestry and Fisheries (MAFF) to private importers based on historical records. The quota access at preferential tariffs for SMP and butter are set at 116 and 1.9 kt, respectively. Typically these quotas remain significantly underfilled. The in-quota ad valorem tariffs are set at 16, 24, and 35% levels for SMP, whole milk powder, and butter respectively. In addition to in-quota tariffs, the government of Japan or its sales agents are able to charge the so-called markup, which can amount to 392, 413, and 594% for SMP, whole milk powder, and butter respectively. The tariffs for out-of-quota imports are set prohibitively high at 210, 316, and 733% levels for SMP, whole milk powder, and butter, respectively (Agricultural Market Access Database (AMAD)). Cheese imports to Japan are not subject to quota. There are various import tariffs for cheese depending on the use of the product, but the average rate is about 31.2%. Although the policy change toward direct payments is in the right direction, the change is relatively small given the design of the policy. The support remains very high and continues to be paid by consumers. The primary
reason for the very modest impact of the new policy is the lack of changes to dairy trade policy, which keeps Japan’s dairy industry highly protected from cheaper imports. Due to very high border measures, the majority of support still falls under the market price support category. In 2008, the market price support stood at 93% of all SCTs.
Australia Background With the Kerin plan in 1986 and the Crean plan in 1992, Australia began a reform process of dairy policies including a gradual reduction in support and a planned elimination of support for manufacturing milk by 1 July 2000. In 1995, a redesigned plan was introduced to ensure that Australia complied with its WTO commitments on export subsidies under the Uruguay Round. The domestic market support (DMS) scheme was restructured so as to ensure that support was provided independently of export sales. In addition to this reform of support policies for manufacturing milk, a regulatory reform process for market milk was initiated in 1995, stipulating that in each state only farm gate price controls would remain in place by January 1999. In July 1999, a review of market milk regulations in Victoria concluded that there was no net public benefit from retaining farm gate price controls. An industry restructuring plan was developed to avoid possible interstate price wars and an industry collapse, which was implemented on 1 July 2000. Following the industry deregulation, support to the Australian dairy sector has declined dramatically and, measured by the PSE, the value of transfers to the dairy industry relative to gross farm receipts fell to 15% in the period 2002–04 (Figure 1). As measured by the SCT, after the
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deregulation, the direct market support to dairy industry has dropped to zero (Figure 2). Policy Reform of the Dairy Industry in 2000 and beyond A new policy reform package was introduced on 1 July 2000, which removed simultaneously the DMS scheme and fresh milk regulations, and allowed the market to determine milk prices. At the same time, a structural adjustment package was introduced through the Dairy Industry Adjustment Act to help producers to cope with the adjustment to lower prices or to choose to leave the industry. The adjustment package was to be funded by a levy of 11 cents (A$) per liter on all domestic sales of fresh milk for 8 years until the package would be fully funded. The individual adjustment programs were called the dairy industry adjustment package, the dairy structural adjustment program, the dairy exit program, and the dairy regional assistance program. Dairy farmers were eligible for dairy structural adjustment program assistance and received a fixed quarterly payment over 8 years, with payments being based on milk production in 1998–99, and subject to income tax. Producers could also opt to leave the dairy industry altogether, and receive an exit payment of up to A$45 000 tax-free under the dairy exit program. The conditions attached to the program prevented the farmers from reentering the industry at a later date. Finally, the dairy regional assistance program was intended to assist dairy-dependent communities in generating alternative employment opportunities and to deal with any social dislocation from deregulation. After the reform, the dairy industry has become fully exposed to world market conditions and emerged as a globally cost-competitive industry. However, following the deregulation, the dairy sector not only had to absorb the reform adjustment pressures but also had to cope with a series of severe droughts that resulted in increased herd contraction. Cow inventories in Australia increased in 2008/09 for the first time in 7 years, however contracted again in 2009/10 and the future industry growth remains sensitive to availability and management of water supply. To address these issues, in 2008 and 2009, the Australian government has strengthened the water policy reforms and environmental programs, and also announced an initiative, Australia’s Farming Future, to help the industry through research and information to manage the impact of climate changes. The Australian Government is also committed to implementing the emissions trading scheme in 2011, which can be expected to impact the dairy sector. Nevertheless, at the same time, a program concentrating on reducing emissions from livestock has been initiated focusing on research into alternative feeds to reduce methane production or genetic approaches to developing low-emitting animals.
Agricultural Policy Schemes: Other Systems
The industry does not use export subsidies to increase its market share of dairy products, although it has a strong focus on export sales. In 2009, the Australian government has announced a reform of the system of export quota allocations to the United States and the European Union. Under tariff rate quotas, certain amounts of Australian dairy products can be exported into the United States and the European Union at reduced or zero tariffs. The old system of distributing fixed shares of quota based on historical entitlements is replaced by a system in which exporters receive a share of quota based on 3-year rolling averages of export performance. Australia has also entered into a number of free trade agreements (FTAs) that have been or are in the process of negotiation. The trade barriers between Australia and New Zealand were fully removed in the Closer Economic Relations Trade Agreement, which came into effect already on 1 January 1983. Australia has FTAs also with Singapore, Thailand, the United States, and Chile. Most recently, the negotiations between ASEAN, Australia, and New Zealand for a free trade agreement (AANZFTA) were concluded on 28 August 2008, and the agreement was signed on 27 February 2009. This was the largest FTA Australia signed to that date. A separate agreement is being negotiated with Malaysia, and there are plans to negotiate an FTA with Indonesia. FTA agreements are also being pursued with China, Japan, and the Gulf Cooperation Council.
New Zealand Background Prior to 1984, the support to farmers in New Zealand went as high as 40% of the farmers’ income. Domestic farm support policies were scaled down dramatically during the 1980s with input subsidies eliminated in 1984 and government involvement in calculation of product prices withdrawn in 1988. The main dairy policy issue following the deregulation of 1984 was related to the export monopoly of the New Zealand Dairy Board (NZDB) and the potential for indirect subsidization of dairy exports. This potential existed as Section 27 of the Dairy Board Act allowed for pooling of revenues from domestic and export markets and, thus, cross-subsidization of lower revenue from export sales by higher revenue from domestic sales. This section was abolished in 1998. The dairy industry is one the most important elements of the New Zealand economy accounting for about one quarter of New Zealand’s total export earnings. Measured by the PSE, total transfers to dairy farmers relative to gross farm receipts were close to zero in 2002–04 (Figure 1). As measured by the SCT, the direct market support to the dairy industry has been zero for more than 20 years (Figure 2).
Policy Schemes and Trade in Dairy Products
Dairy Industry Restructuring Act On 9 April 2001, the New Zealand Government passed the Dairy Industry Restructuring Act (DIRA), which agreed to the formation of a large cooperative Fonterra, originally called GlobalCo, through the merger of most of New Zealand’s cooperative dairy processing companies. The act also stipulated that following the merger, the new company will absorb the activities of the NZDB. The NZDB, established through the Dairy Board Act in 1961, controlled the marketing of all export dairy products and was the largest exporter in New Zealand. An amendment to the Dairy Board Act in 1996 brought the status of NZDB closer to that of a company in which milk processing cooperatives own shares in proportion to their milk deliveries. Nevertheless, the NZDB remained subject to criticism for its export monopoly power. Given the trade agreements and its export power, the NZDB was able to extract quota rents from dairy exports (e.g., to the EU), which were then passed back to individual producers thus increasing the farmers’ marginal returns. The DIRA ended the statutory export monopoly of NZDB and established 11 regulated dairy export markets. On a transitional basis, the act provided Fonterra with exclusive export access to these markets for a fixed period of time. In 2007 the New Zealand Government reviewed the regulated export market established in the DIRA and started the deregulation process to be concluded over the period 2007–10. The DIRA also provided for a regulation that aimed to protect firms from Fonterra’s monopoly pricing. The provision required that 5% of Fonterra’s milk be made available at a predetermined price to other independent processors to allow for a level playing field. The review of this regulation conducted in 2008 concluded that independent processors were able to procure milk at a lower price than what Fonterra paid to its farmers. A new mechanism was proposed under the Dairy Industry Restructuring Bill; this bill (in reading as of October 2009) proposes that the margin be charged from the 2010/2011 dairy season and also provides for raw milk to be allocated through auctions in later years. Government policy in New Zealand affects the dairy industry mainly via policy measures addressing agri– environmental issues. For example, the dairying and clean streams accord, which was agreed between Fonterra and the New Zealand Government in 2003, aims to achieve clean water, including streams, rivers, lakes, and ground water, and wetlands in dairying areas. Moreover, in September 2007, the government released a comprehensive statement on climate change and a range of initiatives across all sectors, including the Emissions Trading Scheme (ETS). Agriculture is likely to be part of the scheme from 2013.
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New Zealand is the largest exporter of butter, SMP, and whole milk powder, and the second largest exporter of cheese in the world. New Zealand achieves this position without relying on production or market subsidies and without protecting the domestic market from overseas competition. In the absence of progress in lowering trade barriers on a multilateral level, New Zealand is seeking trade agreements on a bilateral basis. Apart from New Zealand’s free trade agreement with Australia (already in place since 1983), more recent FTAs were concluded with Singapore, Thailand, the Trans-Pacific Partnership (involving Singapore, Brunei, and Chile), China, and ASEAN (signed in February 2009). Negotiations are currently underway with Malaysia, Hong Kong, and the Gulf Co-operation Council (Saudi Arabia, UAE, Oman, Qatar, Bahrain, and Kuwait). Negotiations are also due to commence for the enlargement of the Trans-Pacific Partnership and bilateral FTAs with Korea and with India. See also: Policy Schemes and Trade in Dairy Products: Agricultural Policy Schemes: Price and Support Systems in Agricultural Policy; Agricultural Policy Schemes: European Union’s Common Agricultural Policy.
Further Reading Australian Competition and Consumer Commission (2001) Impact of Farmgate Deregulation on the Australian Milk Industry: Study of Prices, Costs and Profits. Dickson, ACT: ACCC. Campo IS and Beghin JC (2006) Dairy food consumption, supply and policy in Japan. Food Policy 31: 228–237. Federated Farmers of New Zealand (2009) Life After Subsidies. http://www.fedfarm.org.nz/n215.html (accessed August 2010). Japan Dairy Council (2001) Japan Dairy Farming for Yesterday, Today and Tomorrow: Supporting a Healthy Japanese Diet. Tokyo: Japan Dairy Council. Organization for Economic Cooperation and Development (2005) Dairy Policy reform and Trade Liberalisation. Paris: OECD. Organization for Economic Cooperation and Development (2009) Evaluation of Agricultural Policy Reforms in Japan. Paris: OECD. Organization for Economic Cooperation and Development (2009) OECD Agricultural Outlook 2009–2018. Paris: OECD (and earlier issues). Organization for Economic Cooperation and Development (2009) Agricultural Policies in OECD Countries: Monitoring and Evaluation. Paris: OECD (and earlier issues). Obara K, Dyck J, and Stout J (2005) Dairy policies in Japan. Electronic Outlook Report. US Department of Agriculture, Economic Research Service (USDA, ERS). http://gain.fas-usda.gov/pages/Default.aspx USDA (2008) New Zealand, dairy and products. GAIN Report No NZ8026. USDA-FAS. http://gain.fas-usda.gov/pages/Default.aspx Yasaka M (2001) Dairy Farming and the Dairy Industry. Japan’s Livestock Industry: Now and in the Future. Tokyo: Food and Agriculture Policy Research Center.
Relevant Websites http://www.cdc.ca – Canadian Dairy Commission.
Codex Alimentarius C Heggum, Danish Dairy Board, Aarhus, Denmark ª 2011 Elsevier Ltd. All rights reserved.
Introduction Codex Alimentarius is Latin for food code and refers today to the international food code established under the United Nations. It is a collection of internationally adopted food standards that constitute a global reference point for national food legislators and control agencies, the international food trade, and food handlers and consumers. The code has a great impact on the approach to food quality management throughout the world. The code is being developed by the Codex Alimentarius Commission (CAC), which is an international organization run jointly by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO). One hundred and seventy-eight individual countries are members of the CAC (end of 2008). In addition, about 160 other international intergovernmental and international non-governmental organizations contribute to the work. The CAC’s objective is to establish standards, codes of practices, guidelines, and recommendations concerning foods aimed at protecting consumer’s health, ensure fair practices in trade, and facilitate international trade. With the establishment of the World Trade Organization (WTO), the Codex Alimentarius has gained importance due to the fact that two WTO Agreements (the Agreement on the Applications of Sanitary and Phytosanitary Measures (SPS) and the Agreement on Technical Barriers to Trade (TBT)) refer to Codex Alimentarius texts as being the reference for dispute settlements and for application by national legislation.
The Establishment The Need for Harmonization of National Food Regulations The need for international food regulation has developed with international trade. Quality standards for individual commodities have been known since ancient times, but the first general food laws were established in the 1800s. At the beginning of the 1900s, the establishment of international food standards began; it was of growing concern to food traders worldwide that the national standards and regulations developing independently (and sometimes spontaneously) in individual countries started to create trade barriers. As a response to this development,
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trade associations that were formed as a reaction to such barriers pressured governments to harmonize their various food standards so as to facilitate trade in safe foods of a defined quality. One of the earliest such associations was the International Dairy Federation (IDF), founded in 1903. After World War II, there was heightened international concern about the direction being taken in the field of food regulation. Countries were acting independently and there was little, if any, consultation among them with a view to harmonization. In addition, and as a reaction to the food supply situation during the 1940s, many attempts were made to protect and support domestic food production. Food regulations in different countries were conflicting and contradictory, in particular with regard to nomenclature, and much legislation was not based on scientific knowledge. Many efforts have been made to harmonize national food regulations. In the dairy field, the IDF developed during the 1950s a vast number of codes and standards intended to be applied by the dairy sector and to form the basis of national legislation. These efforts resulted in two initiatives being taken at the government level: establishment of the ‘Stresa Convention’ – a multi• the lateral agreement between a number of European
•
countries that governed the naming and composition of a number of individual cheese varieties (see Policy Schemes and Trade in Dairy Products: Standards of Identity of Milk and Milk Products); the establishment of the Joint FAO/WHO Committee of Government Experts on the Code of Principles Concerning Milk and Milk Products (the ‘Milk Committee’) – a worldwide committee established to develop international identity standards for milk products, most of them prepared by IDF, within the framework of the Code of Principles Concerning Milk and Milk Products (see Policy Schemes and Trade in Dairy Products: Standards of Identity of Milk and Milk Products).
Catalyzed by the success of the Milk Committee, the 1961 FAO Conference decided to establish the Codex Alimentarius. The CAC was established in 1962 to govern the work. Due to the importance of the role of WHO in all health aspects of food, the WHO joined in 1963. Since its founding, many food standards, codes of hygienic and technological practice, and maximum
Policy Schemes and Trade in Dairy Products | Codex Alimentarius 313
The Codex Alimentarius • 204 food standards for commodities • 47 codes of hygienic or technological practice • 2930 maximum limits for 218 evaluated pesticides • 1112 maximum levels for 292 evaluated food additives • 441 maximum residue levels for 49 evaluated veterinary drugs • Guidelines for 12 contaminants Figure 1 Standards, codes, and recommendations established by Codex Alimentarius.
residue limits (MRLs) for food contaminants have been established by Codex Alimentarius (Figure 1). The Milk Committee, since its establishment in 1958, was integrated into the Codex Alimentarius system. However, its rules and procedures were different from those of Codex Alimentarius for many years. As late as 1993, the Milk Committee was replaced by the ‘Codex Committee for Milk and Milk Products’ and the rules and procedures were aligned with those applicable for the rest of the Codex system.
The Scientific Basis The Codex Alimentarius is science based. Experts and specialists in a wide range of disciplines contribute to every aspect of the code to ensure that its standards withstand the most rigorous scientific scrutiny. Much work is carried out in the form of collaborative studies between individual scientists, laboratories, institutes and universities, and joint FAO/WHO expert committees and consultations. The membership of expert consultations is of critical importance. The credibility and acceptability of any conclusions and recommendations depend to a very large degree on the impartiality, scientific skill, and overall competence of the members who formulate them. For this reason, care is taken in the selection of experts invited to participate. Those selected must be preeminent in their specialty, have the highest respect of their scientific peers, and be impartial and objective in their judgment. They are appointed in their own personal right – not as government representatives or as spokespeople for organizations. The Joint FAO/WHO Expert Committee on Food Additives (JECFA), the Joint FAO/WHO Meetings on Pesticide Residues (JMPR), and the Joint FAO/WHO Expert Meetings on Microbiological Risk Assessment (JEMRA) have generated a large amount of scientifically based food data.
JMPR was established in 1963 with the task of recommending MRLs for pesticide and environmental contaminants in specific food products. JMPR members are independent scientists who are expert in aspects of pesticides and environmental chemicals and their residues. There is close cooperation between JMPR and the Codex Committee on Pesticide Residues (CCPR). CCPR identifies substances requiring priority evaluation. After JMPR evaluation, CCPR discusses the recommended MRLs and, if they are acceptable, forwards them to the Commission for adoption as Codex MRLs. JECFA was established in 1955 with the task of considering chemical, toxicological, and other aspects of contaminants and residues of veterinary drugs in foods for human consumption. JECFA provides the Commission and other Codex bodies with expert advice relating to food additives, contaminants, and residues of veterinary drugs. The Codex Committee on Food Additives (CCFA), the Codex Committee on Contaminants in Foods (CCCF), and the Codex Committee on Residues of Veterinary Drugs in Foods (CCVDF) identify food additives, contaminants, and veterinary drug residues that should receive priority evaluation and refer them to JECFA for assessment before incorporating them into Codex standards. JEMRA was established in 2000 in response to the increasing need for risk-based scientific advice and information and tools to undertake microbiological risk assessment. The objectives of JEMRA are the development and optimization of the utility of microbiological risk assessment (MRA) as a tool to inform actions and decisions aimed at improving food safety and to make it equally available to both developing and developed countries.
Purpose and Organization The task of creating a food code is immense. Food standards need to mirror the dynamic environment in which they will be applied. Product development, changes in trade and consumption patterns, consumer perception, and scientific progress make creation and review of food standards virtually endless. Furthermore, it requires more effort and resources to create standards that, on the one hand, aim at protecting consumers and ensuring fair practices in the sale of food and, on the other hand, facilitating trade. The need to involve scientific experts from consumers’ organizations, expertise from production and processing industries, and food control administrators and traders is obvious. The finalization of food standards and their compilation into a code that is credible and authoritative requires extensive consultation followed up by confirmation of
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final results and, sometimes, a compromise to satisfy divergent but scientifically sound views. The above comprehensive process makes developments slow. On the other hand, once a standard has been adopted, it reflects worldwide consensus and is therefore useful in practice. Objectives of Codex The objective of Codex is to conduct the Joint FAO/ WHO Food Standards Programme, the purpose of which is (a) to protect the health of the consumers; (b) to ensure fair practices in the food trade; (c) to promote coordination of all food standards work undertaken by international governmental and nongovernmental organizations; (d) to determine priorities and to initiate and guide the preparation of draft standards through and with the aid of appropriate organizations; and (e) to finalize food standards and to publish them in a Codex Alimentarius as either regional or worldwide standards. Structure of Codex The CAC is the supreme body of Codex Alimentarius. It meets every year, alternately at FAO headquarters in Rome and at WHO headquarters in Geneva. Plenary sessions are attended by as many as 800 people. Representation at sessions is on a country basis. Senior officials appointed by their governments lead national delegations. Delegations may, and often do, include representatives of industry, consumers’ organizations, and academic institutes. A number of international governmental and non-governmental organizations also attend in an observer capacity. Although they are ‘observers’, the tradition of the CAC allows such organizations to put forward their points of view at every stage except in the final decision, which is the exclusive prerogative of Member Governments. The Commission is empowered to establish three kinds of subsidiary bodies: 1. Codex Committees, which prepare draft standards for submission to the Commission. These are classed as either General Subject Committees or Commodity Committees. The work of the General Subject Committees has relevance for all foods and applies across the board to all commodities. Therefore, these are sometimes referred to as ‘horizontal committees’. They develop all-embracing concepts and principles applying to foods in general, specific foods, or groups of foods, endorse or
review relevant provisions in Codex commodity standards, and, based on the advice of expert scientific bodies, develop major recommendations pertaining to consumers’ health and safety. Currently, there are 10 General Subject Committees (see Figure 2). Commodity Committees have responsibility for developing standards for specific foods or classes of food. In order to distinguish them from the horizontal committees and recognize their exclusive responsibilities, they are often referred to as ‘vertical committees’. Currently, there are 11 Commodity Committees (see Figure 2). 2. Coordinating Committees, through which regions or groups of countries coordinate food standards activities in the region, including the development of regional standards. Coordinating Committees play an invaluable role in ensuring that the work of the Commission is responsive to regional interests and to the concerns of developing countries. Currently, there are six Coordinating Committees (see Figure 2). 3. Ad Hoc International Governmental Task Forces are established to consider closely defined issues within a time-limited period. Currently, three such Task Forces are operating (see Figure 2). Each worldwide committee and task force is hosted by a member country, which is chiefly responsible for the maintenance and administration cost of the committee and for providing its chairperson. Regional committees have no standing host countries; the Chair is elected at meetings.
The Codex Step Procedure Typically, the Codex work program consists of revision of older, outdated texts and the development of new texts. The latter is usually initiated with the consideration of discussion papers. Once a standard, a code, or a guideline is identified as a potential subject for work, it will be developed in three phases, normally comprising eight formal steps (Figure 3): decision to initiate work (constitutes step 1), result• the ing in the adding of the subject to the work program
•
and allocation of the responsibility to prepare a Proposed Draft Codex Standard, a Proposed Draft Codex Code of Practice, a Proposed Draft Codex Guideline, or another proposed draft Codex recommendation; the process of furnishing a draft text (constitutes steps 2–5), resulting in preparing an almost finalized draft, which is adopted as a Draft Codex Standard, a Draft
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FAO
Executive Committee
Food Additives (China) Contaminants in Foods (Netherlands) Pesticide Residues (China) Methods of Analysis and Sampling (Hungary)
Codex Secretariat
CODEX ALIMENTARIUS COMMISSION
Horizontal committees
Food Import and Export Inspection and Certification (Australia)
WHO
Residues of Veterinary Drugs in Foods (USA) General Principles (France) Food Labelling (Canada) Food Hygiene (USA) Nutrition and Foods for Special Dietary Uses (Germany)
Vertical committees
Cocoa Products and Chocolate (Switzerland)* Natural Mineral Waters (Switzerland)* Vegetable Proteins (Canada)* Cereals, Pulses and Legumes (USA)* Sugars (United Kingdom)* Meat Hygiene (New Zealand)*
Fish and Fishery Products (Norway)
Ad Hoc task forces
Antimicrobial Resistance (Republic of Korea)
Fats and Oils (United Kingdom) Fresh Fruits and Vegetables (Mexico)
Biotechnology (Japan)
Regional committees
Africa
Asia
Europe
Latin America and Caribbean
Processed Fruits and Vegetables (USA)
Near East
Milk and Milk Products (New Zealand)
North America and Southwest Pacific
Figure 2 Organization of the Codex Alimentarius Commission. -Adjourned sine die.
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Codex Code of Practice, a Draft Codex Guideline, or another draft Codex recommendation; and the process of finalizing a text (constitutes steps 6–8), resulting in a Codex Standard, a Codex Code of Practice, a Codex Guideline, or another Codex recommendation.
Initiation of New Work A proposal for a standard or another text can be submitted by any member country or any of the interested international organizations registered. In the dairy field, most proposals derive from the work of the IDF. Prior to the approval of new work a project document that details the purpose and scope, its relevance, main
aspects to be covered, need for any expert scientific advice, and timeline for completion is required. Furthermore, an assessment of the formal criteria for the establishment of work priorities is needed. For commodity standards, these are 1. consumer protection from the point of view of health and fraudulent practices; 2. volume of production and consumption in individual countries and volume and pattern of trade between countries; 3. diversification of national legislation and apparent resultant impediments to international trade; 4. international or regional market potential; 5. amenability of the commodity to standardization; 6. coverage of the main consumer protection and trade issues by existing general standards;
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Steps
1, 2, 3
Decision of the CAC to draft a text (step 1). The CAC allocates the drafting responsibility to a subsidiary body. A proposed draft text is elaborated (step 2) and circulated by Codex to member countries and international organizations for comments (step 3).
The proposed draft text and the comments submitted to it are considered at a meeting of the subsidiary body responsible for the drafting process. The text, as amended by the meeting, is progressed to step 5, kept at step 4 or returned to step 3 for redrafting.
Steps
5, 6
8
Step
7
Step
The proposed draft text, as amended, is considered by the CAC (step 5). The result may be adoption or return to step 3 for reconsideration. If adopted, the proposed draft text becomes a draft codex text and it is circulated to member countries and international organizations for comments (step 6)
The draft text and the comments submitted to it at step 6 are considered at a meeting of the subsidiary body responsible for the drafting process. The text, as amended by the meeting, is either progressed to step 8 or returned to step 6 for recirculation.
Step
4
The CAC adopts the draft text as a Codex text. It is published in the Codex Alimentarius and constitutes a reference text for application by the WTO.
Figure 3 Standard elaboration procedure of Codex texts.
7. number of commodities that would need separate standards indicating whether raw, semiprocessed, or processed; and 8. work already undertaken by other international organizations in this field. The first drafting is normally assigned to the Codex Secretariat, a Member Government, an ad hoc working group established among interested Member Governments and organizations, or, in the case of dairy standards, the IDF. Commodity standards follow a uniform format. The structure of codes of practices and guidelines varies according to the nature of the content and the traditions within the Codex Committee where the draft is developed. A draft Codex text is sent to governments and international organizations a number of times in a stepwise procedure, which, if completed satisfactorily, results in the draft becoming a ‘Codex standard’. In an accelerated procedure, the number of steps required for the development of a standard varies from a maximum of eight to a minimum of five. In many cases, steps are repeated. Most standards take 8 years to develop.
current scientific knowledge. The procedure for revision follows the same procedure as used for the initial preparation of new standards. The Commission can, however, decide to omit any other step or steps of the procedure where an amendment proposed by a Codex Committee is either editorial in nature or consequential to provisions in similar standards adopted.
Application and Role of Codex Texts The Codex Alimentarius has relevance to the international food trade and also to domestic legislation and regulation. With respect to the ever-increasing global market, in particular, the advantages of having universally uniform food standards are self-evident. Texts developed by the CAC are applied in the following contexts: 1. as reference texts for the SPS and TBT Agreements of the WTO; 2. as reference texts and/or foundation for national legislation, regional regulation, and trade agreements; and 3. as reference texts for commercial trading parties.
Revision of Codex Standards The Commission and its subsidiary bodies are committed to revision of Codex standards and related texts as necessary to ensure that they are consistent with and reflect
SPS and TBT Agreements of the WTO Both the SPS and TBT Agreements acknowledge the importance of harmonizing standards internationally so
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as to minimize or eliminate the risk of national legislation and regulation becoming barriers to trade. The SPS Agreement
In its pursuance of harmonization, the SPS Agreement has identified and chosen the standards, guidelines, and recommendations established by the CAC for food additives, residues of veterinary drugs and pesticides, contaminants, methods for analysis and sampling, and codes and guidelines of hygienic practice. In other words, Codex texts are considered scientifically justified and have become an integral part of the legal framework as accepted benchmarks against which national measures and regulations are evaluated (Figure 4). Codex texts have already been used as the benchmark in international trade disputes, and it is expected that they will be used increasingly in this regard. As a consequence, interest in Codex activities and participation at the meetings of governments and international inter- and non-governmental organizations has increased. There are no obligations for a government to use Codex standards, only an encouragement. However, as Codex texts by definition are recognized as being scientifically based, a government need not perform a formal risk assessment (see Risk Analysis) if a Codex recommendation is followed. Thereby, a government can save considerable resources. Otherwise, a government can be faced with the SPS requirement to defend and justify
according to scientific evidence every deviating detail in their national legislation. This possibility to choose Codex standards provides the opportunity for countries with economic limitations to follow Codex recommendations and simultaneously comply with the SPS requirements. In countries where the necessary resources are available, additional risk assessment might be carried out in order to justify desired deviations from Codex. A government can only implement stricter food safety requirements than those recommended by Codex, and if justified. This means that Codex recommendations relating to food safety serve as minimum provisions. The TBT Agreement
The basic principle of the TBT Agreement is that any measure should be enforced only if a so-called legitimate objective exists (e.g., prevention of deceptive practices, meet quality and performance requirements). The legitimate objective should be transparent in order to avoid disguised protection of domestic production and to avoid arbitrary decisions. The TBT Agreement does not make reference to any particular international organization to be used as the ‘benchmark’. With respect to food, however, it is generally recognized that Codex Alimentarius serves this function (Figure 5). It is relatively easy for a government to justify that a particular part of an international standard, for example, a
The SPS Agreement The Agreement on the Application of Sanitary and Phytosanitary Measures acknowledges that governments have the right to take sanitary and phytosanitary measures necessary for the protection of human health. However, the SPS Agreement requires them to apply those measures only to the extent required to protect human health. It does not permit Member Governments to discriminate by applying different requirements to different countries where the same or similar conditions prevail, unless there is sufficient scientific justification for doing so. Article 2.2 of the SPS Agreement states: "Members shall ensure that any sanitary and phytosanitary measure is applied only to the extent necessary to protect human, animal or plant life or health, is based on scientific principles and is not maintained without sufficient scientific evidence ..." Article 3.1 of the SPS Agreement states: "To harmonize sanitary and phytosanitary measures on as wide a basis as possible, Members shall base their sanitary and phytosanitary measures on international standards, guidelines or recommendations, where they exist, except as otherwise provided for in this Agreement." Figure 4 The Agreement on the Applications of Sanitary and Phytosanitary Measures (SPS).
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The TBT Agreement The Agreement on technical barriers to trade seeks to ensure that technical ,regulations and standards, including packaging, marking, and labeling requirements and analytical procedures for assessing conformity with technical regulations and standards do not create unnecessary obstacles to trade. Article 2.4 of the TBT Agreement states “Where technical regulations are required and relevant international standards exist or their completion is imminent, Members shall use them, or the relevant parts of them, as a basis for their technical regulations except when such international standards or relevant parts would be an ineffective or inappropriate means for the fulfilment of the legitimate objective pursued, for instance because of fundamental climatic or geographical factors or fundamental technical problems.” Article 2.5 of the TBT Agreement states “.... Whenever a technical regulation is prepared, adopted or applied for one of the legitimate objectives......., and is in accordance with relevant international standards, it shall be rebuttably presumed not to create an unnecessary obstacle to international trade.” Article 2.6 of the TBT Agreement states "With a view to harmonizing technical regulations on as wide a basis as possible, Members shall play a full part, within the limits of their resources, in the preparation by appropriate international standardizing bodies of international standards for products for which they have either adopted, or expect to adopt, technical regulations." Figure 5 The Agreement on Technical Barriers to Trade (TBT).
labeling requirement, is not appropriate in a particular country or that additional requirements are needed locally. It is allowed to deviate from Codex TBT-related provisions in both stricter and less strict directions, if an appropriate legitimate objective exists. Codex regulations, which are not aiming at protecting human health, are therefore merely to be seen as guidelines. Codex standards may not be the only body that provides reference provisions, as objectives of the TBT Agreement are broader than those of Codex Alimentarius. National Legislation and Regulation The harmonization of food standards is generally viewed as a prerequisite to the protection of consumer health as well as allowing the fullest possible facilitation of international trade. For that reason, both SPS and TBT Agreements encourage the international harmonization of food standards. While the growing world interest in all Codex activities clearly indicates global acceptance of the Codex philosophy – embracing harmonization, consumer protection, and facilitation of international trade – in practice, it is difficult for many countries to accept Codex standards in the statutory sense. Differing legal formats and administrative systems, varying political systems, and sometimes the influence of national attitudes and concepts of sovereign rights impede the progress of
harmonization and deter the acceptance of Codex standards. Most countries have, however, responded by introducing long-overdue or reviewed/aligned existing food legislation and Codex-based national standards and by establishing or strengthening food control agencies.
Regional Regulation and Trade Agreements The Uruguay Round Agreements provide groups of member countries the opportunity to enter into trade agreements among themselves for the purpose of liberalizing trade. So far, three such agreements have been established, all of them having adopted measures consistent with the principles embraced by the SPS and TBT Agreements and which relate to Codex standards: (North American Free Trade Agreement • NAFTA between Canada, the United States, and Mexico)
•
includes two ancillary agreements dealing with sanitary and phytosanitary measures and technical barriers to trade. With regard to SPS measures, Codex standards are cited as basic requirements to be met by the three member countries in terms of health and safety aspects of food products. The Food Commission of MERCOSUR (Treaty of Asuncio´n establishing the Southern Common Market between Argentina, Brazil, Paraguay, and Uruguay)
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•
recommends a range of Codex standards for adoption by member countries and is using other Codex standards as points of reference in continuing deliberations. APEC (Asia–Pacific Economic Cooperation between 18 Asian and Pacific countries) has drafted a Mutual Recognition Arrangement on Conformity Assessment of Foods and Food Products. This calls for consistency with SPS and TBT requirements as well as with Codex standards.
In addition, the EU (European Union) directives and regulations frequently refer to the Codex Alimentarius as the basis for their requirements. Commercial Trade Besides providing the reference for national legislation, the texts established by the CAC, in particular the commodity standards, are frequently used as references in commercial trade, independent of legislation. Such reference points may be used for price setting and for specifying any deviations agreed.
• • • • • • • •
Coulommiers, Cream Cheese, Camembert, Brie, Extra hard Grating) (2008); whey cheese (2006); fermented milks (2008); evaporated milks (1999); sweetened condensed milks (1999); milk powders and cream powders (1999); edible casein products (2001); whey powders (2006); and lactose (now part of the standards for sugars) (1999).
Revisions have not yet been finalized for named variety processed cheese, processed cheese, and processed cheese preparations. The nonrevised standards date back to the 1960s and 1970s but are still valid as references.
Other Commodity Standards From a dairy perspective, international standards for nondairy foods that contain significant dairy ingredients and/ or are intended to replace dairy products in consumption patterns are of interest. The most important of these commodities regulated by Codex are
Codex Texts Relevant for Dairy Production and Trade
for chocolate, cocoa butter, coconut milk and • standards three standards covering various blends of preserved
The Codex Alimentarius includes general texts applicable across-the board to all foods (general standards, codes of hygienic practices), other codes of practices (technology, control), and commodity-specific texts (commodity standards, commodity-specific codes of practices).
for infant formula, follow-up formula, • standards canned baby foods, and processed cereal-based foods
skimmed milk and vegetable fat;
for infants and young children; and
• vegetable protein products and soy protein products.
Milk Product Standards When Codex decided to adjourn the old Milk Committee in 1993 and replace it with the Codex Committee on Milk and Milk Products, it was agreed that the file of standards established earlier needed extensive revision. This task has almost been accomplished. Updated versions of the milk product standards are as follows (see Policy Schemes and Trade in Dairy Products: Standards of Identity of Milk and Milk Products):
Food Hygiene Food hygiene constitutes the cornerstone in Codex food safety activities. Microbiological hazards constitute the greatest risk for human health. In recent years, focus has been on the development of appropriate tools to assess and manage risks associated with the intake of microbiological hazards through food. New metrics have been identified and described, but they are not implemented as yet. Risk managers including Codex continue using general and specifically targeted good hygienic practices supplemented by the HACCP (Hazard Analysis and Critical Central Point) approach. Of particular interest to the dairy sector are the following Codex hygiene texts that build on well-established concepts:
(2006); • butter dairy fat spreads (2008); • milk fat products (including butter oil, anhydrous milk • fat, and ghee) (2006); and prepared creams; • cream cheese (2008); • unripened cheese, including fresh cheese (2001); • cheese in brine (1999); of Practice of General • individual cheese • Code Hygiene (2003); varieties (Mozzarella, Cheddar, • Danbo, Edam, Gouda, Havarti, Samsø, Emmental, The HACCP • Application (1997);System and Tilsiter, Saint-Paulin, Provolone, Cottage Cheese,
Principles for Food Guidelines for its
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for the Establishment and Application of • Principles Microbiological Criteria (1997); on the Application of General Principles of • Guidelines Food Hygiene to the Control of Listeria monocytogenes in Ready-to-Eat Foods (2007); and
of Hygienic Practice for Powdered Formulae for • Code Infants and Young Children (2008). Other texts that introduce more risk-based approaches for food hygiene management include of Hygienic Practice for Milk and Milk Products • Code (2004); and Guidelines for the Conduct of • Principles Microbiological Risk Management (2007); and for the Validation of Food Safety Control • Guideline Measures (2008). From a dairy perspective, it is also worth noting the existence of the Codex Guidelines for the Preservation of Raw Milk by the Lactoperoxidase System from 1991. The guidelines for this system apply only where the infrastructure does not provide facilities for refrigeration. Food Labeling Labeling constitutes a significant part of most food regulations. A number of standards and guidelines for the labeling of foods, primarily prepackaged foods, have been developed. These standards and guidelines have gained widespread use worldwide and are implemented in the national legislation of most countries. For dairy products, the most relevant are Standard for the Labelling of Prepackaged • General Foods (2008); Guidelines on Claims (1991); • General Guidelines Labelling (2006); and • Guidelines onforNutrition Use of Nutrition and Health Claims • (2008). Among the issues currently being considered are issues related to nutrition labeling and labeling aspects of foods derived from modern biotechnology. The General Standard for the Use of Dairy Terms is especially of interest from the dairy point of view. It provides guidance on where and how to use terms in the labeling and marketing of foods (see Labeling of Dairy Products). Food Additives Codex addresses food additives in horizontal texts as well as in commodity standards. Immense resources have been allocated to the establishment of a comprehensive General Standard for Food Additives. This standard is kept under constant review (see Additives in Dairy
Foods: Consumer Perceptions of Additives in Dairy Products; Emulsifiers; Legislation; Safety; Types and Functions of Additives in Dairy Products). Contaminants Codex addresses contaminants in horizontal texts as well as in commodity standards. A comprehensive General Standard for Contaminants and Toxins in Food is the most important. This standard is kept under constant review. In addition, the Code of Practice for the Reduction of Aflatoxin B1 in Raw Materials and Supplementary Feeding Stuffs for Milk-Producing Animals (1997) and a Code of Practice for the Prevention and Reduction of Dioxin and Dioxin-like PCB Contamination in Food and Feeds (2006) are of interest to the dairy sector. Control of contaminant levels is also addressed in the HACCP System and Guidelines for its Application (see Contaminants of Milk and Dairy Products: Environmental Contaminants; Contamination Resulting from Farm and Dairy Practices; Nitrates and Nitrites as Contaminants). Residues of Veterinary Drugs in Foods Within the veterinary field, Codex has established a database on MRLs for individual foods and categories of foods, including those that specifically relate to milk. Also of specific relevance to the dairy sector are the Guidelines for the Establishment of Regulatory Programme for the Control of Veterinary Drugs in Food and a Code of Practice for Control of the Use of Veterinary Drugs (1993) and a Code of Practice to Minimize and Contain Antimicrobial Resistance. Pesticide Residues Codex has established a huge database on recommended maximum limits for individual foods and categories of foods. Food Import and Export Inspection and Certification Systems The objective of Codex to facilitate the free movement of foods is also pursued through the establishment of recommendations for food control and inspection agencies. For the dairy sector, the most relevant texts developed include for Food Import and Export Certification • Principles (1995); for Design, Production, Issuance and Use of • Guidelines Generic Official Certificates (2007); for Food Import Control Systems (2006); • Guidelines Principles for Traceability/Product Tracing as a Tool • Within a Food Inspection and Certification System (2006);
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Export Certificate for Milk and Milk Products • Model (2008, amended 2010); and for the Judgement of Equivalence of • Guidelines Sanitary Measures Associated with Food Inspection and Certification Systems (2008). Methods of Analysis and Sampling In principle, any criteria specified in an established Codex text need to be followed up by the identification of appropriate and validated methods of sampling and analysis. Codex frequently reviews and updates an inventory of endorsed methods (Analysis of Milk and Dairy Products). See also: Additives in Dairy Foods: Consumer Perceptions of Additives in Dairy Products; Emulsifiers; Legislation; Safety; Types and Functions of Additives in Dairy Products. Contaminants of Milk and Dairy Products: Contamination Resulting from Farm and Dairy Practices; Environmental Contaminants; Nitrates and Nitrites as Contaminants. Labeling of Dairy Products. Policy Schemes and Trade in Dairy Products: Standards of Identity of Milk and Milk Products. Risk Analysis.
Further Reading FAO/WHO (2006) Understanding the Codex Alimentarius, 3rd edn. Rome: Food and Agriculture Organization of the United Nations and World Health Organization. IDF (1996) Codex standards in the context of world trade agreements. Proceedings of the IDF Seminar held in Brussels. November 1995. IDF Bulletin No. 310. Brussels, Belgium: International Dairy Federation. IDF (1997) The influence of Codex standards on international trade in dairy products. Abstracts of the International Symposium. Du¨sseldorf, Germany, 6–7 September 1996. IDF Bulletin No. 319/1997. Brussels, Belgium: International Dairy Federation. IDF (1998) Codex procedures and their importance – the new world for dairy products. Proceedings of the International Symposium. Chicago, IL, USA, 3–4 November 1997. IDF Bulletin No. 331/1998. Brussels, Belgium: International Dairy Federation. IDF (1999) Overcoming barriers to world trade in food and dairy products. Proceedings of the International Symposium. Frankfurt, Germany, 7–8 November. IDF Bulletin No. 349/2000. Brussels, Belgium: International Dairy Federation. Joint FAO/WHO Food Standards Programme (2007) Procedural Manual for the Codex Alimentarius Commission, 17th edn. Rome: Food and Agriculture Organization of the United Nations and World Health Organization. Joint FAO/WHO Food Standards Programme Codex Alimentarius. Rome: Food and Agriculture Organization of the United Nations and World Health Organization. Kozak J (1998) The Influence of Codex Standards on Dairy and the World Trade Organization. IDF Bulletin No. 343/1999. Brussels, Belgium: International Dairy Federation.
Standards of Identity of Milk and Milk Products C Heggum, Danish Dairy Board, Aarhus, Denmark ª 2011 Elsevier Ltd. All rights reserved.
Introduction When compared to other food sectors, the dairy sector has a distinct tradition of regulating production and trade through identity standards. This tradition derives primarily from the cooperative structure of the sector prevailing in the late 1800s and the beginning of the 1900s, and was introduced mainly by exporting countries in support of their trade activities and by countries with a significant domestic competition. Since the mid 1980s, food legislation in general has been subject to substantial changes. General (horizontal) regulation supersedes commodity (vertical) legislation. This change is caused mainly by changed budgetary priorities at national governments level and by the entire focus on food safety issues. The general trend is that vertical legislation decreases, and specific dairy legislation even disappears in some countries. Dairy legislation itself has changed as well. A few decades ago, dairy legislation was, in many countries, characterized by a positive approach (i.e., what is not specified is not permitted), the most significant result being a vast number of identity standards. Today, most dairy legislation has been aligned with the approach used for other food sectors, where everything considered safe and suitable is allowed in principle, and governed primarily by informative labeling. Identity standards fit into the latter approach by providing the specific conditions for referring to a regulated name without by themselves enforcing general restrictions. The dairy trade needs some degree of international regulation to ensure fair practices and to minimize barriers to trade. For the enforcement of the WTO trade agreements, the international trade further needs a sound reference to enable monitoring of whether import restrictions are justified, and if not, to provide the tool for pursuing the goal of avoiding technical barriers to trade. This article focuses mainly on the Codex standards of identity, as these have the greatest potential for widespread use.
Role of Identity Standards Identity standards serve a multifunctional role as follows: 1. As legislative reference texts Nationally, such reference texts may be needed to facilitate understanding and management of other
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regulatory means (e.g., safety limits, additive provisions, inspection practices, certification, statistics, monitoring import/export quotas) Internationally, reference texts are intended to the WTO system to solve trade disputes • enable (Codex standards); governments (and other parties concerned) in • assist the elaboration and implementation of national food legislation in an appropriate manner; and guide international trade. 2. As facilitators of trade International harmonization is a prerequisite for free movement of products, which can be achieved only through international cooperation. The result of harmonization is, as per definition, the minimization of barriers to international trade. The establishment of proper reference texts is a prerequisite for harmonization. If trade is to be facilitated, it is necessary to ensure that such reference texts are kept up-to-date with respect to technological, scientific, and practical knowledge. Otherwise, they may become obstacles to trade. 3. As promoters of fair trade practices The most important objective of an identity standard for milk products is to promote fair trade practices through specifying detailed conditions for the use of specific names reserved for well-defined milk products. International standards also assist in protecting against misleading presentations and practices, for example, a false description of the nature of the product in question. However, achieving international consensus is difficult, mainly because those involved in the process are also commercially competing on the world market. On the other hand, if no difficulties existed, there would be no commercial need for attempting harmonization! With regard to milk and milk products, the most important international text for supporting this objective is the Codex General Standard for the Use of Dairy Terms which reserves, with a few exemptions, names and terms related to dairy products for milk and milk products. Many dairy countries worldwide have established similar regulations.
•
Identity standards normally do not aim specifically at protecting public health, as this objective is typically regulated in more general legislative texts (e.g., Codes of Practices, hygiene rules, MRLs).
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Standard Setting National Standards Several countries do, despite of the general change in the approach to food regulation, retain a significant number of specific identity standards for milk products in their national legislation. This is particularly the case in countries where the dairy industry has played and still plays a significant role in the national economy and retention is generally supported by the domestic dairy industries. On the other hand, very few new identity standards for milk products are being established. Examples of dairy nations that retain a significant number of identity standards for milk products include Canada, Denmark, France, Germany, Greece, Gulf countries, Italy, Japan, MERCUSOR countries (Argentina, Brazil, Uruguay, and Paraguay), South Africa, Spain, Switzerland, and the United States. Certain countries, mainly European, have, in addition to generic identity standards, established systems for reserving certain product names as protected geographical designations. In general, only the basic and the most significant milk products are regulated today by identity standards. Typically, national legislation that includes identity standards for milk products, retain such for drinking milk, traditional fermented milks characterized by specific microorganisms, individual cheese varieties, milk powders, and butter. The cheese varieties most commonly regulated by national identity standards are Brie, Camembert, Cheddar, Cottage Cheese, Cream Cheese, Danbo, Edam, Emmental, Gouda, Mozzarella, Parmesan, Provolone, and Tilsiter. Regional Standards The Stresa Convention
The first international standard-setting body within the dairy sector was the so-called Stresa Convention, named
after the Italian city Stresa. The Stresa Convention, adopted in 1951, lays down a number of standards for individual cheeses and stipulates regulations for the use of these product names. The International Dairy Federation (IDF) played a significant role in its establishment. Originally, eight European countries ratified the Convention. Several of these have now left. For this reason, and since the standards regulated by the Convention have hardly been up-dated since their establishment, the Stresa Convention today plays an insignificant role. However, the principles contained therein have been adopted in other cheese regulations at national, regional, and international levels (Figure 1). EU standards
With the establishment of the European Common Market, a number of regional identity standards have been developed, particularly during the 1970s and 1980s. Identity standards have been established for preserved milk products (milk powder, evaporated milks, sweetened condensed milks), edible casein products, butter, including reduced fat butters, and drinking milk. The EU standards are mandatory in all EU member states. At the beginning of the 1990s, the strategy for establishing regional standards was abandoned and replaced by a system of registering protected designations of origin and certificated products of specific character. Gulf standards
The Gulf Cooperation Council (GCC), established in 1981, develops Gulf standards relating to foodstuffs, intended for adoption by its member states (Saudi Arabia, Kuwait, Bahrain, Qatar, Oman, and the United Arab Emirates). Their influence has become increasingly significant. Most dairy products are currently regulated by the GCC identity standards: raw milk (cow, goat, and
Reservation of four cheese names to be used only by the country in which the names were first developed (Annex A): Rquefort (France), Gorgonzola (Italy), Parmiggiano Romano (Italy), and Pecorino Romano (Italy). Mutual permission to use 30 cheese names on domestic and international markets, on the labels and by reference anywhere, provided adherence to the identity standards subordinated (Annex B): Cheese name: Origin of name: Danablu, Danbo, Elbo, Fynbo, Havarti, Maribo, Denmark Mycella, Samsø, and Tybo Brie, Camembert and Saint Paulin France Gruyere France and Switzerland Asiago, Caciocavallo, Fiore Sardo, Fontina, Italy Provolone Edam, Frisian, Gouda, Leyden The Netherlands Gudbrandsdalsost, Nøkkelost Norway Ädelost, Herregaardsost, Svecia Sweden Emmental, Sbrinz Switzerland Figure 1 Main elements of the Stresa Convention.
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camel), drinking milks (pasteurized, sterilized, UHT, flavored), preserved milk products (dried milk, evaporated milk, sweetened condensed milk, lactose, and caseinates), fermented milk including yogurt (with and without heat treatment after fermentation), cream, butter, milk fat products (anhydrous milk fat, butteroil, and ghee (samn)), processed cheese (including spreadable), cheese, whey cheese, and a number of individual cheese varieties, which besides all varieties standardized by Codex Alimentarius also include Feta, Domiati, Gruyere, Hallom, Kashkaval, and Ras. These standards are subsequently adopted by the GCC member states.
Milk Products in 1993. The new committee has almost completed its work after a thorough revision of all the existing standards as well as elaborating new standards for additional milk products. When the work is fully completed in 2010, approximately 34 specific identity standards for various milk products will have been described. Codex standards are intended as recommendations for adoption by member states and for use by the commercial trade. However, they also serve as international references for application in trade disputes brought to the WTO for settlement (see Policy Schemes and Trade in Dairy Products: Codex Alimentarius).
GMC standards
In 1991, the MERCUSOR (Treaty for the Organization of a Southern Common Market) was established with four countries participating (Argentina, Brazil, Uruguay, and Paraguay). To facilitate trade, harmonized food legislation is being developed by the Common Market Group (GMC). GMC standards are mandatory in all MERCUSOR member states. Identity standards for the following milk products have been established: butter, butteroil, dairy cream, dairy cream for industrial use, UHT milk, fluid milk for industrial use, powdered milk, dulche de leche, food caseinates, food casein, cheese, grated cheese, processed cheese, powdered cheese, and the individual cheese varieties Danbo, Tilsit, Mozzarella, Minas Frescal, Tybo, Cottage Cheese, Tandil, Pategras, Sandwich, and Prato. International Standards Codex Alimentarius
The elaboration of international milk product standards was initiated several years prior to the establishment of Codex Alimentarius. In 1958, on the initiative of the IDF, the FAO established the Joint Committee of Government Experts on the Code of Principles Concerning Milk and Milk Products. The establishment of this ‘Milk Committee’ showed the need for international cooperation in the area of food and triggered the establishment of Codex 4 years later. The Milk Committee was active until 1990, during which period 52 international milk product standards and several other texts related to milk products were developed. However, as the running of the Milk Committee was financed by the FAO, financial priorities resulted in difficulties that hampered the continuation of the work. The Committee was very close to being adjourned at the beginning of the 1990s. In the light of the elaboration of the new WTO trade agreements, however, a FAO/WHO Conference held in 1991 highly recommended the revision of all commodity standards developed by Codex. This was the main reason for establishing the new Codex committee for Milk and
World Customs Organization
The World Customs Organization (WCO) is an independent, inter-governmental organization, the purpose of which is to enhance the effectiveness and efficiency of customs administration on a worldwide basis. The most successful instrument developed by the WCO is the Harmonized Commodity Description and Coding System (Harmonized System). The Harmonized System (HS) is a multipurpose international product nomenclature covering about 5000 commodity groups. Each commodity group is identified by a unique six-digit code and is defined in such a way as to facilitate uniform classification. In many cases, explanatory notes provide identity descriptions of individual commodities. More than 177 countries use the system as a basis for determining customs tariffs and for the collection of international trade statistics. Other uses include the following: the basis for rules of origin; the collection of internal taxes; the basis for trade negotiations (e.g., the WTO schedule for tariff concessions), transport tariffs and statistics, and the monitoring of controlled goods (such as hazardous wastes, narcotics, and chemical weapons). The majority of dairy products are found in Chapter 4 of the Harmonized System. However, Chapter 4 does not cover lactose (Chapter 17), ice cream, and dairy spreads (Chapter 21) or albumins, including concentrates of two or more whey proteins (Chapter 35). The work of the WCO has become increasingly important as world trade in dairy products continues to grow. In particular, product definitions and classification within the Harmonized System greatly influence decisions in product development and marketing. In addition, the Harmonized System is incorporated by individual governments into domestic operating procedures for a variety of purposes. Among these are internal taxes, monitoring of controlled goods, freight tariffs, transport statistics, price monitoring, quota controls, and more. Product definitions developed by the WCO in support of the HS do not necessarily correspond with the
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definitions established in support of food legislation. The individual definitions serve different purposes and are usually developed independently from each other. Consequently, a product labeled with a name in accordance with the food regulation in force may not be classified accordingly by the HS and vice versa.
Codex Milk Product Standards Key Prerequisites for Establishing a Codex Milk Product Standard Consumer protection from the point of view of health and fraudulent practices is one of the key objectives of Codex activities. As health protection alone does not justify the establishment of a commodity standard as such, Codex commodity standards primarily aim at protecting the consumers from fraudulent practices and ensuring fair trade practices. Public health protection is covered by other horizontal and commodity-specific Codex texts concerning hygiene, additives, and contaminants. Whether a risk of fraudulent practice exists depends on the following: degree of consumer’s recognition of the product • The (or designation), expressed as the number of countries
• •
in which the product is manufactured and consumed; The needs of importing-countries to require specific labeling to ensure that adequate consumer information is provided with regard to the nature of the product; and Existing differences in national definitions of the product.
An estimate of the global production may be needed to ensure that drafting resources are not wasted on products that are insignificant in international trade. Production and trade statistics are important tools for evaluating whether an international standard will be justified. Information on the number of countries involved in the trade of the product in question is used for guiding the decision. Local trade between a smaller group of countries (e.g., within one trading block) is not a sufficient justification. It is apparent that the number of countries having established national identity standards and/or industry standards governing the use of a certain product name constitutes a potential for trade problems. Significant deviation between such standards may alone trigger a need to harmonize at international level (Figure 2). Principal Contents of Codex Milk Product Standards Codex milk product standards aim at describing the nature (identity) of the products by addressing the essential
characteristics associated with them. The areas covered by such standards are as follows: characteristics (common understanding of the • Identity meaning of a product name including an end-product
• •
description, principal method(s) of manufacture, compositional requirements, and ingredients) Food additives that are safe and technologically justified Labeling provisions that are needed in addition to general labeling rules and/or that are considered necessary for the correct application of a general labeling principle.
This approach is based on the almost completed revision of the milk product standards developed in the 1960s and 1970s. The former versions contained primarily provisions that aimed at ensuring technical product quality and product identity. Elements that are not justified as essential for the identity of the product cannot be addressed in the standards. Where found appropriate, such material can be provided as information on usual patterns of production in appendices to the standards. The content of an appendix (1) is intended to be applied by commercial trade parties (where found useful), (2) need not be implemented in national legislation, and (3) is not intended to be used by the WTO as reference material. Typical information provided in appendices indicates quality limits on nonhazardous contaminants (e.g., copper); technical quality guidelines; characteristic flavor and taste; nonessential sizes and shapes; and nonessential manufacturing practices. In addition to the principal contents, food safety and general labeling issues are addressed by the Codex milk product standards, mainly by identifying and referring to other relevant Codex texts applicable to the product (e.g., contaminants, hygiene, labeling, and methods of sampling and analysis). General Approach to Codex Milk Product Standards Scope
The Codex milk product standards apply both to retail products sold directly to the consumer and to non-retail products intended for further processing (e.g., as ingredients in other milk products and foods, or for processing into processed cheese, cutting/slicing, drying, fermentation, etc.). Most of the standards do not address addition of nondairy ingredients intended to provide specific non-dairy flavors (such as fruit preparations, meat, vegetables, spices, and sweeteners). The provisions governing such additions are located in the Codex General Standard for the Use of Dairy Terms (GSUDT). According to the GSUDT, such products are identified as ‘composite milk products’ and
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Identification of need
It is concluded that there is a need for a Codex standard for a certain dairy product. Supporting data on production and trade and justification for the work is furnished.. A proposal is submitted for consideration by the Codex Committee for Milk and Milk Products (CCMMP).
If the CCMMP agrees, the proposal is forwarded for approval as new work by the Codex Alimentarius Commission (CAC).
Steps
1, 2, 3
Consideration by the CCMMP
Endorsement of the CAC to establish a standard (step 1). The Proposed Draft Standard, typically prepared by IDF or an ad hoc working group, is circulated by Codex to member countries and international organizations for comments (step 3).
The Proposed Draft Standard and the comments submitted to it are considered at a meeting of the CCMMP. The standard may be amended by the meeting and is either progressed to step 5 or returned to step 3 for redrafting. If returned to step 3, IDF or a new working group is usually requested to redraft it in light of the comments made and the debate and conclusions that took place at the session. The new draft is circulated for comments again at step 3.
Steps
5, 6
8
Step
7
Step
The Proposed Draft Standard, as amended, is considered by the CAC (step 5). The result may be adoption or return to step 3 for reconsideration. If adopted, the Proposed Draft Standard becomes a Draft Codex Standard and it is circulated to member countries and international organizations for comments (step 6). IDF may be requested to redraft the text in light of the comments submitted at this step to provide a further consolidated text for consideration at step 7.
The (further consolidated) Draft standard is considered at a meeting of the CCMMP. The text, as amended by the meeting, is either progressed to step 8 or returned to step 6 for recirculation. If progressed to step 8, the additives provisions are submitted for endorsement by the Codex Committee for Food Additives (CCFA), and the labeling provisions are submitted for endorsement by the Codex Committee for Food Labeling. Endorsements take place at meetings of these horizontal committees.
Step
4
The CAC adopts the Draft standard, eventually with amendments as suggested by the CCFAC and/or the CCFL. It then becomes a Codex Milk Product Standard. It is published in the Codex Alimentarius and constitutes a reference text for application by the WTO.
Figure 2 Typical process of elaboration of a Codex milk product standard.
the milk product names can be used in combined designations of composite milk products, provided that the added nondairy ingredients are not intended to replace any milk constituent(s), in whole or in part. Principal method of manufacture
Milk product designations often originate from descriptive terms that refer to the way in which they are manufactured, for instance, milk powder, evaporated milk, fermented milk, and so on. As a natural consequence, the principal method of manufacturing is reflected in the identity description of many milk products. This approach is often much simpler than attempting to describe all end-product characteristics in full detail. One of the general principles in the WTO Trade Agreements is the principle of equivalence. Since
methods of manufacture applied are not static, and because identity standards should not, unless specifically justified, constitute an obstacle for technological development, most Codex standards for milk products include appropriate wording that, in addition to the principal method of manufacturing, provides for alternative technologies that achieve an equivalent outcome. Raw materials
The general approach is that all milk products derived from any milking animal species can be used as raw material for milk products. This means that milk products can be processed from milk derived from cows, goats, sheep, buffaloes, yaks, camels, reindeer, and so on. Corresponding provisions address whether the dairy species need be labeled (see Labeling of Dairy Products). However, many individual cheese varieties (but not all)
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are characterized by the origin of the milk (texture, color, flavor) wherefore restrictions on type of milk may be imposed. Further, in general, any milk constituents and milk products, including intermediate products, can be used, including those needed for reconstitution and recombination, as long as the compositional criteria and other characteristics of the products are met. There are a few exemptions from this approach (e.g., milk powders). Composition
The minimum and/or maximum requirements for the composition of end products constitute a core part of any identity standards. For all milk product standards established by Codex, such criteria comprise milk fat, and additional criteria as necessary according to the nature and characteristics of the product in question (see Figure 3). The compositional sections of the standards typically specify the reference composition and, in addition, the limits and conditions for modifying the composition of the reference product, by specifying, for example, the range of composition permitted. Therefore, some compositional criteria are absolute (minima or maxima). The Codex General Standard for the Use of Dairy Terms states that products that have been modified in composition beyond the composition of the reference product identified in the relevant standard are only allowed if the following principles are adhered to:
•
That a qualifier that clearly describes the compositional modification made is placed in association with the name of the product
Milk product
Milk fat
Milk protein
Moisture or dry matter
Creams Fermented milks
冑 冑
Butter Dairy fat spreads Butteroil Evaporated milks Sweetened condensed milks Milk and cream powders Cheese Individual cheese varieties Caseins Caseinates Whey powders
冑 冑 冑 冑 冑
冑 冑
冑
冑
冑
冑 冑 冑
冑 冑 冑 冑
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the modification is achieved only by the addition • That and/or withdrawal of milk constituents such modification does not alter the basic identity • That of the product and is within the limitations identified in the Codex identity standard concerned. See Figure 4 for examples of modifications covered. In some cases, compositional modification is not desirable, for instance, protein contents below the minima specified and fat reductions below the absolute minima, where such are specified (Figure 4). Food additives
A positive list of justified and permitted groups of additives and/or individual additives is provided. Technological justification for each functional group of additives and for each additive, with a numerical ADI-value listed, is a prerequisite for acceptance by Codex. The IDF provides the information necessary for this purpose.
Labeling
The labeling section makes cross-reference to generally applicable labeling standards and lays down additional labeling provisions as well as practical guidance on the application of general labeling principles (see Labeling of Dairy Products).
Supporting methods of sampling and analysis
Any criteria specified in a Codex standard are to be supported by appropriate analytical methods for verifying compliance. Recognized methods are published in the Codex Alimentarius.
Solidsnot-fat
Lactose Ash
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Other
Acidity, microorganisms flavoring ingredients 冑
冑 冑
冑 冑 冑
冑 冑 冑
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Ratio of whey protein to casein Variety specific Casein, free acid pH, casein pH
Figure 3 Components regulated by compositional requirements in certain Codex milk product standards.
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Fat-modified products such as high fat, reduced fat (light), low fat, or skimmed/nonfat, Purified products such as demineralized whey powder, lactose-free milk powder, and cholesterol-free butter ; Fortified products such as vitaminized milk powder and calcium enriched yogurt ; Compositionally altered products such as fractionated butter. Figure 4 Examples of compositionally modified milk products.
The Individual Codex Milk Product Standards Drinking milk
Codex has not established, nor does it intend to establish, an identity standard for drinking milk. Although manufactured and marketed in most countries worldwide, drinking milk is primarily sold domestically. Hence, due to significant local differences in consumer perception, attempts to harmonize this area would probably fail. However, some general principles governing drinking milk have been provided in the Codex GSUDT. These principles are targeted national regulations in this area. The GSUDT states that, in general, drinking milk that is modified in composition by the addition and/or withdrawal of milk constituents may be identified with a name using the term ‘milk’, provided that a clear description of the modification to which the milk has been subjected is given in close proximity to the name. However, fat and protein adjustment may be permitted without such description only if milk is sold where such adjustment is permitted in • the the country of retail sale; minimum and maximum limits of fat and/or pro• the tein content (as the case may be) of the adjusted milk
•
are specified in the legislation of the country of retail sale (the protein content shall be within the limits of natural variation within that country); and the adjustment methods permitted by the legislation of the country of retail sale are used. Such methods shall include only the addition and/or withdrawal of milk constituents without altering the whey protein-tocasein ratio (as achieved by traditional ultrafiltration technology).
Creams
The standard for cream addresses ‘cream’ (bulk) and ‘prepared creams’ intended for direct consumption. The standards include a definition of cream and descriptions of recombined and reconstituted cream, respectively. A number of specific consumer products are described, including prepackaged liquid cream, whipping cream, whipped cream, cream packed under pressure, thickened cream, and fermented cream. The standard characterizes creams as milk products comparatively rich in fat (absolute minimum of 10% milk fat), in the form of an emulsion of fat in skimmed milk, obtained by physical separation from milk or by recombination/reconstitution of specified raw materials.
Fermented milks
The standard characterizes fermented milks as milk products obtained by fermentation of milk by the action of specific microorganisms and resulting in a reduction of pH with or without achieving coagulation. These specific microorganisms shall be viable, active, and abundant in the product. In addition, the standard includes specific categories of fermented milks that are additionally characterized by specific microorganism(s) used for the fermentation, which organisms during product shelf life are present in numbers exceeding 107 cfu g 1 (plain part of the end product). Specific categories will include yogurt, kefir, acidophilus milk, and kumys. The products may be heat treated after fermentation, in which case the name shall be ‘heat treated fermented milk’. Reference to the specific names defined by minimum bacterial counts is obviously not relevant in these products. The standard aims also at including fermented milks modified in composition by concentration of the protein to minimum 5.6% – identified as ‘concentrated fermented milks’. This standard (being the only one at that) includes flavored products (i.e., plain fermented milk to which other foods/ingredients, such as fruit, sugar/sweetener, or cereals, have been added to obtain a characteristic nondairy flavor).
Butter and milk fat products
Three milk product standards for yellow milk fats exist: one for butter, one for dairy fat spreads, and a third for milk fat products (covering the names ‘milk fat’, ‘anhydrous milk fat’, ‘butteroil’, ‘anhydrous butteroil’, and ‘ghee’). Butter is, according to the Codex standard, characterized by being a fatty milk product, principally in the form of an emulsion of the water-in-oil type, with minimum 80% milk fat, maximum 16% moisture, and maximum 2% milk solids-not-fat. These compositional criteria are specified as absolute. Unlike many national standards, no upper milk fat limit is specified. Instead, it is stated that fat contents above 95% trigger the use of a qualifier in association with the term ‘butter’; such a qualifier can be, for instance, ‘cooking’. Dairy fat spreads are conceptionally butter with lowered fat contents above 10% and where milk fat constitutes at least two-thirds of the dry matter.
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The milk fat products covered are characterized as fatty milk products obtained by means of processes that result in almost total removal of water and nonfat solids. For ghee, restrictions on milk ingredients as raw material are specified, and the product is further characterized by having a special flavor and physical structure, without further details being provided, however. Preserved milk products
Standards for three categories of traditional preserved milk products have been established: for evaporated milks, for sweetened condensed milks, and for milk powders and cream powder. In common, these products are characterized by being obtained by the partial removal (to various degrees) of water from milk (or cream) by the use of heat or other processes leading to the same composition and characteristics. Milk-based raw materials are restricted. Sweetened condensed milk is further characterized by being preserved with the addition of sugar (sucrose alone or sucrose in combination with other sugars). The adjustment of fat and/or protein is specifically addressed in all three standards, and can be done provided that it is achieved only by addition/withdrawal of milk permeate, milk retentate, and lactose, and provided that the whey protein-to-casein ratio of the milk subjected to adjustment is not altered. Common to all three standards is also that the whole range of fat content is covered by a classification system and that the minimum protein content should be 34% of milk solids-not-fat. Corresponding criteria for milk solids-not-fat content are established for the liquid products, whereas a maximum moisture content of 5% is specified for the powders. These compositional criteria are specified as absolute. Cheese
A general standard for Cheese supplemented by subordinated group standards for cheese in brine and unripened cheeses, respectively, has been established. Cheese is primarily characterized according to the way it is manufactured. Cheese is the ripened or unripened, soft or firm, hard or extra hard, product obtained by (a) coagulating wholly or partly the protein of milk, skimmed milk, partly skimmed milk, cream, whey cream or buttermilk, or any combination of these materials, through the action of rennet or other suitable coagulating agents, and by partially draining the whey resulting from such coagulation, while respecting the principle that cheesemaking results in a concentration of milk protein (in particular, the casein portion), and that consequently, the protein content of the cheese will be distinctly higher than
the protein level of the blend of the above milk materials from which the cheese was made; and/or (b) processing techniques involving coagulation of the protein of milk and/or products obtained from milk which give an end product with similar physical, chemical, and organoleptic characteristics as the product defined under (a). Part (a) reflects the traditional manufacturing method which is still the dominating process used worldwide, and part (b) allows for other processing techniques such as recombination, reconstitution, protein standardization, and membrane filtration in general are covered by subparagraphs. Products complying either to part (a) or to part (b) are equivalent, that is, they are not to be distinguished in any way. Today, the cheese manufacturing process is a combination of (a) and (b). The standard does not specify any compositional criterion but that (1) the protein content is distinctly higher than that of the milk used and that (2) the whey protein-to-casein ratio does not exceed that of the milk used. If the whey protein-to-casein ratio is higher, then the product is to be categorized as ‘whey cheese’. Cheese is generally classified according to principal ripening and firmness as follows: Classification according to principal ripening cheese, which is cheese not ready for • Ripened consumption shortly after manufacture but must be
• • •
held for such time, at such temperature, and under such other conditions as will result in the necessary biochemical and physical changes characterizing the cheese in question; Mold ripened cheese, which is ripened cheese in which the ripening has been accomplished primarily by the development of characteristic mold growth throughout the interior and/or on the surface of the cheese; Cheese in Brine, which is ripened cheese that has been ripened and preserved in brine until delivered to, or prepacked for, the consumer; and Unripened cheese, which is cheese ready for consumption shortly after manufacture.
Classification according to firmness cheese, which is cheese with a content of moisture • Soft on fat-free basis above 67%; (or semihard) cheese, which is cheese with a • Firm content of moisture on fat-free basis between 54 and 69%;
cheese, which is cheese with a content of moist• Hard ure on fat-free basis between 49 and 56%; and hard cheese, which is cheese with a content of • Extra moisture on fat-free basis below 51%. The general cheese standard applies to all cheeses, including individual varieties of cheese.
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Individual cheese varieties
Subordinate to the general cheese standard, 17 standards for individual cheese varieties exist: Cheddar, Danbo, Edam, Gouda, Havarti, Samsø, Emmental, Tilsiter, Saint-Paulin, Provolone, Cottage Cheese, Coulommiers, Cream Cheese, Camembert, Brie, Extra Hard Grating, and Mozzarella. Raw materials for the manufacture of these individual cheese varieties are restricted to milk and milk products derived from cows and buffalos. However, in the case of Extra Hard Grating, the dairy species permitted are goats, ewes, and cows (but not buffaloes), and in the case of Cream Cheese no restrictions in this regard apply. Further, each individual variety will, in addition to the general characteristics applicable to cheeses, be characterized by end-product description including classification according to principal ripening and firmness, as well as color, texture, structure, and ripening characteristics, where appropriate. In certain cases, characteristic elements of the manufacturing methods and dimensions are specified as well. Compositional specifications are unique for each variety and include limitations for compositional modification of the fat content. Specific milk constituents
Two milk product standards regulate whey powders and edible casein products, respectively. A group standard for sugars includes lactose. Whey powders are characterized as being milk products obtained by drying whey or acid whey, where whey means the fluid milk product obtained during the manufacture of cheese, casein, or similar products by separation from the curd after coagulation of milk and/or of products obtained from milk. Reference to ‘whey’ without qualification indicates that coagulation is obtained through the action of rennet-type enzymes, while using the term ‘acid whey’ means that the coagulation is obtained by acidification. Whey powders are further characterized by a reference lactose content, minimum milk protein content, and maximum content of moisture and ash. For whey powder and acid whey powder, the values of these criteria differ slightly. The two powders are principally distinguished by pH. In addition, the standard includes specific reference to demineralization and neutralization as being acceptable compositional modifications. Edible casein products are characterized as being milk products obtained by separating, washing, and drying the coagulum of skimmed milk and/or of other
products obtained from milk. The type of coagulation (acid precipitation or enzymatic coagulation) determines whether the product is classified as acid casein or rennet casein. Differentiation is further supported by specification of ash content (acid casein max. 2.5% and rennet casein min. 7.5% ash; both figures include P2O5). No additives are permitted (enzymes are categorized in milk product standards as ‘ingredients’). Edible caseinate is characterized as being the milk product obtained by the action of edible casein or edible casein curd with neutralizing agents, followed by drying. Caseinates may be manufactured by the use of acidity regulators, including specific neutralizing agents, emulsifiers, bulking agents, and anticaking agents. All casein products are further characterized by criteria for protein content, casein in total milk protein, moisture content, and milk fat content. All compositional criteria specified are absolute. Lactose is characterized as a natural constituent of milk normally obtained from whey with an anhydrous lactose content of not less than 99.0% on a dry basis. Lactose may be anhydrous or may contain one molecule of water of crystallization, or may be a mixture of both forms. No additives are permitted. See also: Labeling of Dairy Products. Policy Schemes and Trade in Dairy Products: Codex Alimentarius.
Further Reading FAO/WHO (2006) Understanding the Codex Alimentarius, 3rd edn. Rome: Food and Agriculture Organization of the United Nations; World Health Organization. IDF (1996) Codex standards in the context of world trade agreements. Proceedings of the IDF Seminar held in Brussels. November 1995. IDF Bulletin No. 310. Brussels: International Dairy Federation. IDF (1997) The influence of Codex standards on international trade in dairy products. Abstracts of the International Symposium. Du¨sseldorf, Germany, 6–7 September 1996. IDF Bulletin No. 319/ 1997. Brussels: International Dairy Federation. IDF (1998) Codex procedures and their importance – the new world for dairy products. Proceedings of the International Symposium. Chicago, IL, USA, 3–4 November 1997. IDF Bulletin No. 331/1998. Brussels: International Dairy Federation. IDF (1999) Overcoming barriers to world trade in food and dairy products. Proceedings of the International Symposium. Frankfurt, Germany, 7–8 November. IDF Bulletin No. 349/2000 Brussels: International Dairy Federation. Joint FAO/WHO Food Standards Programme (2007) Procedural Manual for the Codex Alimentarius Commission, 17th edn. Rome: Food and Agriculture Organization of the United Nations; World Health Organization. Joint FAO/WHO Food Standards Programme (frequently updated) Codex Alimentarius. Rome: Food and Agriculture Organization of the United Nations; World Health Organization.
Trade in Milk and Dairy Products, International Standards: Harmonized Systems K Svendsen, Danish Agriculture and Food Council, Arhus, Denmark ª 2011 Elsevier Ltd. All rights reserved.
The Historical Basis
Nomenclature and Classification
In the aftermath of World War II, several organizations were established to secure, facilitate, and harmonize trade. The General Agreement on Tariffs and Trade (GATT), now the World Trade Organization, is the best known, but other areas have developed their own rules and objectives. In September 1947, the 13 governments represented on the Committee for European Economic Co-operation agreed to set up a study group on the establishment of one or more European Customs Unions based on the principles of GATT. In 1948, the study group, established in Brussels, set up two committees, an Economic Committee and a Customs Committee. The Economic Committee later became the Organization for Economic Cooperation and Development, and the Customs Committee became the Customs Co-operation Council (CCC), created on 15 December 1950, when the convention was signed in Brussels. It took 2 more years before the first session was held on 26 January 1953, a date that 30 years later became known as International Customs Day.
With the growing world trade after World War II, the need for an internationally recognized common nomenclature became more and more obvious. This was discussed in CCC, and the Brussels Convention of 15 December 1950, on Nomenclature for the Classification of Goods in Customs Tariffs laid down the basics. It came into force on 11 September 1959, and was known as the Brussels Tariff Nomenclature (BTN). In 1974, it was renamed Customs Co-operation Council Nomenclature (CCCN). The CCCN was divided into 1241 headings, 96 chapters, and 21 sections, each heading thus being identified by two groups of two digits, one for the chapter and the second for the position in the chapter. The CCCN served only one objective, tariffs, and was purely numerical. At the same time, there were other classifications serving other purposes, the best known of which is the Standard International Trade Classification (SITC) for statistical purposes. During the 1950s and 1960s, great effort was made to correlate these two nomenclatures, but it was still evident that there was a great need for international harmonization, especially concerning commodity description and coding.
Customs Co-Operation Council or the World Customs Organization Harmonized System Committee The aim of this organization is to study all questions relating to customs cooperation and the technical and the economic aspects of customs systems to attain the highest possible degree of harmony and uniformity. This work is done through conventions like the Kyoto Convention on Simplification and Harmonization of Customs Procedures. On the operational level, the work is carried out in technical committees, of which the Harmonized System Committee is central for the topic of this article. In October 1994, the CCC adopted the working name World Customs Organization (WCO), thus mirroring the growing international significance of the organization and the development in world trade.
In 1970, a study group was set up to prepare a Harmonized Commodity Description and Coding system that would handle classification in relation to tariffs, statistics, transport, and production, thus being a multipurpose international products nomenclature. The result of this work was the creation in 1973 of the Harmonized System Committee, which would prepare the Harmonized System (HS) on the background of the CCCN. This resulted in the Harmonized System Convention that entered into force on 1 January 1988. Since that day, an ever-increasing number of countries adhere to this system. According to the WCO, by August 2000 more than 177 countries were using the HS, and 98 countries were contracting parties.
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According to Article 3 of the convention, contracting parties are obliged to ensure that their import customs tariffs and statistical nomenclature for imports and exports are in conformity with the six-digit HS. They are also obliged to make public their import and export statistics at or beyond that level (if at all). The Harmonized System Committee is responsible for the development of the HS and takes care of dispute settlement whenever two contracting parties cannot agree on the nomenclature code for a specific product, a situation that can have substantial economic consequences for the involved parties. The committee meets twice a year to discuss these problems and reach an agreement, eventually by voting on the subject. If one of the contracting parties does not agree with the decision taken by the committee, the party can transfer it to the council. This means that the main tasks of the Harmonized System Committee are to propose amendments to the convention for updating the HS every 4–6 years and to prepare explanatory notes and classification opinions and other advice as guides to the interpretation of the HS and recommendations to secure uniformity in the interpretation and application of the system.
adding another pair of two digits to a total of six digits. In this way, the system lists more than 5000 product lines. The HS as mentioned is dynamic. The latest amendments were decided at the 43rd Session of the Harmonized System Committee in March 2009. They were adopted by the WCO Council at its annual session in June 2009, and the recommendation is now being promulgated under the provisions of Article 16 of the Harmonized System Convention. This implies that HS contracting parties have 6 months during which they can object to a recommended amendment. The amendments will enter into force on 1 January 2012. The Council Recommendation of 26 June 2009, with the HS2012 amendments is the fifth to amend the HS, though it is only the fourth recommendation to make major amendments to the HS since the WCO Council approved the Harmonized System Convention. The main reasons for the latest set of 221 amendments are new environmental and social issues and the use of the HS as the standard for classifying and coding goods of specific importance to food security and early warning data falling within the ambit of the Food Security Information for Action Program of the Food and Agriculture Organization (FAO) of the United Nations.
Harmonized System The HS itself is thus a six-digit products classification system used by most countries in the world to collect tariffs and produce statistics. Some countries still have alternative systems for some uses, like the SIC codes for domestic production in the United States, but more and more the HS is being used for all purposes and by international organizations like the Organisation for Economic Co-operation and Development (OECD) and the World Trade Organization. According to the HS, all goods can be classified in 21 sections but, for more precise classification, sections are divided into chapters. The HS consists of 97 chapters, of which Chapter 77 is reserved for future use. Furthermore, Chapters 98 and 99 are reserved for special uses by adhering countries. To describe a chapter, two digits are always used (e.g., 04 for the chapter containing dairy products and 35 for the chapter containing casein, albumins, and others). The subdivision of chapters is done either by material (e.g., 02 – meat, 03 – fish) or by degree of manufacture or processing (e.g., 01 – live animals, 02 – meat and edible meat offals). Titles in chapters are only guidelines; therefore twodigit chapters are not sufficient. Thus, to clarify and underline the differences between products in the same chapter, most of the chapters are divided into headings (four digits) and even subheadings (six digits), each level
Dairy Products in the Harmonized System Let us take a closer look at the way dairy products are classified. This happens in the first section of the HS, Section I – Live Animal and Animal Products. This section is divided into five chapters: 01. 02. 03. 04.
Live animals Meat and edible meat offal Fish, crustaceans, and other aquatic invertebrates Dairy produce, birds’ eggs, natural honey, edible products of animal origin, not elsewhere specified or included 05. Products of animal origin, not elsewhere specified or included This is followed by the section on vegetable products. In itself, the definition of Chapter 04 tells us that we have to be more specific to find the right code for a product. We therefore have to look at the headings: 04.
Dairy produce, birds’ eggs, natural honey, edible products of animal origin, not elsewhere specified or included 04.01. Milk and cream, not concentrated nor containing added sugar or other sweetening matter 04.02. Milk and cream, concentrated or containing added sugar or other sweetening matter
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04.03. Buttermilk, curdled milk and cream, yogurt, kefir and other fermented or acidified milk and cream, whether or not concentrated or containing added sugar or other sweetening matter or flavored or containing added fruit, nuts, or cocoa 04.04. Whey, whether or not concentrated or containing added sugar or other sweetening matter; products consisting of natural milk constituents, whether or not containing added sugar or other sweetening matter, not elsewhere specified or included 04.05. Butter and other fats and oils derived from milk; dairy spreads 04.06. Cheese and curd 04.07. Birds’ eggs in shell, fresh, preserved, or cooked 04.08. Birds’ eggs, not in shell, and egg yolks, fresh dried, cooked by steaming or by boiling in water, molded, frozen, or otherwise preserved, whether or not containing added sugar or other sweetening matter 04.09. Natural honey 04.10. Edible products of animal origin, not elsewhere specified or included This did bring us one step further, but it did not solve all our problems, as it is evident that, for example, the fat content of different milk powders would qualify for different tariff rates. We therefore have to be even more specific and add a level of subheadings before we can define the right tariff nomenclature code within the HS. 04.
Dairy produce, birds’ eggs, natural honey, edible products of animal origin, not elsewhere specified or included 04.01. Milk and cream, not concentrated nor containing added sugar or other sweetening matter 04.01.10 – Of a fat content, by weight, not exceeding 1% 04.01.20 – Of a fat content, by weight, exceeding 1%, but not exceeding 6% 04.01.30 – Of a fat content, by weight, exceeding 6%. As per 1 January 2012, this last subheading will be replaced by the following: 04.01.40 – Of a fat content, by weight, exceeding 6% but not exceeding 10% 04.01.50 – Of a fat content, by weight, exceeding 10% 04.02. Milk and cream, concentrated or containing added sugar or other sweetening matter 04.02.10 – In powder, granules or other solid forms, of a fat content, by weight, not exceeding 1.5% – In powder, granules or other solid forms, of a fat content, by weight, exceeding 1.5% 04.02.21 – – Not containing added sugar or other sweetening matter 04.02.29 – – Other – Other
04.02.91 – – Not containing added sugar or other sweetening matter 04.02.99 – – Other 04.03. Buttermilk, curdled milk and cream, yogurt, kefir and other fermented or acidified milk and cream, whether or not concentrated or containing added sugar or other sweetening matter or flavored or containing added fruit, nuts, or cocoa 04.03.10 – Yogurt 04.03.90 – Other 04.04. Whey, whether or not concentrated or containing added sugar or other sweetening matter; products consisting of natural milk constituents, whether or not containing added sugar or other sweetening matter, not elsewhere specified or included 04.04.10 – Whey and modified whey, whether or not containing added sugar or other sweetening matter 04.04.90 – Other 04.05. Butter and other fats and oils derived from milk; dairy spreads 04.05.10 – Butter 04.05.20 – Dairy spreads 04.05.90 – Other 04.06. Cheese and curd 04.06.10 – Fresh cheese, including whey cheese, and curd 04.06.20 – Grated or powdered cheese, of all kinds 04.06.30 – Processed cheese, not grated or powdered 04.06.40 – Blue-veined cheese 04.06.90 – Other cheese As exports of dairy products are done by a very limited number of important players, most of the countries using the HS for tariff purposes are importing countries satisfied with this level of specification, as tariff rates in general are rather uniform between these large groups of products. Some countries importing, exporting, and producing a large variety of dairy products do, however, use their right to supplement the six-digit HS codes with their own further subcodes. One example is the US subdivision of Chapter 04.06.20, grated and powdered cheese, into 38 10-digit subheadings according to cheese types, milk used, and tariff quotas.
Classification Principles To classify a given dairy product under the correct HS nomenclature position, one must both consider some general principles and make reference to the explanatory notes given by the Harmonized System Committee. Formally, the descriptions in sections, chapters, and headings cannot be used to classify a product. One must go to the specific subheading texts.
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As the HS is not very specific, this will solve most of the problems. However, when mixing products from different chapters, this may result in a totally different code under a third chapter. If, for example, butterfat is mixed with vegetable oil to make a mixed dairy spread, it will be classified in Chapter 21. This classification is independent of the production process. If vegetable fat is added to a dairy product, according to the explanatory notes it cannot be classified under Chapter 04. In principle, there are then two possible alternatives, Chapter 19 and Chapter 21. A product that needs to be distinguished from a normal dairy product falling under Subheadings 04.01–04.04 will fall under Chapter 19 according to the explanatory notes. This, however, is not the case for dairy spreads or cheeses where the milk fat part has been totally or partly replaced by vegetable fat. In this case, the final products will need to be distinguished from products falling under Subheadings 04.05 and 04.06 of the dairy chapter. Such products according to the explanatory notes must be classified under Chapter 21. In this case, more specific descriptions should come before more general descriptions. This, however, does not mean that one cannot add anything from outside the chapter. If butter or cheese is mixed with small quantities of spices like garlic or cumin, it retains the character of butter or cheese and shall be classified as such. These questions are very delicate as they could be used in an attempt to circumvent high tariff rates or tariff quotas for some products by adding rather neutral or very small quantities of substances that would place the final product in a different chapter with no tariff or unrestricted access. Therefore, this is an important part of the explanatory notes defined by the Harmonized System Committee. Mixing products from within the same chapter is a different matter. If Blue cheese were mixed with processed cheese, the point of departure would be a general rule giving the nomenclature code of the substance with the highest position, in this case, the position of the processed cheese. If the two substances are identifiable, the principle would be to choose the position that makes up more than half of the quantity. However, if one of the substances has a very specific character, like a dominating taste, one should consider using the code for this substance even if it represents less than half of the quantity. The principle of the highest code also applies within a chapter; this means that if a product fits into a subheading, it cannot be placed under a subheading that comes later under the same heading. If, for example, fresh cheeses like Mozzarella, be it the Italian type or the American variety, are grated, the resulting product remains under Subheading 04.06.10 as a fresh cheese and does not fall under Subheading 04.06.20 as a grated cheese.
This, however, does not mean that a fresh cheese cannot be processed with melting salt and classified as a processed cheese under Subheading 04.06.30, as this production process substantially alters the cheese used as raw material, so that this can no longer be identified as such.
Classification Examples With these principles in mind, let us take a closer look at some dairy products and their classification. The author must stress that this relies on his personal opinions and experience and does in no way commit the WCO or the Harmonized System Committee. The official opinions of these bodies are to be found in the relevant texts issued by the WCO. In view of the developments in modern technology, the WCO does also have a website on the Internet (www.wcoomd.org). On this site, HS classification decisions can be found. The decisions will be published as soon as they are approved by the council under the provisions of Article 8.2 of the Harmonized System Convention. This will be about 2 months after the meetings of the Harmonized System Committee at which the decision is taken. The details published will include a complete description of goods, six-digit HS classification, and the legal basis for the classification decision. On the website the user will also find useful information on contracting parties, HS amendments, and amendments to the explanatory notes and a compendium of classification opinions. Heading 04.01 Under Heading 04.01 we find normal fresh drinking milk and cream, with no added sugar. However, we also find Ultra High Temperature (UHT) processed milk and sterilized cream, as these products are in no way concentrated or condensed, and thus cannot fall under Heading 04.02. If any flavor (e.g., chocolate) is added, this milkbased drink no longer falls under Heading 04.01 but under Heading 22.02. Heading 04.02 Take some of the fresh milk or heat-treated products falling under Heading 04.01 and add some sugar, and you have a 04.02.99 product. However, most of the products under Heading 04.02 are either milk powders or condensed milk, which in relation to the HS does not represent big problems. One should, however, bear in mind that lactose in a milk powder is not a sweetening agent. If lactose is added to a milk powder, it will, however, change position to Heading 04.04.90 (see below under Heading 04.04).
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Heading 04.03 All fermented milk products fall under this heading, be it in liquid or solid form. This means that both buttermilk and buttermilk powder will fall under Subheading 04.03.90 in the HS. Heading 04.04 All whey products, except whey butter, will fall under Heading 04.04.10 – as long as the total protein content by weight calculated on the dry matter does not exceed 80%. If it does exceed 80%, it falls under Heading 35.02, which is where you will have to classify whey protein concentrates. In modern dairy production, a lot of products no longer contain the milk constituents in their natural composition. Lactose, whey, permeates, and other constituents are added or deducted. It is even permitted to add small quantities of non-dairy ingredients. These products fall under Heading 04.04.90. This does not mean that all milk powders fall under this heading if their composition is changed, this happens only if they no longer respect the normal natural composition. This problem will have less impact in the future because of the Codex Alimentarius Commission decision to allow protein standardization to a minimum of 34% in milk powders, as this will set a norm for the natural composition and avoid inferior products to be sold as 04.02 products. Heading 04.05 Under this general heading 04.05.10 we find butter, also produced from whey or if recombined. Dairy spreads under 04.05.20 must not contain other fats than butterfat. These products would fall under Heading 21.06 if the butter is mixed with or replaced by vegetable fat. We also find butter oil in this chapter under Heading 04.05.90. Heading 04.06 Here we find all kinds of cheese. As the HS is not very specific, the classification does not represent big problems. We have seen above that all fresh cheeses, also frozen or vacuum-packed Mozzarella, grated or not, will always fall under the Subheading 04.06.10. Subheading 04.06.20 is meant mainly for cheese powder and Subheading 04.06.30 for processed cheese. Here, as was the problem with protein standardization before the Codex decision, the problem is not one of classification but of definition. Another point worth mentioning is the fact that all Blue cheeses fall under Subheading 04.06.40, not only the tasty types like Roquefort and Danish Blue Cheese, but also very mild types and types with mixtures of blue
and white mold. The decisive point is the presence of blue mold. Combined Nomenclature According to Article 3 of the Harmonized System Convention, any contracting party is allowed to establish in its customs tariffs or its statistical nomenclatures subdivisions classifying goods beyond the six-digit level of the HS, provided no changes are made to the HS level. In the European Union, the introduction of the Harmonized System on 1 January 1988, was taken as an opportunity to modernize the European Union nomenclature system. Until that point, customers used the Common Customs Tariff while the statistical instrument was the NIMEXE statistical nomenclature. As per 1 January 1988, the Combined Nomenclature (CN) replaced these two nomenclatures. The CN is, as it should be, based on the HS, but to form the CN one group of two more digits is added to create further subheadings covering some 10 800 eightdigit product groups compared with the approximately 5000 product groups of the HS. For certain import arrangements, the European Union supplements the CN code with a further 2-digit code giving the 10-digit European Union integrated tariff with 14,000 positions.
Dairy Products As shown above, Chapter 04 of the HS contains in total 6 four-digit headings and 20 six-digit subheadings covering dairy products. These are also found in the CN, but at the eight-digit subheading level we now find 153 dairy positions (2009). Within Headings 04.01 and 04.02, the subdivisions mainly take care of packet sizes. In Heading 04.03, the subdivision is made by fat content or sweetening of the product. In Heading 04.04, both fat and protein content and sweetening account for the subdivision. In Heading 04.05, products are at the CN level sorted out by some quality parameters: natural butter, recombined butter, or whey butter, and for the dairy spreads also the fat content. Finally, in Heading 04.06 for cheeses, the subdivision takes care of all the European Union specific varieties. Classifying a product according to the CN is thus more complicated than according to the HS but follows broadly the same principles as mentioned above. Only in this case, the explanatory notes of the HS supplemented with the same notes from the European Union competent authorities on the CN become even more important. Going through all these subheadings is beyond the scope of this article; one example, however, could be shown. As mentioned earlier, the United States is subdividing for import tariff purposes the HS heading 04.06.20,
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grated or powdered cheese of all kinds, into 38 ten-digit subheadings. In the CN, the European Union is only subdividing this heading into 2 eight-digit subheadings: 04.06.20.10 Glarus herb cheese (known as Schabziger), made from skimmed milk and mixed with finely ground herbs 04.06.20.90 Other
be said of an importer’s interest to have the right CN code on imports. It is therefore possible, according to regulation 450/2008 Article 20, to obtain a binding tariff information (BTI) or a binding origin information (BOI) from the customs authorities. With this information, an individual can be sure to use the right classification of his goods, thus knowing his rights or obligations.
Conclusion Refund Nomenclature At the European Union level, one further addition has been made to the CN to make up the Refund Nomenclature (RN). The RN is composed of the eight digits of the CN plus a four-digit extension, thus in total 12 digits. The purpose of the RN is to differentiate the export subsidy according to the real content of milk or milk substances in the final product. During recent years, substantial changes have been made to the RN to exclude positions with no products traded or no subsidy granted. If such a product with no subsidy is exported (e.g., Roquefort cheese), it shall be classified under the relevant CN heading, in this case 04.06.40.10. If we turn once more to the example of the cheese powder chapter, in the RN we find the following subdivision: Ex 04.06.20
–
Ex 04.06.20.90 – – 04.06.20.90.9100 – – –
04.06.20.90.9913 04.06.20.90.9915 04.06.20.90.9917 04.06.20.90.9919 04.06.20.90.9990
Grated or powdered cheese, of all kinds Other Cheeses produced from whey
––– Other – – – – Of a fat content, by weight, exceeding 20%, of a lactose content, by weight, less than 5%, and of a dry matter content, by weight: – – – – – Of 60% or more, but less than 80% – – – – – Of 80% or more, but less than 85% – – – – – Of 85% or more, but less than 95% – – – – – Of 95% or more – – – – Other
The logic here shows us that while the Schabziger cheese must be mentioned in the CN for import purposes – as it is produced in Switzerland – it is not needed in the RN as refunds are granted only on products of European Union origin. Knowing the right position of a product in the RN is of very substantial economic importance to the exporter, as this decides his export subsidy, the refund. The same can
The implementation in international trade of the HS has been of great help to customs officials as well as trading companies all over the world. Problems arising from different interpretations are discussed in a common forum, thus giving more stringent replies. For trading partners, this has led to a higher degree of knowledge of the economic conditions that apply to a specific trade action. The result of this is a general increase in world trade and thus, according to normal economic reasoning, in general welfare worldwide. See also: Policy Schemes and Trade in Dairy Products: Codex Alimentarius; Trade in Milk and Dairy Products, International Standards: World Trade Organization; World Trade Organization and Other Factors Shaping the Dairy Industry in the Future.
Relevant Website On the WCO homepage (www.wcoomd.org), the relevant conventions can be read: *
*
*
Convention establishing a Customs Co-operation Council – signed in Brussels on 15 December, 1950; entered into force on 4 November 1952. Fifteen pages. Convention on the Harmonized Commodity Description and Coding System – entered into force 1 January 1988. Including list of countries, territories, or customs or economic unions applying the HS. 13 pages. International Convention on the Simplification and Harmonization of Customs Procedures (Kyoto Convention) – entered into force 25 September 1974; revised version June 1999. 17 pages.
On the European Union homepage (http://ec.europa.eu/), the relevant regulations can be read: *
*
European Union Combined Nomenclature as expressed in the Annex I to Council Regulation (EEC) 2658/87 last amended by Commission Regulation (EC) No. 948/ 2009 of 30 September 2009, Official Journal L 287, 31/ 10/2009, 897 pages. European Unions Refund Nomenclature as expresseds in Commission Regulation (EC) No. 1298/2009 of 18 December 2009, replacing the Annex to Regulation
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*
(EEC) No. 3846/87 establishing an agricultural product nomenclature for export refunds, Official Journal L 343, 31/12/2009, 40 pages. Council Regulation (EEC) No. 450/2008 of 22 April 2008, laying down the Community Customs Code
(Modernized Customs Code), Official Journal L 145, 04/06/2008, 64 pages. http://ec.europa.eu/taxation_customs/customs/procedural_aspects/general/community_code/ index_en.htm
Trade in Milk and Dairy Products, International Standards: World Trade Organization A M Arve, Danish Dairy Board, Aarhus, Denmark ª 2011 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2752–2758, ª 2002, Elsevier Ltd.
Introduction The World Trade Organization (WTO) is the successor to the former General Agreement on Tariffs and Trade (GATT). The GATT organization was formed in 1948 after World War II as one of three legs in the international economic system; the other legs are the International Monetary Fund (IMF) and the World Bank. The GATT agreement was signed by 23 countries in 1947. In 1995, 123 countries in the multilateral trading system transformed the former GATT into the WTO. Membership by January 2002 is 144. A number of countries are negotiating for membership, amongst them Russia, the only major country of the international economy that is not already a member. China became a member in 2001. Until 1995 the trading system was organized as an agreement, but with the WTO entering into force, the system now consists of a fully fledged international organization with rights and obligations attached to its members. The WTO has its head office in Geneva, Switzerland. The director-general is the former New Zealand minister Mike Moore who took office in 1999. The core functions of the WTO are to ensure a nondiscriminating, smooth, predictable, and free trade between member countries. At the heart of the organization are the following activities: WTO trade agreements • administering for trade negotiations • forum trade disputes • handling national trade policies • monitoring assistance and training for developing • technical countries • cooperation with other international organizations. Both GATT and WTO evolved around trade negotiation rounds. So far there have been eight rounds of negotiations within GATT (Table 1). In 2001, negotiations were in progress on whether to start a new all-encompassing trade round in the WTO or to divide the negotiations into separate subject areas. During the course of time the GATT and now the WTO have increased their agenda according to the developments in the surrounding society. The WTO now covers a wide number of different areas of trade
338
under the three main headings GATT (trade in goods), GATS (trade in services) and TRIPS (trade in intellectual property rights). Within the areas of GATT and GATS there are a number of extra agreements, some of which are listed in Table 2. The decision-making process in the WTO is fundamentally built upon consensus. The top decision-making body is the Ministerial Conference, which consists of the Member Countries’ foreign ministers. This conference convenes at a minimum every second year. On a daily basis, the General Council is the central decision-making forum. All the Member Countries are represented in the Council by their ambassadors or a counterpart. The General Council also acts as Dispute Settlements Body and as Trade Policy Review Body.
Principles of the WTO A number of fundamental principles govern the general agreements and the relations between Member Countries. At the core of these principles is antidiscrimination, amongst trading partners and between domestic and foreign producers of goods. The most important principles are as follows.
Most Favored Nation Status The Most Favored Nation (MFN) clause stipulates that favors such as easier market access (lower duties) given to one country’s produce should be multilateralized and therefore applicable to all member countries. All Member Countries should by this principle be entitled to equal treatment and equal access. The major exception from this rule is free trade areas, customs, economic and political unions that can apply for and under certain conditions be granted exemption.
National Treatment Clause The National Treatment Clause stipulates that imports and domestic or local produce should be equally treated
Policy Schemes and Trade in Dairy Products | World Trade Organization Table 1 GATT trade rounds Year
Name of the round and place
1947 1949 1951 1956 1960–61 1964–67 1973–79 1986–94
Geneva Annecy Torquay Geneva Dillon Round (Geneva) Kennedy Round (Geneva) Tokyo Round (Geneva) Uruguay Round (Geneva)
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Dispute Settlement Body
upon market entrance of the import products. Duties and import taxes are not regulated by this principle. This rule applies to goods, services, trademarks, copyrights and patents. In practice the National Treatment Clause undermines the possibility of governments giving preferences to nationally produced products over imports and is an important instrument in increasing the transparency of the nontariff barriers to trade.
With the creation of the WTO, the trading system established a much more comprehensive dispute settlement system than was the case under the GATT, led by the Dispute Settlement Body (DSB). This dispute settlement system is based on the rule of law and with the strengthened possibilities of enforcement, the WTO has increased its regulatory and arbitrating powers. The Dispute Settlement Body is one of the cornerstones in the transformation from an international agreement to an international organization. Arbitration between members is a vital task for the WTO in order to secure the adherence by members to different agreements and rules under the WTO, but also to obtain the support of the members for the policies for the development of the international trade regime. The Dispute Settlement Body mainly facilitates the process by which Member Countries obtain legal guidance and counseling to solve bilateral disputes concerning trade issues under coverage of the different agreements under the auspices of WTO. A trade dispute taken to the WTO follows a predetermined structural process with set deadlines and obligations to implement the rulings. This allows for the development of jurisprudence and case law precedent within the WTO, and creates a much more predictable trading system. The different stages of a WTO case are shown in Figure 1. A panel makes first rulings in the WTO; their report is approved unless there is a consensus against this. The panel ruling can on legal grounds be taken to appeal to the appellate body. The appellate body’s decision is final, unless there is a consensus against the decision. This procedure implies that no single country or party to a dispute can veto a final decision and by that hinder a ruling against its interest. Member Countries are compelled to implement rulings of the WTO or to pay compensation to cover the opponent’s losses resulting from the illegal trade practice. The WTO may also allow for retaliation and introduction of sanctions, if a party to a case does not intend to follow the final ruling.
Least-Developed Countries
Non-tariff Barriers
More than 100 of the WTO member countries are developing countries. Within the WTO system there is special treatment for these countries with regard to their potential to fulfill their obligations according to the agreements, rules and regulations. For the group of least-developed countries, there are broad exemptions from the obligations. WTO has set up a system in order to help developing countries to gain knowledge and understanding of the organization and particularly to pass on experience with the trade negotiation system.
In the early days of GATT the focus was on reducing tariffs and import duties in order to enhance trade and reduce protectionism. This goal has largely been achieved for industrial produce during the course of the numerous trade rounds. Tariffs within trade in industrial products have been reduced from approximately 40% to less than 5% in the period from the establishment of GATT to the current implementation of the Uruguay Round. This tariff reduction process is only in an early stage with respect to agricultural and food products.
Source: www.wto.org
Table 2 Agreements within the areas of GATT and GATS The ‘extra’ goods agreements (under GATT)
The GATS annexes (under GATS)
Agriculture
Movement of natural persons Air transport
Health regulations for farm products Textiles and clothing Product standards Investment measures Antidumping measures Customs valuation methods Preshipment inspection Rule of origin Import licensing Subsidies and countermeasures Safeguards
Financial services Shipping Telecommunication
Source: http://www.wto.org
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The panel process NOTE: some times The various stages a dispute can go through in the WTO. At all stages, countries in dispute are encouraged to consult each are maximum; other in order to settle ‘out of court’. At all stages, the WTO director-general is available to offer his good offices, to mediate some minimum; or to help achieve a conciliation some binding some no!
60 days
by 2nd DSB meeting
0−20 days 20 days (+10 if director-general asked to pick panel)
6 mths from panel’s composition, 3 mths if urgent
up to 9 mths from panel’s establishment
Consultations [Art 4]
Panel established by Dispute Settlement Body (DSB) [Art 6]
During all stages good offices, conciliation or mediation [Art 5]
Terms of reference [Art 7] Composition [Art 8]
Panel examination (Normally 2 meetings with parties [Art 12] 1 meeting with third parties [Art 10]
Expert review group [Art 13; Appendix 4]
Interim review stage Descriptive part of report sent to parties for comment [Art 15.1] Interim report sent to parties for comment [Art 15.2]
Review meeting with panel upon request [Art 15.2]
Panel report issued to parties [Art 12.8; Appendix 3 par 12(i)]
Panel report circulated to DSB [Art 12.9; Appendix 3 par 12(14)] Appellate review [Art 16.4 and 17]
60 days for panel report, unless appealed
‘REASONABLE PERIOD OF TIME’ determined by: member proposes, DSB agrees; or parties in dispute agree; or arbitrator (~ 15 mths if by arbitrator)
30 days after ‘reasonable period’ expires
NOTE: a panel can be composed (i.e. panelists chosen) up to about 50 days after its establishment (i.e. DSB’, decision to have a panel)
DSB adopts panel/appellate report(s) including any changes to panel report made by appellate report [Art 16.1, 16.4 and 17.14]
Implementation report by losing party of proposed implementation within ‘reasonable period of time’ [Art 21.3] In cases of non-implementation parties negotiate compensation pending full implementation [Art 22.22]
Retaliation If no agreement on compensation, DSB authorizes retaliation pending full implementation [Art 22.2 and 22.6] Cross-retaliation: same sector, other sectors, other agreement [Art 22.3]
30 days for appellate report
Possibility of proceedings including referral to the initial panel on proposed implementation [Art 21.5]
max 90 days TOTAL FOR REPORT ADOPTION Usually up to 9 mths (no appeal), or 12 mths (with appeal) from establishment of panel to adoption of report [Art 20]
90 days
Possibility of arbitration on level of suspension procedures and principles of retaliation [Art 22.6 and 22.7]
Figure 1 Flowchart of the dispute settlement process in the WTO. (Reproduced with permission from www.wto.org.)
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As duties have diminished, the non-tariff barriers (NTB) have attracted increasing attention as they turn out to be as trade-distorting as flat rate tariffs. Non-tariff barriers consist of a number of different rules, regulations, standards, technical issues, administrative and bureaucratic procedures and other market-related obstacles that exporters meet while trying to gain access to a certain market. The WTO tries to highlight this area with a policy of transparency and information, but also with restrictions on the use of nontariff barriers.
Agreement on Technical Barriers to Trade The Agreement on Technical Barriers to Trade (TBT) is closely tied to the above-mentioned non-tariff barriers. This agreement aims at creating a free flow of international trade by regulating the general use of technical standards in a protectionist way. The agreement installs the principle that technical regulations and standards concerning packaging, marking and labeling, and procedures for assessment of conformity with technical regulations and standards should be used in a nondiscriminative way, both in respect to different trading partners and with regards to domestic versus import products. The agreement encourages the use of internationally recognized standards in national and local laws. At the same time member countries have to enhance transparency and public access with regard to applied and upcoming standards.
Agreement on Sanitary and Phytosanitary Standards The Agreement on the Application of Sanitary and Phytosanitary Standards (SPS) defines and gives opportunities for Member Countries to adopt measures necessary to protect human, animal and plant life and
health and at the same time regulates the use of these measures in order to avoid their discriminative use as barriers to trade. In the SPS agreement the scientific principle prevails. Sanitary and phytosanitary measures restricting trade should at all times have a scientific foundation that is widely recognized. Concurrently, countries are to treat different rules and standards alike, if their ultimate effect is the same for the protection of the human, animal and plant life and health. The Codex Alimentarius is recognized in the SPS agreement as a standard-setting reference point in this area and in the case of disputes among member countries. The objective is to harmonize the basis for sanitary and phytosanitary measures and meanwhile to create transparency and access to information concerning different rules and demands within this area.
Agricultural Agreement With the finalization of the Uruguay Round of trade negotiations agricultural trade fully came under the regulation of the WTO. The Agricultural Agreement is the first real attempt to achieve a common understanding of the trade mechanisms for agricultural and food products and the Agreement implements a number of regulations which in the last half of the 1990s and at the turn of the century set fundamental boundaries and rules for governance and policy-making within agriculture worldwide (Table 3). The major elements of the Agreement fall under three headings: 1. Export subsidies and competition. 2. Market access/imports. 3. Internal/domestic support. Together with the three central parts of the Agricultural Agreement, the Sanitary and Phytosanitary Agreement
Table 3 The outline of the support reductions in the agricultural agreement The main demands for reduced agricultural supports 1995 to 2001 Exports with support
Imports
Internal support
21% reduction in export quantities subject to support 36% reduction in budgetary outlays for export subsidies Base period: 1986–90
All non-tariff barriers converted to tariffs
20% reduction in all trade distorting internal supports based on the AMS calculation Base period: 1986–88
Source: http://www.wto.org
341
Average 36% reduction in tariffs including converted non-tariff barriers, at minimum 15% reduction pre product line Minimum access at reduced tariff rates of 3% increasing to 5% of domestic consumption Base period: 1986–88
342 Policy Schemes and Trade in Dairy Products | World Trade Organization
(see above) constitutes an attempt to formulate an overall framework for agricultural trade and by that the domestic policies concerning production and regulation of food supply. Within the WTO there are a number of different views concerning liberalizing versus protecting agricultural production and trade. The most vocal groupings in the agricultural negotiations are the United States, the EU and the Cairns Group, a number of food exporting countries with Australia and New Zealand at the forefront. The developing countries are with respect to their interests mainly divided into two main groups, net food exporters and net food importers. A number of very important trade disputes concern trade in agricultural produce, such as bananas, hormonetreated beef or milk quotas, to mention just a few. These WTO cases between different Member Countries have been some of the most stringent tests to the dispute settlement system within the WTO. Agricultural and consumer-related issues have proved to be the most politicized cases in the short history of the Dispute Settlement Body of the WTO. But they are also acknowledged as the core challenge to the sustainability of the system and to the Member Countries’ genuine support and acceptance of the WTO rules and governance.
Agricultural Agreement entered into force in 1995 running to 2001, with a peace clause extending it to 2003. The Agreement stipulated that further negotiations were to start in the WTO by 1999 in order to prepare for a new agreement. These negotiations are currently (2002) in process with all the parties outlining their specific interests and suggestions for a new agenda and ultimately an agreement.
Peace Clause It was envisaged in the Blair House Accord that a new agreement might not be reached among the trading partners to take over from the Uruguay Round agreement exactly in 2001. Therefore it was decided to extend the results of the final stage of the implementation – the socalled year 6 (2000/2001) – onward to 2003 to provide some time for negotiations on a new agreement. From 2001 to 2003 no further developments in the levels of subsidies, import tariffs and internal support are anticipated unless a new accord is in place. At the same time, the agreed reductions will not be reversed. The situation for the agreement on agriculture is, however, uncertain if a new deal is not in place by 2003. One option is to agree to extend the peace clause; however, a potential conflict is possible.
Blair House Accord The Blair House Accord between the EU and the United States is named after the presidential official guesthouse in Washington DC where the Agricultural Agreement was finalized. This agreement, reached in November 1992, was a breakthrough in the ongoing Uruguay Round of negotiations in GATT. The accord laid the foundations for the current trade liberalization within agriculture and also facilitated an ending to the very long and at times antagonistic negotiations for a general conclusion to the trade round. The Blair House Accord sets the basic reduction factors both for exports and internal support measured in quantities and budgetary outlays. The accord also sets a 6-year implementation period and the reference periods. Alongside this, the EU and the United States agreed on solving a number of outstanding trade disputes particularly the one on oilseeds. The agricultural breakthrough in the GATT system is widely recognized to rest on the Blair House Accord and hence on the hard-won compromises and common understanding between the EU and the United States. The EU has a mandate to negotiate for all Member Countries of the European Union, which act as one within the WTO. In December 1993, one year after the Blair House Accord, the final GATT agreement was reached and it was signed in Marrakesh in Morocco in April 1994. The
Traffic-Light Model – GATT Boxes and Decoupled Support One of the main objectives of the Agricultural Agreement is to reduce support levels in general; however, support is divided into more and less trade-distorting types. The aim of the Agreement is to target the most distorting support forms which directly influence the international markets for agricultural products, and hence the competition situation between different agricultural producers. Aggregated Measurement of Support The Total Aggregated Measurement of Support (AMS) is a calculation of the total amount of support given to agricultural producers in one country, except for domestic support not subject to reductions, because of their nondistorting or decoupled nature. The AMS calculation is used to facilitate comparisons between countries and to equalize different types of support in order to obtain reductions in all types of distorting supports. Traffic-light model In popular terms the different types of agricultural support are labeled with different colors: red, amber,
Policy Schemes and Trade in Dairy Products | World Trade Organization
green – and blue. The red support forms should be stopped immediately, the amber ones should be phased out and the green ones can be left, as they are not seen as directly distorting. This rule-of-thumb makes for the name ‘traffic-light model’. The different colors also give names to the box scheme, which is another way of describing the different support forms: amber, blue and green boxes.
Export subsidies The export subsidies used by various countries fall into the amber box and must be reduced according to the agreement by 21% for supported export quantities and by 36% in total budgetary outlays. The reduction had to be linear over the implementation period, reaching the final commitments in Year 6, 2001. Developing countries must reduce their support by 14% in quantities and 24% in budgetary outlays with an implementation period of 10 years. Least-developed countries are exempt from this obligation. Member Countries have to keep account of the use of export subsidies for the individual product categories.
Decoupled support and blue box subsidies In order to encompass the American deficiency payments and the EU animal and area premiums of the mid-1990s, the blue color was introduced. Blue color support forms are semi-decoupled, whereas the green ones are decoupled altogether. The term ‘decoupled’ is used to describe the situation where the size and amount of support are not linked to the actual form and size of the agricultural production, as opposed to price support that is directly linked to the production output. Green box types of support are within the areas of research, disease control, government services and many more. Direct income support also falls in this category, as long as it is independent of the production. Semi-decoupled support can take the form of direct payments under production limiting programs with fixed references – area, yield or animal numbers. The blue box supports are not targeted by reduction demands because of their limited trade-distorting nature. The introduction of categorized support forms has allowed for a dynamic agricultural policy reform process in different countries. The major agricultural production and trading countries have undergone a number of reforms since the GATT agreement, all directly related to the WTO policies, in order to enhance competitive powers and allow for a more fair trade with agricultural produce. In most WTO member countries development of agricultural policy instruments is under way in order to avoid potential disputes.
343
Imports and Market Access The import rules in the Agreement specify that tariffs have to be reduced by an average of 36%, with a minimum 15% per product line from 1995 to 2001. Prior to the reduction all non-tariff barriers have to be converted into tariff equivalents to enhance transparency as to the actual level of trade restrictions. This conversion is termed tariffication. It is the overall tariffs (duties, levies, quantitative restrictions, non-tariff barriers and so forth – old and new ones) that are to be reduced by 36%. The tariff rates are listed in the country list for each country with initial and bound rates. Developing countries are only obliged to reduce tariffs by 24%, and they have an extended implementation period, to 2004. Least-developed countries are exempt from the agreement to reduce tariffs.
Minimum import access In order to create some immediate effect for market access it was decided to create a certain minimum access to a preferential tariff far below the general and even reduced tariffs. This minimum quota is set in relation to the consumption in the base period 1986–88. At the beginning of the implementation in 1995 the quota was 3% of base period consumption for the respective products. This amount has gradually increased to 5% at the end of the 6-year implementation period in 2000/2001. Current access opportunities are to be maintained and supplemented with the above-mentioned minimum access in case the actual imports are below the 3–5%.
Trade in Dairy Products It was widely believed that the WTO agreement would increase the international trade in agricultural products, including dairy produce. The actual development does indicate that the total trade is developing; however, what is more noticeable is the change in the trading patterns. Table 4 shows the shift from an EU-dominated international trade in dairy products to a situation where Oceania is the predominant exporter. This situation is reflected in different claims and demands in respect of the ongoing negotiations on a WTO II agreement. It was also expected that the price for dairy products would be affected in an upward trend by the Agricultural Agreement and the increased trade, but this element is harder to deduce from the statistics. However, some signs in the market do indicate a general upward trend in prices for dairy products.
344 Policy Schemes and Trade in Dairy Products | World Trade Organization Table 4 The development in world market shares for dairy products World market share (%) EU USA New Zealand Australia
1990
2000
51 13 27 9
39 2 41 18
Source: Danish Dairy Board.
See also: Office of International Epizooties: Mission, Organization and Animal Health Code. Policy Schemes and Trade in Dairy Products: Agricultural Policy Schemes: European Union’s Common Agricultural Policy; Agricultural Policy Schemes: Other Systems; Agricultural Policy Schemes: Price and Support Systems in Agricultural Policy; Agricultural Policy Schemes: United
States’ Agricultural System; Trade in Milk and Dairy Products, International Standards: Harmonized Systems.
Further Reading Hoekman B and Kostecki M (1995) The Political Economy of the World Trading System, Oxford: Oxford University Press. Jackson JH (1998) The World Trading System, Law and Policy of International Economic Relations, Cambridge: MIT Press. Moon BE (1996) Dilemmas of International Trade, Oxford: Westview Press. Nedergaard P, Hansen HO, and Mikkelsen P (1993) EF’s Landbrugspolitik og Danmark, Copenhagen: Handelshøjskolens Forlag. Ritson C and Harvey DR (1997. In) The Common Agricultural Policy, (2nd edn.. Wallingford: CAB International. World Trading Organization, (1995) The Results of the Uruguay Round of Multilateral Trade Negotiations: The Legal Texts,. Geneva, Switzerland: WTO. World Trade Organization (1998) Trading into the Future, Geneva, Switzerland: WTO.
World Trade Organization and Other Factors Shaping the Dairy Industry in the Future P Vavra1, OECD, Paris, France ª 2011 Elsevier Ltd. All rights reserved.
Introduction How would dairy industry look like after the conclusion of WTO (World Trade Organization) Doha negotiations? Is there going to be a final deal? Is there a need for a Doha deal? Starting with the last question, the answer is ‘yes’. In my view it is not necessary to discuss here the importance of the Doha round and the advantages of a multilateral approach. Bilateral and not even regional agreements cannot match the multilateral system. Issues related to standards or dispute settlements are just two examples that need multilateral consideration. The value of WTO trade negotiations that seek broader consensus has also been underlined in empirical studies. For example, an OECD (Organisation for Economic Co-operation and Development) study pointed to the logical fact that the domestic supply adjustment for dairy sector can be expected to be the highest if a country reforms its dairy policy unilaterally. As more countries join the reform process, adjustments become smaller and would be least in the case of a multilateral reform. As there is a need for a multilateral framework to govern global trade, it could be expected that there will be a final deal. However, in the aftermath of the global economic crises, the question mark after the word ‘When’ is not getting smaller. The answer to the first question is even more complex. It is always difficult to predict how the world would look like after a specific event, and it is not easy to isolate the impact of that particular event from other factors influencing the evolution of the world. In the last decade the dairy industry has been going through remarkably dynamic changes worldwide, becoming truly global in scope. Would this have happened even without the WTO Uruguay Round Agreement on Agriculture? Or, was globalization in fact propelled by numerous border measures protecting domestic markets that provided incentives for foreign companies to circumvent national border measures through investment in protected markets? 1
The author is an agricultural markets and policy analyst at the OECD, Paris. The opinions expressed in this article are those of the author and do not necessarily represent those of the OECD or its member countries.
A Doha deal could be expected to have an impact especially on those domestic markets that have relatively high market price support measures in place. But the actual impact depends on the global market situation and the way countries organize support to agriculture. Moreover, the forces of globalization, underpinned by economic growth, urbanization, and technology transfers, will likely continue to shape the dairy industry, be it preor post-Doha. This article will discuss not only concerns related to Doha but also other issues that are likely to have an impact on dairy markets in the near future.
Doha Round in the Context of WTO Negotiations Established on 1 January 1995, the WTO replaced the GATT (the General Agreement on Tariffs and Trade) as the legal and institutional foundation of the multilateral trading system of its member countries. Although GATT has been providing the multilateral rules governing much of the global trading system since 1948, these rules were largely ineffective in disciplining key aspects of agricultural trade. The Uruguay Round was the first trade round that considered agricultural issues, and it became a turning point in the reform of the agricultural trade system. The Uruguay Round Agriculture Agreement (URAA) has accomplished the development and implementation of a framework to address barriers and distortions to trade in three major policy domains: market access, domestic support, and export subsidies. The diverse forms of trade measures were converted under the URAA to tariffs. Market access for sensitive products was provided through a system of tariff rate quotas (TRQs). The use of export subsidies was reduced by the agreement, while domestic policies that affect production and trade of agricultural products were constrained by a set of rules and bindings. The reduction in domestic support was implemented through a commitment to reduce the total aggregate measurement of support (AMS) for each country. The URAA numerical targets for each policy domain in agriculture are summarized in Table 1. The table indicates that in the developed countries the total AMS support was scheduled to be reduced by 20% over 6 years, while in the developing countries the total AMS
345
346 Policy Schemes and Trade in Dairy Products | World Trade Organization Table 1 Uruguay round numerical targets for agriculture Developed countries
Developing countries
6 years: 1995–2000
10 years: 1995–2004
Tariffs Average cut for all agricultural products Minimum cut per product
36% 15%
24% 10%
Domestic support Total AMS cuts for sector (base period: 1986–88)
20%
13%
Exports Value of subsidies Subsidized quantities (base period: 1986–90)
36% 21%
24% 14%
Source: WTO.
support was scheduled to be reduced by 13% over 10 years. Moreover, the agreement required a reduction of tariffs by 36%, on average, for developed countries, and by 24% for developing countries. It is evident from the table that although the Uruguay Round achieved a historic change, the actual level of agricultural support was reduced only moderately. Nevertheless, the achievement of the Uruguay Round should be seen in the establishment of rules for agricultural support and as a start of the process of long-term objective of substantial reduction in support and protection. This process was to continue in the new round of negotiations. At the Fourth Ministerial Conference in Doha, Qatar, in November 2001, WTO member governments agreed to launch a new round – the so-called Doha round – of negotiations. The round embarked on a very complex agenda with a focus on developing countries, trade facilitation, competition rules, environment, investment, liberalization of trade in services, and liberalization of trade in agriculture, which is likely the single most difficult item. The Doha Ministerial Declaration has set several key dates for the negotiations. The modalities for countries’ commitments were expected by 31 March 2003, and countries’ comprehensive draft commitments by the fifth ministerial conference in September 2003 in Cancu´n, Mexico, with the overall deadline set for 1 January 2005. However, after a failed – the so-called – Harbinson proposal in March 2003, the fifth ministerial conference in September 2003 ended up in a stalemate. Ten months after the Cancu´n deadlock, an agreement on a framework for the modalities on agriculture was reached. The socalled July Framework gave a clearer shape to the modalities for the next phase of the negotiations. The 2004 July Framework Agreement was a starting point toward a draft of the detailed modalities to be agreed at the WTO’s sixth ministerial conference held in Hong Kong, from 13 to 18 December 2005. Rather limited progress was made in reaching an agreement on
precise numerical formulae or targets for liberalizing agricultural trade, the original aim of the Hong Kong Ministerial. Perhaps the most tangible outcome of the Hong Kong Ministerial was the continuing support to eliminate all forms of export subsidies, and disciplines on measures with equivalent effects. The next deadline for reaching agreement on modalities was set for 1 August 2006. As no agreement could be reached, the negotiations had been suspended at the General Council meeting on 27–28 July 2006. In 2007, the negotiations were resumed and a new set of modalities were circulated in July and August 2007. A series of working documents followed, as well as a series of revised draft modalities on 8 February and 19 May 2008, respectively. A revision of the previous versions was circulated on 10 July 2008. But the meeting of ministers in Geneva over 21–30 July did not reach an agreement. The disagreement occurred over the special safeguard mechanism (SSM) for agricultural products in developing countries. Safeguard mechanisms are used to restrict imports in special circumstances such as a sudden surge in imports. The unresolved issue was the size of the trigger allowing to invoke a special safeguard measure. In particular, the disagreement was related to the situation where the SSM raises tariffs above the commitments made by the countries in the 1986–94 Uruguay Round – the pre-Doha Round bound rates. Some commentators viewed the July 2008 failure more as a collapse of negotiations; others noted the progress on issues other than the SSM. It is difficult to estimate what would happen if the questions of the SSM were resolved. In his report to the trade negotiations committee, the chairman of the special session of the committee on agriculture, Ambassador Crawford Falconer, noted that despite the fact that members were prepared to accept compromises it could not be taken for granted that even with the SSM agreement the rest could have fallen into place. There are still unresolved questions related to new tariff quota
Policy Schemes and Trade in Dairy Products | World Trade Organization
347
Table 2 Overview of GATT and WTO negotiation rounds Name
Start
Duration
Countries
Subjects covered
Geneva Annecy Torquay Geneva II Dillon Kennedy Tokyo Uruguay
April 1947 April 1949 September 1950 January 1956 September 1960 May 1964 September 1973 September 1986
7 months 5 months 8 months 5 months 11 months 37 months 74 months 87 months
23 13 38 26 26 62 102 123
Doha
November 2001
?
141 (November 2001)
Tariffs Tariffs Tariffs Tariffs, admission of Japan Tariffs Tariffs, antidumping Tariffs, nontariff measures, framework agreements Tariffs, nontariff measures, rules, services, intellectual property, dispute settlement, textiles, agriculture, creation of WTO, and so on Tariffs, nontariff measures, agriculture, labor standards, environment, competition, investment, transparency, patents, and so on
?
153 (September 2008)
Adopted from Neary JP (2004) Europe on the road to Doha: Towards a new global trade round? CESifo Economic Studies 50(2): 319–332. ? – not yet known.
creation, tariff simplification, and issues related to cotton. These could be the other deal-breakers. Nevertheless, it was clear from the outset that the agenda is ambitious and that a lot of time and work would be needed to successfully conclude the round. Moreover, the time spent so far on negotiations cannot be considered excessive, despite the slow progress. Table 2 summarizes the time-bound efforts of the previous GATT and WTO rounds.
Implications of the Doha Round for the Dairy Sector The Doha round has not fundamentally changed the rules as agreed by the URAA, but larger reductions (or even elimination) have been considered. Although the actual modalities have not been agreed to and are subject to change, the key factors so far could be described as follows: (1) Elimination of export subsidies in all forms (already agreed in July 2004 Framework) and improved disciplines on all export measures whose effects are equivalent to those of export subsidies. (2) Depending on the base of Overall Trade-Distorting Domestic Support (OTDS), a reduction is envisaged in the range of 50–85% using a tiered formula; the framework also widened the range of support that would be disciplined in the Doha round; Blue Box supports are to be capped at no more than 5% of the value of a country’s agricultural production, in the 1995–2000 period. (3) Tariffs shall be reduced using a tiered formula that requires deeper cuts for higher tariffs. The least developed countries would not be required to make any reduction on domestic support and tariffs. The negotiated framework also provides a number of flexibilities intended to meet specific concerns of
individual or groups of countries. These flexibilities, which are in fact numerous exceptions – such as the designation of sensitive products and special products for developing countries, special agricultural safeguard measures – have substantially increased the complexity of the negotiations and introduced doubts about the effectiveness and success of tariff cuts. What would be the implication of the Doha round for the dairy sector? Dairy markets have traditionally been among the more distorted, and even after the full implementation of the URAA, dairy trade continued to be among the most protected agricultural sectors with high average bound tariffs, low minimum access requirements, a number of special safeguard provisions, complex systems of tariff-rate quotas (TRQs), and large domestic support and export subsidies and other export support measures. In almost all instances, tariffs on dairy products are above the country average for all agri-food products and are among the highest on agricultural products (Table 3). Thus, it could be expected that, after a Doha deal, countries with high tariffs would need to reduce them considerably, but, as noted above, dairy products could be listed as sensitive products falling under the exemption category. Under the current legislation it has been possible to avoid reductions in dairy AMS by adjusting the AMS amounts in other sectors. Such compensation mechanisms are limited in the Doha framework, which specifies product-specific AMS limits and envisages capping of the product-specific funding. The product-specific AMS limits for all developed country WTO Members other than the United States shall be the average of the product-specific AMS during the Uruguay Round implementation period (1995–2000) as notified to the Committee on Agriculture. For the United States, the
348 Policy Schemes and Trade in Dairy Products | World Trade Organization Table 3 Average (scheduled) tariffs in 2000 for main commodities
Coarse grains Wheat Rice Sugar Beef Pig meat Poultry Sheep Butter Cheese Skim milk powder Whole milk powder Whey powder Average of all commodities
In-quota
Out-of-quota
100 73.2 15 15.8 36.3 55.5 39 30.9 48.3 31.8 48.1 79.5 37.8 52.67
217.8 184.4 197.5 126.7 166.9 180.2 171.7 153.3 369.5 121.1 191.6 260.7 545.7 184.18
From OECD (2002) Agriculture and Trade Liberalisation: Extending the Uruguay Round Agreement. Directorate for Food, Agriculture and Fisheries, Committee for Agriculture. Paris: OECD. Average tariff was calculated as an unweighted average of each tariff line for the following countries: Argentina, Australia, Canada, European Union, Hungary, Japan, Korea, Mexico, New Zealand, Poland, United States, Iceland, Norway, and Switzerland.
product-specific AMS limits shall be the resultant of applying proportionately the average product-specific AMS in the 1995–2004 period to the average product-specific total AMS support for the Uruguay Round implementation period (1995–2000) as notified to the Committee on Agriculture. It is not necessary to go through all the details of modalities as these can be found in the original WTO document. However, an important point needs to be made here about the overall process. The WTO negotiations are not about eliminating agricultural policies but about shifting to more effective policies. Hence, countries will be able to implement or keep policies that do not distort trade. It follows that the green box is likely to remain in existence and act as a home for measures that are decoupled from production as far as possible and targeted at specific objectives and beneficiaries. (The green box support measures include those deemed to distort trade only minimally, or not at all, such as some forms of direct payments to producers, decoupled income support, and government financial support for income insurance and income safety net programs.) The simulation results of studies that have analyzed the impact of further trade reforms on the global dairy sector have indicated that, following the reforms, world dairy prices would be lifted while supply would shift toward more efficient areas, although there would not be any significant change in total world milk production. It is however difficult to extrapolate these results in the context of recent developments as the agricultural markets have undergone dramatic changes. This is especially
true of the dairy sector, which has been going through rapid structural changes for some time with several countries also embarking on policy reforms. As a consequence, international dairy markets have slowly shifted from a supply-driven paradigm distorted by price-depressing policies and serving as an outlet for excess supplies, to a more demand-driven paradigm, responsive to market signals and changing consumer preferences. The very recent events on the markets have further refocused attention on food security, availability, and safety. These profound market changes, some of which are believed to be structural and long-term in nature, will have a significant impact on the dairy sector, be it pre- or post-Doha. In order to get a better grasp on global dairy prospects it is essential to understand this shift.
Global Market Changes and Prospects The prices of nearly all agricultural commodities have risen sharply in the 2007–08 period but the prices of dairy products were the first to start the climb. International dairy prices recorded strong gains in the first half of 2007, already peaking in the second half of that year well ahead of similar developments for other commodities (Figure 1). On a year-over-year basis between 2006 and 2007, world butter prices increased by 66% and cheese prices rose by 50%, while prices of milk powders soared by more than 90%. The OECD–FAO Agricultural Outlook report expects that all dairy prices will weaken over the short-term as demand softens and supply, with some lag, reacts to the strong price incentives. Nevertheless, dairy prices in real terms are expected to average 20–30% higher as compared to those of the last decade. The prices in real terms are also expected to resume a modest declining trend, albeit from a much higher level than in the past (Figure 2). However, it is important to note that these projections are conditional on the underlying macroeconomic assumptions, most notably solid economic growths and high crude oil prices. Figure 2, which depicts butter and skim milk powder (SMP) prices in real terms, also illustrates two additional points. First, when viewed from the perspective of last couple of decades, the recent spike of prices in real terms is much less impressive, certainly for butter. Second, over the last several decades the value of milk components on the international market changed considerably and shifted toward non-fat solids away from fat. (The steady decline in milk fat value on world markets could be, to some extent, attributed to the policy decision in heavily protected countries to tilt butter/SMP support prices in favor of butter, which has favored the production of fat for which demand has been stagnating.)
1200
6000
1000
5000
800
4000
600
3000
400
2000
200
1000
0 Jan-04 Mar-04 May-04 Jul-04 Sep-04 Nov-04 Jan-05 Mar-05 May-05 Jul-05 Sep-05 Nov-05 Jan-06 Mar-06 May-06 Jul-06 Sep-06 Nov-06 Jan-07 Mar-07 May-07 Jul-07 Sep-07 Nov-07 Jan-08 Mar-08 May-08 Jul-08 Sep-08 Nov-08 Jan-09 Mar-09 May-09 Jul-09 Sep-09 Nov-09 Jan-10 Mar-10 May-10 Jul-10
0
349
USD tonne–1
USD tonne–1
Policy Schemes and Trade in Dairy Products | World Trade Organization
Wheat
Coarse grains
Rice
WMP(sd. axis)
Figure 1 International monthly commodity prices. Source: OECD–FAO.
5000 4500 4000 3500 Cheese USD/t
3000 WMP
2500
SMP
2000
Butter
1500 1000 500 2019
2017
2015
2013
2011
2009
2007
2005
2001
2003
1999
1997
1993
1995
1989
1991
1987
1985
1983
0
Figure 2 Historical and projected international prices (in real terms) of SMP and butter. Source: OECD.
The reasons for expectations of a higher plateau for global dairy prices merit a short consideration. Some of the factors behind the higher prices are related to more structural shifts while others could be considered as transitory. For example, a more permanent change in the markets relates to changes in demand patterns particularly in developing countries where consumers are switching to a more protein-based diet fueled by urbanization, westernization, and growth in per caput income. Consumption of milk and dairy products is rising nearly everywhere, exhibiting the highest growth rates among agricultural food commodities. The rise is particularly marked in rapidly growing economies of the Pacific Rim where an expanding middle-class population is consuming more sophisticated processed foods. Over the medium term, in developing countries, demand growth is expected for all dairy products with whole milk powder
(WMP) consumption showing the strongest growth, followed by butter. Nevertheless, OECD countries continue to dominate cheese consumption and maintain their three-quarter share of the world total (Figure 3). Another important development that slowly changed the usual picture was the decline in the importance of intervention products on world markets, particularly from the European Union and the United States. While in the period 2002–03 the share of EU and US SMP stocks alone amounted to half of the global exports of SMP, in the period 2005–07 this share dropped to below 10%, reducing the buffer against shocks in supply and demand (Figure 4). The lower stock levels have added to market and price volatility, and there is a strong nonlinear relationship of changes in stock levels to the changes in price. When ending stocks are sizable, large
350 Policy Schemes and Trade in Dairy Products | World Trade Organization 25
Million tonnes
20
OECD
Non-OECD
15 10 5 0 2007-09 2019 Butter
2007-09 2019 Cheese
2007-09 2019 SMP
2007-09 2019 WMP
Figure 3 Outlook for dairy product consumption. Source: OECD.
0.7 0.6 0.5 0.4 Share 0.3 0.2 0.1 0 2001
2002
2003
2004
2005
2006
2007
2008
2009
Figure 4 Ratio of EU and US stocks of SMP to global exports. Source: OECD.
changes in stock levels may be needed to change prices by a small amount. When stock levels are low, very small changes in stock levels can be associated with major price swings. The tight situation on the market in 2007 was further aggravated by the decline in milk production in Australia and Argentina. Production everywhere was hindered by a strongly increasing cost of production – rising oil and feed prices. Oil, energy, and feed prices are critically important factors in the increased production costs for milk, and a higher plateau of these prices seems to be a more permanent factor that could keep prices above past average levels. The situation on the dairy markets was also to some extent exacerbated by policy decisions in certain countries to tax or ban exports. These ad hoc actions should be considered temporary, and introducing policies that create distortions and that undermine appropriate market responses should be avoided in the future. Finally, an important factor, not unique to the dairy sector, has been the depreciation of the US dollar. Stronger currencies vis-a`-vis the US dollar mitigated the
producer price gains in local currencies and at the same time facilitated higher demand by importers, thus driving world prices higher in terms of US dollars. In general terms, when the dollar is weak, commodity prices tend to be higher, and when the dollar is strong, commodity prices tend to be lower (Figure 5). Nevertheless, in discussing the prospects for the global dairy markets it is important to keep in mind that the most certain thing about the future is that it is uncertain. Weather, economic conditions, and the evolution of policies (induced by Doha deal or not) remain among the key factors influencing the dairy market’s future, with a considerable uncertainty about them. For example, a slowdown in economic growth would moderate international prices. A severe drought in any important dairyproducing region could have a critical impact on the sector in any given year, pushing prices higher. These factors are uncertainties that to some extent form an integral part of the dairy markets. What are the other factors that will likely shape the dairy markets in the near future – be it pre- or post-Doha? Although the choice for the discussion might be subjective, it seems
Policy Schemes and Trade in Dairy Products | World Trade Organization 1.6
5000
1.4
4500
USD/Euro
4000
Butter
1.2 3000
0.8
2500
0.6
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Figure 5 Exchange rate and global prices (in nominal terms). Source: OECD.
to me that the shifts in the markets will be reinforced by the following mutually inclusive factors: continued globalization, technological progress, and vertical integration of food supply chains. Globalization It is evident that the dairy industry is becoming more global in scope. It could be expected that globalization will continue to reshape the dairy markets in the future and will be fueled by the processes of economic growth, urbanization, technology transfer, and a convergence in consumption patterns. Moreover, the ability to expand, reduce costs, and secure milk supplies will remain additional drivers behind industry consolidation, and the development of discount stores and private labels will quite probably put additional pressure on milk processors, forcing them to look for further cuts in costs. Mergers, strategic alliances, joint ventures with foreign partners, and direct foreign investment and acquisitions will be the main vehicles of the structural change. Competition among dairy firms in well-established developed markets is set to intensify with the focus turning to health and convenience, and increased penetration of foodservice, catering, and restaurant sectors. As a result, many firms will try to enter growing but less established markets in developing countries to source milk and dairy products from multiple locations while the original domestic market will become less relevant. This is also linked to the continued expansion of supermarkets, which will likely contribute to the further weakening of the position of local dairy firms but will help to spread international brands. Thus, for international dairy companies this means that a branded product can be promoted in multiple markets, but perpetuation of local products and catering for local tastes and preferences are to remain important.
Vertical Integration of Food Supply Chains Globalization of the dairy industry goes hand in hand with the expansion of supermarkets and transformation of the agri-food sectors in general. It could be expected that the transition from independent markets toward much more tightly aligned food supply or value chains will continue. The profound changes in the global food system are marked by (1) increase of trade in food, (2) rapid rise of economic concentration of supermarkets, (3) shift to centralized procurement via distribution centers from spot market procurement toward dedicated wholesalers and direct purchase from growers or grower associations, (4) creation of a multiplicity of private standards, often built on top of public standards, (5) rise of third-party certification of food production, (6) development of new technologies, biotechnologies, and process control throughout the entire chain, (7) shift toward nonprice competition among supermarket chains, (8) greater differentiation of food products by class, and (9) the development of new forms of contractual relationships between supplies and buyers. This transition has also been (and will be) accompanied by an increasing use of contracts. The results of several studies indicate an increased use of contracts in most agricultural sectors and dairy is not an exception. However, an increased use of contracts together with a rising upstream concentration in the supply chain could create concerns about the impact of this form of supply chain governance on farmers and issues related to market transparency and market power. The growing market power in the supply chain might have an impact not only on farmers but also on established dairy companies. The growing power of retailers, and in particular the developments of retailers’ private labels, will increasingly represent a challenge for established brands of dairy companies, forcing these firms to continuously innovate.
352 Policy Schemes and Trade in Dairy Products | World Trade Organization
However, the overriding concern for the future seems to be the capability to assure the quality and safety of food. The importance of consumer confidence in the dairy supply chain is ever more evident following one of the largest food safety crises in recent years which spiraled as a result of milk adulteration with melamine in China. The toxic industrial chemical melamine has been added to milk to make it appear higher in protein. A number of babies died and thousands fell ill after drinking melamine-contaminated milk formula. It could be expected that this incidence will irreversibly change dairy markets and the way the milk and dairy production process is monitored and tested. The share of milk and dairy products in consumers’ diets may suffer, so the dairy industry needs to remain proactive and innovative in order to maintain the image of a safe and healthy product. The substitution effect was evident in the recent melamine scare when Chinese consumers sought available alternatives, mainly soy milk. In fact, Starbucks in China announced that all milk used at its cafes in China will be soy-based for the near future. In fact, Starbucks in China announced after the incidence that all milk used at its cafes in China would be soya-based. Technological Progress Technology has been changing the dairy sector for decades, and only a true pessimist would say that the progress has arrived at the end of the road. Given the higher commodity price situation, more attention has been and can be expected to be paid to food production. It follows that private and public money flowing to research and development activities and agricultural extension services could push the technology frontier further. Productivity gains stimulated by increased automation of the production process, improved feed efficiency, improved health and longevity of cattle, and the ability to improve productivity via GM technology could be some of the alternatives. In the milk-processing sector, the availability of ultrafiltration technology has enabled the development of milk component-based markets for milk solids with increasingly broad applications. This trend is expected to continue. Similarly, the growth of demand for dairy products as ingredients in other food products (particularly in pizzas, hamburgers, sandwiches, etc.) will continue. The future will also see a myriad of new dairy-based products. Recent years have already witnessed product developments such as new functional foods; cosmeceutical, nutraceutical, and pharmaceutical products; and new beverages such as omega 3- and calcium-fortified milk. A promising recent development is also the introduction of a new lactose-free dairy drink produced by a special filtration process that removes half of the milk lactose.
Lactose-free milk could be an important factor, driving higher milk consumption, particularly in Asia, where more than half of the population is believed to have some form of lactose intolerance. Finally, in the context of consumer-driven food safety and health concerns, traceability becomes the norm, and this will require the adoption of new technologies and tests for the analysis of residues.
Conclusions In the context of the current global economic situation and the lack of progress in the Doha round negotiations, it is difficult to guesstimate when the final deal of the Doha round could be sealed. It could indeed be expected that the final modalities will impact future dairy markets. However, it is important to keep in mind that the Doha process is not about eliminating agricultural policies but about increasing transparency, fairness, and efficiency of agricultural trade. It follows that adjustment pressure, following the Doha round deal, on producers in developed countries that support domestic agriculture might not be excessive, although those domestic markets that have relatively high market price support measures in place will likely be affected more. But, the actual impact depends on the global market situation and the way countries organize future support to agriculture. Many support policies decoupled from production are already in place and one could expect further shifts toward more effective policies better targeted at specific objectives, possibly including disadvantaged producers or production zones, and delivery of social benefits related to environmental and regional concerns. In fact, good agricultural policies do not need to depend on the WTO negotiations. Moreover, even without a Doha deal it seems that it would become increasingly difficult for governments to continue domestic support based on trade barriers for the traditional dairy products in the face of the rapidly evolving trade in new dairy product and dairy ingredient markets, and globalization of the dairy markets in general. For example, the emergence of a sophisticated ultrafiltration process and expanding markets for milk ingredients have already diminished, to some extent, the importance of increasingly dated dairy support policies. Moreover, the process of globalization is crossing traditional trade barriers and is changing the structure of dairy markets, which have already started to be much more responsive to market signals and changing consumer preferences. Globalization of the dairy sector is set to continue, and international dairy companies will continue to penetrate the less developed markets to satisfy both local and growing export demand. The investments
Policy Schemes and Trade in Dairy Products | World Trade Organization
of multinational dairy processing firms will influence the development of new products and the transfer of technologies that improve market size and reach. The investments of multinational dairy processing firms will influence the development of new products and the transfer of technologies that improve market size and reach. These developments will however need to respect environmental considerations. It could be expected that increasingly important factors which are to influence dairy industry in the future are deterioration of natural grasslands, limited water resources and water pollution. The attention on food security and safety will persist. Safety of milk and dairy products could be expected to become an overriding requirement for producers and dairy supply chain in the future. A related issue for the future dairy sector is the ability of milk and dairy products to keep a good-and-safe image in a broader sense. The industry will need to remain proactive and innovative in order to maintain the share of milk and dairy products in consumers’ diets. Nevertheless, milk is a very unique product that contains very unique components, and it is difficult to see how the dairy industry would not be able to profit from this natural advantage. See also: Policy Schemes and Trade in Dairy Products: Agricultural Policy Schemes: European Union’s Common Agricultural Policy; Agricultural Policy Schemes: Other Systems; Agricultural Policy Schemes: Price and Support Systems in Agricultural Policy; Agricultural Policy Schemes: United States’ Agricultural System; Codex Alimentarius; Standards of Identity of Milk and Milk Products; Trade in Milk and Dairy Products, International
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Standards: Harmonized Systems; Trade in Milk and Dairy Products, International Standards: World Trade Organization.
References Busch L (2004) The Changing food system: From markets to network. Paper presented at the XI World Congress of the International Rural Sociological Association. Trondheim, Norway, July. Cox TL and Zhu Y (2004) Assessing world dairy markets and policy reforms: Implications for developing countries. In: Aksoy MA and Beghin JC (eds.) Global Agricultural Trade and Developing Countries., Washington, pp. 161–176. DC: World Bank. Langley S, Somwaru A, and Normile MA (2006) Trade liberalization in international dairy markets: Estimated impact. Economic Research Report Number 16. ERS, USDA. Neary JP (2004) Europe on the road to Doha: Towards a new global trade round? CESifo Economic Studies 50(2): 319–332. OECD (2002) Agriculture and Trade Liberalisation: Extending the Uruguay Round Agreement. Directorate for Food, Agriculture and Fisheries, Committee for Agriculture. Paris: OECD. OECD (2005) Dairy Policy Reform and Trade Liberalisation. Directorate for Food, Agriculture and Fisheries, Committee for Agriculture. Paris: OECD. OECD (2008) Role, Usage and Motivations for Contracting in Agriculture. Paris: OECD. OECD-FAO (2008) OECD-FAO Agricultural Outlook 2008–2017. Paris: OECD. Reardon T and Hopkins R (2006) The supermarket revolution in developing countries: Policies to address emerging tensions among supermarkets, suppliers, and traditional retailers. European Journal of Development Research 18: 4. WTO (2005) Doha work programme. Draft Ministerial Declaration. Ministerial Conference, Sixth Session. Hong Kong, China, 13–18 December, WTO. WTO (2008a) Chairperson’s Report on July 2008 Package Negotiations, with unofficial notes. http://www.wto.org/english/tratop_e/agric_e/ chair_report_11aug08_e.htm WTO (2008b) Revised draft modalities for agriculture. Committee on Agriculture, Special Session, TN/AG/W/4/Rev.3. 10 July.
PREBIOTICS
Contents Types Functions
Types T Sako and R Tanaka, Yakult Europe B.V., Almere, The Netherlands and Yakult Central Institute for Microbiological Research, Tokyo, Japan ª 2011 Elsevier Ltd. All rights reserved.
Introduction The human gastrointestinal tract becomes inhabited by a huge number of microbes immediately after birth. It has been calculated that in adults this complex open ecosystem, or the intestinal microflora formed in the colon (cecum to proximal and distal colons to rectum), is composed of some 1014 bacteria of hundreds of different species. The microflora as a whole or individual microbes are likely to play pivotal roles in the development of normal gut functions and maturation of mucosal immune system, and in the prevention and/or stimulation of intestinal disorders. The composition and metabolic activity of the gut microflora are influenced by various environmental factors, namely diet, age, stress, health status, and medication. Among all, dietary carbohydrates are the predominant carbon and energy sources for the gut microbes, and hence affect the growth of individual bacterial species in the colon. It has been calculated that 20–60 g of dietary carbohydrates ingested escapes digestion by human digestive enzymes daily, and they become substrates for fermentation in the colon. Among these nonabsorbed carbohydrates, 5–35 g is resistant starch, 10–25 g is nonstarch polysaccharides, and 2–8 g is nondigestible oligosaccharides (for terminology, see below). The diversity and amounts of these carbohydrates influence the composition and metabolic activity of the colonic bacterial ecosystem, which in turn strongly affect human health. The term ‘prebiotics’ was introduced by Gibson and Roberfroid in 1995 to describe the ‘‘nondigestible food ingredients that beneficially affect the host health by selectively stimulating the growth and/or the activity of one or a limited number of bacteria in the colon’’. A characteristic underlying the
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prebiotic concept is to increase ‘indigenous’ beneficial bacteria in the gut by virtue of feeding specific substrates that are preferentially utilized by these bacteria, in contrast to that of ‘probiotics’, which are themselves beneficial bacteria and therefore should directly influence the composition and metabolism of the gut microflora. In the past two decades a substantial number of food ingredients that definitely or possibly exert prebiotic effects have been described. The vast majority of them so far are shortchain carbohydrates that are not absorbed or are poorly digested by human enzymes, and are often called nondigestible oligosaccharides (NDO). In addition, recent extensive studies have revealed that certain nondigestible polysaccharides, which are often referred to as dietary fiber, exert health benefits through being fermented by a limited number of colonic bacteria into short-chain fatty acids, and so are capable of being prebiotics. In this article, the current knowledge of prebiotics especially from a technological and biochemical point of view is summarized.
What Are Prebiotic Effects? The principal effect of prebiotics is to improve the balance of the gut microflora by increasing the numbers of beneficial bacteria and decreasing those of potentially harmful bacteria, as defined above. This is achieved by the preferential utilization of prebiotic carbohydrates by beneficial bacteria such as bifidobacteria and lactobacilli. As a consequence of the alteration of the gut microflora composition, the metabolic activity and the systemic effects of the gut microflora will influence the host health status. In general, toxin production, intestinal
Prebiotics | Types
putrefaction leading to production of harmful and carcinogenic substances, unbalanced immune response, (opportunistic) infection, and the overgrowth of harmful bacteria are suppressed, and the enterocyte activity, bowel movement, and the mucosal immune system are optimized. It is widely accepted that lactobacilli and bifidobacteria are typically beneficial for human health. Primary fermentation products of bifidobacteria and lactobacilli from dietary carbohydrates are acetic and lactic acids. However, the final colonic fermentation products from dietary carbohydrates are short-chain acids (SCA) (mainly acetic, propionic, and butyric), some other organic acids (lactic and succinic), and gases (H2, CO2, and CH4). The proportion of each organic acid in the cecal and fecal contents depends on the composition of the gut microflora and the amounts and forms of supplied carbohydrates. Main players of these diverse fermentation processes are bacteria of clostridia and Eubacterium clusters, which not only directly utilize dietary carbohydrates but also further ferment acetic acid and lactic acid to butyric acid and propionic acid, although the detailed characters of these bacterial groups are not well known yet. There would be some other prebiotic effects based on the production of SCFA and other organic acids, for instance, improvement of mineral absorption in the colon, activation of colonocytes, acidification of cecal and fecal contents, or improvement of lipid metabolism.
Classification and Terminology of Dietary Carbohydrates Carbohydrates are classified into monosaccharides, disaccharides, oligosaccharides, and polysaccharides based on the number of monosaccharide units contained in them (which is often referred to as degree of polymerization or DP) (Table 1). Oligosaccharides are defined as carbohydrates with a DP from 2 to 10, according to the IUB–IUPAC nomenclature. However, some authorities recommend using the term disaccharides for those having two monosaccharide units (DP ¼ 2). In fact, most disaccharides fit into simple digestible sugars, while there are some disaccharides that resemble longer oligosaccharides in physiological and biochemical characteristics; for example, they are poorly digested and absorbed in the small intestine, but fermented thoroughly in the colon like a sort of nondigestible oligosaccharides, as will be described later. It is difficult to find chemical, structural, and physiological reasons to fix the definition for oligosaccharides. In this article, oligosaccharides with a DP from 2 to 10 that are not digested by mammalian digestive enzymes in the small intestine are defined as NDO.
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The sources of NDO are diverse. Some are isolated from natural origins (human milk oligosaccharides (HMO), soybean oligosaccharides (SOS), levan-type fructans, etc.) and some can be enzymatically or chemically produced from polysaccharides (maltooligosaccharides and isomaltooligosaccharides (for both, -glucooligosaccharides), oligofructose, xylooligosaccharides, chitin oligosaccharides, etc.) or from mono- and disaccharides (galactooligosaccharides (GOS), fructooligosaccharides (FOS), lactosucrose, gentiooligosaccharides, etc.). Polysaccharides occur naturally and have more complex structures and lengths than oligosaccharides, and can be classified into starch ( -glucans) and nonstarch polysaccharides (NSP) (Table 1). In both classes, there are soluble and insoluble polysaccharides. Of the carbohydrates in foods 80–90% are starch consisting of -1,4-linked amylose and -1,4- and -1,6-linked amylopectin, which are both principally hydrolyzed by human -amylase. However, the physical structure and DP of starch are diverse, and thus not all starch molecules consumed are hydrolyzed by human digestive enzymes and absorbed in the upper small intestine. The undigested starch entering the colon is called resistant starch (RS) and provides colonic bacteria with a carbon and energy source. On the other hand, NSP are the sum of non- -glucans and -glycans mainly found in plant cell walls such as cellulose, hemicellulose, xylan, arabinoxylan, mannan, pectin, and lignin. Some NSP are intracellular polysaccharides of plant cells such as gums, mucilage, and inulin. All these NSP are poorly digested and absorbed in the small intestine, and hence enter the colon undigested and are readily fermented by colonic bacteria to various extents. Different bacterial groups consume different polysaccharides; bacteroides mainly utilize amylose, amylopectin, and pullulan, which are all -glucan-type RS, while various anaerobic clostridial species utilize NSP. The term ‘dietary fiber’ was originally defined by Trowell, in 1972, as remnants of plant cells remaining after digestion in the mammalian gastrointestinal tract. Nowadays a number of other indigestible carbohydrates of plant and animal origin have been proposed and considered for inclusion in the group of dietary fiber. Hence it is most likely that dietary fiber will be defined as food carbohydrate polymers that are not hydrolyzed by the mammalian digestive enzymes in the small intestine and includes NSP, RS, and NDO. Among these, NDO occupy the most important position in prebiotic substances as they have been extensively studied and shown to be specific substrates for a limited number of colonic bacteria, especially bifidobacteria and/ or lactobacilli, in colonic fermentation, and are more readily assimilated in the colon than NSP and RS. Therefore, NDO’s exertion of the prebiotic effects could be quicker and more tangible than others’ after they enter
Table 1 Classification of dietary carbohydrates Carbohydrate classes (DP)
Subclasses
Examples
Fate in the gastrointestinal tract
Monosaccharides (1)
Sugar
Glucose, fructose, galactose
Disaccharides (2)
Sugar alcohol Digestible sugar
Sorbitol, xylitol, mannitol Sucrose, maltose, trehalose, (lactose)a
Nondigestible disaccharides
(Lactose),a lactulose
Sugar alcohol
Maltitol, lactitol
-Glucans
Maltooligosaccharides (isomaltooligosaccharides)b
Nondigestible oligosaccharides
Soybean oligosaccharides Galactooligosaccharides Fructooligosaccharides Fucosyllactose Sialyllactose Lacto-N-tetraose, etc. Amylose, amylopectin, pullulan
Absorbed in the small intestine Glucose gives rapid glycemic response Absorbed in the small intestine Absorbed in the small intestine Digestible by endogenous hydrolyzing enzymes Rapid glycemic response Not absorbed Nondigestible, but fermented in the large intestine Poorly digested and absorbed in the small intestine Partly or fully fermented in the large intestine Digestible but partly undigested in the small intestine and give rapid glycemic response Nondigestible Fermented in the large intestine No glycemic response Nondigestible Partly fermented in the large intestine
Oligosaccharides (2–10)
Human milk oligosaccharides
Polysaccharides (>10)
Starch ( -glucans) Resistant starch ( -glucans) Nonstarch polysaccharides ( -glycans)
a
Cellulose, hemicellulose, inulin, guar gum
Lactose may be both a digestible and nondigestible sugar. Isomaltooligosaccharides are less susceptible to digestive enzymes in the small intestine.
b
Digested and absorbed in the small intestine Rapid glycemic response Digestible but undigested in the small intestine Fermented in the large intestine Nondigestible Partly fermented in the large intestine
Prebiotics | Types
Lactose
the colon. The other reasons are that they are easy to handle in food processing and have organoleptic characteristics as mild sweeteners, both of which are important causes for NDO to be widely spread as commercial products.
Lactose (4- -D-galactopyranosyl-D-glucopyranose or -D-Galp-(1 ! 4)-D-Glcp or Gal 1-4Glc) is the primary sugar of mammalian milk. Human milk contains 7% lactose, and cow’s milk 4.8%. Even though lactose is the major carbon source for suckling infants, hydrolysis of lactose is rather a rate-limiting step. In addition, the lactase ( -galactosidase) activity in the small intestine gradually declines as an infant grows: According to a survey of Pima Indians in the United States, lactose malabsorption was seen in 40% by age 3–4 years, 71% by age 4–5 years, and almost 100% by age 8 years. The onset and degree of lactase deficiency are not homogenous among individuals and races. While most Caucasians in Northern European countries, Australia and New Zealand, and North America retain lactase activity, most Africans, Asians, and Native Americans are nonpersistent.
Disaccharides A certain class of disaccharides characterized with a -linkage between the two units could have a role as prebiotics. This class of disaccharides includes lactose, lactulose, lactitol, and several by-products from various oligosaccharide production processes (Figure 1(a)). These disaccharides are poorly or very slowly hydrolyzed by human digestive enzymes. Human studies, as well as in vitro growth analyses, published so far have shown their possible prebiotic effect particularly on stool habits. (a)
O
HOH2C CH2OH
CH2OH
O
O
HO
O
OH
CH2OH
O
O
CH
O
OH
OH
OH
OH
OH
Lactose
HCOH
CH2OH
O
O
O
OH
CH2OH
O OH CH2
CH2 O
O
H2C
O O
OH CH2OH
HO
O
O
HO
CH2OH
OH
O
OH HO
OH
n (n = 1–3)
Isomaltooligosaccharides
CH2OH OH
Soybean oligosaccharides
O
OH
~ OH
OH
O
OH
~ OH
HO OH
HO
~ OH
CH2OH
CH2OH
O
O
O
O
O
HO
HO OH
HO
Stachyose
O OH
O O
OH Raffinose
OH
Fructooligosaccharides
O
CH2OH O
O OH
OH
CH2
OH
O OH
OH
CH2
CH2
CH2 O
OH
HO OH n (n = 0–4)
O
OH
n (n = 0–7) CH2OH
Gentiooligosaccharides
O
OH
O OH
~ OH
OH
HO
CH2OH
~ OH
OH
Galactooligosaccharides (β1,4-type)
OH m OH (m = 0, 1)
O
OH OH
O
OH
CH2OH
O
HO
HO
OH
HO
CH2OH
OH
O
O
OH n (n = 0–5)
CH2OH O
OH
OH
O
CH2OH O
CH2OH
O
O
OH
HO
O
H2C
O
CH2OH
CH2OH O
O
Lactosucrose
CH2OH
HCO
Maltitol
OH
CH2OH
OH
OH
OH
CH2OH
Lactitol
HO CH2OH
CH
O
HO
CH2OH
Lactulose
(b)
HO
HCOH
OH
HCOH HCO
OH
CH2OH
CH2OH
HCOH
O
HO
OH
O
HO
~ OH
OH
CH2OH
CH2OH
HO
CH2OH
357
OH
O
OH
CH2OH O
O
OH
HO OH
OH n (n = 0–5)
Xylooligosaccharides
OH
H3COCNH
H3COCNH
n H3COCNH (n = 0–4)
Chitin oligosaccharides
Figure 1 Chemical structure of major prebiotic disaccharides (a) and oligosaccharides (b). Vertical bars without any formula at the tips of angles indicate a hydroxyl group. Hydrogen atoms on the main frames are not indicated.
358 Prebiotics | Types
Therefore, a substantial number of people are lactose malabsorbers. In these populations lactose behaves like nondigestible carbohydrates especially in lactose maldigesters. While the adverse effects of lactose are extensively studied, few reports concerning the effect on gut microflora are available. Although lactose is utilized preferentially by bifidobacteria and lactobacilli in in vitro fermentation, additional human studies are still needed to elucidate its prebiotic effect. Lactulose Lactulose (Gal 1-4Fru) is a synthetic disaccharide produced from lactose by chemical isomerization under alkaline conditions in the presence of sodium hydroxide and boric acid. Lactulose also naturally appears in heattreated cow’s and human milks. The generation of lactulose during lactose preparation was first reported in 1930. In the history of searching growth-promoting factors for bifidobacteria (bifidus factors) in human milk, Petuely described lactulose as a bifidus factor in 1957. Since then there are a large number of reports published about the effects of lactulose on the gut microflora, stool habits, SCA production, fecal enzyme activity, gut physiology, and so on. Lactulose is not hydrolyzed by human digestive enzymes and is preferentially utilized by bifidobacteria and lactobacilli as well as by bacteroides and some strains of clostridia and Gram-positive cocci inhabiting the human gut. According to these extensive studies, lactulose is now widely used not only as a food additive but also as a drug for constipation, hepatic encephalopathy, and Salmonella infection worldwide.
situations and is also used as a drug for treatment of chronic constipation and hepatic encephalopathy, although it may show a colonic fermentation profile different from that of lactulose.
Oligosaccharides The main and the most important constituents of prebiotics are NDO. Research and application of NDO have attracted much attention since the 1990s as the importance and the role of the gut microflora in human health are becoming more and more documented. As an intrinsic characteristic of NDO, they must escape hydrolysis by human digestive enzymes and be fermented by a limited number of colonic bacteria. Human pancreatic and intestinal digestive enzymes include those hydrolyzing the -glycosidic bonds of various monosaccharide moieties like glucose, galactose, and fructose, except for lactase ( -galactosidase) (EC 3.2.1.108), which mainly hydrolyzes the -linkage of lactose, whereas many colonic bacteria produce a variety of carbohydrate-hydrolyzing enzymes that act on oligo- and polysaccharides with -glycosidic bonds. Therefore, the principal NDO are -glycans (Table 2 and Figure 1(b)). The calorific values of most NDO are about half of those of digestible sugars, namely 2 kcal g1, which are calculated from energy values available by utilization of organic acids produced in the colon after fermentation. Major NDO that are commercially available or of physiological importance are listed in Table 2.
Sugar Alcohol (Polyol) Sugar alcohols are derivatives of mono- and disaccharides obtained by reducing a hexose moiety. Major sugar alcohols available and of commercial interest are the monosaccharide polyols sorbitol, mannitol, and xylitol, and the disaccharide polyols lactitol (Gal 1-4-sorbitol) and maltitol (Glc 1-4-sorbitol). In recent years, most of these sugar alcohols have been developed and widely applied for commercial use as noncariogenic sweeteners. They all have less sweetness than sucrose and lower calorific values than normal sugars. While the monosaccharide polyols are all efficiently absorbed from the small intestine, the digestion and thus the absorption of disaccharide polyols, namely, lactitol and maltitol, are much less than those of their parent disaccharides, lactose and maltose, respectively. The average rates of hydrolysis of lactitol and maltitol in human small intestine were shown to be 1.5 and 10% of those of lactose and maltose, respectively. These disaccharide polyols are good substrates for fermentation with colonic bacteria. Lactitol exerts quite similar effects to lactulose in clinical
Production of Nondigestible Oligosaccharides There are three ways to produce NDO: partial hydrolysis of polysaccharides, synthesis by transglycosylation from mono- and disaccharides, and extraction of naturally occurring oligosaccharides. Figure 2 shows the fundamental processes of industrial production of the former two types of NDO. In the industrial transglycosylation process, a high concentration of a substrate solution of mono- or disaccharides at more than 40–50% is used, and more than 50 up to 70% of the crude products are the target oligosaccharides after enzyme reaction. On the other hand, when polysaccharides are used as substrates, oligosaccharides are obtained either by direct endoglycosidase treatment (fructooligosaccharides, xylooligosaccharides, chitin oligosaccharides) or by liquefaction with complete glycolysis followed by transglycosylation (isomaltooligosaccharides, pannose oligomers). The substrates and enzymes used in the production process are indicated in Table 2.
Table 2 Nondigestible oligosaccharides and their structural features Name of NDO
Structures
Sources
Methods of preparation
Lactulose Galactooligosaccharides
-D-Gal-(1 ! 4)-D-Fru [ -D-Gal-(1 ! 4)]n-D-Glc (n ¼ 2 to 6) or[ -D-Gal-(1 ! 6)]n- -D-Gal-(1 ! 4)-DGlc (n ¼ 2 to 5) -D-Glc-[(1 ! 2)- -D-Fru]n (n ¼ 2–4)
Lactose Lactose
Inulin
Raffinose Soybean oligosaccharides Xylooligosaccharides
-D-Glc-(1 $ 2)- -D-Fru-[(1 ! 2)- -D-Fru]n (n ¼ 1 to 8)D-Fru-[(1 ! 2)- -DFru]n (n ¼ 2 to 9) -D-Gal-(1 ! 6)- -D-Glc-(1 $ 2)- -D-Fru [ -D-Gal-(1 ! 6)]n- -D-Glc-(1 $ 2)- -D-Fru (n ¼ 1, 2) -D-Xyl-[(1 ! 4)-D-Xyl]n (n ¼ 1 to 6)
Human milk oligosaccharides Chitin oligosaccharides
-L-Fuc-(1 ! 2)- -D-Gal-(1 ! 4)-D-Glc, -NeuAc-(2 ! 3)- -D-Gal-(1 ! 4)-DGlc, -D-Gal- -GlcNAc-(1 ! 3)- -D-Gal-(1 ! 4)-D-Glc, etc. -D-GlcNAc-[(1 ! 4)-D-GlcNAc]n (n ¼ 1 to 5)
Isomerization in alkali Enzymatic transgalactosylation with galactosidase (EC 3.2.1.23) Enzymatic transfructosylation with -fructosylfuranosidase (EC 3.2.1.26) Partial enzymatic hydrolysis with inulinase (EC 3.2.1.7) Natural product Extraction Partial enzymatic hydrolysis with xylanase (EC 3.2.1.8) Natural products
Lactosucrose
-D-Gal-(1 ! 4)- -D-Glc-(1 $ 2)- -D-Fru
Isomaltooligosaccharides ( -glucooligosaccharides)
-D-Glc-[(1 ! 6)-D-Glc]n (n ¼ 1 to 3)
Fructooligosaccharides Inulin-type fructans
Gal, galactose; Fru, fructose; Glc, glucose; Xyl, xylose; GlcNAc, N-acetylglucosamine; Fuc, fucose; NeuAc, sialic acid.
Sucrose
Sugar beet Soybean extract Xylan Human milk Chitin Lactose, sucrose Starch
Enzymatic hydrolysis with chitinase (EC 3.2.1.14) or acid hydrolysis Enzymatic transfructosylation with -fructosyltransferase (EC 2.4.1.9) Enzymatic hydrolysis followed by enzymatic transglucosylation with transglucosidase (EC 3.2.1.70)
360 Prebiotics | Types (a)
(b) Substrate (disaccharides or monosaccharides)
Substrate (polysaccharides)
Transglycosylation (batch reactor or immobilized enzyme reactor)
Solubilization and fragmentation (hydrolysis, transglycosylation, endoglycosidation)
Decoloration (activated charcoal filter)
Decoloration (activated charcoal filter)
Demineralization (ion-exchange chromatography)
Demineralization (ion-exchange chromatography)
Sterilization (filtration)
Sterilization (filtration)
Purification (ion-exchange chromatography)
Concentration (ultrafiltration)
Drying (spray dry)
Drying (spray dry)
Syrup-type NDO
Powder-type NDO
Concentration (ultrafiltration)
Drying (spray dry)
Syrup-type NDO
Powder-type NDO
Pure NDO
Purification (ion-exchange chromatography) Drying (spray dry)
Pure NDO
Figure 2 Flowcharts of the synthesis of NDO by transglycosylation using mono- and disaccharides (a) or by hydrolysis/fragmentation of polysaccharides (b).
Galactooligosaccharides GOS are industrially produced from lactose by enzymatic transgalactosylation. -Galactosidase (EC 3.2.1.23) of various origins such as Bacillus circulans, Aspergillus oryzae, and Cryptococcus laurentii is used for the industrial production of GOS. The enzymes from Bifidobacterium strains also have this transgalactosylation activity. The enzyme reaction basically proceeds by the addition of the galactose moiety to the nonreducing end of lactose and transgalactosylated oligomers, resulting in the production of tri-, tetra-, and pentasaccharides, traces of multioligosaccharides, and some disaccharide by-products with different -glycosidic bonds. The products have mainly 1,4- or 1,6-glycosidic bonds between the added galactose moieties (DP from 3 to 6) and a glucose unit at the reducing end of the molecule. GOS are physically stable in various conditions; they were not degraded at 160 C at a neutral pH or at 120 C at pH 3 for 10 min. GOS are not digested by human digestive enzymes at all, but are readily fermented in the colon. From extensive studies of the utilization of GOS, it has been revealed that Bifidobacterium and Bacteroides strains predominantly grow utilizing GOS as the sole carbon source. The prebiotic effect of GOS was first demonstrated by the pioneering work of Tanaka and colleagues in 1983, which showed an increase in indigenous bifidobacteria and a decrease in Bacteroidaceae after a daily intake of 10 g GOS for 2 weeks, in a human study. This was further confirmed by additional human studies. The potential of GOS to
improve defecation in subjects with a tendency toward constipation, to reduce harmful enzyme activities, to reduce the incidence of cancer, to stimulate bone mineralization, and to reduce the production of secondary bile acids in feces has been documented in human and/or animal studies.
Fructooligosaccharides There are two different ways to produce FOS: one is to partially hydrolyze fructose polymers of plant origin, and the other is to transfer the fructose moiety onto sucrose. Fructose polymers occur naturally in a number of vegetables and fruits as -2,1-linked inulin or -2,6-linked levan. Inulin is mainly used for the production of FOS having a DP of 2 to 10 by partial enzymatic hydrolysis using endoinulinase. This type of FOS, sometimes called inulin-type oligofructose, is a mixture of Glc 1-2 Fru[12 Fru]n (n ¼ 1 to 8) and Fru[1-2 Fru]n (n ¼ 1 to 9). FOS are also industrially produced from sucrose by enzymatic transfructosylation using Aspergillus niger -fructosylfuranosidase (EC 3.2.1.26). This type of FOS has a DP of 3–5 including an -1,2-linked glucose residue at the terminal of each molecule, and thus is nonreducing. The stability of FOS at neutral pH is as high as that of sucrose, and FOS do not degrade up to 150 C. However, FOS are less stable in acidic conditions; when boiled at pH 3, most FOS molecules degrade into smaller molecules within 15 min.
Table 3 Utilization of NDO by various intestinal bacteria
Bifidobacterium adolescentis Bifidobacterium bifidum Bifidobacterium breve Bifidobacterium infantis Bifidobacterium longum Lactobacillus acidophilus Lactobacillus casei Lactobacillus gasseri Lactobacillus salivarius Bacteroides distasonis Bacteroides fragilis Bacteroides ovatus Bacteroides thetaiotaomicron Bacteroides vulgatus Mitsuokella multiacidus Rikenella microfusus Megamonas hypermegas Clostridium butyricum Clostridium difficile Clostridium innocuum Clostridium perfringens Clostridium ramosum Eubacterium aerofaciens Eubacterium limosum Peptostreptococcus anaerobius Peptostreptococcus prevotii Peptostreptococcus productus Propionibacterium acnes Fusobacterium varium Veillonella alcarescens ssp. dispar Megaphaera elsdenii Enterococcus fecalis ssp. fecalis Enterococcus faecium Escherichia coli
Glucose
Lactose
Lactulose
GOS
FOS
SOSa
XOS
COS
Lactosucrose
þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ
þþþ þþþ þþþ þþþ þþþ þþþ þþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþ þþþ þþ þþþ þþþ þþþ þ þþþ þþþ þþ þþ
þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþþ þþ þþþ þþ þþþ þþ þþþ þþþ þ þþ þþþ þþþ þþ þ þþ þþ þ þþþ
þþþ þþþ þþþ þþþ þþþ þþ þþþ þþþ
þþþ þþ þþþ þþþ þþ
þþ þþþ þþþ þþþ þþþ þ þ þþ þþ þþþ þ þþþ þ þþ þþþ þ þ þþ þþ þþþ þþþ þ þþ þ þþ þ þ þþþ þþþ þ þþ þþ
þþþ þ þþþ þþ þþþ
þþ þþ þþ þ þþ þ þþ
þþþ þþþ þþþ þþþ
þ þþ þ þ þþ þþ þ
þþ
þþþ þþþ
þþþ þþþ
þþþ þ þþþ þþþ þþþ þþþ
þþþ
þþþ þþþ
þ þþ
þþ þþþ
þþ
a The data include raffinose. Indication for the growth of bacteria: þþþ, same as that on glucose; þþ, less than that on glucose; þ, slight growth; , no growth; no symbol, no data available. Adapted from Hayakawa Y and Committee for New Materials of Foods (eds.) (1998) New Knowledge of Oligosaccharides. Tokyo (in Japanese): Food Chem. Newspaper Co Ltd.
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Bifidogenic effect and other prebiotic effects of FOS such as lowering pH in the colon, reducing potentially harmful bacteria, reducing putrefactive substances, and improving stool habit have been demonstrated in human studies. In addition, beneficial effects of FOS on lipid metabolism and mineral absorption have been suggested in animal studies. While the effect on calcium absorption was further confirmed in several human studies, evidence of beneficial effects on lipid metabolism in humans is not conclusive.
Raffinose, stachyose, and soybean oligosaccharides SOS can be readily isolated from soybean extract and constitute raffinose (Gal 1-6Glc 1-2 Fru) and stachyose (Gal 1-6-raffinose) as oligosaccharides, as well as sucrose, glucose, and fructose. The contents of raffinose and stachyose in SOS are usually 8 and 24%, respectively, whereas the content of sucrose plus glucose and fructose is 55%. Pure raffinose is also commercially produced from beet syrup. Raffinose and stachyose (Figure 1(b)) are not digested in the human upper intestine, but are readily fermented by colonic bacteria, and so are NDO. Most strains of Bifidobacterium species except B. bifidum can grow in a medium containing SOS, raffinose, or stachyose as the sole carbon source, since they usually express -galactosidase activity, which can hydrolyze SOS. The bifidogenic effect of SOS and raffinose has been shown in human studies, where the minimum effective dose could be as low as 0.5 g oligosaccharides equivalent day1. In addition, SOS have the potential to reduce fecal levels of ammonia, p-cresol, and indole, to reduce harmful enzyme activities, and to alleviate constipation at the dose of 1 g oligosaccharides equivalent day1.
Xylooligosaccharides Xylooligosaccharides (XOS) are -1,4-linked xylose oligomers with a DP of 3 to 8, and industrially produced exclusively in Japan from xylan by partial enzymatic hydrolysis using endoxylanase (EC 3.2.1.8). Xylan, a sort of hemicellulose, is usually found in plant cell walls in conjunction with cellulose and pectin. For the commercial production of XOS, plant materials containing large amounts of xylan such as bagasse and cottonseeds are used. XOS is fermented by limited types of colonic bacteria such as Bifidobacterium spp., Lactobacillus spp., Bacteroides vulgatus, and Peptostreptococcus products. Bifidogenic effect in vivo has been shown in a couple of human studies where the effective minimal dose of XOS was as low as 0.4 g day1. Alleviation of constipation and stimulation of
mineral absorption were also documented in human and rat studies, respectively. Chitin Oligosaccharides Chitin oligosaccharides (COS) are N-acetylglucosamine (GlcNAc) oligomers (DP ¼ 2–6) with -1,4-linkages, and are produced from chitin derived from crabs and shrimps by partial acid hydrolysis in a hydrochloride solution. COS can be produced by enzymatic hydrolysis of chitin using bacterial chitinase (EC 3.2.1.14) as well. In addition to the beneficial effects on the gut microflora, attention has been paid to COS due to their immunomodulatory and antimicrobial activities, although the mechanisms behind these effects are mostly obscure. Human Milk Oligosaccharides A French pediatrician, Tissier, observed more than a century ago that bifidobacteria were predominant microbes in the feces of breast-fed infants but not of formula-fed infants, and had an idea that this bifidus flora played a role in the reduced incidence of infection in breast-fed infants. A number of possible substances as bifidogenic factors in human milk have been proposed and utilized to maintain the bifidus flora in formula-fed infants since then. Examples of substances that had been tried include lactose, N-acetylglucosamine-containing oligosaccharides, whey proteins, and vitamins, none of which, however, provided any evidence of modulation of the host gut microflora so far. The composition of HMO is complex. A variety of neutral and acidic oligosaccharides are found in human milk and colostrum. Although the major carbohydrate component of human milk is lactose, the total HMO levels reach up to 20% of the total carbohydrates, or over 12 g l1 in mature milk and 22 g l1 in colostrum, depending on individuals and the stages when the milk/ colostrum is collected. The core carbohydrates in HMO are lactose and lacto-N-tetraose (Gal 1-3GlcNAc 13Gal 1-4Glu), which are usually fucosylated and/or sialylated at nonreducing ends and other sites. Genomic and molecular biology studies have revealed that strains of Bifidobacterium longum ssp. longum, B. longum ssp. infantis, B. bifidum, and B. breve have various combinations of genes coding for enzymes responsible for the utilization of HMO, while HMO are not digested and absorbed in human small intestine. Therefore, HMO are most likely to be the bifidogenic factor in human milk. A certain group of HMO share the structural motifs with the cell surface glycoconjugates (glycoproteins or glycolipids) and mucins to which pathogens adhere at an initial step of infection. Thus, HMO could also be important as absorbers of pathogens to prevent infection during breast-feeding.
Prebiotics | Types
A practical method to produce lacto-N-biose, one of the active bifidobacteria-specific carbon sources derived from lacto-N-tetraose, from sucrose and N-acetylglucosamine with the enzymes sucrose phosphorylase (EC 2.4.1.7), UDP-glucose-hexose-1-phosphate uridylyltransferase (EC 2.7.7.12), UDP-glucose 4-epimerase (EC 5.1.3.2), and lacto-N-biose phosphorylase (EC 2.4.1.211) in large quantities has been established. However, it is still to be confirmed what components in HMO are and to what extent the HMO are responsible for the predominant growth of bifidobacteria in breast-fed infants. Other Oligosaccharides Other commercially available oligosaccharides are maltooligosaccharides ( -1,4-linked D-glucose oligomers) and isomaltooligosaccharides ( -1,6-linked D-glucose oligomers), both of which are often called -glucooligosaccharides as well, palatinose oligomers (oligomers of 2–4 palatinose (Glc 1-6Fru) units), -glucosylsucrose (coupling sugar), lactosucrose, nigerooligosaccharides ( -1,4linked D-glucose oligomers with an -1,3-linked D-glucose at the nonreducing end), gentiooligosaccharides ( -1,6linked D-glucose oligomers), chitosanoligosaccharides ( -1,4-linked D-glucosamine oligomers), and so on. Although they have not been necessarily intended to be used as prebiotic food additives, but rather to be used as alternative sweeteners with low calorific values and a low sweetness, evidence is accumulating that some of them have bifidogenic activity. In addition, oligosaccharide fractions obtained from partially hydrolyzed NSP such as guar gum, acacia gum, and wheat bran are possible prebiotic agents.
Polysaccharides Recent studies on dietary polysaccharides have revealed that a variety of dietary polysaccharides have physiological roles, which include significant fermentability by colonic bacteria leading to the production of SCA, influence on colonic microflora, stimulation of mineral absorption, and so on. While numerous studies have shown an increase in SCA production in the colon after the ingestion of RS, NSP, or even starch polysaccharides, an increasing number of studies have shown the effect of dietary polysaccharides on the gut microflora and other physiological parameters in humans or animals. In this section some examples of these polysaccharides are described. Fructans Fructan is the general name of soluble polysaccharides in which one or more fructosyl–fructose links constitute the
363
majority of glycosidic linkages. Two types of fructans have been identified: one is inulin, which is mainly of plant origin and has a 2,1-linkage between fructosyl residues, and the other is levan, which is mainly produced by fungi and bacteria and has a 2,6-linkage. Both types of fructan are neither digested by hydrolases of human origin nor absorbed in the intestines. Inulin has been manufactured, and thus has been studied extensively, and is of industrial importance. The biosynthesis of inulin in plant cells involves two enzymes: sucrose-sucrose fructosyltransferase (EC 2.4.1.99) leading to the formation of 1-kestose (Glc 1-2 Fru1-2 Fru) followed by chain elongation by fructan-fructan fructosyltransferase (EC 2.4.1.100) leading to the formation of inulin ( -D-fructofranan). A number of plants contain fructans as storage carbohydrates, some of which we eat as vegetables and fruits; examples are onion, garlic, asparagus, artichoke, chicory, and bananas. Among all, the root of chicory and the tuber of Jerusalem artichoke are the exclusive, if not the only, materials utilized for the industrial production of inulin because of the simplicity of extraction and purification. While native chicory inulin has a DP of 3–70 (average, 35), native inulin preparation from Jerusalem artichoke has a DP of 2 (sucrose) to 15 (average, 7). Inulin shows physiological properties as dietary carbohydrates similarly to the shorter FOS as evidenced in a number of studies published so far. Inulin has a bifidogenic effect like that of FOS, although inulin itself is not fermented by bifidobacteria in in vitro cultivation. This could be because the natural inulin preparation contains shorter oligomers like FOS in addition to longer polymers or because the fructosyl–fructose linkage in polymers may be labile in acidic conditions in the stomach or be digested to oligomers by other colonic bacteria, thereby being preferentially utilized by bifidobacteria. Its bifidogenic effect and fecal bulking with increased water content have been observed in human studies as well as in those using human fecal batch cultures or pure bacterial cultures. Other preliminary physiological effects of fructans reported so far are improved bowel habit, reduced putrefactive fermentation in the large intestine, improved calcium and magnesium absorption, and reduced total serum lipids and cholesterol. All these predictive health effects still await further confirmation in well-designed human trials. Resistant starch RS is a generic term for starches that escape hydrolysis by human digestive enzymes and absorption in the upper gastrointestinal tract. Starches are storage carbohydrates of plant cells consisting of linear 1,4-D-glucan chains (amylose) and those having some additional 1,6-linkages (amylopectin). During food processing, extensive
364 Prebiotics | Types
treatment of starches leads to breakages and conformational changes of starches to various forms, depending on the source and due the amylose-to-amylopectin ratio, resulting in the generation of retrograded starch with a crystalline structure. In addition, there is another type of RS that just escapes digestion in the small intestine due to its physical structure and due to other materials surrounding the starch. Englyst and colleagues, in 1992, classified RS into three groups: retrograded starch, physically indigestible starch, and RS granules. The bifidogenic effect of RS was first suggested by a feeding study on rats, followed by synbiotic (both probiotic and prebiotic) application to pigs, in which concurrent feeding of high-amylose maize starch and bifidobacteria resulted in higher fecal excretion of bifidobacteria. However, this effect needs to be confirmed by human studies. Other polysaccharides It has been reported that germinated barley foodstuff (GBF), which contains low-lignified hemicellulose and cellulose, has the ability to increase the number of bifidobacteria in the gut microflora and to produce more butyrate in the colonic contents. This could be explained as the production of butyrate by the coordinated action of bifidobacteria and Eubacterium, because the batch culture with both B. longum and Eubacterium limosum strains in a medium with GBF as the sole carbon source resulted in the accumulation of butyrate in the medium, whereas no or little butyrate was detected in the single cultures. This indicates that cellulose and hemicellulose, which cousititute a major part of NSP, may have the bifidogenic effect through an indirect supply of fermentable oligosaccharides for bifidobacteria, which are generated by partial breakage of the polysaccharides by Eubacterium. As such, bifidogenic and/or prebiotic effects of various indigestible polysaccharides could be substantiated in the future, as the research in this field will proceed.
Conclusions and Prospects After establishment of the definition of prebiotics in conjunction with that of probiotics, scientific research on food components and additives that influence the composition and function of human gut microflora in health and disease has been accelerated. While the ‘bifidogenic’ effect is recognized as a fundamental for prebiotics, other effects of oligo- and polysaccharides on the host health have been described. However, as it has been defined and revised later, the term ‘prebiotics’ should be used for the food components that have the ability to change the
composition and/or activity of the intestinal microflora to healthier states. Nowadays more than 10 different di- and oligosaccharides are considered as prebiotic agents due to their bifidogenic effect, and the number is still increasing as research and development on dietary carbohydrates proceeds. In addition, the health benefits of prebiotics or dietary carbohydrates are extended wider than previously expected. This is typically explained by the effect on mineral absorption, which may be attributed to the increased production of SCA or to the acidification of the intestinal contents, although the precise mechanism underlying the effect is still to be confirmed. However, there are substantial reports that also describe the stimulating effect of dietary polysaccharides (dietary fiber) on mineral absorption. As such, while a number of different prebiotics with health benefits have been developed, which are composed of a variety of monosaccharide units, with different linkages and lengths, and have different physicochemical properties, the mechanism of action and the outcome of the effects could be similar to each other’s. In this respect, we may need some common biomarkers and analysis procedures with which sound scientific evaluation of each prebiotic agent can be made. See also: Prebiotics: Functions.
Further Reading Cummings JH and Englyst HN (1995) Gastrointestinal effects of food carbohydrates. The American Journal of Clinical Nutrition 75: 733–747. Cummings JH, Roberfroid MB, Andersson H, et al. (1997) A new look at dietary carbohydrates: Chemistry, physiology and health. European Journal of Clinical Nutrition 51: 417–423. Englyst HN, Kingman SM, and Cummings JH (1992) Classification and measurement of nutritionally important starch fractions. European Journal of Clinical Nutrition 46: S33–S50. Gibson GR and Roberfroid MB (1995) Dietary modulation of the human colonic microflora: Introducing the concept of prebiotics. The Journal of Nutrition 125: 1401–1412. Grizard D and Barthomeuf C (1999) Non-digestible oligosaccharides used as prebiotic agents: Mode of production and beneficial effects on animal and human health. Reproduction, Nutrition, Development 39: 563–588. Kunz C, Rudloff S, Baier W, Klein N, and Strobel S (2000) Oligosaccharides in human milk: Structural, functional, and metabolic aspects. Annual Review of Nutrition 20: 699–722. Macfarlane GT and Cummings JH (1991) The colonic flora, fermentation and large bowel digestive function. In: Phillips SF, Pemberton JH, and Shorter RG (eds.) The Large Intestine: Physiology, Pathophysiology and Disease, pp. 51–92. New York: Raven Press. Roberfroid MB (2007) Prebiotics: The concept revisited. The Journal of Nutrition 137: 830S–837S. Roberfroid MB and Delzenne NM (1998) Dietary fructans. Annual Review of Nutrition 18: 117–143. Sako T, Matsumoto K, and Tanaka R (1999) Recent progress on research and applications of non-digestible galactooligosaccharides. International Dairy Journal 9: 69–80. Voragen AGJ (1998) Technological aspects of functional food-related carbohydrates. Trends in Food Science & Technology 9: 328–335.
Functions T Sako and R Tanaka, Yakult Central Institute for Microbiological Research, Kunitachi, Tokyo, Japan ª 2011 Elsevier Ltd. All rights reserved.
Introduction At the end of the nineteenth century, H. Tissier discovered a huge number of specific bacteria, bifidobacteria, in the feces of breast-fed infants. It was believed after his discovery and from the subsequent studies that the bifidobacteria-dominated microflora, called ‘bifidus flora’, played an important role in the reduction of infectious diseases in breast-fed infants. In the same line of evidence E. Metchnikoff speculated in his book The Prolongation of Life published in 1907 that fermented milk with lactic acid-producing bacteria could have a role in keeping the intestines healthy, thus leading to longevity. In addition, there was accumulating evidence indicating that the healthy gut microflora helps the animal to resist infections, which was hence called ‘colonization resistance’ or ‘competitive exclusion’. All these observations in conjunction with practical applications of certain bacteria to treat infections in humans and animals generated an idea that certain beneficial bacteria can modulate the gut microflora to maintain a healthy balance of the flora, thus relieving the adverse effects of disturbed gut microflora and keeping the host animal healthy. R. Fuller proposed in 1989 to call these beneficial bacteria ‘probiotics’, and lactic acid-producing bacteria, namely, lactobacilli and bifidobacteria, have been recognized so far as typical probiotics. Considering the determinants of the composition of the gut microflora, in turn, dietary components of our daily life strongly affect the growth and metabolism of the gut microbes; especially, dietary carbohydrates are the major energy and carbon source for the bacteria inhabiting the colon. Although the colonic bacteria as a whole have glycolytic activities against a variety of carbohydrates consisting of different monosaccharide units with different linkages and different lengths, the individual bacterial species/strains have a different set of enzymes with different substrate specificity. Therefore, the diversity of dietary carbohydrates has a strong influence on the composition of the gut microflora. As scientific evidence showing the effects of various carbohydrates on the composition of microflora accumulates, it has been recognized that certain carbohydrates can stimulate the growth of beneficial bacteria such as lactobacilli and bifidobacteria, and can provide the host with health benefits. Based on these observations, G. Gibson and M. Roberfroid proposed in 1995 the term ‘prebiotic’ for a food component
that beneficially modulates the gut microflora to improve host health. As the research on prebiotics proceeds through the years, the health-promoting effects of prebiotics seem to be wider than initially expected. There have been published reports on a wide variety of dietary carbohydrates with various health benefits. The overall fate of prebiotics in the large intestine and their health benefits are briefly illustrated in Figure 1. In this article the possible health effects of prebiotics are described.
Definition of Prebiotics A prebiotic is defined as ‘‘a nondigestible food ingredient that beneficially affects the host health by selectively stimulating the growth and/or the activity of one or a limited number of bacteria in the colon’’. As prerequisites of a prebiotic agent, the food ingredient must be neither degraded nor absorbed in the upper intestinal tract and be a selective substrate for a limited number of indigenous beneficial bacteria; thus it alters the balance of the gut microflora in favor of a healthier composition. While carbohydrates, proteins, lipids, and other minor components of foods like vitamins and minerals that are supplied unabsorbed through the small intestine could be candidates for prebiotics, only nondigestible carbohydrates of different monosaccharide units with a rather short chain length are recognized and established so far as prebiotic agents. Among dietary carbohydrates, nondigestible oligosaccharides (NDO) including some disaccharides are the main prebiotics, which can either be extracted from natural plants and animals or be manufactured by enzymatic or chemical reactions (for a review, see Prebiotics: Types). Nowadays, a substantial number of NDO with different structures and lengths are commercially available. In addition, fewer differences between the effects of prebiotics and those of indigestible dietary polysaccharides (or dietary fiber) are detected now than in the past, as the research on both NDO and dietary fiber advance. Especially the production of short-chain fatty acids (SCFA) from these compounds and the subsequent physiological effects in response to SCFA are probably common for prebiotics and dietary fibers. In addition, certain indigestible polysaccharides were reported to be bifidogenic, thus being able to be prebiotics. As a conclusion, the bifidogenic effect is a key criterion to
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366 Prebiotics | Functions
Prebiotics
Bifidobacteriapredominated microflora
Lower pH
Lower putrefactive substances
Mineral absorption
Dietary polysaccharides
Butyrate Propionate Acetate
Energy supply
Unfermented fiber
Higher water content
Lower secondary bile acids
Lower putrefactive enzyme activity
Cancer prevention
Stool bulking
Improvement of bowel movement
Lipid metabolism
Figure 1 Flow of metabolism of indigestible carbohydrates in the large intestine and their proposed effects.
distinguish prebiotics from other fibers. However, it is conceivable that this definition may be open for revision in the future.
Composition of the Human Gut Microflora and Health The human gastrointestinal (GI) tract, especially from cecum to rectum, is heavily colonized by microbes, reaching 1012 g1 contents or 1014 in total, with more than 200 species in a person or probably a total of 500–1000 species. This implies that about half of the solid content of the colon or feces is bacteria. After birth, the composition of the gut microflora of a newborn undergoes changes in response to factors such as changes of diet, health status, stress, age, and medication. The fetal GI tract is sterile, but the colonization initiates during birth. It is well understood that during the period of feeding with mother’s milk, the composition of the gut microflora of the infant is rather simple and that the predominant microbes are bifidobacteria. At the weaning period, there is a drastic change in the composition of the gut microflora from the infant type to the adult type, which is characterized by a more complex composition with increased contents of Bacteroides and clostridia, and a wider variety of different species. These commensal bacteria, about 70% of which are still uncultivable or unidentified, not only interact with the host at the mucosal surface but also constitute a complex metabolic machinery that provides the host with a variety of metabolites.
The most numerous microbes isolated from the adult colon are obligate anaerobes such as Bacteroides (1010–1011 g1 wet feces), Eubacterium (1010–1010.5 g1), Peptostreptococcus Bifidobacterium (109–1010.5 g1), 9 10 1 (10 –10 g ), and Clostridium (109–1010 g1). Facultative anaerobes such as Enterobacteriaceae, Enterococcus, and Lactobacillus are also indigenous but less numerous (105–108 g1). Some aerobes such as Bacillus, Staphylococcus, Pseudomonas, and yeasts are occasionally isolated at very low levels (103–105 g1), and are thought to be transient passengers. While the composition and the activity of the gut microflora of healthy persons are relatively stable in individuals, they could be easily disturbed by environmental changes such as illness, medication, stress, and a drastic change of the diet. For instance, antibiotic treatment often causes complete disruption of the composition of the gut microflora and severe diarrhea, and parenteral nutrition also disturbs the gut microflora as well as the gut functions. The intestinal microflora is a complex open ecosystem where the inhabiting microbes in the highly dense microbial community interact with each other and with the host animal, thus constituting the front line of defense against infection or modulating the host mucosal immune system. This could generate a barrier function, which is often called ‘colonization resistance’ or ‘competitive exclusion’, against pathogenic agents. Based on numerous studies, it has been observed that there are beneficial as well as potentially harmful microbes inhabiting the human GI tract. Lactic acid-producing bacteria like Lactobacillus
Prebiotics | Functions
and Bifidobacterium are considered beneficial as they produce acids (lactic acid and acetic acid) that contribute to maintain an acidic condition within the intestines, produce vitamins, and potentially modulate the host immune system, whereas some species of Bacteroides, Clostridium, Enterobacteriaceae, and yeasts are potentially harmful as they produce toxins and putrefactive substances, and sometimes become opportunistic infectious agents. Furthermore recent studies have provided indications that some indigenous bacteria and yeasts could have roles in initiating and activating intestinal inflammatory responses. Therefore it is widely accepted that the homeostasis and improvement of the healthy gut microflora in the direction of increasing beneficial bacteria and decreasing potentially harmful bacteria are definitely valuable to keep the host healthy.
Fermentation of Prebiotic Carbohydrates in the Large Intestine Production of Short-Chain Fatty Acids It has been estimated that among the dietary carbohydrates a person consumes everyday, about 20–60 g escape hydrolysis by the intestinal digestive enzymes and become substrates for fermentation in the colon: 5–35 g are resistant starch (RS), 10–25 g nonstarch polysaccharides (NSP), 2– 10 g unabsorbed mono- and disaccharides, and 2–8 g NDO. The pathway of carbohydrate metabolism in the colon is schematically illustrated in Figure 2. Most colonic bacteria have a variety of glycolytic enzymes with different substrate specificity. The major products of microbial fermentation of these carbohydrates in the large intestine are SCFA (mainly acetic, propionic, and butyric acids) and
gases (H2, CO2, and CH4). It is difficult to precisely measure the profile of fermentation of dietary carbohydrates in the colon, especially in human, because most SCFA produced are rapidly absorbed at the site of production. Many researchers have tried to estimate the amounts and available energy values of SCFA by using animal models, isotope-labeled substrates, and in vitro fermentation system, or by indirect calculations. The overall stoichiometry for the hydrolysis of dietary carbohydrates in the intestines can be drawn from G. Liversy and M. Elia’s calculation using the following equation: 58C6 H12 O6 þ 36H2 O ! 60CH3 COOH þ 24CH3 CH2 COOH þ 16 CH3 ðCH2 Þ2 COOH þ 92CO2 þ 256½Hþ
where Hþ will be further accepted by another Hþ or some other molecule, and the total yield of SCFA from 100 g of carbohydrates is calculated to be 64 g. This value is almost the same as that obtained from in vitro fermentation of starch using a human fecal sample. However, the fermentability and the molar ratio of acetic, propionic, and butyric acids produced from carbohydrate substrates vary considerably. Thus the yield of SCFA from mixed carbohydrates is usually between 30 and 50%. In contrast, the contribution of prebiotics in the production of SCFA is different. Considering the predominant utilization of prebiotics by bifidobacteria and/or lactobacilli where the contribution of bifidobacteria is much more than that of lactobacilli due to their numerical advantage, the fermentation profile of prebiotics in the colon will be shifted to a bifidobacteria-driven one. The stoichiometric equation for the hydrolysis of hexoses by bifidobacteria is as follows: 2C6 H12 O6 ! 3CH3 COOH þ 2CH3 CHOHCOOH
Carbohydrates (starch, NSP, NDO)
Hexose Pentose
Nitrogen source
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Pyruvate
Bacterial cell mass
Acetic acid Propionic acid Butyric acid
H2 CO2 CH4
Excretion in feces
Absorption as energy source
Excretion from mouth or anus
Figure 2 The pathway of fermentation of indigestible carbohydrates in the large intestine. NSP = non-starch polysaccharides, NDO = non-digestable oligosaccharides.
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where the available energy value remaining as SCFA (acetic acid) is about 50%, since absorption of lactate in the colon is very slow. In this reaction, gases are not produced as primary fermentation products, although other colonic bacteria such as Megasphaera elsdenii, Eubacterium hallii, and Anaerostipes caccae can further metabolize lactate into butyrate plus hydrogen and carbon dioxide gases. The fermentation pattern by lactobacilli is somewhat different. There are two types of lactobacilli, homofermentative and heterofermentative, which produce only lactate and a mixture of lactate, acetate, and ethanol, respectively, from carbohydrates. The contribution of these lactic fermentations in the physiology of the lower small intestine could be substantial, because lactobacilli are the major inhabitants of that region, although that in the large intestine is probably negligible. Nutritional Values The SCFA produced in the fermentation process are rapidly absorbed from the mucosal surface of the large intestine and used as energy source in various ways. The calorific value of indigestible and fermentable carbohydrates has been a subject of debate due to the difficulty of direct measurement. Considering that the calorific values of digestible carbohydrates absorbed from the small intestine are 4 kcal g 1 (16.8 kJ g1), the yield of SCFA from indigestible carbohydrates that are completely fermented in the colon is approximately 60%, and the efficiency of availability of SCFA in the colon is about 0.85. The practical calorific values of indigestible but easily fermentable carbohydrates like NDO are calculated to be approximately 2 kcal g 1 (8.4 kJ g1) for most of these compounds. The fates of SCFA in the body are distinctive: butyrate is exclusively utilized by the colonocytes, which derive 60–70% of their energy from butyrate; acetate is probably metabolized by skeletal and cardiac muscles and brain, is always detected in the bloodstream at the basal level of 50 mmol l 1, and rises to 100–300 mmol l 1 after meals containing indigestible carbohydrates. Acetate is also utilized for the synthesis of long-chain fatty acids, glutamine, glutamate, and so on. Propionate is a major glucose precursor in ruminants, but the fate of propionate in man is much less known. Probably it is also a substrate for hepatic gluconeogenesis in man, and its effect on the lipid metabolism has been proposed. Modulation of the Gut Microflora A prerequisite characteristic of a prebiotic substance is to be utilized by a limited number of beneficial colonic bacteria. A fermentability profile of a variety of NDO by different colonic bacteria in vitro has revealed that most strains of the genus Bifidobacterium can utilize these carbohydrates efficiently, while the fermentation of NDO
by other major genera inhabiting the colon such as Bacteroides, Clostridium, Eubacterium, and Peptostreptococcus is limited (for details, see Bacteria, Beneficial: Bifidobacterium spp.: Applications in Fermented Milks; Probiotics, Applications in Dairy Products. Prebiotics: Types). In fact, from the cell extracts of bifidobacteria grown in a medium with glucose as a sole carbon source, hydrolyzing activities against -glucosyl, -glucosyl, galactosyl, and -fucosyl bonds have been detected. This is not necessarily achieved by different enzymes. A couple of -galactosidases (EC 3.2.1.23) and -glucosidases (EC 3.2.1.21) with diverse substrate specificity have been identified in various strains of bifidobacteria of human origin. In contrast, animal strains of bifidobacteria analyzed so far except for Bifidobacterium animalis produce fewer glycolytic enzymes, the phenomenon being possibly associated with the presence of complex oligosaccharides in human milk. The production of the enzyme -fructosylfuranosidase (EC 3.2.1.26) responsible for the digestion of fructooligosaccharides (FOS) is induced by FOS in the medium. All these characteristics of bifidobacteria enable the identification of prebiotics as bifidogenic substances. Numerous studies have been conducted to substantiate the bifidogenic effect of prebiotic preparations. Petuely discovered in 1957 that lactulose produced from lactose has a bifidogenic effect in formula-fed infants. Supplementation of lactulose in the cow milk-based formula causes the formation of the so-called bifidus flora and a reduction of fecal pH in formula-fed infants. It also reduces the production and absorption of ammonia in the colon, and hence is approved as a medicine for constipation as well as hepatic encephalopathy. The first oligosaccharide found to exert a bifidogenic effect was galactooligosaccharide (GOS). Tanaka et al. demonstrated that after 1 week of GOS intake at doses of 3–10 g day1, the fecal bifidobacteria increased in a dose-dependent manner, which often accompanies the change of the composition of the gut microflora from a Bacteroidaceaepredominant to a bifidobacteria-predominant one and/or a decrease in Bacteroidaceae. This is also the case for FOS, lactosucrose, xylooligosaccharides (XOS), sucrosyloligosaccharides (SOS), gentiooligosaccharides, and isomaltooligosaccharides (or -GOS). The generation of bifidus flora in breast-fed infants has been confirmed in recent studies with both the authentic plating method and the molecular method, indicating that human milk oligosaccharides (HMO) or certain components in human milk act as prebiotic substances. Effective doses of prebiotics to exert the bifidogenic effect in man have been estimated to be approximately 3–10 g day1 for most NDO. However, XOS has been reported to show the effect at a dose less than 1 g day1, and NDO having -glycosidic linkages like isomaltooligosaccharides usually need
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more than 10 g day1 to show the effect similar to that of -linked NDO due to their partial digestibility in the upper intestine.
Physiological Effects Improvement of Stool Frequency Beneficial effects of intake of NDO on the nature of feces have been shown in several human studies. NDO improve both the frequency and the consistency of defecation after habitual intake. For example, administration of GOS at a dose of 2.5–5 g day1 for 1 week led to a significant increase in the frequency of defecation in a group of women in a double-blind placebo-controlled trial. The effect was more apparent for subjects who tended to be constipated. The mechanism behind this effect is not precisely known yet. However the intake of prebiotics in addition to normal diet results in an increase in acids especially acetic acid and lactic acid due to the predominant utilization of the substrate GOS by bifidobacteria. In addition, it has been recognized that in some cases succinic acid also accumulates in the cecal and colonic contents after ingestion of GOS in rats with humanized gut microflora and in humans. Unlike the SCFA that are rapidly absorbed from the mucosal surface of the large intestine, lactic acid and succinic acid are less efficiently absorbed, and thus contribute to the decline of the pH of the colon and to the increase in fecal water content. All these alterations of the physiology of the colon could have a role in improving the stool frequency. In contrast, it has been observed that FOS exert an effect to prevent traveler’s diarrhea, which is probably due to the stabilization of bifidobacteria- and lactobacilli-predominated healthy gut microflora. Reduction of Putrefaction The colonic microflora is an agent for the metabolism of various substrates. It provides the host with a variety of enzymes, and the metabolic activity of the gut microflora is estimated to be as high as that of the liver. While dietary carbohydrates are fermented into SCFA and gases, proteins and amino acids that reach the colon are fermented into SCFA as well as branched-chain fatty acids, isobutyrate, isovalerate, and 2-methylbutyrate arising from valine, leucine, and isoleucine, respectively. In addition, proteolysis followed by amino acid catabolism causes an accumulation of ammonia, phenolic compounds, amines, and sulfur compounds, which are all putrefactive substances. These substances are absorbed into the bloodstream, and, either directly or after further metabolization in the liver, show detrimental effects on human health. In a study with rats approximately 40% of blood ammonia was derived from the intestine. It has been
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demonstrated that the amount of urea in rat urine, the final product of ammonia metabolism, is significantly lower in germ-free rats than in normal rats. In a human study with healthy volunteers, the ingestion of GOS not only reduced the fecal ammonia concentration significantly, but also reduced other putrefactive products such as phenol, p-cresol, and indole in the urine. The reduction of blood ammonia concentration by GOS was further confirmed in an additional study using hyperammonemia patients. Lactulose and lactitol have been approved as medicines for hepatic encephalopathy, because they are effective for reducing blood ammonia level of the patients probably due to their effect on intestinal putrefaction. Therefore it is concluded that NDO such as GOS and lactulose can modulate the gut microflora to reduce its putrefactive metabolic activity. Colon Cancer Prevention Several bacterial enzymes such as -glucuronidase, -glucosidase, and nitroreductase derived from the gut microflora can activate precarcinogens to proximal carcinogens. For instance, bile salts secreted from the liver are converted to secondary bile acids by the enzyme glucuronidase derived from bacteria, and the resultant products are potential promoters of colon carcinogenesis. In a couple of studies with human volunteers, a daily intake of GOS at a dose of 10 or 15 g significantly reduced the fecal -glucuronidase activity. In model systems using rats and chemical carcinogens, there are a few reports that have analyzed the suppressive effect of prebiotics on the development of cancer. In a model that monitored the development of colorectal cancer induced by 1,2-dimethylhydrazine (DMH) in rats, fully fermentable GOS appeared to be highly protective, while poorly fermentable cellulose was not effective. In another model, the effect of dietary carbohydrates including FOS and inulin on the development of aberrant crypt foci (ACF), which are recognized as early preneoplastic lesions in the colon, caused by the treatment with azoxymethane (AOM) was analyzed. The formation of AOM-induced ACF was significantly reduced by treatment with inulin, FOS, pectin, or coffee fiber (rich in arabinogalactan). The increase in butyrate concentration in the colon was suggested to be an effective change for the reduction of ACF formation in the colon, because only carbohydrates that resulted in the production of large amounts of butyrate reduced AOM-induced ACF formation. This supposed effect of butyrate on the suppression of cancer development could be explained in part by the inhibitory effect of butyrate on the proliferation of cells including colon tumor cells. In addition, FOS and inulin showed enhanced apoptotic effect in the distal colon of rats after treatment with DMH, where inulin was more effective than FOS. SCFA – acetate, propionate, and butyrate – can in fact induce
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apoptosis in colorectal tumor cell lines at a concentration of 0.5 mmol l1, where butyrate is the most effective agent. All these results imply that SCFA, especially butyrate, produced by the colonic fermentation of dietary carbohydrates may have a role in protecting against the development of cancer in the colon by inducing apoptosis in the injured cells or proliferating cells. However, the enhanced frequency of apoptosis may also imply that the colonic cells become more susceptible to the carcinogen by the increased butyrate concentration or that the activation of the procarcinogen was stimulated by the higher concentration of butyrate. There also appears a conflicting view that fully fermentable carbohydrates such as inulin, as compared with wheat bran, may enhance colon carcinogenesis in the distal colon based on the increased PKC activity and PKC 2 level in response to increased diacylglycerol in the colon in rats fed with a high-fat diet with inulin. Thus, the suppressive effect of prebiotics and dietary carbohydrates on colon carcinogenesis is still inconclusive. Immune Modulation There have been very few reports suggesting modulation of the immune system by prebiotics and dietary carbohydrates. It is not likely that prebiotics directly impact the body’s immune system; however, the improvement of the intestinal environment could enhance the immune system. As described above, prebiotics and dietary carbohydrate supplementation may reduce the development of colonic neoplasia. In general, cells having neoplastic lesions are excluded through the body’s immunological defense mechanism. The fact that the supplementation of FOS, inulin, or GOS in the diet resulted in the reduction of colon carcinogenesis by chemical carcinogens in rats suggests that the immune system involved in this process may be activated by these substances. Stimulation by FOS and inulin of apoptosis of colonocytes induced by treatment with a chemical carcinogen supports this idea. The question remains whether or not, and if so how, prebiotics and dietary carbohydrates directly or indirectly affect the immune system. An alleviation of the symptoms of atopic dermatitis in infants by raffinose has been reported. It could be mediated by the improvement of the colonic microflora; especially a reduction of Candida level in the gut microflora is supposed to be effective in alleviating the symptoms. However, this should be confirmed by additional sound scientific clinical studies. Stimulation of Mineral Absorption Evidence is accumulating showing the enhancing effect of NDO on the absorption of minerals including calcium, magnesium, iron, and zinc. An increasing interest is focused especially on the intake of calcium because of
its role in preventing osteoporosis. From animal and human studies, it has been shown that indigestible polysaccharides, NDO, and other carbohydrate compounds stimulate mineral absorption, and that the major site of action for absorption of minerals is the large intestine. This implies that the large intestine has a significant capacity to absorb minerals. Among NDO, inulin, FOS, GOS, lactulose, isomaltooligosaccharides, and raffinose have been demonstrated to stimulate mineral absorption in animal models. In normal rats, it has been shown that the enhancement of calcium and magnesium absorption was totally dependent on the reduction of cecal pH due to the enhanced production of SCFA by colonic bacteria, since simultaneous addition of neomycin with GOS did not show increased calcium and magnesium absorption. Increased bone mineralization and increased bone strength were also shown by using GOS, FOS, and lactulose in ovariectomized rat models. Unlike the numerous animal studies, however, human studies with clear positive effects of NDO on mineral absorption are not yet available. Ingestion of 15 g day1 of inulin, FOS, or GOS for 3 weeks did not affect mineral (calcium and iron) absorption significantly in 12 healthy young men. Feeding of a larger dose of inulin (40 g day1) significantly increased calcium absorption in nine healthy men. More recently by using postmenopausal women as subjects, it has been shown that feeding of 10 g day1 of FOS significantly increased magnesium absorption. Since there have not been many human trials regarding the effect of NDO or dietary carbohydrates on mineral absorption and bone mineralization, more studies are clearly needed. Modulation of Lipid Metabolism The possibility that prebiotics may have some effects on blood lipid metabolism is an attractive idea. In rats it has been demonstrated that feeding FOS significantly reduced triglycerides in very low-density lipoprotein (VLDL), which is likely to be due to a reduction of lipogenesis in the liver. Regulation of hepatic cholesterol synthesis by SCFA and precipitation of bile acids due to deconjugation and acidification in the intestines have been proposed as likely mechanisms of this effect. However, only very slight effects have been observed in human studies using healthy volunteers, diabetic patients, or hypercholesterolemic persons, which are not yet conclusive. It is still an open question whether or not prebiotics can exert beneficial effects on lipid metabolism and cholesterol lowering.
Conclusion and Perspectives Our daily diet is at the base of our healthy life. We eat a variety of foods derived from animals and plants every day, which basically include all the necessary components
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of nutrients we need. However, the balance of nutrients is not always sufficient to keep our health. Especially the modern dietary habits often cause the shortage of certain nutrient factors. A typical example is that of formula-fed infants who consume cows’ milk-based foods prior to weaning. It has been demonstrated scientifically that cow’s milk-based formula needs supplementation to fulfill completely the baby’s needs to prevent infection and to keep the infant’s gut microflora healthy. As the role of the gut microflora in human health is recognized more, the importance of management of the intestinal microflora will receive more attention. In the last two decades, a variety of dietary carbohydrates that fulfill the criteria for prebiotics have been developed and have become commercially available. At the same time numerous studies have been conducted in animal models and in humans to show different health effects of prebiotics, thus increasing their health claims. However, we must recognize what the true health benefits of the prebiotics are, and which ones are supported by sound scientific evidence. Unfortunately not every health effect of each of the prebiotics described in this article is sufficiently substantiated in human clinical studies, not even the principal effects of certain established prebiotics. However, these putative effects may counteract any additional physiological effects of prebiotics, and the elucidation of the mechanisms underlying the effects may add a new insight into the field of nutrition. Our knowledge of the composition and the function of the gut microflora is still limited. Recently established molecular identification techniques for bacteria have revealed that a number of bacteria even predominant in the intestinal microflora are still uncultivable. Although a prebiotic is required to be bifidogenic, the influence of the particular prebiotic on the fate of other bacteria is not precisely known. Considering the more than 200 or even 400 different bacteria inhabiting the colon, there may be other beneficial as well as harmful bacteria that
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preferentially utilize the prebiotic in the flora. Individual prebiotics are probably utilized by different sets of bacteria, thereby influencing the gut microflora and physiology in different ways. However, most physiological effects of prebiotics described so far are almost all possessed by every prebiotic uniformly. It may be very difficult to distinguish one prebiotic from another in their physiological characteristics, but when this will be achieved, the era of prebiotics will come. See also: Bacteria, Beneficial: Bifidobacterium spp.: Applications in Fermented Milks; Probiotics, Applications in Dairy Products. Prebiotics: Types.
Further Reading Cummings JH and Englyst HN (1995) Gastrointestinal effects of food carbohydrates. American Journal of Clinical Nutrition 75: 733–747. Cummings JH, et al. (eds.) Physiological and Clinical Aspects of ShortChain Fatty Acids. Cambridge, UK: Cambridge University Press 1995. de Vries M and Schrezenmeir J (2008) Probiotics, prebiotics, and synbiotics. Advances in Biochemical Engineering/Biotechnology 111: 1–66. Gibson GR and Roberfroid MB (1995) Dietary modulation of the human colonic microflora: Introducing the concept of prebiotics. The Journal of Nutrition 125: 1401–1412. Liversey G and Elia M (1988) Estimation of energy expenditure, net carbohydrate utilization, and net fat oxidation and synthesis by indirect calorimetry: Evaluation of errors with special reference to the detailed composition of fuels. American Journal of Clinical Nutrition 47: 608–628. Louis P, et al. (2007) Understanding the effects of diet on bacterial metabolism in the large intestine. Journal of Applied Microbiology 102: 1197–1208. Macfarlane GT, Steed H, and Macfarlane S (2008) Bacterial metabolism and health-related effects of galacto-oligosaccharides and other prebiotics. Journal of Applied Microbiology 104: 305–344. Roberfroid M (1993) Dietary fiber, inulin, and oligofructose: A review comparing their physiological effects. Critical Reviews in Food Science and Nutrition 33: 103–148. Sako T, Matsumoto K, and Tanaka R (1998) Recent progress on research and application of non-digestible galacto-oligosaccharides. International Dairy Journal 9: 69–80.
PSYCHROTROPHIC BACTERIA
Contents Arthrobacter spp. Pseudomonas spp. Other Psychrotrophs
Arthrobacter spp. G Comi, University of Udine, Udine, Italy C Cantoni, University of Milan, Milan, Italy ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by G. Comi, C. Cantoni and L. Cocolin, Volume 1, pp 111–116, ª 2002, Elsevier Ltd.
Introduction The genus Arthrobacter belongs to the ecologically and industrially important class Actinobacteria, family Micrococcaceae, which includes microorganisms that live in soil, subterranean cave silts, sea, glacier silts, sewage, water sludge, aerial surfaces of plants, vegetables, fish, and various animal species. In the environment, they are often the most numerous bacteria because of their versatility. Some species are psychrophilic and psychrotrophic, can use a wide range of organic substrates as sole or principal sources of carbon and energy, and do not require vitamins or other organic growth factors. Aromatic compounds can also be utilized. Arthrobacters are widespread in nature and they readily contaminate raw food, milk and milk products, meat and meat products, and fish and fish products. In food, arthrobacters may be recognized as indicators of sanitation or hygiene quality, or as contaminants of no particular importance. However, they may also grow and be involved in spoilage or ripening of food products. Some Arthrobacter strains have been isolated from human sources and consequently are considered to be opportunistic pathogenic microorganisms. The taxonomy of the genus Arthrobacter has been redefined many times. Great difficulty has been encountered in identifying and classifying Arthrobacter and related coryneforms such as Brevibacterium, Caseobacterium, Cellulomonas, Corynebacterium, Curtobacterium, and Microbacterium. For
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these reasons, sometimes many isolates have been identified as arthrobacters or ‘arthrobacter-like’ simply because they showed the rod–coccus growth cycle (Figure 1) and staining reactions that are characteristic of the genus. Strains of Arthrobacter can be readily recognized in different environments by their morphological properties, although they cannot easily be distinguished from closely related coryneform genera. The development of taxonomy for the genus Arthrobacter is as follows: 1928 – isolation from soil; 1933–38 – similar microorganisms confirmed in soil; 1957 – genus included in the family of Corynebacteriaceae; 1986 – two groups distinguished: A. globiformis/A. citreus and A. nicotianae.
Taxonomy The genus Arthrobacter is closely related to Aureobacterium, Caseobacterium, Cellulomonas, Corynebacterium, Curtobacterium, and Microbacterium and is more distantly related to Brevibacterium. Phylogenetically, it is a member of the high-GC Actinomycetes, and Arthrobacter species could not be separated from members of the genus Micrococcus. These are Gram-positive eubacteria. Only minor differences enable the genus to be distinguished from
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Figure 1 Growth cycles of Arthrobacter globiformis AC 166 starting from coccoid stage, on a rich medium at 25 C. Reproduced from Crombach WHJ (1974) Morphology and physiology of coryneform bacteria. Antonie van Leeuwenhoek 40: 361–376, with kind permission from Kluwer Academic Publishers.
coryneform bacteria. Several tests must be employed simultaneously to classify and identify Arthrobacter spp. and avoid confusion with closely related genera. Molecular and chemotaxonomic techniques are important for the characterization of coryneforms and Arthrobacter spp. because traditional methods based on morphological and physiological features only are insufficient to describe their biodiversity. In recent years, many methods have been developed to classify and identify arthrobacters. Traditional approaches are still used, but must be applied in conjunction with chemotaxonomic and molecular techniques, as the modern taxonomy of bacteria requires a multiphase classification strategy. The following approaches are the most recent and widely used approaches to Arthrobacter taxonomy: 1. Deoxyribonucleic acid (DNA) base composition and DNA–DNA homologies (DNA hybridization). 2. Analysis of particular cell constituents such as peptidoglycans, fatty acids, phospholipids (diphosphatidylglycerol, phosphatidylglycerol, and phosphatidylinositol), and glycolipids, and analysis for the presence or absence of teichoic acids. Numerous studies of the cellular fatty acid composition of coryneform bacteria have been used for their classification. In
many cases, acyl types allow for a more precise characterization. Recently, the identification of cellular fatty acids has enabled the classification into four groups of coryneform bacteria belonging to the genera Arthrobacter, Brevibacterium, Caseobacterium, Caseobacter, Cellulomonas, Corynebacterium, and Curtobacterium. 3. Isoprenoid quinone analysis. It evaluates the presence of dehydrogenated menaquinones with 8 (MK-8), 9 (MK-9), or 10 (MK-10) isoprene units. This is another new method of characterization, but its application has given rise to several problems in distinguishing species and genera. 4. PCR analysis. It is a new method of identifying and classifying Arthrobacter based on the analysis of 16S rRNA by polymerase chain reaction (PCR) and various electrophoresis techniques, such as temperature-gradient gel electrophoresis (TGGE) or denaturing-gradient gel electrophoresis (DGGE). Comparative TGGE is considered more useful in taxonomic studies of coryneform soil bacteria because a high number of strains from the principal species of the genera Aeromicrobium, Agromyces, Arthrobacter, Aureobacterium, Cellulomonas, Curtobacterium, Nocardioides, and Terrabacter can be tested and characterized. In addition, positive results obtained by comparative TGGE can be confirmed by whole-cell fatty acid methyl ester analysis. Finally, PCR amplification of 16S rRNA gene (rDNA analysis), followed by sequencing, allows the identification of new species of Arthrobacter (Figure 2). 5. Biochemical and physiological characteristics. The phenotypic characteristics do not enable differentiation of Arthrobacter species. The multiphase approach has led to the discovery of new species such as A. rhombi sp. nov. (Figure 3), isolated from the Greenland halibut (Reinhardtius hippoglossoides), in addition to A. albus sp. nov. and A. luteolus sp. nov., both isolated from human clinical specimens. It is only by simultaneous employment of several methods (biochemical characteristics, DNA G þ C content, wall murein composition and structure, 16S rRNA gene sequence) that researchers can identify and classify old and new species of Arthrobacter with certainty, and distinguish them from closely related genera.
Morphological and Physiological Characteristics The genus Arthrobacter includes a group of microorganisms with a rod–coccus growth cycle. Initially, the microorganisms grow as rods in a simple medium during the log phase, subsequently becoming shorter in the stationary phase and taking on the appearance of large cocci. In aged cultures, cells may have entirely coccoid conformations, but mixed rod–coccus types are often seen. When aged cells are transferred into fresh broths, they
374 Psychrotrophic Bacteria | Arthrobacter spp. Arthrobacter atrocyaneus Arthrobacter agilis 100 Arthrobacter axydans Arthrobacter polychromogenes Arthrobacter citreus Arthrobacter aurescens Arthrobacter tlicls 82 Arhrobacter ureafactens Arhrobacter histidinolovorans 86 Arhrobacter nicotinovorans Renibacterium salmoninarum Arthrobacter woluwensis Arthrobacter globiformis 86 Arthrobacter pascens Arthrobacter ramosus Arthrobacter sulfureus Arthrobacter creatinolyticus Arthrobacter uratoxydans Arthrobacter protophormiae Arthrobacter nicotianae Brevibacterium ligvefaciens 73 100 Micrococcus hneus Micrococcus lylae Arthrobacter cummensn Nesterenkonia halobia Arthrobacter crystallopoietes Kocuria rosea Stomatococcus mucilaginosus 100 Rothia dentocariosa 2% Figure 2 Phylogenetic relatedness among authentic species of the genus Arthrobacter, which have been subgrouped based on the results of 16S rDNA analysis. Organisms the names of which are displayed in the same color exhibit the same peptidoglycan structure. Numbers within the dendrogram indicate the percentages of occurrence of the branching order in 500 bootstrapped trees (only values of 70 and above are shown). Sequences of the species of the genera of the family Micrococcaceae served as root. The scale bar represents 2 nucleotide substitutions per 100 nucleotides. Reproduced from Stackebrandt E and Schumann P (2006) Introduction to the taxonomy of Actinobacteria. In: Dworkin M, Falkow S, Rosembreg E, Schleifer CK, and Stackebrandt E (eds.) The Prokaryotes: A Handbook on the Biology of Bacteria, 3rd edn., Vol. 3, pp. 297–321. New York: Springer, with kind permission from Springer (New York, USA) and the authors.
become irregular rods, sometimes rudimentarily branched and arranged in V-shaped formations. Cell size is variable and the diameter can be anywhere between 0.6 and 1.2 mm. This life cycle is observed in nonselective media, especially if seeded with food. Many studies have demonstrated that the life cycle matures within 24 h when the cells are isolated from mixed broth food and grown at 25 C. Both conformations are Gram-positive, but on aging, they may be rapidly decolorized and appear Gramnegative. The cell wall mureins contain L-lysine as the main dibasic amino acid. All Arthrobacter strains are non-acid-fast and nonspore-forming. The rods are nonmotile or occasionally motile. They are obligate aerobes, catalase-positive and
oxidase-negative, but a few soil and sea strains have been recognized as oxidase-positive. A large number of arthrobacters are mesophilic, with optimum temperature of 20–30 C. However, some strains are psychrophilic or psychrotrophic and may grow at 4–6 C, or even at close to 5 C (A. glacialis) or 0 C, in some cases. Psychrophilic strains, usually isolated from soil or sea, are characterized by an optimum temperature of 20 C. Mesophilic strains can be adapted to grow at 6 C. Finally, a few strains can grow at 37 C. Temperature seems to have a significant influence on the life cycle. At 25 C, rod–coccus transformation takes place faster than at 15 C. This effect does not seem to be restricted to A. globiformis. In contrast, pigment production appears to be unaffected by temperature. Orange, yellow, and pale red pigments may occur in Arthrobacter. Pigment development seems to depend on various factors such as the strains involved, exposure to light or dark, the growth medium, and the presence or absence of salt in the medium. Nevertheless, many Arthrobacter strains are not pigmented. The cells are rapidly killed by heating at 63 C for 30 min in skimmed milk or in some other nonselective broths. All Arthrobacter strains are chemoorganotrophic and strictly aerobic. Metabolism of carbohydrates and other carbon sources is exclusively respiratory and never fermentative. The most widespread strains of Arthrobacter, especially those from soil, can utilize glucose, saccharose, glycerol, acetate, and citrate. Numerous studies have demonstrated that Arthrobacter strains may utilize more than 90 different carbon sources. Furthermore, Arthrobacter strains seem to have no particular nutritional requirements. Only a few species require biotin, B-vitamins, amino acids, and a siderophore. Many arthrobacters are able to utilize as nitrogen sources either ammonium nitrogen salts or a mix of ammonium nitrogen salts and a single amino acid. In general, it seems that only strains isolated from cheese, sea fish, or food require organic nitrogen. Arthrobacter strains are not inhibited by 3–5% NaCl at pH >6. In contrast, growth slows down at pH 104 ml1) of spores or vegetative cells of Bacillus spp. have been reported. Both Bac. cereus group, Bac. licheniformis and Bac. coagulans, are the species of sporeforming bacteria predominantly in fresh raw milk. The number of spores in freshly pasteurized milk varies widely between dairy plants and on a daily basis in the same dairy plant. The spoilage potential of thermoduric/sporeforming psychrotrophs has been well demonstrated by incubating milk or cream free from postpasteurization contaminants and therefore free from Pseudomonas spp. and other heatlabile microorganisms. Spoilage may occur at 3 C after approximately 7 weeks of storage (Table 2). The shelflife of pasteurized, noncontaminated milk is approximately three times longer at 7–10 C than the shelf-life of commercially produced milk, which becomes contaminated after pasteurization and stored at 3–5 C (Table 4). Coryneform bacteria dominate freshly pasteurized cream or milk (Table 5). Very often, only 0.05–1 spore of psychrotrophic Bacillus spp. is detected in freshly pasteurized milk or cream by the MPN technique. Vegetative cells of Bacillus spp. can probably be detected on a selective medium such as polymyxin–egg-yolk–mannitol– bromothymol-blue agar in every package of freshly pasteurized milk which has been preincubated at room temperature. Raw milk has been shown to be a markedly more important source of psychrotrophic spores than postpasteurization contamination. Bacillus circulans occurs in both raw and freshly pasteurized milk at lower numbers than Bac. cereus. However, data from different sources show that Bac. circulans dominates spoiled milk or cream, free from postpasteurization contaminants, stored at 3–7 C. At 12 C, a significant proportion of bacteria at the time of spoilage are Bac. cereus, coryneform bacteria, micrococci and streptococci (Table 5).
Table 4 Effect of postpasteurization contamination (PPC) on shelf-life and psychrotrophic count of pasteurized milk or cream. Postpasteurization recontamination was avoided using aseptic packing or laboratory pasteurization Effect on shelf-life
Effect on psychrotroph count Count (cfu ml1) after storage at 6 C
Shelf-life (days) of milk or cream Storage at
PPC-free
Contaminated
Storage of cream for
PPC-free
Contaminated
3–5 C 7–10 C
49–28 35–20
11–6 7–5
6 days 13 days
4 103 7 105
7 105 5 107
Adapted from: Muir, 1996a; Muir, 1996b and Muir, 1996c and Stepaniak, L., 1991. Factors affecting quality and possibilities of predicting shelf-life of pasteurized and ultra-high temperature heated milks. Italian Journal of Food Science 3, pp. 11–26. Stepaniak (1991).
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Table 5 Microbial population patterns (% occurrence among isolated bacteria) of aseptically packed fresh and cold stored cream and cold stored concentrated milk
Bacillus circulans Bacillus cereus Other Bacillus spp. Streptococci Micrococci Coryneforms
Fresh cream, pasteurized at
Cream, pasteurized at 72 C for 15 s, by the end of shelf-life at
Concentrated 1:2 milk, pasteurized at 72 C for 15 s, by the end of shelf-life at
72 C for 15 s
80 C for 15 s
3 C
7 C
12 C
3 C
7 C
12 C
nd nd 3 5 22 70
nd 2 5 nd 3 90
100 nd nd nd nd nd
50 2 nd 2 5 41
18 30 5 15 15 17
90 10 nd nd nd nd
95 5 nd nd nd nd
65 35 nd nd nd nd
nd, not detected by plate count. Adapted from Dommett (1992).
Incidence of Psychrotrophs in Commercially Pasteurized Nonaseptically Packed Milk Postpasteurization contamination of commercially pasteurized, nonaseptically packed milk is unavoidable. Recontamination in modern dairy plants can be as low as one bacterial cell per liter, and frequently is in the range of the number of psychrotrophic Bacillus spp. spores in freshly pasteurized milk. Major contaminants are Gram-negative rods, especially Pseudomonas spp., which are the most significant bacteria determining shelf-life of nonaseptically packed milk stored at 7 C or lower. The generation time and the lag time of microflora in pasteurized milks with an initial psychrotrophic count 107 cfu ml1 (Table 2). Occasionally, flavor defects are noted at a population of Bacillus spp. 10 mg ml or serum 1
1
• •
protein >5.5 g dl between 1 and 7 days of age. Ninety percent of calves double their birth weight by 56 days of age. Less than 30% of calves are treated for disease during the first 30 days.
Key factors to consider in the preruminant feeding program include management • colostrum provision of high-quality liquid diets fed in sufficient • quantity to encourage biologically normal growth and
• • •
immunity weaning at a reasonably early age provision of adequate amounts of high-quality water and calf starter grain provision of a favorable rearing environment
Colostrum Management Consumption of adequate quantities of high-quality colostrum early in life is the single most important factor determining health and survival of the calf. The first milk produced by the dam is a rich source of immunoglobulins (Igs), nutrients, and immune cells. As shown in Table 1, the level of Igs declines rapidly over the first three milkings.
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Fortunately, the intestine of the newborn calf is able to absorb these Igs, unchanged for the first 6–24 h of life. Successful absorption is achieved by the consumption of 100–200 g of Ig as soon as possible after birth. Although the level of Ig is variable, good-quality colostrum contains approximately 50 g Ig l 1. The period of time that the calf is able to absorb colostrum Ig is also quite variable. It may cease within 6 h of birth, but generally ceases within 24 h. Reasons for cessation of absorption are unclear, but research indicates that the presence of large quantities of bacteria in the intestine may inhibit absorption of Ig. Feeding contaminated colostrum or a dirty calving environment may accelerate bacterial colonization of the intestine and impair Ig absorption. Thus, successful immunity transfer occurs when the calf consumes 3–4 l of ‘clean’ colostrum within the first 12 h of life. Colostrum may also be involved in the establishment of cellular immunity in the calf. Additional feedings of colostrum beyond the first day result in improved growth of the intestinal epithelium as well as improved absorptive capacity.
Liquid Diets for Calves Many alternatives exist for feeding the neonatal calf after the first day. They include whole saleable milk, waste milk unsuitable for human consumption, and milk replacer. Milk replacers vary widely in nutrient content and ingredient composition. Before selecting an alternative, one should consider the benefits and risks of each alternative feeding program for calves. Whole milk usually fosters the best growth of the calf as it contains high levels of protein (24% on a dry matter (DM) basis) and fat (28.7% on a DM basis) to support calf growth. In addition, it is likely that these nutrients are more highly digestible than those from other sources. However, in nearly all cases, whole milk is more expensive and there is a risk of transmission of disease to calves by feeding raw milk. On most dairies, there is a supply of waste milk from cows that have calved within the past 3 days or from cows that have been treated with antibiotics. Generally, waste milk contains similar levels of protein, fat, and lactose as whole milk. However, fat levels can vary from 2.0 to more than 4% and protein from 2.5 to 4.0%. Field studies with dairies utilizing waste milk for calves indicate that the
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Table 1 Summary of the composition of colostrum, transition milk, and normal milk Milking number Parameter
1
2
3
Milk
Specific gravitya Solids (%)a Protein (%)a Casein (%)a Immunoglobulin (mg ml 1)a Fat (%)a Lactose (%)a Vitamin A (mg dl 1) Vitamin E (mg g 1 fat)c
1.056 23.9 14.0 4.8 48.0 6.7 2.7 233–400b 45–206
1.040 17.9 8.4 4.3 25.0 5.4 3.9 190a
1.035 14.1 5.1 3.8 15.0 3.9 4.4 113a
1.032 12.9 3.1 2.5 0.6 3.7 5.0 34a–38b
1, Colosrum; 2 and 3, transition milk. a Foley JA and Otterby DE (1978) Availability, storage, treatment, composition, and feeding value of surplus colostrum: A review Journal of Dairy Science 61: 1033–1060. b Franklin ST Sorenson CE and Hammell DC (1998) Influence of vitamin A supplementation in milk on growth, health, concentrations of vitamins in plasma, and immune parameters of calves Journal of Dairy Science 81: 2623–2632. c Weiss WP Todhunter DA Hogan JS Smith KL (1990) Effect of duration of supplementation of selenium and vitamin E on periparturient dairy cows. Journal of Dairy Science 73: 3187–3194.
supply of waste milk varies from 2.5 to 9 kg per calf per day. On many dairies, the supply of waste milk is adequate to meet the needs of less than 50% of the calves prior to weaning. Therefore, feeding programs based upon use of waste milk must make accommodations for supplementation with additional milk solids when the supply of nutrients is inadequate. In addition to challenges with varying supply and nutrient content, waste milk frequently contains antibiotic residues (in the United States) and microorganisms that are potentially harmful to the calf. Fortunately, systems have been developed to effectively pasteurize either whole milk or waste milk, which renders waste milk less likely to cause disease in calves. Successful pasteurization occurs when milk is heated to a sufficient temperature for an adequate time period to destroy 98% of the microorganisms present. Most systems used for pasteurizing waste milk can be described as being batch or high-temperature short-time (HTST) units. Batch systems (Figure 1) are typically simpler and more suitable for feeding smaller number of calves (160, 108, 95, 78, 57, 47, 32 and 29 kDa forms of inhibin have been isolated. However, bioactive inhibin is usually defined as being the 32 kDa form of the – dimer. There is a lot of confusion as to the exact mechanisms by which all the inhibin forms control and affect follicular growth. Evidence exists that inhibins have a local as well as a systemic role in controlling follicular growth.
Corpus Luteum Function The CL forms from the collapsed preovulatory follicle after ovulation. In the cow, the weight and progesterone content of the CL increase rapidly between days 3 and 12 of the estrous cycle and remain relatively constant until day 16. The main function of the CL in cattle is to secrete progesterone. In cattle progesterone and its metabolite -pregnene-20 -ol-3-one are the major progestagens secreted by the CL. Progesterone is secreted both from CL formed during normal estrous cycles and pregnancy. During pregnancy, progesterone plays a similar role in decreasing gonadotropin secretion and prevention of behavioural estrus as occurs during the luteal phase of the estrous cycle. Luteinizing hormone is the major luteotropic hormone in cattle and is responsible for stimulating luteinization of the theca and granulosa cells of the preovulatory follicle into luteal cells. Luteal cells may be classified into small and large cell types both of which secrete progesterone. Small bovine luteal cells appear to secrete progesterone in response to LH stimulation, while large bovine luteal cells produce greater amounts of progesterone under basal conditions and are generally insensitive to exogenous LH stimulation.
Luteolysis of the Corpus Luteum Prostaglandin F2 (PG) is secreted by the uterus in cows. It is the major luteolytic hormone in ruminants. During the late luteal phase of a normal cycle PG is secreted in a pulsatile pattern from the uterus, but during the equivalent period of early pregnancy, pulsatile PG secretion is attenuated. The presence of an embryo prevents luteolysis by suppressing the ability of the uterus to release PG in a pulsatile manner rather than reducing the ability of the
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uterus to synthesize PG. This pulsatile secretion of PG induces luteolysis. Uterine PG reaches the CL through a local mechanism of countercurrent exchange between the uterine vein and the ovarian artery (Figure 3). Oxytocin plays an integral role in induction of PG release required for luteolysis. It stimulates the uterine endometrium to secrete PG in vitro and in vivo. Oxytocin along with estradiol potentiates the release of PG from the uterus; estradiol from the ovulatory dominant follicle appears to stimulate the development or formation of oxytocin receptors in the uterus and enables increased binding of oxytocin, which in turn stimulates PG synthesis from the nonpregnant uterus. Pulsatile PG secretion in ruminants is associated with pulsatile oxytocin secretion. Pulses of oxytocin occur concurrently with PG during luteolysis and most of this oxytocin appears to be luteal in origin. Uterine PG and luteal oxytocin comprise a positive feedback loop, and PG can stimulate luteal oxytocin secretion. The trigger for luteolytic pulses of PG to be secreted from the uterus has not been identified but oxytocin from the posterior pituitary has been suggested by some authors to be involved. In species such as cattle that require PG for luteolysis, oxytocin can only stimulate the uterus to secrete pulsatile PG during the late luteal phase. Thus, one or more components of pulsatile PG release must be absent in the uterine endometrium during the nonresponsive stage of the estrous cycle. Endometrial oxytocin receptors only increase approaching the time of luteolysis and their absence is thus a likely candidate for limiting the responsive period for PG secretion. The control mechanisms of induction of oxytocin receptors in the uterine
Uterine horn PG released into uterine vein
Corpus luteum Oviduct Ovary
Uterine vein
Ovarian pedicle
endometrium and the secretion of PG appear to involve the steroid hormones progesterone and estradiol. In ovariectomized ewes or cows, oxytocin will only stimulate PG secretion after the animal has been exposed for 7–10 days to luteal phase progesterone concentrations. Some of the processes that are required to supply precursors for PG secretion appear to be progesterone-dependent, such as accumulation of lipid droplets and triglycerides in the uterine endometrium. Estradiol administration during the mid-luteal phase of the cycle will induce premature CL regression. In sheep, acute treatment with estradiol on days 9 and 10 of the cycle induces an increase in endometrial oxytocin receptors within 12–24 h and premature luteal regression. Thus, progesterone and estradiol both appear to be necessary in the development of uterine oxytocin receptors. Estradiol appears to have the additional role of enhancing secretion of oxytocin from the posterior pituitary and infusion of low doses of estradiol to ovariectomized ewes results in pulsatile secretion of oxytocin from the posterior pituitary. Thus, the mechanism of luteolysis appears to be initially triggered by increased estradiol from the dominant follicle that increases oxytocin pulse frequency from the posterior pituitary, which in turn will stimulate PG secretion from the uterus during the late luteal phase, i.e. when oxytocin receptors are present on the endometrium. The initial secretion of PG stimulates luteal oxytocin secretion which in turn stimulates further PG secretion from the uterus and causes the uterus to become temporarily refractory to oxytocin for 6–8 h, thus establishing a pulsatile pattern of uterine PG secretion at 6–8 h intervals. In cattle and sheep, the presence of an embryo appears to inhibit the formation of oxytocin receptors in the endometrium, thereby preventing pulsatile release of PG required for luteolysis. The presence of certain proteins from the developing embryo in the uterus, e.g. trophoblast protein-1 (interferon- ), prolongs the estrous cycle, presumably because they inhibit pulsatile release of PG by some mechanism. Interferon- is now recognized as the key mediator of maternal recognition of pregnancy in cattle.
PGF
Ovarian artery
PGF into ovarian artery by countercurrent exchange
Figure 3 Schematic diagram illustrating the role of prostaglandin F2 (PG) in controlling luteolysis. Prostaglandin released from the uterine endometrium into the uterine vein is picked up by the ovarian artery through countercurrent exchange and is delivered back to the CL as a local mechanism where it causes luteolysis. (Adapted and reprinted from CD-ROM Learning Reproduction in Farm Animals, with permission of Rodney D. Geisert, Oklahoma State University.)
Conclusions It is concluded that the estrous cycle in cattle is typically 18–24 days in duration, with estrous behavior being expressed for an 8- to 24-h period during the late follicular phase. During the normal estrous cycle there are typically two to three and occasionally four waves of follicular growth each involving a period of emergence and selection followed by either atresia or ovulation of the dominant follicle. The gonadotropin hormones FSH and LH are the main regulators of folliculogenesis and
Reproduction, Events and Management | Estrous Cycles: Characteristics
steroidogenesis with LH being the major luteotropic hormone. LH pulse frequency is the major determinant affecting the ultimate fate of a selected dominant follicle. Pulsatile prostaglandin F2 of uterine origin is the main hormonal signal that induces luteolysis of the corpus luteum and the switch from the luteal to the follicular phase.
See also: Reproduction, Events and Management: Estrous Cycles: Postpartum Cyclicity; Estrous Cycles: Puberty; Mating Management: Detection of Estrus.
Further Reading Adams GP, Matteri RL, Kastelic JP, et al. (1992) Association between surges of follicle-stimulating hormone and the emergence of follicular waves in heifers. Journal of Reproduction and Fertility 94: 177–188. Bao B, Garverick HA, Smith GW, et al. (1997) Changes in messenger ribonucleic acid encoding luteinizing hormone receptor, cytochrome P450-side chain cleavage, and aromatase are associated with recruitment and selection of bovine ovarian follicles. Biology of Reproduction 56: 1158–1168.
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Campbell BK, Scaramuzzi RJ, and Webb R (1995) Control of antral follicle development and selection in sheep and cattle. Journal of Reproduction and Fertility 49 (supplement): 335–350. Cooke DJ, Crowe MA, Roche JF, et al. (1996) Review: Gonadotrophin heterogeneity and its role in farm animal reproduction. Animal Reproduction Science 41: 77–99. Cooke DJ, Crowe MA, and Roche JF (1997) Circulating FSH isoform patterns during recurrent increases in FSH throughout the oestrus cycle of heifers. Journal of Reproduction and Fertility 110: 339–345. Crowe MA (1999) Gonadotrophic control of terminal follicular growth in cattle. Reproduction in Domestic Animals 34: 157–166. Crowe MA, Kelly P, Driancourt MA, et al. (2001) Effects of folliclestimulating hormone with and without luteinizing hormone on serum hormone concentrations, follicle growth and intra-follicular estradiol and aromatase activity in gonadotrophin releasing hormoneimmunized heifers. Biology of Reproduction 64: 368–374. Ireland JJ and Roche JF (1987) Hypothesis regarding development of dominant follicles during a bovine estrous cycle. In: Roche JF and O’Callaghan D (eds.) Follicular Growth and Ovulation Rate in Farm Animals, pp. 1–18. The Hague: Martinus Nijhoff. McCracken JA, Custer EE, and Lamsa JC (1999) Luteolysis: a neuroendocrine-mediated event. Physiological Reviews 79: 263–324. Roche JF (1996) Control and regulation of folliculogenesis: a symposium in perspective. Reviews of Reproduction 1: 19–27. Savio JD, Keenan L, Boland MP, et al. (1988) Pattern of growth of dominant follicles during the oestrus cycle of heifers. Journal of Reproduction and Fertility 83: 663–671. Sunderland SJ, Crowe MA, Boland MP, et al. (1994) Selection, dominance and atresia of follicles during the oestrus cycle of heifers. Journal of Reproduction and Fertility 101: 547–555.
Estrous Cycles: Postpartum Cyclicity H A Garverick and M C Lucy, University of Missouri, Columbia, MO, USA ª 2011 Elsevier Ltd. All rights reserved.
Introduction In dairy cows, the interval from calving to resumption of ovulatory ovarian cycles has increased and fertility has decreased over the past half century as average milk production per cow has increased more than threefold. Understanding the physiological processes that regulate ovarian follicular development and ovulation is a necessary prerequisite for shortening the interval to first ovulation, increasing fertility, and optimizing reproductive management in modern dairy operations. During pregnancy, cows have a corpus luteum (CL) and do not ovulate additional follicles. Nevertheless, follicular growth in waves continues throughout pregnancy. Wave activity decreases as pregnancy progresses and dominant follicles are less prominent. Coincident with the reduction in follicular wave activity during pregnancy is a reduction in the pulsatile release of circulating luteinizing hormone (LH) in blood. Following parturition, ovarian follicular growth and ovulatory follicular cycles must be reinitiated if the subsequent pregnancy is to be established within a reasonable amount of time. The mechanisms associated with the resumption of ovulatory waves postpartum are complex and there is a large variation in the interval from parturition to first ovulation in lactating dairy cows. This article will review the timing of postpartum ovarian cyclicity in dairy cows and the mechanisms associated with normal and abnormal ovarian cycles during the postpartum period. The cellular and molecular mechanisms regulating ovarian follicular development and ovulation as influenced by body condition and energy balance will be discussed.
Ovarian Follicular Dynamics during Estrous Cycles in Cattle The characteristics of estrous cycles in cattle have been reviewed (see Reproduction, Events and Management: Estrous Cycles: Characteristics). However, a brief summary here is pertinent to the discussion of postpartum ovarian activity. The dynamic nature of ovarian follicular growth in cattle was unknown for a considerable period of time. A typical estrous cycle in cattle has two or three waves of follicular growth. The initiation of each follicular wave (recruitment) is characterized by the growth of a cohort (usually 2–6) of small follicles
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from approximately 2–4 to 5 mm in diameter. The initiation of each wave of follicular growth is preceded by a transient increase in circulating follicle-stimulating hormone (FSH). The recruited follicles continue their growth to approximately 7–8 mm in diameter. At this time, one follicle is typically selected (selection) to continue to grow to ovulatory size (14–18 mm in diameter; dominant follicle). The remaining subordinate follicles undergo atresia. If the cow is in the luteal phase of the estrous cycle, the dominant follicle maintains its maximum size for 3–6 days, but undergoes atresia and another wave of follicular growth is initiated. The dominant follicle in the second or third wave will ovulate if luteal regression occurs during the growing phase.
Postpartum Follicular Growth Gonadotropins At parturition, concentrations of LH, but not FSH, are low. In particular, mRNA expression of the subunit of LH is low, and there is little LH in the pituitary or in blood circulation. With increasing time following parturition, synthesis and release of the gonadotropins increase. There is little release of LH following gonadotropinreleasing hormone (GnRH) injection for the first week postpartum, but the mean concentration of LH and the pulsatile release of LH increase thereafter, and a GnRHinduced release of LH capable of inducing ovulation is possible within 2 weeks postpartum. Similar to initiation of follicular waves during normal estrous cycles, a transient increase in FSH precedes initiation of waves of follicular growth postpartum. The first wave of follicular growth is usually initiated within 5–10 days postpartum. Growth of follicles to approximately 9 mm in diameter follows the stimulation of the transient increase of FSH. Growth beyond this size is dependent upon additional stimulation with LH in addition to the FSH. When adequate concentrations of LH are present, follicles continue their growth to ovulatory size. Follicular Growth Waves of follicular growth following calving are similar to those seen in normal estrous cycles and are usually initiated within 10–14 days. With each wave of follicular growth, a cohort of follicles is recruited to grow above
Reproduction, Events and Management | Estrous Cycles: Postpartum Cyclicity
5 mm in diameter and the follicles continue their growth to about 7–8 mm in diameter, whereupon one follicle is selected for further growth. The selected follicle of the first follicular wave follows one of three fates: (1) it continues its growth to ovulatory size and ovulates (cyclic cows); (2) it grows to various sizes but not ovulatory size, stops growth, and undergoes atresia, following which a new wave of follicular growth is initiated (anovulatory anestrous cows); or (3) it surpasses ovulatory size and develops into an ovarian follicular cyst (cystic cows).
Estradiol
Estradiol
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LH Surge
CL
Estradiol
IGF-I LH
Postpartum Ovulatory Follicles Postpartum follicles that ovulate probably do so through the stimulatory effects of normal levels and secretory patterns of FSH and LH. Dairy cows that ovulate the first wave dominant follicle postpartum are generally in good body condition and are not experiencing extreme negative energy balance. Cows in poor body condition, in extreme negative energy balance, or with metabolic or infectious diseases at calving often have delayed initiation of follicular waves, multiple follicular waves before first ovulation, and extended intervals to first postpartum ovulation.
Postpartum Anovulatory Follicles In some cows, the first follicular wave postpartum does not end in ovulation, but instead ends in atresia. In cows that do not ovulate the first wave dominant follicle that occurs following parturition, initiation of follicular growth may occur at the same or at a later time than those that ovulate the first wave dominant follicle. Recurrent follicular waves usually occur in postpartum cows that do not ovulate the dominant follicle (Figure 1). While the processes of recruitment, selection, dominance, and atresia of follicles in anovulatory waves are generally similar to those observed in ovulatory waves, some differences have been noted. Anovulatory follicular waves are usually longer than ovulatory waves, and the maximum size of the selected follicle is usually smaller. The growth rate from recruitment (5 mm in diameter) to selection (7–8 mm in diameter) and to maximum size of the anovulatory dominant follicle is usually similar to that of the ovulatory follicle. Instead of reaching ovulatory size (16 mm in diameter), however, the anovulatory follicle usually stops growing when it is 10–14 mm in diameter. The smaller-sized follicles produce less estradiol than the larger ovulatory follicles, and the amount of estradiol produced is likely less than the threshold amount needed to induce the preovulatory LH surge. The reason that anovulatory follicles stop growing at the smaller size and have decreased synthesis and release of estradiol may be because of decreased LH secretion or decreased
Figure 1 Development of ovulatory follicles in postpartum cows. Ovarian follicles grow in waves during the postpartum period. Successive waves produce larger dominant follicles that secrete greater amounts of estradiol. The luteinizing hormone (LH) surge is induced and the corpus luteum (CL) is formed when estradiol concentrations reach a threshold level. Blood concentrations of insulin-like growth factor I (IGF-I) (dashed line) and LH (pulses) increase during the postpartum period from basal levels (first few days postpartum) to greater levels (3–4 weeks postpartum). The postpartum increase in LH and IGF-I depends on the nutrition and body condition of the cow. The LH and IGF-I synergistically promote follicular growth and development.
responsiveness of follicles to LH support. These mechanisms will be discussed in the following sections. In some dairy cows, the initiation of follicular waves is delayed for extended periods of time after parturition. Cows that do not initiate follicular waves postpartum are usually in extremely poor body condition at calving or have severe metabolic or infectious diseases that cause excessive loss of body condition and poor health. In general, any deleterious postpartum health problem increases the interval to initiation of follicular waves and ovulation, and decreases fertility (Table 1) .
Mechanisms Associated with Ovulatory and Nonovulatory Postpartum Follicles Initiation of postpartum ovarian cyclicity is related to body condition at calving and to negative energy balance following calving, which affects the change in body condition during the postpartum period. Cows should be in good Table 1 Influence of health status on reproductive performance of dairy cows
Days to first estrus Days to first insemination Days to pregnancy Cumulative pregnancy rate (%)
Healthy cows (n ¼ 38)
Cows with major health problems (n ¼ 26)
37.7 58.7
51.2 68.4
71.9 88.9
84.1 63.2
Adapted from Barton, et al. (1996) Journal of Dairy Science 79: 2225–2236.
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body condition at calving (body condition score (BCS) should be 3–3.5 on a 5-point scale, where 5 is obese and 1 is very thin). High-producing dairy cows are usually in a negative energy balance following parturition because there is a dramatic change in energy requirements to meet the energy demands of lactation. There is an immediate shift in metabolism from nutrient partitioning toward body reserves and fetal mass to one of nutrient mobilization of energy and protein stores to meet the demands of lactation. Energy and feed intake are not maximized in lactating dairy cows for a few weeks following parturition. It is during this time that negative energy balance reaches its maximum, and the resumption of postpartum cyclicity is dependent upon the severity of the negative energy balance and body condition of the cow. The effects of various nutritional and environmental factors on postpartum cyclicity are described below. Body Condition Attaining the optimum BCS of 3.0–3.5 during the dry period is important for reestablishment of ovarian cyclicity during the postpartum period. Cows that are overly fat (BCS near 5) have a decreased appetite following parturition compared with more ideally conditioned cows (BCS 3.0–3.5) and, thus, are in a greater negative energy balance and have a much larger change (decrease) in BCS. Cows that have increasingly larger negative changes in BCS during the postpartum period take a longer time to achieve first ovulation postpartum, and fertility is decreased. In addition, some cows calve with less than optimum body condition. Cows calving with BCSs of 1.5 or less have a longer interval to first ovulation than those that calve in better condition. Cows in very poor body condition do not have energy stores available to mobilize for maintenance and lactation requirements. It has long been known that the body diverts energy from reproductive processes when conditions do not meet the needs for maternal survival. Cows that experience the greatest change in body condition after parturition take longer to achieve ovulation than those that have less change in body condition, and conception rates of cows with a greater BCS loss are lower than those of cows with less BCS loss postpartum. Similarly, cows in a lesser negative energy balance or in a positive energy balance have greater conception rates than those with a more negative energy balance. Energy Balance As stated previously, high-producing dairy cows are in a negative energy balance following parturition. The negative energy balance increases for a period of time as milk production increases faster than feed intake. When the amount of negative energy balance decreases, events
leading up to the first ovulation begin. Ovulation of a dominant follicle postpartum is dependent upon stimulation through increasing mean concentration and pulsatile release of LH (Figure 1). Pulsatile release of LH is greater in cows that ovulate a dominant follicle in the postpartum period than in those that have recurrent follicular waves, and the size of the ovulatory dominant follicle is usually larger than the nonovulatory dominant follicles. In most cases, follicles that fail to ovulate do not reach full ovulatory size. Low energy availability decreases LH pulsatility and, thus, follicular stimulation and estradiol synthesis are less. Also the responsiveness of follicles to LH may be decreased because of lower concentrations of circulating insulin-like growth factor I (IGF-I) (Figure 2). The concentrations of circulating IGF-I are directly correlated with energy status. Cows in a greater negative energy balance have lower concentrations of circulating IGF-I. The IGF-I concentrations are greater in cows that are ovulating.
GH LH
Liver –
+
+
Ovary F
F
F Ovarian IGF-I
Blood IGF-I Energy balance Nutrition Disease Aging
Figure 2 Control of follicular growth by luteinizing hormone (LH) and insulin-like growth factor I (IGF-I) secretion in postpartum cows. At parturition, pulses of LH and concentrations of IGF-I in blood are low. Blood growth hormone (GH) concentrations are elevated and GH drives nutrient partitioning for milk synthesis. Most of the IGF-I in blood is derived from the liver and is released in response to GH. In early postpartum cows, the GH–IGF-I axis is uncoupled so that high concentrations of GH do not lead to elevated blood IGF-I. Negative energy balance, undernutrition, disease, and aging increase the amount of uncoupling and reduce IGF-I synthesized and secreted from the liver. The GH–IGF-I axis is recoupled postpartum so that the synthesis and secretion of IGF-I into the blood are increased. Pulses of LH increase postpartum and stimulate follicular growth. The greatest LH pulsatility is found in cows with better body condition and less negative energy balance. The effects of LH on the ovary are synergistic with IGF-I in blood. Greater IGF-I and more LH pulsatility postpartum act in a synergistic manner to increase the growth and development of ovarian follicles. Factors such as negative energy balance may decrease IGF-I by preventing the recoupling of the GH–IGF-I axis. Negative energy balance may also inhibit LH pulses. Collectively, low IGF-I and low LH pulsatility may not provide adequate stimulation for the development of a preovulatory follicle.
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Abnormalities of the Puerperium Cows must be healthy for efficient postpartum reproduction. Diseased cows are less fertile and the effects of disease on reproductive performance are greater than any other factor. Both metabolic and reproductive diseases and disorders can negatively affect reproduction. Cows with metabolic and reproductive diseases are usually in poorer general health, lose a greater amount of body condition, and experience delayed postpartum ovarian cyclicity. Thus, cows with abnormal puerperium require additional time to establish ovarian follicular waves and develop ovulatory follicles. In addition, fertility is lower in affected cows than in cows with no abnormalities during the periparturient period. Metabolic disturbances and diseases include dystocia, retained placenta, metritis, pyometra, milk fever, ketosis, acidosis, mastitis, laminitis, brucellosis, and tuberculosis. Several studies have demonstrated the relationship between health and reproduction. For example, healthy cows in one study had a shorter interval to first estrus, shorter days to first insemination, shorter days to pregnancy, and fewer services per conception than cows that needed veterinary assistance for postpartum health problems (Table 2). Mastitis also has a major effect on reproduction in postpartum dairy cows. Cows that develop clinical mastitis have delayed intervals to first insemination, greater services per conception, and greater days open. A regular herd health program for veterinary care can prevent many deleterious effects of postpartum disease on reproduction.
Ovarian Follicular Cysts (Cysts) The third fate of follicles during the postpartum period is the development of cysts. Cysts have been classified as anovulatory ovarian follicular structures of at least 2.5 cm in diameter that persist in the absence of a CL for a period of at least 10 days. This definition may no longer be accurate due to the dynamics of follicular growth and the dynamics outlined in previous sections. Nonetheless, the cystic condition is a serious cause of reproductive inefficiency in dairy cattle because cows are infertile as
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long as the condition persists. It is estimated that 10% of dairy cows develop cysts annually.
Characteristics of Cysts Follicular dynamics in cows with cysts has similarities to follicular dynamics in normal cows. Development of cysts begins when a cohort of follicles less than 4 mm is recruited to grow beyond 5 mm in diameter. At approximately 7–8 mm in diameter, one follicle (sometimes more than one) is selected for continued growth to become dominant over the other follicles as occurs in normal ovulatory follicles. The growth phase to ovulatory size is similar to ovulatory follicles. However, instead of ovulating, the follicle destined to become a cyst continues to grow for several more days and becomes enlarged and is anovulatory. In some cases, more than one follicle continue growth and codominant or multidominant cysts are formed. The size of the cysts may be slightly less than in the classical definition when more than one cystic structure develops. Earlier research suggested that cysts persisted for considerable periods of time if left untreated. More recently, studies using ultrasonography or charcoal marking have shown that cysts do not always persist as previously thought. Three fates of cysts have been shown to occur: 1. Persistence, as originally thought. The percentage of cysts that are persistent is approximately 15–20%. Some cysts persist for longer than 60 days, remain dominant, and inhibit follicular growth during this time. 2. Cyst turnover, whereby the original cyst loses dominance, and a new wave of follicular growth is initiated. One (or more) follicle is selected to become dominant from the cohort of new follicles that are recruited, and develops into a new cyst. Cysts that have lost dominance have morphological and endocrine characteristics of atretic follicles. This condition may continue for repeated waves of cyst development, and the anovulatory condition, but not a single cyst, persists. The period of the waves of cyst growth may be similar in length to normal follicular waves, but is, on
Table 2 Effects of problems occurring during lactation on reproductive traits
Item
Average days to postpartum breeding
Average calving interval (days)
Average services/ conception
No problem Metritis Cystic ovaries Retained placenta Anestrus Aborted
86 99 107 92 141 80
395 433 447 419 480 402
1.8 2.3 2.1 2.0 2.2 2.4
Data are from 2352 observations in dairy herds (HA Garverick, unpublished data).
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the average, twice as long. Cyst turnover is prevalent in most cases (60–65%) of cows with cysts. 3. Turnover with initiation of a new wave of follicular growth whereby the cow self-corrects and ovulates a new dominant follicle. Approximately 20% of cows with cysts self-correct the condition.
Etiology of Cysts A number of factors including endocrine imbalances, heredity, milk production, and seasonality have been associated with the development of cysts. Endocrine imbalances include various abnormalities of the hypothalamic–hypophyseal–ovarian axis. There is an increase in mean circulating and pulse amplitude secretion of LH during cyst development, and pulse frequency is similar to that observed in a normal follicular phase (Figure 3). Both mean concentration and pulse amplitude of LH are nearly twice as high in cows with cysts compared with cows that ovulate. However, there is an absence of the preovulatory LH surge in cows with cysts. Cysts may produce more estradiol than ovulatory follicles, but the LH response to estradiol is absent in cows with cysts. There is no difference in pituitary concentrations of FSH and LH in cows with cysts and cows that ovulate. The concentration of GnRH in the hypothalamus is lower in cows with cysts, but the GnRH content of the median eminence is greater in cows with cysts. Thus, the GnRH content of the median eminence is likely released and caused increased secretion of basal LH.
Cystic follicle >25 mm
16 mm Ovulatory size
High LH pulse frequency no LH surge LH
Figure 3 Formation of ovarian follicular cysts in cows. Cysts form when postpartum luteinizing hormone (LH) secretion is highly pulsatile. A large follicle develops on the ovary and secretes estradiol. Estradiol secretion, however, fails to trigger an LH surge and the cow becomes cystic because the follicle does not ovulate.
Heredity has also been associated with cyst development. However, the estimation of heritability has been difficult because of confounding factors such as nutrition, body condition, and milk production. Increased milk production has also been associated with cyst development. However, it is unclear whether increased milk production produced cysts or whether cows produced more milk because they were cystic and were not pregnant for a longer period of time. Season of the year has also been associated with the development of cysts. However, there are reports that did not find a relationship between cysts and the level of milk production or seasonality. Numerous miscellaneous factors have been linked to cyst development. These include estrogen content of forages, which is consistent with the altered response of the cows with cysts to estradiol as previously mentioned. Abnormal reproductive and metabolic events during the postpartum period have also been linked to development of cysts, suggesting that the increased stress associated with these events contributes to cyst development. Diagnosis and Treatment of Cysts Classical diagnosis of cysts was based on behavioral symptoms of intense sexual desire or nymphomania. Cows exhibiting such behavior exhibited estrus for extended periods of time, sometimes with repeated periods between times of no estrual activity. However, it is now clear that most cows with cysts do not exhibit estrous activity (anestrous). Diagnosis of cysts is usually based upon finding a follicular structure of 2.5 cm in diameter or larger following a single examination via manual palpation per rectum or ovarian ultrasonography. While diagnosis based upon the single examination is efficacious for producers, the diagnosis may not be accurate for several reasons. First, size alone is not an absolute criterion because size is influenced by stage of development, which is difficult to know with one examination. Second, there are often large follicles on the ovaries of cows during a normal estrous cycle as previously described. Thus, the dynamic nature of follicular and cyst growth complicates diagnosis. Third, some CLs developing during the first 5–7 days following estrus exhibit characteristics similar to cysts when diagnosis is by manual palpation. Luteal structures during this period are often soft and contain fluid-filled structures that rupture during manual palpation. Diagnosis with ultrasonography greatly reduces this type of diagnostic error. Cysts are typically treated with GnRH to induce an endogenous LH release, or treated with human chorionic gonadotropin (hCG) that has LH-like activity. In both cases, successful treatment is based upon luteinization of the cystic structure and subsequent production of progesterone in response to the GnRH-induced LH release or the exogenous hCG. Success rates are about 80% with
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these treatments. Response of the cystic structure is dependent upon its state at treatment. Responding cysts are those that are ‘healthy’ in that theca and granulosa cells appear morphologically intact and are producing estradiol. More recently, progesterone implants have been used successfully to treat cysts. Treatment with progesterone must raise blood levels of progesterone to high enough levels to mimic luteal phase concentrations. Success of the aforementioned treatments is dependent upon increased concentrations of circulating progesterone that restore the sensitivity of the hypothalamic– pituitary axis to estradiol. With these treatments, concentrations of LH are inhibited, the cyst(s) undergo atresia, and a new follicular wave follows that results in selection of an ovulatory dominant follicle that secretes estradiol. The sensitivity of the hypothalamic–pituitary axis to estradiol is restored and an LH surge and ovulation of the dominant follicle occur.
Conclusion Initiation of ovulatory ovarian cycles following parturition is a prerequisite for the establishment of pregnancy within an opportune time interval. Following parturition, waves of ovarian follicular growth are usually established within 10–14 days. There are three fates of the first wave dominant follicles. The selected follicle may (1) continue its growth to normal ovulatory size and ovulate, (2) grow to less than ovulatory size, fail to ovulate, and undergo atresia, or (3) surpass ovulatory size and develop into an ovarian follicular cyst. Body condition at calving, negative
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energy balance, and disease determine the fate of ovarian follicles postpartum (ovulation, anovulation, or cystic) by affecting the endocrinology of the postpartum cow (LH, FSH, and IGF-I secretion). See also: Reproduction, Events and Management: Estrous Cycles: Characteristics.
Further Reading Barton BA, Rosario HA, Anderson GW, Grindle BP, and Carroll DJ (1996) Effects of dietary crude protein, breed, parity and health status on the fertility of dairy cows. Journal of Dairy Science 79: 2225–2236. Chagas LM, Bass JJ, Blanche D, et al. (2007) Invited review: New perspectives on the roles of nutrition and metabolic priorities in the subfertility of high-producing dairy cows. Journal of Dairy Science 90: 4022–4032. Garverick HA (1997) Ovarian follicular cysts in dairy cows. Journal of Dairy Science 80: 995–1004. Garverick HA (2007) Ovarian follicular cysts. Current Therapy in Large Animal Theriogenology 2: 379–383. Lucy MC (2003) Mechanisms linking nutrition and reproduction in postpartum cows. Reproduction Supplement 61: 415–427. Lucy MC (2007a) Fertility in high-producing dairy cows: Reasons for decline and corrective strategies for sustainable improvement. Society of Reproduction and Fertility Supplement 64: 237–254. Lucy MC (2007b) The bovine dominant ovarian follicle. Journal of Animal Science 85: E89–E99. Stevenson S (2007) Clinical reproductive physiology of the cow. Current Therapy in Large Animal Theriogenology 2: 258–270. Webb R and Campbell BK (2007) Development of the dominant follicle: Mechanisms of selection and maintenance of oocyte quality. Society of Reproduction and Fertility Supplement 64: 141–163. Wiltbank MC, Gu¨men A, and Sartori R (2002) Physiological classification of anovulatory conditions in cattle. Theriogenology 57: 21–22.
Estrous Cycles: Seasonal Breeders S T Willard, Mississippi State University, Mississippi State, MS, USA ª 2011 Elsevier Ltd. All rights reserved.
Introduction The effects of seasonal influences on reproduction are directly linked to milk yield, as the production of offspring is required for initiation of lactation, and is important in relation to targeting milk markets. For example, in India and Pakistan, water buffaloes calve primarily between July and December, which can result in excess milk production in the winter months and milk shortages during the summer months. Similarly, dairy sheep producers are particularly cognisant of the effects of seasonality on lambing intervals of ewes and on an ewe’s lifetime lactation yield in light of the strict seasonal nature of some sheep breeds used in intensive dairy sheep operations. While an understanding of seasonality is critical from a production standpoint, from an evolutionary perspective seasonal breeding has evolved as an adaptation to ensure a favorable reproductive rate and the survival of offspring in regions with great variations in climatic, nutritional, and/or other adverse environmental conditions. The reasoning behind the evolution of these strategies in the context of agriculturally important livestock species will be explored herein, in addition to the physiological basis for seasonality and how it might be controlled in a production setting. For comparative purposes, the seasonal nature of several multipurpose livestock species will be indicated, with emphasis on those used worldwide for the production of milk and milk by-products.
Strategies and Theories for the Seasonal Regulation of Reproduction Some species do not exhibit seasonal cycles in reproductive activity (nonseasonal breeders), while others may display ‘clusters’ of reproductive cycles that occur only during a certain season of the year (seasonal breeders). Of the seasonal breeding species, some exhibit reproductive cycles during the short day lengths (autumn; e.g., sheep and goats), while others exhibit reproductive cycles only during the long day lengths (spring; e.g., mare). Patterns of seasonal breeding range from species that have one period of estrus (receptivity and mating) each year (monoestrus), to species that exhibit a series of estrous cycles limited to a portion of the year (seasonally polyestrus). True seasonal breeding patterns are inherent in some species
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(e.g., ewe, doe, and mare), while other species may show seasonal patterns due to environmental or other overriding influences. Of these, climatic, nutritional, and behavioral effects on seasonal cycles will be described below. However, one should be cognisant of the fact that seasonality is a coordinated effort in which multiple exogenous (environmental) and endogenous (hormonal) rhythms may be involved in the integration of seasonal reproductive cycles.
Climatic Climatic events that regulate seasonal reproductive processes encompass primarily the effects of photoperiod and temperature, with climatic variables including drought and precipitation influencing reproduction as related to nutrient availability (nutritional considerations will be described in greater detail below). Of these, photoperiod is seen as a primary mechanism driving the endogenous circannual rhythm that synchronizes mating and birthing seasons. The effects of photoperiodism (photic cues) are translated into reproductive effects via hormonal mediators (e.g., melatonin), which augment or suppress endocrine and neuroendocrine pathways critical to reproductive processes (see ‘Endocrine and Neuroendocrine Regulation of Reproduction in Seasonal Breeders’). The influence of photoperiod on the reproductive system was first observed in relation to the timing of puberty for lambs born at different times of the year. Specifically, spring-born lambs attain puberty in about 30 weeks of age, which they reach during the breeding season, while fall-born lambs reach the pubertal age of 30 weeks during the nonbreeding season, and thus do not exhibit reproductive cycles until the following breeding season at nearly 1 year of age. Such dramatic effects illustrate the prevailing and central role that photoperiod plays in the reproductive lives of strict seasonal breeders. In conjunction with or independently from photoperiod, which changes incrementally during the year, alterations in ambient temperatures (high and low) can contribute to shifts in seasonal breeding activities as well. For dairy cattle bred by natural or artificial means in the southern United States and elsewhere, it has been observed that fertility is lowest in late summer when ambient temperature and humidity are high, and is often followed by a slow recovery time thereafter producing a lag effect into the fall. To this end, heat stress in cattle has
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been the primary focus of research, which has illustrated how severe thermal stress can suppress reproductive processes, negatively impacting livestock production operations – particularly in dairy cattle. Summer heat stress has been shown to lower semen quality in bulls, alter hormonal secretory patterns, suppress estrous behavior, reduce conception rates, and negatively affect embryo quality and survival. Moreover, heat stress during late gestation can adversely affect fetal growth in cattle and sheep, with summer-born calves and lambs being generally smaller than winter-born calves and lambs, and an increased incidence of stillbirths has been observed in swine. Low temperatures (i.e., cold stress) at the time of birth also have implications relative to offspring survival (e.g., Bos indicus calves are more susceptible to cold stress than Bos taurus calves), yet in relation to mating success the effects of cold stress are less well characterized in livestock than the effects of heat stress. This is due to the confounding effects of food intake, which increases during colder periods to facilitate metabolic heat production (i.e., maintenance of thermoneutrality) as part of an adaptive response to low environmental temperatures. Nevertheless, appropriate adaptation periods to low environmental temperatures are required to alleviate both endocrine and exocrine effects on reproductive processes in some breeds. For example, in Brahman bulls translocated to the northern United States, reduced concentrations of testosterone and decreased semen quality have been observed during the winter months (0 to 10 C). When considering both heat and cold stress together, it seems reasonable that seasonal breeding strategies would have evolved, in part, to coordinate breeding periods for an increased probability of mating success and postparturient neonatal survival in relation to annual changes in environmental temperatures. Nutritional Late pregnancy, birth, and lactation require energy and nutrient demands above and beyond what is required for normal body maintenance. This means that conception must occur months earlier in relation to other environmental cues (e.g., photoperiod) to achieve a birthing season that will coincide with the season of greatest abundance in nutrient quantity and quality. When energy and protein, for example, become limiting, a number of reproductive processes may be affected, resulting in delayed puberty, suppressed estrus and ovulation, reduced conception rates, an increased incidence of fetal resorption, and premature or weak offspring. As evident from these examples, the seasonal suppression of puberty or estrous cycles due to nutritional deficiencies could delay transitions into seasonal breeding periods, while deficiencies
later in the year may influence survival of the fetus late in pregnancy or the neonate postpartum. Conversely, an abundance of nutrients may permit animals to exhibit reproductive cycles earlier in the season, and adequate nutritional reserves during pregnancy and lactation would directly benefit offspring survival postpartum. Food in this regard has been described as having a ‘proximate’ and ‘ultimate’ action in relation to seasonal breeding. Specifically, the quantity of nutrients available can have an immediate beneficial or detrimental effect on an animal’s reproduction (a proximate action), and the fact that the presence of nutrient resources can vary seasonally in an animal’s environment is an important factor in the evolution of that animal’s reproductive strategy (an ultimate action). The tendency toward seasonal breeding begins to manifest primarily in regions where nutrient availability varies somewhat, with increases in the severity of this variation leading to stricter and stricter breeding and birthing seasons out of an apparent necessity for nutrient resources. This is, of course, superimposed on other climatic events (photoperiod, temperature, precipitation, etc.) that can influence growing seasons and plant vigor. Social/Behavioral Reproductive processes can be dramatically affected by social cues relayed from one individual to another of the same or opposite sex. This can occur via pheromones, which are chemical substances liberated from one animal (through urine or other secretions) and received by another (olfactory cues), or through visual or tactile cues associated with complex mating rituals. These behavioral or chemical cues have a priming effect that can alter hormonal secretions (primarily luteinizing hormone (LH) and prolactin from the pituitary) and advance the breeding season. In sheep, this is often referred to as the ‘ram effect’, as ram exposure can increase LH pulsatility in the ewe and elicit signs of estrus in the female that would not normally be present in the absence of a ram. Furthermore, introduction of a ram into an ewe flock during the transition from anestrus to estrus can in turn result in a high degree of synchrony in first mating. A similar reaction is achieved in wapiti (North American elk) and red deer, in which vocalizations from the stag during the early rut can hasten seasonal reproductive cyclicity in females. While in today’s livestock management systems such cues have become less vital from a mating strategy standpoint, for animals in the wild with varying social structures (e.g., dominance hierarchies, single-sex groups) and a need to locate receptive mates, such behavioral cues are critical to mating success and genetic survival. While social interactions are not a singular cause for initiating or terminating seasonal reproductive events in most species, they can greatly augment the degree to
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which an animal responds to other environmental cues regulating seasonal processes.
Endocrine and Neuroendocrine Regulation of Reproduction in Seasonal Breeders Seasonal breeders are often referred to as undergoing an annual puberty, in that reproductive cycles must begin anew following a period of anestrus (i.e., no estrus or the absence of heat cycles). The principal mechanism responsible for transitions into and out of periods of sexual activity in strict seasonal breeders is mediated by the retinal-hypothalamo-pituitary pathway (Figure 1). Specifically, photic cues detected by the sensory neurons in the retina of the eye are transmitted via the
suprachiasmatic nucleus of the hypothalamus to excitatory cervical ganglia that can alter the release of the hormone melatonin from the pineal gland and, in turn, influence hypothalamic gonadotropin-releasing hormone (GnRH) and pituitary LH release. The pineal gland is located posterior to the hypothalamus between the hemispheres of the brain, and increased sympathetic activity induced by darkness increases the secretion rate of its primary hormone, melatonin. Exactly how melatonin acts singularly or in a coordinated fashion with other hormones (e.g., norepinephrine) to influence reproductive processes is still unresolved. Nevertheless, in shortday breeders (e.g., sheep and deer), cyclic activity that occurs during the short photoperiods (longer nights) of fall and winter is characterized by greater melatonin release and an active hypothalamic GnRH neurosecretory system, while the long photoperiods (short nights) of
Figure 1 Integration of environmental cues on endocrine and neuroendocrine pathways regulating seasonal reproduction. A multitude of exogenous environmental factors and endogenous hormonal cues coordinate the seasonal reproductive cycle in short- (e.g., sheep) and long- (e.g., horse) day breeders. Central to seasonal regulation is the role of photoperiod (light:dark cycles), which changes annually (see Figure 2c). To this end, photic cues are relayed via the retino-hypothalamo-pituitary pathway using melatonin as a primary regulator of GnRH and LH/FSH release either directly or indirectly by mediating changes in the sensitivity of the hypothalamus and pituitary to the negative feedback effects of gonadal steroids. It has been said that seasonal breeders undergo an annual puberty, with spermatogenesis and estrous cycles beginning anew each breeding season as they make the transition from sexual inactivity into periods of reproductive competence and back again. While strict seasonal breeders are driven principally by photoperiodic cues, other species may exhibit seasonal cycles directed by a variety of climatic, nutritional, and/or behavioral indicators. FSH, follicle-stimulating hormone; GnRH, gonadotropin-releasing hormone; LH, luteinizing hormone.
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spring and summer are characterized by lower melatonin release, and thus periods of reproductive dormancy. In long-day breeders like the horse, the relationship between melatonin and season remains the same (high during short days and low during long days), but the effects on the reproductive axis are opposite to that seen in short-day breeders (i.e., for the mare, reproductive dormancy during fall and winter and reproductive competence during spring and summer). The role of melatonin in coordinating the seasonal regulation of reproduction has been demonstrated in studies where melatonin has been administered to short-day breeders during long days (thus, increasing melatonin and mimicking the effects of short days) to induce gonadal recrudescence. In sheep, the switch from the breeding season to anestrus, or vice versa, is associated with marked changes in hypothalamic GnRH pulse frequency, which has downstream effects on pituitary LH release, gonadal steroid hormone production, and gamete development. There is conclusive evidence that changes in photoperiod can specifically alter the communicative relationship between the gonads and higher brain centers. Indeed, during seasonal transitions in and out of the breeding season in response to changes in photoperiod, there are marked changes in the sensitivity of hypothalamus (GnRH release) and pituitary (LH release) to the negative feedback effects of gonadal steroid hormones in both males and females. These coordinated activities influence not only gonadal activity, but also related behavioral processes and secondary sex characteristics. Opposite to melatonin, pituitary secretion of prolactin is high when melatonin is low (long days) and vice versa. While prolactin has been implicated as being inhibitory to reproductive function in some short-day breeders and induced (reflex) ovulators (i.e., species that require stimulation of the vagina and/or cervix for ovulation to occur), there is strong evidence that fluctuations in prolactin are not related to the seasonality of mating; however, an endogenous rhythm of prolactin is noted in the ram and stag. Changes in prolactin have been linked specifically to secondary seasonal characteristics, such as coat growth and molt in red deer stags, suggesting that seasonal changes in prolactin may be more related to alterations in temperature. This notion is supported by studies of blind bulls and steers that have shown that photoperiod does not affect prolactin secretion, implicating temperature as the dominant environmental cue regulating prolactin. Thus while photoperiod has been described as being central to the regulation of seasonality, multiple factors can positively or negatively affect the sensitivity and integration of the endocrine and neuroendocrine systems in mediating seasonal cycles and seasonal reproductive transitions (Figure 1).
Artificial Manipulation of Seasonal Breeders Advancement or prolongation of the breeding season in seasonal breeders used in livestock production has been desired in some areas to coordinate breeding seasons with other management-related events (e.g., forage availability). An example specific to the equine racing industry is that foals are routinely assigned a universal birth date of 1 January (northern hemisphere) regardless of when they are born, making advancement of the breeding season beneficial to achieve the birth of foals as early in the year as possible. At present, the primary means to alter circannual rhythms in strict seasonal breeders includes manipulation of photoperiod through exposure of animals to alternate light cycles, and the use of pharmacological (hormonal) means. While these methods will be highlighted in more detail, it should be noted that a variety of other management-related alterations have similarly resulted in a dampening of seasonal influences for some species. For example, seasonal fluctuations in libido and semen quality, estrous activity, and conception rates have been overcome in dairy cattle and water buffalo by providing cooling facilities during heat stress. Additionally, other management practices including early weaning (beef cattle and small ruminants) and increased nutrition (e.g., flushing) have also aided in facilitating early returns to estrus to override any seasonal influences on reproductive function. Finally, behavioral influences should also not be overlooked, as the exposure of ewes to a ram prior to the breeding season can induce early cyclicity (the ‘ram effect’).
Artificial Manipulation of Light–Dark Cycles The artificial manipulation of light–dark cycles is achieved primarily by altering housing strategies. This can be accomplished by blocking natural light from entering stalls or barns for specified periods of time at the beginning and end of each day, or through controlled lighting. In a long-day breeder like the mare, changes in photoperiod to mimic long days (16 h of light:8 h of darkness) during the nonbreeding season (short days) will stimulate reproductive function in anestrous mares. Conversely, periods of seasonal anestrus in the ewe, a short-day breeder, can be altered by changing day length during long days to mimic short days (8 h of light:16 h of darkness). While dairy cattle are not traditionally considered as seasonal breeders, supplemental lighting (16–18 h of light:6–8 h of darkness) has been shown to boost milk production through increased secretion of insulin-like growth factor-1 (IGF-1), which acts on the mammary gland, and concomitant decreases in melatonin secretion. How IGF-1 is regulated in response to reduced
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concentrations of melatonin when day length increases remains unclear. To this end, the manipulation of photoperiod to alter melatonin release may have numerous implications in relation to the reproductive and lactational abilities of animals sensitive to photoperiodic cues.
Pharmacological Control: Exogenous Melatonin and Other Hormonal Means Pharmacological control of seasonal breeding has been achieved in a number of species, and has been implemented as part of routine production management strategies in some areas. As described previously, increasing concentrations of melatonin of pineal origin during short days arouse dormant reproductive processes in short-day breeders. Thus melatonin implants have been inserted in ewes for periods of 30–40 days to advance the breeding season for matings in spring or early summer. However, one problem with using these types of manipulations (melatonin and changes in photoperiod) is that animals can become refractory (i.e., temporarily unresponsive) after a period of time to the stimulatory effects of melatonin and light, thus limiting their use. Moreover, use of melatonin for advancement of the breeding season may not be effective in all seasonal breeding species. For example, in the female goat, melatonin administration has been less successful than in sheep in advancing the breeding season. In addition to melatonin, a whole host of other hormones have been utilized to stimulate reproductive activity during the nonbreeding season or as methods for prolonging the breeding season itself. Specifically, hormonal treatments have included equine chorionic gonadotropin (eCG), human chorionic gonadotropin (hCG), crude pituitary extracts, GnRH, progesterone, and prostaglandins. In camels, GnRH treatment can stimulate sexual activity in males during the nonbreeding season, while in other induced ovulators such as the llama and alpaca, hCG and GnRH have been used to induce ovulation outside of normal periods of sexual receptivity. Taking management strategies a step further, combinations of artificial lighting and pharmacological approaches have also been used with some success. For example, in the mare, initiation of a 16-h photoperiod for 60 days prior to treatment with altrenogest (a synthetic progestin) for 12 days followed by the administration of hCG on day 2 of estrus has been reported to be an effective regime for induction of estrus and ovulation in the mare early in the year outside of the normal breeding period. Such lighting and hormonal combinations and other clinical therapies abound for short-day and longday breeders alike, with the intent to modify periods of sexual activity to meet management constraints, whether environment- (e.g., temperature or forage availability) or industry- (e.g., the equine racing industry) related.
Seasonal Breeding in Domesticated and Semidomesticated Multipurpose (Meat and Dairy) Livestock While not all of the livestock species described herein are used in typical dairy production operations (e.g., swine), for comparative purposes the seasonal nature of reproductive cycles, whether endogenously generated or due to exogenous environmental cues, will be discussed briefly for each species indicated. As described previously, photoperiod, temperature, and a multitude of other climatic and/or nutritional factors are the driving forces regulating the timing of breeding and birthing seasons in most species.
Domestic Cattle: Temperate (Bos taurus) and Tropical (Bos indicus) Cattle are nonseasonal and polyestrous, yet the onset of puberty and postpartum reproduction are often stimulated by exposure to long days. Moreover, seasonal trends emerge in some climates due to adverse environmental conditions. Specifically, heat stress is often implicated as the cause of reduced reproductive performance, particularly in temperate, European-type cattle (B. taurus). Summer heat stress conditions can lower semen quality in the bull, reduce fertilization rates, affect embryo quality and viability, and result in an overall decrease in conception rates. Of all temperate breeds, dairy cattle (e.g., Holstein) in particular show marked seasonal fluctuations in reproductive function due to the effects of environmental heat stress and to meet the metabolic demands of lactation. In the southern United States, cows calving in spring and summer have reduced reproductive performance, with milk production depressed for cows that calve in summer and fall. During heat stress, dairy cows exhibit shorter less intense periods of estrus (as much as 6–8 h less) and a reduced frequency of mounting activity than during cooler seasons. These effects contribute to a lower estrus detection rate, an increased number of artificial breeding services per conception, and an overall decrease in conception rates in production dairy operations during the summer months. Nevertheless, through the implementation of housing strategies to offset environmental extremes (e.g., cooling with fans and sprinklers during heat stress), seasonal influences on fertility in cattle can be markedly reduced. In contrast to heat stress, cold stress has not been implicated in causing seasonal depressions in fertility in cattle, with the exception of when tropically adapted cattle (Zebu; B. indicus) have been translocated to colder environments without appropriate periods for adaptation. To this end, Zebu cattle exhibit the greatest entrainment to seasonal cycles (primarily temperature-
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related) than all other breeds, with the frequency of estrus, ovulation, and conception rates being higher during the summer months than during the winter months in equatorial Africa. Water Buffalo (Bubalus bubalus) Water buffaloes are polyestrous and can breed yearround. However, peaks in calving during the year do occur, which indicates possible seasonal effects on fertility that are most likely the result of temperature, photoperiod, and nutritional interactions. The impact of these effects is seen in buffaloes that calve in winter and spring and do not exhibit postpartum estrous cycles as early as cows that calve in summer and fall. Those calving in winter and spring would be returning to reproductive function during the summer months when high temperatures, increased photoperiods, and elevated prolactin levels might prolong periods of anestrus. Moreover, high temperatures (heat stress) may contribute to reduced sexual activity of male buffaloes during this time. In tropical regions where water buffaloes are maintained, conception rates have been observed to be greatest 2–4 months following the peak in the rainy season. This coincides with cooler temperatures and increasing forage availability. Yak (Bos grunniens) Yaks are considered seasonally polyestrous in their native environments, although female yak showing only a single estrus in a season, even if mating and conception does not occur, is not uncommon. The driving force affecting the onset and end of the breeding season is primarily climatic factors including forage availability and location (latitude). When ambient temperatures and vegetation increase as the winter thaw progresses, females will show an increase in body condition and weight gain, which can initiate cyclicity. The breeding season begins in June and reaches its peak in July and August (in China and upper Mongolia), when temperatures are highest and forage availability is maximal. Estrous activity decreases in frequency and generally stops around November. As the yak is usually found at high altitude, it has been observed that at lower elevations of 1400 m breeding seasons begin earlier (late May), while at higher elevations of 2700 m breeding seasons tend to begin later (late June). Sheep (Ovis aries) and Goats (Capra hircus) In temperate regions, both sheep and goats are seasonally polyestrous. Seasonality is driven by photoperiodism with increased estrous activity during decreasing day lengths. In tropical regions, sheep and goats tend to breed throughout the year. Nevertheless, even in tropical
environments, feed restriction (dry seasons) and high temperatures may cause a suppression of sexual activity, but when rainy seasons resume sexual activity increases. Genetics plays a large role in the breeding seasons of sheep and goats, with some breeds showing longer breeding seasons (sheep: Dorset, Merino, and Rambouillet; goats: Anglo-Nubian) than others with more restrictive breeding seasons (sheep: Southdown, Shropshire, and Hampshire; goats: Toggenburg, Saanen, and French Alpine). Unlike the female, the male is less restrictive with respect to seasonal breeding activity, although sexual activity is greatest in the fall in response to decreasing day length when the secretion of testosterone, testis size, and testicular spermatogenesis increase. As such, melatonin interacts with the neuroendocrine axis mediating the sensitivity of higher brain centers (hypothalamus and pituitary) to the negative feedback effects of steroid hormones in both sheep and goats (see general model depicted in Figure 1). Deer (Cervidae species) The majority of deer are classified as seasonal breeders that are polyestrous, short-day breeders. Nevertheless, 19 species of the 40 or more existing deer species are found in equatorial regions (between 20 N and 20 S latitude) and exhibit nonseasonal breeding capabilities, although peaks in breeding and fawning seasons differ markedly among tropical deer species – some of which inhabit the same ecosystem. In white-tailed deer (Odocoileus virginianus), for example, the distribution of this species extends from 55 N to 18 S latitude, with white-tailed deer in temperate regions breeding strictly seasonally, while those in tropical climates (Caribbean, Central America, and northern part of South America) breeding yearround. In addition to short-day and nonseasonal breeders, one species, Pere´ David’s deer (Elaphurus davidianus), has an advanced onset of the breeding season, which begins mid-summer (3–4 months before typical short-day breeders) when day lengths are long, melatonin is low, and prolactin levels are high. Thus, some have referred to the Pere´ David’s deer as a long-day breeder. While photoperiod is the primary factor that mediates seasonal cycles in most deer, an inherent rhythmicity in metabolism, antler and coat (pelage) growth, and hormonal cycles is evident when photoperiods are altered dramatically or eliminated completely. This suggests entrainment of reproductive and metabolic cycles to an endogenous rhythm that is overlaid on the influence of photoperiodic cues. Even in tropical species of deer (e.g., axis deer; Axis axis), circannual cycles of antler growth, testis size, and body weights are observed, yet estrous cycles, testicular spermatogenesis, breeding, and fawning occur throughout the year. For comparative purposes, the year-round estrous cycle activity of a strict seasonal breeder
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during periods that would favor fawn survival. This is true for all deer, as evidenced by the fact that late-born fawns show lower survival rates due to a shortened lactation (early weaning), low birthweights, and winter death loss, while early-born fawns exhibit similarly low birthweights and may succumb to summer thermal stressors. Thus a window of opportunity exists for fawns born neither too late nor too early, which would favor their survival. For reindeer (Rangifer tarandus) in the arctic, highly variable rates of fertility are noted with reproductive success intimately linked to body fat reserves and the timing of births directed toward snow melt and the emergence of new plant growth. As in sheep and goats, reproductive cyclicity in deer is driven by the myriad of hormonal interactions that occur between melatonin, prolactin, GnRH, gonadotropins, and gonadal steroid hormones in response to photoperiodic, metabolic, and/ or other exogenous and endogenous cues. Camel (Camelus dromedarius)
Figure 2 Serum concentrations of progesterone depicting the estrous cycles of nonseasonal (axis deer (a)) and seasonal (fallow deer (b)) species of farmed deer in relation to photoperiod and ambient temperature (c). The axis deer is a tropical deer species that is a nonseasonal breeder and exhibits continuous estrous cycles irrespective of changes in photoperiod (a). Note the presence of 18 estrous cycles throughout the 346-day sampling period for the axis doe depicted here (serum samples for progesterone analysis were collected twice weekly). In contrast, the seasonally polyestrous fallow doe shown in panel b exhibits only 6–7 estrous cycles annually, which are restricted to the short photoperiods between October and March. Both deer were maintained at the same location at the Texas Agricultural Experiment Station in Overton, Texas (32 169N; ST Willard and RD Randel, unpublished data).
(e.g., fallow deer (Dama dama)) and a nonseasonal breeder (e.g., axis deer) is shown in Figure 2 for axis and fallow does maintained at the same location in Texas. Irrespective of the nonseasonal nature of some deer species, seasonal peaks in the frequency of breeding and fawning are still noted in tropical deer, and are attributed to climatic and/or nutritional cues to achieve fawning
Female camels are typically seasonally polyestrous and are induced ovulators. Decreasing day length appears to be the stimulus for reproduction in most regions, although in equatorial locations when adequate rainfall and nutrients are available year-round breeding can occur. It is well documented that by providing sufficient food, nutrition may override the effects of photoperiod and increase sexual receptivity in the female. Male camels also exhibit seasonal sexual activity, with higher concentrations of testosterone and increased spermatogenesis during cooler months. Nevertheless, spermatogenesis can continue throughout the year in the male, reaching a peak during the rutting period. Increased prolactin (hyperprolactinemia) during the nonbreeding season has been suggested as the cause of reduced fertility and sexual activity via prolactin-induced inhibition of gonadotropin (FSH and LH) secretion, although more research in this area is needed. Llama (Lama glama) and Alpaca (Lama pacos) Like camels, llamas and alpacas are induced ovulators that show rhythmic patterns of follicular development and periods of sexual receptivity. In their native highlands of Peru, llamas and alpacas exhibit seasonal sexual cycles from December to March, which are the warmer summer months for this region. However, in these wild settings, males and females are generally together throughout the year, and when females are separated from males in production management settings and pair-mated monthly, they will exhibit sexual activity year-round. Therefore, seasonal breeding can be directly influenced by the continuous contact of females with males, versus when males and females are managed
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separately. Ovulation rates, fertilization rates, and embryo survival do not appear to be affected by the season in which breeding occurs under these management circumstances. Male llama and alpaca produce fertile ejaculates throughout the year, although the quality of the ejaculate is directly affected by season and nutrient availability, with higher testosterone and greater spermatogenesis during the spring and summer months (the peak breeding periods). The degree to which other environmental cues (visual, olfactory, etc.) may influence reproductive processes in the llama or alpaca is unclear. However, like camels, food availability may directly influence the existence of nonseasonal breeding activity. In North America, llama births are observed throughout the year, reaching a peak during the warmer months of June–November. Horse (Equus caballus) Mares are seasonally polyestrous, long-day breeders. However, considerable variation exists among breeds and with respect to location (latitude). Some mares exhibit a strict breeding season accompanied by estrus and ovulation, while others may have a defined fertile breeding period preceding and followed by a transitory period in which estrous cycles are present but may not be accompanied by ovulation. Still others may show continuous, year-round periods of estrus and ovulation such as for those mares maintained in equatorial regions. It is well accepted that photoperiod is the primary regulatory mechanism controlling seasonal breeding in the mare as mediated by the hormonal interactions of melatonin, prolactin, GnRH, FSH, LH, and estradiol. Unlike the mare, the stallion does not show as defined a breeding season, with fertile ejaculates capable of being collected throughout the year. Nonetheless, seasonal differences in reaction time, mounting frequency, testis size, semen volume, numbers of spermatozoa, and other semen quality characteristics are observed in the stallion, decreasing during short photoperiods and increasing during long photoperiods. Swine (Sus domesticus) Swine are polyestrous and nonseasonal. Nevertheless, fertility (mean litter size) declines sharply when photoperiods are long and temperatures become elevated (summer months). In addition to effects on litter size, increased ambient temperatures can cause sperm output and the motility of spermatozoa in the boar to decrease,
which undoubtedly contribute to a decrease in fertilization rate and subsequently litter size. Unlike dairy cattle, which show a decrease in the duration of estrus during the hotter summer months, periods of estrus in sows and gilts are longest during summer and shortest in winter. Today, any traces of seasonality in swine breeds have been, for the most part, completely controlled or eliminated due to the enclosed housing environments within which most swine are currently maintained. See also: Stress in Dairy Animals: Heat Stress: Effects on Milk Production and Composition; Heat Stress: Effects on Reproduction.
Further Reading Al Eknah MM (2000) Reproduction in Old World camels. Animal Reproduction Science 60–61: 583–592. Amoah EA, Gelaye S, Guthrie P, and Rexroad CE (1996) Breeding season and aspects of reproduction of female goats. Journal of Animal Science 74: 723–728. Bearden HJ, Fuquay JW, and Willard ST (2003) Applied Animal Reproduction, 6th edn. Upper Saddle River, NJ: Prentice-Hall Inc. Bronson FH and Heideman PD (1994) Seasonal regulation of reproduction in mammals. In: Knobil E and Neill JD (eds.) The Physiology of Reproduction, 2nd edn. New York: Raven Press Ltd. Chemineau P, Martin GB, Saumande J, and Normant E (1988) Seasonal and hormonal control of pulsatile LH secretion in the dairy goat (Capra hircus). Journal of Reproduction and Fertility 83: 91–98. Commission on International Relations – National Research Council (1981) The Water Buffalo: New Prospects for an Underutilized Animal. Washington, DC: National Academy Press. Foster DL (1994) Puberty in the sheep. In: Knobil E and Neill JD (eds.) The Physiology of Reproduction, 2nd edn. New York: Raven Press Ltd. Godfrey RW, Lunstra DD, Jenkins TG, et al. (1990) Effect of season and location on semen quality and serum concentrations of luteinizing hormone and testosterone in Brahman and Hereford bulls. Journal of Animal Science 68: 734–749. Hafez ESE and Hafez B (2000) Reproduction in Farm Animals, 7th edn. Baltimore, MD: Lippincott Williams & Williams. Li C and Wiener G (1995) The Yak. Bangkok, Thailand: Regional Office for Asia and the Pacific of the Food and Agriculture Organisation of the United Nations. McKinnon AO and Voss JL (1995) Equine Reproduction. Hoboken, NJ: John Wiley & Sons, Inc. Ray DE, Halbach TJ, and Armstrong DV (1992) Season and lactation number effects on milk production and reproduction of dairy cattle in Arizona. Journal of Dairy Science 75: 2976–2983. Senger PL (2005) Pathways to Pregnancy and Parturition, 2nd revised edn. Pullman, WA: Current Conceptions, Inc. Thatcher WW (1973) Effects of season, climate and temperature on reproduction and lactation. Journal of Dairy Science 57(3): 360–368. Tucker HA and Petitclerc D (1982) The role of the eye on secretion of prolactin during various photoperiods and seasons in cattle. In: Ortavant R, Pelletier J, and Ravault JP (eds). Photoperiodism and Reproduction in Vertebrates, pp. 147–156. Les Colloques de l’INRA – 6. Nouzilly, France, (Sept. 24-26 1981): INRA Publishing. Turek FW and Van Cauter E (1994) Rhythms in reproduction. In: Knobil E and Neill JD (eds.) The Physiology of Reproduction, 2nd edn. New York: Raven Press Ltd.
Control of Estrous Cycles: Synchronization of Estrus Z Z Xu, Livestock Improvement Corporation Ltd., Hamilton, New Zealand ª 2011 Elsevier Ltd. All rights reserved.
Introduction Techniques for synchronizing the onset of estrus in dairy cattle and other species have been available since the 1960s. Research effort to improve the performance of estrus synchronization programs continues to this day and more work is required to make estrus synchronization more acceptable on the farm. The reasons for using estrus control vary between breeds and species and between different farming systems. In dairy cattle, estrus synchronization is often used to aid mating management by improving the efficiency and accuracy of detection of estrus (heat) or by reducing the labor requirement for estrus detection. Estrus synchronization is especially useful in small herds with year-round calving where there may be only one animal in estrus at any given time or in animals, such as nulliparous heifers on pasture, that cannot be easily accessed for estrus detection. Estrus synchronization can also be used to increase the percentage of cattle conceiving within a defined period of time. This is achieved by improving the efficiency and accuracy of estrus detection and by allowing most eligible cattle in a herd to be bred within a few days rather than spread over an entire estrus cycle. Another important usage of estrus synchronization in dairy cattle is to synchronize recipient animals for embryo transfer so that the desired number of recipients at the appropriate stage of the estrous cycle are available. There are other likely benefits from estrus synchronization in dairy cattle, such as facilitating the adoption of treatments or management practices that must be implemented at a specific stage of pregnancy or lactation. A successful estrus synchronization program should have the following features: implementation with minimal distress to animals; • easy applicability to animals of different physiological sta• tus, for example, cyclic versus noncyclic; precise onset of estrus to minimize or eliminate estrus • detection; detrimental effect on reproductive performance • nocompared with that achieved under the current system; cost-effectiveness relative to the objectives to be • achieved. This article discusses the techniques available to synchronize dairy cattle for breeding after detection of estrus. Techniques for synchronizing ovulation so that breeding can be carried out at a fixed time after treatment
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without estrus detection are discussed elsewhere (See Reproduction, Events and Management: Control of Estrous Cycles: Synchronization of Ovulation and Insemination). Ovulation synchronization removes the need for estrus detection and is well suited for production systems where accurate estrus detection is difficult and costly. However, a successful ovulation synchronization program usually involves synchronization of follicular wave development, which requires additional treatments with hormones. There may be semen wastage associated with ovulation synchronization because not all treated animals ovulate around the time of artificial insemination (AI).
Principles of Estrus Control During each bovine estrus cycle, there are characteristic changes in sexual behaviors, follicular development, and the circulating profiles of several reproductive hormones (see Reproduction, Events and Management: Estrous Cycles: Characteristics). Among all the reproductive hormones, progesterone can be considered as the main ‘orchestrator’ of events during an estrus cycle. During the luteal phase of the estrus cycle when circulating progesterone concentration is high, no estrous behavior or ovulation occurs. The decrease in circulating progesterone concentration after the onset of luteolysis relieves the reproductive system from the negative feedback control of progesterone and, consequently, estrous behavior and ovulation ensue within a few days. Therefore, estrus control mainly involves manipulating the circulating concentrations of progesterone. This can be achieved either by artificially prolonging the luteal phase of the estrus cycle using exogenous progesterone or a synthetic progestogen or by shortening the luteal phase using prostaglandin F2 (PG) or one of its analogues, or by a combination of both mechanisms.
Estrus Control Using Progestogens For a group of cattle at random stages of the estrus cycle, treatment with progestogen for more than 14 days will produce a synchronized onset of estrus within 2–3 days after cessation of the progestogen treatment. The progestogen treatment prevents cows whose corpora lutea (CLs) undergo spontaneous luteolysis during the treatment
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period (cows on day 5 or later of the estrus cycle at treatment initiation) from showing estrous behavior and ovulating until after the end of treatment. For animals in the early stage of the estrus cycle (days 0–4), the progestogen treatment either prevents the formation of CLs or shortens the life span of freshly formed CLs. Early studies on estrus synchronization with progestogens involved daily injection of sufficient amounts of progesterone or the feeding of orally active and highly potent progestogens, such as melengestrol acetate (MGA). The development of progestogen application devices, including the norgestomet ear implant, the progesterone-releasing intravaginal device (PRID), and the controlled internal drug release (CIDR) device, has facilitated the use of progestogens for estrus synchronization in dairy cattle. However, a common adverse effect of estrus synchronization with progestogen alone is the reduction in conception rate at the synchronized estrus. The longer the duration of progestogen treatment, the better the synchrony, but the lower the conception rate. It is now known through studies of follicular dynamics using ultrasonography that the reduction in conception rate at the synchronized estrus is due to the development of persistent dominant follicles. The doses of progestogens administered in these programs, while effective in suppressing estrus and ovulation, are ineffective in suppressing the development of persistent dominant follicles in the absence of a functional CLs. Oocytes from persistent dominant follicles can be fertilized, but the resulting embryos have reduced developmental capability. As a result, estrus synchronization programs using progestogens alone are no longer widely used commercially.
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single injection of PG can theoretically show estrus over a 3-day period. Estrous response to PG injections can be lower in Bos indicus than in Bos taurus, which may be related to poor estrus expression in B. indicus rather than luteal responsiveness to PG. Several approaches have been developed to circumvent the problem that not all cows in a group will respond to a single PG treatment (Figure 1). The most widely used approach is to administer two injections of PG 11–14 days apart (Figure 1, program (1)). This treatment program ensures that all animals are at a stage of the estrus cycle when they are capable of responding to the second PG treatment, irrespective of whether they have responded to the first PG treatment or not. A variation of the above program is to treat all cattle with PG and breed on detection of estrus, followed by retreatment 11 days later of those that have not responded to the first PG (Figure 1, program (2)). A third approach is to mate cows for 5–7 days on detection of estrus and then to treat with PG animals that have not been mated (Figure 1, program (3)). Another approach is to treat only cows that are identified, using rectal palpation, ultrasonography, or progesterone measurement, to have responsive CLs. This approach is not often used systematically at the herd level because of errors in, and costs associated with, identifying cows with responsive CLs. Initially, it was hoped that the double-PG program would result in a synchronized onset of estrus that was precise enough for a single fixed-time insemination to achieve an acceptable conception rate. Such a hope has never been realized because the interval from PG injection to onset of estrus is influenced, among other things, by the developmental stage of the dominant follicle at the time of PG treatment. In nonlactating heifers, estrous response rate
Estrus Control Using Prostaglandin The luteolytic property of PG and its analogues was discovered in the early 1970s. This was followed by numerous studies on the use of PG for estrus synchronization. Several PG products are licensed for use on dairy cattle and there does not appear to be significant differences among products in their efficacy for estrus synchronization. A single injection of PG will reliably induce regression of the CLs between days 7 and 18 of the estrus cycle. Regression of the CLs results in a drop in circulating progesterone concentration. This allows the normal sequence of physiological and endocrinological events associated with the follicular phase to proceed, leading to estrus and ovulation. However, PG is not effective at all stages of the estrus cycle. It has no consequence if administered after the spontaneous onset of luteolysis. The developing CLs before day 5 of the estrus cycle are not responsive to PG and young CLs (days 5 and 6) are less responsive to PG than mature CLs. Consequently, about two-thirds of cows treated with a
Figure 1 Diagrammatic illustration of various estrus synchronization programs involving PGF2 or its analogues (PG). AI, artificial insemination; h, hour.
450 Reproduction, Events and Management | Control of Estrous Cycles: Synchronization of Estrus Table 1 Estrous response rate (%) of cyclic lactating cows synchronized with two injections of PG 14 days apart and the effect of progesterone supplementation for 5 days before the second PG Day after second PG
No_progesterone (n ¼ 572)
Progesterone (n ¼ 605)
Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Total over 6 days
7.9 40.6 14.9 9.6 7.3 2.5 82.9
9.9 30.9a 25.1b 12.1 8.1 3.5 89.6a
a p < 0.01 compared with the corresponding value for cows in the no_progesterone group. b p < 0.001 compared with the corresponding value for cows in the no_progesterone group. PG, prostaglandin F2 . From Xu ZZ, Burton LJ, and Macmillan KL (1997) Reproductive performance of lactating dairy cows following estrus synchronization regimens with PGF2 and progesterone. Theriogenology 47: 687–701.
within 7 days after the second PG treatment can exceed 90% with a large peak response (up to 60%) between 48 and 72 h. By contrast, estrous response of lactating dairy cows to the double-PG treatment is inconsistent and less precise compared with that of heifers (Table 1). The percentage of cows that are noncyclic at the time of PG treatment can affect the estrous response. Stage of the estrus cycle at the time of PG treatment can also affect estrous response, with advanced stages of the luteal phase being associated with increased estrous response rate (Table 2). Thus, a 14-day interval between the two PG treatments will result in a higher estrous response rate compared with an 11-day interval due to an increase in the proportion of animals in the middle to late stages of the luteal phase. Progesterone supplementation for 5 days before the second PG injection can affect the pattern of onset of estrus and increase the estrous response rate (Table 1). The increase in estrous response rate mainly occurs in cows in the early to middle stages of the luteal phase (Table 2).
Many studies have found that conception rate after PG treatment is normal or even improved compared with nonsynchronized animals. Some of the improvement in conception rate could be due to improved estrus detection accuracy in synchronized cows. In herds with high estrus detection efficiency and accuracy, estrus synchronization with PG can reduce conception rate. The reduction in conception rate mainly occurs in cows in the early to middle stages of the estrus cycle at the time of the second PG injection. Therefore, it is not the PG treatment per se that reduces conception rate, rather the reduction is probably caused by shortening of the luteal phase, thus reducing the total amount of progesterone the reproductive system is exposed to before ovulation. The reduction in conception rate can be largely eliminated by supplementing progesterone for 5 days before the second PG injection (Table 2). In some countries, PG is the only drug that is licensed for estrus synchronization in lactating dairy cows. Systematic breeding programs based on PG have been developed. Targeted breeding is a systematic breeding program that is advocated by the manufacturer of Lutalyse, Pharmacia-Upjohn (now a division of Pfizer) (Figure 1, program (4)). It consists of three PG injections at 14-day intervals. For simplicity of implementation in nonseasonal herds, PG is usually administered on 1 day of the week to all cows that qualify in that week. To get more cows bred early, the first set-up injection of PG could be given to cows that are between 7 and 14 days before the end of the voluntary waiting period. Cows are not mated after the first set-up injection. The set-up injection ensures that cows will be in a stage of the estrus cycle when the CLs are responsive to the second PG injection. The second PG injection is administered 14 days later and cows are mated after detection of estrus. Those that have not been detected in estrus after the second PG treatment are given a third PG injection 14 days later, and the cycle can continue. For the targeted breeding program, a fixed-time insemination is carried out at 80 h after the third PG injection on cows that have not displayed estrus by that time. Alternatively,
Table 2 Effects of stage of the estrous cycle at second PG and progesterone supplementation for 5 days before second PG on ORR (%) and CR (%) of postpartum lactating cows synchronized with two injections of PG 14 days apart No_progesterone
Progesterone
Stage of estrous cycle
ORR
CR
ORR
CR
Days 5–9 Days 10–13 Days 14–19
75.9 85.5 93.1
52.3 59.3 71.3
86.8a 91.5a 94.3
64.8b 66.2 71.4
a
p < 0.05 compared with the corresponding value for cows in the no_progesterone group. p < 0.1 compared with the corresponding value for cows in the no_progesterone group. CR, conception rate; ORR, estrous response rate; PG, prostaglandin F2 . From Xu ZZ, Burton LJ, and Macmillan KL (1997) Reproductive performance of lactating dairy cows following estrus synchronization regimens with PGF2 and progesterone. Theriogenology 47: 687–701. b
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the first PG injection in the targeted breeding program could be given to those cows that have just passed the voluntary waiting period and cows are mated after detection of estrus. This treatment program will be cheaper due to the reduced total number of PG injections, but the interval from calving to first AI will be longer because only two-thirds of the cows can potentially respond to the first PG injection.
Combination Treatment Programs To improve the precision of synchrony and to reduce the adverse effects on fertility, various treatment programs involving a combination of two or more drugs have been developed. Some of the popular combination programs for synchronizing estrus are discussed here. Progestogen and Prostaglandin Progestogen in combination with PG is a widely used combination treatment program for estrus synchronization. It usually involves a short period (commonly 6–8 days) of progestogen treatment with a PG injection 1–2 days before or at the time of termination of the progestogen treatment (Figure 2, program (5)). This combination program ensures that, at the time of PG injection, animals either do not have functional CLs or have CLs that are responsive to PG. Most treated animals (85% or more) will show estrous behaviors between 2 and 5 days after the end of treatment. The time and the magnitude of the peak estrous response are affected by when PG is administered relative to the termination of progestogen treatment. If PG is injected 1–2 days before the end of progestogen treatment, peak estrous response occurs on the second day after progestogen treatment, whereas it occurs on the third day if PG is injected at termination of progestogen treatment. Conception rate to inseminations at the synchronized estrus has been reported to be normal or slightly reduced, but the reduction is generally less compared with the situation in which long-term progestogen treatment is used for synchronization. Persistent dominant follicles can still develop in some animals that are in the late stage of the estrus cycle at the start of progestogen treatment. Another combination program involving progestogen and prostaglandin is to presynchronize animals with a long-term (e.g., 14 days) progestogen treatment, followed by an injection of PG during the late luteal phase of the synchronized cycle (e.g., 17–18 days after the end of the progestogen treatment) (Figure 2, program (6)). This program takes advantage of the ability of a long-term progestogen treatment to precisely synchronize estrus and the high estrous response and normal fertility when PG is administered in the late luteal phase (Table 2). However, this program requires that progestogen
Figure 2 Diagrammatic illustration of the various estrus synchronization programs involving a combination of two or more hormones. PG, prostaglandin F2 or its analogue; GnRH, gonadotropin-releasing hormone; P4, progesterone or synthetic progestogen; E2, estradiol-17 or its derivatives; AI, artificial insemination.
treatment be initiated more than 30 days before the start of breeding when many postpartum cows may have not resumed ovarian cyclicity. Therefore, this program may not be well suited for postpartum lactating dairy cows.
Estrogen and Progestogen Studies have shown that an injection of progestogen and estrogen at the start of an estrus synchronization program using progestogen can reduce the duration of progestogen treatment from >14 to 9 days. This has formed the basis for the Synchro-Mate-B (SMB) treatment for estrus synchronization in beef cattle and dairy heifers. The SMB program involves a 9-day treatment with an ear implant containing 6 mg of norgestomet plus an injection of 5 mg of estradiol valerate and 3 mg norgestomet at the time of implant insertion. The injection of estradiol valerate and norgestomet serves two functions. First, the injection causes regression of large antral follicles and initiation of a new follicular wave 4–5 days after treatment so that a newly developed dominant follicle is available for ovulation after the 9-day treatment program. Second, the injection, presumably the estradiol valerate in the injection, causes premature luteolysis of CLs during the treatment period, irrespective of the stage of the estrus cycle at the start of
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SMB treatment. Estrogen induces luteolysis by stimulating PG secretion from the uterus. In addition, progestogen treatment during metestrus can also prevent normal CLs development in some animals. Estrous response following SMB treatment is typically greater than 90% and fixedtime insemination between 48 and 54 h after implant removal can achieve acceptable reproductive performance. However, SMB has been withdrawn from the market. Gonadotropin-Releasing Hormone and Prostaglandin Studies, mainly in North America, have shown that treatment with gonadotropin-releasing hormone (GnRH) followed 7 days later by PG can be used for estrus synchronization (Figure 2, program (7)). The dose of GnRH used in this program is typically half of that recommended for treating follicular cysts. The GnRH treatment induces ovulation of existing dominant follicles and the formation of new or accessory CLs. This prevents most animals in the late luteal and follicular phases of the estrus cycle from showing estrus before PG injection. However, between 5 and 10% of treated cows can still show estrus between the GnRH and PG treatment, thus reducing the effectiveness of this program for estrous synchronization. Nevertheless, some studies have shown similar or improved reproductive performance after this program compared with the double-PG program. Progestogen, gonadotropin-releasing hormone, and Prostaglandin Studies in New Zealand and Ireland have investigated synchronization programs that incorporate progesterone treatment between GnRH and PG injections (Figure 2, program (8)). A CIDR device is inserted at the time of GnRH injection and removed at PG injection. The progesterone treatment prevents estrus and ovulation before PG injection and may also improve conception rate at the synchronized estrus by increasing circulating progesterone concentrations in cows without a functional CLs. An estrous response rate of greater than 90% has been obtained and the conception rate at the synchronized estrus is similar to that of nonsynchronized herd mates inseminated at detected estrus. Estrogen, Progestogen, and Prostaglandin Estrogen has been used at the beginning of combination treatment programs involving progestogen and PG (Figure 2, program (9)). The purpose of this estrogen treatment is to regress dominant follicles that are present at the time of estrogen treatment so that freshly developed dominant follicles are ready to ovulate after the program. A gelatin capsule containing 10 mg of estradiol benzoate is
developed for intravaginal use together with the CIDR device or PRID. Injection of 5 mg of estradiol-17 or 2 mg of estradiol benzoate has also been found to improve the precision of synchrony and conception rate compared with no estrogen treatment. Estrogen has also been used after the end of progestogen and PG treatment to increase the precision of onset of estrus. An injection of 1 mg of estradiol benzoate 48 h after the end of progesterone and PG treatment can significantly increase the percentage of cows showing estrus between 48 and 72 h (85 vs. 57%). However, in 2006, the European Union banned the use of estradiol and its derivatives for estrus synchronization in food-producing animals. This has led other countries, such as New Zealand and Australia, to adopt the EU Directive and ban the use of estrogens for estrus synchronization. Consequently, the use of GnRH at the beginning of a progesterone–PG program to increase the precision of onset of estrus and/or after the progesterone–PG program to synchronize ovulation has gained popularity.
Treatment of Noncyclic Cows In a group of cows eligible for breeding, some may be noncyclic. The problem of noncyclic cows at the start of the breeding season is particularly severe in high-producing dairy cows or in seasonal dairy cows grazing on pasture. Therefore, an effective estrus synchronization program should also be able to induce estrus and ovulation in noncyclic cows. In New Zealand, a popular program for treating noncyclic cows involves progesterone treatment in the form of an intravaginal CIDR device for 6–7 days, followed by an injection of 1 mg of estradiol benzoate either 24 or 48 h after CIDR removal. An estrous response rate of close to 90% and conception rate of around 35% have been obtained with this treatment program. However, this program does not work for cyclic cows and special effort is therefore needed to separate cyclic from noncyclic cows. Recent studies have shown that a combination program involving GnRH, progesterone, PG, and estradiol may be used to synchronize all cows in a herd regardless of their cyclic status. Cows are treated with a CIDR device for 7 days, along with GnRH at CIDR insertion and PG at CIDR removal. At 48 h after CIDR removal, 1 mg of estradiol benzoate is injected to cows that have not been detected in estrus by that time. This program has been tested for treating noncyclic cows due to nutritional stress and has been found to result in better estrous response (93 vs. 89%) and conception rate (47 vs. 29%) than the program based on progesterone and estradiol benzoate only. The GnRH and PG used in this program could also be beneficial for treating noncyclic cows due to ovarian cysts and uterine infection.
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Following the ban on the use of estrogens in foodproducing animals, the available programs for both cyclic and noncyclic cows in New Zealand have been changed to Ovsynch-type programs involving a combination of GnRH and PG, with or without progesterone in the form of the CIDR device. A second GnRH injection around 56 h after PG and fixed-time insemination at 72 h may improve pregnancy rate compared with insemination after detected estrus.
Practical Considerations Despite the aforementioned advantages from using estrus synchronization, it remains a major challenge to make this technique widely accepted by commercial dairy producers. Costs of drugs and labor for implementing an estrus synchronization program are among the first things considered by dairy farmers when deciding whether to use estrus synchronization. Estrus detection can be more difficult in a large group of synchronized cattle because so many animals are in estrus at the same time and it is difficult to identify those that are in genuine estrus. This problem can be solved by developing synchronization programs that allow fixed-time insemination. Herd managers need to have good organizational skills and some technical knowledge of the program in order to implement a successful estrus synchronization program. Good communication and cooperation among herd managers, veterinarians, and AI technicians are essential. Good record keeping is also important because the use of PG on pregnant animals will lead to abortion.
The Future The challenge for future research on estrus synchronization will be to increase the estrous response rate, to improve the precision of synchrony, and at the same time to maintain and increase conception rate at the synchronized estrus. A reduction in conception rate at the synchronized estrus is a common feature following most estrus synchronization programs. Although many studies have reported improved reproductive performance after estrus synchronization compared with nonsynchronized control animals, most of this increase is probably due to improvement in the efficiency and accuracy of estrus detection and not due to improved fertility. The objective is to achieve a conception rate that equals the conception rate to inseminations at correctly detected natural estrus or to natural mating. It is likely that achieving this objective will require the use of multiple drugs. Therefore, the other challenge for research is to develop smart drug delivery systems that simplify the implementation of estrus synchronization
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programs. Furthermore, the development of semen products that allow sperm to survive for several days in the female reproductive tract will eliminate the need for tight synchrony. Finally, the challenge will be even greater to develop estrus synchronization systems that can effectively synchronize the onset of estrus in those animals that return after a synchronized insemination. See also: Reproduction, Events and Management: Control of Estrous Cycles: Synchronization of Ovulation and Insemination; Estrous Cycles: Characteristics; Mating Management: Detection of Estrus.
Further Reading Bo GA, Cutaia L, Peres LC, Pincinato D, Marana D, and Baruselli PS (2007) Technologies for fixed-time artificial insemination and their influence on reproductive performance of Bos indicus cattle. Society of Reproduction and Fertility Supplement 65: 223–236. Ferguson JD and Galligan DT (1993) Prostaglandin synchronization programs in dairy herds – part I. Compendium on Continuing Education for the Practicing Veterinarian 15: 646–655. Gordon I (ed.) (1996) Artificial control of oestrus and ovulation. In: Controlled Reproduction in Cattle and Buffaloes, pp. 133–166. Wallingford, UK: CAB International. Jo¨chle W (1993) Forty years of control of the oestrous cycle in ruminants: Progress made, unresolved problems and the potential impact of sperm encapsulation technology. Reproduction Fertility and Development 5: 587–594. Kesler DJ and Favero RJ (1995) Estrus synchronization in beef females with norgestomet and estradiol valerate. Part 1: Mechanism of action. Agri-Practice 16: 6–11. Lane EA, Austin EJ, and Crowe MA (2008) Oestrous synchronisation in cattle – current options following the EU regulations restricting use of oestrogenic compounds in food-producing animals: A review. Animal Reproduction Science 109: 1–16. Larson LL and Ball PJH (1992) Regulation of estrous cycles in dairy cattle: A review. Theriogenology 38: 255–267. Macmillan KL and Peterson AJ (1993) A new intravaginal progesterone releasing device for cattle (CIDR-B) for oestrous synchronization, increasing pregnancy rates and the treatment of post-partum anoestrus. Animal Reproduction Science 33: 1–25. Nebel RL and Jobst SM (1998) Evaluation of systematic breeding programs for lactating dairy cows: A review. Journal of Dairy Science 81: 1169–1174. Roche JF, Austin EJ, Ryan M, O’Rourke M, Mihm M, and Diskin MG (1999) Regulation of follicle waves to maximize fertility in cattle. Journal of Reproduction and Fertility Supplement 54: 61–71. Twagiramungu H, Guilbault LA, and Dufour JJ (1995) Synchronization of ovarian follicular waves with a gonadotropin-releasing hormone agonist to increase the precision of estrus in cattle: A review. Journal of Animal Science 73: 3141–3151. Watts TL and Fuquay JW (1985) Response and fertility of dairy heifers following injection with prostaglandin F2 during early, middle or late diestrus. Theriogenology 23: 655–661. Xu ZZ, Burton LJ, and Macmillan KL (1997) Reproductive performance of lactating dairy cows following estrus synchronization regimens with PGF2 and progesterone. Theriogenology 47: 687–701. Xu ZZ, Burton LJ, McDougall S, and Jolly PD (2000) Treatment of anestrous lactating dairy cows with progesterone and estradiol or with progesterone, GnRH, prostaglandin F2 and estradiol. Journal of Dairy Science 83: 464–470. Zimbelman RG, Lauderdale JW, Sokolowski JH, and Schalk TG (1970) Safety and pharmacologic evaluations of melengestrol acetate in cattle and other animals: A review. Journal of the American Veterinary Medical Association 157: 1528–1536.
Control of Estrous Cycles: Synchronization of Ovulation and Insemination W W Thatcher and J E P Santos, University of Florida, Gainesville, FL, USA ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by W. W. Thatcher, Volume 4, pp 2178–2184, ª 2002, Elsevier Ltd.
Introduction Intensive genetic selection for milk production without attention to reproductive performance has contributed to an inverse relationship between milk production and reproduction. Inclusion of productive life and daughter pregnancy rate and, more recently, the availability of sire conception rate, as a measure of phenotypic service-sire fertility, appear to have reduced the rate of decline in fertility in the United States. Reproductive management of the lactating dairy cow has been a challenge because of poor expression of estrus and low fertility to insemination at a detected estrus. The duration of estrus is reduced as milk production increases, and the frequency of double ovulations and subsequent occurrence of twins is also increased in cows with high levels of milk production at the time of the breeding period. The high-producing dairy cow of today expresses estrus for approximately 7 h during which time an average of 6.5 standing events take place with an accumulative period of standing of 20 s (i.e., 3 s per standing event). Pregnancy rate over a 21-day period for the national herd of dairy cows in the United States is approximately 16.2%. The component parts of pregnancy rate are the rate of estrus detection and conception rate. Technology is available for systems to detect estrus accurately, but a major issue is that lactating dairy cows do not display strong symptoms of estrus. Expression of estrus has been affected adversely by high milk production and associated metabolism of hormones, as well as housing facilities (e.g., concrete floors) that reduce the cow’s willingness to be sexually active. An additional challenge is the high occurrence of nonovulatory dairy cows that either have reoccurring follicle waves without ovulation or develop ovarian cysts. A major advance in reproductive management that has addressed how to improve pregnancy rate has been the development of timed artificial insemination (TAI) programs based on the development of systems to control or program optimal development of ovarian follicles, induce ovulation, and develop a corpus luteum (CL) capable of supporting pregnancy. The component pharmaceutical agents available to the dairy industry in many countries for use with dairy cattle are gonadotropin-releasing hormone (GnRH), luteolytic prostaglandins, and intravaginal
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progesterone (using a controlled intravaginal drug release (CIDR) insert, or similar device). These are pharmaceuticals that mimic the actions of the cow’s endogenous hormones, are physiological, and pose no health hazard to the cow. The original TAI protocol is the Ovsynch procedure. This protocol has been in use for approximately 12 years. During this period, both basic and applied research has led to major advancements in optimizing the system. As a consequence, pregnancy responses have increased, the system has been extended to resynchronization of nonpregnant cows, and programs have been developed for TAI in dairy heifers. The dynamics of various cow factors such as body condition score, parity, and health status in the transitional-periparturient period have been shown to influence pregnancy rates in the controlled breeding program. The present objective is to update major advancements that will increase reproductive performance in controlled breeding in dairy cattle.
Lactating Dairy Cattle It is essential that producers and veterinarians understand the physiological reasons why certain components of the reproductive management program are able to improve reproductive performance or conversely why a misunderstanding of the program can lead to catastrophic pregnancy results. No one reproductive breeding program is practical and economically optimal for all dairy production units due to differences in available facilities, size of the unit, labor that places reproduction as a high priority, and a functionally dynamic record system.
Optimizing Stage of the Estrous Cycle at the Onset of Ovsynch The original Ovsynch program involved two injections of GnRH administered 7 days before and 48 h after an injection of prostaglandin F2 (PGF2 ), and cows were inseminated 16–20 h after the second injection of GnRH. If TAI in the Ovsynch protocol is performed at the same time as the second GnRH injection, then the protocol is referred to as Co-synch.
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Figure 1 Follicle dynamics and hormonal responses to the Ovsynch protocol. FSH, follicle-stimulating hormone; GnRH, gonadotropin-releasing hormone; LH, luteinizing hormone; PGF2 , prostaglandin F2 ; P4, Progesterone; TAI, timed artificial insemination.
Optimization of stage of the estrous cycle (i.e., days 5–9) at the onset of the Ovsynch protocol is important to achieve a subsequent synchronized ovulation at the second GnRH preceding the TAI (Figure 1). Programming the stage of the estrous cycle at the time the Ovsynch protocol is implemented (e.g., days 5–9 of estrous cycle) ensures there is progesterone availability throughout the period between the first injection of GnRH and injection of PGF2 , and that there is a CL to respond to the luteolytic injection of PGF2 (Figure 1). The continual exposure to progesterone is important for sequentially programming the brain, oviduct, and uterus with the appropriate changes in hormones, receptors, and secretions leading to an induced ovulation, fertilization, and development of an embryo capable of maintaining a pregnancy with minimal embryonic and fetal losses. Programming the start of the Ovsynch protocol to occur between days 5 and 9 of the estrous cycle increases the probability that the first injection of GnRH will induce
ovulation of the first wave follicle and recruitment of a new follicle wave (Figure 1), which upon induction of ovulation in response to the second GnRH increases the probability of producing a viable oocyte for fertilization and a robust CL. Indeed ovulation of the first follicle wave results in the presence of both the original CL and an accessory CL, induced by the GnRH injection, which are responsive to the injection of PGF2 . The Ovsynch protocol preceded by a PGF2 presynchronization program (Presynch–Ovsynch) has become the nucleus program for reproductive management in the industry. Successful use of such a program is highly dependent upon obtaining good compliance in implementing all component parts of the protocol. The original Presynch–Ovsynch program entailed two injections of PGF2 given 14 days apart with the Ovsynch protocol initiated 12 days after the second injection of PGF2 for presynchronization (Figure 2). This system increased pregnancy rates compared to Ovsynch alone for
Figure 2 Presynch/Ovsynch protocol for TAI at the first postpartum service. GnRH, gonadotropin-releasing hormone; PGF2 , prostaglandin F2 ; TAI, timed artificial insemination.
456 Reproduction, Events and Management | Control of Estrous Cycles Table 1 Pregnancy rates for lactating dairy cows receiving various reproductive management systems for timed insemination
Treatment (n)
Control (n)
Treatment (Percent pregnant to AI)
Control (Percent pregnant to AI)
References
Presynch-12d/Ovsynch (269) Presynch-12d/Ovsynch (304) 11-Day Presynch (410) 33-Day Resynch (180) 38-Day Resynch (GnRH (357)/CIDR (316))
Ovsynch (274) Ovsynch (310) 14-Day Presynch (412) 26-Day Resynch (189) 38-Day Resynch (386)
48.3 46.8 40.5 39.4 33.6/31.3
36.9 37.5 33.5 28.6 24.6
Moreira et al. (2001) El-Zarkouny et al. (2004) Galvao et al. (2007) Sterry et al. (2006) Dewey et al. (2009)
AI, artificial insemination; CIDR, controlled intravaginal drug release; GnRH, gonadotropin-releasing hormone.
the reasons outlined above, when the Ovsynch protocol is initiated in early diestrus (Table 1). Dairy producers were keen to extend the period when Ovsynch was initiated to a 14-day interval such that four of the five sequential hormonal injections would be given on the same day of week. Field experiences indicate that 60% of detected estruses occur on days 3–6 after the second injection of PGF2 of presynchronization. A recent study indicated that an 11-day interval after presynchronization (i.e., cows would be predominately 5–8 days of the estrous cycle) is better than a 14-day interval to begin the TAI protocol. The overall ovulation rate in response to the first injection of GnRH was greater for an 11-day than a 14-day interval (62 vs. 44.7%). This was attributed to GnRH being given at 11 days when the first wave follicle will ovulate whereas the 14-day interval increased the proportion of cows injected early in the second follicle wave at a time the follicle was developed insufficiently to ovulate in response to GnRH. The latter follicle would continue to develop and be slightly more aged and/or dominant compared to the newly recruited follicle from the day 11 injection interval for GnRH. Indeed pregnancy per TAI was 6.6% greater for the 11-day interval (40.1 vs. 33.5% at day 38 after TAI; Table 1). Thus, subtle changes in presynchronization protocols can cause substantial increases in pregnancy rate, and the optimal period to start the Ovsynch protocol is 10–12 days after the second PGF2 injection of presynchronization (Figure 2).
after the injection of GnRH. In contrast, percent pregnant to AI was decreased when inseminations were made at the time of GnRH injection or 28 h later. Producers often favor the convenience of carrying out a TAI at the time of GnRH injection (i.e., referred to as a Co-synch program) to reduce the number of times cows need to be held up. Alternatively, some producers prefer to perform TAI on the following day at approximately 24–28 h after the GnRH injection for convenience. Either option likely will reduce percent pregnant to AI. The importance of the correct timing is indicated by a study completed at the University of Wisconsin. All cows were presynchronized with two injections of PGF2 , and the Ovsynch protocol was started 11 days later. The optimal timing program was to inject GnRH 56 h after the injection of PGF2 and inseminate the cows 16 h after the injection of GnRH, which was 72 h after the injection of PGF2 (see Figure 2). Percent pregnant to AI was 36.1% compared to Co-synch 48 h (26.7%) and to 72 h (27.3%) programs. The last two programs injected GnRH and TAI concurrently at 48 or 72 h, respectively. Clearly, subtle changes in the timing of the GnRH injection and time of insemination result in substantial differences in percent pregnant to AI responses. If a Co-synch program is to be followed, one needs to understand the physiology of the injection sequence so that functionally active ovarian follicles are at an optimal stage analogous to a follicle in the close periestrus period when GnRH/TAI is performed.
Interval from PGF2 to Ovulatory Injection of GnRH and Timing of AI
Resynchronization of Nonpregnant Cows Following First Service
It has been well documented that cows should be inseminated 8–16 h after the onset of estrus for an optimal conception rate. The preovulatory surge of luteinizing hormone (LH) occurs very close to the onset of estrus with ovulation occurring approximately 28 h after the LH surge. It is important to recognize that the second injection of GnRH of an Ovsynch program is analogous to the onset of estrus since an LH surge is induced immediately. Indeed maximal rate of pregnancies per artificial insemination (AI) was achieved when a timed insemination was made at 16 h
A reproductive management challenge following first service is to reinseminate cows that did not conceive as quickly as possible. The same principles to optimize the Presynch–Ovsynch program are applicable to development of a resynchronization program. However, a resynchronization system is somewhat constrained in that programming nonpregnant cows to ovulate must be done in a manner that will not interfere with cows that are pregnant to first service. Thus, accurate identification of nonpregnant and pregnant cows is important, and timing
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of the diagnosis is dependent upon the technology applied (i.e., rectal palpation at 35–42 days, ultrasound diagnosis at 30–32 days, blood pregnancy test at 27–30 days (measurement of PAG)). To some degree, there is a natural presynchronization of nonpregnant cows because those detected in estrus have a median return to estrus interval of 22 days in which 64.3% show estrus within 17–24 days after first service. Thus, initiation of Ovsynch at 30 days after first service would mean most cows would be at approximately day 8 of the cycle. GnRH injection would induce ovulation of a first wave follicle and initiate recruitment of a new follicular wave under a high progesterone environment. At 37 days after first service, a decision can be made to inject PGF2 in cows diagnosed nonpregnant (e.g., rectal palpation). These cows would then be injected with GnRH and TAI at 56 and 72 h after the PGF2 injection, respectively. Several days after first service (days 19, 26, and 33) have been examined to begin resynchronization of nonpregnant cows with Ovsynch. Starting resynchronization on day 33 resulted in the highest pregnancy rate for the second service. Ultrasound technology was used for detection of nonpregnant cows at day 26 or day 33 after first service for the day 19–26 and 33 resynchronization groups, respectively. Hypothetically, the timing of GnRH at day 26 would tend to target the majority of cows too early in their follicle wave (i.e., day 4 of the wave) to induce follicle turnover, whereas at day 33 they would be ovulating potential first or second wave follicles and a sustained progesterone environment would be present for cows potentially returning to estrus between 17 and 24 days after first service. Experimental results clearly document that fertility was increased for the day 33 resynchronization group (i.e., 33.7%) compared to the day 19 and 26 groups (27.1 and 26.6%, respectively). The benefit of the day 33
resynchronization on pregnancy per TAI compared to the day 26 resynchronization group was repeated (39.4 vs. 28.6%; Table 1) with the benefit most apparent in primiparous cows. In the latter study, insertion of a CIDR insert in cows without a CL improved pregnancy rate per TAI in the multiparous cows to a level comparable to that of primiparous with or without a CL. An alternative resynchronization strategy is a more conventional system based solely on pregnancy diagnosis per rectal palpation at day 38 (Figure 3). In this scenario, an Ovsynch 72 h Co-synch (GnRH, 7 days later PGF, and 72 h later GnRH and TAI) was initiated at day 38 after first service in three groups of nonpregnant cows (Group 1: control, GnRH; Group 2: received a GnRH injection on day 31 at 7 days before pregnancy diagnosis; Group 3: received a CIDR insert on day 38 that was removed at the time of PGF2 injection; Figure 3). Pregnancy rate per TAI was greater and tended to be greater for GnRH/Group 2 (33.6%) and Group 3/CIDR (31.3%) cows than Group 1 (24.6%) cows (Table 1). It is likely that presynchronization with a single injection of GnRH at day 31 programmed a new follicle wave and increased the occurrence of a CL at the beginning of the Ovsynch 72 h Co-synch protocol. Insertion of a CIDR insert likely improved the synchronization of ovulation associated with the 72 h Co-synch response because it held ovarian follicles from ovulating prematurely in cows that were in late diestrus at the time the Ovsynch 72 h program was started. It is clear that several alternatives are available for resynchronization of lactating dairy cows. With the acquisition of new technology for a cow side diagnosis of nonpregnant cows early after insemination (e.g., 27, 28, or 30 days), it will be possible to implement even earlier resynchronization systems for TAI within 3 days (e.g., day
Figure 3 Resynchronizations of cows diagnosed nonpregnant at 38 days after first AI. AI, artificial insemination; CIDR insert, controlled intravaginal drug release insert GnRH, gonadotropin-releasing hormone; NP, nonpregnant; PGF2 , prostaglandin F2 ; TAI, timed artificial insemination.
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30, 31, or 33) after the diagnosis of a nonpregnancy. This would offer a reduction in reinsemination interval of 9.5–17 days compared to the promising systems described above.
Timed Artificial Insemination for Dairy Heifers A major limitation for using AI in dairy replacement heifers is time and effort associated with daily estrus detection. Unfortunately, however, the Ovsynch has resulted in unacceptable pregnancy rates of approximately 38% in dairy heifers (Table 2). Compared to lactating cows, heifers have a faster rate of follicular growth and a higher frequency of three wave follicular cycles. Consequently, approximately 57% of the cycle is comprised of times when follicles are unresponsive to the first injection of GnRH. Furthermore, rapid turnover and growth of follicles lead to asynchrony with heifers expressing estrus during different stages of the protocol prior to the second ovulatory injection of GnRH for TAI. Investigators at Ohio State University working with beef cattle deduced that an increase in percent pregnant per TAI could be achieved by insertion of a CIDR insert at the time of GnRH injection and, after
5 days, withdrawing the CIDR insert and injecting PGF2 . An extended proestrus period was achieved by allowing a 3-day interval from the time of PGF2 injection to the time of GnRH injection and a concurrent TAI. The entire protocol takes only 8 days to be accomplished. Since the interval from the first GnRH injection and CIDR insertion to PGF2 injection is 5 days, a second injection of PGF2 was given 12 h after the first PGF2 . This program in beef cows resulted in a higher pregnancy rate compared to a 7-day Ovsynch with a CIDR in which the second GnRH and TAI occurred at 60 h. This program has been further modified for use in dairy heifers in which only a single injection of PGF2 is given at the time of CIDR removal (5-day CIDR Co-synch 72 h with one injection of PGF2 ; Figure 4). Pregnancy rates to first and second services at 32 days after TAI were 60.3 and 52.5%, respectively (Figure 4). Essentially, 81% (337/416) of the heifers were pregnant after two programmed TAIs following a 5-day CIDR Co-synch 72 h with one injection of PGF2 . This is an efficient reproductive management program that successfully synchronizes ovulation for TAI and reduces labor costs associated with estrus detection. Indeed all of the TAI procedures described in Table 2 incorporated some degree of estrus
Table 2 TAI in dairy heifers Protocol
n
Percent pregnant to AI
References
Ovsynch Ovsynch Ovsynch 6-Day Co-synch 48 h 6-Day Co-synch 48 h 6-Day Co-synch 48 h + CIDR 6-Day Co-synch 48 h Overall
187 77 113 175 95 94 82 823
45.5 35.1 42.5 34.3 29.5 31.9 45.1 38.3
Schmitt et al. (1996) Pursley et al. (1997) Stevenson et al. (2000) Rivera et al. (2004) Rivera et al. (2005) Rivera et al. (2005) Rivera et al. (2006)
AI, artificial insemination; TAI, timed artificial insemination.
Figure 4 Pregnancy rate of dairy heifers to a 5-day CIDR Co-synch 72 h with one injection of PGF2 . AI, artificial insemination; CIDR, controlled intravaginal drug release; GnRH, gonadotropin-releasing hormone; PGF2 , prostaglandin F2 ; TAI, timed artificial insemination.
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detection that is not necessary with the present program. The concept of a 5-day interval between GnRH and PGF2 (i.e., with or without a CIDR insert) and a subsequent 3-day proestrus period (i.e., 72 h Co-synch) warrants investigation in lactating dairy cows.
Conclusion Tremendous advances have been made in improving milk production, but have in turn resulted in an overall decline in reproductive efficiency for the dairy industry. Problems associated with the cow include inability to properly express estrus and altered hormonal profiles resulting in low conception rates and increased early embryonic death. Coordinated systems of reproductive management offer means to improve herd reproductive performance, and major advances have been made for synchronization of ovulation in both lactating dairy cows and dairy heifers. Such systems are predicated on a greater understanding of the factors controlling follicle development, ovulation, and CL development. The programs as described require the producer, veterinarian, and reproductive management staff to understand the programs and make an effort to obtain a high level of compliance. The platforms used for controlling first service and resynchronized subsequent services in cows that do not conceive provide valuable platforms to implement new technology such as the use of sexed semen, embryo transfer, and cow-side chemical diagnosis of nonpregnant cows. Functional and efficient computer record programs are essential to implement such reproductive management programs. For the research scientist, the reproductive management systems provide the infrastructure to quantify the effects of nutritional, health, and physiological interventions on pregnancy rate. With the advent of new technologies to precisely manipulate reproductive function in lactating dairy cows, dairy producers are presented with a new opportunity. Coordination of management strategies to maximize both milk production and reproductive performance may optimize the economical return of dairy herds, and allow the industry to take complete advantage of the genetic potential to improve milk production through AI. See also: Reproduction, Events and Management: Control of Estrous Cycles: Synchronization of Estrus; Estrous Cycles: Characteristics; Estrous Cycles: Postpartum Cyclicity; Estrous Cycles: Puberty; Estrous Cycles: Seasonal Breeders; Mating Management: Artificial Insemination, Utilization; Mating Management: Detection of Estrus; Mating Management: Fertility; Pregnancy: Characteristics; Pregnancy: Parturition;
Pregnancy: Periparturient Disorders; Pregnancy: Physiology.
Further Reading Bartolome JA, Sozzi A, McHale J, et al. (2005) Resynchronization of ovulation and timed insemination in lactating dairy cows, II: Assigning protocols according to stages of the estrous cycle, or presence of ovarian cysts or anestrus. Theriogenology 63(6): 1628–1642. Bridges GA, Helser LA, Grum DE, Mussard ML, Gasser CL, and Day ML (2008) Decreasing the interval between GnRH and PGF2alpha from 7 to 5 days and lengthening proestrus increases timed-AI pregnancy rates in beef cows. Theriogenology 69(7): 843–851. Brusveen DJ, Cunha AP, Silva CD, et al. (2008) Altering the time of the second gonadotropin-releasing hormone injection and artificial insemination (AI) during Ovsynch affects pregnancies per AI in lactating dairy cows. Journal of Dairy Science 91(3): 1044–1052. Dewey ST, Mendonc¸a LG, Lopes G, Jr., et al. (2009) Resynchronization strategies to improve fertility in lactating dairy cows utilizing a presynchronization injection of GnRH or supplemental progesterone: I. Pregnancy rates and ovarian responses. Journal of Dairy Science 92(supplement 1): 267; Abstract. El-Zarkouny SZ, Cartmill JA, Hensley BA, and Stevenson JS (2004) Pregnancy in dairy cows after synchronized ovulation regimens with or without presynchronization and progesterone. Journal of Dairy Science 87(4): 1024–1037. Fricke PM, Caraviello DZ, Weigel KA, and Welle ML (2003) Fertility of dairy cows after resynchronization of ovulation at three intervals following first timed insemination. Journal of Dairy Science 86(12): 3941–3950. Galva˜o KN, Filho MFS, and Santos JEP (2007) Reducing the interval from presynchronization to initiation of timed artificial insemination improves fertility in dairy cows. Journal of Dairy Science 90(9): 4212–4218. Lopez H, Caraviello DZ, Satter LD, Fricke PM, and Wiltbank MC (2005) Relationship between level of milk production and multiple ovulations in lactating dairy cows. Journal of Dairy Science 88(8): 2783–2793. Lopez H, Satter LD, and Wiltbank MC (2004) Relationship between level of milk production and estrous behavior of lactating dairy cows. Animal Reproduction Science 81(3–4): 209–223. Lucy MC (2001) Reproductive loss in high-producing dairy cattle: Where will it end? Journal of Dairy Science 84(6): 1277–1293. Moore K and Thatcher WW (2006) Major advances associated with reproduction in dairy cattle. Journal of Dairy Science 89(4): 1254–1266. Moreira F, Orlandi C, Risco CA, Mattos R, Lopes F, and Thatcher WW (2001) Effects of presynchronization and bovine somatotropin on pregnancy rates to a timed artificial insemination protocol in lactating dairy cows. Journal of Dairy Science 84(7): 1646–1659. Norman HD, Wright JR, Hubbard SM, Kuhn MT, and Miller RH (2007) Genetic selection for reproduction: Current reproductive status of the national herd; Application of selection indexes for dairy producers. In: Thatcher WW and Jordan ER (eds.) Proceedings of the Dairy Cattle Reproductive Conference, pp. 69–78. Hartland, WI: Dairy Cattle Reproductive Council. Pursley JR, Kosorok MR, and Wiltbank MC (1997) Reproductive management of lactating dairy cows using synchronization of ovulation. Journal of Dairy Science 80(2): 301–306. Pursley JR, Wiltbank MC, Stevenson JS, Ottobre JS, Garverick HA, and Anderson LL (1997) Pregnancy rates per artificial insemination for cows and heifers inseminated at a synchronized ovulation or synchronized estrus. Journal of Dairy Science 80(2): 295–300. Rabaglino MB, Risco CA, Thatcher MJ, Kim IH, Santos JEP, and Thatcher WW (2009) Application of one injection of PGF2 in the 5 d Co-Synch + CIDR protocol for estrous synchronization and resynchronization of dairy heifers. Journal of Dairy Science 93(3): 1050–1058.
460 Reproduction, Events and Management | Control of Estrous Cycles Savio JD, Keenan L, Boland MP, and Roche JF (1988) Pattern of growth of dominant follicles during the oestrous cycle of heifers. Journal of Reproduction and Fertility 83(2): 663–671. Schmitt EJ, Diaz T, Drost M, and Thatcher WW (1996) Use of a gonadotropin-releasing hormone agonist or human chorionic gonadotropin for timed insemination in cattle. Journal of Animal Science 74(5): 1084–1091. Silva E, Sterry RA, Kolb D, et al. (2007) Accuracy of a pregnancyassociated glycoprotein ELISA to determine pregnancy status of
lactating dairy cows twenty-seven days after timed artificial insemination. Journal of Dairy Science 90(10): 4612–4622. Sterry RA, Welle ML, and Fricke PM (2006) Effect of interval from timed artificial insemination to initiation of resynchronization of ovulation on fertility of lactating dairy cows. Journal of Dairy Science 89(6): 2099–2109. Stevenson JS, Smith JF, and Hawkins DE (2000) Reproductive outcomes for dairy heifers treated with combinations of prostaglandin F2alpha, norgestomet, and gonadotropin-releasing hormone. Journal of Dairy Science 83(9): 2008–2015.
Mating Management: Detection of Estrus R L Nebel and C M Jones, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA Z Roth, The Hebrew University of Jerusalem, Rehovot, Israel ª 2011 Elsevier Ltd. All rights reserved.
Introduction Estrus detection is one of the key components in fertility management programs on dairy farms. Excellent reproductive performance can be defined as the ability to consistently have 90% or more of the cows in a herd conceive and maintain pregnancies in a timely, economically justified manner. On the other hand, low detection rate is strongly associated with poor fertility, long calving interval, intensive replacement of heifers, and reduced genetic progress, resulting in heavy economic losses. Maintaining a consistently high-performing reproductive program requires a substantial investment in management, labor, and other costs, such as semen and pharmaceuticals. The goal of an estrus detection program should be to identify estrus positively and accurately in all cycling cows and to identify all of the cows that are not cycling or are expressing irregular cyclicity. The ultimate goal should be to predict the time of ovulation, thus allowing for insemination that will maximize the opportunity for conception. Dairy farming is one of the most intensive technologically integrated systems in the world of production agriculture. In general, the market sorts out which technologies offer a competitive advantage and which do not. Most of the aids that have been developed are not reliable or sensitive enough to relieve the farmer from frequent visual observation of the herd. Furthermore, none of the technologies is appropriate for every farm. New approaches are being developed to provide automated systems for estrus detection using remote-sensing technology, but the development of these new tools is in its infancy.
silent ovulation (i.e., ovulation without the expression of estrous behavior), which occurs mostly during the postpartum period. Occasionally, pregnant cows exhibit signs of estrus, particularly during middle to late gestation. Also, cows with ovarian follicular cysts may have a hormonal milieu that leads to estrous behavior similar to that of cyclic cows in estrus. Therefore, estrous behaviors other than ‘standing’ are crucial for accurate identification of estrus coincident with ovulation. Secondary signs of estrus include attempting to mount other cows, clear mucus discharge from the vulva, swelling and reddening of the vulva from increased blood flow, bellowing, restlessness, trailing other cows, chin resting, sniffing the genitalia of other cows, and lip curling. These signs may serve as clues that cows are near estrus so that they can then be observed more intensely for ‘standing’ behavior, but cannot be used as a practical predictor of ovulation. Other characteristics are reduction in food intake followed by reduced milk production during estrus, but these are not overt in all animals. The time of the day and duration of observation are the most important factors for a high detection rate. Traditional management of visual estrus detection is based on a twice-a-day detection regime or observation (20 min each) 3 times a day while taking into account the aforementioned primary and secondary signs of estrous characteristics. Observations are mostly performed in coincidence with each milking. Additional observations are recommended during periods of high activity, such as feeding time or while going to and coming back from the milking parlor. Nevertheless, estrus detection rate in dairy cows is low (20
Figure 3 Percentage of pregnant cows by 4-h intervals relative to timing of artificial insemination (AI) from first standing event detected by the radiotelemetric HeatWatch system across 17 herds and 2661 inseminations.
466 Reproduction, Events and Management | Mating Management: Detection of Estrus
estrus and palpation of the uterus 35–75 days following insemination. The bar graph shown in Figure 3 represents the proportion of pregnant cows for each 4-h interval from first standing event to insemination. Inseminations performed between 4 and 12 h following onset of estrus achieved a conception rate of approximately 50 versus 30% for inseminations performed after 16 h from onset (Figure 3). From previous studies, nearoptimal conception rates would be expected for cows submitted for insemination 12–18 h after detection of estrus. Mathematical modeling to predict the optimal time for AI using activity pedometers and visual signs of estrus estimated 11.8 h from onset as the optimal time for AI, which coincides with the approximate midpoint of the 5 16 h optimum using the HeatWatch System. Since the chance of fertilization strongly depends on the interval from insemination to ovulation, it is reasonable that insemination time be based on time of ovulation rather than detection of estrus. Pedometer activity systems and pressure sensing to monitor mounting activity appear to be promising tools for predicting ovulation and hence could serve for the improvement of fertilization rate. Use of these systems showed that ovulation takes place 22–32 h after the first increase in activity. Since the optimal insemination time is 24–12 h before ovulation, the optimal time of insemination becomes 4 17 h after the increase in locomotive activity or 0–12 h following the first standing event associated with the onset of estrous behavior.
Conclusion Remote-sensing systems for the detection of estrus are expected to be more efficient but not necessarily more accurate than visual observation. Differences in housing and environmental conditions, in addition to labor, cost, and efficacy, have resulted in variable acceptance of remote-sensing technologies. Detection efficiency and accuracy can be improved by the simultaneous use of more than one technology. Combining technologies for simultaneous measurements of several physiological events associated specifically with the onset of estrus and ovulation time should provide more accurate predictions of the optimal time for insemination. Ultimately, herd management must interpret the information
gathered by these technologies and judge whether and when to inseminate the identified cows based on visual inspection. See also: Body Condition: Effects on Health, Milk Production, and Reproduction. Replacement Management in Cattle: Breeding Standards and Pregnancy Management. Reproduction, Events and Management: Control of Estrous Cycles: Synchronization of Estrus; Control of Estrous Cycles: Synchronization of Ovulation and Insemination; Estrous Cycles: Characteristics; Mating Management: Artificial Insemination, Utilization; Mating Management: Fertility.
Further Reading Allrich RD (1994) Endocrine and neural control of oestrus in dairy cows. Journal of Dairy Science 7: 2738–2744. Arney DR, Kitwood SE, and Phillips CJC (1994) The increase in activity during oestrus in dairy cows. Applied Animal Behavioral Science 40: 211–218. Dransfield MBG, Nebel RL, Pearson RE, and Warnick LD (1998) Timing of insemination for dairy cows identified in oestrus by a radiotelemetric oestrus detection system. Journal of Dairy Science 81: 1874–1882. Hurnik JF, King GJ, and Robertson HA (1975) Oestrous and related behaviour in postpartum Holstein cows. Applied Animal Ethology 2: 55–68. Klemm WR, Rivard GF, and Clement BA (1994) Blood acetaldehyde fluctuates markedly during bovine oestrous cycle. Animal Reproduction Science 35: 9–26. Lehrer AR, Lewis GS, and Aizinbud E (1992) Oestrus detection in cattle: Recent developments. Animal Reproduction Science 28: 355–361. Maatje K, Loeffler SH, and Engel B (1997) Optimal time of insemination in cows that show visual signs of oestrus by estimating onset of oestrus with pedometers. Journal of Dairy Science 80: 1098–1105. Nebel RL, Altemose DL, Munkittrick TW, Sprecher DJ, and McGilliard ML (1989) Comparisons of eight on-farm milk progesterone tests. Theriogenology 31: 753–764. Roelofs JB, van Eerdenburg FJCM, Soede NM, and Kemp B (2005) Pedometer reading for estrous detection and as a predictor for time of ovulation in dairy cattle. Theriogenology 64: 1690–1703. Senger PL (1994) The oestrus detection problem: New concepts, technologies, and possibilities. Journal of Dairy Science 77: 2745–2753. Shipka MP (2000) A note on silent ovulation identified by using radiotelemetry for estrous detection. Applied Animal Behavior 66: 153–159. Van Eerdenburg FJCM (2008) How to beat the bull: Oestrus detection in dairy cattle. Veterinary Quarterly 30(1): 1–97. Walker WL, Nebel RL, and McGilliard ML (1996) Time of ovulation relative to mounting activity in dairy cattle. Journal of Dairy Science 79: 1555–1561.
Mating Management: Artificial Insemination, Utilization M T Kaproth, Genex Cooperative, Ithaca, NY, USA R H Foote, Cornell University, Ithaca, NY, USA ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by R.H. Foote, Volume 3, pp 1764–1770, ª 2002, Elsevier Ltd.
Introduction Artificial insemination (AI) of cattle represents the most successful sophisticated program of animal breeding ever implemented to improve the quality, productivity, and reproductive health of dairy cattle and other farm animals. This article, in conjunction with other articles on AI (see Gamete and Embryo Technology: Artificial Insemination), provides an overview of the advanced technology developed, the facilities and management required, and the genetic improvement in cattle as a result of the use of AI during the past half century. Other species are considered briefly. Recent advances in genomics, computerized mating programs, gender sorting of semen, and cloning relevant to AI programs are considered.
Components of a Successful Artificial Insemination Program The key to any successful program is capable, welltrained, and dedicated people. Expertise represented by
number of progey per sire per year ¼
the array of people in AI encompasses geneticists to select bulls, expert bull handlers, semen collectors and laboratory technicians, highly trained field staff, skilled inseminators, and superior farm managers. All require appropriate facilities and equipment to conduct a highquality program. The two major factors responsible for the success of AI are (1) improved reproductive health, particularly through the control of venereal diseases, and (2) genetic improvement in productivity and a reduction in lethal genes. All of the components of AI and their relationship can be quantified by two simple equations. A sire’s genetic contribution will depend upon its genetic superiority and the number of progeny produced: genetic impact per sire ¼ ðgenetic superiority of the sireÞ ð number of progeny per sireÞ ð1Þ
The physiology and management that impact on the number of progeny produced per sire are represented by the equation
ðnumber of sperm harvested per sireÞ ðnumber of sperm inseminated per cowÞ
ð2Þ
ðfraction of the semen used for inseminationÞ ðfertility : % of inseminations producing progenyÞ ð2Þ
All of the improvements in harvesting sperm from the bull, preserving sperm with minimal loss, and skillfully placing the right number of sperm in the well-managed cow at the proper time will affect the number of progeny.
Landmarks in the Development of Artificial Insemination Facilities Early in the development of AI for livestock breeding, facilities were very limited, with a modified existing barn to house bulls, an area equipped to serve as a simple laboratory, and a semen collection chute, often outdoors. Originally, developed around a liquid semen program, regionally sited bull studs were needed. Following the
introduction of semen cryopreservation, nationally sited centers were developed. With sophisticated facilities allowing assured health surveillance, international trade became possible. Semen cryopreservation required special equipment for processing, packaging, storing, and transportation of semen. The equipment developed for bull sperm provides the basis for the worldwide cryopreservation of biologics today (see Gamete and Embryo Technology: Artificial Insemination). Modern facilities that were better, larger, and more expensive emerged. Many small bull studs were merged for efficiency, as climate-controlled bull barns, herd health surveillance and isolation facilities, special semen collection areas, animal clinic areas, and modern laboratory facilities were built by consolidated larger AI organizations. Today in the field, supervisors and
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reproductive specialists help AI technicians and herdsmen to manage the on-farm AI program.
Frozen Semen in the Field Equipment and techniques were developed for handling semen stored in liquid nitrogen at 196 C in the laboratory and moving it safely to the field for each inseminator’s storage unit. Today, inseminating technicians are given special training to handle frozen semen into and out of the liquid nitrogen tank, and to retrieve the proper breeding unit for insemination without exposing the remaining units in storage. Proper handling of frozen semen and maintenance of an unbroken chain of cryogenic temperature (less than 130 C) are important. Otherwise, carefully prepared high-quality sperm could be damaged with resultant lowering of fertility. Proper thaw and insemination methods are discussed later in this article. Inseminations today are performed by both professional inseminators and herdsmen who buy semen from a producer. As herd size has increased, many onfarm inseminators have gained proficiency by inseminating several hundred cows, one or more times.
Farm Facilities and Detection of Estrus Upon adoption of AI, a very important task faced by dairy farmers is accurate detection of estrus, so that cows could be inseminated at the proper time. Extensive efforts are made to ensure that all users of AI implement sound programs for estrus detection. This includes proper identification of each animal (highly visible cow ID), turning out cows in stanchions, and watching of cows for estrus for about 30 min each morning and evening. Some herdsmen manage this program better than others. Many aids for detection of estrus have been developed. Several will be listed here because poor detection of estrus is the largest single cause of prolonged, uneconomic calving intervals (see Reproduction, Events and Management: Mating Management: Detection of Estrus). Estrus detection aids include using surgically altered bulls that could not mate with animals, but could mount and roll colored paint on the rump of animals that stood when they were mounted. Alternatively, a colored crayon or especially brittle paint could be used to stripe the tailhead of any animals due to be inseminated. This stripe is smudged or the paint broken up when that cow is mounted. Different types of pressure-sensitive patches, which are easily attached to the rump, were developed that become more visible when pressed hard by a mounting animal. One version uses small digital radio transmitters incorporating a pressure switch in the tailhead patch. The transmitter monitors mounting activity and transmits the data (cow
ID, date and time of mount, duration of the mount) to the herd computer. Electronic probes to measure changes in electrical resistance of cervical mucus are also effective in revealing changes at estrus. Pedometers of various types record walking activity of the animal, indicated on a mechanical component of the pedometer. More advanced types transmit activity electronically, along with the cow identification, to a receiver. To develop effective estrus detection programs and evaluate their efficiency, it was necessary to monitor the estrous cycle of cows. This became possible with the discovery that the cyclic hormone progesterone could be measured in milk. The milk progesterone followed a similar pattern as blood progesterone, so simply collecting small samples of milk 2 or 3 times per week for progesterone determination permitted the cyclic activity of each cow to be tracked. In addition, this monitoring enabled one to determine missed heats, plus cows that were inseminated at the wrong stage of the estrous cycle or when pregnant. Studies in Israel and at Cornell University have shown that the use of some of these technological aids, plus training of the farm managers and the inseminators, can minimize mating at the incorrect time, and thereby maintain an optimal calving interval. Heifers often are housed in open areas with bulls. However, they should be managed to use AI because more genetic progress is made when they are inseminated with conventional or sexed semen from genetically superior bulls.
Procedures for Artificial Insemination Effective care needs to be taken to prevent temperature fluctuations of thawed semen, abrupt cooling of semen (cold shock), and semen or supplies from sun exposure or warming beyond body temperature. Loading the AI gun should take place in a protected area, free of extreme temperatures and close to the cryostorage unit. All AI should be completed within 15 min of straw thawing. The number of straws thawed at one time is dependent on the quantity that can be used within 15 min. In large herds, teams of inseminators work together to prepare AI guns, and perform AI. Unless specified otherwise, semen should be ‘warmwater thawed’. Some organizations produce semen as straws processed by alternative methods that permit straws to be ‘pocket thawed’ as well as ‘warm-water thawed’. Upon retrieval from the cryostorage unit, straws that require warm-water thawing are thawed in water (0.5 l) in an insulated vessel at 33–35 C for a minimum of 40 s. A maximum of four straws at a time can be thawed in the vessel. This prevents the water temperature from cooling to temperatures below specifications. Straws should be agitated slightly to ensure uniform thawing. Straws that are ‘pocket thawed’ are immediately placed in a folded paper towel for protection following
Reproduction, Events and Management | Mating Management: Artificial Insemination, Utilization
retrieval from the cryostorage unit. After this preparation, straw and towel are placed into a thermally protected pocket. A minimum of 2–3 min of thawing time within the pocket is provided before preparing the AI guns. For retrieval of multiple straws, straws are placed into separate towels to ensure uniform thawing. Straw forceps should be used at all times to prevent contact between bare fingers and the straw. If needed, the temperature of the AI gun is tempered by friction and prior placement within the inseminator’s coveralls. Before sliding the thawed straw into the barrel of the AI gun, the temperature should be checked by touch, as a subjective method to avoid temperature extremes. The loaded gun is covered with a paper towel for insulation while cutting the straw end. A sheath is slid over the loaded gun and is secured. The loaded gun is then placed within a clean breeding glove, providing an added layer of thermal protection, and is finally tucked inside the coveralls. The following is a conventional rectovaginal insemination procedure. Generally, the left arm, covered with a disposable glove and lubricated with mineral oil, enters the rectum. Through the thin tract layers, the cervix is located and grasped. Folded paper toweling is used to spread the vulva, allowing clean entrance of the gun into the vestibule of the vagina. Care is taken to gently manipulate the cervical rings of the lumen over the end of the gun until the gun tip reaches just past the anterior cervical ring. Location of the gun tip in the uterine body is determined with an extremely light touch through the uterine body wall. When satisfied with the position, the outside end of the AI gun is braced on the opposing arm and the plunger is pushed to deliver semen to the uterine body in 3–5 s. The gun tip is not extended past the internal uterine bifurcation to avoid the possibility of any injury to the uterine mucosal tissue. Cows that have been bred once, but then exhibit estrus behavior again should be rebred with caution as an abortion can be initiated in a pregnant female. Therefore, the AI gun should be passed completely through the cervix only if the tract is felt to be typical for a female in normal estrus.
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files of sire information, potential mating sires are selected, emphasizing corrections to worst faults for maximum genetic progress. A very important benefit of using computerized mating program is that it is possible to control and restrict the level of inbreeding in the herd. A mating program will ensure that no member of a three-generation pedigree is duplicated in the mating. This is expected to maintain inbreeding below 6.25%. Furthermore, mating programs can be set up so that embryo losses that result from harmful gene interactions can be avoided. Cattle that carry the same lethal recessive gene should not be mated.
Artificial Insemination in Estrus-synchronized Cattle Several programs have been developed to synchronize estrus and ovulation so that a group of cows can be inseminated at a fixed time. These programs involve the injection of prostaglandin F2 or analogues to regress the corpus luteum (the source of progesterone), and an injection of gonadotropin-releasing hormone (GnRH) to stimulate ovulation (see Reproduction, Events and Management: Control of Estrous Cycles: Synchronization of Estrus; Control of Estrous Cycles: Synchronization of Ovulation and Insemination). In viewing 2008–09 data (500 000+ inseminations) from a company providing extensive professional AI service in US herds, AI to synchronized cattle approximates 27% of total inseminations; however, in many herds, AI to synchronized cattle accounts for 80% of inseminations. Of these AIs, Cosynch and Ovsynch accounted for 25 and 75%, respectively. Differences in fertility (as unadjusted nonreturn rate means) between the two synchronization protocols were essentially zero. An inspection of adjusted fertility rates revealed that AI to synchronized cattle approaches, but does not equal, AI to nonsynchronized cattle (1.5% for probability of conception). There is an interaction of bulls and synchronization. That is, while bulls can be ranked with respect to overall fertility, bulls will rerank in a different order when semen is used on synchronized cattle.
Use of Computerized Mating Programs in Artificial Insemination In dairies that utilize computerized mating programs, each cow in a herd is examined and scored in a linear trait evaluation format. Cows are compared to their contemporaries for each trait and the differences are weighted by the heritability of the specific trait. Deviations from contemporaries are adjusted for the herd’s genetic level. Pedigree information is also included. When a mating is planned, the cow’s complete phenotypic evaluation linear score is viewed and from computer
Use and Efficiency of Artificial Insemination in the United States The changes in dairy cow numbers and the use of AI in the United States are summarized in Table 1. Milk production per cow has tripled since 1925 while the number of cows has been reduced by two-thirds. Consequently, the many fewer cows today produce as much milk nationally as was produced in 1925. This production meets demands as milk consumption per capita has decreased.
470 Reproduction, Events and Management | Mating Management: Artificial Insemination, Utilization Table 1 Dairy and beef cow numbers and the percentage inseminated artificially in the United States Dairy cowsa
Beef cows
Year
Number
Artificially inseminated (%)
Number
Artificially inseminated (%)
1925 1950 1975 2000
25 000 000 21 500 000 12 000 000 9 000 000
0 12 57 65
10 000 000 15 000 000 45 000 000 34 000 000
0 Pcrit – in this case, vaporization is instantaneous). 5. Form of flow promotion. The working fluid may travel through the boiler by natural convection or by forced convection. 6. Flow location. In water-tube boilers, the water flows inside the tubes while the hot gas products of combustion heat the tubes from the exterior. If, instead, the combustion gases flow inside the tubes, heating them internally, and the water surrounds the tubes exteriorly, then the boiler is of the fire tube type.
Utilities and Effluent Treatment | Heat Generation
7. Tubular bank configuration. Tubes may be positioned horizontally, vertically or inclined. The tubes connect to boiler headers that are used to collect steam and water for distribution to other parts of the boiler or users. 8. Furnace position. The boiler is internally fired if the boiler shell contains an internal furnace, or externally fired if the combustion takes place outside the boiler shell and the products of combustion are directed to flow within the tubes inside the shell. 9. Firing arrangements. The firing arrangements may be horizontal (flame travels horizontally into the furnace; used in small- to medium-capacity boilers), vertical (the burner is located at the top of the furnace and the flame travels downward to the bottom of the furnace; used in small-capacity, fire-type tube boilers and also in largecapacity water-tube boilers that burn pulverized coal) or tangential (the furnace has a square or rectangular geometry and, at each of the four corners, the flame travels tangentially to a ‘fire ball’ where all the flames meet, located at the center of the furnace). The great turbulence favors the mixing of the fuel and air. 10. Number of combustion gas passes. The design may include one, two, three or four passes through the boiler. The latter configuration is the most efficient; however, the greater the number of gas passes, the more fan power is required. In the dairy industry, small- to medium-capacity unit boilers are used. They may be water-tube or fire-tube boilers, and are equipped with all the boiler auxiliaries, such as water pumps, fans, burners, fittings, controls, etc. The only exterior connections that need to be made are electrical, water, fuel and stack. Stacks, made of steel or concrete, are used to deliver the flue gases to the atmosphere. In this way, dispersion of particles is simplified and has a low impact on the environment. Prefabricated unit boilers are more advantageous than boilers constructed on site due to ease of installation, compactness of size and lower cost. They are limited to the existing design and produce small steam flow rates, below 250 103 kg h1. The heart of the boiler is the furnace where combustion takes place.
Combustion Combustion is a process of rapid chemical combination of fuel with air that releases the chemical energy of the fuel. Air and fuel are the reactants in the combustion reaction and the by-product is the flue gases (products of combustion) and heat. It may be represented by the following relation:
fuel þ air ! products of combustion þ heat
591 ð3Þ
For this process to occur efficiently, good mixing between the fuel and the air (essentially a mixture of oxygen (O2) and nitrogen (N2)) must be accomplished by intensified turbulence, and the ignition temperature of the fuel must be reached. In addition enough time must be allowed for the fuel to burn in the furnace. Normally, fossil fuels are burnt and these always have in common carbon (C) and hydrogen (H). However, the composition varies greatly with the fuel type: 1. Coal is a solid fuel consisting of carbon, hydrogen, moisture (water), nitrogen, sulfur and ash. It is classified according to the carbon content: anthracite coal has 86–98% carbon (it has a caloric value of approximately 35 MJ kg1, determined experimentally), bituminous coal has 70–86% carbon (and a caloric value of 25–36 MJ kg1), lignite coal has a carbon content up to 70%. Coal needs to be prepared before combustion and its supply to the boiler has to be controlled. It is difficult to burn and produces a high level of ash and sulfur. 2. Fuel oil is a liquid fuel classified according to its ash and moisture content. Its caloric value is the highest of all fossil fuels and may be as high as 46 MJ kg1. Fuel oil has advantages over coal in requiring less storage space, yielding less ash, being easier to control and requiring less equipment. However, it is more expensive because its distribution is not so even around the world. 3. Natural gas is a gaseous fuel with a caloric value of approximately 37 MJ m3. It has advantages over other fossil fuels in requiring the least amount of equipment, being easy to control, mixing well with air and requiring the least amount of excess air, and producing little or no ash (it is the cleanest fuel to burn). Combustion air is supplied to the reaction in a quantity greater than the theoretically least amount of air needed to burn all of the fuel, so that the combustion reaction is not limited by insufficient air. The amount of excess air depends on the fuel type. Relative to the theoretical amounts, the following are medium values for excess air: large coal particles, 30–40%; pulverized coal particles, 15–20%; fuel oil, 10–15%; and natural gas, 5–10%. In theory, the fuel is completely burned if the products of combustion are composed mainly of CO2 and H2O, and no traces of fuel exist in these products. In practice, this ideal situation does not occur and, due to furnace design, insufficient turbulence, or insufficient residence time of the fuel in the furnace, some traces of fuel, such as CO, always remain in the flue gases, causing incomplete combustion. These gases are undesirable since they are poisonous and explosive and the caloric value is half of the value on complete combustion. The combustion process may be measured by the combustion efficiency. Among the several notions that
592 Utilities and Effluent Treatment | Heat Generation
exist for this parameter, a simple one is to consider the conversion of carbon to carbon dioxide, given by c: c ¼
ðXco2 Þ real ðXco2 Þ theoretical
Combustion and stoichiometry affect the global heat transfer from the fuel to the water in the boiler or, in other words, the boiler efficiency.
ð4Þ
where (Xco2)real is the measured CO2 molar fraction and (Xco2)theoretical is the CO2 molar fraction in the off-gas in the case of complete combustion. The theoretical amount of air needed for combustion is determined by the stoichiometry of the reaction.
Calculation of Boiler Efficiency Boiler efficiency, b, is the ratio between the heat power received by the water, Q_ w , and the heat content of the fuel, Q_ f , since the electrical energy that is necessary to drive the boiler’s auxiliary equipment is comparatively much smaller than these values and is normally neglected:
Stoichiometry
b ¼
As mentioned above, normally the fuels burned in boilers are hydrocarbons of the type CxHy. The theoretical amount of air needed to burn this fuel completely is given by the following stoichiometric relation: y Cx Hy þ aðO2 þ 3:76N2 Þ ! xCO2 þ H2 O þ 3:76aN2 2
ð5Þ
where a ¼ x þ y/4. It must be noted that, since air is a mixture of roughly 21% of O2 with 79% N2 by volume (having insignificant traces of other gases), each mole of O2 is mixed with 79/21 ¼ 3.76 moles of N2. From eqn [5] it can be observed that (4.76 a) moles of air are necessary to burn 1 mol of fuel completely. Normally, the stoichiometric air–fuel ratio, (A/F)stoich, represents this relation on a mass basis as: A mair að1 þ 3:76Þ Mair ¼ ¼ F stoich 1 mfuel stoich Mfuel
ð6Þ
where Mair and Mfuel are the molar masses of air and fuel, respectively, Mair ¼ 0.21 MO2 þ 0.79 MN2 ¼ 28.85 g mol1, and Mfuel ¼ xMC þ y MH where x and y are the number of carbon and hydrogen atoms in the fuel molecule, and MC and MH are the atomic mass of carbon and hydrogen, respectively 12.011 g mol1 and 1.00794 g mol1. If a smaller amount of air is supplied, then the reactant mixture is said to be rich in fuel; if excess air is supplied, it is lean in fuel. The equivalence ratio, j, is the ratio between the stoichiometric air–fuel ratio and the real air–fuel ratio, (A/F)real: j¼
A A = F stoich F real
ð7Þ
This parameter allows one to determine whether the combustion is stoichiometric, j ¼ 1, the reaction mixture is lean, j < 1, or the reaction mixture is rich, j > 1, and it is related to the following parameters: the percentage stoichiometric air is given by 100%/j, the percentage excess air is equal to (1 j)/j 100%, and the percentage lack in air is given by (j 1)/j 100%.
Q_w m_ w hw ¼ m_ f LCVf Q_f
ð8Þ
where m_ w and m_ f are, respectively, the water and fuel mass flow rates; hw is the enthalpy difference the water undergoes while it travels through the boiler, and LCVf is the lower caloric value of the fuel (this is the caloric value usually considered since the water leaves the boiler as a vapor). Normally, not all the parameters in eqn [8] are easy to determine, so the boiler efficiency must be calculated, by an indirect approach, from the following equation: b ¼ 100 –
X
Li
ð9Þ
This definition considers that the difference between the input and the output energy of the boiler is due to several energy losses. So, from the flue energy P content, one subtracts the various energy losses, Li, expressed as a percentage of the LCVf value, namely: X
Li ¼ Luf ðunburned fuelÞ þ Lig ðflue gasÞ þ Lp ðpurgesÞ þ Lb ðheat losses to surroundingsÞ
These values may be calculated approximately by the expressions shown in Table 1. The unburned fuel may be present together with the ash, and the energy loss is Lufa (unburned fuel in the ash) because carbon may be carried away by the ash – either the fly-ash, which escapes in the flue gases, and/or the bottom ash, which settles in the boiler. The flue gases may also contain unburned fuel and the energy loss is Luff (unburned fuel in the flue gases) because CO may exist in the products of combustion due to incomplete combustion. The energy loss due to the energy content of the fuel gases, besides unburned fuel, is represented by Lfg (flue gas). It must be noted that the latent heat of the water in the flue gases is not accounted for because it normally leaves the boiler in the vapor phase. Periodic removal of debris from the bottom drums is necessary, as well as the removal of water for pH control purposes. The energy content of the water removed represents a loss designated Lp (purges).
Utilities and Effluent Treatment | Heat Generation
593
Table 1 Boiler energy losses in eqn 9 Energy losses (Li) LufLufa Lutt Lfg Lp Lh
Expression or value (%LCVf)
Parameters in expressions
¼ ACLCVc 100ð1 – CÞLCVf Fð1 – LÞufa COLCVco ¼ LCVf
A ¼ mass of ash kg1 of fuel C ¼ mass of carbon kg1 of ash
¼ ¼
ð1 – Lufa ÞFCpfg ðTfg Tat Þ
CO ¼ CO mass percentage dry basis
LCV1 Wh1 LCV1
¼ 2.0% for Qw 2 MW ¼ 1.6 % for 2MW < Qw < 5 MW ¼ 1.4% for Qw 5 MW
Heat loss to the surroundings, Lh, is very difficult to determine accurately. It is usually obtained by the difference due to all the other losses, so that the energy balance of the boiler is satisfied. Medium values for fire-tube or water-tube boilers at full rate depend on the boiler power, as can be seen from Table 1. By far the most important of the above energy losses is that in the flue gases. For this reason it is usual to recover heat from the flue gases after they leave the boiler, by passing them through economizers (to heat boiler feed water) and air heaters (to preheat combustion air). To attain good boiler efficiency it is necessary to implement a control strategy that acts on several parameters during boiler operation.
Basic Control Techniques Basically, the control strategy is implemented as follows: measuring instrumentation detects physical values, such as temperatures, pressures and flow rates; transducers convert these values into electrical signals and send them to data processing systems; these take a controlling action, by comparing the measured values to their preset ones, and send an electrical signal to control systems, e.g. electro-valves, that actuate on the components and regulate the physical values. By this means it is possible to control the properties of the water vapor produced, the water supply flow and the water level that exists at the boiler’s upper drum, the combustion process (regulating the operation of burners or fans), and also ash-removal systems, when applicable. Obviously, the pressure level of the water vapor produced must be controlled, not only to attain the goal of the boiler, but also to protect it from excessive pressure build-
Cp1g ¼ specific heat of the flue gases F ¼ fuel gas mass kg1 fuel mass LCVc ¼ lower caloric value of carbon LCVco ¼ lower caloric value of carbon monoxide LCV1 ¼ lower caloric value of fuel Qw ¼ heat power transferred to water Tfg ¼ flue gas temperature Tat ¼ atmospheric temperature W ¼ mass of water purged kg1 of fuel h1 ¼ enthalpy different between leaving and entering boiler liquid
up that may cause boiler explosion. By controlling the pressure, the corresponding saturated temperature is fixed automatically (during vaporization, pressure and temperature are dependent variables). Therefore, temperature control acts on the temperature of overheated vapor that is produced in the boiler. One technique, known as attemperation, may be implemented by regeneration of water vapor or by a spray process. Another technique uses an independent energy source at the boiler exit. It is also essential to control the water supply flow and the water level that exists at the upper drum in order to guarantee that water in the liquid state is always present inside the boiler (ready to be vaporized) and to avoid a tube explosion due to an excessively high temperature. The steam produced in the boiler is delivered by a steam piping system (normally made of steel) to the sites where it is used. A return piping system reintroduces the condensed water into the boiler. The design of these piping systems requires great attention because steam leakage losses and hot water losses occurring as a result of deficient design may assume such importance that they may reduce the measures adopted to increase efficiency of the steam generator and of the steam user.
Design of Steam Piping Systems The design of the steam piping system is normally determined on an economy basis. The total cost of the system is equal to the sum of the capital, installation (an important part of the total cost) and operating costs. These costs depend upon the tube’s internal diameter, D, as can be seen in Figure 5 which shows the relationship between cost and D.
594 Utilities and Effluent Treatment | Heat Generation
Cost
Total (a + b + c)
Installation cost (b) Capital cost (a) Operating cost (c) D Figure 5 Cost of piping systems as a function of tube diameter (D).
The dependency of the operating cost on diameter results from the pressure drop due to friction between the steam and the tube’s internal surface. Assuming a given flow rate, V_ , and considering suggested values for the fluid velocity, , saturated steam velocity between 30 and 50 m s1 and overheated steam velocity in the range 50 to 100 m s1, the diameter, D, results from:
4 V_ D v
1=2 ð10Þ
The next step is to select a normalized diameter close to this value, as well as at least two diameter sizes immediately above and immediately below it. The pressure drop, p, is then calculated for each of these diameters from: 2 L X v K p ¼ p f þ D 2
1 pffiffiffi ¼ f
– 2:0log
"=D 2:51 þ pffiffiffi 3:7 Re f
1. The operating pressure may differ from the design pressure; review the capital cost of the steam generator or steam user due to variation of friction losses. 2. Additional operating costs of returned feed water may be incurred due to an increase in operating pressure; the condensed water is collected and reintroduced into the boiler. 3. Heat loss may differ from the design value; steam enthalpy change affects the steam user and the operating costs.
ð11Þ
where is the specific mass given by steam tables (¼1/); f is the friction P factor; L is the tube length (a known quantity); and K is the localized pressure P drop due to accessories (some authors convert K to Leq, i.e. an equivalent straight pipe length of the same diameter having the same pressure drop as the accessories). The friction factor in eqn [11] is given by the Colebrook equation: "
recommended to redesign the piping system by choosing another value for D. The outlined procedure allows calculation of the pressure drop, and hence the operating cost shown in Figure 5, for a range of possible sizes of tube (such that the steam velocity is within admissible values). Based on the economic criterion, the trend is to favor smaller pipe diameters, i.e. high steam velocities. An important aspect not to be neglected is that steam at a high temperature flowing in a pipe loses heat to the surroundings (depending on tube insulation), which may cause superheated steam or saturated steam to condense. To prevent damage by erosion or water hammer, the condensed water should be drained by allowing the tube to have a continuous fall in the direction of flow of at least 4–5 mm in every 1 m, and by providing an adequate number of drain points (e.g. in a straight main pipe one every 20–40 m). During operation, condensed water is removed using steam traps; these automatic valves are able to remove liquid but prevent the escape of steam. The piping system can be optimized using the following parameters:
!# ð12Þ
where Re is the Reynolds number; Re ¼ D/; is the steam dynamic viscosity; " is the tube rugosity; and " ¼ 0.000 05 m/D (m) (for commercial steel tubes). The pressure drop normally adopted is approximately 5% of the value of the pressure in the main steam pipe. Should the calculated value be greater, it is
See also: Plant and Equipment: Flow Equipment: Principles of Pump and Piping Calculations; Instrumentation and Process Control: Process Control; Process and Plant Design; Utilities and Effluent Treatment: Water Supply.
Further Reading Abrial JR, Bo¨rger E, and Langmaack H (1996) Formal Methods for Industrial Applications: Specifying and Programming the Steam Boiler Control. New York: Springer-Verlag. American Society of Mechanical Engineers (2000) ASME International Steam Tables for Industrial Use: Based on the International Association for the Properties of water and Steam Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam. New York: American Society of Mechanical Engineers. Basu P (2000) Boilers and Burners: Design and Theory. Springer-Verlag: New York. Energy Technology Supply Unit (1998) Coal-fired Commercial Boilers. Harwell: ETSU. Energy Technology Supply Unit (1998) Industrial Boilers. Harwell: ETSU.
Utilities and Effluent Treatment | Heat Generation Goodall PM (1980) The Efficient Use of Steam. Guildford: Westbury House. Granet I (1996) Thermodynamics and Heat Power. Englewood Cliffs: Prentice-Hall. Johnson CD (1982) Process Control Instrumentation Technology. New York: John Wiley.
595
Kakac¸ S (1991) Boilers, Evaporators, and Condensers. New York: John Wiley. Payne FW (1985) Efficient Boiler Operations Sourcebook. Atlanta: Fairmont Press. Rhine JM and Tucker RJ (1991) Modelling of Gas-Fired Furnaces and Boilers and Other Industrial Heating Processes. London: British Gas.
Refrigeration A C Oliveira and C F Afonso, University of Porto, Porto, Portugal ª 2011 Elsevier Ltd. All rights reserved.
Vapor Compression Cycle Principles Refrigeration is the most common technology used for the conservation of perishable products. It involves the production and maintenance of a level of temperature in a space or object that is lower than ambient temperature. A consequence of lowering the temperature of perishable products is that the reactions that cause their deterioration, mainly microbial and enzymatic reactions, slow down, enabling the conservation of products for longer periods of time. The lower temperatures needed for conservation of perishable products can be subdivided into two groups: positive temperatures, which are referred to as refrigeration, and negative temperatures, below the freezing point of the product, which are referred to as freezing. Whereas in the former, all water in the product is in the liquid phase, in the latter most can be in solid phase. However, we must bear in mind that the microbial and enzymatic reactions do not cease, they just slow down. As soon as the product is exposed again to ambient temperature, the reactions resume their normal rate. An advantage of freezing is that the products can be stored for much longer periods compared with that for refrigeration. As deteriorative reactions occur in aqueous media, the loss of liquid water to ice substantially reduces water availability, and hence reactions can be severely restricted well beyond the lowering temperature effect. In principle, at temperatures even lower, below the glass transition temperature, all water is in either ice or part of the amorphous vitreous structure, molecular mobility is restricted to mutarotation and vibration, and all reactions cease. Unfortunately, such temperatures depend on water content, and for most foods they are typically well below practical storage applications (20 to 50 C for typical foods). In the old days, refrigeration was understood as natural refrigeration, that is, the lower temperatures were obtained with ice found in nature. Nowadays, it is understood as artificial refrigeration (i.e., the lower temperatures are obtained by mechanical systems, the most common one being the vapor compression system, shown schematically in Figure 1). The basic system shown is composed of four components, namely the evaporator, which is generally located inside the refrigerated space, the compressor, the condenser, and the expansion valve, connected in series by
596
piping. Inside the system there is a flowing fluid, called refrigerant, which exchanges energy in those components. In state 1, the refrigerant is in the liquid phase, either saturated or sub-cooled. From state 1 to state 2 the liquid flows through the expansion valve, a device that controls the refrigerant flow rate to the evaporator, where its pressure and temperature are lowered. As in the expansion valve, the refrigerant does not exchange heat or work with the outside, it maintains its total energy – enthalpy (h). In state 2, due to the pressure drop in the expansion valve, the refrigerant has two phases in equilibrium: saturated liquid and vapor. Then it flows through the evaporator where it absorbs heat from the refrigerated space in which the products are stored, lowering or maintaining its temperature. This refrigerant heat gain in the evaporator (increase in enthalpy) causes the boiling of the liquid so that state 3 corresponds with saturated vapor or even super-heated vapor. This process occurs at constant pressure and at constant temperature if there is no super-heating at the outlet of the evaporator. The vapor then enters the compressor where it is compressed to a higher pressure – the same as in state 1 – and with an increase in temperature, and consequently with an increase in enthalpy, state 4. At this point the vapor flows through the condenser, again in a constant pressure process (ideally). In this component, the refrigerant loses heat to the outside (either ambient air or water, or both) with a decrease in enthalpy, changing phase again – condensation – so that at the outlet it is in the same state referred above as state 1. As can be seen, this cycle operates between two constant pressure levels: a higher one in the condenser and a lower one in the evaporator, the pressure drop and increase being carried out respectively by the expansion valve and by the compressor. To visualize the refrigerant’s evolutions in the vapor compression cycle, different types of thermodynamic diagrams may be used, the most common one in refrigeration being the pressure–enthalpy (p–h) one. Figure 2 shows a typical p–h diagram of the cycle shown in Figure 1. It was considered that no super-heating or sub-cooling exists in the refrigerant at the outlet of the evaporator and condenser. By applying the first law of thermodynamics to the whole cycle and to each of its components and neglecting changes in kinetic and potential energy, it is possible to calculate the different energy fluxes in the cycle: :
Q
:
:
evap
þQ
cond
þW ¼ 0
Utilities and Effluent Treatment | Refrigeration Heat rejection
1 Expansion valve
Condenser
2
Evaporator
4 Electrical energy
Comp
3
Heat from refrigerated space Figure 1 Vapor compression system.
p
1
4
2
3
h Figure 2 Pressure–enthalpy diagram of the cycle shown in Figure 1. :
evaporator – refrigeration effect : Q
evap: :
¼ mðh3 – h2 Þ :
compressor – compression power : W ¼ mðh4 – h3 Þ :
condenser – condensation heat : Q
:
cond
¼ mðh1 – h4 Þ
expansion valve: h2 ¼ h1
where m_ is the refrigerant flow rate, Q is the heat exchanged, W is the energy (work) supplied by the compressor, and hi is the specific enthalpy of the refrigerant at the different points of the cycle. As can be seen, all the energy fluxes can be easily evaluated if the refrigeration cycle is conveniently plotted in a p–h diagram of the refrigerant used. It is only necessary to read the different enthalpy values and make the above calculations. However, nowadays all the calculations can be performed analytically because the equations of state (equation that enables the evaluation of the different properties of the fluid used) of the different refrigerants are well known. Existing software allows these calculations to be performed easily.
Equipment There is a wide range of equipment for each component in the vapor compression cycle. The choice of one or another depends mainly on the purpose of the system.
597
In this text, only a general classification of the equipment will be given. Evaporators are heat exchangers where the refrigerant boils while receiving heat from the surroundings. One possible classification of evaporators is based on their application. In that way, they can be classified as direct expansion or indirect expansion evaporators. In the first type, the coils of the evaporator are in direct contact with the space or body to be refrigerated (i.e., the refrigerant absorbs the heat directly from there). In the second type, the refrigerant takes the latent heat of vaporization from a secondary fluid, usually brine or water. This fluid flows in a closed loop making the connection between the evaporator itself and the objects to be cooled, where it withdraws heat. The evaporators can be classified into two groups: direct expansion and liquid recirculation type. In the first type, the refrigerant coming from the expansion valve boils completely in the tubes of the evaporator, leaving it as a saturated vapor. The second type is designed so that only part of the liquid boils in the coils. At the outlet of the evaporator there are then two phases in equilibrium, liquid and vapor. The vapor flows to the compressor, while the remaining liquid is recirculated back to the evaporator. The compressors can be classified as centrifugal compressors, vane compressors, rotary screw compressors, or reciprocating compressors, with the last types used in most refrigeration applications. When the pressure ratio of the compressor is typically above 10 (ratio between condensation pressure and evaporation pressure), the performance of the compressor falls and it is not possible to use only one compressor if it is of the reciprocating type. In this case, it is necessary to either use more than one compressor or choose another type. Usually, the compressors are coupled with electrical motors that provide the necessary running power. However, it is not unusual to find internal combustion engines instead of electrical motors driving the compressors. Condensers, like evaporators, are heat exchangers, and they are classified as air-cooled, water-cooled, or evaporative. In the first type, the condensing refrigerant loses heat to the ambient air, whereas in the second type the removal of heat is to water that flows in a closed loop, where usually a cooling tower cools the warm water. In the third type, air and water in a packed tower are used in counterflow over the coils of the condenser, inside which the refrigerant condenses. This kind of condenser must be located outside the building and as the refrigerant flows inside it, the length of the pipe carrying it is much longer than the first two types of condensers. Therefore, the pressure drop in the high-pressure part of the system is also higher. Also, as the length of the piping increases, the probability of leakage is increased. As already mentioned, the expansion valve controls the flow of refrigerant into the evaporator. There are different
598 Utilities and Effluent Treatment | Refrigeration
types of expansion valves, namely, the manually operated, automatic low side float valve, automatic high side float valve, automatic valve, thermostatic valve, and the capillary tube, the last two being very common in most applications. The capillary tube is used in small-capacity refrigeration systems, namely refrigerators and small-size air-conditioning equipment, whereas the application of the thermostatic valve is wider. This valve also controls the degree of refrigerant superheating at the outlet of the evaporator, comparing it with some pre-set value.
Heat rejection
Condenser Comp.
Electrical energy
Comp.
Electrical energy
Evaporator
Coefficient of Performance Heat from refrigerated space
The cycle analyzed so far is an inverse thermal machine. It is therefore possible to evaluate its performance, like in any other thermal machine, as the desirable effect of the system divided by what must be paid for this effect. The performance of refrigeration cycles is expressed through the coefficient of performance (COP), which is the ratio of refrigeration effect (desirable effect) divided by the compression power (what must be paid): :
COP ¼
Q
evap: :
W
¼
h3 – h2 h4 – h3
COP values are always positive and usually greater than one, due to the fact that the refrigeration effect is greater than the compression power. Typical values of COP for the vapor compression systems are in the range 2–3. Even if the evaporation temperature is held constant throughout the year, the COP is not constant due to changes in air or water temperature feeding the condenser, which causes changes in the condensing temperature and also in the enthalpies appearing in the COP equation.
Refrigeration Systems
Figure 3 Multistage vapor compression system.
the two compressors, and a higher one at the condenser. Multistage systems usually have higher COP values than basic vapor compression systems. This is due to the fact that there is a decrease in compression work and an increase in the refrigerant effect. There are different ways to implement this technique, one of them being to couple the system with several evaporators, each one with a typical operating temperature. To achieve very low temperatures – much lower than the freezing point of the products – with a good performance, the so-called cascade systems are frequently used. In its simplest form it is composed of two basic vapor compression systems in a way that the evaporator of one cycle is simultaneously the condenser of the second system (see Figure 4).
Heat rejection
Condenser
Vapor Compression Systems The system analyzed so far is the basic vapor compression system that is used in several applications of refrigeration. However, and keeping in mind this basic system, better performances can be achieved if some modifications are introduced. There are several possible modifications that can be implemented, for specific applications. A very common modification is the use of multi-stage compression (i.e., the use of more than one compressor), with inter-cooling of the refrigerant between each pair of compressors. Inter-cooling is carried out with the refrigerant at a lower temperature withdrawn from other parts of the system. This technique reduces the system total work. Figure 3 shows schematically such a system. As can be seen, in this system there are three levels of pressure, a lower one in the evaporator, an intermediate one between
Comp.
Evaporator condenser
Comp.
Evaporator
Heat from refrigerated space Figure 4 Cascade system.
Utilities and Effluent Treatment | Refrigeration
In that way, the evaporator of the upper system absorbs the heat lost in the condenser of the lower system. Usually two different refrigerants are used, one in each cycle. The refrigerant in the lower cycle should have good characteristics at lower temperatures while the other refrigerant should have good characteristics at higher temperatures. It is also possible for each of the subsystems considered to operate as a multistage system. Other Systems One variant of the vapor compression system is the absorption system, also used for refrigeration. This system is as old as the vapor compression system but only recently has its utilization increased, due to the ozone depletion potential of most of the synthetic refrigerants used in the vapor compression system, as will be described later. The absorption system differs from the vapor compression system in that low compression of the refrigerant is carried out, having in common the other three components: the evaporator, the condenser, and the expansion valve. Figure 5 shows only the part of the cycle that is different. In the absorption system, the compression is done using a secondary fluid that has the capacity of absorbing the main refrigerant flowing in the other three components. At the absorber outlet, where heat is lost to the outside in order to carry out the absorption process, there is a homogeneous liquid solution that is pumped to another component, the generator. Here, it is necessary to supply heat to separate the two fluids, a process opposed to the one in the absorber. The work of compression in the absorption system is much lower than in the vapor compression system due to the fact that a liquid solution is pumped instead of a vapor. But in an opposite way, a large quantity of heat at a higher temperature (typically over 100 C) must be supplied to the generator. These two combined effects lower the COP value of the absorption system, compared with that of vapor compression systems, to values below 1.0, typically around 0.7. It is however possible to obtain higher COP values if the heat supply in the generator is waste heat (found in many industrial processes) or is complemented with solar energy. Because of the need to supply heat to carry out the compression process, this part of the system Heat supply Refrigerant for condenser
Generator
Liquid solution (refrigerant + absorbent) Pump
Refrigerant from evaporator
Absorber
Heat rejection Figure 5 Compression in the absorption system.
599
(see Figure 5) is also called a thermal compressor in opposition to the vapor compression system where a mechanical compressor is used. The absorption system is nowadays very common in household and camping refrigerators as well as in air-conditioning equipment. The most common fluids for the absorption system are H2O–LiBr (water as refrigerant and lithium bromide as secondary fluid) and NH3–H2O (ammonia as refrigerant and water as secondary fluid). The first pair of fluids is used for positive temperatures in the evaporator (water freezes below 0 C at ambient pressure) while the second one can also be used for negative temperatures. In spite of a fast increase in use, absorption systems are still more expensive than the classic vapor compression systems and are also larger. Other types of refrigeration systems are available, some already commercially, and some at the development stage. They can either be operated electrically (like the vapor compression system) or thermally (like the absorption system). An example of electrically operated systems is the one using thermoelectric coolers, where direct current is used to produce a cooling effect. There are more examples of thermally operated systems, namely, adsorption, desiccant, or ejector systems. The combination of solar energy with refrigeration/ cooling equipment is a way of reducing energy consumption and harmful emissions to the environment. Solar thermal collectors can be used with thermally operated cooling equipment, and solar photovoltaic (PV) collectors can be used with electrically operated cooling equipment. Solar cooling systems are interesting, due to the fact that cooling demands in summer are associated with high solar energy availability, which allows operation with maximum collector efficiencies.
Refrigerants The first refrigerants used in vapor compression systems were inorganic or natural, and some are still widely used, namely NH3 and H2O. However, new refrigerants were produced synthetically from methane (CH4) and ethane (C2H6) being divided into two groups, depending on whether or not chlorine is in the molecular structure. In the first group there are two different kinds of refrigerants: the chlorofluorocarbons (CFCs), namely R-11, R-12, R-113, R-114, R-115, R-500, and R-502, and the hydrochlorofluorocarbons (HCFCs), namely R-22, R-123, R-141b, and R-142b. The second group is hydrofluorocarbons (HFCs), and some refrigerants belonging to this group are R-32, R-134a, R-143a, and R-152a. Due to the ozone depletion potential (ODP) of CFCs and HCFCs, it was established in 1987 at the Montreal Protocol that the production and use of these refrigerants
Table 1 Characteristics of some synthetic and natural refrigerants
Refrigerant Natural substanceNo ODPa GWPb Toxicity TLVd (ppm, volume) Flammability Critical point temperature ( C) Critical point pressure (bar) Normal boiling point ( C) Maximum refrigeration capacity at 0 C (kJ m3) a
R-12 (CFC)
R-22 (HCFC)
R-134a (HFC)
R-717 (NH3)
No 0.9 3 1000 No 115.5 40.1 30 2733
No 0.05 0.34 500 No 96.2 49.9 40.8 4344
Yes 0 0.29 1000 No 100.6 40.7 26 2864
Yes 0 0 25 Yes 133 114.2 33.3 4360
Ozone depletion potential – compared with R-11. Global warming potential – compared with R-11. Zero effective GWP, because more than sufficient quantities of it can be recovered from waste gases. d Threshold limit value (TLV) for exposure of 8 h day1, 40 h week1, without any adverse effect. e At 100 C. b c
R-744 (CO2)
R-290 (propane)
R-600 (butane)
R-718 (H2O)
Yes 0 0c 5000 No 31.1 73.7 78.4 22 600
Yes 0 12:1; respiration – microbial mass converted to the ditch (developed by Paasver in 1953) – • endogenous • the oxidation new cell material for new cells. aeration tank is laid out as a racing track, and The operating principle of the activated sludge process is that wastewater containing biodegradable organics is fed to a reactor containing a wellmixed, well-aerated population of microbes (biomass, in the form of a flocculent suspension). The resulting mixture of biomass and water is separated, with the solids (sludge) being returned to the reactor (Figure 3).
• •
oxygen transfer and mixing are effected by horizontal rotors (Figure 6); the carousel – this is similar to the oxidation ditch; however, the oxygen transfer and mixing duties are frequently split. This configuration allows the establishment of an anoxic zone; and the sequencing batch reactor – aeration and clarification take place in the same tank (Figure 7).
Oxygen
Input Aeration stage
Preaeration stage (optional)
Figure 3 The basic activated sludge process.
Sludge recycle
Sludge separation
Treated effluent
624 Utilities and Effluent Treatment | Design and Operation of Dairy Effluent Treatment Plants
% BOD removal
100 90 80 70 60 0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
F/M
kg oxygen kg–1 BOD removed
Figure 4 Percentage BOD removal versus food-to-mass (F/M) ratio for the activated sludge process.
2.5 2 1.5 1 0.5 0 0.02
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
F/M 1
Figure 5 Oxygen demand (kg O2 kg
BOD removed) versus food-to-mass (F/M) ratio for the activated sludge process.
Oxidation ditch
Clarifier
Rotor Rotor Excess activated sludge
Return sludge Figure 6 Typical oxidation ditch plant.
Biological Filtration The principle of the biofiltration process is similar to that of the activated sludge process. In this process, the organic matter (food) is brought into contact with high numbers of microbes (film adhering to media) in the presence of oxygen (Figure 8). Biological filters are not normally mechanically aerated, as the heat generated during the microbial degradation process is usually sufficient to maintain a temperature gradient between the wastewater and the surrounding air, ensuring an adequate draught. The most common form of biofilter used in the treatment of dairy wastewater is the high-rate biofilter. The biofilter
media, which are usually in the form of open-textured plastic, can be either random-packed or modular. High-rate biofilters are normally loaded above 0.6 kg BOD m3 and generally remove 50–70% of the applied BOD (Figure 9). The wastewater is distributed over the surface of the media at a minimum irrigation rate of 1.5 m3 per m2 plan area per h, and this ensures that no clogging of the media occurs and discourages insect life (Figure 10). The most critical parameters in the operation of a biofilter are rate – it is essential that the irrigation rate is • irrigation maintained at all times to ensure that the filter media do not become clogged;
Utilities and Effluent Treatment | Design and Operation of Dairy Effluent Treatment Plants
625
Wastewater in
Fill 1
Aeration 2
Clarified outflow
Sludge
Settlement 3
Decant and waste sludge 4
Figure 7 Sequencing batch reactor.
– the presence of fats and grease in concen• fats/grease trations above 50 mg l can result in the coating of the
Effluent
1
• Film Media
biological film; this can lead to uncontrolled anaerobic activity and significant odors in extreme cases; and temperature – a reduction in efficiency will occur when the temperature within the biofilter drops below 8 C.
Usually, the outflow from high-rate biological filters, even after settlement, is not of sufficiently high quality to be discharged to watercourses and will require further treatment; activated sludge process is frequently used.
Nutrient Removal Air Figure 8 Activity on biofilter media.
applied – the application of excessive loading • BOD rates (shock loads) can also result in clogging of the
•
media and ponding of the surface; prolonged BOD loading can give rise to odor problems; pH – inadequate control of the pH will reduce the efficiency of the biofilter and may even result in damage to the media and support structures;
Nitrogen
This is a two-stage process: nitrification, which is carried out under strongly aerobic conditions, and denitrification, which is carried out under anoxic conditions. In the nitrification stage, ammonia is converted to nitrite and nitrate. For each kilogram of ammonia oxidized kg O is consumed; • 4.18 14.1 kg as CaCO is destroyed; • 0.15 kg alkalinity of cells is created sludge); and • 0.09 kg of inorganic carbon(extra is consumed. • 2
2
626 Utilities and Effluent Treatment | Design and Operation of Dairy Effluent Treatment Plants 100 % BOD removal
90 80 70 60 50 40 1
2
3
4
5
Applied load (kg BOD m–3 day–1) Figure 9 Distribution of wastewater over modular plastic media.
Distribution channel
• Hole in channel floor Splasher bracket
Splasher plate Spacer
•
(SCFA), which are stored in the cell as polyhydroxyl butyrates (PHB); under aerobic conditions, the stored PHB is oxidized and energy is released, allowing the assimilation of soluble orthophosphate; and the orthophosphate is metabolized by the cell and excess quantities are stored in the cell as polyphosphate. The storage of excess phosphorus is known as ‘luxury uptake’ of phosphorus, and it is this ability of the cell that is exploited in the biological phosphorus removal process.
A number of biological processes have been developed, many based on the activated sludge process, that are very effective in the biological removal of nitrogen and phosphorus from wastewater. The A2O process
Flocor module
Figure 10 Biofiltration efficiency.
In the denitrification stage, the nitrate and nitrite are converted to nitrogen gas (N2). For each kilogram of nitrate reduced kg O is recovered; • 2.86 3.0 kg as CaCO is recovered; and • 0.4 kgalkalinity of cells is created (extra sludge). • 2
2
Biological phosphorus removal
Biological phosphorus removal is dependent mainly on the ability of the Acinetobacter spp. to release phosphorus under anaerobic conditions and to absorb it under aerobic conditions. The mechanism can be summarized as follows: anaerobic conditions, readily degradable organic • under matter (BOD) is fermented to short-chain fatty acids
This continuous process (Figure 11), developed in the United States, is a refinement of the activated sludge process and takes advantage of the ability of denitrifying bacteria (abundant in the anoxic denitrification (DN) tanks) to convert the nitrate (which is recirculated from the nitrification (N) tanks) to nitrogen gas and phosphorusaccumulating bacteria in the anaerobic (AN) tanks to take up the available P. This process is capable of producing an effluent with NTOT 30 mmol l1, given normal plasma lipid levels and in conjunction with a plasma vitamin C concentration >50 mmol l1 and a -carotene level >0.4 mmol l1. This has not been proven in large-scale human intervention trials, but even in the absence of conclusive evidence for a prophylactic effect of vitamin E on the prevention of chronic diseases, some experts believe that a recommendation of a daily intake of 87–100 mg of -tocopherol is justifiable based on the current evidence. Realistically, these levels can be achieved only by using nutritional supplements. The tolerable upper intake level (UL) for vitamin E is 1000 mg day1, based on studies showing hemorrhagic toxicity in rats, in the absence of human dose–response data. The Scientific Committee for Food proposed that the intake should not exceed 2000 mg -TE day1.
See also: Milk Lipids: Lipid Oxidation; Nutritional Significance. Vitamins: Vitamin C.
Further Reading Azzi A and Stocker A (2002) Vitamin E: Non-antioxidant roles. Progress in Lipid Research 39: 231–255. Bramley PM, Elmadfa I, Kafatos A, et al. (2000) Review: Vitamin E. Journal of the Science of Food and Agriculture 80: 913–938. Brigeluis-Flohe R, Kelly FJ, Salonen JT, Neuzil J, Zingg J-M, and Azzi A (2002) The European perspective on vitamin E: Current knowledge and future research. American Journal of Clinical Nutrition 76: 703–716. DellaPenna D and Pogson BJ (2006) Vitamin E synthesis in plants: Tocopherol and carotenoids. Annual Review of Plant Biology 57: 711–738. Esposito E, Rotilio D, and Di Matteo V (2002) A review of specific dietary antioxidants and the effects on biochemical mechanisms related to neurodegenerative processes. Neurobiology of Aging 23: 719–735. Frei B (1994) Natural Antioxidants in Human Health and Disease. London: Academic Press. Institute of Medicine (2000) Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium and Carotenoids. Washington, DC: National Academy Press. Jiang Q, Christen S, Shigenaga MK, and Ames BN (2001)
-Tocopherol, the major form of vitamin E in the US diet, deserves move attention. American Journal of Clinical Nutrition 74: 712–722. Morrissey PA, Buckley DJ, and Galvin K (2000) Vitamin E and the oxidative stability of pork and poultry. In: Decker EA, Faustman C, and Lopez-Bote CJ (eds.) Antioxidants in Muscle Foods: Nutritional Strategies to Improve Quality, pp. 263–287. New York: John Wiley. Neuzil J, Weber C, and Kontush A (2001) The role of vitamin E in atherogenesis: Linking the chemical, biological and clinical aspects to the disease. Atherosclerosis 157: 257–283. Packer L and Fuchs J (eds.) (1993) Vitamin E in Health and Disease. New York: Marcel Dekker. Pryor WA (2000) Vitamin E and heart disease: Basic science to clinical intervention trials. Free Radical Biology and Medicine 28: 141–164. Rimbach G, Minihane AM, Majewicz J, et al. (2002) Regulation of cell signalling by vitamin E. Proceedings of the Nutrition Society 61: 415–425. Thomas SR and Stocker R (2000) Molecular action of vitamin E in lipoprotein oxidation: Implications for atherosclerosis. Free Radical Biology and Medicine 28: 1795–1805. Traber MG and Sies H (1996) Vitamin E in humans: Demand and delivery. Annual Review of Nutrition 16: 321–347. Tucker JM and Townsend DM (2005) Alpha-tocopherol: Roles in prevention and therapy of human disease. Biomedicine & Pharmacotherapy 59: 380–387. Wagner KH, Kamal-Eldin A, and Elmadfa I (2004) Gamma-tocopherol – an underestimated vitamin? Annals of Nutrition and Metabolism 48: 169–188.
Vitamin K T R Hill and P A Morrissey, University College Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by P. A. Morrissey, Volume 4, pp 2677–2683, ª 2002, Elsevier Ltd.
Introduction Vitamin K (the coagulation vitamin) was discovered in the 1930s as a result of investigations into the cause of an excessive bleeding disorder in chickens fed on a fat-free diet. Its isolation and structural determination were accomplished in 1939 and its metabolic function was defined only after a new amino acid, -carboxylglutamic acid, was discovered in bovine prothrombin in 1974. Vitamin K is essential for the blood clotting process, where it serves as an essential cofactor for the specific carboxylation of a number of vitamin K-dependent coagulation proteins.
Chemistry The term ‘vitamin K’ is a group name for a number of related compounds that have in common a 2-methyl1,4-naphthoquinone ring system, but differ in the length and degree of saturation of their isoprenoid side chain at the 3-position. Three vitamin K compounds have biological activity (Figure 1). Phylloquinone, vitamin K1 (2-methyl-3-phytyl-1,4naphthoquinone), is found in green leafy vegetables and represents the main dietary source of vitamin K in Western diets. Menaquinones (MKs), vitamin K2 (2-methyl-3-1,4-naphthoquinone), are synthesized by the gut microflora, and have fully or partially unsaturated isoprenoid side chains of various length at the 3-position. The predominant forms of the MK compounds contain between 6 and 10 isoprenoid units, but Makes containing up to 13 units have been isolated. The parent structure of the vitamin K group of compounds is 2-methyl-1,4naphthoquinone, commonly called menadione (vitamin K3). This compound is not found in nature but is a synthetic form that can be metabolized to phylloquinone or MK and thus may be regarded as a provitamin. Menadione is also used as an animal feed supplement and in this way may indirectly enter the human food chain as preformed MK-4. Previous analytical techniques to measure vitamin K compounds, such as the chick bioassay, were cumbersome and tended to overestimate the vitamin K content of foods. However, at present, the method of choice for vitamin K analysis in foodstuffs is high-performance liquid chromatography (HPLC) separation after lipid extraction.
Electrochemical or fluorescence detection (after reduction to the hydroquinone form) offers the sensitivity and selectivity needed for quantification of the small amounts of vitamin K compounds. Food composition data for vitamin K derived from HPLC are generally lower than earlier data derived from the chick bioassay. The use of these HPLC-derived data on the vitamin K content of foods allows for a more accurate determination of the phylloquinone content of a typical Western diet.
Dietary Sources of Vitamin K Green leafy vegetables are the best dietary source of vitamin K (as phylloquinone) (see Table 1). Some plant oils such as soybean oil and rapeseed oil are good dietary sources, containing 173 and 123 mg of phylloquinone per 100 g, respectively. Some vegetable oils, such as peanut, corn, sunflower, and safflower oils, have much lower phylloquinone content (1–10 mg 100 g1). In general, meat, cereals, fish, and milk are poor sources of phylloquinone. MKs seem to have a more restricted distribution in the diet than does phylloquinone. In the Western diet, nutritionally significant amounts of long-chain MKs have been found in animal livers and fermented foods such as cheeses. The Japanese food ‘natto’ (fermented soybeans) has an MK content higher than the content of phylloquinone in green leafy vegetables. Mean dietary phylloquinone intakes were reported for a nationally representative sample of US consumers (n ¼ 3967), aged 13þ years, at levels of 81 and 73 mg day1 in men and women. There are limited data on dietary phylloquinone levels in European populations and, of those that are available, the use of different dietary tools precludes comparison in some cases. For example, mean intake estimates of phylloquinone in the United Kingdom, Ireland, and Norway of 60–85 mg day1 were obtained using food records, while estimates in the Netherlands (250 mg day1) were based on a food frequency questionnaire. Phylloquinone intake decreases with age, especially for adults over the age of 65 years and, more notably, over the age of 85 years. However, consistently higher intakes for older adults (>40 years) than younger adults are reported, most probably due to lower green vegetable consumption by younger adults.
661
662 Vitamins | Vitamin K
Figure 1 Structure of vitamin K1 (a), K2 (b), and K3 (c).
Table 1 Vitamin K1 (phylloquinone) concentration in commonly consumed vegetables
Vegetables
Phylloquinone content (g 100g1 raw food)
Kale Spinach Broccoli Brussels Onions Lettuce Cabbage, savoy Cauliflower Celery Carrots Green pepper
816 483 102 139–193 207 23–173 69 16 29 13 7
Source: USDA National Nutrient Database for Standard Reference. http://www.nal.usda.gov/fnic/foodcomp/Data/SR17/wtranks/ sr17a430.pdf
Absorption, Metabolism, and Excretion Dietary vitamin K, mainly as phylloquinone, is absorbed into the lymphatic system from the proximal intestine after solubilization into mixed micelles composed of bile salts and the products of pancreatic lipolysis. In healthy adults, the efficiency of absorption of phylloquinone is about 80%. Intestinal bacteria can synthesize a variety of MKs, which are absorbed to a limited extent from the large intestine, transported into the lymphatic system, cleared by the liver, and released in very low-density
lipoprotein (VLDL). However, it is not fully clear to what extent intestinal MK contributes to the vitamin K requirement. Approximately 50% of vitamin K is carried in the plasma in the form of VLDL, about 25% in lowdensity lipoprotein (LDL), and about 25% in high-density lipoprotein (HDL). Once in the circulation, phylloquinone is cleared rapidly at a rate consistent with its continuing association with chylomicrons. Vitamin K is extensively metabolized in the liver and excreted in the urine and bile. It has been demonstrated in tracer experiments that about 20% of an injected dose of phylloquinone is recovered in urine, whereas about 40–50% is excreted in the feces via the bile and the proportion excreted was the same regardless of whether the injected dose was 1000 or 45 mg. It seems likely, therefore, that about 60–70% of the amount of phylloquinone absorbed from each meal will ultimately be lost to the body by excretion. These results suggest that the body’s stores of phylloquinone are constantly replenished. Vitamin K itself is too lipophilic to be excreted in the bile and is excreted as side chain-shortened carboxylic acid metabolites. There is no evidence that phylloquinone and MK are toxic. However, high intakes of phylloquinone can negate the effects of the anticoagulant warfarin. The synthetic form of vitamin K, menadione, can interfere with the function of glutathione, one of the body’s natural antioxidants, resulting in oxidative damage to cell membranes. Menadione given by injection has been shown to induce liver toxicity, jaundice, and hemolytic anemia (due to the rupture of red blood cells) in infants, and is no longer used for the treatment of vitamin K deficiency. No tolerable upper level (UL) of intake has been established for vitamin K.
Metabolic Function of Vitamin K Vitamin K acts as a cofactor for a specific carboxylation reaction that transforms selective glutamate (Glu) residues to -carboxyglutamate (Gla) residues. The reaction is catalyzed by the microsomal enzyme vitamin K-dependent -glutamyl carboxylase, which, in turn, is linked to a cyclic pathway known as the vitamin K epoxide cycle. The resultant Gla residues are common to all vitamin K-dependent proteins and these have increased affinity for calcium. Prothrombin and other proteins of the blood clotting system, as well as certain bone matrix proteins, contain Gla. The vitamin K epoxide cycle serves to recycle the nutrient via a cyclic interconversion. In this cycle, the vitamin K quinone form is reduced by the FADcontaining enzyme DT-diaphorase (NAD(P)H:quinone oxidoreductase) into the vitamin K hydroquinone (KH2), which then serves as a cofactor for vitamin K carboxylation of Gla proteins and, in so doing, is oxidized
Vitamins | Vitamin K 663
to vitamin K epoxide. Vitamin K epoxide is then recycled back to the quinone form by the enzyme vitamin K epoxide reductase (VKOR), completing the cycle. At a molecular level, vitamin K epoxide is reduced in two steps: first to the quinone form by VKOR and then to KH2 by DT-diaphorase.
Vitamin K-Dependent Proteins Vitamin K-Dependent Coagulation Proteins There are seven vitamin K-dependent proteins involved in blood coagulation, namely, prothrombin (factor II), factors VII, IX, and X, and proteins C, S, and Z, all of which are synthesized in the liver and contain between 10 and 12 Gla residues (Table 2). The Gla residues enable Ca2þ-mediated binding of the proteins to the negatively charged phospholipid surfaces provided by blood platelets and endothelial cells at the site of injury. Prothrombin and factors VII, IX, and X possess procoagulant activity and participate in the cascade that results in the formation of the fibrin clot. A key element in the formation of fibrin is the conversion of prothrombin to thrombin by activated factor X (which is, in turn, activated by activated factors VII and IX). In contrast, proteins C and S act as anticoagulants. Protein C inhibits coagulation by inactivating activated factors V and VIII and enhancing fibrinolysis, with protein S as a cofactor.
Bone Vitamin K-Dependent Proteins There are two bone matrix proteins that contain Gla: osteocalcin (OC) and matrix Gla protein (MGP) (Table 2). OC is an osteoblast-derived, specific vitamin K-dependent protein that also contains hydroxyproline and is the most abundant of all the noncollagenous bone matrix-bound proteins. It has a molecular mass of 5700 Da and contains three Gla residues, which give this protein a high affinity for hydroxyapatite, in fact much higher than its affinity for calcium. The synthesis of OC is under the regulatory control of the active vitamin D metabolite, 1,25 dihydroxyvitamin D (1,25OHD), and its release into the circulation provides a sensitive index of vitamin D action. While a high proportion of newly synthesized OC is incorporated into bone, approximately 30% of it is released into the circulation and serum levels of the protein are used widely as an indicator of the rate of bone formation. The precise physiological function of OC remains unclear. The less well characterized MGP has a molecular mass of 9600 Da and contains five Gla residues and in contrast to OC, which is exclusively associated to mineralized tissues, MGP is present in cartilage and is expressed at a high rate in many soft tissues (heart, kidney, lungs), in addition to bone.
Vitamin K and Health Deficiency Newborn infants are at serious risk of hemorrhaging because of poor placental transfer of vitamin K, lack of
Table 2 The main vitamin K (Gla)-dependent proteins and their physiological function Gla protein
Tissue
Physiological function
Liver (then plasma)
Procoagulants
Liver (then plasma) Liver (then plasma), endothelium Liver (then Plasma)
Anticoagulant Cofactor for protein C Exact function unknown Unknown, may be a matrix signal for osteoclasts Inhibitor of calcification
Protein S
Bone Bone, cartilage, and most soft tissues Bone
Others Nephrocalcin
Renal tissue
Undetermined, may inhibit the growth of calcium oxalate monohydrate crystals Undetermined
Blood coagulation Prothrombin (factor II), factors VII, IX, and X Protein C Protein S Protein Z Bone Osteocalcin (bone Gla protein) Matrix Gla protein
Plaque Gla protein Growth arrest specific gene 6 (Gas 6) Proline-rich Gla protein 1,2 (PRGP 1,2)
May be present in artherosclerotic plaque Detected in cartilage and numerous soft tissues Broad tissue distribution
Unknown
Cellular growth regulation factor Undetermined
Data from Ferland G (1998) The vitamin K-dependent proteins:an update. Nutrition Reviews 56: 223–230; Shearer MJ and Bolton-Smith C (2000) Food Chemistry 68: 213–218.
664 Vitamins | Vitamin K
intestinal bacteria, and the low vitamin K content in breast milk. For this reason, vitamin K is routinely administered prophylactically at birth in many countries. The risk of bleeding is greatest in prematurely born infants, in breast-fed infants, and in those with gastrointestinal conditions that impair vitamin K absorption. In normal infants, plasma prothrombin concentrations and those of the other vitamin K-dependent factors are approximately 20% of adult values at birth. Normal or near-normal blood coagulation is usually maintained in older children and adults. Several factors protect adults from a lack of vitamin K and these include widespread distribution of vitamin K in plant and animal tissues, the vitamin K cycle, which conserves the vitamin, and the microbiological flora of the normal gut, which synthesizes MKs. The causes of the reduced levels of vitamin K-dependent coagulation factors in adults are largely secondary to diseases such as cystic fibrosis, celiac disease, ulcerative colitis, and short-bowel syndrome. Biliary obstruction and liver disease may also lead to vitamin K deficiency. There are numerous reports of bleeding episodes in patients treated with anticoagulant drugs and broad-spectrum antibiotics. In children and adults, ‘clinical’ vitamin K deficiency in terms of blood coagulation is rare. However, ‘subclinical’ vitamin K deficiency in extrahepatic tissues, particularly in bone, is not uncommon in the adult population. From the multitude of proteins that require carboxylation of Glu to Gla residues for proper functioning, it is clear that poor vitamin K status may contribute to certain chronic vascular and skeletal diseases. Furthermore, it has been suggested that dietary phylloquinone levels that are sufficient to maintain normal blood clotting (which forms the basis of the recommended dietary allowance) may be suboptimal for adult bone health. Vitamin K and Bone Health The identification of -carboxyglutamyl-containing proteins in bone, notably OC and MGP, has generated considerable interest in the role of vitamin K in bone metabolism and bone health. In addition, another functional index of vitamin K status in bone metabolism is the level of undercarboxylated osteocalcin (ucOC). The extent to which OC is uncarboxylated has been assessed with respect to age, bone status, and risk of hip fracture. A high concentration of circulating ucOC has been associated with low bone mineral density and increased risk of hip fracture. The percentage of uncarboxylated OC is high (by 40%) in post-menopausal women compared with pre-menopausal women. The post-menopausal women responded to phylloquinone supplementation with an increase in total and carboxylated OC and a decrease in urinary calcium and hydroxyproline. The
incidence of hip fractures in aged women correlates directly with the increase in ucOC and bone mineral density correlates negatively with the rise in ucOC. The relationship between ucOC and bone health in young growing teenagers has also received attention recently. For example, a significant inverse association has been reported between ucOC and bone mineral content of the total body and lumbar spine in peripubertal Danish girls. Vitamin K intake has been associated with bone health in epidemiological studies. A cohort of elderly men and women from the Framingham Study in the United States showed an association of vitamin K intake with the incidence of hip fracture. In addition, there was evidence that phylloquinone intakes 50 years), it appears that phylloquinone supplementation does not protect against loss of bone mineral in some skeletal sites (lumbar spine, total body, mid-distal radius). Furthermore, the evidence base for bone health benefits at the femoral neck from phylloquinone supplementation is mixed and may require further research. In particular, the inconsistent findings in relation to the effects of phylloquinone supplementation on bone mineral density of the hip do not explain the mechanism underpinning the protective effect of high phylloquinone intake/status against hip fracture observed in a number of prospective cohort studies. More research is needed on whether phylloquinone supplementation may be lowering the risk of fractures through other mechanisms such as effects on bone quality parameters. The finding that relatively lowdose phylloquinone supplementation improved bone mineral density of the forearm (ultradistal radius) of post-menopausal women is interesting even though it was investigated in only one study. It has been suggested that ultradistal forearm has a higher metabolic turnover rate than predominantly cortical bone and thus may be more responsive to dietary treatment. Vitamin K and Cardiac Health A role for vitamin K in atherosclerosis was hypothesized when proteins containing Gla residues were isolated from hardened atherosclerotic plaque, which were later identified as OC and MGPs. Increasing evidence is emerging suggesting a role for vitamin K in the calcification of
Vitamins | Vitamin K 665
arteries and atherogenesis. Moreover, the therapeutic potential of vitamin K2 as an antihepatoma drug has been recently highlighted. Results from human observational studies investigating relations between vitamin K intake and cardiovascular diseases are inconsistent. The Nurses’ Health Study showed a modest risk reduction of coronary heart disease (CHD) for high phylloquinone intakes, while no significant associations were observed in the Health Professionals Follow-up Study and the Rotterdam Study. On the other hand, in the Rotterdam Study, a strong inverse association between MK intake and CHD mortality and severe aortic calcification was observed. These inconsistencies may relate to different effects of phylloquinone and MK on coronary calcification. In a large study on 16 057 women, MK intake was inversely associated with coronary events, while phylloquinone intake was not related to CHD. Similarly, in animals, MK-4-but not phylloquinone-appears to inhibit warfarin-induced coronary calcification. The different effects of MK and phylloquinone probably reflect differences in metabolism as a result of different distributions over plasma lipoproteins.
Vitamin K Status and Requirements Defining reliable indicators of vitamin K status has proven to be a difficult task. The serum concentration of ucOC is a more sensitive indicator of vitamin K status than the traditional blood coagulation tests, and a high serum level of ucOC is indicative of low vitamin K status and vice versa. UcOC has been reported to have a negative association with plasma phylloquinone concentrations. The difference between the vitamin K-dependent coagulation factors (all synthesized in the liver) and the bone Gla protein OC suggests that different tissues (at least bone and liver) may have different vitamin K requirements; hence, bone tissue may be more prone to vitamin K deficiency than liver. If this is the case, impaired synthesis of some vitamin K-dependent proteins may be far more prevalent in the human population than coagulation assays previously indicated, potentially resulting in an increase in dietary recommendations for vitamin K, especially for the elderly. A number of clinical trials have shown that high circulating ucOC levels are common in postmenopausal women as well as healthy young and elderly adults but levels are reduced significantly with vitamin K supplementation. Even in healthy newborns, whose vitamin K status is known to be precarious, very low levels of undercarboxylated prothrombin are detectable, whereas all babies tested exhibited high
concentrations of serum ucOC. These data together with other evidence suggest that circulating OC is the most sensitive known marker for vitamin K status. Until recently, the only widely accepted criterion for vitamin K sufficiency was the maintenance of plasma prothrombin concentration. It has been estimated that 0.5–1.0 mg kg1 day1 was required to correct induced clotting changes. In adults, primary vitamin K-deficient states that resulted in bleeding were almost unheard of, except in a hospital setting. This is due to the widespread distribution of vitamin K in foods, the ability of the vitamin K cycle to conserve vitamin K, and endogenous bacterial syntheses of MKs. Therefore, a healthy population is not at risk of dietary vitamin K deficiency as the recommendation for optimal blood clotting is readily achievable. However, recent attention has focused on the importance of vitamin K for optimizing bone health and it has been proposed that vitamin K supplies believed sufficient to maintain normal blood coagulation may be suboptimal for bone health. The Food and Nutrition Board (2001) has recently established an adequate intake (AI) value for vitamin K. The recently discovered indicators sensitive to vitamin K intake, although useful to describe relative diet-induced changes in vitamin K status, were not used for establishing an estimated average requirement (EAR) because of the uncertainty surrounding their true physiological significance and the lack of sufficient dose–response data. Therefore, the AI for adults was based on reported vitamin K dietary intake in apparently healthy populations. A large review, including 11 different studies, reported that phylloquinone intake ranged from 60 to 210 mg day1 with an average intake of approximately 80 mg day1 for younger adults (55 years). Healthy individuals with a phylloquinone intake approaching 80 mg day1 have been investigated and showed no signs of deficiency, suggesting that this level is probably adequate for the majority of the adult population. Because dietary assessment methods tend to underestimate the actual daily intake of foods, the highest intake value reported for four adult age groups was used to set the AI for each gender rounding up to the nearest 5 mg. Therefore, the most recent guideline (AI) for vitamin K intake in the United States for adults (aged 19 years and older) is 120 and 90 mg day1, for men and women, respectively. To date, no adverse effect has been reported for individuals consuming greater than the AI for vitamin K. However, the data on adverse effects from high vitamin K intake are not sufficient for a quantitative risk assessment and a tolerable UL of intake has not been established by the Institute of Medicine in the United States or by the Scientific Committee of Food in the European Union.
666 Vitamins | Vitamin K See also: Nutrition and Health: Nutritional and HealthPromoting Properties of Dairy Products: Bone Health; Vitamins: General Introduction.
Further Reading Bentley R and Meganathan R (1982) Biosynthesis of vitamin K (MK) in bacteria. Microbiological Reviews 46: 241–280. Cashman KD (2005) Vitamin K status may be an important determinant of childhood bone health. Nutrition Reviews 63: 284–289. Ferland G (1998) The Vitamin K-dependent proteins: an update. Nutrition Reviews 56: 223–230.
Ferland G (2001) Vitamin K. In: Bowman BA and Russell RM (eds.) Present Knowledge in Nutrition, 8th edn., pp. 164–172. Washington, DC: ILSI Press. Institute of Medicine (2001) Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academies Press. Shea MK and Booth SL (2008) Update on the role of vitamin K in skeletal health. Nutrition Reviews 66: 549–557. Shearer MJ (2000) Role of vitamin K and Gla proteins in the pathophysiology of osteoporosis and vascular calcification. Current Opinion in Clinical Nutrition and Metabolic Care 3: 433–438. Shearer MJ and Bolton-Smith C (2000) The UK food database for vitamin K and why we need it. Food Chemistry 68: 213–218. Suttie JW (1995) The importance of menaquinones in human nutrition. Annual Reviews of Nutrition 15: 399–417.
Vitamin C P A Morrissey and T R Hill, University College Cork, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by P. A. Morrissey, Volume 4, pp 2683–2690, ª 2002, Elsevier Ltd.
Introduction
Chemistry
Among specific nutritional deficiency diseases, scurvy was the dreaded disease of seamen and explorers forced to subsist for months on diets of dried beef and biscuits. The symptoms of scurvy are rather characteristic and consist of bleeding and rotting gums, swollen and inflamed joints, dark blotches on the skin, and muscle weakness. Scurvy afflicted nineteenth-century populations on land, including armies of the Crimean and United States Civil wars and the California gold rush communities. In 1907, scurvy was produced experimentally in the guinea pig and from 1928 to 1930, Albert Szent-Gyorgy and Glen King independently published their isolation of vitamin C or hexuronic acid. It was later named ascorbic acid for its antiscorbutic properties and its molecular structure was determined in 1933. Ascorbate, also known as ascorbic acid (AA) or vitamin C, is synthesized de novo from glucose in the liver of most adult mammals. D-Glucose is converted into L-ascorbic acid via D-glucuronic acid, L-gulonic acid, L-gulonolactone, and L-gulono- -lactone as intermediates. However, humans and non-human primates, guinea pigs, the Indian fruit bat, several species of birds, and some fish have lost the ability to synthesize ascorbate de novo. As a result of a gene mutation, they lack a key ascorbate-oxidizing enzyme, L-gulono- -lactone oxidase, an essential oxidizing enzyme in the liver for the conversion of L-gulono- -lactone into 2-oxo-L-gulono- -lactone, a tautomer of L-ascorbic acid, which transforms spontaneously into the vitamin. In plants, the biosynthesis of ascorbate is more complicated than in animals. The vitamin is synthesized from guanosine diphosphate (GDP)-mannose, and the pathway shares GDP-sugar intermediates with the synthesis of cell wall polysaccharides and those glycoproteins that contain D-mannose, L-fucose, and L-galactose. Ascorbate is quantitatively the predominant antioxidant in plant cells and is found in all subcellular compartments, including the apoplast, and has an average cellular concentration of 2–25 mmol l1 or more in the chloroplast stroma. This article discusses the chemistry of vitamin C. In addition, the role of vitamin C as a biological antioxidant, specific functions in humans, and role in health and disease are highlighted.
Ascorbic acid is the enolic form of an -ketolactone (2,3-didehydro-L-threo-hexano-1,4-lactone). The molecular structure (Figure 1) contains two ionizable –OH groups at C2 and C3 that give the compound its acidic character, and since pKa1 at C3 is 4.17 and pKa2 at C2 is 11.79, a monoanion is the favored form at physiological pH where 99.95% of AA is present as ascorbate monoanion (AscH), 0.05% as AA (AscH2), and 0.004% as ascorbate dianion (Asc2). Thus, the antioxidant chemistry of vitamin C is the chemistry of AscH. The asymmetric carbon 5 atom allows two enantiomeric forms, of which the L-form is naturally occurring. Oxidation of AA takes place as either two one-electron transfer processes or as a single two-electron reaction without detection of the intermediate ascorbyl radical. In the two one-electron oxidation processes, the first step involves loss of one electron from AscH to form the neutral ascorbyl radical (AscH? ), which is not protonated in biological systems and is present as the resonance-stabilized tricarbonyl ascorbate free radical (Asc – ? ), which is relevant in biology. Asc – ? is a weakly reactive radical, and in vivo it is likely that reducing enzymes are involved in its removal, resulting in the recycling of ascorbate. Loss of an additional electron yields L-dehydroascorbic acid (DHA). The oxidation of AA to DHA is reversible via the same intermediate radical process, and for this reason DHA also exhibits biological activity, since it can be easily converted to AA in the human body. However, DHA is highly unstable because of the susceptibility to hydrolysis of the lactone bridge. DHA has a half-life, in aqueous solutions at 37 C, of approximately 6–20 min as a function of concentration, and catabolism beyond DHA is enhanced by alkaline pH and metals, especially copper and iron. Hydrolysis of DHA irreversibly forms 2,3-diketogulonic acid and leads to the loss of vitamin C activity (Figure 1). Further catabolism leads to the formation of a wide array of other nutritionally inactive products such as L-xylonic acid, L-lyxonic acid, L-xylose, oxalic acid, and L-threonic acid. The rate of oxidative degradation of the vitamin is a nonlinear function of pH because the various ionic forms of AA differ in their susceptibility to
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668 Vitamins | Vitamin C
Figure 1 Ascorbic acid and its oxidation products. Dehydro-L-ascorbate may exist in multiple forms. Formation of 2,3-diketogulonic acid by hydrolytic cleavage is probably irreversible.
oxidation: fully protonated AscH2 < AscH < Asc2. Under conditions relevant to most biological systems, the pH dependence of oxidation is governed mainly by the relative concentrations of AscH2 and AscH species and this, in turn, is governed by pH (pKa1 4.17). The rate of oxidation of ascorbate is generally observed to be first order with respect to the concentration of AscH, molecular oxygen, and the metal ion.
Dietary Sources More than 80% of the vitamin C in western diets comes from fruits and vegetables, with citrus fruits, tomatoes and tomato juice, and potatoes being major contributors. A minor portion comes from enriched or fortified products, meats, fish, poultry, eggs, and dairy products, and essentially none from grains. The mean content of vitamin C is 2.11 mg per 100 g (range 1.65–2.75 mg per 100 g) in cow’s milk, 5.48 mg per 100 g in goat’s milk, 3.9 mg per 100 ml in summer human milk, and 3.02 mg per 100 ml in winter human milk. There is some evidence that the concentration of vitamin C in cow’s and goat’s milk changes with season. It has been observed that in raw milk sampled in March
or August the concentration of vitamin C was higher (2.0–2.7 mg per 100 ml) than in samples collected in October (1.2 mg per 100 ml). The mean concentration of vitamin C in human milk also appears to be affected by the stage of lactation and declines from 6.18 mg per 100 ml in colostrum to 4.68 mg per 100 ml at 9 months. The influence of maternal vitamin C intake and its effect on the vitamin C content of human milk have not been clearly defined. It has been observed that the vitamin C level in human milk did not increase significantly in response to increasing maternal intake (up to 10-fold). It appears that a regulatory mechanism may be present in mammary cells to prevent an elevation in the concentration of vitamin C in milk beyond a certain saturation level. On the other hand, when the intake of vitamin C is low, breast milk levels are sensitive to supplementation. In the United States, the median dietary intake of vitamin C by adult men from 1988 to 1994 was about 105 mg day1 and the median total intake (including supplements) was about 120 mg day1. For women, the median intake was estimated to be 90 mg day1 and median total intake (including supplements) was about 108 mg day1. The average consumption for children was 84 mg day1. The recent North/South Food
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Consumption Survey in Ireland (2001) showed that mean daily intake of vitamin C was not significantly different in men (116 mg) and women (108 mg). The primary sources of vitamin C for the total population were potatoes and potato products (25.9%); fruit juices; nuts and seeds; herbs and spices (25.6%); and vegetable and vegetable products (22.1%). The contribution from supplements was 5.8% for men and 8.6% for women. Ascorbic acid is also added to some processed foods for its antioxidant or functional properties and consequently the mean total vitamin C intake may be considerably higher than indicated above. Ascorbic acid is the nutrient taken most frequently as a supplement, particularly among the elderly population. The Boston Nutritional Status Survey of the Elderly (1992) estimated that 35 and 44% of males and females, respectively, took some form of vitamin supplements, with a median supplemental intake of 300 mg day1. Clinical signs of vitamin C deficiency are rarely seen in developed countries. The content of vitamin C in foods may be reduced significantly because of thermal destruction that occurs during cooking, losses in cooking water, and subsequent holding prior to consumption.
Absorption, Metabolism, and Excretion In rats and hamsters (for which AA is not a vitamin), intestinal absorption is passive. In the case of guinea pigs and humans, both of which have an absolute requirement for exogenous AA in their diet, there is a sensitive sodium-dependent active transport system for AA in the brush border of the duodenum and upper ileum, and another sodium-independent transfer process in the basolateral membrane. There is also a passive transport mechanism, which in humans is predominant only at high intake levels. Ascorbate transport has been specifically shown to require metabolic energy, with a stoichiometry for Naþ from 1.1 to 2.1. Intestinal absorption of AA and its entry into cells are facilitated by conversion to DHA, which is transported across cell membranes more rapidly than ascorbate. Because DHA is structurally similar to glucose, its transport across membranes is facilitated by glucose transporters (GLUTS). Transport of DHA is primarily Naþ-independent in animal and human tissues, and does not require metabolic energy. Upon cell entry, DHA is reduced immediately to AA, which produces an effective gradient of DHA across the membrane. Intracellular reduction of DHA to AA is mediated by two major pathways: chemical reduction by glutathione and enzymatic reduction. The flux of ascorbate in and out of the cell via facilitated diffusion and active transport is mediated by distinct classes of proteins such as facilitative glucose transporters and sodium–vitamin C cotransporters, respectively.
Information on the bioavailability of vitamin C in foods is limited. It is generally agreed that at relatively low intakes (less than 30 mg day1), ascorbate is nearly completely absorbed, and 70–90% of the usual dietary intake of ascorbate (30–180 mg day1) is absorbed. Similar levels of absorption (80%) have been reported for pure ascorbate, ascorbate in orange juice, and ascorbate in cooked broccoli, which suggests that the absorption of vitamin C is almost complete. However, absorption falls to approximately 50% or less with increasing doses above 1.5 g day1. Following absorption, ascorbic acid circulates freely in plasma, leukocytes, and red cells, and enters all tissues, with maximum concentrations of 68–86 mmol l1 plasma being achieved with an oral intake of 90–150 mg day1. Excess is excreted by the kidney, which conserves the vitamin at plasma levels of up to 46–86 mmol l1 by a saturable, sodium-dependent reabsorption process. The upper limit of plasma ascorbic acid concentration is controlled by the gastrointestinal absorption and renal reabsorption mechanisms, and fasting plasma concentration rarely exceeds 100 mmol l1, even with dietary supplementation. Specific proteins mediate the entry and exit of vitamin C in cells by facilitated diffusion or active transport. These cellular transport systems are responsible for high intertissue ascorbate levels found in the pituitary and adrenal glands (30–400 mg per 100 g tissue), followed by the brain, spleen, pancreas, kidney, liver, and tissues of the eye with 10–50 mg per 100 g of tissue. Vitamin C concentration also varies widely in different blood cell types. About 70% of blood-borne ascorbate is in plasma and erythrocytes. The remainder is in white cells, which have a marked ability to concentrate ascorbate; mononuclear leukocytes achieve 80-fold concentration, platelets 40-fold, and granulocytes 25-fold, compared with plasma concentration. Tissuespecific cellular mechanisms of transport and metabolism allow for wide variation of tissue ascorbate concentration in order to enhance its function as an enzyme cofactor and antioxidant. Intracellularly, and in plasma, vitamin C exists predominantly in the free form as AscH. DHA is either not detectable or found at only very low levels in the circulation of healthy people. The total body pool of ascorbate is affected by limited intestinal and renal tubular absorption. It reaches a maximum value of about 20 mg kg1 body weight or about 1500 mg for the average-size man when the ascorbate intake is increased from 30 to 180 mg day1; above this level of intake, excretion of ascorbate in the urine rises rapidly. Unabsorbed ascorbate is degraded in the intestine, a process that may account for the diarrhea and intestinal discomfort sometimes reported by persons ingesting large doses.
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Antioxidant Activity of Ascorbic Acid Ascorbate is often called the outstanding antioxidant. In chemical terms, this is simply a reflection of its redox properties as a reducing agent. In physiological terms, this means that ascorbate provides electrons for enzymes, for chemical compounds that are oxidants, or for other electron acceptors in biological systems. In addition to its redox potential, other properties of ascorbate make it an excellent electron donor in biological systems. Ascorbate undergoes two consecutive, reversible, one-electron oxidation processes forming the ascorbate radical (Asc – ? ) as an intermediate. The Asc – ? has an unpaired electron, making it a relatively unreactive free radical, especially with oxygen, and the ascorbate oxidation product, DHA, is reduced by cells to ascorbate, which then becomes available for reuse. These properties make ascorbate an excellent biological donor system. Thus, ascorbate is a reversible biological reductant and, as such, it provides reducing equivalents for a variety of biochemical reactions, is essential as a cofactor for reactions requiring a reduced metal ion (Fe2þ, Cuþ), and serves as a protective antioxidant that operates in the biological aqueous phase and can be regenerated in vivo when required. Ascorbate is thermodynamically close to the bottom of the list of one-electron reducing potentials of oxidizing free radicals (E 9 ¼ þ282 mV). For this reason, ascorbate is considered to be the most important antioxidant in extracellular fluids and is the first line of defense against reactive oxygen species (ROS) and reactive nitrogen species (RNS) (e.g., nitric oxide, NO? , and nitric dioxide, NO?2 ) in plasma. It efficiently scavenges all oxidizing species with a greater one-electron potential (higher E 9 – values), which include the superoxide anion (O2 ? ) and hydroxyl radical (? OH), and oxygen-centered radicals of organic compounds (peroxyl, LOO? , and alkoxyl, LO? ) can be repaired by ascorbate as follows: AscH – þ X? ! Asc – ? þ XH
where X? is any of the oxidizing radicals. Although ascorbate itself forms a radical in the reaction, a potentially very damaging radical (X? ) is replaced by the relatively unreactive Asc? . Overall, ascorbate is reactive enough to affectively interrupt oxidants in the aqueous phase before they can attack and cause detectable oxidative damage to DNA and lipids. In aqueous solutions, ascorbate also scavenges RNS efficiently, preventing nitrosation of target molecules. Consequently, both thermodynamically and kinetically, ascorbate can be considered to be an excellent aqueous antioxidant. Ascorbate may also regenerate -tocopherol ( -TOH) from the tocoperoxyl radical (TO? ), which is formed upon inhibition of lipid oxidation by -tocopherol. Ascorbate has a lower redox potential (E 9 ¼ þ282 mV) than
-TOH (E 9 ¼ þ500 mV) and, in addition, the -TO? is at the membrane–water interface, thereby allowing watersoluble ascorbate access to membrane-bound -TO? for the repair reaction and recycling of -tocopherol: 9
– E ¼þ200 mV AscH – þ -TO? ! Asc? þ -TOH
The rate constant for the reaction is 1.5 106 l mol1 s1. Thus, in cellular membranes, ascorbate plays an indirect antioxidant role to reduce the -tocoperoxyl radical ( -TO? ) to -tocopherol ( -TOH). Recycling of -tocopherol by ascorbate has been demonstrated in liposomes and cellular organelles and may also spare and recycle -tocopherol in erythrocyte membranes and intact erythrocytes (see Vitamins: Vitamin E). The Asc – ? formed in the above reaction dismutates to DHA and is then regenerated to ascorbate at the expense of glutathione, dihydrolipoate, thioredoxin, and other enzyme systems. This process allows for the transportation of a radical load from a lipophilic compartment to an aqueous compartment where it is taken care of by efficient enzymatic defenses. It should be noted that as a reducing agent, ascorbate has the ability to reduce Fe3þ to Fe2þ and Cu2þ to Cuþ, thereby increasing the prooxidant activity of the metals and generating HO? , O2–?, and H2O2 that initiate lipid peroxidation in biological systems. It is considered unlikely that ascorbate shows prooxidant properties in vivo since the concentrations of ‘free’ transition metals in healthy biological systems are very small because they are effectively bound by metal ion storage and transport proteins.
Biological Functions Many of the biological functions of ascorbic acid are based on its ability to provide reducing equivalents for a variety of biochemical reactions. The vitamin can reduce most physiologically relevant reactive species and, as such, functions primarily as a cofactor for reactions requiring a reduced iron or copper metalloenzyme and as a protective antioxidant that operates in the aqueous phase both intra- and extra-cellularly. Ascorbate is known to be a specific electron donor for eight human enzymes; three enzymes participate in collagen hydroxylation, two in carnitine biosynthesis, and three in hormone and amino acid biosynthesis. Evidence also suggests that ascorbate plays a role in or influences collagen gene expression, cellular procollagen secretion, and the biosynthesis of other connective tissue components, including elastin, proteoglycans, bone matrix, and elastin-associated fibrillin. Ascorbate is also involved in the synthesis and modulation of some hormonal components of the nervous system.
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Collagen Formation Scurvy, the classical disease of severe ascorbate deficiency, is characterized by symptoms related to connective tissue defects. Clinically, signs of scurvy are seen when the total body pool of ascorbate is below 300 mg. Clinical features of scurvy include skin bruises, perifollicular hemorrhages, bleeding gums, joint pain and swelling, and fatigue. Oxidative degradation of some blood coagulation factors due to a low concentration of plasma ascorbate may contribute to hemorrhagic symptoms. Ascorbate-dependent aspartate -hydroxylase is known to be required for the postsynthetic modification of protein C, the vitamin K-dependent protease that hydrolyses activated factor V in the blood-clotting cascade. Ascorbic acid affects the biosynthesis of collagen at several levels from collagen transcription, to expression, including the regulation of the processing enzymes. It acts as a cofactor for several metaldependent oxidative reactions, catalyzed by both monooxygenases and dioxygenases. Other cofactors required by the dioxygenases are Fe2þ, -ketoglutarate, and O2, whereas the monooxygenase requires Cuþ and O2 for activity. Ascorbate functions as a reductive cofactor for posttranslational hydroxylation of peptide-bound proline and lysine residues during the formation of collagen. The hydroxyproline is required for normal triple-helical backbone structure and the hydroxylysine cross-linkages are needed for normal collagen fiber formation. The enzyme involved in proline hydroxylation, prolyl hydroxylase, requires molecular oxygen, ascorbic acid, iron, and -ketoglutarate. The first step in the reaction is the attack on peptide-bound proline by oxygen, followed by condensation with -ketoglutarate, the release of the hydroxylated substrate, and decarboxylation to release succinate. During the hydroxylation reaction, the enzyme-bound iron is oxidized to Fe3þ, which is catalytically inactive. The ascorbate is involved in reactivating the enzyme by reduction of Fe3þ back to the loosely bound ferrous form. In an analogous reaction, ascorbate participates as a cofactor in the hydroxylation of lysine residues catalyzed by copper-dependent lysyl hydroxylase. Hydroxylysine cross-linkages are central for normal collagen fiber formation. Prolyl and lysyl hydroxylases are also called dioxygenases, referring to the ability of the enzymes to provide two oxygen atoms to the same or separate substrates. Ascorbate may also serve as a reductant for other metal-dependent polymerization and cross-linking reactions of connective tissue and as a carrier for sulfate groups needed for the production of glycosaminoglycans (e.g., chondroitin).
A deficiency of ascorbate results in a weakening of collagenous structures, causing tooth loss, joint pains, bone and connective tissue disorders, and poor wound-healing, all of which are characteristic of scurvy. This disease is now rare in developed countries, but is occasionally seen in individuals in classes with exceptionally poor or restricted diets, such as low socioeconomic groups and those who have a near total lack of fruit and vegetables, or those who abuse alcohol or drugs. Low ascorbate levels and scurvy are most often noted in men who live alone and eat a diet frequently low in fruit and vegetables. Because breast milk provides adequate ascorbic acid, infantile scurvy is seen more often after weaning, between 6 and 12 months. Modern infant formulae are fortified with sufficient ascorbic acid such that infantile scurvy is now almost nonexistent. Neurotransmitter Synthesis Ascorbic acid appears to be involved in catecholamine metabolism in two mixed-function oxidases, dopamine -hydroxylase and para-hydroxyphenylpyruvate oxidase. Ascorbic acid is required as a cofactor for the coppercontaining dopamine- -monooxygenase enzyme, which catalyzes hydroxylation of the dopamine side chain to form norepinephrine. Ascorbate provided electrons for reduction of molecular oxygen, transferred by copper to dopamine, and hydrogen atoms to reduce the other oxygen to water. The active enzyme contains Cuþ, which is oxidized to Cu2þ during hydroxylation of the substrate: reduction back to Cuþ specifically requires ascorbate, which is oxidized to AscH? . Depression, hypochondria, and mood changes frequently occur during scurvy and could be related to deficient dopamine hydroxylation. Ascorbic acid also appears to be involved in the hydroxylation of tryptophan to form serotonin in the brain and in the degradation of tyrosine by p-hydroxyphenylpyruvate hydroxylase. Carnitine Biosynthesis Carnitine plays a central role in transporting long-chain fatty acids across the mitochondrial membrane wherein -oxidation provides energy to cells, especially for cardiac and skeletal muscles. Esterification with carnitine appears to provide a mechanism for transport, storage, and excretion of long-chain fatty acid acyl groups. The biosynthesis of carnitine involves the methylation of lysine, with methionine as methyl donor, and requires ascorbate, ferrous iron, vitamin B6, and niacin as cofactors for various enzymes of the pathway. The loss of fatty acid-based energy production because of limited carnitine biosynthesis may explain the fatigue and muscle weakness observed in humans with ascorbic acid deficiency.
672 Vitamins | Vitamin C
Other Functions of Ascorbate
Ascorbate and Cardiovascular Disease
Ascorbate is also involved in the hepatic microsomal hydroxylation of cholesterol in the conversion and excretion of cholesterol as bile acids via 7 -hydroxycholesterol. These reactions require the microsomal enzymatic system containing cytochrome P-450 hydroxylase. Impaired cholesterol transformation to bile acids causes cholesterol accumulation in the liver and blood, and atherosclerotic changes in coronary arteries. Hydroxylation and demethylation of aromatic drugs and carcinogens by hepatic cytochrome P-450 appear to be enhanced by reducing agents such as ascorbate. Limited data suggest that ascorbate modulates prostaglandin synthesis and thus exerts bronchodilatory and vasodilatory function as well as anticlotting effects. Vitamin C has been shown to affect various components of the human immune response, including antimicrobial and natural killer cell activity and lymphocyte proliferation. The ability of phagocytes and lymphocytes to concentrate vitamin C at levels up to 100 times higher than in plasma may indicate that the vitamin has a physiological role in these immune cells. Cataracts which appear to be due to oxidation of lens proteins in the eye may also be protected by ascorbate. One report has shown that the use of vitamin C supplements (ranging from 400 to 700 mg day1) for 10 years or more reduced the number of lens opacities by about 80%. Women who consumed vitamin C supplements for less than 10 years were not protected. Data from other studies suggest that dietary measures to increase plasma ascorbate may be an important public health strategy for reducing the prevalence of diabetes. Ascorbic acid is a potent enhancer of nonheme iron absorption, both in its natural form in fruit and vegetables, and when added as the free compound. In addition, ascorbic acid increases the bioavailability of all iron fortification compounds. The mechanism of ascorbate action is believed to involve the reduction of intraluminal iron by ascorbate to the more absorbable ferrous state and/or the formation of soluble iron complexes in the duodenum. Generally, the enhancement of iron absorption is proportional to the amount of ascorbic acid in the meal, although observed differences in the effect of ascorbic acid may result from varying the amounts of substances in the food that promote or inhibit iron absorption. Ascorbate reacts with nitrite and other nitrosating agents, forming nitric oxide and nitrous oxide and thereby preventing the formation of carcinogenic nitrosamines by reaction between nitrites and amines present in foods in the acid conditions in the stomach.
It is generally accepted that the oxidation of low-density lipoprotein (LDL) particles and the accumulation of oxidized LDL in the vessel wall are key early events in the progression of atherosclerosis. Studies have shown that high plasma concentrations of ascorbate not only correlate with lower concentrations of oxidized LDL, but also function to protect endothelial cells against the detrimental effects of oxidized LDL once this is formed. Since ascorbate is water soluble and is not incorporated in LDL particles, it has been proposed that it may prevent oxidation of LDL particles by scavenging aqueous ROS and RNS in the aqueous milieu. Ascorbate is also capable of regenerating -TOH from -TO? , which is formed on inhibition of lipid peroxidation by vitamin E. Ascorbyl radicals formed in this process may be reduced to ascorbate by dismutation, chemical reduction, or enzymatic reduction. Several epidemiological studies have examined the association between vitamin C concentration in blood and the risk of cardiovascular disease. A prospective study of 1605 Finnish men showed that those with increased plasma vitamin C (greater than 11.4 mmol1) had a 60% decreased risk of coronary heart disease. The Basel Prospective Study of 2974 Swiss men reported that plasma vitamin C concentrations greater than 23 mmol1 were associated with nonsignificant reduction in the risk of coronary artery disease and stroke. In a 20-year followup study of elderly adults (n ¼ 730) in Britain, plasma concentrations greater than 28 mmol1 were associated with a 30% decreased risk of death from stroke compared with concentrations less than 12 mmol l1. The Second National Health and Nutrition Examination Survey (NHANES II) reported that the relative risk of coronary heart disease and stroke was reduced by about 26% with serum vitamin C concentrations of 63153 mmol l1 (1.1–2.7 mg dl1) compared with concentrations of 6–23 mmol l1 (0.1–0.4 mg dl1). However, supplementation with vitamin C did not reduce the risk of major cardiovascular events. The EPIC–Norfolk Prospective Study in the United Kingdom showed that plasma ascorbate levels were inversely related to mortality from all causes and from cardiovascular disease and ischemic heart disease in men and women. A 20% fall in the risk of allcause mortality, independent of other risk factors, was associated with a 20 mmol l1 rise in plasma ascorbate, approximately equivalent to a 50 g day1 increase in fruit and vegetable intake. It was also noted that a high plasma concentration of ascorbate was inversely related to various cardiovascular risk factors. Compared with people in the lowest quartile of the ascorbate distribution, those in the highest quartile had a 33% lower risk of coronary artery disease, independent of other known risk factors,
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including age, blood pressure, plasma lipids, cigarette smoking, body mass index, and diabetes. Several prospective cohort studies have shown that vitamin C intakes between 45 and 113 mg day1 are associated with reduced risk of cardiovascular disease. Results from the First US National Health and Nutrition Examination Survey (NHANES I) showed that cardiovascular mortality rates were 50% lower than average among participants with the highest vitamin C intake, defined as 50 mg or more per day from the diet plus regular supplements. A Finnish study on 5000 men and women found that women who consumed more than 91 mg day1 vitamin C had a lower risk of coronary artery disease than those who consumed less than 61 mg day1. However, a similar association was not found for men. The NHANES I Epidemiologic Follow-up Study cohort of more than 11 000 adults showed a reduction in cardiovascular disease of 45% in men and 25% in women whose vitamin C intake from both food and supplements was approximately 300 mg day1. However, in contrast to the above, other studies reported no association between vitamin C intake and risk of cardiovascular disease. It is important to emphasize that much of these data were obtained from well-nourished populations.
Vitamin C and Cancer Early epidemiological evidence indicated that high intakes of vitamin C-rich fruit and vegetables and a high vitamin C concentration in serum are inversely associated with the risk of certain cancers. Of 46 such studies in which a dietary vitamin C intake index was calculated, 33 found a statistically significant protective effect, with high intakes conferring approximately a two-fold protective effect compared with low intakes. The evidence for a risk-reducing role of vitamin C is not as strong as for fruit and vegetables. However, an extremely strong and consistent protective effect of vitamin C was found in 17 of 19 studies of stomach, esophageal, and pharyngeal cancers. The Iowa Women’s Health Study found a 20% decrease in breast cancer risk with greater than 500 mg day1 of vitamin intake from supplements; in contrast, the Nurses’ Health Study, which used the same dietary assessment instrument, found no decreased risk of breast cancer at intake greater than 357 mg day1. In a large case–control study in New York, the data showed that increased intake of vitamin C from food and supplements was associated with a reduced risk of rectal cancers. In contrast, the Iowa Women’s Cohort Study found no association between vitamin C intake from fruit and supplements of approximately 300 mg day1 and colon cancer risks. However, in women who consumed more than 60 mg day1 vitamin C from supplements compared to no supplements, the risk was
reduced by 30%. The association between vitamin C intake and the risk of lung cancer is generally weak, but still in a protective direction in several studies. Epidemiological and experimental evidence has suggested that vitamin C may protect against the development of gastric cancer by several potential mechanisms, including the following: vitamin C reduces gastric mucosal oxidative stress, DNA damage, and gastric inflammation by scavenging ROS; it inhibits gastric nitrosation reaction for the formation of N-nitroso compounds by reducing nitrous acid to nitric oxide and producing dehydroascorbic acid in the stomach; it enhances host immunologic functions; it has a direct effect on Helicobacter pylori growth and virulence; and it inhibits gastric cell proliferation and induces apoptosis. Recent reports on the NHANES II survey in the United States and the EPIC–Norfolk Prospective Survey in the United Kingdom showed that men with a low serum ascorbate concentration may have an increased risk of mortality, probably because of an increased risk of dying from cancer. In contrast, serum ascorbate concentrations were not related to mortality among women. The EPIC–Norfolk report concluded that increases in dietary foods rich in ascorbic acid might have benefits for all-cause mortality in men and women. A report from the World Cancer Research Fund and the American Institute of Cancer Research rated the anticancer effect of ascorbate as ‘probable’ only for stomach; ‘possible’ for prostate, mouth, pharynx, esophagus, lung, pancreas, and cervical cancer; and ‘insufficient data’ for cancers of the colon, rectum, larynx, breast, and bladder.
Vitamin C Status and Requirements In setting values for average population requirements and individual nutrient intakes, the important question is how do we differentiate between preventing deficiency symptoms, ensuring an adequate intake, and promoting optimal intake for the prevention of disease? The recommended dietary allowance (RDA) of 60 mg day1 in the United States, the reference nutrient intake (RNI) of 40 mg day1 in the United Kingdom, and the population reference intake (PRI) of 45 mg day1 in the European Union were aimed at prevention of the clinical deficiency state, scurvy. However, no obvious deficiency does not necessarily indicate adequacy, and subclinical or marginal deficiency of vitamin C owing to insufficient intake and/or to increased utilization may be common in many disease situations. Increased risk of chronic disease, including cancer, cataract, and coronary heart disease, is associated with low intake or plasma concentrations of vitamin C. However, the contribution of high intake or plasma levels of vitamin C to lowered risk of disease is
674 Vitamins | Vitamin C
difficult to assess, as other health-promoting habits generally accompany high vitamin C intake, and clinical trials have shown inconsistent and inconclusive results. The Institute of Medicine in the United States (2000) established an estimated average requirement (EAR) for vitamin C, which is the nutrient intake value that is estimated to meet the requirements of half of a specific gender and life-stage group and was based on evidence that 75 mg day1 vitamin C can maintain near-maximal neutrophil concentration with minimal urinary loss. Thus, the EAR for men aged 19–50 years is 75 mg day1, with a value of 60 mg day1 for women, based on women having less lean body mass and body water, and a smaller body size than men. There are no data on the distribution of vitamin C requirements in healthy adults; therefore the US RDA for vitamin C, which is the intake value considered to meet the requirements of 97.5% of the relevant life-stage and gender population group, is set at 90 mg day1 for men and at 75 mg day1 for women (RDA ¼ EAR þ 2CV), assuming a coefficient of variation (CV) of 10%. In Japan, Germany, Austria, and Switzerland, an uptake of 100 mg day1 is recommended for both men and women. There is evidence to show that an average intake of 90 mg day1 of vitamin C can maintain a plasma ascorbate concentration at 50 mmol l1 and for this reason a ‘potential protective plasma level’ of 50 mmol l1 has also been proposed. This concentration has been shown to inhibit plasma LDL oxidation in vitro and may have relevance for the prevention of heart disease in vivo. Smokers have been recommended by the United States to consume an additional 35 mg over and above the RDA value, but this recommendation has not been made explicit in other countries. Excessive consumption of vitamin C is unusual, and the upper intake level (UL) set by the United States is 2000 mg day1,
which is achievable only by using chronic megadoses of concentrated vitamin C supplementation. See also: Milk Lipids: Lipid Oxidation. Vitamins: Vitamin E.
Further Reading Benzie IFF (1999) Vitamin C: Prospective functional markers for defining optional nutritional status. Proceedings of the Nutrition Society 58: 469–476. Block G (1991) Vitamin C and cancer prevention: The epidemiologic evidence. American Journal of Clinical Nutrition 53: 270s–282s. Boekholdt SM, Meuwese MC, Day NE, et al. (2006) Plasma concentrations of ascorbic acid and C-reactive protein and risk of future coronary artery disease, in apparently healthy men and women: The EPIC-Norfolk prospective population study. British Journal of Nutrition 96: 516–522. Carr AC and Frei B (1999) Towards a new recommended dietary allowance for vitamin C based on antioxidant and health effects in humans. American Journal of Clinical Nutrition 69: 1086–1107. Halliwell B (2001) Vitamin C and genomic stability. Mutation Research 475: 29–35. Institute of Medicine (2000) Dietary Reference Intakes for Vitamin C, Vitamin E Selenium and Carotenoids. Washington, DC: National Academy Press. Khaw KT, Bingham S, Welch A, et al. (2001) Relation between plasma ascorbic acid and mortality in men and women in EPIC-Norfolk prospective study: A prospective population study. Lancet 357: 657–663. Lee KW, Lee HJ, Surh Y-J, and Lee CY (2003) Vitamin C and cancer prevention. American Journal of Clinical Nutrition 78: 1074–1078. Loria CM, Klag MJ, Caulfield LE, and Whelton PK (2000) Vitamin C status and mortality in US adults. American Journal of Clinical Nutrition 72: 139–145. Packer L and Fuchs J (1997) Vitamin C in Health and Disease. New York: Marcel Dekker, Inc. Rumsey SC and Levine M (1998) Absorption, transport and disposition of ascorbic acid in humans. Journal of Nutritional Biochemistry 9: 116–130. Smirnoff N (2000) Ascorbic acid: Metabolism and functions of a multi-facetted molecule. Current Opinion in Plant Biology 3: 229–235.
Vitamin B12 D Nohr and H K Biesalski, Universita¨t Hohenheim, Stuttgart, Germany E I Back, Novartis Pharma GmbH, Nu¨rnberg, Germany ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by H. K. Biesalski and E. I. Back, Volume 4, pp 2721–2726, ª 2002, Elsevier Ltd.
Cobalamin or Vitamin B12 The terms vitamin B12 and cobalamin, represent a group of several cobalt-containing corroids. A corrin ring with four reduced pyrrole rings and cobalt as central atom, a nucleotide-like compound, and an additional variable compound are their common features (Figure 1). B12 is the only vitamin containing a metal ion. In biological systems, hydroxo-, aquo-, methyl-, and 59-deoxyadenosylcobalamin occur, while cyanocobalamin is a decomposition product which, however, is used for therapeutic purposes as also is hydroxycobalamin. Only microorganisms are able to synthesize vitamin B12. Thus, some animal species have sufficient supply from their intestinal microorganisms. In humans, however, the synthesizing organisms are localized in the colonic part of the intestine which is too distal from the small intestine (ileum), where vitamin B12 must be taken up. Consequently, humans obtain B12 exclusively from their diet and only animal-derived foods contain sufficient amounts of vitamin B12 (Tables 1 and 2). Another prerequisite for the uptake of vitamin B12 is an intrinsic factor which is secreted from gastric parietal cells and facilitates ileal uptake of cobalamin. While storage has only minor effects on the concentration of cobalamin in milk (30–40% in sterilized milk after 90 days at room temperature) and radiation also has small effects, heat destruction plays a major role. Losses in cow milk caused by heat treatment are, sterilization: 20–100%; evaporation: 50%; boiling: 20%; pasteurization: 4 months) Breast feeding
0.1 (estimated) 0.3 0.4 0.5 0.7 1 1.4 1.6 1.5 1.5 1.4
Female
1.2 1.2 1.2 1.2 1.9 1.9
From DGE (Deutsche Gesellschaft fu¨r Erna¨hrung) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/ modules.php?name¼St&file¼w_referenzwerte (accessed April 2010).
in plasma • PLP 4-Pyridoxic in 24 h urine (short-term) • Assessment ofacidtheexcretion activation • transaminase (long term) coefficient of erythrocyte PN is highly toxic when taken over an extended period of time. A dose of 150 mg day–1 over several months leads to (reversible) peripheral neuropathy with dysreflexia and insensibility. However, therapies with megadoses of vitamin B6 showed high positive potential in the treatment of PN dependency (2–11 mg day–1), cystathioninuria (400 mg day–1), homocystinuria (250–1250 mg day–1), primary oxalosis type I (‘spine syndrome’, 150 mg day–1), and also isoniazid intoxication (1 g PN g–1 isoniazid). In some cases, beneficial effects have been described for carpal tunnel syndrome, premenstrual syndrome, and rheumatic diseases, although for the latter it is still unclear. See also: Vitamins: Folates; Vitamin B12.
Vitamin B6 Deficiencies Further Reading The vitamin is essential for humans, most animals, and some microorganisms. Some recommendations concerning uptake relate the concentration of B6 to protein uptake; the German Society for Nutrition, for example, recommends a minimum intake as shown in Table 3 based on a quotient of 20 mg g–1 recommended protein uptake. Bioavailability is negatively correlated with the amount of glycosylated forms of vitamin B6 in the respective food. The glycosylated form mainly appears in plant-derived foods but not animal-derived foods. As an estimation, the bioavailability of vitamin B6 in a ‘normal, mixed diet’ is about 75%. A specific vitamin B6 deficiency in humans can hardly be detected, as the first symptoms resemble the symptoms of niacin and riboflavin deficiency (stomatitis, dermatitis like pellagra). Sometimes, in children, neurological problems occur, maybe due to changes in neurotransmitter metabolism (PLP functions as a coenzyme of an amino acid decarboxylase). Longer-lasting deficiency might lead to peripheral neuropathy (nerve demyelination and hypochromic anemia that cannot be cured by iron supplementation (vitamin B6 functions in heme synthesis)), and also the risk of dementia is recently under discussion. Some drugs, hydrazines, chelators, antibiotics, oral contraceptives, L-DOPA (L-3,4-dihydroxyphenylalanine), and alcohol, reduce vitamin B6 concentration, especially when they are taken over an extended period of time (then vitamin B6 status should be monitored.
Arkaravichien T, Sattayasai N, Daduang S, and Sattayasai J (2003) Dose-dependent effects of glutamate in pyridoxine-induced neuropathy. Food and Chemical Toxicology 41: 1375–1380. Aufiero E, Stitik TP, Foye PM, and Chen B (2004) Pyridoxine hydrochloride treatment of carpal tunnel syndrome: A review. Nutrition Reviews 62: 96–104. Balk EM, Raman G, Tatsioni A, Chung M, Lau J, and Rosenberg IH (2007) Vitamin B6, B12, and folic acid supplementation and cognitive function: A systematic review of randomized trials. Archives of Internal Medicine 167: 21–30. Bolander FF (2006) Vitamins: Not just for enzymes. Current Opinion in Investigational Drugs 7: 912–915. Carrero JJ, Fonolla´ J, Marti JL, Jime´nez J, Boza JJ, and Lo´pez-Huertas E (2007) Intake of fish-oil, oleic acid, folic acid, and vitamins B6 and E for 1 year decreases plasma C-reactive protein and reduces coronary heart disease risk factors in male patients in a cardiac rehabilitation program. The Journal of Nutrition 137: 384–390. Cheng CH, Chang SJ, Lee BJ, Lin KL, and Huang YC (2006) Vitamin B6 supplementation increases immune responses in critically ill patients. European Journal of Clinical Nutrition 60: 1207–1213. Chiang EP, Selhub J, Bagley PJ, Dallal G, and Roubenoff R (2005) Pyridoxine supplementation corrects vitamin B6 deficiency but does not improve inflammation in patients with rheumatoid arthritis. Arthritis Research & Therapy 7: R1404–R1411. Clarke R, Lewington S, Sherliker P, and Armitage J (2007) Effects of B-vitamins on plasma homocysteine concentrations and on risk of cardiovascular disease and dementia. Current Opinion in Clinical Nutrition and Metabolic Care 10: 32–39. Clayton PT (2006) B6-responsive disorders: A model of vitamin dependency. Journal of Inherited Metabolic Disease 29: 317–326. Cook S and Hess OM (2005) Homocysteine and B vitamins. Handbook of Experimental Pharmacology 170: 325–338. DGE (Deutsche Gesellschaft fu¨r Erna¨hrung) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/ modules.php?name¼St&file¼w_referenzwerte (accessed April 2010). Fabian E, Majchrzak D, Dieminger B, Meyer E, and Elmadfa I (2008) Influence of probiotic and conventional yoghurt on the status of vitamins B1, B2 and B6 in young healthy women. Annals of Nutrition & Metabolism 52: 29–36.
700 Vitamins | Vitamin B6 Ganji V and Kafai MR (2004) Frequent consumption of milk, yogurt, cold breakfast cereals, peppers, and cruciferous vegetables and intakes of dietary folate and riboflavin but not vitamins B-12 and B -6 are inversely associated with serum total homocysteine concentrations in the US population. The American Journal of Clinical Nutrition 80: 1500–1507. Herrmann W, Herrmann M, and Obeid R (2007) Hyperhomocysteinaemia: A critical review of old and new aspects. Current Drug Metabolism 8: 17–31.
Smith AD (2008) The worldwide challenge of the dementias: A role for B vitamins and homocysteine? Food and Nutrition Bulletin 29: S143–S172. Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart, Germany: Medpharm Scientific Publ. Thaver D, Saeed MA, and Bhutta ZA (2006) Pyridoxine (vitamin B6) supplementation in pregnancy. Cochrane Database of Systematic Reviews 19: CD000179.
Thiamine D Nohr and H K Biesalski, Universita¨t Hohenheim, Stuttgart, Germany E I Back, Novartis Pharma GmbH, Nu¨rnberg, Germany ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by H. K. Biesalski and E. I. Back, Volume 4, pp 2690–2694, ª 2002, Elsevier Ltd.
Introduction Thiamine or vitamin B1 is a water-soluble vitamin and is unstable and loses its biological activity in alkaline solutions (pH >7) as well as in the presence of oxidants and radiation. The chemical name of thiamine is 3-[(4-amino-2-methyl5-pyrimidinyl)methyl]- 5-(2-hydroxyethyl)-4-methylthiazolium; its coenzyme form is thiamine pyrophosphate (TPP; Figure 1). In pharmaceutical and other preparations, thiamine is used in the form of water-soluble thiazolium salts (thiamine chloride hydrochloride, thiamine mononitrate); synthetic lipophilic derivatives (allithiamins) also exist. The latter can pass through biological membranes more easily and in an almost dose-related manner, thus offering a possibility to develop thiamine stores by supplementation, which are normally low and last for only 4–10 days. In the presence of oxidizing agents and in strongly alkaline solutions, thiamine is converted into thiochrome, a fluorescent substance used to determine the thiamine content of feeds, foods, or pharmaceutical preparations.
Functions of Thiamine A number of enzymes (pyruvate dehydrogenase complex; -ketoglutarate dehydrogenase complex; branched-chain -keto acid dehydrogenase complex) involved in intermediary metabolism and playing a role in the oxidative decarboxylation of -keto acids require TPP as a coenzyme. Thus, metabolites from carbohydrate metabolism and keto analogues from amino and fatty acid metabolism are made available for energy metabolism. In addition, a TPP-dependent transketolase is involved in the formation of NADPH and pentose in the pentose phosphate pathway. Both metabolites play important roles in several other synthetic pathways. There are hints that the above-mentioned enzymes are also involved in neural functions; however, the exact mechanisms of action need to be elucidated further. Interestingly,
a decrease of glutamate uptake in the prefrontal cortex of thiamine-deficient mice is described.
Sources of Thiamine Tables 1 and 2 show the thiamine content of various foods. Table 2 focuses on dairy products, including milk from different species, that are consumed by humans. It has to be taken into account that heat treatment, as well as storage conditions, can lead to losses of the thiamine content of the foods: pasteurization 3–4% • low boiling 4–8% • spray-drying • roller-drying 10% • pasteurization15% • condensed milk9–20% 3–75% • sterilization 20–45% • evaporated milk 20–60% • Fresh milk in dark bottles loses 24% of its initial thiamine content on storage for 24 h at 4 C, 14% on storage at 12 C, and 16% on storage at 20 C. Evaporated milk loses 15–50% over periods >12 months; spray-dried whole milk shows no changes up to 12 months. Thiamine is lost during cheese manufacture mainly during drawing of the first whey; no significant changes occur during maturation. UV light-induced inactivation of thiamine can, under certain conditions (cheese, fresh milk), be counterbalanced by thiamine-synthesizing microorganisms. Modern highpressure-assisted thermal sterilization methods result in almost stable vitamins, although the decay in model solutions (acetate-buffered, pH 5.5) was about 30 times higher than in minced pork. Thus, a general deduction of the test results to routine food preparation needs further investigations. The recommended daily uptake of thiamine given by the DGE (German Nutrition Society) is shown in Table 3.
701
702 Vitamins | Thiamine
Figure 1 Structure of thiamine (left) and thiamine pyrophosphate (TPP, right). Table 1 Thiamine concentration in selected foods
Food
Concentration (g 100 g1)
Brewers’ yeast, dried Wheat germ Sunflower seed, dry Soybean, dry Pork Pea seed, dry Oat flakes Wheat, wholemeal flour Hazelnut Pig, kidney or liver Ox, kidney or liver Eel Potato
12 000 2000 1900 999 900 765 590 470 390 310–340 290–300 180 110
Data from Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart, Germany: Medpharm Scientific Publ.
Table 2 Thiamine concentration in dairy products and milk
Food Dried whole milk Condensed milk (min. 10% fat) Camembert (45% fat in dry matter) Cream cheese (min. 60% fat in dry matter) Quark/fresh cheese, from skim milk Skim milk Consumer milk (min. 3.5% fat) Sweet whey Yogurt (min. 3.5% fat) Buttermilk UHT milk Gouda Cottage cheese Cream (min. 30% fat) Sterilized milk Parmesan Milk from Buffalo Goat Sheep Donkey Cow Horse Human
Concentration (g 100 g1) 270 88 45 45 43 38 37 37 37 34 33 30 29 25 24 20 50 49 48 41 37 30 15
UHT, ultra-high temperature. Data from Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart, Germany: Medpharm Scientific Publ.
Table 3 Recommended daily uptake of thiamine Thiamine (mg day1) Age
Male
Sucklings 65 years Pregnant Breast feeding
1.3 1.2 1.1 1.0
Female
1.0 1.1 1.0 1.0 1.0 1.0 1.2 1.4
From DGE (Deutsche Gesellschaft fu¨r Erna¨hrung) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/ modules.php?name¼St&file¼w_referenzwerte (accessed April 2009).
Thiamine Deficiencies Because of the relatively small and short-lasting thiamine stores, marginal deficiencies are quite common, but early symptoms are rarely recognized. Symptoms of thiamine deficiency are cardiac failure, muscle weakness, peripheral and central neuropathy, and gastrointestinal malfunction. Reasons for deficiency besides a thiamine-free diet (e.g., parenteral nutrition) might be reduced absorption (gastrointestinal diseases), impaired transport, increased requirements (pregnancy, lactation, infancy, childhood, adolescence, increased physical activity, infections, trauma, surgery), or increased losses and impaired biosynthesis of TPP. Clinically manifest deficiency appears in several forms of an illness called beriberi, which is nowadays mostly a problem in some regions of Southeast Asia, mainly because of the consumption of thiamine-free rice or raw fish (which contains thiaminase) or chewing of betel nuts or fermented tea leaves (which contain ‘antithiaminic’ tannins). Another risk group is chronic alcoholics who often consume low-quality meals, have poor appetite,
Vitamins | Thiamine
and suffer from gastrointestinal problems and malabsorption. One can differentiate infantile beriberi (often lethal in sucklings fed by thiamine-deficient mothers) from two forms of adult beriberi: dry beriberi is characterized by peripheral neuropathy (‘burning feet syndrome’, exaggerated reflexes, diminished sensation, and weakness in all limbs, muscle pain, problems rising from squatting position, and, in severe cases, eventually seizures). Wet beriberi is characterized by cardiovascular symptoms (rapid heart rate, enlargement of the heart, edema, breathing problems, and ultimately congestive heart failure). ‘Cerebral’ beriberi mostly leads to Wernicke’s encephalopathy and Korsakoff’s psychosis, both together appearing as the Wernicke–Korsakoff syndrome, which is, however, not easily diagnosed but can be treated by thiamine supplementation.
Thiamine Supplementation For the therapeutic treatment of diseases of the central (CNS) and the peripheral nervous system (PNS) and of exhaustion and during cytostatic treatment, doses of 50–200 mg thiamine day1 are administered orally. Clinically manifest beriberi is treated by administering 50–100 mg day1 subcutaneously or intravenously for several days, followed by the same dose orally for several weeks. Other than single cases of anaphylactic shock after intravenous application, no side effects of higher doses of thiamine (e.g., up to 200 mg day1) are known.
See also: Vitamins: General Introduction.
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Further Reading Attard O, Dietemann JL, Diemunsch P, Pottecher T, Meyer A, and Calon BL (2006) Wernicke encephalopathy: A complication of parenteral nutrition diagnosed by magnetic resonance imaging. Anesthesiology 105: 847–848. Biesalski HK (2004) Vitamine. In: Biesalski HK, Fu¨rst P, Kasper H, Kluthe R, Po¨lert W, Puchstein C, and Sta¨helin HB (eds.) Erna¨hrungsmedizin, 3rd edn., pp. 111–158. Stuttgart, Germany: Thieme. Bitsch R (2002) Vitamin B1 (thiamin). In: Bieslaksi HK, Ko¨hrle J, and Schu¨mann K (eds.) Vitamine, Spurenelemente und Mineralstoffe, pp. 70–74. Stuttgart, Germany: Thieme. Bolander FF (2006) Vitamins: Not just for enzymes. Current Opinion in Investigational Drugs 7: 912–915. DGE (Deutsche Gesellschaft fu¨ r Erna¨ hrung) (2007) Die Referenzwerte fu¨ r die Na¨ hrstoffzufuhr. http://www.dge.de/ modules.php?name¼St&file¼w_referenzwerte (accessed April 2009). Fabian E, Majchrzak D, Dieminger B, Meyer E, and Elmadfa I (2008) Influence of probiotic and conventional yoghurt on the status of vitamins B1, B2 and B6 in young healthy women. Annals of Nutrition & Metabolism 52: 29–36. Harper C (2006) Thiamine (vitamin B1) deficiency and associated brain damage is still common throughout the world and prevention is simple and safe! European Journal of Neurology 13: 1078–1082. Heath ML and Sidbury R (2006) Cutaneous manifestations of nutritional deficiency. Current Opinion in Pediatrics 18: 417–422. Liepa GU, Ireton-Jones C, Basu H, and Baxter CR (2007) B vitamins and wound healing. In: Molnar JA (ed.) Nutrition and Wound Healing, pp. 99–119. Boca Raton, FL: CRC Press. Lonsdale A (2006) A review of the biochemistry, metabolism and clinical benefits of thiamin(e) and its derivatives. Evidence-Based Complementary and Alternative Medicine 3: 49–59. Meier S and Daeppen JB (2005) Prevalence, prophylaxis and treatment of Wernicke encephalopathy. Thiamine, how much and how do we give it? Revue Me´dicale Suisse 1: 1740–1744. Nohr D (2009) Thiamin deficiency. In: Lang F (ed.) Encyclopedia of Molecular Mechanisms of Disease, 2nd edn., pp. 2044–2045. Berlin; Heidelberg, Germany: Springer (in press). Said HM and Mohammed ZM (2006) Intestinal absorption of water-soluble vitamins: An update. Current Opinion in Gastroenterology 22: 140–146. Smith AD (2006) Prevention of dementia: A role for B vitamins? Nutrition and Health 18: 225–226. Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart, Germany: Medpharm Scientific Publ.
Riboflavin D Nohr and H K Biesalski, Universita¨t Hohenheim, Stuttgart, Germany E I Back, Novartis Pharma GmbH, Nu¨rnberg, Germany ª 2011 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by H. K. Biesalski and E. I. Back, Volume 4, pp 2694–2699, ª 2002, Elsevier Ltd.
Riboflavin or Vitamin B2 The chemical name for riboflavin is 7,8-dimethyl-10-(19D-ribityl)isoalloxazine; riboflavin exists in an oxidized and a reduced form (Figure 1), from which two coenzymes are formed: flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD; Figure 2). The ending ‘flavin’ refers to its yellowish color (in Latin flavus means yellow). Free as well as protein-bound riboflavin occurs in the diet, and milk in general is the best source. In cow’s milk, the free form, with a higher bioavailability, is the major one (61% riboflavin, 26% FAD, 11% hydroxyethyl form, and others), whereas the protein-bound, and thus less bioavailable, form predominates in other foods. In human breast milk, approximately one- to two-thirds of riboflavin occurs as FAD. Riboflavin is very heat stable but it is extremely photosensitive. It is photodegraded to lumiflavin (under alkaline conditions) or lumichrome (under acidic conditions), both of which are biologically inactive. Concentrations are significantly reduced in high-pressure low-temperature treated milk as compared to raw milk. UV light excites riboflavin to a high degree of natural fluorescence, which is used for its detection and determination in yogurt or non-fat dry milk.
Functions of Riboflavin Riboflavin-dependent enzymes are called flavoproteins or flavoenzymes, because of their yellowish appearance. They catalyze hydroxylations, oxidative decarboxylations, dioxygenations, and reduction of oxygen to hydrogen peroxide, serving as electron carriers, mediators of electron transfer from pyridine nucleotides to cytochrome c or to other one-electron acceptors, and as catalysts of electron transfer from a metabolite to molecular oxygen. The two flavoenzymes, FMN and FAD, play major roles in the metabolism of glucose, fatty acids, amino acids, purines, drugs and steroids, folic acid, pyridoxine, vitamin K, niacin, and vitamin D.
704
The FAD-dependent enzyme, glutathione reductase, plays a major role in the antioxidant system by restoring reduced glutathione (GSH) from oxidized glutathione (GSSH). GSH is important in protecting lipids from peroxidation and in stabilizing the structure and function of red blood cells; it is the most important antioxidant in erythrocytes and in keeping lens proteins in solution (thus preventing cataracts). The formation of FMN and FAD is ATP dependent and takes place mainly in the liver, kidney, and heart. All enzymatic steps are under the control of thyroid hormones. riboflavin þ ATP ! r/FMN þ ADP • Flavokinase: FAD pyrophosphorylase: þ ATP ! /FAD þ PP • FAD þ apoenzyme/proteinFMN ! covalently bound flavins •
Sources of Riboflavin Tables 1 and 2 summarize dietary sources of riboflavin and its concentration, especially in the milk of various species and in dairy products. Heat treatment has only negligible effects on riboflavin concentrations, whereas exposure of milk to sunlight results in the loss of 20–80% of riboflavin. Thus, storage in dark bottles, light-tight wax cartons, or special polyethylene terephthalate (PET) bottles is recommended. Photo-degradation of riboflavin catalyzes photochemical oxidation and loss of ascorbic acid. Gamma radiation of 10 Gy destroys about 75% of riboflavin in liquid milk, whereas milk powder shows no losses even at higher doses. Storage influences riboflavin concentration as follows: condensed milk loses 28% (33%) of its initial riboflavin content when stored at 8–12 C for 2 years (10–15 C for 4 years), ice cream loses 5% when stored at –23 C for 7 months. No losses were found in fresh milk stored at 4–8 C for 24 h or in milk powder stored for 16 months. In cheese, most losses (66–88%) of the original riboflavin content of the milk appear to occur during whey
Vitamins | Riboflavin Table 2 Riboflavin in milk, dairy products, and cheese
5′ CH2OH
5′ CH2OH HO
HO Ribitol
OH
OH HO
HO
CH2
CH2 H3C
N
H3 C
N
N
O
H3C
N
H3C
N H
NH
H N
O NH
O
O 7,8-Dimethylisoaloxazine
Figure 1 Structures of oxidized (flavoquinone, left) and reduced (flavohydroquinone, right) forms of riboflavin (vitamin B2).
Adenosine(-5′)-diphosphate NH2 O 5′
CH2 O R
P
–
O
5′ CH2 O
O–
R
N
O
O
P O
P O CH2
O–
O–
O
HO
N
705
N N
OH
Figure 2 Structure of flavin mononucleotide (FMN, left) and flavin adenine dinucleotide (FAD, right). R: riboflavin.
Food
Concentration (g per 100 g)
Dried whole milk Parmigiano Camembert (45% fat in dry matter) Blue cheese (50% fat in dry matter) Condensed milk (min. 10% fat) Limburger (40% fat in dry matter) Quark/fresh cheese (from skim milk) Cream cheese (min. 60% fat in dry matter) Consumer milk (3.5% fat) UHT milk Yogurt (min. 3.5% fat) Skim milk Buttermilk Cream (min. 30% fat) Sweet whey Sterilized milk
1400 620 600 500 480 350 300 230 180 180 180 170 160 150 150 140
Milk from Sheep Cow Goat Buffalo Donkey Human
230 180 150 100 64 38
Reproduced with permission from Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart: Medpharm Scientific Publishers.
Table 1 Riboflavin concentration in food Food
Concentration (g per 100 g)
Brewers’ yeast Pig’s liver Ox liver Wheat germ Almonds Wheat bran Soybean, seed, dry Mushroom Egg Mackerel Eel Lentil, seed, dry Beef Pork Herring Maize
3800 3200 2900 720 620 510 460 436 408 360 320 262 260 230 220 200
Reproduced with prermission from Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart: Medpharm Scientific Publishers.
drainage, while ripening has almost no effects. However, in some cheese varieties, the concentration is higher in the outer layers due to microbial synthesis. High-pressure tests for thermal sterilization processes led to different results concerning the decay of the vitamin, depending on the matrix of the food tested.
Riboflavin Deficiency Riboflavin is essential for humans, animals, and some microorganisms. Among humans, seniors and adolescents seem to be at particular risk of deficiency; the recommended uptake is given in Table 3. In some cases, recommended Table 3 Recommended daily uptake of riboflavin Riboflavin (mg day–1) Age
Male
Sucklings 65 years Pregnant Breast feeding
0.3 0.4 0.7 0.9 1.1 1.4 1.6 1.5 1.4 1.3 1.2
Female
1.2 1.3 1.2 1.2 1.2 1.2 1.5 1.6
Reproduced with permission from Deutsche Gesellschaft fu¨r Erna¨hrung (DGE) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http:// www.dge.de/modules.php?name¼St&file¼w_referenzwerte (accessed April 2009).
706 Vitamins | Riboflavin
uptake is related to energy intake, and 0.6 mg riboflavin per 1000 kcal is considered adequate. Milk and milk products (without butter) can contribute about 30% of the total riboflavin supply. A major portion of riboflavin is bound to proteins and these flavoproteins have to be hydrolyzed before absorption by specialized transporters in the upper gastrointestinal tract. The amount that can be stored depends on the availability of proteins providing binding sites. Although a limited uptake makes sense in preventing accumulation in tissues, it increases the body’s dependence on dietary supply. Under normal conditions, riboflavin stores last for 2–6 weeks, but in cases of protein deficiency, they last significantly shorter. Symptoms of a marginal deficiency are often nonspecific: weakness, fatigue, mouth pain, glossitis, stomatitis, burning and itching of the eyes, and personality changes. Signs of increased deficiency are cheilosis; angular stomatitis; seborrheic dermatitis at the mouth, nasolabial sulcus, and ears (later extending to the trunk and extremities); desquamative dermatitis with itching in genital regions; opacity of the cornea; cataract; and brain dysfunction. The major reasons for riboflavin deficiency are dietary intake by seniors and adolescents • Insufficient (especially girls) abnormalities, insufficient adrenal and thyr• Endocrine oid hormones (psychotropic, anti-depressant, cancer therapeu• Drugs tics, anti-malarial) intake interfering with the digestion and • Alcohol absorption of food flavins that chelate or form complexes with riboflavin • Agents or FMN, affecting their bioavailability: copper, zinc, iron, caffeine, theophylline, saccharine, nicotinamide, ascorbic acid, tryptophan, urea. As riboflavin (via FAD-dependent glutathione reductase) is involved in antioxidant mechanisms, riboflavin deficiency may considerably affect erythrocyte metabolism. However, several studies have reported protective effects of a deficiency against malaria infection. A study in the United States showed that the uptake of yogurt, milk, cereals, and also riboflavin was inversely correlated with homocysteine levels in plasma, which, in turn, seem to be positively correlated with a higher risk of developing atherosclerosis. Assessment of the riboflavin (mainly by HPLC methods) status uses the following parameters: glutathione reductase activity coefficient, • Erythrocyte Excretion in urine (mg g creatinine to assess • short-term effects), and Riboflavin in erythrocytes (mg g hemoglobin). • –1
–1
Concerning supplementation, no case of intoxication has been described. Thus, riboflavin is regarded as safe even at high doses. Supplements are usually given to reverse deficiency symptoms or to support high-risk groups: intake of drugs (e.g., anti-depressants, oral • Regular contraceptive) • Malnutrition after trauma • Patients Malabsorption • Chronic alcoholics • Hyperbilirubinemia can be treated much quicker by phototherapy when 0.5 mg riboflavin per kg of bodyweight is given. Finally, persons with congenital methemoglobinemia might benefit from 20–40 mg day–1. See also: Milk Proteins: Minor Proteins, Bovine Serum Albumin, Vitamin-Binding Proteins. Vitamins: General Introduction.
Further Reading Ahmad I, Fasihullah Q, and Vaid FH (2006) Effect of light intensity and wavelengths on photodegradation reactions of riboflavin in aqueous solution. Journal of Photochemistry and Photobiology. B, Biology 82: 21–27. Biesalski HK (2004) Vitamine. In: Biesalski HK, Fu¨rst P, Kasper H et al. (eds.) Erna¨hrungsmedizin, 3rd edn., pp. 111–158. Stuttgart: Thieme. Bitsch R (2002) Vitamin B2 (riboflavin). In: Bieslaksi HK, Ko¨hrle J, and Schu¨mann K (eds.) Vitamine, Spurenelemente und Mineralstoffe, pp. 95–103. Stuttgart: Thieme. Bolander FF (2006) Vitamins: Not just for enzymes. Current Opinion in Investigational Drugs 7: 912–915. Deutsche Gesellschaft fu¨r Erna¨hrung (DGE) (2007) Die Referenzwerte fu¨r die Na¨hrstoffzufuhr. http://www.dge.de/modules.php?name¼St&file¼ w_referenzwerte (accessed April 2009). Fabian E, Majchrzak D, Dieminger B, Meyer E, and Elmadfa I (2008) Influence of probiotic and conventional yoghurt on the status of vitamins B1, B2 and B6 in young healthy women. Annals of Nutrition & Metabolism 52: 29–36. Ganji V and Kafai MR (2004) Frequent consumption of milk, yogurt, cold breakfast cereals, peppers, and cruciferous vegetables and intakes of dietary folate and riboflavin but not vitamins B-12 and B-6 are inversely associated with serum total homocysteine concentrations in the US population. The American Journal of Clinical Nutrition 80: 1500–1507. LeBlanc JG, Burgess C, Sesma F, Savoy de Giori G, Vansinderen D, and Powers HJ (2003) Riboflavin (vitamin B2) and health. The American Journal of Clinical Nutrition 77: 1352–1360. LeBlanc JG, Rutten G, Bruinenberg P, Sesma F, de Giori GS, and Smid EJ (2006) A novel dairy product fermented with Propionibacterium freudenreichii improves the riboflavin status of deficient rats. Nutrition 22: 645–651. LeBlanc JG, Sesma F, de Giori G, and vanSinderen D (2005) Ingestion of milk fermented by genetically modified Lactococcus lactis improves the riboflavin status of deficient rats. Journal of Dairy Science 88: 3435–3442. Said HM and Mohammed ZM (2006) Intestinal absorption of watersoluble vitamins: An update. Current Opinion in Gastroenterology 22: 140–146. Souci SW, Fachmann W, and Kraut H (2008) Food Composition and Nutrition Tables, 7th edn. Stuttgart: Medpharm Scientific Publishers. Woolf K and Manore MM (2006) B-vitamins and exercise: Does exercise alter requirements? International Journal of Sport Nutrition and Exercise Metabolism 16: 453–484.
W WATER IN DAIRY PRODUCTS
Contents Water in Dairy Products: Significance Analysis and Measurement of Water Activity
Water in Dairy Products: Significance Y H Roos, University College Cork, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Properties of Water and Water Activity Water is a well-characterized compound that exhibits physical and chemical properties that differ significantly from those of other compounds with a corresponding molecular structure. These include relatively high phase transition temperatures, heats of changes in phase, and other thermodynamic quantities. The latent heat of melting of ice at 0 C, Hm, is 334 J g1 (6.012 kJ mol1), the latent heat of vaporization of water, Hv, at 100 C is 2255 J g1 (40.63 kJ mol1), and the heat of sublimation of ice at 0 C is 2826 J g1 (50.91 kJ mol1). The solid, liquid, and gaseous states of water may coexist in equilibrium at the triple point, which is located at 0.0099 C and a pressure of 610.4 Pa. Water may solidify in various forms of ice depending on the pressure. Water may also solidify as an amorphous glass. Vapor-deposited glassy water undergoes the glass transition with onset temperature, Tg, at 138 C. The fundamental physical properties of water in dairy products are the main determinants of energy and temperature requirements as well as economics of all heat treatments and the evaporation and dehydration processes, in particular, in the dairy industry. The purest forms of water in dairy products are crystalline ice and gaseous water vapor. The vapor pressure of
water is lower in solutions as well as in dairy products than the vapor pressure of pure water at the same temperature. In ideal dilute solutions, vapor pressure is defined by Raoult’s law: p ¼ xp0
½1
where p is the vapor pressure of water in the solution, p0 is the vapor pressure of pure water at the same temperature, and x is the mole fraction of water. Raoult’s law defines that water in a solute–solvent system has a lower vapor pressure than that of pure water. This results in a lower freezing temperature and a higher boiling temperature than those of pure water at the same pressure. Real solutions, such as milk, do not obey Raoult’s law, but an ‘effective’ mole fraction for the solutes can be defined. The effective mole fraction of water is often referred to as water activity, aw. Water activity is equal to the equilibrium relative vapor pressure (RVP) of water in the surrounding atmosphere, i.e., aw as the ratio of the vapor pressure in a solution to that of pure water at the same temperature: aw ¼
p p0
½2
Therefore, the equilibrium or steady-state water activity is related to equilibrium relative humidity (ERH)
707
708 Water in Dairy Products | Water in Dairy Products: Significance
corresponding to the equilibrium RVP of the surrounding atmosphere by aw ¼
ERH 100
½3
Although water activity is a measure of water availability, it should be emphasized that water activity is a temperature-dependent property of water in a material, such as food. In most dairy products, temperature and pH are more important factors that control rates of deteriorative changes and the growth of microorganisms than water activity. This is because the average water content of milk is very high, 87.1%, and milk contains only about 8.9% of non-fat solids. The water activity of milk is, therefore, very high, 0.993. The pH of milk is close to neutral, about 6.7, which allows the growth of almost all microorganisms. Thus, in high-water, nonfermented dairy products, temperature is the main variable controlling microbial growth. In fermented milk products and in the water phase of butter, the pH is reduced, for example, to about 4.6 in ripened cream butter, which significantly reduces the growth of spoilage microorganisms. Water activity is, however, an important factor controlling the microbial flora in ripening cheese, and quality changes of some cheeses and dairy powders during storage. The reduction of water activity in these products affects the predominant microbial culture, and, in some cases, an increase in water activity improves shelf life due to reduced availability of water for microbial growth. The water activity of evaporated milk is 0.986 and a relatively rapid removal of water by dehydration or freezing results in supersaturation of soluble compounds. Evaporation of water also reduces the pH of milk to about pH 6, depending on the extent of concentration.
and the surrounding atmosphere is reached. The sorption properties are strongly dependent on temperature. Moreover, sorption properties of low-water solids and desorption of high-water solids may differ resulting in water sorption hysteresis. Sorption isotherms, which show the water content as a function of water activity at a constant temperature, are useful tools in describing the relationships between water content and steady-state RVP. Typical sorption isotherms of dairy powders, such as that of skim milk solids in Figure 1, with amorphous components, and milk and whey proteins are sigmoid curves and exhibit hysteresis. However, the amorphous lactose in dairy powders is unstable and it tends to crystallize during the storage of powder above a critical water content or water activity. Such crystallization is observed from time-dependent loss of sorbed water and a break in the sorption isotherm. The water sorption properties of the nonhygroscopic, crystalline lactose differ significantly from the water sorption properties of amorphous lactose. Therefore, crystallinity and crystalline forms of lactose may greatly affect sorption properties and one of the most significant differences between dairy powders with glassy or precrystallized lactose is the water sorption behavior. Amorphous lactose is very hygroscopic and it may sorb high amounts of water at low relative humidities. Crystalline lactose shows little sorption of water at low humidities and its water sorption becomes significant only at the higher relative humidities as a result of partial solubilization. In addition, differences in salt content may affect water sorption; for example, the presence of salts may increase water sorption by cheese and milk proteins.
Water Sorption Water sorption characteristics, as well as most other interactions of solids with water, are defined by the composition of the non-fat solids of dairy products. The water sorption properties are affected mainly by the component carbohydrates and proteins, which represent most of the non-fat fraction of milk solids, as well as by the physical state. The sorption properties may also be affected by time-dependent phenomena as a result of structural transformations and solute crystallization. Water sorption in low-water dairy products results from the difference between the vapor pressure of water in the material and the vapor pressure of water in the surrounding atmosphere. Water sorption occurs when the solids are exposed to conditions where the vapor pressure of water is higher than that within the solids. Therefore, the solids may sorb water until an equilibrium vapor pressure within the food
Figure 1 Sorption isotherm of skim milk solids (___). The break in the sorption isotherm resulting from crystallization of amorphous lactose is shown schematically (...).
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Phase and State Transitions Water-soluble milk solids often form amorphous, supercooled liquids or glasses as a result of dehydration or freeze concentration, for example in dairy powders and frozen desserts. The dominant component in defining the physical state is lactose. The formation of the non-crystalline, amorphous state of lactose results either from the rapid removal of solvent water by dehydration or from freeze concentration in freezing of water. In the amorphous solids, water behaves in a manner similar to plasticizers in synthetic polymers. Water plasticization is observed from a softening of the amorphous material, which is accompanied by increasing rates of quality changes. Plasticization may also result from an increase in temperature, or an increase in both temperature and water content. At a sufficient level of plasticization by temperature or water, the amorphous solids exhibit the glass transition. The glass transition occurs over a temperature or water content (water activity) range, and it can be observed from changes in heat capacity, dielectric properties, various mechanical properties, volume, and molecular mobility. The effect of water on the physical state of milk solids can be observed from decreasing glass transition with increasing water content (Figure 2) and structural changes that occur above a critical temperature, water activity, or water content, as the material suffers the glass transition. The temperature–water combinations that support the various states or that result in state or phase transitions of amorphous solids and freeze-concentrated solutions can be described using state diagrams. State diagrams are simplified phase diagrams that describe the concentration dependence of the glass transition of solutes and relationships between ice formation and solute concentration at low temperatures. State diagrams are useful in the characterization of the physical state and physical properties of milk solids at various temperatures
Figure 3 State diagram of lactose showing the decrease of the glass transition temperature, Tg, with increasing water content (___), the glass transition temperature of maximally freezeconcentrated lactose solutions, T9g, and onset temperature for ice melting in the maximally freeze-concentrated state, T9m. C9g shows lactose concentration in the maximally freezeconcentrated, unfrozen solution. The equilibrium ice melting temperature, Tm, curve is shown schematically (---).
and water contents. The state diagram, as shown for lactose in Figure 3, shows the glass transition of the solids and the decrease in the glass transition temperature, Tg, with increasing water content. At sufficiently high water contents, ice formation before vitrification cannot be avoided, separating ice from the material with concurrent freeze concentration of solutes in an unfrozen water-solute phase. Therefore, the state diagrams often show the effect of ice formation on the phase and state behavior. A maximally freezeconcentrated solute has the glass transition at T 9g, which corresponds to a solute concentration of Cg9. Moreover, a full state diagram shows the onset temperature for ice melting in the maximally freeze-concentrated solution, Tm9, equilibrium ice melting temperature, Tm, curve, and the solubility curve. The solute concentration of maximally freeze-concentrated solute matrices, including non-fat milk solids, has been found to be about 80% (w/w).
Water in Milk Solids and Dairy Powders Stickiness and Caking
Figure 2 Glass transition temperature, Tg, of skim milk solids as a function of water content.
Various time-dependent structural transformations or changes in mechanical properties may occur in dairy powders at temperatures or water contents resulting in the glass transition. These transformations include stickiness and caking of powders, plating of particles on amorphous granules, and structural collapse of dehydrated structures, which are related to a rapid
710 Water in Dairy Products | Water in Dairy Products: Significance
decrease in viscosity and increase in flow above the glass transition. The main cause of stickiness is water or thermal plasticization of particle surfaces, which allows a sufficient decrease of surface viscosity for adhesion. Since viscosity is extremely high in the glassy state, the contact time must be very long for the occurrence of stickiness. A dramatic decrease in viscosity above Tg reduces the contact time and causes stickiness that can be related to the timescale of observation. A contact time of 1–10 s is sufficient at a surface viscosity less than 106–108 Pa s to cause stickiness. The decrease in viscosity is orders of magnitude over a fairly narrow water activity range, which results from the transformation of the solid material into the free-flowing liquid state. Obviously, water activity or storage relative humidity is often a more important indicator of stability than water content. The most common caking mechanism in food powders is plasticization due to water sorption and subsequent interparticle fusion. Caking of amorphous powders results from the change of the material from the glassy to the less viscous liquid-like state, which allows liquid flow and the formation of interparticle liquid bridges. The close relationships between collapse phenomena and glass transition suggest that the former occur above Tg with rates that are defined by the temperature difference, T–Tg. Agglomeration is an important step in achieving instant solubility properties for dairy powders. The process is based on controlled thermal and water treatment of fine particles. Common agglomeration methods are based on rewetting of fine powders or on agglomeration during and after spray drying using a straight-through process. The straight-through process is accomplished by producing plasticized particles with a temperature and water content that allow sufficient plasticization of particle surfaces and the formation of interparticle liquid bridges. The plasticized agglomerates enter a vibrating fluidized bed dryer, which completes dehydration and allows sufficient cooling of the product with concurrent solidification and vitrification of the particle surfaces. Agglomeration by both the rewetting and straight-through processes requires that amorphous solids are allowed to exist for a sufficiently long time in the plasticized state at appropriate temperature–humidity conditions allowing controlled stickiness. The proper agglomeration conditions are defined by the Tg of the particles and their water plasticization properties. Lactose Crystallization Drying of milk and whey by spray drying or roller drying produces a glass that is composed of a noncrystalline mixture of - and -lactose. The existence of lactose in
the glassy state and lactose crystallization due to increased molecular mobility have been confirmed by several studies, which have determined the physical state using polarized light microscopy, electron microscopy, differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) spectroscopy, and X-ray techniques. Crystallization of amorphous lactose in dairy powders may accompany the glass transition due to thermal or water plasticization and the increase in molecular mobility. Such crystallization is often detrimental to powder quality and it may significantly alter rehydration characteristics and reduce shelf life. In general, the crystallization time of amorphous sugars above Tg depends on temperature and water content. The crystallization behavior of amorphous lactose is also temperature dependent. An increase in storage temperature shifts the break in the sorption isotherm, indicating loss of sorbed water, to a lower relative humidity. Typical DSC heating scans of milk powders with amorphous lactose show a glass transition followed by a crystallization exotherm. Lactose crystallization during water sorption may occur either into the anhydrous -form or into -lactose monohydrate. The crystalline form produced depends on relative humidity and temperature. Lactose crystallization occurs into the anhydrous -form at relatively low water activities and the -lactose monohydrate form often crystallizes at water activities above 0.57 aw at room temperature. Crystallization into the anhydrous -lactose crystals releases water associated with the amorphous lactose while the -lactose monohydrate contains 5% water in the crystalline lactose phase. At higher temperatures, crystallization behavior may change according to the stability of the crystalline form at the crystallization temperature. The kinetics of crystallization at a constant temperature above glass transition can be related to water content and water activity, which define the T–Tg. Therefore, lactose crystallization may occur above a critical water content or water activity at a constant temperature with a rate defined by T–Tg. An increasing relative humidity increases water sorption by amorphous lactose, which causes water plasticization and increases the temperature difference, T–Tg. Combined Tg and water sorption data have suggested that a water content of 7.6 g per 100 g non-fat solids depresses the glass transition to room temperature. The corresponding water content for pure lactose is 6.8 g per 100 g solids and the critical aw is 0.37. This water activity or storage relative humidity of 37% RH is empirically known as critical to the stability of dairy powders, including milk and whey powders. Milk powders with lactose hydrolyzed to galactose and glucose show no break in the sorption isotherm. Both the water sorption and crystallization behavior of these sugars differ significantly from that of lactose, and the behavior
Water in Dairy Products | Water in Dairy Products: Significance
of the sugar mixture differs from that of typical skim milk solids. For example, component crystallization in the protein–glucose–galactose mixture is delayed in comparison to lactose crystallization in common dairy powders. Skim milk powders containing hydrolyzed lactose show a glass transition well below that of amorphous lactose. The glass transition of lactose-containing anhydrous skim milk powder has an onset at 92 C. Anhydrous powder produced from skim milk with lactose hydrolyzed to galactose and glucose has the glass transition onset at 49 C, and the critical water content that depresses the glass transition to room temperature is as low as 2.0 g per 100 g. The decrease in the Tg and the low critical water content are responsible for difficulties in the production of lactose-hydrolyzed dairy powders. These powders are extremely sensitive to temperature and water and they show hygroscopicity and stickiness during processing and storage. Chemical Stability Rates of deteriorative changes at reduced water activities are often related to water content and molecular mobility. Water as a plasticizer has a significant effect on molecular mobility above a critical, temperature-dependent water activity or water content. Molecular mobility is governed by the physical state and water plasticization of solids, and rates of several deteriorative changes are probably affected by diffusion. Diffusion below Tg may be assumed to be restricted, and a chemical reaction may become diffusion limited in a glassy matrix. Although diffusion of water occurs in glassy systems, the diffusion of larger reactant molecules is most likely to be affected by the glass transition. A significant increase in a reaction rate may occur as the material is transformed into the supercooled liquid state as a result of the glass transition. The temperature dependence of chemical changes often follows the Arrhenius equation, but kinetics may show deviations from Arrhenius kinetics at reduced water contents due to diffusional limitations. Non-enzymatic browning is one of the most important, water content-related deteriorative reactions in lowmoisture dairy foods. The non-enzymatic browning reaction is a series of condensations, but it may be considered as a bimolecular reaction. Browning rates in non-fat milk powder below the critical water activity (water content) are low, but the rate of browning is dependent on water content and it increases substantially above the critical water activity. In general, non-enzymatic browning occurs very slowly in glassy dairy products. However, above the glass transition, the rate of the reaction increases and a further increase often results from lactose crystallization and release of the sorbed water. Lactose crystallization must be prevented to avoid caking and impaired solubility. The loss of lysine is most rapid at
711
water activities that allow lactose crystallization. It should also be taken into account that crystallization of amorphous lactose in closed containers or packages is more detrimental as the water released from amorphous lactose remains in the system, accelerating deterioration of the noncrystalline solids. Diffusion of reactants is probably the main requirement for the occurrence and increasing rates of chemical reactions above some critical temperature or water content. In some cases, flow through pores may increase reaction rates. Such exceptions include oxidation of free fat in dairy powders. Oxygen may diffuse in the material and enhance oxidation on the pore membranes. Crystallization of lactose coincides with an increase in free fat, which presumably facilitates lipid oxidation. In powders containing amorphous lactose, milk fat is encapsulated within the amorphous lactose–protein matrix and it is protected from oxidation. Exceeding the Tg and subsequent crystallization releases the encapsulated lipids, which become accessible to atmospheric oxygen and undergo oxidation rapidly.
Frozen Dairy Products and Ice Cream The freezing temperature of milk, about 0.53 C, is relatively constant. At the freezing temperature, all ice formed at lower temperatures is melted into water. The initial ice formation in milk, dairy products, and in foods, in general, requires supercooling to below the equilibrium melting temperature and it is followed by further crystallization of water as the temperature is decreased. Freezing behavior of water, for example, in ice cream is significantly affected by the component compounds, and by sugars in particular. The main component affecting freezing behavior is lactose. Ice formation in a lactose solution, provided that no lactose crystallization is taking place, occurs at temperatures above 30 C. At 30 C, the maximum ice formation in the solution can be achieved and a highly viscous, freeze-concentrated lactose solution with approximately 80% lactose and 20% unfrozen water remains unfrozen, as described by the state diagram. During further cooling, this unfrozen solution suffers the glass transition. Such nonequilibrium ice formation is a typical phenomenon of carbohydrate solutions and probably the most common form of ice formation in frozen foods, including frozen dairy products. The viscosity of a freeze-concentrated solute phase is an important factor that may affect time-dependent crystallization phenomena, ice formation and recrystallization, and material properties. At a sufficiently low temperature, the viscosity of a freeze-concentrated solute matrix becomes high enough to retard diffusion and delay ice formation. The ice formation in real time ceases at the T 9g, since the high viscosity of the freeze
712 Water in Dairy Products | Water in Dairy Products: Significance
concentrated solute matrix prevents diffusion of water molecules to the surface of ice crystal lattice and crystal growth. Ice formation and the extent of freeze concentration are dependent on temperature according to the melting temperature depression of water caused by the solute phase. Maximum freeze concentration may occur at temperatures slightly below the onset temperature of ice melting, T 9m, in the maximally freeze-concentrated material. The size of ice crystals that are formed during freezing depends on the freezing method and freezing rate. Rapid freezing at a low temperature produces a large number of small ice crystals, while slow freezing at a higher temperature results in the formation of relatively few large ice crystals. The ice crystals, which form during freezing, are not stable, and recrystallization is common at typical storage temperatures of frozen dairy products. Recrystallization is a temperature-dependent process, which is enhanced by temperature fluctuations. Recrystallization with a decrease in the number of crystals and an increase in the average crystal size is referred to as Ostwald ripening. Recrystallization by fusion of smaller crystals resulting in the formation of large ice crystals is also an important recrystallization mechanism in ice cream. Melt–refreeze crystallization, which involves melting of ice and refreezing of unfrozen water, may occur under fluctuating temperatures, especially at relatively high temperatures. An average ice crystal size of 40 mm with a distance of 6–8 mm between the crystals is acceptable. The critical size, which produces a grainy texture, is 40–55 mm. Recrystallization of ice in ice cream and other products that are consumed in the frozen state produces a coarse, icy, undesirable texture. In addition, solute crystallization in freeze-concentrated products can be retarded by the use of sugar blends and syrups. Evaluation of kinetic data on ice recrystallization should consider the effect of ice melting above T 9m. The viscosity of the unfrozen matrix is increased by stabilizers, which decrease the rate of recrystallization. Recrystallization of ice, as well as lactose crystallization during frozen storage, can be reduced by using hydrocolloids, such as carrageenans, guar gum, or locust bean gum, as stabilizers. Polysaccharide stabilizers do not significantly alter the T 9g of ice cream mixes, but ice crystal growth in stabilized ice cream above T 9g is a function of kinetic properties of the unfrozen solute matrix and the mobility of water within the unfrozen matrix. An increase in the amount of unfrozen water increases the recrystallization rate, but stabilizers reduce the recrystallization rate.
Water and Microbiological Stability Microbial growth requires a minimum amount of water in an environment supporting the growth of microorganisms. In dairy products, the effect of water
on the growth of microorganisms is probably most important in the ripening, texture, and quality of cheeses. Water availability may also be an important factor in controlling mold growth in low-fat dairy spreads and butter. Water activities of milk products vary widely, from 0.1 to 0.3 for dried dairy products to above 0.99 for liquid milk and whey. Sweetened condensed milk with 0.77–0.85 aw has an intermediate water activity, but most other dairy foods have high water activities supporting the growth of bacteria and other microorganisms. The minimum requirement for microbial growth is aw 0.62, which allows the growth of xerophilic yeasts. An increasing aw allows the growth of molds, other yeasts, and finally bacteria at high water activities. The most important water activity value for the safety of food materials is 0.86, which is the limit for the growth of Staphylococcus aureus (Table 1). The water activity of various cheeses and processed cheeses varies between 0.86 and 0.99 (Table 2). There are also critical aw values for the multiplication of bacteria used in cheese manufacture. For example, propionibacteria, which are responsible for eye formation in Swiss cheese, are very Table 1 Minimum water activities (aw) for the growth of selected pathogenic bacteria in dairy products Pathogen
Minimum aw
Bacillus cereus Campylobacter jejuni Clostridium perfringens Escherichia coli Listeria monocytogenes Salmonella spp. Shigella spp. Staphylococcus aureus Vibrio parahaemolyticus Yersinia enterocolitica
0.930 0.990 0.945 0.935 0.920 0.940 0.960 0.860 0.936 0.960
Table 2 Typical water activity (aw) of common cheeses at 25 C Cheese type
Water activity
Appenzeller Brie Blue Camembert Cheddar Cottage cheese Edam Emmentaler Gouda Mozzarella Parmesan Tilsiter
0.96 0.98 0.94 0.98 0.95 0.99 0.96 0.97 0.95 0.99 0.92 0.96
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Figure 4 Food stability map showing the effect of water activity on the relative rates of various changes in food systems. The critical aw refers to the water activity at which the glass transition occurs at the storage temperature.
sensitive to changes in aw over the range 0.95–0.99. Water activity in cheese ripening may affect growth and CO2 production. Inhibition of the growth of most microbes in salted butter may be accounted for by the high concentration of salts in the water fraction and reduced water activity. The water activity of salted butter is 0.91–0.93, while that of unsalted butter is >0.99. In low-fat dairy spreads, a low pH with a reduced water activity is necessary to prevent the growth of pathogens and molds.
Stability Maps The relative rates of deteriorative changes in food materials are traditionally related to water content and water activity on the assumption that stability at common storage temperatures can be maintained at a low water content. Structural transformations in milk solids may occur at temperatures above the glass transition, which corresponds to a water content that can be quantified. Such transformations include collapse of the physical structure, which reduces diffusion through pores and crystallization of amorphous lactose. Crystallization of amorphous lactose may also release encapsulated fat, which becomes susceptible to oxidation. The effect of water activity on the relative rates of deteriorative changes is often described by stability maps, which are used to show the relative rate of enzymatic changes, non-enzymatic browning, lipid oxidation, microbial growth, and overall stability as a function of water activity (Figure 4). Various reactions rates may also be related to the physical state, molecular mobility, and water plasticization and glass transition of
amorphous food solids. It is obvious that structural transformations, as well as diffusion-limited deteriorative reactions and those affected by lactose crystallization, occur at increasing rates with increasing water activity above the critical aw.
See also: Butter and Other Milk Fat Products: Anhydrous Milk Fat/Butter Oil and Ghee; Fat Replacers; Milk Fat-Based Spreads; Modified Butters; Properties and Analysis; The Product and its Manufacture. Dehydrated Dairy Products: Milk Powder: Physical and Functional Properties of milk Powders; Milk Powder: Types and Manufacture. Ice Cream and Desserts: Dairy Desserts; Ice Cream and Frozen Desserts: Manufacture; Ice Cream and Frozen Desserts: Product Types. Plant and Equipment: Milk Dryers: Dryer Design; Milk Dryers: Drying Principles.
Further Reading Chuy LE and Labuza TP (1994) Caking and stickiness of dairy-based food powders as related to glass transition. Journal of Food Science 59: 43–46. Fox PF and McSweeney PLH (1998) Dairy Chemistry and Biochemistry. London: Blackie Academic & Professional. Haque MK and Roos YH (2004) Water sorption and plasticization behavior of spray-dried lactose/protein mixtures. Journal of Food Science 69: E384–E391. Haque MK and Roos YH (2005) Crystallization and X-ray diffraction of spray-dried and freeze-dried amorphous lactose. Carbohydrate Research 340: 293–301. Haque MK and Roos YH (2006) Differences in the physical state and thermal behavior of spray-dried and freeze-dried lactose and lactose/protein mixtures. Innovative Food Science and Emerging Technologies 7: 62–73. Jouppila K, Kansikas J, and Roos YH (1997) Glass transitions, water plasticization, and lactose crystallization in skim milk powder. Journal of Dairy Science 80: 3152–3160.
714 Water in Dairy Products | Water in Dairy Products: Significance Jouppila K and Roos YH (1994a) Water sorption and time-dependent phenomena of milk powders. Journal of Dairy Science 77: 1798–1808. Jouppila K and Roos YH (1994b) Glass transitions and crystallization in milk powders. Journal of Dairy Science 77: 2907–2915. Roos YH (1995) Phase Transitions in Foods. San Diego, CA: Academic Press. Roos YH (2009) Solid and liquid states of lactose. In: McSweeney PLH and Fox PF (eds.) Advanced Dairy Chemistry Volume 3: Lactose, Water, Salts and Minor Constituents, 3rd edn., pp. 17–33. New York: Springer ScienceþBusiness Media. Roos YH, Jouppila K, and Zielasko B (1996) Nonenzymatic browning induced water plasticization: Glass transition temperature depression and reaction kinetics determination using differential scanning calorimetry. Journal of Thermal Analysis and Calorimetry 47: 1437–1450.
Roos Y and Karel M (1991) Amorphous state and delayed ice formation in sucrose solutions. International Journal of Food Science and Technology 26: 553–566. Roos Y and Karel M (1992) Crystallization of amorphous lactose. Journal of Food Science 57: 775–777. Roos YH, Karel M, and Kokini JL (1996) Glass transitions in low moisture and frozen foods: Effects on shelf life and quality. Food Technology 50(11): 95–108. Shimada Y, Roos Y, and Karel M (1991) Oxidation of methyl linoleate encapsulated in amorphous lactose-based food model. Journal of Agricultural and Food Chemistry 39: 637–641. Vega C and Roos YH (2006) Spray-dried dairy and dairy like emulsions – compositional considerations. Journal of Dairy Science 89: 383–401. Walstra P, Geurts TJ, Noomen A, Jellema A, and van Boekel MAJS (1999) Dairy Technology. New York: Marcel Dekker.
Analysis and Measurement of Water Activity D Simatos, G Roudaut, and D Champion, ENSBANA–Universite´ de Bourgogne, Dijon, France ª 2011 Elsevier Ltd. All rights reserved.
G ¼ w – 0 w ¼ RT ln aw
Definition and Significance of Water Activity Definition Water activity of a system is a way of characterizing the potential energy of the contained water, which is thought to be related to the difficulty to remove it, for example, in drying, and to its availability to allow the functioning of living cells. It can be viewed, for instance, as the difference between the water vapor pressure measured over pure water and that measured over a food product (Figure 1(a)), or as the energy necessary to compensate for the osmotic pressure of a solution (Figure 1(b)). Figures 2 and 3 show schematic views of water activity of dairy products as compared to their water content. The chemical potential (i, J mol–1) of the component i in a mixture is defined as the partial derivative of the free energy, G, when the number of molecules of i (ni) is varied, whereas the temperature, pressure, and total number of molecules in the system are kept constant.
qG qni
¼ i
½1
T ;P;n
If the component considered is water, the subscript w will be used. For a process where the water concentration (expressed as the mole fraction Xw) is changed from X 0w to Xw, the change in free energy, G, is G ¼ w – 0w
½2
where X 0w and 0w concern a state of reference, namely, pure water under the temperature and pressure conditions of the system. As we will see later, G can be calculated for various processes, for example, as the work corresponding to the upward motion of the piston if water is allowed to enter the concentrated solution in the system shown in Figure 1(b), or as the change in free energy as the pressure is changed from pw0 to pw in the system shown in Figure 1(a). If the system is a dilute solution, G is observed to be proportional to the logarithm of the solvent molar fraction (Raoult’s laws and van’t Hoff’s law): G ¼ w – 0w ¼ RT ln Xw
½3
Solutions obeying eqn [3] are called ‘ideal’ solutions. For nonideal systems, Xw is replaced by a new characteristic named ‘water activity’ (aw):
½4
Comparing eqns [3] and [4], aw = Xw for ideal solutions. For nonideal solutions, a parameter, (activity coefficient), was introduced to represent the deviation from ideality: aw ¼ Xw
½5
Water activity is a colligative property; that is, it depends on the number of solute molecules in the solution. The presence of solutes induces a disorder in the water structure, that is, an increase in entropy, which results in a reduced chemical potential. With small solutes, aw is controlled mainly by Xw, that is, by the number of solute molecules. In the presence of macromolecules or hydrophilic surfaces (cell membranes), the mixing entropy plays a minor role in the depression of aw (Xw remains high); low values of w (and, in turn, of aw) are attributed to interactions of the water molecules with the other constituents. When interactions occur between water and solutes (dipole–dipole, ionic interactions, or hydrogen bonds), or when the size of the solute is much larger than the size of the water molecule, < 1. When solute–solute interactions dominate over water–solute interactions, > 1 (remember, however, that aw is always 0.66 indicate that lactose is crystallizing (crystals of anhydrous lactose are able to adsorb much less water than amorphous lactose). Lines are from GAB or Halsey models, as indicated in the figure. (ads, adsorption; des, desorption). Freeze-dried skim milk: Jouppila K and Roos YH (1994) Glass transitions and crystallization in milk powders. Journal of Dairy Science 77: 2907–2915; yogurt, freeze-dried and spray-dried yogurt: Kim SS and Bhowmik SR (1994) Moisture sorption isotherms of concentrated yogurt and microwave vacuum dried yogurt powder. Journal of Food Engineering 21: 157–175; yogurt powder: Wolf W, Spiess WEL, and Jung G (1973) cited by Iglesias HA and Chirife J (1982) Handbook of Food Isotherms: Water Sorption Parameters for Food and Food Components. New York: Academic Press.
Water content (g water 100 g−1 dw)
35 30 25
Na caseinate Whey protein isolate 1 Whey protein isolate 2 Micellar casein Lactose
20 15 10 5 0 0.0
0.2
0.4
0.6
0.8
1.0
Water activity Figure 6 Water sorption isotherms for lactose (adsorption, 20–38 C, Bronlund J and Paterson T (2004) Moisture sorption isotherms for crystalline, amorphous and predominanthy crystalline lactose powders. International Dairy Journal 14: 247–254), micellar casein and whey protein isolate 2 (adsorption, 4–37 C, Foster KD, Bronlund JE, and Paterson T (2005) The prediction of moisture sorption isotherms for dairy powder. International Dairy Journal 15: 411–418), whey protein isolate 1 (adsorption, 23 C, Zhou P and Labuza TP (2007) Effect of water content on glass transition and protein aggregation of whey protein powders during short-term storage. Food Biophysics 2: 108. DOI: 10.1007/s11483-007-9037-4), and Na caseinate (adsorption, 25 C, Weisser H (1985) Influence of temperature on sorption equilibria. In: Simatos D and Multon J-L (eds.) Properties of Water in Foods, pp. 95–118. Dordrecht: Martinus Nijhoff Publishers). The lines are from the GAB model.
Water in Dairy Products | Analysis and Measurement of Water Activity 100
β Anhydrous
Pasteurization 80
Atomization
Spray-drying
Concentration Homogenization
60 Temperature (⬚C)
719
Solution (emulsion)
40
Ts
Spontaneous nucleation
Viscous state crystal growth α Hydrate Lactose crystals and solution
20 Milk 0
Powder
Delay 10 min 1h
Tm
Eutectic
Rubbery zone β Anhydrous crystallization
Tg
1 day
−20 Ice and solution
−40 −60
Glassy solid state Cg⬘, Tg⬘
0
10
20
30
40
50
60
70
80
90
100
Total solids (%) Figure 7 State diagram for milk, based on lactose (Vuattaz G (2002) The phase diagram of milk: A new tool for optimising the drying process. Lait 82: 485–500). Ts, solubility curve; Tm, freezing point versus concentration; Tg, temperature of glass transition versus concentration. The dry product (with a water content below 5%) is a glass at room temperature. If the ambient temperature is increased, or if Tg is decreased as a consequence of an increase in water content, the product becomes ‘rubbery’. An increase in molecular mobility allows crystallization of lactose. The larger the distance of water content/temperature conditions to Tg, the shorter the delay, as indicated on the graph.
transition, as determined by its temperature and water content and (2) the duration of its stay under these conditions. A food material such as skim milk powder in the dry state is in a glassy state at room temperature (its glass transition temperature Tg is 100 C). When water is sorbed, the material is plasticized, that is, its Tg decreases to 20 C for a critical water content of 8%. For a higher water content, the product is transformed into a viscoelastic material (supercooled liquid or rubber depending on the composition) (Figure 7). In the rubbery state, the product is in a metastable state: amorphous constituents (e.g., lactose) may crystallize; the more distant the product is from its glass transition, the faster the crystallization. In the glassy state, the product is out of equilibrium: it may undergo some evolution of its structure (physical aging); the closer the temperature is to Tg, the faster the evolution, but in practice it is always very slow. In both the rubbery and glassy states, the mobility of water remains rather high, and one may expect that equilibration of aw will be usually accomplished within times of interest to the food technologist, as suggest some observations. In some situations, however, it must be recognized that what is measured is the relative humidity of the atmosphere in contact with the product, at best in a pseudoequilibrium state. Hence it would be safer to use the term ‘apparent water activity’ (Expert Panel, ISOPOW, 2000).
Water Activity versus Bound/Free Water Water activity is a way of measuring the energy status of water in a product. It gets depressed as a result of water structure being perturbed and due to interactions between water and solute molecules. Nevertheless, it does not allow one to define a fraction of bound water. The first point is the broad range of interaction energies between water and solutes: from the van der Waals interactions (1 kJ mol1) to hydrogen bonds (10–40 kJ mol1) and ion–water interactions (50–100 kJ mol1 for univalent ions and even more for multivalent ions). It can be noted that water–water and water–solute interactions that occur through H bonds have strength values of the same order; water molecules cannot therefore be viewed as strongly bound to solutes. Actually, spectroscopic observations and molecular dynamics simulations show that water molecules remain highly mobile, even when in direct contact with solute molecules. In liquid water at room temperature, water molecules tumble about with a reorientation time of 2 ps (2 1012 s). Although the properties (orientation, mobility) of some water molecules belonging to the primary hydration shell of ions are strongly modified, they still exchange with bulk water, albeit more slowly (e.g., lifetime 109 s for Na+). Similarly, molecular dynamics simulations of a sugar molecule in an aqueous solution show water molecules located at specific sites on the sugar molecule; however, within a few picoseconds,
720 Water in Dairy Products | Analysis and Measurement of Water Activity
these molecules escape into the bulk water and are replaced by other water molecules. From spectroscopic methods, the ratio s =bulk of the rotational correlation time of water molecules in direct contact with the surface of solutes and that of bulk water is found to be in the range 1.0–2.5 at room temperature for free amino acids and other small organic molecules. For proteins in solution, only water molecules in direct contact with the protein surface are significantly perturbed, although they are still highly mobile, with mean residence times in the range 10–100 ps and the ratio s =bulk averaging around 5.5. Only water molecules buried within the protein have residence times longer than 1 ns (in the range 108–104 s at room temperature). It is estimated that reduction of the mobility of water molecules in contact with proteins is not due to the interaction with the protein per se but rather due to their physical entrapment within the protein matrix. Even in low-moisture solid products, water molecules appear to have a relatively high freedom of motion. The translational diffusion coefficient of water in a hydrated polysaccharide (pullulan with 20% water) has been estimated at 5 1012 m2 s1 at 0 C, that is, 1000 times lower than in liquid water, whereas the viscosity of the system in this glassy state (50 C below the glass transition temperature) would be 1015 times higher. Based on the multilayer adsorption process, mathematical expressions have been derived to describe sorption isotherms (Table 1). The BET expression correctly describes the experimental curves of food materials for 0.2 < aw < 0.5; the GAB expression, which is derived from the BET expression, can be fitted satisfactorily to experimental data up to aw 0.9. The fitting parameters of these expressions are commonly used to calculate the water content corresponding to the monolayer and sorption energies, which are supposed to give information about the interactions of water with the material components. However, this use of the BET and GAB expressions is very questionable. First, the hysteresis observed between sorption and desorption points to the non-equilibrium character of the isotherms. Moreover, it is increasingly being admitted that the basic assumptions of the BET model are not fulfilled in the case of water sorbed on polar materials (energy equivalence of all sites on the sorbing solid surface). In the end, the plastifying action of water on the solid certainly plays a role in determining the form of the sorption curves. A plausible view would be that the sorption process changes at glass transition: in the glassy state, where the conformation is ‘frozen’, an adsorption model (such as the Freundlich model, assuming a distribution of independent sorption sites with different energies) would be suitable, whereas in the supercooled state, the isotherm could be based on the Flory–Huggins theory of polymer solutions.
Water Activity versus Food Quality and Food Processing Operations In the 1960s, water activity became the favored parameter to characterize the availability of water to control the physical, chemical, or biological evolutions in foods. This originated in observations showing that the aw values of media generally correlated well with the potential for growth and metabolic activity of microorganisms. Stability maps were produced, indicating aw thresholds and aw ranges corresponding to the maximal rates of chemical and biological evolutions. In the late 1980s, the value of aw as a predictive index of food stability was questioned, first because most food products are not in a state of thermodynamic equilibrium, as discussed before; moreover, emphasis was placed on the importance of molecular mobility, namely in connection with the glass transition phenomenon. The respective relevance of both approaches, aw and glass transition, has been discussed vigorously. Currently, a consensus appears to have become established, to recognize that both may have an essential role, in a particular domain, depending on the type of product or the objectives. Microbial cells cannot be considered to behave as true osmometers; other parameters, such as pH, nature of the solutes in the medium, and mobility of the metabolites, must also be taken into account. Glass transition concepts, however, do not provide any better alternatives than aw as a predictor of microbial behavior. Water activity is now generally recognized as an essential parameter for all aspects of microbial activity: germination and growth, and production of toxins and aroma. As regards texture, water content seems a better predictor than aw; for instance, the texture of cheese was found to be better correlated to water content (coefficient of correlation with an extrusion force = 0.867) and fat content than to aw (coefficient of correlation = 0.548). Crystallization (e.g., of lactose in milk powder) is a good example of evolution, the kinetics of which are controlled by water content and temperature, in connection with glass transition. With regard to chemical and biochemical reactions, the implication of water is complex: besides being a reactant for many reactions in foods and being necessary for the establishment of the appropriate conformation of enzymes, it constitutes the usual solvent for reactants and imparts the necessary mobility to reactants and reaction products. Water activity does not seem to be directly involved in the control of reaction kinetics; the observation that a reaction (e.g., non-enzymatic browning) occurs, in various food products, with a maximum rate in a characteristic aw range most likely can be explained by these products having similar sorption isotherms and similar Tg values (e.g., because of a high content of biopolymers). Actually, if mobility is increased in these products, through the addition of a liquid fat or of a
Table 1 Expressions to describe or predict relations between water activity and water content Model Raoult’s law
Norrish
Pitzer
Equation aW ¼ Xw ¼
m=18 m=18 þ ð100=Ms Þ
i n n n n 0:5 M X M X ¼ 1 þ jzM zX jF þ 2 CMX B MX þ 22 n n
i z2i jzM zX j ¼ P i i
Dilute solutions
References (for dairy products)
Nonelectrolyte solutions
Chirife and Ferro Fontan (1980), Miracco et al. (1981)
¼ osmotic coefficient i ¼ molality of ion i ZM, ZX, nM, nX = charges and numbers of ions M and X n ¼ nM + nX I ¼ ionic strength BMX(0), BMX(1), CMX = Pitzer coefficients for the electrolyte MXb
Electrolyte solutions
Ferro Fontan et al. (1980)
2 ¼ volume fraction of the polymer n = number of polymeric segments = fitting interaction parameter
aw > 0:90
n>1
Glassy state
m1B ¼ water content of the « monolayer »
0.2 < aw < 0.5
Ruegg amd Blanc (1979)
m1G ¼ water content of the « monolayer »
0.2 < aw < 0.9
Bronlund and Paterson (2004), Jouppila and Ross (1994), Kim and Bhowmik (1994), Lin et al. (2005), Lomauro et al. (1985), Weisser (1985) Jouppila and Rose (1994)
K ¼ empirical constant for the solutea
i
P
Xw ¼ mole fraction of water
Xs ¼ mole fraction of solute
P
I0:5 F ¼ – 0:392 1 þ 1:2I0:5
Range
Ms ¼ molecular weight of the solute ¼ dissociation constant of electrolyte
aW ¼ Xw exp K Xs2
ln aw ¼ – 0:180 2
Parameters
I ¼ 0:5
P i
i z2i
BMX ¼ BMX ð0Þ þ BMX ð1Þexp – 2l0:5
i
Flory–Huggins
1 ln aw ¼ lnð1 – 2 Þ þ 1 – 2 þ 22 n
Freundlich
1=n m ¼ Ca w
BET
m¼
m1B CB aw ð1 – aw Þ½1 þ ðCB – 1Þaw
GAB
m¼
m1G CG Ka w ð1 – Ka w Þ½1 þ ðCG – 1ÞKaw
Kuhn Halsey Peleg Lewicki
K1 þ K2 ln aw P ln aw ¼ – 1 mP2 n n m ¼ k1 aw1 þ k2 aw2 1 b–1 m ¼ Að – 1Þ aw m¼
Iglesias and Chirife (1982), Kim and Bhowmik (1994), Miracco et al. (1981)
(Continued )
Table 1 (Continued) Model
Equation
Parameters
Ross
awmix ¼ ðaw1 Þ . . . ðawi Þ . . . ðawn Þ
SalwynSlawson
P Mi aw i tani awmix ¼ P Mi tani
awmix ¼ aw of a mixture of n solutes awi = aw of a solution where the solute i would be dissolved in all the water of the mixture awmix = aw of a mixture of n components for which SI are known Mi = dry weight of the component i awi = initial aw of component i tani = average slope of the SI of component i in the range of awi
Additive model
mðaw Þ ¼
a
n P 1
M i miðaw Þ
m=predicted water content at aw Mi = mass fraction of component i (db) Mi(aw) = water content of i at aw
Range
References (for dairy products)
4
K = 10.2 for lactose; K=1.59 for lactic acid. For NaCl, BMX(0)¼0.076 5, NaCl, BMX(1)=0.266 4, CMX¼0.001 27. Bronlund J and Paterson T (2004) Moisture sorption isotherms for crystalline, amorphous and predominantly crystalline lactose powders. International Dairy Journal 14: 247–254. Cheirife J and Ferro Fontan C (1980) The prediction of water activity in aqueous solutions in connection with intermediate moisture foods. V. Experimental investigation of the aw lowering behaviour of sodium lactate and some related compounds. Journal of Food Science 45: 802–804. Ferro Fontan C, Benmergui EA, and Chirife J (1980) The predication of water activity of aqueous solutions in connection with intermediate moisture foods. III: aw prediction in multicomponent strong electrolyte aqueous solutions. Journal of Food Technology 15: 47–58. Foster KD, Bronlund JE, and Paterson AHJ (2005) The prediction of moisture sorption isotherms for dairy powder. Internation Dairy Journal 15: 411–418. Iglesias HA and Chirife J (1982) Handbook of Food Isotherms: Water Sorption Parameters for Food and Food Components. New York: Academic Press. Jouppila K and Roos YH (1994) Glass transitions and crystallization in milk powders. Journal of Dairy Science 77: 2907–2915. Kim SS and Bhowmik SR (1994) Moisture sorption isotherms of concentrated yogurt and microwave vacuum dried yogurt powder. Journal of Food Engineering 21: 157–175. Lin SXQ, Chen XD, and Pearce DL (2005) Desorption isotherm of milk powders at elevated temperatures and over a wide range of relative humidity. Journal of Food Engineering 68: 257–264. Lomauro CJ, Bakshi AS, and Labuza TP (1985) Evalution of food moister sorption isothermm equation. Part II: milk, coffee, tea, nuts, oilseeds, spices and starchy foods. Lebensmittel Wissenschaft und technologie 18: 118–124. Miracco JL, Alzamora SM, Chirife J, and Ferro Fontan C (1981) On the water activity of lactose solutions. Journal of Food Science 46: 1612–1613. Ruegg M and Blanc B (1979) Hydration of casein micelles: kinetics and isotherms of water sorption of micellar casein isolated from fresh and heat - treated milk. Journal of Dairy Research 40: 325–328. Weisser H (1985) In: Simatos D and Multon J-L (eds.) Properties of Water in Food, pp. 95–118. Dordrecht: Martinus Nijhoff Publishers.
b
Water in Dairy Products | Analysis and Measurement of Water Activity
723
Table 2 Water activity of cheese vs. chemical composition
Equation
Range
Std error of estimate
Concentration units
References
aw ¼ 0.94 0.005 6(NPN) 0.005 9(NaCl) 0.001 9(Ash-NaCl) þ 0.015pH aw ¼ 1.004 8 0.038 6(NaCl)
aw > 0.90
0.009
g per 100 g water
Ruegg (1985)
Fresh cheeses (moisture > 40% no proteolysis) Bacterial-ripened cheeses Blue cheeses French Emmental after brining after ripening
0.01
mol kg1 water
Esteban and Marcos (1990)
aw ¼ 1.023 4 0.007 0(Ash) aw ¼ 0.980 8 0.005 8(Ash) aw = 0.99 0 0.936(NaCl) þ 0.951(water)(NaCl) aw = 1.066 0.194(water) 3.490(NaCl) 0.331(NH2) þ 6.509(water)(NaCl) þ 0.571(water)(NH2)
g per 100 g water
0.006 0.006
g per 100 g water kgNaCl kg1 water kgwater kg1 dry solids mol eq glycine kg1 cheese
Saurel et al. (2004)
From Ruegg M (1985) Water in dairy products related to quality, with special reference to cheese. In: Simatos D and Multon J-L (eds.) Properties of water in Foods, pp. 603–625. Dordrecht: Martinus Nijhoff Publishers; Esteban MA and Marcos A (1990) Equations for calculation of water activity in cheese from its chemical composition: A review. Food Chemistry 36: 179–186; Saurel R, Pajonk A, and Andrieu J (2004) Modelling of French Emmental cheese water activity during salting and ripening periods. Journal of Food Engineering 63: 163–170.
plasticizer such as glycerol, the aw range for maximal reaction rate can be shifted widely. However, aw continues to serve as a useful guide for chemical stability because it allows prediction of the water content of the product in a given environment (so long as the specific sorption isotherm of the product is known). More generally, aw is an essential tool in food technology, because it allows description of the gradient that will determine the transfer of water between two compartments having different initial relative vapor pressures in a multidomain food system, or between a food product and its environment during drying or osmotic dehydration, or during storage.
Principles of Measurement Physical Properties to Be Measured Water activity cannot be measured directly, but eqn [4] allows derivation of relations between aw and some
physical properties (Table 3), which lead to measurement methods. Water vapor pressure
When the pressure of water vapor is changed from p0 to p (Figure 1(a)), the change in free energy can be calculated from basic thermodynamics (and assuming that water vapor behaves as a perfect gas) to be G ¼ RT ln p=p0 . Then aw ¼
p p0
½7
100 p/p0 (%) defines the relative humidity (RH) of the atmosphere in equilibrium with the product, and aw can be obtained from the measurement of p by various methods and calculation using the known p0 values at the temperature of measurement. measurement with a manometer: The air must be • Direct evacuated from the apparatus; drying of the sample during this operation must be kept at a negligible
Table 3 Relations between water activity and physical properties (1) Equilibrium relative humidity (2) Freezing point depression
(3) Osmotic pressure
aw ¼
p ERH ¼ p0 100
ln aw ¼
H m T – T0 Cp ðT – T0 Þ2 þ R TT0 2RT 2
V ln aw ¼ – w RT
p ¼ partial water vapor pressure (Pa) p0 ¼ saturated water vapor pressure (Pa) at temperature T ERH ¼ equilibrium relative humidity T0, T ¼ temperature of freezing of pure water and of the sample (K) Hm ¼ melting enthalpy of ice at T0 (¼ 6 kJ mol1) Cp ¼ difference in the specific heat of ice and liquid water (¼ 37.697 J K1 mol1) R ¼ 8.314 J K 1 mol1 Q ¼ osmotic pressure (Pa) V ¼ molar volume (8106 m3 mol1) T ¼ temperature (K) R ¼ 8.314 J K 1 mol1
724 Water in Dairy Products | Analysis and Measurement of Water Activity
Mechanical/electrical properties varying with RH Fan
Unlike the preceding methods, which can be absolute measurements, these methods require calibration of the sensor. The sensor can be a thread-like material (a hair or a synthetic polymer) the length of which, when exposed to a force of given strength, depends on its water content and is measured. The sensor can also be a material the electrical conductivity or dielectric constant of which depends on the water content and which is measured.
Optical sensor Mirror
Infrared sensor
Sample
Sorption isotherms
Figure 8 Schematic diagram of a dew point cell. The mirror is cooled progressively (e.g., via a Peltier device). The optical sensor emits light onto the mirror and detects the reflected light. When condensation occurs, the temperature of the mirror is recorded (giving the value of pW). The temperature of the sample is recorded via the infrared sensor (giving the value of p0 w ). Diagram from Decagon.
•
level, for instance, by freezing it. This method is not suitable for products containing volatiles. Moreover, because of its technical requirements, its use is restricted to the laboratory as a standard method. Dew point temperature: Figure 8 shows the experimental setup for measuring dew point temperature. As the mirror is progressively cooled, condensation occurs when its temperature is that for which the saturated vapor pressure is equal to p. Commercial instruments claim a measurement range of 0.030–1.000 aw with an accuracy of 0.003 aw.
Water activity can be determined from SI of the product after measurement of the water content. In this case, it is more practical to have a mathematical expression of the SI, allowing interpolations. Besides the ones cited before, many expressions have been proposed to describe SI, a few examples of which are given in Table 1. For milk products, as for other foods, GAB expression was shown to be fitted satisfactorily to experimental data up to aw 0.90. To create SI, representative food samples that are initially dried (for adsorption isotherms) or hydrated (for desorption) are placed in controlled humidity chambers at constant temperature and are weighted periodically until a constant weight is reached. In the static desiccators method (Figure 9), different levels of RH are obtained using 1
2
3
4
5
Freezing point
The second equation in Table 3 is derived from thermodynamics. Cp is assumed to be independent of temperature in the range T–T0. This assumption does not result in any significant loss of accuracy. Considering that chemical potential must be equal in both the phases present in a frozen solution, that is, ice and the concentrated solution resulting from the separation of ice, the vapor pressure at equilibrium with the frozen product is pice. The reference vapor pressure (p0) is the vapor pressure of supercooled water at the same temperature (T). Then aw ¼
pice p0
½8
Both expressions give very similar results, confirming the validity of both. The measurement of T, where the first ice crystals are formed, by a classical cryoscopic measurement, gives accurate values of aw (up to 0.001 aw) in the range 0.80–1. Actually, what is measured is aw of the product at T. The differences with aw at 25 C are shown to be not more than 0.01 aw. The values may be corrected to obtain more accurate ones at the desired temperature.
Figure 9 Sorption device as standardized for the COST Project 90 (Wolf W, Spiess WEL, and Jung G (1985) Standardization of isotherm measurement (COST Project 90 and 90 bis). In: Simatos D and Multon J-L (eds.) Properties of Water in Foods, pp. 661–679. Dordrecht: Martinus Nijhoff Publishers). 1. water bath, 2. sorption container (1-l glass jar, with a vapor-tight lid), 3. weighing bottle with a ground-in stopper, 4. Petri dish on trivet, 5. saturated salt solution.
Water in Dairy Products | Analysis and Measurement of Water Activity
saturated salt slurries that have known aw values. Commercial devices control RH by mixing wet and dry gas streams and continuously monitor weight changes of the samples.
Equilibrium The issue of equilibrium has already been mentioned concerning the internal moisture equilibrium of the product; equilibration of water vapor pressure between the sample, headspace of the measurement chamber, and the probe is also an important practical problem. Theoretically, the equilibration process is slowed as vapor pressures come closer, and equilibration time is infinite. Practically, therefore, the rate of change of RH is monitored continuously and the measurement is ended when the rate of change falls below a chosen limit. Equilibration of most products typically requires 45–60 min and can take as long as a couple of hours. Gentle ventilation in the measuring chamber may reduce equilibration time by 50%. For the generation of SI by the desiccators method, reducing the total pressure in the containers also reduces the equilibration time by a factor of 2–3. The volume and geometry of the sample are important parameters. Increasing its surface area (possibly by grinding) will reduce equilibration time; care should also be taken to ensure that the amount of sample is large enough, as compared to the headspace volume of the chamber (and to the surface area of the dew point mirror), so that the water lost by the sample will not significantly decrease its water content. Several commercial instruments designed to generate SI change the controlled RH in a stepwise progression; some another instruments uses only air saturated with
725
water (for adsorption) or dry air (for desorption), and continuously monitor weight changes and RH in the chamber with a dew point sensor. While the SI obtained with the former devices may be considered to represent equilibrium states, the latter are expected to provide information on the evolutions (glass transition, crystallization) occurring in the sample during sorption (Figures 10 and 11).
Temperature Water activity of a product shows only small variations with temperature. For ideal solutions, aw, being identical to Xw, is independent of temperature; even for nonideal systems, changes are small. SI of various dairy powders show no obvious temperature dependence between 4 and 38 C; only at 50 C the amounts of sorbed water are lower. Similarly, the aw measured for six different cheeses between 5 and 30 C showed no significant temperature dependence. The temperature of a sample, however, is an important concern for aw measurements. For methods relying on the measurement of pw (direct measurement of pw, dew point), an error in the sample temperature measurement will result in an error in p0 w and consequently in aw. Between 20 and 25 C, a 1 C error in the sample temperature measurement represents a 6% error in p0 w and aw. Similarly, to achieve an accuracy of 0.003 aw within the range of 0.800–1.000 aw, the temperature of a dew point sensor is to be measured with an accuracy of 0.05 C. Because the temperature dependence of aw is small, the actual temperature need not to be known precisely with apparatus measuring RH, so long as both temperatures of sample and of sensor are the same.
Figure 10 Two dynamic methods of sorption isotherm generation: dynamic vapor sorption (DVS): change in mass (blue) and change in target RH (red) versus time; dynamic dewpoint isotherm (DDI): sample weight (red) and measured RH (blue) versus time. Carter B (Decagon), personal communication.
726 Water in Dairy Products | Analysis and Measurement of Water Activity
Moisture content (% d.b.)
Traditional desiccator 20 18 16 14 12 10 8 6 4 2 0
GAB model fit
DDI method
Dissolution onset Crystallization onset Surface and bulk adsorption Surface adsorption
Glass transition 0
0.2
0.4 0.6 Water activity
0.8
1
Figure 11 Sorption isotherm of milk powder (adsorption) obtained by continuously changing RH above the sample (DDI method), as compared to that obtained with the desiccators method. As water is adsorbed by the dry product, the temperature of glass transition is lowered to the working temperature; the glassy product is plasticized, water is then more easily adsorbed in the bulk of the sample. With the increase in molecular mobility,crystallization of lactose develops. Redrawn from Carter B (Decagon), personal communication.
See also: Cheese: Microbiology of Cheese. Concentrated Dairy Products: Sweetened Condensed Milk. Dehydrated Dairy Products: Milk Powder: Physical and Functional Properties of Milk Powders. Water in Dairy Products: Water in Dairy Products: Significance.
Further Reading Chirife J and Buera MP (1996) Water activity, water glass dynamics and the control of microbiological growth in foods. Critical Review in Food Science and Nutrition 36: 465–513. Fontana AJ (2007) Measurement of water activity, moisture sorption isotherms, and moisture content of foods. In: Barbosa-Canovas GV, Fontana AJ, Schmidt SJ, and Labuza TP (eds.) Water Activity in
Foods: Fundamentals and Applications, pp. 155–171. Ames, IA: Blackwell Publication. Halle B (2004) Protein hydration dynamics in solution: A critical survey. Philosophical Transactions of the Royal Society of London. Series B 359: 1207–1224. Karel M (1999) Food research tasks at the beginning of the new millennium. A personal vision. In: Roos YH, Leslie RB, and Lillford PJ (eds.) Water Management in the Design and Distribution of Quality Foods (ISOPOW VII), pp. 535–559. Lancaster, PA: Technomic. LeMeste M, Champion D, Roudaut G, Blond G, and Simatos D (2002) Glass transition and food technology: A critical appraisal. Journal of Food Science 67: 2444–2458. Simatos D, Champion D, Lorient D, Loupiac C, and Roudaut G (2009) Water in dairy products. In: McSweeney PLH and Fox PF (eds.) Advanced Dairy Chemistry-3. Lactose, Water, Salts and Minor Constituents 3rd edn., 457–526, New York, Springer Science.
WELFARE OF ANIMALS, POLITICAL AND MANAGEMENT ISSUES H D Guither and S E Curtis, University of Illinois–Urbana, Urbana, IL, USA ª 2002 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, Volume 4, pp 2735–2739, ª 2002, Elsevier Ltd.
Introduction Since World War II, a major revolution in social concern with the welfare and moral status of agricultural animals has emerged. The animal rights movement has arisen from old ideas but with new philosophies, emphasizing moral and ethical standards for how human beings should treat animals. Public policy establishing the animal welfare movement began in the United Kingdom with the passage of an act in 1835 to ‘‘consolidate and amend the several laws relating to the cruelty and improper treatment of animals’’. In 1911 the UK Parliament passed the Protection of Animals Act which is still in force. It was established on the principle that, although human beings are free to subjugate animals, it is wrong for people to cause animals to suffer unnecessarily. The cultural and social evolution of animal protection in Europe has led to changes in the United States.
Terms Defined Animal protection refers to all efforts to prevent cruelty, improve humane treatment, reduce stress and monitor research with animals. Animal welfare generally describes the philosophy espoused by those who support the humane treatment of all animals without concern for their ultimate use. An ‘animal welfarist’ believes that human beings have the right to use animals so long as suffering is reduced or eliminated. Those who believe in animal welfare work for the reform of abusive or neglectful situations to alleviate animal suffering. Farmers have historically been perceived as strong supporters of animal welfare because they believed that animals raised under humane conditions and practices would be the most productive and profitable. The animal rights philosophy, encompassing animal liberation, includes some fundamental differences from animal welfarism. It involves the idea that nonhuman animals are sentient beings – that they have the capacity consciously to experience pain and pleasure, among other things. Accompanying this belief is the notion that
animals have certain inalienable moral rights which humans should not violate.
Philosophers, Activists and Political Action Ruth Harrison, an English homemaker, initiated much of the public concern for the welfare of farm animals under modern production methods when her book Animal Machines was published in 1964. Following publication of her book, the UK Parliament called for an investigation. In 1965, the Brambell Committee, a group of scientists and concerned citizens, issued their report calling for certain mandatory standards that would conform to good husbandry in agricultural/animal production systems. The political dimension of the animal rights and animal welfare movements involves individual and group efforts supporting or opposing specific issues. The methods include campaigns to influence legislation through letter-writing and other direct contacts; seminars and media events to influence members of legislative bodies and public opinion; demonstrations to draw public attention to what activists see as improper treatment; inviting sympathetic legislators and government officials to speak or receive awards at meetings and other special events; and securing sponsorship of bills in various legislative bodies. The participating activists may be classified as reformists or abolitionists. Political action by animal rights and animal welfare advocates covers many issues from many different perspectives. However, four phases in these movements to influence political action can be identified: (1) identifying the problems of animal mistreatment; (2) developing appropriate ideology to cover the principles and concerns; (3) understanding how change occurs; and (4) developing explicit standards of ethics for advocating change. Although intensive methods of animal production, which use more capital and less labor than traditional methods do, have improved production efficiency, they have at times put milk and meat producers in defensive positions because animal activists have branded certain
727
728 Welfare of Animals, Political and Management Issues
ones of these contemporary methods as ‘factory farming’. Producers adopted high-technology, intensive production systems because they would allow them to produce more product by substituting capital for labor to achieve lower cost per unit product. Critics, however, see intensive animal agriculture differently because their views are based on philosophical thinking, feelings or opinions, often with little exposure to or understanding of the economics, the science or the actual practice of agricultural/animal production.
Dairy Cattle, Animal Welfare and Management Issues A British report in 1983 identified animal protectionists’ major animal welfare concerns for dairy animals: of quality and quantity of individual atten• reduction tion in larger herds of calves with caustic chemicals with or • dehorning without anesthetic stanchion tying of cows, especially without • prolonged exercise for separation of cow and calf • need neglect of unwanted bull calves • raising replacements in individual hutches rather than • in groups of veal calves in small crates • confinement failure to employ research knowledge • production-relatedwelfare-related susceptibility to disease and meta• bolic disorders • transportation of injured and sick animals to slaughter. All of these issues continue to be mentioned to this day (but much progress has been made in correcting those issues that deserved attention). In addition another issue has come on the scene – docking cows’ tails. Several of these issues have been addressed by scientists and government officials around the western hemisphere in the intervening two decades. The UK Ministry of Agriculture, Fisheries and Food (now the Department of the Environment, Food and Rural Affairs) issued its codes of recommendations for the welfare of cattle emphasizing avoiding discomfort or distress and allowing the animals to fulfil their ‘basic needs’. The recommendations called for these provisions to be considered: comfort and shelter, readily accessible fresh water and a diet to maintain full health and vigor; freedom of movement; company of other animals, particularly of like kind; and opportunity to exercise most normal patterns of behavior. Specific recommendations were identified for buildings, fire and other emergency precautions, ventilation and temperature, lighting, mechanical equipment
and services, space allowance, feed and water and management. Recommended codes of dairy cattle and veal calf husbandry practices also have been published in Canada. Guidelines for the care of dairy cattle and veal calves have been published by dairy-industry stakeholders and scientists in the United States. With respect to some of the issues listed above, much progress has been made, and general consensus currently stands as follows: 1. Cow behavior and care in large groups can be satisfactory. 2. Dehorning is beneficial, and its conduct has been refined to make it more humane. 3. Very few dairy cows are stanchioned for long periods nowadays. 4. Separating calf from cow very soon after birth is justifiable in terms of the dam’s udder health so long as the calf receives an adequate dose of appropriate colostrum the first day after delivery. If a calf is to be weaned early, in terms of minimizing the stress of separation and loss it should be done as soon after birth as possible. 5. Dairy farmers are being educated as to the necessity of ensuring that surplus bull calves (to be finished as veal calves or dairy beef) be cared for just as heifer calves being kept as herd replacements, especially with respect to receiving an adequate dose of colostrum the first day after birth. 6. Individual outdoor hutches – in terms of calf sanitation, health and performance – are preferable to group housing for calves for the first 2 months after birth. This is so, regardless of the nature of the local climate. Benefits of the opportunity to socialize with other calves are outweighed by vices and other practical problems associated with group-rearing of young calves. 7. Although there have been numerous studies in many places seeking a suitable alternative to the conventional veal-calf stall, no alternative has emerged. Applied discovery research continues along this line. 8. There remains in the industry a strong tendency to follow economic dictates rather than ethical ones when the two are in conflict. Some of the reasons for this seem to be that, unfortunately, the correspondence of high animal state-of-being with high animal performance rate has not been adequately demonstrated by scientists, so the whole economic situation in such cases may be neither understood nor considered. Ironically, criticism and charges by animal protection advocates have probably dampened the support resources the industry and the governments of the various nations have devoted to such research, the results of which would probably for the most part be ‘win–win’ for agriculturists and animal protectionists alike.
Welfare of Animals, Political and Management Issues 729
9. Simply put, with modern animal production systems come the smouldering, multifactorial production diseases characterized by long-term, moderate morbidity and low mortality. But on balance the overall health of the animals is roughly the same in intensive production systems as in extensive systems. In the latter systems, the animals are more likely to suffer from parasitic diseases and the acute infectious diseases characterized by short-term, severe morbidity and high mortality. 10. Most abattoirs nowadays refuse to permit nonambulatory animals to be off-loaded at their docks, so most nonambulatory cows (which became nonambulatory at the farm) are not on-loaded and transported in the first place. 11. A consensus regarding tail-docking of dairy cows is now forming. On balance the practice seems to have few, if any, advantages but several disadvantages.
Policy and Legal Aspects Calls for regulation of agricultural/animal care practices have been more successful in western Europe than in North America. The US House of Representatives did conduct hearings on the issues of veal calf husbandry and handling and transportation of nonambulatory animals in the late 1980s and early 1990s, but so far no legislation regulating these matters has been passed and signed into law. Some European countries, however, have set legal standards for animal husbandry on farms, although these standards often differ among nations. In 1986 the European Communities Council issued its directive for protection of animals used for ‘experimental and other scientific purposes’. The directive was designed to provide guidelines for uniform laws in the member countries. The objectives were to reduce the use of animals for experimental purposes to a minimum, ensure that they were adequately cared for, and avoid or minimize pain, suffering, distress and harm. The farm animal welfare policies and regulations in the United Kingdom are developed in line with European Union (EU) directives and have led the way for other European countries. The major issues around which all European animal welfare policies have evolved focus on housing, rearing, feeding, transporting, marketing and killing. In 1996 the EU Commission proposed that French, Italian and Dutch farmers could continue to use crates for raising veal calves until the year 2008, but new crates would be banned after 1998. The UK Department of the Environment, Food and Rural Affairs (DEFRA) recognizes that both ethical and scientific issues play a part in this issue. For advice and counsel on animal welfare matters, DEFRA looks first to the Farm Animal Welfare Council (FAWC), comprised of scientists, educators and producers.
The FAWC is expected to combine the use of appropriate new technology with efficient use of available resources and adequate provision for the welfare and behavioral needs of animals. More practices requiring a veterinary surgeon are spelled out. Citizens who believe a livestock owner is not following the welfare guidelines can file a complaint, and government inspectors then determine whether violations have occurred. In Sweden the 1988 Animal Protection Act established the most detailed and comprehensive laws dealing with animal welfare in any country. Livestock buildings had to have windows and provide space so all animals could lie at once and be able to move freely. Milk cows had to be sent out to pasture in the summer. In Switzerland, veal calves must receive iron and roughage in their rations. Differences within the EU exist on animal welfare policies. The northern countries tend to be more sympathetic to welfare policies than the southern countries. Eastern European countries are in transition, and animal welfare policies have much lower priority than other economic and social concerns. Producer attitudes toward animal welfare regulations in the western hemisphere have changed in recent years. Many now recognize that public opinion cannot be ignored if they are to maintain a market for their products. The development of welfare-oriented regulations for production practices is only part of the evolution of government influence. Along with concerns for the humane treatment of animals is the concern for the quality and safety of products and the environment. Production regulation also involves pollution controls, manure disposal, dead-animal disposal and the use of medicines and feed additives that could affect the safety of the processed animal product. Producers are consulted as new animal welfare regulations are developed, but in their minority position they must accept the final policy decision. Many of the regulatory guidelines simply represent good management practices that any considerate producer would follow. In Europe the policies and regulations established are primarily welfare-oriented, with less noticeable activism for animal rights per se than is observed in the United States. There is a growing consumer interest and awareness in Europe and North America about how food is produced. Although the primary concern is food safety, the humane treatment of animals is second and interest is growing. The rising profile of animal welfare in public awareness is contributing to growing demands for food that is labeled as having been produced under certain standards. The legal framework regarding animals in the United States has focused on concerns that they should be treated humanely. Successful legislative efforts fall into these categories: (1) humane treatment of animals in slaughter plants, in research facilities and in transit; (2) protection of
730 Welfare of Animals, Political and Management Issues
endangered animal species; (3) protection of fish, marine mammals and wildlife; (4) establishment of standards for conducting research with laboratory and other animal species; (5) protection of pets; and (6) control of terrorism. Dairy cattle owners have the most concern with categories (1), (4) and (6). One of the oldest federal laws deals with livestock transportation. The act applies to the transport of animals and requires a respite period unless the vehicle itself provides feed, water and space. In the United States, many bills dealing with animal protection have been introduced but none has been enacted. Those that would target dairy animals included bills attempting to identify humane animal husbandry practices for livestock, to establish a farm animal husbandry committee to investigate all aspects of intensive farm animal husbandry and to mandate diets and accommodations for veal calves. In 1989 the US House of Representatives Agriculture Subcommittee on Livestock, Dairy and Poultry held a hearing on a bill (HR 84) that attempted to prohibit certain practices in raising veal calves. Testimony revealed support for the bill from the Humane Society of the United States, Humane Farming Association and other animal rights/welfare groups. Veal producers, the US Secretary of Agriculture, and members of Congress with major producer constituencies opposed the bill. The bill failed to receive a favorable vote in committee. In the United States, advocates of a humane ethic for animals are gaining momentum based on a philosophy regarding the sacredness of life. Animal-welfare advocates emphasize that animals are sensing, living beings capable of feeling fear and pain and that they must be respected as such. Some members of Congress recognize the emotional commitment of animal-welfare advocates. However, the US animal industry’s strong public support, the close ties between trade associations and government agencies and the rapport between producers, state legislators and members of the US Congress provide major advantages over organizations and individuals’ philosophies that would disrupt the economically sound management practices used on dairy, livestock and poultry farms. See also: Office of International Epizooties: Mission, Organization and Animal Health Code.
Further Reading Albright JL (1983) Status of animal welfare awareness of producers and direction of animal welfare research in the future. Journal of Dairy Science 66: 2208–2226. Albright JL (1987) Dairy animal welfare: current and needed research. Journal of Dairy Science 70: 2711–2731.
Albright JL and Arave CW (1997) The Behaviour of Cattle. Wallingford: CAB International. Arave CW and Albright JL (1997) Animal welfare issues: dairy. In: Reynnells RD Eastwood BR and Editors (eds.) Animal Welfare Issues Compendium. Washington, DC: US Department of Agriculture, Cooperative State Research, Education and Extension Service. Birbeck AL (1991) A European perspective on farm animal welfare. Journal of the American Veterinary Medical Association 198: 1377–1380. Brambell FWR (1974) Report of the Technical Committee to Enquire into the Welfare of Animals Kept under Intensive Livestock Husbandry Systems. London: HMSO. Brown GE Jr (1997) Thirty Years of the Animal Welfare Act. Beltsville: National Agricultural Library. Canadian Agri-Food Council (1998a) Recommended Code of Practice for the Care and Handling of Farm Animals: Dairy Cattle. Ottawa, Canada: CARC. Canadian Agri-Food Council (1998b) Recommended Code of Practice for the Care and Handling of Farm Animals: Veal Calves. Ottawa, Canada: CARC. Curtis SE (1988) Animals in food production: American issues. Applied Animal Behavioral Science 20: 151–157. Curtis SE (1991) The welfare of agricultural animals. In: Blatz CV (ed.) Ethics and Agriculture: An Anthology on Current Issues in World Context, pp. 447–457. Moscow: University of Idaho Press. Curtis SE and Baker FH (eds.) (1997) The Well-Being of Agricultural Animals. Ames: Council for Agricultural Science and Technology. Dairy Quality Assurance Center (1995a) Caring for Dairy Animals: Reference Guide. Stratford: DQAC, Agri-Education. Dairy Quality Assurance Center (1995b) Caring for Dairy Animals: On-Farm Evaluation Guide. Stratford: DQAC, Agri-Education. Federation of Animal Science Societies (1999a) Guidelines for dairy cattle husbandry. In: Mench JA (ed.) Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching. Savoy: FASS. Federation of Animal Science Societies (1999b) Guidelines for veal calf husbandry. In: Mench JA (ed.) Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching. Savoy: FASS. Finsen L and Finsen S (1994) The Animal Rights Movement in America. New York: Twayne. Fox MW (1983) Animal welfare and the dairy industry. Journal of Dairy Science 66: 2221–2225. Garner R (1993) Animals, Politics and Morality. Manchester: Manchester University Press. Grandin T (ed.) (2000) Livestock Handling and Transport, 2nd edn. Wallingford: CAB International. Guither HD (1998) Animal Rights: History and Scope of a Radical Social Movement. Carbondale: Southern Illinois University Press. Guither HD and Curtis SE (1983) Animal Welfare: Developments in Europe: A Perspective for the United States. Urbana: University of Illinois at Urbana, Illinois Agriculture Experimental Station. Jasper JM and Nelkin D (1992) The Animal Rights Crusade: The Growth of a Moral Protest. New York: Free Press. Leahy MPT (1991) Against Liberation: Putting Animals in Perspective. London: Routledge. Ministry of Agriculture, Fisheries and Food (1983) Codes of Recommendations for Welfare of Livestock: Cattle. London: MAFF. Marquardt K, Levine HM and LaRochelle M (1993) Animal Scam. Washington, DC: Regnery Gateway. Matthews LR, Phipps A, Verkerk GA et al. (1995) The Effects of Tail Docking and Trimming on Milker Comfort and Dairy Cattle Health, Welfare and Production. Report to Ministry of Agriculture and Food, Animal Behavior and Welfare Research Center. Hamilton, New Zealand: AgResearch Ruakura. Regan T (1983) The Case for Animal Rights. Berkeley: University of California Press. Rollin BE (1981) Animal Rights and Human Morality. Buffalo: Prometheus Books. Van Horn HH and Wilcox CJ (eds.) (1992) Large Dairy Herd Management. Champaign: American Dairy Science Association.
WHEY PROCESSING
Contents Utilization and Products Demineralization
Utilization and Products P Jelen, University of Alberta, Edmonton, AB, Canada ª 2011 Elsevier Ltd. All rights reserved.
Introduction Whey, the greenish translucent liquid obtained from milk after precipitation of casein, has been viewed until recently as one of the major disposal problems of the dairy industry. The biological oxygen demand (BOD) of whey is very high (40 000 mg kg 1 or more), constituting a major ecological burden if disposed off as a waste material. Thus, the disposal practices of the past, including drainage into waste treatment facilities or spraying onto fields, are currently seldom practiced. Use of whey as cattle or pig feed is still one of the significant alternatives to utilization in the human food chain, now being predominantly favored due to the economic opportunities provided by some of the milk nutrients contained in the whey.
Whey Types and Composition There are several types of whey, depending mainly on the processing sequence resulting in casein removal from fluid milk. The type of whey most often encountered originates from the manufacture of cheese or certain industrial casein products, where the processing is based on coagulating the casein by rennet, an industrial casein-clotting preparation containing chymosin or other casein-coagulating enzymes. Since the rennetinduced coagulation of casein and the subsequent whey drainage occur at a pH value of approximately 6.5–6.0, this type of whey is referred to as sweet whey. The second basic whey type, acid whey, results from processes using fermentation or addition of organic or mineral acids to coagulate the casein as in the manufacture of fresh acidcoagulated cheeses (e.g., Cottage cheese or quark) or most industrial acid casein.
The main components of both sweet and acid wheys, after water (which constitutes approximately 93% of the whey on an ‘as is’ basis), are lactose (approximately 70–72% of the total solids), whey proteins (approximately 8–10%), and minerals (approximately 12–15%). Table 1 gives a more detailed breakdown of these components of the two basic whey types. The main differences between the two whey types are in the mineral content, the acidity, and the composition of the whey protein fraction (WPF). Although these differences are relatively minor on an ‘as is’ basis, they can have a profound effect on the technological as well as nutritional properties of the wheys and must be taken into consideration in applications of the various whey processing technologies now available to whey processors. The acid coagulation approach (using conversion of some of the lactose in milk to lactic acid by lactic acid bacteria and/or addition of acidulants such as glucono-lactone or various acids such as sulfuric, phosphoric, hydrochloric, citric, or lactic acid) results in substantially increased acidity (final pH approximately 4.5) necessary for casein precipitation. At this low pH, the colloidal calcium contained in the casein micelles in normal milk is solubilized and partitioned into the whey. On the other hand, rennet clotting produces a fragment of the -casein molecule, termed glycomacropeptide (GMP), which ends up in the whey. Thus, the GMP constitutes approximately 20% of the WPF of sweet, rennet-based wheys but is not found in acid wheys unless use of rennet was included in the fresh cheese manufacturing process (as sometimes happens in the Cottage cheese manufacture for increased firmness) in addition to the acid coagulation. Various technological steps used in the pretreatment of milk before the main processes (such as various thermal treatments before the casein-clotting operation) may also influence the composition of the whey resulting from such
731
732 Whey Processing | Utilization and Products Table 1 Typical composition of sweet and acid whey (g l 1 whey) Component
Sweet whey
Table 2 Typical composition of major types of dried whey products (%, w/w)
Acid whey Product type
Total solids Lactose Protein Calcium Phosphate Lactate Chloride
63.0–70.0 46.0–52.0 6.0–10.0 0.4–0.6 1.0–3.0 2.0 1.1
63.0–70.0 44.0–46.0 6.0–8.0 1.2–1.6 2.0–4.5 6.4 1.1
Illustrative data compiled from various sources.
milk. Typically, the composition of the mineral fraction may be altered slightly and the content of heat-labile whey proteins may be reduced; these changes may result in further alterations in the technological properties of such wheys. New technological alternatives for processing of dairy fluids, including membrane processing by ultrafiltration (UF) of milk in cheese manufacture or fractionation of the various wheys into various whey-based products, produce a whey-like residue termed UF permeate. The main difference between UF permeates and the various whey types is typically the virtual absence of whey proteins from the permeate. Although technically UF permeate does not fit the definition of whey, it is referred to in this article where appropriate, as its processing and utilization often present similar challenges and opportunities as for whey.
Industrial Technologies Used in the Processing of Whey and UF Permeates As a general rule, about 9 l of whey is obtained for every kg of cheese produced; thus, the volume of whey to be processed, originating from just one typical large-scale cheesemaking operation, can exceed 1 106 l day 1. Most of the technological alternatives used in specialized whey-processing plants are thus large-scale operations, some with a capacity to handle up to 107 l of whey daily. The simplest technology for the conversion of whey to industrially valuable products is drying. Typical traditional whey-drying operations consist of evaporation in multistage vacuum evaporators, followed by spray-drying. The equipment used does not differ greatly from other such dairy plant installations but the evaporation and drying conditions must be adjusted to accommodate the specific properties of the whey. In particular, the differences between evaporation or spray-drying of skim milk and whey include the need to precrystallize the lactose in whey before the drying step to minimize the problems of hygroscopicity, as well as careful manipulation of the heat conditions to minimize problems related to heat sensitivity of whey proteins. Dried whey powders can differ rather substantially in composition and
Regular whey powder Demineralized (70%) whey powder Demineralized (90%) whey powder Ultrafiltration permeate powder Whey protein ‘concentrate’ (skim milk replacer) Whey protein concentrate Whey protein isolate
Total protein
Lactose
Minerals
12.5
73.5
8.5
13.7
75.7
3.5
15.0
83.0
1.0
1.0
90.0
9.0
35.0
50.0
7.2
65.0–80.0 88.0–92.0
4.0–21.0 0.97, growth of P. roqueforti isolates is stimulated by propionate, another commonly used weak acid preservative. This resistance to weak acid preservatives, which are routinely used to prevent fungal spoilage of foods, coupled with its ability to grow at refrigeration
Yeasts and Molds | Penicillium roqueforti
temperatures, makes the fungus a common cause of spoilage in cool-stored preserved commercial and domestic foods. The microenvironment of Blue cheese is characterized by profound NaCl gradients from the core to the surface of the cheese, which reach equilibrium slowly during ripening. These differences are known to affect the growth, germination, and sporulation of P. roqueforti. Penicillium roqueforti has an optimum water activity (aw) value of 0.998 for growth at 25 C, and a colony growth rate of 13.4 mm day1. The lag phase of growth for P. roqueforti is relatively stable at aw > 0.92, but increases for aw < 0.94. This is advantageous for the use of the fungus as a starter culture, as the final aw values of Blue cheeses are in the range of 0.91–0.94, which allows P. roqueforti to germinate quickly and grow through the entire cheese processing and ripening process. The pH and NaCl concentrations of the cheese are also known to influence the proteolytic activity of the fungus, with proteolysis typically being less pronounced in the high salt environment in the outer parts of the cheese. Growth of P. roqueforti strains is stimulated at low salt concentrations, with 1% salt (NaCl) having the highest stimulating effect. In addition, while it is known that P. roqueforti strains can grow at low temperatures, the rate of growth at 10 C is around 2–3 times lower than that at 25 C, the optimum temperature for the species. At 25 C, P. roqueforti strains have been reported to produce around 10% more mycophenolic acid (MPA) at an aw value of 0.97 when compared to that at an aw value of 0.95. This effect does not appear to be significantly affected within the pH range of 4.7–7.4. At aw values >0.97, growth of P. roqueforti is stimulated by propionate, another commonly used weak acid preservative. There are a number of conflicting results reported in the scientific literature with respect to the effects of preservatives on growth and mycotoxin production by P. roqueforti. Some reports appear to indicate that at subinhibitory levels preservatives inhibit mycotoxin production, whereas the opposite has been reported by other groups. Thus, it is likely that the mechanisms of mycotoxin regulation are quite complex and not readily generalized and are most probably not only speciesdependent but also affected by the growth medium and by the concentration of the preservative. In a study involving 30 P. roqueforti strains, the effects of various physiological conditions on both esterase and lipase activities were monitored, using diffusion assays on tributyrin and olive oil agars, and growth at either 10 or 25 C in butterfat emulsions containing up to 7% NaCl was also monitored. This study reported that extracellular lipase production is stimulated at low NaCl concentrations and that lipases show a higher activity against shortchain fatty acids while triolein is hydrolyzed at a much
773
lower rate. Mathematical models combining the effects of temperature and salt concentration have been developed to predict their effects on the growth rate of P. roqueforti, in an attempt to prevent food spoilage by the fungus. Other approaches to prevent growth of the fungus have involved the use of an antifungal compound produced by a Bacillus subtilis strain and which has been reported to inhibit the germination of P. roqueforti conidiospores. This iturin-like compound is believed to act by permeabilizing the fungal spores, thereby inhibiting germination. The addition of essential oils has also been shown to inhibit the growth of P. roqueforti, with the addition of eugenol, caryophyllene, p-cymene, and thymol being reported to be particularly effective.
Production of Volatiles A number of methods have been developed to study the volatile compounds produced by Penicillium species, including P. roqueforti. Three popular methods include diffusive sampling from headspace on carbon black adsorbent in glass tubes, purging and trapping of headspace gases with carbon black adsorbent tubes, and simultaneous distillation extraction (SDE) with diethyl ether solvent. The diffusive sampling method is regarded as the most appropriate method because with the purgeand-trap method purge flow significantly determines the quantitative volatile metabolite profile and SDE causes formation of lipid oxidation products. Such an approach has been successfully employed to profile volatile metabolites to allow the differentiation of species from the P. roqueforti group. It has also been shown that P. roqueforti strains that produce PR toxin (7-acetoxy5,6-epoxy-3,5,6,7,8,8a-hexahydrocarboxaldehyde) produce the volatile metabolite (þ)-aristolochene, which is considered a biomarker for P. roqueforti within the Penicillium genus.
Genetics Penicillium roqueforti is quite a heterogeneous species and has recently been divided, based on differences in its internal transcribed spacer (ITS) regions and its secondary metabolite patterns, into three distinct species, namely, P. roqueforti, P. carneum, and P. paneum. While all three species are morphologically very similar, there are marked differences in their ability to produce secondary metabolites. Penicillium roqueforti can produce PR toxin, marcfortines, and fumigaclavine A, P. carneum can produce patulin, MPA, and penitrem A, while P. paneum produces patulin and botryodiploidin. DNA-based molecular techniques have been developed and applied in the detection and identification of
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Penicillium species. Polymerase chain reaction (PCR) primers based on the ITS region have been developed to monitor P. roqueforti in a variety of foods. These PCR primer pairs, which specifically amplify a 300-bp fragment, not only specifically identify all members of Penicillium subgenus Penicillium, but also specifically recognize P. roqueforti and P. carneum. Even though many of the P. roqueforti strains that have been isolated from Blue cheeses are known to produce both PR toxin and roquefortine and these secondary metabolites have been shown to be present in cheese, they are not thought to pose a significant health risk to consumers as they are very unstable in cheese. Notwithstanding this, P. roqueforti strains that do not produce secondary metabolites or mycotoxins would be preferable as starter cultures for cheese manufacture, from a food safety perspective. Thus, several groups have set out to develop DNA-based methods to identify P. roqueforti starter strains that do not produce toxic secondary metabolites. In this respect, Geisen and coworkers targeted the ari1 gene encoding aristolochen synthase, one of the key enzymes in the PR toxin biosynthetic pathway, in a PCR-based approach to screen for PR toxin-free strains of P. roqueforti. Using the ari1-specific PCR primers, a product of the expected length was observed in many of the 21 strains tested. However, some of the strains that were PCR-negative were also toxin producers. These were subsequently shown to be positive following dot-blot hybridization using an ari1-specific gene probe, indicating the presence of ari1 genes in some P. roqueforti strains with altered PCR primer binding sites. Another potential problem with this method was also identified whereby ari1 gene homologues were observed in Penicillium species, such as P. italicum and P. nalgiovense, which are known not to produce PR toxin. Thus the group advise that care should be taken when using a monomeric PCR reaction, which targets only one mycotoxin biosynthetic gene, as the primers may not be sufficiently specific to detect the mycotoxin-producing fungus. More recently, the group have successfully performed random amplified polymorphic DNA (RAPD) analysis, using three primers (ari1 (CTGCTTGGCA CAGTTGGCTTC), nor1 (ACCGCTACGCCGGCAC TCTCGGCAC), and omt1 (GTGGACGGACCTAGT CCGACATCA)), of 76 P. roqueforti starter culture strains and reported a correlation between RAPD patterns and the production of MPA. In addition, they reported on one fungal genotype, which was distinguishable with the ari1 primer, that produced fewer secondary metabolites than other genotypes and which did not produce PR toxin. Thus, this strain may be a good candidate for use as a safe starter culture. The group advocate that before being used as starter cultures in the dairy industry P. roqueforti strains should be checked for their inability to produce toxins in the
cheese, and suggest the approach they employed as a reliable method for achieving this goal.
Mycotoxins Produced by Penicillium roqueforti PR Toxin PR toxin is one of the most acutely toxic metabolites produced by the fungus and is frequently detected in Blue cheese. PR toxin produces acute toxic effects in animals via an increase in capillary permeability and due to direct damage to lungs, heart, liver, and kidneys. PR toxin also inhibits RNA and protein synthesis, DNA polymerase activity as well as mitochondrial respiration and oxidative phosphorylation in animal cells. It has also been reported to result in gene alterations and gene conversions in Saccharomyces cerevisiae and Neurospora crassa strain N24, respectively. A number of P. roqueforti strains have been isolated from Blue cheese, which when grown under different culture medium produce PR toxin, with levels of toxin production being highly dependent on environmental conditions. For example, when P. roqueforti is grown in yeast extract–sucrose medium, which favors the production of PR toxin, levels of between 82 and 770 mg l1 are produced. It has also been reported that toxin production is highest in stationary cultures at temperatures ranging from 20 to 24 C and at pH 4; the addition of octanoic acid to P. roqueforti cultures growing on wheat kernel medium has recently been reported to inhibit PR toxin biosynthesis. However, despite the ability of P. roqueforti strains to produce the toxin, no PR toxin or at most very low levels can be detected in cheese. Researchers believe that the microaerophilic conditions that prevail in most cheeses appear not to favor the production of PR toxin. In addition, the toxin appears to be very unstable in cheese, where it is believed to react with ammonia and free amino acids, which are present in high concentrations in Blue cheese, to form PR, which is unstable and is subsequently degraded to PR acid. Roquefortine This is an indole mycotoxin and is identical to roquefortine C. It has been assigned the structure 10b-(1,1-dimethyl2-propenyl)-3-imidazol-4-methylene-5a,10b,11,11a-tetrahydro-2H-pyrazino-[19,29:1,5]pyrrol[2,3,b]indole-1,4(3H,6H)-dione. Roquefortine is a relatively weak neurotoxin and in studies in ruminants that have consumed contaminated silage, clinical symptoms include muscle weakness and lack of coordination. Roquefortine is also reported to cause convulsive seizures in mice when injected intraperitoneally. Penicillium roqueforti strains
Yeasts and Molds | Penicillium roqueforti
isolated from Blue cheeses have been reported to produce between 0.18 and 8.44 mg l1 of roquefortine in culture medium containing yeast extract, while in experiments in which cheese was inoculated with a toxigenic strain of the fungus, levels of between 2.1 and 2.4, and 2.1 and 3.8 mg kg1 have been reported in cheese ripened at 5 and 12 C, respectively. Roquefortine C levels ranging from 0.05 to 12 mg kg1 have been reported in cheeses, while in a recent study roquefortine at concentrations of 0.8–12 mg kg1was detected in all of the 10 blue mold cheese samples obtained from Finnish supermarkets. Although roquefortine is produced by most strains of P. roqueforti that have been isolated from Blue cheese or which are used as starter cultures, the low levels of the toxin that are present in Blue cheese together with the relatively low toxicity of roquefortine are such that roquefortine is believed not to present a major health hazard to the consumer and make the consumption of Blue cheese safe. Mycophenolic Acid This is a mycotoxin and is reported to be produced by many strains of P. roqueforti that have been tested and by some other Penicillium strains, particularly P. brevicompactum and P. paneum. For example, in a study where 80 P. roqueforti strains were tested, of which 62 of the strains were starter culture strains from western Europe, only 20 were able to produce up to 600 mg of the toxin in 2% yeast extract–5% sucrose broth. MPA has antibiotic activity against bacteria and dermatophytic fungi and is also known to interfere with viral multiplication. For mammals, the toxicity of MPA is low. There are reports of toxicity in rats, with oral administration of daily doses of 30 mg kg1 resulting in anemia and death. Interestingly, MPA is routinely used in the treatment of psoriasis and in addition both MPA and MPA derivatives have been reported to have both antitumor and immunosuppressive effects. MPA is the active
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ingredient in mycophenolate mofetil (MMF), which is widely used to prevent rejection after solid organ transplantation. It acts as a reversible, noncompetitive inhibitor of inosine monophosphate dehydrogenase (IMPDH), the rate-limiting enzyme in de novo purine biosynthesis in T and B lymphocytes. Penicillium roqueforti strains isolated from baled grass silage have been reported to produce MPA, and thus subsequent consumption of this silage by livestock should be a concern for livestock producers. In one study, all 16 strains of P. roqueforti isolated from Blue cheeses have been reported to produce MPA, at levels of between 0.8 and 4 mg g1 dry culture, with the highest levels of the toxin being reported following 10 days of incubation of fungal cultures at 15 C. However, the yeast Geotrichum candidum has been reported to inhibit the growth of P. roqueforti when cocultured on agar medium at both 18–25 C and in addition to inhibit the production of MPA. See also: Yeasts and Molds: Penicillium camemberti.
Further Reading Biotechnology Program Under Toxic Substances Control Act (TSCA) (1997) Penicillium roqueforti Final Risk Assessment Attachment I. http://www.epa.gov/oppt/biotech/pubs/fra/fra008.htm (accessed May 2010). Edwards SG, O’Callaghan J, and Dobson ADW (2002) PCR-based detection and quantification of mycotoxigenic fung. Mycological Research 109: 1005–1025. Ernstrom CA and Wong NP (1974) Milk-clotting enzymes and cheese chemistry. In: Webb BH, Johnson AH, and Alford JA (eds.) Fundamentals of Dairy Chemistry, 2nd edn. Westport, CT: AVI Publishing. Karlshoj K and Larsen TO (2005) Differentiation of species from the Penicillium roqueforti group by volatile metabolite profiling. Journal of Agricultural and Food Chemistry 53: 708–715. Pitt JI and Hocking AD (1997) Penicillium and related genera. In: Pitt JI and Hocking AD (eds.) Fungi and Food Spoilage, 2nd edn.,ch.7, pp. 203–338. London: University Press Cambridge.
Penicillium camemberti A Abbas and A D W Dobson, University College, Cork, Ireland ª 2011 Elsevier Ltd. All rights reserved.
Introduction Penicillium camemberti was first described by Thom and is thought to be a domesticated form of P. commune. A number of synonyms exist for the species including P. rogeri, P. candidum, P. album, and P. caseicolum. The fungus is mainly (almost exclusively) found either on cheese or in the cheese factory environment and is rarely found away from this environment. Penicillium camemberti is used in the production of Camembert and Brie cheeses, on which colonies of the fungus form a white crust. It is also used as a starter culture for fermented meat products and is often found as a spontaneous colonizer of fermented sausages originating from the mycobiota of the production facility. There have been reports on the wider exploitation of P. camemberti especially in the decontamination of softwood bleach effluents, which contain high levels of ecologically undesirable phenolic and chlorinated phenolic compounds. Therefore, P. camemberti, which to date has been predominantly used in the dairy industry, may also find future utility in other nondairy-related areas.
Growth Characteristics of Penicillium camemberti Colony diameter on Czapek yeast extract agar (CYA) is typically 19–27 mm at room temperature (24–26 C) after 10 days. Colonies on CYA appear yellow/orange or green to fawn to pale brown/blue in color. The reverse sides of the colonies on CYA typically appear either yellow/ orange or green brown in color. Colony diameter on malt extract agar (MEA) is typically 12–27 mm. Colonies on MEA also appear yellow/orange or green in color, with the reverse sides of the colonies being red, olive, green, or brown in color depending on the growth medium. The optimum growth temperature range is 20–25 C, with growth being recorded at 5 C but not at 37 C. With respect to pH, growth can take place in the pH range of 3.5–6.5. Penicillium camemberti has similar water activity (aw) limits for growth as P. roqueforti with an optimum aw value of 0.998 for growth at 25 C and an ability to grow in the aw range from 0.91 to 0.94. Thus, from a pH standpoint, P. camemberti is ideal as a starter culture given that the pH of Camembert and related types of cheese reaches about 4.6 during the first 24 h and eventually following maturation increases to around 5.5
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in the center of the cheese and around 7.0 in the outer part of the cheese. Similarly, it is suitable as a starter culture from an aw standpoint given that the aw of the surface and center of Camembert cheese has been recorded as 0.93 and 0.97, respectively. The salt tolerance of the fungus coupled with its ability to grow at an aw of 0.93 results in it growing on the surface of Camembert cheese during the cheese maturation process. However, it is only after 1 week of ripening that P. camemberti is observed, and within 2–3 weeks it covers the entire surface of the cheese. During this process, the fungus also metabolizes lactate to CO2 and H2O at the surface of the cheese to establish a pH gradient, which is a key factor in the maturation process, and results in a higher pH. This effect is pronounced on the surface of the cheese, with a pH gradient becoming established toward the center of the cheese, resulting in lactate migrating toward the surface, where it is assimilated as a carbon source by the fungus. This depletion of lactate in the center of the cheese results in casein being degraded primarily by enzymes from the rennet, the plasmin from the milk, and by enzymes from the lactic acid starter cultures. Ammonia is formed at the surface of the cheese from amino acids, the consequence of which is a further increase in pH. The proteinases from P. camemberti are activated by the increasing pH and they migrate only slowly into the cheese. During ripening, the dynamics of sporulation of P. camemberti is affected by the concentration of CO2 in the atmosphere. For example, the number of P. camemberti spores present in the rind is fairly constant at around 104 cfu g1 during the first 6 days of ripening at 6% CO2. However, at 2% CO2, the fungus is known to sporulate at a faster rate and spore counts can reach levels as high as 106 cfu g1 on the 6th day of growth. After day 11 and until day 40, sporulation remains stationary, close to 106 cfu g1. Regardless of CO2 concentration, the mycelium of P. camemberti begins to grow from day 4 onward with both mycelium and aerial mycelia being visible. Between days 5 and 12, the mycelia grow and uniformly cover the entire cheese surface. From day 10 to 16, if the cheese is wrapped, the rind color remains white and is around 3 mm thick. Increases in CO2 concentration above 2% negatively affect the growth of P. camemberti on cheese. Because in Camembert-type cheese, P. camemberti is generally inoculated in a mixed culture with Geotrichum candidum, CO2 is known to alter the equilibrium between
Yeasts and Molds | Penicillium camemberti
these two strains, with higher CO2 concentrations favoring G. candidum and resulting in poorer development of P. camemberti mycelium.
Enzymes Produced by Penicillium camemberti Penicillium camemberti produces a variety of different proteinases including two extracellular endopeptidases. One of the two extracellular endopeptidases is a metalloprotease and is the principal proteolytic enzyme active at close to neutral pH values (pH 6.5). It is similar to the metalloprotease produced by P. roqueforti. At acidic pH (pH 4.0), P. camemberti produces an acid protease. Other proteolytic enzymes produced by P. camemberti include an aminopeptidase and a carboxypeptidase. These proteolytic enzymes play an important role in cheese ripening. There are some differences between strains with respect to the production of different types of proteinases. There is, however, greater variation between P. camemberti strains in their ability to produce extracellular lipolytic enzymes. The lipase system is active within broad pH (5.5–9.5) and temperature (1–35 C) ranges.
Penicillium camemberti as a Biocontrol Agent in Cheese Starter cultures are known to contribute to the inhibition of the undesirable growth of fungal contaminants and mycotoxin production in fermented foods. When P. camemberti is used as secondary starter culture, it exerts a powerful inhibitory effect on many common cheese contaminants such as Cladosporium herbarum, P. roqueforti, P. caseifulvum, and P. commune. The antagonistic power of P. camemberti is strain dependent in that the growth inhibition of C. herbarum is not affected by the choice of the strain of P. camemberti, whereas the Penicillium contaminants are very sensitive to the choice of strain. The antagonistic activity is much stronger when P. camemberti is used as pure culture, with the inhibitory activity being reduced considerably if the fungus is used in a mixed culture, for example with G. candidum.
Secondary Metabolism in Penicillium camemberti A number of Penicillium toxins have been identified in contaminated cheese, including roquefortin C, isofumigaclavine A, cyclopiazonic acid (CPA), mycophenolic acid, and, much less frequently, ochratoxin A and PR toxin. A few strains of P. camemberti are known to produce a number of secondary metabolites such as cyclopaldic
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acid, rugulovasine A, and rugulovasine B as well as palitantin. However, CPA, which is a neurotoxic and immunosuppressive compound, remains the most significant toxin produced by P. camemberti, particularly at higher storage temperatures. The toxicity of CPA results in a large part from its specific inhibition of calciumdependent ATPase in the sarcoplasmic reticulum, leading to altered cellular (Ca2þ) levels and resulting in increased muscle contractions. CPA is almost exclusively found in the rind but not in the core of the cheese. This is due to the inability of P. camemberti to grow in the cheese core. CPA does not appear to constitute a major threat to the consumer with the highest levels in cheese being reported to date at >2 ppm, which would constitute 0.5 mm per 0.3 m3 of air, providing a room that is considered to be bacteria-free, because there are 0.98), lag times vary from a few hours to several days, and they can even extend to several months at lower aw. The salinity and osmotic pressure of the growth medium affect the production of conidia. The vegetative growth of A. flavus increases with an increase in the NaCl content up to 9% NaCl, but at higher salt concentrations inhibitory effects are observed on the production of conidia. However, A. flavus growth and aflatoxin production on processed cheese have been shown to be reduced through the addition of 6% NaCl. The lower limit of moisture for growth
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of A. flavus on cereal grains such as maize, wheat, sorghum, and rice is 18.0–18.5%; for soybeans it is 17–17.5%; and for peanuts, sunflower seeds, and copra it is 11.0–12.0%. Survival of conidia of A. flavus in a variety of dried foods (aw 0.32–0.78) at 21 C is reduced at high aw and low pH. The effect of aw on colony growth rate for each species has been employed to quantify the ‘relatedness’ of four species belonging to Aspergillus sect. Flavi (A. flavus, A. oryzae, A. parasiticus, and A. nomius). A linear model was subsequently proposed in which A. oryzae and A. parasiticus are very close to each other, placed between A. nomius and A. flavus and closer to the latter species. Temperature Aspergillus flavus grows at temperatures as low as 10–12 C and as high as 50–55 C, with optimal growth occurring at temperatures near 33 C. At optimal growth temperatures specific growth rates can reach 500 mm h 1 (or approximately 25 mm day 1). While most storage fungi have a minimum temperature for growth of 0–5 C, optimum of 25–30 C, and a maximum of 40–45 C, A. flavus has been reported to grow on Cheddar cheese at 15, 18, or 25 C and to produce aflatoxin on the cheese at 25 C. Aspergillus flavus can grow vigorously at 50–55 C and can raise the temperature of the materials in which it is growing to that level, maintaining it there for some weeks. The fungus is not very heat resistant, with a D45 value of more than 160 h, a D50 of 16 h, a D52 of 40–45 min, and a D60 of 1 min, at neutral pH and high aw, with z-values from 3.3 to 4.1 C being reported. aw provides a degree of protection. At 52 C, the D-values for conidia increase from 44 to 54 min with increase in level of sucrose from 0 to 60% (aw 0.99–0.89). In addition, high sucrose concentrations reduce the effect of preservatives on D-values. Thus, in general, preservatives act synergistically with heat at low aw values to reduce heat resistance in A. flavus. The combined and independent effects of sucrose, sodium chloride, potassium sorbate, and sodium benzoate on heat inactivation of conidia of A. flavus have shown that increasing concentrations of sucrose results in increased tolerance to heat by the fungus, while low concentrations (3 and 6%) of sodium chloride also protect A. flavus. Potassium sorbate and sodium benzoate acted synergistically with heat to reduce sensitivity to preservatives and reduced aw, whether achieved by the presence of sucrose or sodium chloride, thus demonstrating heat-induced injury. At the same concentration, potassium sorbate is more inhibitory than sodium benzoate to colony formation by A. flavus, and the presence of sucrose and sodium chloride enhances this inhibition. Conidia of A. flavus have been reported to be resistant to freezing in water at 73 C. It is believed that this survival may be partially due to a very low water content such that little or no ice formation occurs, which can affect the integrity of the
spore. Aspergillus flavus is also extremely tolerant to freezing injury, remaining viable for over 20 years in liquid nitrogen vapor. pH Several reports have singled out the importance of pH on mold growth and indicated that the pH effect may vary with mold type, acid, and levels of other variables. Growth of A. flavus is largely unaffected by pH; it can grow over the entire pH range from 2.1 to 11.2, although growth rates are slower at pH G1 > B2 > G2). In an in vitro experiment, the dihydrobisfuran moiety in aflatoxin B1 easily formed a covalent by bonded adduct with the base part of nucleic acid by way of an 8,9-epoxide type intermediate, suggesting that the carcinogenicity of aflatoxins B1 and G1 is the result of the dihydrobisfuran
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Figure 1 Structures of aflatoxins B1, B2, G1, and G2, and sterigmatocystin.
moieties in their molecules, which inhibit normal protein biosynthesis by the formation of an adduct with the base part of nucleic acid (Figure 2). Sterigmatocystin was first isolated as a yellow pigment from A. versicolor in 1954, and the structure was established in 1962 (Figure 1). Sterigmatocystin has also been isolated from Aspergillus aurantio-brunneus, Aspergillus amstelodami, Aspergillus chevalieri, A. flavus, Aspergillus multicolor, Aspergillus nidulans, A. parasiticus, Aspergillus quadrilineatus, Aspergillus ruber, Aspergillus unguis, and Aspergillusustus. Sterigmatocystin, the dihydrobisfuran moiety, which has the same configuration as that of aflatoxins, has already been shown to be a natural biosynthetic precursor of aflatoxin produced by A. parasiticus. Although sterigmatocystin has a dihydrobisfuran moiety quite similar to that of aflatoxin B1, the carcinogenicity of sterigmatocystin is only about onehundredth of that of aflatoxin B1 because the solubility of sterigmatocystin is so much lower than those of aflatoxins. Sterigmatocystin has been reported in Gouda and Edam cheese contaminated by A. versicolor (see Yeasts and Molds: Mycotoxins: Aflatoxins and Related Compounds).
Bisanthraquinonoids: ()-Luteoskyrin and (þ)-Rugulosin Rice contaminated with P. islandicum, P. rugulosum, P. citrinum, and P. citreoviride becomes yellow. ()-Luteoskyrin has been isolated as a yellow pigment from rice infected with P. islandicum; it possesses a unique cage-type dimeric bisanthraquinonoid structure and shows levorotatory optical activity (Figure 3). The bisanthraquinonoid structure of ()-luteoskyrin is formed from two molecules of anthraquinone, which are synthesized from octaketide through the acetate–malonate pathway. ()-Luteoskyrin causes hepatopathy, including liver necrosis, fatty degeneration, and hepatic cancer. Hepatoma was induced by ()-luteoskyrin in a dose-dependent manner when administered to mice for 216 days at 16.7, 68.8, and 84.6% at 50, 150 and 500 mg day1, respectively. This tumorigenic effect on the livers of mice was greater in males than in females. Another yellow pigment, (þ)-rugulosin, has been isolated from P. rugulosum. The structure of (þ)-rugulosin is also a cage-type bisanthraquinonoid very similar to that of ()-luteoskyrin, but this compound is dextrorotatory (Figure 3). (þ)-Rugulosin also causes hepatic necrosis, fatty degeneration, and hepatic cancer in mice, but the
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Figure 2 Suggested role of the dihydrobisfuran moiety of aflatoxin B1 in its carcinogenicity.
Figure 3 Structures of ()-luteoskyrin, (þ)-rugulosin, citrinin, and ochratoxin A.
toxicity of this compound is about one half of that of ()luteoskyrin. Citrinin and Ochratoxin A The yellow pigment, citrinin, has been isolated from P. citrinum found on yellow rice called ‘citrinum yellow rice’. Citrinin, which is biosynthesized from a pentaketide
through the acetate–malonate pathway with three C1-sources, causes renal damage in swine. It has also been shown to possess antibacterial, antifungal, and antiprotozoal activity. Citrinin was previously used as an antibiotic, but was later banned because of its nephrotoxicity. Ochratoxin A has been isolated from A. ochraceus, which grows on many types of farm produce. It is an amide formed from a bicyclic carboxylic acid synthesized
Yeasts and Molds | Mycotoxins: Classification, Occurrence and Determination
from a pentaketide with a C1-source and L-phenylalanine, and has been shown to cause kidney necrosis and cancer. It is now known that a renal inflammation (nephropathy), which sometimes appears in swine in Northern Europe, results from poisoning by citrinin and ochratoxin A produced by Penicillium viridicatum, which contaminates feed (Figure 3). There is some evidence that ochratoxin A can be produced in cheese contaminated by Penicillium spp. Fumonisins Fumonisins have been isolated from a fungal contaminant of maize, F. verticillioides (formerly Fusarium moniliforme), which occurs worldwide (the teleomorphic state: Gibberella fujikuroi), and Fusarium proliferatum. It has been shown that fumonisins cause leukoencephalomalacia in horses and pulmonary edema in swine. Several congeners of fumonisins, that is, fumonisins A1, A2, B1, B2, B3, and B4, are known (Figure 4). It has been established that fumonisin B1 causes hepatocarcinoma in male rats fed with feed containing 50 mg kg1 for prolonged periods, and also causes nephrosis in male rats fed with 9 mg kg1. Fumonisins, which have a long carbon chain aminoalcohol structure as their basic skeleton, are structurally similar to sphingosines (sphingoids). In fact, it has been demonstrated that fumonisins inhibit sphingolipid metabolism, and consequently, disrupt critical sphingolipid-mediated cell signaling pathways or sphingolipid-dependent physiological functions.
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Other Carcinogenic Mycotoxins A cyclic chlorine-containing pentapeptide named ‘cyclochlorotine’ has been isolated together with ()-luteoskyrin from P. islandicum growing on rice (Figure 4). It has been shown that cyclochlorotine causes hepatopathy in mice, which results in hepatic cancer. Cyclochlorotine also has a cytotoxic effect on cultured cells. Patulin, which has been isolated from P. patulum and Aspergillus clavatus, and penicillic acid, which has been isolated from P. cyclopium, P. puberulum, and many other Penicillium and Aspergillus fungi, are the compounds possessing an , -unsaturated -lactone structure, which is formed via opening of an aromatic ring from tetraketide through the acetate–malonate pathway (Figure 4). Subcutaneous injection of patulin or penicillic acid causes sarcoma in experimental animals. The presence of patulin has been reported in cheese contaminated with Penicillium spp.
Neurotropic Mycotoxins Citreoviridin In 1940, an extract of Penicillium toxicarium (the synonym of P. citreoviride), which contaminated Formosan rice called ‘toxicarium yellowed rice’, was found to cause ascending paralysis, hypothermia, and breathing
Figure 4 Structures of fumonisins, cyclochlorotine, patulin, and penicillic acid.
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Figure 5 Biosynthesis of citreoviridin.
difficulties in mice. These symptoms were thought to be similar to those of cardiac beriberi, which was widespread until about 1925 in Japan and later disappeared. At that time, vitamin B1 was ineffective against cardiac beriberi. In 1947, a yellow pigment named ‘citreoviridin’ was isolated from P. citreoviride, and some time later, this compound was found to be the toxic factor of this fungus. Citreoviridin is formed from 2-pyrone, a conjugated polyene chain, and a tetrahydrofuran moiety is synthesized from nonaketide and C1-sources through the acetate–malonate pathway (Figure 5). Citreoviridin causes neural damage including ascending paralysis in mice, suggesting that the conjugated polyene system in this compound may affect the electron transport system in mice. It is now being suggested that cardiac beriberi, a disease of the past, may have resulted from ingestion of rice contaminated with citreoviridin.
Tremorgenic Dioxopiperazines In 1971, it was discovered that the extract of A. fumigatus grown on miso (bean paste) and rice caused marked tremor in mice and rats. Subsequently, tremorgenic constituents named ‘fumitremorgins A and B’ were isolated from the extract. Fumitremorgins A and B are composed of a basic skeleton of 2,5-dioxopiperazine formed from L-tryptophan and L-proline, with three and two isoprenyl (C5) units in fumitremorgins A and B, respectively (Figure 6). The ED50 values of fumitremorgins A and B needed to cause tremor in mice are 0.18 and 3.5 mg kg1 i.p., respectively. The tremor induced by fumitremorgin A increases with a high level of serotonin, which is an excitatory neurotransmitter in the central nervous system in the brain of mice, and decreases at a high level of
-aminobutyric acid (GABA), which is a suppressive neurotransmitter. Verruculogen isolated from P. verruculosum obtained from peanuts has the structure of fumitremorgin A except that the isopentenyl ether group is replaced with a hydroxyl group in verruculogen (Figure 6). Verruculogen shows tremorgenic activity similar to that of fumitremorgin A. Both fumitremorgin B and verruculogen are produced by Aspergillus caespitosus and Penicillium piscarium. Verruculogen is also produced by Penicillium paraherquei, and both fumitremorgins A and B are produced by Neosartorya fischeri (the teleomorphic state of A. fumigatus). Roquefortine (the synonym: roquefortine C) was isolated in 1976 from P. roqueforti, which is a mold used in the production of blue cheese. Roquefortine, which possesses a dioxopiperazine skeleton composed of tryptophan and histidine with an isopentenyl unit, also exhibits tremorgenic activity (Figure 6). Roquefortine has also been isolated from Penicillium crustosum.
Tremorgenic Indoloditerpenes Paxilline, a tremorgenic compound, was isolated from P. paxilli grown on pecans in 1974, and the structure was determined by X-ray crystallographic analysis in the following year (Figure 7). This was the first tremorgenic indoloditerpene (meaning: indole þ diterpene) to reveal its structure. Paspalinine was isolated from Claviceps paspali as its tremorgenic factor in 1977. Claviceps paspali was suspected to be the causative mold of a neuroataxia of cattle in the United States called ‘paspalum staggers’; its structure was determined in 1980 (Figure 7). Metabolites such as paxilline and paspalinine are thought to be synthesized from
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Figure 6 Structures of fumitremorgins A and B, verruculogen, and roquefortine.
Figure 7 Structures of paxilline, paspalinine, aflatrem, and penitrem A.
tryptophan and geranylgeraniol through the pathway shown in Figure 8. Aflatrem was isolated from A. flavus in 1964 as the tremorgenic agent in this fungus (probably the first tremorgenic metabolite to be isolated from fungi), and its
structure was established in 1980 (Figure 7). In 1968, penitrem A was isolated from P. cyclopium obtained from peanuts implicated in a case of sheep poisoning; it was later also isolated from Penicillium palitans and P. crustosum. The structure of penitrem A was established in 1981
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Figure 8 Suggested biosynthetic route for indoloditerpenes. Adapted from Turner WB and Aldridge DC (1983) Fungal Metabolites II. London: Academic Press.
(Figure 7). It is a derivative of tremorgenic indoloditerpenes; the skeleton of this metabolite is formed from tryptophan, geranylgeraniol, and two further isoprenyl units. This compound is believed to be one of the substances that causes a neuroataxia of cattle named ‘ryegrass staggers’, which occurs in New Zealand and Australia.
including various macrocyclic-type trichothecenes such as verrucarin A isolated from M. verrucaria, are known (Figure 9). These macrocyclic-type trichothecenes are particularly toxic. Various trichothecenes are produced by some species in the genera Fusarium, Trichothecium, Trichoderma, and Myrothecium. Sporidesmins
Other Mycotoxins Trichothecenes Fusarium toxicosis results from toxic metabolites of Fusarium nivale and other Fusarium spp. isolated from wheat and pasture. The causative agents of this toxicosis are nivalenol, deoxynivalenol, T-2 toxin, fusarenon-X, and related compounds, which belong to a sesquiterpene group named ‘trichothecenes’ (Figure 9). Trichothecenes, which possess the unique sesquiterpene skeleton named ‘trichothecane’, cause hemorrhage, vomiting, diarrhea, anorexia, and malfunction of hematopoietic organs, resulting in decreased lymphocyte production and, consequently, immunodeficiency in mice, rats, and swine. The key target cells of trichothecenes are leukocytes, and the toxicity of trichothecenes is complicated because they are immunostimulatory at low doses, but immunosuppressive at high doses. Many compounds belonging to trichothecenes,
In New Zealand, a photohypersensitive exudative eczema called ‘facial eczema’ occurs sometimes in sheep. Sporidesmins have been isolated from the fungus Pithomyces chartarum (the synonym of Sporidesmium bakeri) found in the feed associated with this disease of sheep. This disease is characterized by both photohypersensitive eczema and hepatopathy, which ultimately result in death several weeks later. Sporisdesmins are composed of many congeners, that is, sporidesmin (synonym: sporidesmin A), and sporidesmins B–J. Each sporidesmin possesses a 2,5-dioxopiperazine skeleton formed from tryptophan and alanine as the basic common structure. The dioxopiperazine ring is bridged with a disulfide chain in sporidesmin and sporidesmin B, with a trisulfide chain in sporidesmin E, and with a tetrasulfide chain in sporidesmin G to form epidithio-, epitrithio-, and epitetrathio-dioxopiperazine structures, respectively. These sulfide bridges are eliminated or modified in sporidesmins C, D, and F (see Figure 9). The relative ratio of
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Figure 9 Structures of five trichothecenes, seven sporidesmins, and zearalenone.
cytotoxic activity of di-, tri-, and tetrasulfides against HeLa epithelial cells is 1:4:1. Sporidesmins whose sulfide bridges have been eliminated or modified show no activity. Zearalenone Zearalenone was isolated from Fusarium roseum (F. graminearum, teleomorphic state: Gibberella zeae), which grows on the maize fed to swine. Zearalenone exhibits estrogenic activity, enlarging the uterus and mammary glands, and causing swelling of the vulva (vulvovaginitis) in sows. Hyperestrogenism resulting from zearalenone has also been reported in other animals (and in humans), but swine is perhaps the species most sensitive to this compound. Zearalenone is thought to be synthesized from nonaketide through the acetate–malonate pathway (Figure 9).
from Phomopsis leptostromiformis, which infects the lupin, interferes with tubulin function. Cytochalasins isolated from Helminthosporium dematioideum and chetoglobosins isolated from Chaetomium globosum show inhibition of cytoplasmic cleavage in mammalian cell culture to form large multinuclear cells. For information on the occurrence and significance of mycotoxins in milk and dairy products, see Contaminants of Milk and Dairy Products: Environmental Contaminants.
See also: Contaminants of Milk and Dairy Products: Environmental Contaminants. Yeasts and Molds: Aspergillus flavus; Mycotoxins: Aflatoxins and Related Compounds.
Further Reading Miscellaneous Mycotoxins There are many other important mycotoxins known today. Lysergic acid amides isolated from Claviceps purpurea (ergot), which contaminate rye, are notorious as the causative agents of ergotism. Rubratoxins isolated from Penicillium rubrum obtained from grains and other feedstuffs have a cytotoxic effect. Phomopsin A isolated
Betina V (1984) Zearalenone and brefeldin A. In: Betina V (ed.) Mycotoxins Production, Isolation, Separation and Purification, pp. 237–257. Amsterdam, The Netherlands: Elsevier Science. Bullerman LB (2000) Mycotoxins: Classification. In: Robinson RK, Batt CA, and Patel PD (eds.) Encyclopedia of Food Microbiology, Vol. 2, pp. 1512–1520. London: Academic Press. de Nijs M and Notermans SHW (2000) Mycotoxins: Occurrence. In: Robinson RK, Batt CA, and Patel PD (eds.) Encyclopedia
800 Yeasts and Molds | Mycotoxins: Classification, Occurrence and Determination of Food Microbiology, Vol. 2, pp. 1520–1526. London: Academic Press. Fujimoto H (1991) Chemistry of food-contaminated mycotoxins. Japanese Journal of Food Microbiology 8: 27–35. Iwasaki S (1992) Chemistry and biological activity of the mycotoxins interfering with tubulin function. Proceedings of the Japanese Association of Mycotoxicology 35: 1–6. Kumeda Y (2008) A simple genetic method for identification of mycotoxigenic fungi – Development of heteroduplex panel analysis and its field application. Mycotoxins (Journal of the Japanese Society of Mycotoxicology) 58(1): 29–40. Nagarajan R (1984) Gliotoxin and epipolythiodioxopiperazines. In: Betina V (ed.) Mycotoxins: Production, Isolation, Separation and Purification, pp. 351–385. Amsterdam, The Netherlands: Elsevier Science. Pestka JJ, Zhou H-R, Moon Y, Chung Y, and Islam Z (2004) Molecular mechanisms of trichothecene toxicity. In: Yoshizawa T (ed.) New Horizon of Mycotoxicology for Assuring Food Safety (Proceedings of the International Symposium of Mycotoxicology in Kagawa 2003), pp. 17–31. Tokyo: Japanese Association of Mycotoxicology.
Turner WB and Aldridge DC (1983) Fungal Metabolites II. London: Academic Press. Ueno Y (1984) Trichothecenes: Recent researches and topics. Proceedings of the Japanese Association of Mycotoxicology 19: 2–7. Van Egmond HP (ed.) (1989) Mycotoxins in Dairy Products. London: Elsevier Applied Science. Van Egmond HP, Svensson UK, and Fremy JM (1997) Mycotoxins. In: Residues and Contaminants in Milk and Milk Products, pp. 79–88. International Dairy Federation. Special Issue 9701. Brussels: IDF. Voss KA, Chamberlain WJ, Riley RT, Bacon CW, and Norred WP (1994) In vitro and In vivo effects of fumonisins: Toxicity and mechanism of action. Mycotoxins 39: 1–12. Voss KA, Riley RT, Gelineau-van Waes JB, and Bacon CW (2004) Fumonisins: Toxicology, emerging issues, and prospects for control and detoxification. In: Yoshizawa T (ed.) New Horizon of Mycotoxicology for Assuring Food Safety (Proceedings of the International Symposium of Mycotoxicology in Kagawa 2003), pp. 41–48. Tokyo: Japanese Association of Mycotoxicology. Weidenbo¨rner M (2001) Encyclopedia of Food Mycotoxins. Berlin: Springer-Verlag.
Mycotoxins: Aflatoxins and Related Compounds S Tabata, Tokyo Metropolitan Institute of Public Health, Tokyo, Japan ª 2011 Elsevier Ltd. All rights reserved.
Introduction Aflatoxins (AFs) are very important mycotoxins due to their extremely high toxicity, carcinogenic activity for animals (including humans), and frequent occurrence in various foods and feedstuffs. AFs found in 1961 in Brazilian groundnut meal were the source of the toxicity associated with ‘turkey X’ disease; more than 100 000 turkeys died in the United Kingdom. Since then, many researchers have vigorously investigated AFs, particularly AFB1, in various fields.
Structure and Chemical Properties More than 10 types of AFs and related compounds have been identified. Among them AFB1, AFB2, AFG1, and AFG2 are especially important because they are highly toxic and often occur in foods and feeds. The structures of the major AFs are shown in Figure 1. AFB1 is representative of the AFs and contains a dihydrobisfuran and coumarin nucleus fused to cyclopentanone. AFB2 is 8,9-dihydro-AFB1. In the AF-G group, sixmembered lactone is substituted by the cyclopentanone of AF-B group. The origins of the names AF-B and AF-G lie with the ‘b’ and ‘g’ of the blue and green fluorescent colors produced under ultraviolet (UV) light on thin-layer chromatography (TLC). AF-M group are 9a-hydroxy derivatives of the AF-B group and are found in cows’ milk as metabolites of the AF-B group in their feeds. Ingested AFB1 is converted to AFM1 in the cows’ liver, and approximately 0.9% of ingested AFB1 is found in the milk as AFM1. AFM1, a major animal metabolite of AFB1, is found in the urine of AFB1-exposed animals at levels of up to 20% of the ingested oral dose. AFB2a and AFG2a are 8-hydroxy AFB1 and AFG1, respectively, formed under acidic conditions (below pH 3) from parent AFs. Aflatoxicol (AFL)-I is a major metabolite of AFB1 formed by microorganisms, and AFL- is the stereoisomer of AFL-I. These are reduced to AFB1; the keto moiety on the terminal cyclopentanone of AFB1 is reduced to a hydroxy group. Most of the other AFs known are hydroxylated metabolites of AFs, such as AFP1 (O-demethylated AFB1), AFQ1 (3-hydroxy AFB1), AFGM1 (10a-hydroxy AFG1), AFL-M1 (9a-hydroxy AFL), and AFL-H1 (3-hydroxy AFL). AFs are slightly soluble in water, insoluble in nonpolar solvents, and soluble in moderately polar or polar organic
solvents such as chloroform, acetonitrile, and methanol. Most AFs have intense blue or green fluorescence (emission wavelength: 420–450 nm) under UV light (excitation wavelength: 350–370 nm).
AF-Producing Fungi AFs are produced in nature only by some strains of Aspergillus flavus, most strains of Aspergillus parasiticus, and Aspergillus nomius. Aspergillus flavus, the origin of the name of aflatoxin, is the main source of AFs, but not all strains produce AFs. It has recently been reported that Aspergillus tamarii also produces the AF-B group. Generally, A. flavus produces only the AF-B group, whereas A. parasiticus and A. nomius produce the AF-B and AF-G groups. In most strains, AFB1 is produced in the largest quantities. AFB2 and AFG2 are produced at one-tenth to one-third of the amount of AFB1 and AFG1, respectively. Aspergillus oryzae, the domesticated form of A. flavus, adapted by centuries of use in fermented food manufacture, never produces AFs.
Condition Favoring Production of AFs The limiting temperature and relative humidity for AF production vary slightly depending on the kind and quality of food. The lower limiting temperature for AF production is approximately 12 C, whereas the upper limiting temperature is 41 C at 99% relative humidity. The limiting relative humidity is approximately 83% or higher at 30 C, varying with the type of growth medium and length of the incubation period. Reducing oxygen concentration generally leads to a reduction in the amount of AF produced, notably so at an oxygen concentration of less than 1%. The presence of certain amino acids, fatty acids, and zinc ions stimulates the formation of AFs.
Biosynthesis The intermediates in the biosynthetic pathway of AFB1, AFB2, AFG1, and AFG2 have been determined, and the synthetic steps were revealed by feeding studies
801
802 Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds
Figure 1 Structures of major aflatoxins.
with radioactive precursors, pathway-blocked mutant strains, and metabolic inhibitors. AFs are formed by head-to-tail condensation of acetyl units to form a cyclized polyketide, which is enzymatically altered through a series of intermediates. At least 18 enzymatic steps are required for conversion of acetyl coenzyme A (acetyl-CoA) and malonyl coenzyme A (malonyl-CoA) to its final product, AFB1. The generally accepted pathway for the production of AFB1 and AFG1 is as follows: acetylCoA þ malonyl-CoA ! hexanoyl-CoA ! norsolorinic acid ! averantin ! 59-hydroxyaverantin ! averufin ! versiconal acetate ! versiconal ! versicolorin B ! versicolorin A ! demethylsterigmatocystin ! sterigmatocystin ! Omethylsterigmatocystin ! AFB1 and AFG1. The enzymatic reactions in the synthesis of AFB2 and AFG2 are the same as AFB1 and AFG1, except for the formation of dihydrodemethylsterigmatocystin from versicolorin B.
Acute Toxicity in Animals AFs are toxic to many forms of life, including animals, birds, and fish. LD50 values of AFB1 are shown in Table 1. The sensitivity toward AFs differs with animal species. Mice and hamsters are relatively resistant to acute AFB1,
whereas ducks, rabbits, and rainbow trout are relatively sensitive. Structure–activity relationship has been studied for four major AFs: AFB1, AFB2, AFG1, and AFG2. Their acute toxicity in rats and ducklings followed the order AFB1 > AFG1 > AFB2 > AFG2. AFs containing an unsaturated terminal furan (AFB1 and AFG1) are much more potent than AFs containing a saturated terminal furan (AFB2 and AFG2). These results indicate that the presence of the double bond in the terminal furan is an important determinant of potential for acute toxicity, and that AFs containing cyclopentanone are more acutely toxic than AFs containing six-membered lactone.
Mutagenicity AFB1 is potently mutagenic for Salmonella strains (TA100 and TA98) at a low dose level (0.1 mg plate1) in the presence of S-9 mix, coenzymes and buffer. It is known that activated AFB1 induces guanine-cytosine to thymine-adenine transistion in genes. The activated K-ras gene detected in AF-induced primary liver tumor contained a guanine to adenine transition in codon 12.
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Table 1 Oral LD50 of aflatoxin B1 Animal
LD50 (mg kg1)
References
Rabbit Duck Cat Dog Pig Horse Rainbow trout Calf Sheep Turkey Guinea pig Monkey Rat Mouse Hamster
0.3–0.4 0.3–0.6 0.5 0.5–1.0 0.6–1.0 0.6–1.0 0.8 1.0–1.5 1.0–2.0 1.4 1.4 2.2–7.8 1.0–17.9 9.0 10.2
Butler (1974), Pier (1992) Butler (1974), Pier (1992), Robens and Richard (1992) Butler (1974) Butler (1974), Robens and Richard (1992) Butler (1974), Pier (1992) Pier (1992) Bauer et al. (1969) Pier (1992) Butler (1974), Pier (1992) Pier (1992) Butler (1974) Campbell and Stoloff (1974) Butler (1974), Robens and Richard (1992) Butler (1974) Butler (1974), Robens and Richard (1992)
Butler WH (1974). Chapter 1 ALFATOXIN In: Purchase IFH (ed.) Mycotoxins, pp. 10–28. Amsterdam – Oxford – New York: Elsevier Scientific Company. Pier AC (1992). Major biological consequences of aflatoxicosis in animal production. Journal of Animal Science 70: 3964–3967. Robens JF and Richard JL (1992). Aflatoxins in animal and human health. Reviews of Environmental Contamination and Toxicology 127: 69–94. Bauer DH, Lee DJ, and Sinnhuber RO (1969). Acute toxicity of aflatoxins B1 and G1 in the rainbow trout (Salmo gairdneri). Toxicology and Applied Pharmacology 15: 415–419. Campbell TC and Stoloff L (1974). Implication of mycotoxins for human health. Journal of Agricultural and Food Chemistry 22: 1006–1015.
Among AFs and related compounds, AFB1 is the most potent, followed by AFL, AFG1, AFM1, AFB2, AFG2, and AFB2a.
classified AFs under group 1 carcinogens, which means that they are carcinogenic to humans.
Metabolism and Mechanism of Toxicity Carcinogenicity AFB1 is one of the most potent carcinogens known. The major target organ of AFB1 is the liver. One hundred percent (12/12) of male rats given 15 mg kg1 dietary AFB1 for 68 weeks, and 100% (13/13) of female rats fed the same diet for 82 weeks developed hepatocellular carcinomas. The carcinogenicity of AFs has been demonstrated in a variety of animals such as ducks, rats, monkeys, and rainbow trout. Other AFs (AFB2, AFG1, AFL, AFM1, and AFQ1) have also been proved to be carcinogenic. The order of carcinogenic potency in rainbow trout was AFB1 > AFL > AFM1 > AFQ1 > AFG1, whereas AFB2 and AFG2 were inactive. Overall, these results indicate that the presence of the double bond in the terminal furan ring is the most important determinant for toxic and carcinogenic activity. The importance of the substitutes on the lactone portion of the molecule is also illustrated by the difference in the potency of AFB1 and AFG1 in all systems studied. The International Agency for Research on Cancer (IARC) evaluated the carcinogenic risk of AFs and
The metabolic pathways for AFB1 in animals are shown in Figure 2. After intake, AF is metabolized by cytochrome p450 in the liver to several compounds; most of them are hydroxylated derivatives, such as AFM1 and AFP1, and are less toxic than AFB1. AFM1 is a major animal metabolite of AFB1. Ingested AFB1 is converted to AFM1 in the cows’ liver, and approximately 0.9% of ingested AFB1 is found in the milk as AFM1. AFM1 is also found in the urine of AFB1-exposed animals at levels of up to 20% of the ingested oral dose. Among the metabolites, AFB1-8,9-epoxide is the source of the potent mutagenicity and carcinogenesis of AFB1. This intermediate binds to cellular macromolecules such as DNA, RNA, and protein (Figure 3) because of which the presence of the double bond in the terminal furan in AFs is such an important determinant of acute toxicity, mutagenicity, and carcinogenicity. The existence of the intermediate, AFB1-8,9-epoxide, was confirmed by the isolation and identification of the absolute structure of 8,9-dihydro-8-(N7-guanyl)9-hydroxy-AFB1 (AFB1-N7-Gua), formed in vitro. It is considered that binding of AFB1 to DNA causes mutation
804 Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds
Figure 2 Metabolic pathways of aflatoxin B1.
in genes, resulting in the activation of ras oncogene and inactivation of p53 tumor suppressor gene.
Effects on Cattle The general effect of AFs in cattle is liver disease. High levels of AF cause acute aflatoxicosis, such as liver
Figure 3 Mechanism of the toxicity of aflatoxin B1.
lesions, reduced feed consumption, weight loss, and reduction in milk production. The chronic effects of low-level consumption of AFs in cattle are reduced reproductivity, immunosuppression, and reduced feed efficiency. Dairy cattle convert ingested AFB1 in their liver to AFM1, which is secreted in milk. When calves consume milk contaminated with AFM1, they may contract aflatoxicosis.
Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds
Effects on Human Acute Toxicity Most of the recorded outbreaks of acute aflatoxicosis have occurred in tropical countries. In India (1974–75), a total of 397 patients were affected, and 106 died. The disease was characterized by jaundice, rapidly developing ascites, portal hypertension, and a high mortality rate and was associated with the consumption of maize contaminated with AF; the AF concentration ranged from 6250 to 15 600 mg kg1, which means the affected people consumed 2–6 mg of AF daily over a month. In Kenya (1981), 12 out of 20 patients died. They ingested maize that contained 12 000 mg kg1 of AFB1. The liver tissue at necropsy showed centrobulbar necrosis and contained up to 89 mg kg1 of AFB1. In 2004, more than 100 people died following consumption of maize highly contaminated with AFs. Reye’s syndrome, manifested by a rapid onset of vomiting, convulsions, coma, and a high mortality rate, was considered to be a kind of aflatoxicosis, because autopsy specimens of the children who died from the syndrome contained AFB1. However, many researchers have recently reported that Reye’s syndrome is caused by other factors, concluding that it is likely to be caused by a combination of factors; AFB1 is probably not an important etiological agent of this disease in the United States.
Cancer In tropical areas, such as Southeast Asia, India, and Africa, the incidence of primary hepatocellular carcinoma (PHC) is high. Epidemiological surveys carried out over the past 25 years in Asia and Africa have revealed a strong statistical association between AF ingestion and PHC incidence. A high rate of mutation at codon 249 of the human p53 tumor suppressor gene has been reported in these tumors.
Exposure to AFB1 and infection with human hepatitis B virus (HBV) are considered to be the major risk factors in the development of PHC. The G to T transversion was found in p53 tumor suppressor gene of hepatocellular carcinomas from patients at high risk of exposure to AFs. The combined experimental and epidemiological evidence has led to designation of AFs as human carcinogens. Collectively, current evidence strongly suggests that PHC is of multifactorial origin, with probable interactions between viral and chemical agents in populations concurrently exposed to both classes of risk factors.
Regulation Because AFs are highly toxic to humans and animals and are frequently found in various foods and feeds, they are of worldwide concern. Regulations concerning AFs have been established in many countries to protect people from the harmful effects of AFs. More than 79 countries regulate the permissible levels of AFs in foods and feeds. The maximum permitted levels have been set for AFB1 alone or total AFs (the sum of AFB1, AFB2, AFG1, and AFG2) (Table 2). The maximum levels range from 1 to 20 mg kg1 for AFB1 and from 0 to 35 mg kg1 for total AFs. More than 60 countries set limits on AFM1 in milk by the end of 2003. The maximum permitted levels are 0 (not detectable) to 15 mg kg1 (Table 3). The levels of the limits for AFM1 in milk are much lower than those for AFB1 in food, because babies or infants are considered to be highly sensitive. AFM1 is a metabolite of AFB1. Therefore, regulation on AFB1 in feed for cattle is most effective for controlling levels of AFM1 in milk. Regulations for AFB1 in feed for dairy cattle exist in at least 39 countries. Although the maximum limits range from 5 to 50 mg kg1, most of these countries set the limit at the level of 5 mg kg1.
Table 2 Regulation for aflatoxins in food Country
Aflatoxin
Limit (mg kg1)
Commodity
Codex EU
B1 þ B2 þ G1 þ G2 B1 B1 þ B2 þ G1 þ G2 B1 þ B2 þ G1 þ G2 B1 þ B2 þ G1 þ G2 B1 B1 B1 þ B2 þ G1 þ G2 B1
15 2–8 4–15 20 20 20 10 20 10
Peanut, raw Foods (nut, cereals, spices, dry fruits)
Mercosur United States China Thailand Japan
805
Peanut, maize and products All foods Maize, peanut (products), rice, edible oil All food products All foods
Extracted from FAO (2004). In: FAO Food and Nutrition Paper 81, Worldwide regulations for mycotoxins in food and feed in 2003. Rome, Italy: FAO.
806 Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds Table 3 Regulation for aflatoxin M1 in food 1
Country
Limit (mg kg )
Commodity
Codex EU Mercosur
0.5 0.05 0.5 5 0.5 0.5 5 0.5
Milk Milk Fluid milk Powdered milk Milk Milk and milk products Milk, cheese Milk and milk products
United States China Indonesia Vietnam
Extracted from FAO (2004) Worldwide regulation for mycotoxins in food and feed in 2003. FAO Food and Nutrition Paper 81. Rome, Italy: FAO.
Determination
Purification AFs are purified using an immunoaffinity column, or solid phase extraction, such as florisil or a multifunctional column. The most effective purification is obtained by an immunoaffinity column; the shortcomings of this type of column are high cost and low sample capacity. After purification with an immunoaffinity column, few peaks of ingredient are found in a HPLC (high-performance liquid chromatography) chromatogram. Although multifunctional columns have the same shortcomings as immunoaffinity columns, the process is easy and speedy. With a florisil column, AFs are effectively purified at low cost and high sample capacity. The disadvantage of this column is the necessity to use chloroform.
Standards Standards of AFB1, AFB2, AFG1, AFG2, AFM1, AFM2, AFB2a, AFG2a, AFP1, AFQ1, AFL-A, and AFL-B are commercially available. AFs are unstable in some polar solvents, such as methanol; therefore, the storage solvent system must be carefully selected. AFs are stable in chloroform and benzene:acetonitrile (9:1) in the dark and at low temperatures.
Sampling Sampling is one of the most important steps in AF determination, because the distribution of AFs in naturally contaminated samples is extremely heterogeneous. Usually only a few percentage of kernels in a sample lot are highly contaminated with AFs, whereas other kernels are free of AFs. For example, it was reported that only 0.03% of peanut kernels were contaminated with AFs, the mean concentration was 5 mg kg1, and the content in a single kernel was 1100 mg kg1. Therefore, it is very difficult to collect a sample that actually represents the mean concentration. An inappropriate sampling plan leads to wrong results, even if the analytical method is very precise. Several theoretical distributions for AFs have been reported. Among them negative binomial distribution is usually applied to determine the sample size and sampling procedure.
Extraction Samples are comminuted, and AFs are extracted by shaking or homogenizing with organic solvents, such as methanol–water, acetonitrile–water, or chloroform. Generally, one portion of sample is extracted with 4–5 volumes of solvent. For dry samples, a small amount of water is necessary to extract naturally contaminated AFs, although AFs are rarely dissolved with water.
Detection As AFs have intense fluorescence under UV light, they are determined quantitatively by the measurement of their fluorescence intensity. AFs are usually determined by HPLC or TLC. In HPLC analysis, usually an ODS (octadecyl silane) column and polar mobile phase are used. Generally, the reverse phase mode HPLC is used. The fluorescence of AFB1 and AFG1 is quenched in the polar solvent used as mobile phase; therefore, these AFs cannot be determined without making derivatives with trifluoroacetic acid (TFA) or using a photochemical reactor. It is at times difficult to determine AFs in spice samples such as red pepper, paprika, and white and black pepper by HPLC methods because they contain many impurities, which are difficult to remove by the purification methods. Reliable results are obtained by two-dimensional TLC, with a high-performance TLC (HPTLC) plate and two kinds of developing solvents. Chloroform:acetone (9:1) and diethyl ether:methanol:water (94:4.5:1.5) are commonly used. Because AFs are intensely fluorescent on TLC under UV light, the sensitivities of AFs by TLC method are so high that they enable detection of AFs at the level of 0.1–0.2 ng/spot. The shortcoming of the TLC method is that it needs a densitometer for quantitative analysis. Enzyme-linked immunosorbent assay (ELISA) has been employed for AF screening, but the method should be applied to limited samples because matrices of the samples often give false positive and negative results. Immunochromatography, which is useful for screening for AFs, has been recently developed for AF analysis. Confirmation When AFs are detected, it is necessary to confirm their presence by another analytical method, because some interfering substances remain in the sample solution despite the various purification steps. The comparison
Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds
of the peak with or without TFA treatment in reverse mode HPLC is not sufficient. The most popular and reliable confirmatory method for AFs with unsaturated terminal furan, such as AFB1, AFG1, and AFM1, is twodimensional TLC following derivatization with TFA. After the first development, a small amount of TFA is dropped on the spot presumed to be AF and developed in the second dimension. The AFs that have a double bond in the terminal furan ring react with TFA to form their hemiacetals (AFB2a, AFG2a, and AFM2a), which have a lower Rf value than their parent AFs on TLC. Presently, AFs are sometimes confirmed by liquid chromatography-tandem mass chromatography (LC/ MS/MS).
Occurrence in Foods and Feedstuffs Many reports about AF contamination in foods and feedstuffs are available. AFs are frequently detected in various foods and feeds produced in hot, humid climates. AF contamination of corn is considered to be the greatest health risk to humans and animals throughout the world because the incidence and level of AF contamination of corn are high, and a large amount of corn is consumed worldwide. AF-contaminated commercial foods and feedstuffs are listed in Table 4. AFs are found in nuts and seeds (e.g., peanut, pistachio nut, Brazil nuts, and sesame), cereals (e.g., corn, rice, buckwheat, and Job’s tears), spices (e.g., nutmeg, red pepper, paprika, and white pepper), beans (butterbean), and dairy products (cheese). AFB1 is the most frequent type present in contaminated samples and is usually found in the greatest quantity. AFB2, AFG1, and AFG2 are never detected in the absence of AFB1.
807
Comparing these results by year, aflatoxin contamination in foods was variable (Figure 4). Aflatoxin M1 in dairy foods is a metabolite of aflatoxin B1 in dairy cattle. Therefore, these results indicated that aflatoxin contamination in feed for dairy cattle decreased after 1985. The reason for this seems to be that the number of countries with legislation controlling aflatoxin in feedstuffs increased from 22 in 1981 to 35 in 1986. Also, the European Community directive was tightened in 1984, when the tolerance for aflatoxin B1 in feedstuffs for dairy cattle was reduced from 20 to 10 mg kg1. Aflatoxin contamination in buckwheat was found in 1982–85. The highest incidence was 46%, found in 1985. Since then, no aflatoxin has been detected, possibly because buckwheat from Brazil has not been imported to Japan after 1985. Until 1992, the incidence of aflatoxins in white pepper was over 30%, but was low in recent years. A high incidence was found in nutmeg throughout the period, reaching over 80% during 1985–90. The contamination level and incidence were then reduced by the efforts of trading companies that collected only good-quality nutmeg from the country of origin. Some causes of the change in AF contamination in commercial food in Japan were factors in the country of origin, including its weather and regulation for mycotoxins. Other causes were factors in Japan such as examination of mycotoxins at port of entry for imported foods, choice of county of origin, and provision of education about mycotoxins to farmers.
AF in Dairy Products AFM1 is sometimes found in dairy products, such as milk and natural cheese (Table 5). The level of AFM1 in dairy products is usually not more than 1 mg kg1.
Table 4 Aflatoxin contamination in commercial foods (Japan) Range (mg kg1) Foods
No. of samples
No. of positive samples
AFB1
AFB2
AFG1
AFG2
AFM1
Peanut Pistachio nut Brazil nut Sesame seed Job’s tears Buckwheat White pepper Red pepper Paprika Nutmeg Natural cheese
459 481 8 47 212 252 220 81 44 257 354
35 9 1 5 48 23 21 31 26 155 44
0.4–21.7 0.8–1380 10.2 0.6–2.4 0.1–14.9 0.1–8.8 0.1–2.3 0.2–27.7 0.2–6.5 0.2–60.3 ND
0.1–5.3 0.1–260 0.8 0.2–0.5 0.1–1.8 0.1–0.9 0.1–0.3 0.1–1.2 0.1–0.3 0.1–6.5 ND
0.3–22.1 306 3.2 ND 0.3–0.7 0.2–0.8 ND 0.1–2.1 ND 0.1–0.4 ND
0.1–6.8 48.3 0.3 ND ND 0.1 ND 0.1–0.2 ND 0.1–0.4 ND
NDa ND ND ND ND ND ND ND ND ND 0.1–1.2
Not detected (detection limit: 0.1 mg kg1). Adopted from Tabata S (1998). Aflatoxin contamination in foods and foodstuffs Mycotoxins; 47: 9–14.
a
808 Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds
Figure 4 Change in the incidence of aflatoxins.
AFM1 in cheese is not produced in the fermentation process because of the AF-contaminated feedstuffs consumed by cows. Ingested AFB1 is converted to AFM1 in the cows’ liver and approximately 0.9% of ingested AFB1 is found in the milk as AFM1. Feedstuffs for cows often contain imported materials. Therefore, AFM1 is also found in dairy products produced in areas not normally associated with AF contamination. AFM1 is stable in the fermentation or heating process in cheesemaking, and its levels are not reduced on storage.
Detoxification or Elimination of AFs from Foods and Feeds For the purpose of reducing the human and animal risk of exposure to AFs, various approaches, including physical, chemical, and biological ones, have been attempted to degrade or eliminate AFs from foods and feeds. It is fairly easy to degrade pure AFs by various methods, such as UV irradiation, heating, boiling, and treatment with chemical reagents. However, AFs in foods are very stable and the mechanisms of their stability are unknown. Cooking processes, such as roasting, boiling, and frying, cannot reduce AFs. To degrade AFs, many procedures have been proposed, such as gamma irradiation, extraction with solvents, and treatment with ozone, hydrogen peroxide, sodium hypochlorite, and alkali. Most procedures are neither practical nor very effective in reducing AFs to safe levels without damaging the quality of the foods. Before AFs are destroyed, foods
are damaged by the treatments. Ammoniated corn may be used for animal feed but not for human food. An exception is the edible oil refining process. In a normal commercial procedure, all AFs in crude oil are removed by washing with water after adding alkali. Attempts at biological degradation of AFs have not been satisfactory. AFB1 is enzymatically converted to AFL, or chemically converted to AFB2a, under acidic conditions of the media by various mycelia. Another biological method, using fungi that do not produce AF to compete with AF-producing fungi, has not succeeded. Detoxification or elimination of AFs in foods without damage to the quality of the product is hardly possible. Therefore, the efforts to avert the occurrence of AFs in foods seem to be the most effective protection against AFs.
Sterigmatocystin Sterigmatocystin is a precursor of AFs in their biosynthesis and is also toxic and carcinogenic. Structure and Chemical Properties Sterigmatocystin consists of a xanthone nucleus attached to a bisfuran structure (Figure 5), similar to AFs. Sterigmatocystin is soluble in acetone, benzene, ethyl acetate, and chloroform, slightly soluble in ethanol, methanol, and diethyl ether, but insoluble in petroleum ether and water.
Table 5 Aflatoxin M1 contamination in dairy products Country
Period of sampling
Type of product
No. of samples
No. of positive samples
Range (ng g1)
Detection limit (mg kg1)
References
USA
1979
209
1
0.3
0.08
Stoloff and Wood (1984)
190
0
0.08
Stoloff and Wood (1984)
1982–85
Cottage cheese Cheddar cheese Nonfat dry milk Ice cream Yogurt Natural cheese
121 328 144 272
0 0 0 44
0.1–1.2
0.4 0.08 0.08 0.1
Stoloff and Wood (1984) Stoloff and Wood (1984) Stoloff and Wood (1984) Tabata et al. (1987)
USA (imported)
1986–96 Before 1985
Natural cheese Cheese
82 118
0 8
0.1–1.0
0.1 0.05
Spain Brazil Japan Taiwan
1985 1992 2001 2005
Milk Milk Milk Milk
47 52 208 144
14 4 207 100
0.02–0.1a 0.073–0.37 0.001–0.029 0.001–0.055
Tabata et al. (1987) Trucksess and Page (1986) Blanco et al. (1988) de Sylos et al. (1996) Nakajima et al. (2004) Peng and Chen (2009)
Japan (imported)
a
0.02a 0.001 0.001
mg/L
Stoloff L and Wood G (1981). Aflatoxin M1 in manufactured dairy products produced in the United States in 1979. J.Dairy Science 64:2426-2430. Tabata S., Kamimura H., Tamura Y., et al. (1987). Investigation of aflatoxins contamination in foods and foodstuffs. J. Food Hygienic Society of Japan 28:395-401. Trucksess MW and Page SW (1986). Examination of imported cheese for aflatoxin M1. J. Food Protection 49:632-633. Blanco JL, Domı´nguez L, Go´mez-Lucı´a E, Garayzabal JF, Garcı´a JA, and Sua´rez G. (1988). Presence of aflatoxin M1 in commercial ultra-high temperature-treated milk. Applied and Environmental Microbiology 54:1622-1623. de Sylos CM, Rodriguez-Amaya DB, and Carvalho PR.(1996). Occurrence of aflatoxin M1 in milk and dairy products commercialized in Campinas, Brazil. Food Additives and Contaminants 13:169-172. Nakajima M, Tabata S, Akiyama H, et al., (2004). Occurrence of aflatoxin M1 in domestic milk in Japan during the winter season. Food Additives and Contaminants 21:472-478. Peng K and Chen C. (2009). Prevalence of aflatoxin M1 in milk and its potential liver cancer risk in Taiwan. J. Food Protection 72:1025-1029.
810 Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds
occurrence of sterigmatocystin are few. Sterigmatocystin has been found in stored grains or cheese, but not in the field.
See also: Yeasts and Molds: Mycotoxins: Classification, Occurrence and Determination. Figure 5 Structure of sterigmatocystin.
Further Reading Producing Fungi Sterigmatocystin is produced by several species of Aspergillus, including Aspergillus versicolor, Aspergillus nidulans, Aspergillus sydowii, and some species of Bipolaris. Among them, A. versicolor is the major producer of sterigmatocystin, and almost all the isolates produce sterigmatocystin. Toxicity The biological activity of sterigmatocystin is much like that of AFB1, but it is much less toxic than AFB1. The LD50 value of ST for male rats is 60–800 mg kg1, whereas that of AFB1 is 5.5 mg kg1. Sterigmatocystin is a potent mutagen. ST is mutagenic at 10 mg/plate; this potency is 1/100 of AFB1s, which is mutagenic at 0.1 mg/plate. Sterigmatocystin is a primary hepatotoxic agent. All male rats given 150 mg day1/rat of dietary sterigmatocystin for 58 4 weeks developed hepatocellular carcinomas. The heopatotoxigenic activity of sterigmatocystin is approximately 1/10 to 1/1000 of that of AFB1. The IARC classified sterigmatocystin as a group 2B carcinogen, which means that it is possibly carcinogenic to humans. No outbreak of the disease in humans and domestic animals attributed to sterigmatocystin has been reported. Regulation Although sterigmatocystin is highly toxic, no country has set maximum permitted levels for sterigmatocystin owing to the low incidence of natural occurrence. Determination Sterigmatocystin is extracted from ground samples with acetonitrile:4% potassium chloride (9:1). After solvent partition, sterigmatocystin is cleaned up with column chromatography and determined by TLC, HPLC, or LC/MS. Contamination in Foods Although sterigmatocystin-producing fungi are widely distributed in the world, reports concerning natural
Bauer DH, Lee DJ, and Sinnhuber RO (1969) Acute toxicity of aflatoxins B1 and G1 in the rainbow trout (Salmo gairdneri ) Toxicology and Applied Pharmacology 15: 415–419. Blanco JL, Domı´nguez L, Go´mez-Lucı´a E, Garayzabal JF, Garcı´a JA, and Sua´rez G (1988) Presence of aflatoxin M1 in commercial ultrahigh-temperature-treated milk. Applied and Environmental Microbiology 54: 1622–1623. Butler WH (1974) Aflatoxin. In: Purchase IFH (ed.) Mycotoxins, pp. 10–28. Amsterdam-Oxford-New York: ELSEVIER Scientific publishing company. Campbell TC and Stoloff L (1974) Implication of mycotoxins for human health. Journal of Agricultural and Food Chemistry 22: 1006–1015. Chapman HR and Sharp ME (1990) Microbiology of cheese. In: Robinson RK (ed.) Dairy Microbiology, Vol. 2: The Microbiology of Dairy Products, 2nd edn., pp. 280–282. London; New York: Elsevier Applied Science. Cole RJ and Cox RH (1981) Handbook of Toxic Fungal Metabolites. New York; San Francis co CA: Academic Press. Cucullu AF, Lee LS, Mayne RY, and Goldblatt LA (1966) Determination of aflatoxins in individual peanuts and peanut sections. Journal of the American Oil Chemists’ Society 43: 89–92. de Sylos CM, Rodriguez-Amaya DB, and Carvalho PR (1996) Occurrence of aflatoxin M1 in milk and dairy products commercialized in Campinas, Brazil. Food Additives and Contaminants 13: 169–172. FAO (2004) Worldwide regulations for mycotoxins in food and feed in 2003. FAO Food and Nutrition Paper 81. Rome, Italy: FAO. James W, Dickens JW, and Pattee HE (1966) The effects of time, temperature and moisture on aflatoxin production in peanuts inoculated with toxic strain of Aspergillus flavus. Tropical Science VIII: 11–22. Nakajima M, Tabata S, Akiyama H, et al. (2004) Occurrence of aflatoxin M1 in domestic milk in Japan during the winter season. Food Additives and Contaminants 21: 472–478. Peng K and Chen C (2009) Prevalence of aflatoxin M1 in milk and its potential liver cancer risk in Taiwan. Journal of Food Protection 72: 1025–1029. Pier AC (1992) Major biological consequences of aflatoxicosis in animal production. Journal of Animal Science 70: 3964–3967. Pitt JI and Hocking AD (eds.) (1999) Fungi and Food Spoilage, 2nd edn. Frederick, MD: Aspen Publishers. Robens JF and Richard JL (1992) Aflatoxins in animal and human health. Reviews of Environmental Contamination and Toxicology 127: 69–94. Stoloff L, Wood G, and Carter L (1981) Aflatoxin M1 in manufactured dairy products produced in the United States in 1979. Journal of Dairy Science 64: 2426–2430. Tabata S (1998) Aflatoxin contamination in foods and foodstuffs. Mycotoxins 47: 9–14. Tabata S, Kamimura H, Tamura Y, et al. (1987) Investigation of aflatoxins contamination in foods and foodstuffs. Journal of Food Hygienic Society of Japan 28: 395–401. Terao K (1983) Sterigmatocystin – a masked potent carcinogenic mycotoxins. Journal of Toxicology. Toxin Reviews 2: 77–110. Trucksess MW (ed.) (2007) Official Methods of Analysis of AOAC International, 18th edn., ch. 49, pp. 2–50. Gaithersburg, MD: AOAC International. Trucksess MW and Page SW (1986) Examination of imported cheese for aflatoxin M1. Journal of Food Protection 49: 632–633.
Yeasts and Molds | Mycotoxins: Aflatoxins and Related Compounds Van Rensburg SJ (1977) Role of epidemiology in the elucidation of mycotoxin health risks. In: Rodricks JV, Hesseltine CW, and Mehlman MA (eds.) Mycotoxins in Human and Animal Health, pp. 699–711. Park Forest South, IL: Pathotox Publishers Inc. Wang JS and Groopman JD (1999) DNA damage by mycotoxins. Mutation Research 424: 167–181. WHO (2002) IARC Monographs on the Evaluation of Carcinogenic Risks to Humans Volume 82, pp. Lyon France: IARC Press. 171–300.
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Wogan GN and Newberne PM (1967) Dose–response characteristics of aflatoxin B1 carcinogenesis in the rat. Cancer Research 27: 2370–2376. Wong JJ and Hsieh DPH (1976) Mutagenicity of aflatoxins related to their metabolism and carcinogenic potential. Proceedings of National Academy of Sciences of the United States of America 73: 2241–2244. Yabe K and Nakajima H (2004) Enzyme reactions and genes in aflatoxin biosynthesis. Applied Microbiology and Biotechnology 64: 745–755.
GLOSSARY
Abomasum The ‘true stomach’ of the ruminant animal with digestive functions similar to the stomach of monogastric species. The abomasum is preceded by the forestomach compartments, the rumen, the reticulum, and the omasum. See also Rumen. Absorption The movement of ions, metabolites or a chemical substance through a body membrane. In the case of magnesium it is the movement of Mg ions from the digestive tract into the bloodstream, either by passive diffusion down a concentration gradient, or active transfer requiring an energy source and usually against a concentration gradient. Acaricide A chemical that kills ticks and mites. It may be mixed with water and put in a dip tank, spray race or used in a knapsack sprayer; there are also pour-on versions available. Acid detergent fiber (ADF) A method for determining the relative digestibility of fibrous feeds. Acidulation The process in which cooked acidprecipitated casein curd and whey are gently agitated in a holding vessel (e.g. a vat) to ‘condition’ the curd. During this period (usually up to 15min), the minerals, especially calcium, in the curd and whey come to equilibrium. Acrosome reaction A change in the membrane at the apical end of the sperm head in a matured spermatozoon which results in release of enzymes needed for the sperm to penetrate the ovum during fertilization. Activation energy (Ea) The minimum energy required for a reaction to occur; expressed in Joules (J). It is independent of temperature or concentrations. Ad libitum A term (literally, ‘according to pleasure’) that refers to the consumption of food at will. In experimental animal studies, ad libitum refers to the provision of food in a manner that allows the animal to consume as much of the food, and at any time, as it desires. Adhesion The surface reaction between a surface and a particle due to intermolecular attraction forces such as van der Waals’ forces or electrostatic forces. Adjunct culture An adventitious non-starter lactic acid bacteria culture consisting mainly of Lactobacillus spp. used in addition to a standard mesophilic starter to improve and to enhance the flavour of cheese. In order to maximize the role of the adjuncts in cheese ripening, the intracellular enzymes must be released
from the cells into the cheese matrix. This fact explains the great deal of attention given to cell autolysis during ripening. It is believed that attenuated adjunct cultures with enhanced autolytic properties provide a more controlled and consistent ripening resulting in flavour and texture improvement, particularly in lower fat cheese. Adjunct cultures are modified or attenuated to enable them to play an appreciable role during cheese ripening without producing excess lactic acid. Physical methods of sublethal treatments such as freeze-shocking, heat-shocking and spray-drying are the most studied techniques for the attenuation of the adjunct cells. These treatments lead to varying levels of the cell viability, modification of the ability to produce acid and intracellular proteinase or esterase activities. Agricultural agreement The agreement within the framework of the World trade organization (WTO). With the establishment of the WTO the regulation of the trade in food and agricultural produce was finally incorporated into the international trading system. This agreement covers export subsidies and competition, market access and imports, and internal/domestic support. All major agricultural trading countries have been forced into changing their agricultural policy according to the agreement. Alkaline phosphatase An indigenous milk enzyme which is denatured by pasteurization. It is used to demonstrate that milk is adequately pasteurized. Allergy An abnormal immune response to an allergen, causing adverse clinical reactions. Allergens may be from the environment, e.g. pollens, or from food, e.g. milk proteins. Symptoms are manifest on the skin (e.g. pruritus and urticaria), or the gastrointestinal (e.g. abdominal pain and diarrhea) or respiratory tracts (e.g. asthma). See also Intolerance. AM system An automated milking machine that can milk cows without human supervision. The AM system has electronic cow identification, robotic teat cleaning and teat-cup attachment systems and a milking machine to milk the cow. The cow visits the AM system voluntarily, with the inducement of the supply of concentrate. Computer controlled sensors are present to detect any abnormalities in the milking process or the milk.
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814 Glossary
Aminopeptidases Enzymes, highly conserved in dairy lactic acid bacteria, that release N-terminal amino acids from dipeptides (except for those containing proline), tripeptides and oligopeptides. Animal model A statistical model used in genetic evaluation in which an animal’s estimated genetic merit is a function of its own performance and the genetic merit of its parents and offspring. All relationships among animals are considered, and males and females can be evaluated simultaneously. Anionic salts Inorganic salts (usually chloride-based) added to close-up dry cow rations to lower urine pH, increase calcium mobilization and raise blood calcium levels to prevent milk fever or hypocalcemia. Anestrus Absence of cyclicity in a mature intact female. The condition can be caused by seasonal factors, severe underfeeding and suckling of offspring. Anestrus, lactational The generalized situation in which an animal that is lactating has diminished, delayed or absent reproductive cyclicity. This is usually exacerbated by decreased energy intake. Anthelmintic A medication used to expel or destroy parasitic worms found in the digestive system. Antibody An immunoglobulin molecule synthesized in response to a foreign substance which provides an animal with means of protection against that substance by combining specifically with it. Artificial insemination The introduction of fresh, chilled or frozen-thawed semen into the female reproductive tract using specific devices. Undiluted or diluted semen can be deposited either into the uterus or the oviduct. Artificial neural network (ANN) A highly interconnected computational structure of elementary processing units (termed neurons) and parameters (termed weights) that are adjusted by an optimization procedure, known as network training. ANNs are implemented for data processing and information storage with its main application in pattern recognition, process modelling, signal filtering and control structure design. Asthma A reaction involving wheezing and breathing difficulty (or sometimes coughing) caused by reversible narrowing of the lung’s airways and often connected with allergic problems. Atopic dermatitis Eczema, an allergic skin reaction, most commonly seen in small children and often affecting the groin, the creases of the elbows and knees, and the hands and face. Atopy A genetic predisposition to produce immunoglobulin E against common antigens in the environment with atopic symptoms, e.g. bronchial asthma, allergic rhinitis and atopic dermatitis. Azadirachtin A compound that exhibits effective insect repellent and sterilization properties. It works on the tick’s hormonal system and does not lead to development of resistance in future generations. Generic name: tetranortriterpenoid.
Bacteriocins Antimicrobial ribosomally synthesized peptides that kill species other than the producer species, bacteriocins usually kill closely related bacteria. The three classes of bacteriocins produced by lactic acid bacteria include the lantibiotics, the small heat-stable peptides not containing lanthionines, and the large heat-labile bacteriocins. Bacteriophage (or phage) A virus that infects a bacterial cell. While the virulent phages usually kill the cells they infect, the temperate phages do not cause cell lysis but exist in a state called lysogeny where most virus genes are not expressed. Bacteriophages are used as a vector for DNA cloning. Phage infection can rapidly destroy the acid-producing activity of starter cultures. Bactofugation A technique in which milk is treated in a type of centrifuge with a continuous separation of a small amount of milk that contains dense particles. This heavy phase contains most of the spores of the anaerobic bacterium Clostridium tyrobutyricum which have a higher density than those of most other bacteria. Bifidus factors Compounds of natural origin able to pass intact to the colon, and which are able to enhance the growth of species of Bifidobacterium spp. Examples are the complex carbohydrates containing N-acetyl glucosamine and L-fucose attached to galacto-oligosaccharide chains in human milk. Other identified bifidus factors include some casein and whey protein digests, lactulose, and cell extracts from Propionibacterium spp. Bioavailability The proportion of a dietary constituent that is utilized for normal body functions. Biochemical oxygen demand (BOD) An important measure of water quality. It is a measure of the amount of oxygen needed (in milligrams per liter) by bacteria and other microorganisms to fully oxidize the organic matter present in a water sample. It is also called the biological oxygen demand. A five-day biochemical oxygen demand (BOD5) is commonly determined. The amount of oxygen reported with this method represents only the carbonaceous oxygen demand (CBOD) or the easily decomposed organic matter. BOD5 is commonly used to measure natural organic pollution. The BOD5 of drinking water should be less than one, while that of raw sewage may run to several hundred. The BOD5 of dairy waste may run from several hundred to hundreds of thousand. See also Chemical oxygen demand (COD). Biofilm A life community based on the capability of microorganisms to adhere to solid surfaces, to proliferate at the surface and to form a microenvironment characterized by the excretion of exopolysaccharides (called glycocalyx). Biofilms growing on stainless steel surfaces, particularly in heat exchangers, can be an important source of contamination of dairy products. Biogas A mixture of gases resulting from anaerobic fermentation of whey, or any other biological matter, and containing methane, carbon dioxide, hydrogen sulfide and other minor gaseous components.
Glossary
Biohydrogenation the process by which unsaturated fatty acids in the diet are converted to trans fatty acids and stearic acid by microorganisms in the rumen. Biopsy A technique in which small amounts of tissue, such as a single cell, can be removed from a tissue or embryo for examination of the genetic makeup of the particular tissue or embryo from which it was derived and/or examination of changes in cell morphology. Biosecurity Management practices designed to prevent transmission of disease agents into, or within, a livestock operation. Biosensor An analytical device including a biological recognition component and a signal transducer. The biological material undergoes a physicochemical change in the presence of the analyte(s). This change is detected by the transducer, amplified and then reported to the operator. Blastocyst An early embryonic stage represented by a spherical mass of cells with a fluid-filled cavity which forms from the cleavage of a fertilized ovum and exists from approximately 8 to 12 days after fertilization in cattle. Blitz therapy An antibiotic therapy technique used against mastitis. All infected cows are treated in all quarters simultaneously in an attempt to maximize treatment success. Bloat A serious and sometimes fatal disorder of ruminants. It is characterized by extreme distension or inflation of the animal’s rumen or first stomach, due to the accumulation of gases. Body condition A general term referring to the relative amount of body fat and muscle on an animal. Body condition score (BCS) A scale for assessing the level of body fat on an animal. It runs from 1 ¼ very thin to 5 ¼ obese, and may be expressed in decimal values, e.g. 3.5. Boiler efficiency (hb) Ratio between the heat received by the water and the heat content of the fuel. The electrical energy that drives the boiler’s auxiliary equipment is comparatively much smaller than these values, and is normally neglected. Bovine lymphocyte antigen (BoLA) genes Genes restricted to the genus Bos that are responsible for tissue compatibility between individuals and function in cell-to-cell signalling between lymphocytes and antigen-expressing cells. Brown mid rib (BMR) A group of mutants in maize, sorghum and millet with higher plant digestibility. Lignin reduces and cellulose and hemicellulose increases BMR. Leaf midrib, stem sheath and pith show a brown coloration in BMR plants. Browse To feed on buds, leaves or twigs, as distinct from grass (grazing). Goats are typical browsing animals. Buttermilk, cultured (fermented) A product made from fresh pasteurized skimmed milk or homogenized, pasteurized low-fat milk by fermentation with flavor-producing mesophilic lactic acid bacteria. Buttermilk, natural (conventional) A byproduct of buttermaking. Depending on the processing con-
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ditions, either sour cream or sweet cream buttermilk is obtained. Sweet cream buttermilk can be processed further to fermented buttermilk by flavor-producing mesophilic lactic acid bacteria. Traditionally, buttermilk was the fresh serum that was separated during buttermaking on farms after churning cream ripened with naturally occurring lactic acid bacteria. Byproduct feed A feed generated during the production of food and fiber products for human consumption. Usually not of the quality or composition for human use, they provide economical sources of feed for cattle. Calcium-induced precipitation An isoionic precipitation mechanism caused by progressive addition of calcium which decreases the net negative charge of caseins to such an extent that the caseins have little, if any, net charge. Electrostatic repulsive forces are at a minimum and precipitation occurs. Calf hutches Shelters designed to provide individual housing for calves. Hutches can be made of wood, plastic or fiberglass and are intended to provide adequate ventilation. Calving interval The time between calving and reimpregnation of the cow. Calving rate The number of calves born as a percentage of cows mated over a 12-month period. Canonical transformation A procedure commonly used to reduce computational requirements for simultaneous genetic evaluation of more than one trait. Correlated traits are ‘transformed’ to uncorrelated traits, which can be evaluated separately and then retransformed, thus reducing computer processing. CAP genes A group of genes activated at the onset of labor. Contraction-associated protein (CAP) gene expression is increased as estrogen concentration rises at term. CAPs include oxytocin and prostaglandin receptors, Naþ and Ca2þ channels and gap junction proteins (connexin-43), which when activated, increase spontaneous activity of the myometrium. Capillary electrophoresis (CE) A technique that resolves analytes based on net charge, their mass and Stokes’s radius under the infuence of an electric field in a buffer-filled capillary. Capillary electrophoresis is a relatively new technique with the first applications in the early 1980s. One of the major advantages of this technique over traditional electrophoretic techniques is the ease with which quantitative data may be obtained. Casein The acid-insoluble proteins of milk, which occur as large colloidal aggregates called micelles. Casein solubilization (1) The process in which, after casein hydrolysis, the peptides become water soluble. (2) The process in which intact casein molecules become dissociated from casein micelles due to an alteration in pH, electrostatic charge or temperature. Cataract An opacity in the crystalline lens of the eye, which may be partial or complete.
816 Glossary
Cation exchange capacity (CEC) A measure of a soil’s capacity to hold the plant nutrient cations calcium (Ca2þ), potassium (Kþ), sodium (Naþ) and aluminum (Al3þ) to surfaces of negatively charged particles of clay and/or organic matter. Extracts containing ammonium ions displace cations into solution. Individual exchangeable cation concentration is measured in the extract as milliequivalents 100 g1 (meq%) and added to estimate the CEC. Cheese slurry A semi-solid paste containing about 40% solids and possessing the characteristic flavor of the particular cheese used in its preparation. Chemical oxygen demand (COD) The oxygen equivalent (in milligrams of O2 per liter) of the organic portion of the sample that is susceptible to oxidation by a strong chemical oxidant. COD does not distinguish between refractory and ‘inert’ organic matter. COD tests require approximately 3 hours. See also Biochemical oxygen demand (BOD). Chocolate bloom Fat or sugar on the surface of chocolate giving a white ‘mold-like’ appearance. It can be caused by heat damage or by the crystallization of cocoa butter in the wrong form. Chocolate conche A machine for coating the solid particles in the chocolate with fat and at the same time producing the final flavor. The latter is achieved by removing some acidic volatile components and/or developing other flavors by means of heating. Chymosin A milk-clotting enzyme produced in the glandular cells of the ruminant abomasum (fourth stomach). Chymosin is an aspartic (acid) proteinase (EC 3.4.23.4) and has a high specifc milk-clotting activity; it primarily hydrolyzes the peptide bond between Phe105–Met106 in bovine -casein. Chymosin dominates the milk-clotting activity of calf rennets. See also Rennet. Cleanroom A room that is constructed to minimize the introduction of airborne microorganisms or particles and where the concentration of those microorganisms, or particles, is controlled. Closed flock A flock where all female and some male breeding replacements are produced on the same farm as the breeding flock. This system significantly reduces the risk of introducing new diseases into the farm from purchased replacement stock. Coagulant A preparation of milk-clotting enzymes of nonruminant origin. Most often they are milkclotting enzymes derived from different fungi or plants. Coagulants are considered to give a lower yield of cheese and a different cheese flavor compared to calf rennet. Coagulum See also Gel, Coagulum. Celiac disease A disorder caused by a reaction to the gluten of wheat and other cereals in the diet and accompanied by (most notably) bowel disturbances and anemia. Coffee cream A cream product that usually contains 10% or 12% fat and is manufactured for a long shelf-
life either by in-bottle sterilization or, more frequently, by UHT sterilization, followed by aseptic filling. Storage stability (prevention of creaming and sedimentation) and coffee stability (resistance against coagulation or ‘feathering’) are most important for the quality of the product. Cold housing A system of housing for cattle in which barn indoor temperature fluctuates with outdoor temperature. Ventilation maintains indoor temperature within 3–6 C of outdoor temperatures in winter. Usually, the barn is not insulated and ventilation is largely unregulated, except to adjust for seasonal changes. Coliform bacteria Bacteria that produce acid and gas from lactose. Many, but not all, are of enteric origin. They are killed by mild heat, but occasionally recontaminate pasteurized products. Colloid A state of matter in which the particles are in the size range of 10 to 1000 nm. Colloidal particles are approximately of the same size as the wavelength of light and therefore strongly scatter light; they are largely unaffected by gravity. Colloidal calcium phosphate Calcium phosphate that is attached through electrostatic interactions to serine phosphate residues on casein molecules. It is the portion of calcium and (inorganic) phosphate that can potentially be removed from the casein when milk or cheese is acidified. In contrast, the noncolloidal or organic phosphate is directly attached to serine (covalently linked) and can be removed only by enzymatic activity, i.e. phosphatases. Colostrum Mammary secretions during the early period (3-4 days) post-partum. Combustion A rapid chemical combination process of fuel with air that releases the chemical energy of the fuel. Air and fuel are the reactants in the combustion reaction, and the byproducts are the flue gases (products of combustion) and heat. Communal area An area where animals from different herds are communally grazed but may be housed as individual herds at night. Usually, there are no fences in the grazing areas but they may have paddocks. Concentration polarization An increase in the concentration of a component in the boundary layer of a membrane as a result of its rejection. The phenomenon is characterized by a decrease in permeate flux through a membrane to a constant value, irrespective of increasing transmembrane pressure. Conception rate The proportion of cows maintaining pregnancy beyond three weeks. Confocal microscopy A light microscopy technique which greatly reduces out-of-focus blur, enabling optical sectioning of bulk materials. This is particularly useful for shear-sensitive, opaque food materials requiring minimal sample preparation. The most common configuration used in dairy research is the confocal scanning laser microscope. Conjugated linoleic acid A family of 18-carbon fatty acids with conjugated double bonds. These fatty
Glossary
acids are produced in the rumen during biohydrogenation and by action of the 9-desaturase enzyme within the mammary gland. Isomers can have important effects on human health. Consumer nominal assistance coefflicient The ratio of the Consumer support estimate (CSE) to the total value of consumption expenditure on farm commodities produced domestically and valued at world market prices, excluding budgetary support to consumers. Consumer support estimate (CSE) An indicator of the annual monetary value of gross transfers to (from, if negative) consumers of agricultural commodities, arising from policy measures. Contemporary group A group of animals that are subjected to the same environmental influences (e.g. same age, same herd, same calving season, same location). Comparison of an animal with its closest contemporaries allows a more accurate determination of its genetic merit. Continuous ice cream freezer A swept-surface heat exchanger, jacketed with a refrigerant, through which ice cream (or frozen dairy dessert) mix is pumped in order to freeze a portion of its water and incorporate small air bubbles. Cooking of casein Heating of precipitated casein by means of steam injection, or through a heat exchanger, from precipitation temperature to a temperature at which the individual particles of casein agglomerate to form curd of sufficient strength to withstand subsequent wet processing. Copolymer a polymer made up of monomers of two or more types. Corpus luteum An ovarian structure that forms following ovulation. It is responsible for the secretion of progesterone during the luteal phase of the estrous cycle and pregnancy. Luteinizing hormone is the major luteotropic hormone that stimulates luteinization of the theca and granulosa cells of the preovulatory follicle into luteal cells. Cottonseed Seed separated from cotton lint during ginning. It contains a moderate concentration of oil and protein and a high concentration of fiber from lint remaining on hull. Meal is produced from protein and hull as a byproduct when whole seeds are crushed to extract cottonseed oil. Cow comfort A general term that implies that animals are provided with an environment that minimizes stress, illness, mortality, injury and behavioral problems; an environment that permits them to grow, mature, maintain health, reproduce and produce. Cream liqueur A cream product combining the flavor of an alcoholic drink with the texture of cream, and expected to have a shelf-life of several years at ambient temperature. Besides a sufficient amount of alcohol and sugar (for microbiological stability), a very fine milk fat dispersion, non-fat milk solids (from cream), water, sodium caseinate and trisodium citrate are the main ingredients.
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Cream The part of milk, rich in fat, that can be separated by centrifugation of milk. The fat content of the different liquid and cultured products ranges from 10% to 50%. The special ‘creaminess’ results from the fine dispersion of the fat globules protected by a special membrane against de-emulsification. Cross-flow microfiltration A pressure-driven membrane separation process. It could be described as a more porous form of ultrafiltration where instead of molecular weight cut-off criterion, membranes are defined by their pore size in mm. The selective permeation of protein may be facilitated by choice of membrane and optimization of processing conditions. Cryopreservation A system whereby live cells are preserved using an ultra-low temperature freezing process that allows most of the cells to recover after thawing. Cultured cream A cream product with various applications as an ingredient in sauces or dressings. The fat content of cultured creams ranges from 10% to more than 40%. The manufacturing process is similar to that for other fermented products. Fermentation may take place in retail packages or in a fermentation tank. Cytotoxin A toxin that kills mammalian cells. D value Time in minutes at a defined temperature, required to reduce the microbial population by one log (i.e. to cause destruction of 90% of microorganisms); the temperature is indicated in a subscript, i.e. D70 for 70 C. See also z value. de novo fatty acid synthesis The synthesis of fatty acids within the mammary gland, primarily from acetate. It can also be initiated from b-hydroxybutyrate. Key enzymes include acetyl-CoA carboxylase and fatty acid synthase complex. The resulting fatty acids have an even carbon chain length between 4 and 16 carbon atoms. Dewatering of casein curd The final separation of casein curd and water before the curd is conveyed to the drier. It involves mechanical means for expressing the maximum amount of water from the curd consistent with a friable texture for maximum drying efficiency. Dewheying of casein curd The separation of casein curd and whey before the curd is washed in water. This may be effected by means of inclined stationary screens and/or by mechanical separation, such as a roller press or a decanter centrifuge. Dip tank A long, narrow, deep tank into which acaricide solution is poured and through which cattle are herded. The tank should be deep enough so that cattle have to swim through and become covered in acaracide. Also called plunge dip. Direct government payment A subsidy to producers in the form of transfers from taxpayers rather than through import barriers or government-set minimum prices. Discounts for multiples of maintenance A method used by the US National Research Council (NRC) to account for decreased digestibility as animals
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increase energy intake at multiples above the energy required for maintenance. The NRC system for dairy cattle uses discount factors of approximately 8% at 3 and 12.5% at 4 maintenance. Dispute settlement body A part of the machinery of the WTO. The Dispute Settlement Body and Dispute Settlement System together form the core legal institution within the WTO when solving bilateral disputes concerning trade. Member countries within the WTO are obliged to implement the rulings of the Dispute Settlement Body and no single country has a veto right over the dispute rulings. DNA array A rigid slide or flexible membrane containing a series of up to tens of thousands of single- or double-stranded DNA polymers used to qualitatively or quantitatively evaluate complementary DNA present in a sample using nucleic acid hybridization. Domestication The process of genetic adaptation of a species so that it supplies and receives benefits to and from a human population. Downer cow A cow that lies down and cannot get up. This condition may be due to several causes, such as severe lameness, temporary loss of nerve function after calving, or an acute metabolic disease such as milk fever (calcium deficiency) or magnesium deficiency. Drench To dose an animal orally with a solution using a bottle, syringe or specifically designed drenching apparatus (drench gun). Dry matter (DM) The forage component remaining after water has been removed by oven-drying at a controlled temperature (80 C) until constant weight is attained. Heating to 105 C will remove all water (oven dry). Pasture and crop yield are often reported as kilograms of dry matter per hectare (kg DM ha 1). Dry matter intake (DMI) The weight (kg) of dry matter consumed by an animal each day after feed refusals have been subtracted. Dry period The days during which pregnant cows are not being milked. The recommended dry period is the 60-day period preceding calving. Dynamic compressor A compressor that operates continuously, subjecting air to steady-flow processes. Such a machine has no means of preventing backflow. Distinction is made between axial and radial compressors, depending on the direction of the air flow. Dystocia A prolonged or difficult delivery. It can be due to either fetal factors (size, birth position) or maternal factors (pelvic size). Early embryo loss Loss of embryo during the first three weeks of pregnancy. Edometry The measurement of the physical locomotion of a cow by means of a device attached to its leg. Pedometry is reported to identify 70–80% of the cows in estrus; their activity increases approximately 4 h prior to the onset of standing estrus. The predicted optimum time for artifcial insemination is between 6 and 17 h after increased activity.
Effective fiber Fiber (neutral or acid detergent fiber) provided by plants that are effective at stimulating rumination. Effective population size The size of a population relative to the amount of inbreeding which is expected to accumulate in that population, frequently smaller than the census number of animals in the population. Electrochemical process The process by which chemical change is introduced into a system with electricity, e.g. an electrolytic cell, or by which electricity is produced though a chemical change in a system, e.g. a galvanic cell. Electron microscopy A technique of microscopy in which accelerated electrons, rather than photons, produce images. This offers a much higher resolution than light microscopy. A beam of electrons interacts with the sample to reveal fine structural detail. The two main electron microscopy techniques are scanning electron microscopy (SEM) which reveals topographic features with a high depth of field and transmission electron microscopy (TEM), which is capable of revealing two-dimensional macromolecular structures. Electrophoresis The migration of charged particles under the infuence of an electric field. Electrophoresis is commonly applied for separation, identification, purification and characterization of a variety of proteins and peptides. Electrophoretic mobility (m) The rate of migration of a particle in an electric field. It is dependent on the conditions under which electrophoresis is conducted. Electrophoretic mobility is equal to the vector sum of the driving force and a number of resisting forces. Endocrine A term to describe the secretion of a hormone by an internal gland; the hormone is transported (usually via the blood) and received by a distant gland to exert an effect (i.e. stimulation or inhibition). Enterohemorrhagic Causing hemorrhage in the gastrointestinal tract of the host. Enzyme A protein formed in cells that acts as a catalyst in initiating or speeding up specific chemical reactions. Equine chorionic gonadotropin (eCG) A protein hormone produced by the placenta of pregnant mares from about 40 days post mating until mid-pregnancy. This hormone has biological actions similar to follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Also called pregnant mare serum gonadotropin (PMSG). Equivalence ratio (f) Ratio between the stoichiometric air–fuel ratio and the real air–fuel ratio, A/Freal. This parameter allows one to determine if the combustion is stoichiometric, ¼ 1, if the reaction mixture is lean, < 1, or if it is rich, > 1. Essential amino acids Amino acids that cannot be synthesized by an organism at a sufficient rate and must be supplied in the diet. Estrous behavior The behavior expressed by female animals during the period when they are receptive
Glossary
to mating by males. In heifers and cows, the definitive sign of estrus is standing to be mounted by herdmates or a bull. Estrus typically lasts for 8 to 24 hours in cattle and occurs at 18-to 24-day intervals. Estrus The period of sexual receptivity and behavior in the female brought about by a high systemic concentration of estradiol-17b produced by the preovulatory follicle which stimulates behavior coincident with the ovulatory surge of luteinizing hormone. Ethylene vinyl alcohol (EVOH) A compound formed by reacting ethylene vinyl acetate with methanol in the presence of catalysts. It is a packaging material with high strength, clarity and good odor and oxygen barrier characteristics and is used as an oxygen barrier in multilayer coextruded plastic containers. Eutectic The term used to describe the situation in which two dissimilar materials are blended so that they can combine in such a way that the resulting melting point is lower than the melting point calculated from those of the individual components. Eutherians See also Placental mammals. Evaporative cooling The transfer of heat from the body of an animal to the environment by sweating and/or panting. Export subsidy A government payment conditioned on the export of a commodity that may allow exports even when the domestic market price is higher than the price in export markets. Such subsidies are still used to a small extent by the United States and quite extensively by the EU. Extended shelf-life (ESL) milk A product processed in such a manner that the shelf-life is extended to 60 to 90 days. The milk still must be held at refrigeration temperature (100 C) due to thermal oxidation of lactose, precipitation of primary and secondary phosphate as tertiary phosphate. Heat-shocking A means for reducing the acid-producing capability of bacterial cells without a significant decrease in their proteolytic activities, where the optimum heat treatment varies from 56 to 70 C with heating time varying from 15 to 22 seconds. Helminths A broad term that includes many parasitic worms and flukes that are parasites of animals, and thus of veterinary importance, belong to four phyla: (1) Nematoda or roundworms and (2) Platyhelminthes, which include Trematoda (flukes) and Cestoda (tapeworms), (3) Acanthocephala or thorny-headed worms and (4) Annelida or leeches. Phyla (1) and (2) are most important in dairy animals. Heritability The percentage of phenotypic superiority or inferiority of parents transmitted to offspring. Also, the percentage of phenotypic differences that are explained by additive genetic effects, which ranges from 0 (no genetic control) to near 1 for traits unaffected by the environment. Heterofermentative See also Lactic acid bacteria.
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Heterosis The average advantage of crossbred animals in comparison to the average of purebred animals from the component breeds. Also known as ‘hybrid vigour’. High-density polyethylene (HDPE) A compound of which the basic building unit is polymerized ethylene. It is a high molecular weight packaging material of great strength, good gas barrier properties, and low clarity. It is generally of low cost. High-performance liquid chromatography (HPLC) A widely used, highly developed analytical technique for separation of analytes in a complex mixture. The basic theory is the partitioning of the analyte between two phases, one mobile and the other stationary. High-temperature, short-time pasteurization (HTST) A continuous heat treatment process which destroys all pathogenic bacteria and most spoilage bacteria. The heat treatment is sufficient to denature alkaline phosphatase. Products are heated to a minimum of 72 C for at least 15 seconds. Homofermentative See also Lactic acid bacteria. Hydrocyanic or prussic acid (HCN) An acid contained in cyanogenic plants, particularly sorghum species, which causes cyanide poisoning and death of livestock. Glucosides in the plant combine sugar and HCN. Glucoside concentration increases when plant growth is restricted. Enzymes released in plants that are damaged (e.g. by chewing, frost or wilting) break down the glucoside and release HCN. Hydrolytic rancidity Enzymatically catalysed release of free fatty acids from triglycerides. It leads to soapy, goaty or bitter off-flavours in milk. Hydrophilic Term (literally ‘water-loving’) used to describe those segments or parts of a protein molecule that prefer to be in water. Hydrophobic Term (literally ‘water-fearing’) used to describe those segments of a protein molecule that prefer to interact with the oil phase or other hydrophobic groupings. Hyperglycemia Elevated blood glucose concentration. This finding is typical in dairy cows, sheep and goats with milk fever. Hypersensitivity A form of allergy; this term is sometimes also applied to nonimmune-mediated reactions such as intolerance due to an enzyme deficiency. Hypocalcemia (nonparturient) A depression in blood calcium concentration in dairy cows, sheep and goats that does not occur around parturition. Hypocalcemia in these cases is usually secondary to some other disease problem. Hypocalcemia (subclinical) A depression in blood calcium concentration around parturition in dairy cows, sheep and goats that causes no apparent clinical signs. Affected animals are at risk of reduced milk yield, ketosis, retained placenta and displaced abomasum. Hypomagnesemia Decreased blood magnesium concentration. Clinical signs include hyperesthesia and tetany. Also known as grass tetany. Hypomagnesemia can also be a cause of milk fever.
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Hypostome The central mouthpart of a tick which serves as the feeding apparatus. Hypothalamic–pituitary–adrenal axis The endocrine axis that controls the regulation and release of cortisol, which involves the release of hypothalamic (CRH) and pituitary (ACTH) hormones to stimulate the release of cortisol by the adrenal cortex. Hypothalamic–pituitary–gonadal axis The endocrine system controlling reproduction in animals. It comprises gonadotropin releasing hormone neurons in the hypothalamus, gonadotroph cells in the pituitary (responding to gonadotropin releasing hormone by secreting luteinizing hormone and folliclestimulating hormone), and the ovary or testis (responding to luteinizing hormone and folliclestimulating hormone). Ice cream mix A combination of liquid and solid ingredients, including sources of fat, milk solids-not-fat, sugars, stabilizers, emulsifiers and water, that is blended together, pasteurized and homogenized from which ice cream (or frozen dairy dessert) is manufactured by whipping and freezing. Immune system The scattered bodily cells and tissues that react to foreign and potentially harmful agents (such as bacteria and viruses) but can sometimes react inappropriately (and unpleasantly) to harmless substances such as foods or pollens, causing allergic reactions. Immunoglobulins Proteins of the immune system produced by B lymphocytes. They augment phagocytosis and cell-mediated cytotoxic reactions by leucocytes, activate complement system and agglutinate and neutralize microbes and toxins. Immunoglobulins in milk and colostrum protect the offspring against microbial pathogens and toxins and the mammary gland against microbial and viral infections. Immunoglobulins (Ig) occur in five classes: IgM, IgG, IgA, IgD and IgE. Import barrier Any of a set of policy tools that inhibit imports and protect domestic producers. Examples include import tariffs or duties, limits on the quantity of imports or import quotas, and tariff-rate quotas which comprise a combination of tariffs and quotas. In vitro dry matter digestibility (disappearance) (IVDMD) A laboratory estimate of feed digestibility. A mixture of rumen fluid, enzymes and feed is incubated at body temperature (39 C). In a second stage, the incubated mixture is acidifed and digested with pepsin. The residue is dried and weighed. The weight loss is expressed as a percentage of the feed dry matter. In vitro A term (literally, ‘in glass’) that refers to an experiment conducted using isolated tissues, cells or biochemical reactions outside of a living animal. Such experiments can be performed, for example, in cell culture dishes or test tubes. See also In vivo. In vivo A term (literally, ‘in life’) that refers to scientifc experiments performed in a whole, living animal, as
opposed to using isolated tissues or cells. See also In vitro. In-line measurement The set of real-time measurements used in process control. Process control can only be based on the measurement of the quantity of interest. Beside physical quantities (temperature, pressure, etc.), the in-line measurement of chemical quantities (constituent concentrations) becomes more important. Infrared spectroscopy offers the possibility to determine the constituent concentrations directly in the production line. Inbreeding The mating of relatives. Incidence The new cases of a disease in a specifed population of humans or animals. Incidence may be measured as the proportion or percentage of new cases over a particular time interval, or as the rate of new cases as a function of the length of time that each individual in the population is at risk of becoming a new case. Infant formulae Foodstuffs intended for particular nutritional use by infants during the first 4–6 months of life and satisfying by themselves the nutritional requirements of this category of persons. Infrared instrument calibration Procedure for validating infrared absorption data. The infrared absorption measurement is an indirect method, i.e. one has to correlate the measured absorption with the chemically obtained constituent concentration value by using multivariate statistical methods (calibration procedure). Infrared instrument network Any of several networks, having in common the aim of reducing the amount of calibration work, to check the calibration and to harmonize the results. Infrared spectroscopy A technique that excites vibrational states of specifc groups of atoms in molecules. It measures the absorption of infrared radiation as a function of the wavelength. The information is used for identification of the substance or quantitative determination of constituent concentrations in the product. Infusion heating A method of heat transfer in which the target medium is infused into a high temperature steam environment as a fine mist; it effects a rapid increase in temperature with minimal nutrient and flavour degradation. Condensed steam is removed in a subsequent vacuum chamber. See also Injection heating. Injection heating A method of heat transfer wherein the target medium is injected with culinary-quality steam under pressure and at sufficient velocity through a specialized port. It effects a rapid increase in temperature with minimal nutrient and flavour degradation. Condensed steam is removed in a subsequent vacuum chamber. See also Infusion heating. Intensive management Management of animals in a confined area with permanent housing and equipment for feeding, watering, milking and other activities.
Glossary
Intolerance An adverse, reproducible reaction to a food or a food component, which is not mediated by the immune system. Food intolerance may be related to an enzyme deficiency (e.g. lactose intolerance) or may have other underlying mechanisms. See also Allergy. Ion exchange A process by which ions present in a solution (e.g. in milk or whey) are exchanged for ions that are electrostatically bound to an ion exchanger. The molecules bound to the ion exchange resin can be eluted with buffers of different ionic strength, pH or composition. Ion exchange process is often used to soften hard water. See also Water hardness. Ion-selective electrodes (ISEs) Potentiometric analysers that measure the activities of ions in solution. Activity differs from concentration by the activity coefficient and depends on the overall ionic strength of the analyte solution. The most common type is the glass membrane pH electrode. Isoelectric focusing (IEF) A technique involving separation of analytes based on differences in their isoelectric point, exploiting the fact that each protein has a unique isoelectric point. Analytes migrate through a gel medium containing a pH gradient and cease to migrate at a pH value corresponding to their isoelectric point. Kelvin model A model of linear viscoelastic behavior. The Kelvin model comprises a Hookean spring and a Newtonian dashpot connected in parallel. See also Maxwell model. Kishk A dried fermented milk product made from mixed ‘burghol’ (preboiled dried wheat grains) and low-fat yogurt or laban zeer (concentrated fermented buttermilk). The mixture is fermented naturally, shaped into balls or nuggets and sundried or dried in warm shade. It is consumed mainly as a porridgelike product. Knowledge-based hybrid modelling A combination of different modelling techniques based on available process knowledge sources in an integrated hybrid model. The main sources of process knowledge are: (1) classical mechanistic models, (2) heuristic (empirical) knowledge expressed by fuzzy rules and expert systems and (3) data-driven knowledge hidden in the acquired process data. Kraal An enclosure where animals are housed. Also known as corral. Kumys Fermented horse milk, containing at mean 2% alcohol, due to the action of bacteria and yeast species. It is frequently consumed in some parts of Russia, West Asia and Mongolia. Laban kad (rob) A low-fat fermented buttermilk obtained by direct churning of sour milk in goatskin bags called ‘kerbah’. Laban kad is made into either Kariesh cheese or concentrated in earthenware jars (‘zeer’) as laban zeer. Laban rayeb A low-fat fermented milk obtained after removal of the top sour cream layer from naturally fermented milk. Laban rayeb is consumed either
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directly, in salads or used for the manufacture of Kariesh cheese. Labneh A concentrated fermented milk made by straining full cream yogurt or zabady. Addition of table salt (0.2–0.5%) to stirred yogurt before whey removal is optional. Labneh has a soft, smooth, spreadable and creamy texture, with a clean acid taste. Lactase An enzyme occurring in the small intestine of mammals, as well as in some bacteria and yeasts, which hydrolyzes lactose, yielding a mixture of glucose and galactose; also called b-galactosidase. Lactic acid bacteria Bacteria that generate lactic acid as the primary product of fermentation and most are associated with dairy fermentations. They are Grampositive, non-sporeforming and do not produce catalase. They can be either homofermentative (lactic acid makes up over 90% of the end products) or heterofermentive (lactic acid makes up less than 50% of the end products). The main species are from six genera: Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Pediococcus and Streptococcus. Lactobacillus, Lactococcus and Streptococcus are typical genera found and used in fermented milk products. Lactoferrin An iron-binding glycoprotein composed of a single-chain polypeptide sequence of about 700 amino acids with a molecular weight of about 78 kDa. Lactoferrin is found at much higher (>10 times) concentrations in human than in bovine colostrum or milk. It has, among other things, antimicrobial and immunomodulatory functions, and may thus play an important role in the natural nonspecifc defense of the body. Lactose A disaccharide present in milk made up of galactose and glucose. Lantibiotic A class of bacterially-derived inhibitory peptides characterized by signifcant posttranslational modifications. In particular, lantibiotics possess internal rings formed by the condensation of a dehydrated hydroxy amino acid and a cysteine to form crosslinking lanthionine residues. See also Bacteriocins. Leptin A recently discovered protein hormone which is made in the adipose tissue and functions in the brain to partially regulate food intake and reproductive function. Defects or mutations in the gene for this hormone, or for its receptor in the brain, result in genetic obesity in rodents and perhaps in humans. Limiting amino acids The essential amino acids in digested protein that are in shortest supply relative to body requirements for absorbed amino acids. The first-limiting amino acid is the essential amino that is provided in shortest supply relative to body need. The second limiting amino acid is the essential amino acid that is in the second shortest supply relative to body need. Lipases enzymes that hydrolyze esters at an oil/water interface. Lipolysis The enzymatic breakdown of triglycerides into mono-and diacylglycerols and free fatty acids. The
824 Glossary
enzymes involved are lipases that act at the fat–water interface and esterases that act on water-soluble acylglycerols. The release of fatty acids from the adipose tissue supplies energy to tissues and milk fat precursors to the mammary gland. It increases during glucose or fat deficit as that associated with early lactation. Lipolytic bacteria Bacteria that are able to produce lipases necessary for splitting fats into partial acylglycerols and fatty acids. Liposomes An assemblage of phospholipids and other lipids sustaining a biomolecular configuration and not requiring mechanical support for their stability; they are now established as a useful model membrane system. Attempts have been made to use enzymes entrapped in liposomes for the acceleration of cheese ripening and the enhancement of cheese flavor. Lodging The falling over of certain forage species due to weak stems. Lodging occurs more frequently as the plants mature and may be precipitated by wind or rain. Low birth weight (LBW) infants Infants born prematurely with a gestational age (GA) of less than 36 weeks or infants born small for GA, i.e. which weigh
