Nonthermal Processing Technologies for Food (Institute of Food Technologists Series)

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Nonthermal Processing Technologies for Food

Nonthermal Processing Technologies for Food Edited by H. Q. Zhang, G. V. Barbosa-Cánovas, V. M. Balasubramaniam, C. P. Dunne, D. F. Farkas, and J. T. C. Yuan © 2011 Blackwell Publishing Ltd. ISBN: 978-0-813-81668-5

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The IFT Press series reflects the mission of the Institute of Food Technologists – to advance the science of food contributing to healthier people everywhere. Developed in partnership with Wiley-Blackwell, IFT Press books serve as leading-edge handbooks for industrial application and reference and as essential texts for academic programs. Crafted through rigorous peer review and meticulous research, IFT Press publications represent the latest, most significant resources available to food scientists and related agriculture professionals worldwide. Founded in 1939, the Institute of Food Technologists is a nonprofit scientific society with 22,000 individual members working in food science, food technology, and related professions in industry, academia, and government. IFT serves as a conduit for multidisciplinary science thought leadership, championing the use of sound science across the food value chain through knowledge sharing, education, and advocacy. IFT Book Communications Committee Dennis R. Heldman Joseph H. Hotchkiss Ruth M. Patrick Terri D. Boylston Marianne H. Gillette William C. Haines Mark Barrett Jasmine Kuan Karen Nachay IFT Press Editorial Advisory Board Malcolm C. Bourne Dietrich Knorr Theodore P. Labuza Thomas J. Montville S. Suzanne Nielsen Martin R. Okos Michael W. Pariza Barbara J. Petersen David S. Reid Sam Saguy Herbert Stone Kenneth R. Swartzel

A John Wiley & Sons, Ltd., Publication

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Nonthermal Processing Technologies for Food Howard Q. Zhang, Gustavo V. Barbosa-C´anovas, V.M. Balasubramaniam, C. Patrick Dunne, Daniel F. Farkas, and James T.C. Yuan EDITORS

A John Wiley & Sons, Ltd., Publication

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C 2011 by Blackwell Publishing Ltd. and Institute of Food Technologists This edition first published 2011
Chapters 7, 8, 14, 15, 17, 20, 25, 32, 37, 38 remain with the U.S. Government.

Blackwell Publishing was acquired by John Wiley & Sons in February 2007. Blackwell’s publishing program has been merged with Wiley’s global Scientific, Technical and Medical business to form Wiley-Blackwell. Registered office:

John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK

Editorial offices: 2121 State Avenue, Ames, Iowa 50014-8300, USA The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK 9600 Garsington Road, Oxford, OX4 2DQ, UK For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at www.wiley.com/wiley-blackwell. Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by Blackwell Publishing, provided that the base fee is paid directly to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923. For those organizations that have been granted a photocopy license by CCC, a separate system of payments has been arranged. The fee codes for users of the Transactional Reporting Service are ISBN-13: 978-0-8138-1668-5/2011. Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold on the understanding that the publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional should be sought. Disclaimer The publisher and the author make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation warranties of fitness for a particular purpose. No warranty may be created or extended by sales or promotional materials. The advice and strategies contained herein may not be suitable for every situation. This work is sold with the understanding that the publisher is not engaged in rendering legal, accounting, or other professional services. If professional assistance is required, the services of a competent professional person should be sought. Neither the publisher nor the author shall be liable for damages arising herefrom. The fact that an organization or Website is referred to in this work as a citation and/or a potential source of further information does not mean that the author or the publisher endorses the information the organization or Website may provide or recommendations it may make. Further, readers should be aware that Internet Websites listed in this work may have changed or disappeared between when this work was written and when it is read. Library of Congress Cataloging-in-Publication Data Nonthermal processing technologies for food / edited by Howard Q. Zhang, Gustavo V. Barbosa-C´anovas, V.M. Balasubramaniam. p. cm. Includes bibliographical references and index. ISBN 978-0-8138-1668-5 (hardcover : alk. paper) 1. Food–Preservation. 2. Sterilization. I. Zhang, Howard Q. II. Barbosa-C´anovas, Gustavo V. III. Balasubramaniam, V. M. TP371.2.N664 2011 664 .028–dc22 2010027047 A catalogue record for this book is available from the British Library. This book is published in the following electronic formats: ePDF 9780470958421; Wiley Online Library 9780470958360; ePub 9780470958483 R Set in 10/12 pt Times by Aptara
Inc., New Delhi, India

1 2011

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Titles in the IFT Press series

r Accelerating New Food Product Design and Development (Jacqueline H. Beckley, Elizabeth J. Topp, M. Michele Foley, J.C. Huang and Witoon Prinyawiwatkul)

r Advances in Dairy Ingredients (Geoffrey W. Smithers and Mary Ann Augustin) r Bioactive Proteins and Peptides as Functional Foods and Nutraceuticals (Yoshinori Mine, Eunice Li-Chan and Bo r r r r r r r r r r r r r r r r r r r r r r r r r r r r r r

Jiang) Biofilms in the Food Environment (Hans P. Blaschek, Hua H. Wang, and Meredith E. Agle) Calorimetry and Food Process Design (G¨on¨ul Kaletunc¸) Food Ingredients for the Global Market (Yao-Wen Huang and Claire L. Kruger) Food Irradiation Research and Technology (Christopher H. Sommers and Xuetong Fan) Food-borne Pathogens in the Food Processing Environment: Sources, Detection and Control (Sadhana Ravishankar, Vijay K. Juneja and Divya Jaroni) High-Pressure Processing of Foods (Christopher J. Doona and Florence E. Feeherry) Improving Import Food Safety (Wayne C. Ellefson, Lorna Zach and Darryl Sullivan) Microbial Safety of Fresh Produce: Challenges, Perspectives and Strategies (Xuetong Fan, Brendan A. Niemira, Christopher J. Doona, Florence E. Feeherry and Robert B. Gravani) Microbiology and Technology of Fermented Foods (Robert W. Hutkins) Multiphysics Simulation of Emerging Food Processing Technologies (Kai Knoerzer, Pablo Juliano, Peter Roupas and Cornelis Versteeg) Multivariate and Probabilistic Analyses of Sensory Science Problems (Jean-Franc¸ois Meullenet, Rui Xiong, and Christopher J. Findlay) Nanoscience and Nanotechnology in Food Systems (Hongda Chen) Natural Food Flavors and Colorants (Mathew Attokaran) Nondestructive Testing of Food Quality (Joseph Irudayaraj and Christoph Reh) Nondigestible Carbohydrates and Digestive Health (Teresa M. Paeschke and William R. Aimutis) Nonthermal Processing Technologies for Food (Howard Q. Zhang, Gustavo V. Barbosa-C`anovas, V.M. Balasubramaniam, Editors; C. Patrick Dunne, Daniel F. Farkas, James T.C. Yuan, Associate Editors) Nutraceuticals, Glycemic Health and Type 2 Diabetes (Vijai K. Pasupuleti and James W. Anderson) Organic Meat Production and Processing (Steven C. Ricke, Michael G. Johnson and Corliss A. O’Bryan) Packaging for Nonthermal Processing of Food (J. H. Han) Preharvest and Postharvest Food Safety: Contemporary Issues and Future Directions (Ross C. Beier, Suresh D. Pillai, and Timothy D. Phillips, Editors; Richard L. Ziprin, Associate Editor) Processing and Nutrition of Fats and Oils (Ernesto M. Hernandez, and Afaf Kamal-Eldin) Processing Organic Foods for the Global Market (Gwendolyn V. Wyard, Anne Plotto, Jessica Walden and Kathryn Schuett) Regulation of Functional Foods and Nutraceuticals: A Global Perspective (Clare M. Hasler) Resistant Starch: Sources, Applications and Health Benefits (Yong-Cheng Shi and Clodualdo Maningat) Sensory and Consumer Research in Food Product Design and Development (Howard R. Moskowitz, Jacqueline H. Beckley, and Anna V.A. Resurreccion) Sustainability in the Food Industry (Cheryl J. Baldwin) Thermal Processing of Foods: Control and Automation (K. P. Sandeep) Trait-Modified Oils in Foods (Frank T. Orthoefer and Gary R. List) Water Activity in Foods: Fundamentals and Applications (Gustavo V. Barbosa-C`anovas, Anthony J. Fontana Jr., Shelly J. Schmidt, and Theodore P. Labuza) Whey Processing, Functionality and Health Benefits (Charles I. Onwulata and Peter J. Huth)

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Contributors, xi Foreword, xvii Dietrich Knorr Preface, xviii Introduction, xx Gustavo V. Barbosa-C´anovas and Daniela Berm´udez-Aguirre Section I.

Physical Processes, 1

1.

Fundamentals of Food Processing Using High Pressure, 3 Loc Thai Nguyen and V.M. Balasubramaniam

2.

High-Pressure Processing Equipment Fundamentals, 20 Edmund Ting

3.

High-Pressure Processing Pathways to Commercialization, 28 Daniel F. Farkas

4.

Case Studies on High-Pressure Processing of Foods, 36 Carole Tonello

5.

Microbiological Aspects of High-Pressure Food Processing, 51 Elaine P. Black, Cynthia M. Stewart, and Dallas G. Hoover

6.

Biochemical Aspects of High-Pressure Food Processing, 72 Maite A. Chauvin and Barry G. Swanson

7.

Sensory Quality of Pressure-Treated Foods, 89 Alan O. Wright

8.

Hydrodynamic Pressure Processing of Meat Products, 98 M.B. Solomon, M. Sharma, and J.R. Patel

9.

Physicochemical Effects of High-Intensity Ultrasonication on Food Proteins and Carbohydrates, 109 Jochen Weiss, Ibrahim Gulseren, and Gunnar Kjartansson

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Ultrasonic Processing, 135 Hao Feng and Wade Yang

Section II.

Electromagnetic Processes, 155

11.

Pulsed Electric Fields Processing Basics, 157 Olga Mart´ın-Belloso and Robert Soliva-Fortuny

12.

Engineering Aspects of Pulsed Electric Fields, 176 Bilge Altunakar and Gustavo V. Barbosa-Cánovas

13.

Pulsed Electric Field Assisted Extraction—A Case Study, 190 Stefan Toepfl and Volker Heinz

14.

Improving Electrode Durability of PEF Chamber by Selecting Suitable Material, 201 Minjung Kim and Howard Q. Zhang

15.

Radio Frequency Electric Fields as a Nonthermal Process, 213 David J. Geveke

16.

Use of Oscillating Magnetic Fields in Food Preservation, 222 Nuria Grigelmo-Miguel, Robert Soliva-Fortuny, Gustavo V. Barbosa-C´anovas, and Olga Mart´ın-Belloso

17.

Irradiation of Ground Beef and Fresh Produce, 236 Christopher Sommers and Xuetong Fan

18.

Pulsed Ultraviolet Light, 249 Ali Demirci and Kathiravan Krishnamurthy

19.

Ultraviolet-C Light Processing of Liquid Food Products, 262 J.A. Guerrero-Beltr´an and G.V. Barbosa-C´anovas

20.

Nonthermal Plasma as a Novel Food Processing Technology, 271 Brendan A. Niemira and Alexander Gutsol

Section III. Other Nonthermal Processes, 289 21.

Basics of Ozone Sanitization and Food Applications, 291 Ahmed E. Yousef, Mustafa Vurma, and Luis A. Rodriguez-Romo

22.

Case Studies of Ozone in Agri-Food Applications, 314 Rip G. Rice, Dee M. Graham, and Charles D. Sopher

23.

Ozone Pathway to Commercialization, 342 James T.C. Yuan

24.

Effects of Dense Phase CO2 on Quality Attributes of Beverages, 347 Sibel Damar and Murat O. Balaban

25.

Chlorine Dioxide (Gas), 359 Lindsey A. Keskinen and Bassam A. Annous

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26.

Electrolyzed Oxidizing Water, 366 Ali Demirci and Katherine L. Bialka

Section IV.

Combination Processes, 377

27.

Novel Technologies in Combined Processes, 379 Santiago Cond´on, Pilar Ma˜nas, and Guillermo Cebri´an

28.

Nonthermal Processes as Hurdles with Selected Examples, 406 Robert Soliva-Fortuny, Nuria Grigelmo-Miguel, Gustavo V. Barbosa-C´anovas, and Olga Mart´ın-Belloso

29.

Bacteriocins as Natural Antilisterial Food Preservatives, 428 Li Liu, R. Paul Ross, Colin Hill, and Paul D. Cotter

30.

Antimicrobial Packaging, 462 Dong Sun Lee and Jung H. Han

Section V.

Driving Forces, 473

31.

Consumer Trends and Perception of Novel Technologies, 475 Christine M. Bruhn

32.

Consumer and Sensory Issues for Development and Marketing, 482 Armond V. Cardello, Robert Kluter, and Alan O. Wright

33.

Effects of High-Pressure Processing and Pulsed Electric Fields on Nutritional Quality and Health-Related Compounds of Fruit and Vegetable Products, 502 Concepci´on S´anchez-Moreno, Bego˜na De Ancos, Luc´ıa Plaza, Pedro Elez-Mart´ınez, and M. Pilar Cano

34.

Industrial Evaluation of Nonthermal Technologies, 537 Huub Lelieveld

35.

Transferring Emerging Food Technologies into the Market Place, 544 Authos Yannakou

36.

New Tools for Microbiological Risk Assessment, Risk Management, and Process Validation Methodology, 550 Cynthia M. Stewart, Martin B. Cole, Dallas G. Hoover, and Larry Keener

37.

Regulations and Alternative Food-Processing Technologies, 562 Stephen H. Spinak and John W. Larkin

38.

Future Prospects for Nonthermal Processing Technologies—Linking Products with Technologies, 571 C. Patrick Dunne

Section VI.

Appendices: Fact Sheets, 593

Appendix 1.

High Pressure Processing, 595 The Ohio State University Extension

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Appendix 2.

Pulsed Electric Field Processing, 599 The Ohio State University Extension

Appendix 3.

Ozone, 603 The International Ozone Association

Appendix 4.

Food Irradiation, 611 University of California, Davis

Appendix 5.

Irradiation: A Safe Measure for Safer Iceberg Lettuce and Spinach, 614 Food and Drug Administration

Appendix 6.

Pulsed Light Treatment, 617 Cornell University

Appendix 7.

Power Ultrasound, 621 Washington State University

Index, 626 Color Plate is located at the end of the book.

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Contributors

Altunakar Bilge, Chapter 12 Department of Food Science and Human Nutrition University of Illinois at Urbana-Champaign 1304 W Pennsylvania Ave Urbana, IL 61801

´ Bermudez-Aguirre Daniela Center for Nonthermal Processing of Food Washington State University Pullman, WA 99164-6120

Annous Bassam A., Chapter 25 USDA-ARS Food Safety Intervention Technologies Research Unit Eastern Regional Research Center 600 E. Mermaid Ln Wyndmoor, PA 19038

Bialka Katherine L., Chapter 26 Department of Agricultural and Biological Engineering The Pennsylvania State University University Park, PA 16802

Balaban Murat O., Chapter 24 University of Alaska Fairbanks 118 Trident Way Kodiak, AK 99615 Balasubramaniam V.M., Chapter 1 Department of Food Science and Technology and Department of Food Agricultural and Biological Engineering The Ohio State University 333 Parker Food Science and Technology Building 2015 Fyffe Court Columbus, OH 43210-1007 ´ Barbosa-Canovas Gustavo V., Chapters 12, 16, 19, 28 Center for Nonthermal Processing of Food Washington State University Pullman, WA 99164-6120

Black Elaine P., Chapter 5 Department of Animal & Food Sciences University of Delaware 17 Townsend Hall Newark, DE 19716-2150 Bruhn Christine M., Chapter 31 University of California, Davis Center for Consumer Research Department of Food Science & Technology One Shields Avenue Davis, CA 95616-8598 Cardello Armand V., Chapter 32 Science, Technology and Applied Research Directorate U.S Army Natick Soldier R, D & E Center 15 Kansas Street Natick, MA 01760

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Contributors

´ Guillermo, Chapter 27 Cebrian Tecnolog´ıa de los Alimentos Facultad de Veterinaria Universidad de Zaragoza C/ Miguel Servet, 177 50013, Zaragoza. Spain Chauvin Maite A., Chapter 6 School of Food Science Washington State University FSHN 208 Pullman, WA 99164-6376 Cole Martin B., Chapter 36 CSIRO Food and Nutritional Sciences Riverside Corporate Park, 11 Julius Avenue North Ryde, NSW 2113, Australia ´ Santiago, Chapter 27 Condon Tecnolog´ıa de los Alimentos Facultad de Veterinaria Universidad de Zaragoza C/ Miguel Servet, 177 50013, Zaragoza. Spain Cotter Paul D., Chapter 29 TEAGASC Biotechnology Centre Moorepark, Fermoy Cork, Ireland Damar Sibel, Chapter 24 University of Alaska Fairbanks 118 Trident Way Kodiak, AK 99615 ˜ Chapter 33 De Ancos Begona, Department of Plant Foods Science and Technology Instituto del Fr´ıo Consejo Superior de Investigaciones Cient´ıficas (CSIC) C/ Jos´e Antonio Novais, 10 Ciudad Universitaria E-28040 Madrid, Spain Demirci Ali, Chapter 26 Department of Agricultural and Biological Engineering

The Pennsylvania State University 231 Agricultural Engineering Building University Park, PA 16802 Elez-Mart´ınez Pedro, Chapter 33 Department of Plant Foods Science and Technology Instituto del Fr´ıo Consejo Superior de Investigaciones Cient´ıficas (CSIC) C/ Jos´e Antonio Novais, 10 Ciudad Universitaria E-28040 Madrid, Spain Fan Xuetong, Chapter 17 USDA-ARS Food Safety Intervention Technologies Eastern Regional Research Center 600 East Mermaid Lane Wyndmoor, PA 19038 Farkas Daniel F., Chapter 3 Department of Food Science and Technology Oregon State University Corvallis, OR 97331-6602 Feng Hao, Chapter 10 Department of Food Science and Human Nutrition University of Illinois at Urbana-Champaign 382F-AESB, 1304 W Pennsylvania Ave Urbana, IL 61801 Fett William F. USDA-ARS Eastern Regional Research Center 600 E. Mermaid Ln Wyndmoor, PA 19038 Geveke David J., Chapter 15 USDA-ARS Eastern Regional Research Center Food Safety Intervention Technologies Research Unit 600 East Mermaid Lane Wyndmoor, PA 19038

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Graham Dee M., Chapter 22 R and D Enterprises 2747 Hutchinson Court Walnut Creek, CA 94598 Grigelmo-Miguel Nuria, Chapters 16, 28 Department of Food Technology. University of Lleida Av. Alcalde Rovira Roure, 191. 25198 Lleida, Spain ´ J.A., Chapter 19 Guerrero-Beltran Depto. Ing. Qu´ımica y Alimentos Universidad de las Am´ericas-Puebla Cholula, Puebla 72820 M´exico Gulseren Ibrahim, Chapter 9 Department of Food Science Pennsylvania State University 337 Food Science Building University Park, PA 16802 Gutsol Alexander, Chapter 20 Chevron Energy Technology Company 100 Chevron Way Richmond, CA 94801 Han Jung H., Chapter 30 PepsiCo Advanced Research 7701 Legacy Dr. Plano, TX 75024 Heinz Volker, Chapter 13 DIL Prof.-von-Klitzing-Str. 7 49610 Quakenbr¨uck, Germany Hill Colin, Chapter 29 Department of Microbiology University College Cork Cork, Ireland

Hoover Dallas G., Chapters 36, 5 Department of Animal & Food Sciences University of Delaware 17 Townsend Hall Newark, DE 19716-2150 Keener Larry, Chapter 36 International Product Safety Consultants 4021 W Bertona St Seattle, WA 98199 Keskinen Lindsey A., Chapter 25 USDA-ARS Food Safety Intervention Technologies Research Unit Eastern Regional Research Center 600 E. Mermaid Ln Wyndmoor, PA 19038 Kim Minjung, Chapter 14 Department of Food Science and Technology 2015 Fyffe Court The Ohio State University Columbus, OH 43210 Kjartansson Gunnar, Chapter 9 Department of Food Science and Biotechnology University of Hohenheim Garbenstrasse 25 70599 Stuttgart, Germany Kluter Robert, Chapter 32 Science, Technology and Applied Research Directorate U.S Army Natick Soldier R, D & E Center 15 Kansas Street Natick, MA 01760 Knorr Dietrich, foreword Berlin University of Technology Department of Food Biotechnology and Food Process Engineering Koenigin-Luise-Str. 22, D-14195 Berlin, Germany

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Krishnamurthy Kathiravan, Chapter 18 Department of Agricultural and Biological Engineering The Pennsylvania State University 231 Agricultural Engineering Building University Park, PA 16802

Nguyen Loc Thai, Chapter 1 Department of Food Science and Technology The Ohio State University 333 Parker Food Science and Technology Building 2015 Fyffe Court Columbus, OH 43210-1007

Larkin John W., Chapter 37 National Center for Food Safety and Technology Food and Drug Administration 6502 S. Archer Rd. Summit-Argo, IL 60501

Niemira Brendan A., Chapter 20 USDA-ARS Eastern Regional Research Center 600 E. Mermaid Ln. Wyndmoor, PA 19038

Lee Dong Sun, Chapter 30 Department of Food Science and Biotechnology Kyungnam University 449 Wolyong-dong Masan, 631-701, Korea

Patel Jitu R., Chapter 8 Food Technology and Safety Laboratory USDA-ARS Bldg. 201 10300 Baltimore Avenue Beltsville, MD 20705-2350

Lelieveld Huub, Chapter 34 Ensahlaan 11 3723 HT Bilthoven The Netherlands Liao Ching-Hsing USDA-ARS Eastern Regional Research Center 600 E. Mermaid Ln Wyndmoor, PA 19038 Liu Li, Chapter 29 Conway Institute Glycobiology, NIBRT Dublin, Ireland ˜ Pilar, Chapter 27 Manas Tecnolog´ıa de los Alimentos Facultad de Veterinaria Universidad de Zaragoza C/ Miguel Servet, 177 50013, Zaragoza. Spain Mart´ın-Belloso Olga, Chapter 11, 16, 28 Department of Food Technology University of Lleida Av. Alcalde Rovira Roure, 191. 25198. Lleida, Spain

Patrick Dunne C., Chapter 38 Science, Technology and Applied Research Directorate U.S Army Natick Soldier R, D & E Center 15 Kansas Street Natick, MA 01760 Pilar Cano M., Chapter 33 Department of Plant Foods Science and Technology Instituto del Fr´ıo Consejo Superior de Investigaciones Cient´ıficas (CSIC) C/ Jos´e Antonio Novais, 10 Ciudad Universitaria E-28040 Madrid, Spain Plaza Luc´ıa, Chapter 33 Department of Plant Foods Science and Technology Instituto del Fr´ıo Consejo Superior de Investigaciones Cient´ıficas (CSIC) C/ Jos´e Antonio Novais, 10 Ciudad Universitaria E-28040 Madrid, Spain

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Rice Rip G., Chapter 22 RICE International Consulting Enterprises 1710 Hickory Knoll Road Sandy Spring, MD 20860 Rodriguez-Romo Luis A., Chapter 21 Department of Food Science and Technology The Ohio State University 2015 Fyffe Road Parker Food Science Building Columbus, OH 43210 Ross Paul, Chapter 29 Moorepark Biotechnology Centre Teagasc, Moorepark Fermoy, Cork, Ireland ´ ´ Chapter 33 Sanchez-Moreno Concepcion, Department of Plant Foods Science and Technology Instituto del Fr´ıo Consejo Superior de Investigaciones Cient´ıficas (CSIC) C/ Jos´e Antonio Novais, 10 Ciudad Universitaria E-28040 Madrid, Spain Sharma Manan, Chapter 8 Food Technology and Safety Laboratory USDA-ARS Bldg. 201 10300 Baltimore Avenue Beltsville, MD 20705-2350 Soliva-Fortuny Robert, Chapters 11, 16, 28 Department of Food Technology University of Lleida Av. Alcalde Rovira Roure, 191. 25198. Lleida, Spain Solomon Morse B., Chapter 8 Food Technology and Safety Laboratory USDA-ARS Bldg. 201 10300 Baltimore Avenue Beltsville, MD 20705-2350

Sommers Christopher, Chapter 17 USDA-ARS Food Safety Intervention Technologies Eastern Regional Research Center 600 East Mermaid Lane Wyndmoor, PA 19038 Sopher Charles D., Chapter 22 C&S AgriSystems, Inc. PO Box 1479 Washington, NC 27889 Spinak Stephen H., Chapter 37 Spinak Consulting 5 Park Place, Suite 317 Annapolis, MD 21401 Stewart Cynthia M., Chapters 5, 36 Silliker, Inc. 160 Armory Drive South Holland, IL 60473 Swanson Barry G., Chapter 6 School of Food Science Washington State University 106K FSHN Building Pullman, WA 99164-6376 Ting Edmund, Chapter 2 Pressure BioSciences Inc. 23642 123rd PL SE Kent, WA 98031 Toepfl Stefan, Chapter 13 DIL Prof.-von-Klitzing-Str. 7 49610 Quakenbr¨uck, Germany Tornello Carole, Chapter 4 NC Hyperbaric Poligono Industrial Villalonquejar Calle Condado de Trevino 6-09001 Burgos, Spain

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Contributors

Vurma Mustafa, Chapter 21 Department of Food Science and Technology The Ohio State University 2015 Fyffe Road Parker Food Science Building Columbus, OH 43210 Weiss Jochen, Chapter 9 Department of Food Physics and Meat Sciences Institute of Food Science and Biotechnology University of Hohenheim Garbenstrasse 25 70599 Stuttgart, Germany Wright Alan O., Chapter 7, 32 Science, Technology and Applied Research Directorate U.S Army Natick Soldier R, D & E Center 15 Kansas Street Natick, MA 01760 Yang Wade, Chapter 10 Department of Food and Animal Science Alabama A&M University Normal, AL 35762

Yannakou Anthos, Chapter 35 CSIRO Food and Nutritional Sciences 671 Sneydes Road (Private Bag 16) Werribee, VIC 3030, Australia Yousef Ahmed E., Chapter 21 Department of Food Science and Technology The Ohio State University 2015 Fyffe Road Parker Food Science Building Columbus, OH 43210 Yuan James T.C., Chapter 23 Pepsico Beverages & Foods 100 Stevens Avenue Valhalla, NY 10595 Zhang Howard Q., Chapter 14 USDA Western Regional Research Center 800 Buchanan St. Albany, CA 94710

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Foreword

The consumer demand for fresh-like products generated gentle processing. Emerging technologies such as high hydrostatic pressure and pulsed electric field treatment did fit well into the hurdle concept and into the minimal processing scheme promising retention of freshness while providing safety and functionality of the product. Today, we have industrial high-pressure and pulsed electric field treated products. Ozone, supercritical CO2 , ultrasound, and plasma treatment are either at pilot scale, industrially used, or on the verge of application. However, for me, after working for the first time with the first high-pressure unit at the University of Delaware, Newark, USA, exactly 25 years ago, there are still several issues to be addressed. Research work is still going on regarding inactivation, activation, or retention kinetics and mechanisms of microorganisms, nutrition, allergens, toxins, and viruses subjected to nonthermal processes. Furthermore, it is my belief that many nonthermal processes described in the book also have the potential to do more than just mimicking existing conventional thermal processes. Our own approach to understand the potential of nonthermal processes and

then use them based on their unique mode of actions will lead to additional and unique applications. For example, high-pressure modification of proteins and polysaccharides, stress response induction by pulsed electric fields are examples of potential future applications of nonthermal processes for the generation of tailor-made foods. Finally, it is essential for me to acknowledge the people who were the pioneers in the development of the “new” nonthermal processes. Amongst many, I want to mention about the pioneering work by Grahame Gould, then Head of Microbiology, Colworth House, Unilever Research, UK, and Daniel Farkas, then the Chair of the Department Food Science, University of Delaware, USA. It is my firm belief that without those individuals the field of nonthermal processing would not be where it is today. I wish this book all the success it deserves. Dietrich Knorr Berlin University of Technology Department of Food Biotechnology and Food Process Engineering Berlin, Germany

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Looking forward into the future of food science/ technology/engineering, in the emerging area of nonthermal processing of foods, is definitely an adventure. It is open ended and full of uncertainties. Lessons learned from the past should always serve as a good basis for envisioning the future of this growing field, even though emerging and unexpected challenges in food processing are making the integration of “what is known” with “what is coming” difficult. This integration not only embraces the fascination with the new but also addresses the responsibility demanded of scientists for accuracy of research, and proper extrapolations from the laboratory bench to the production floor, and to the marketplace where the best predictions are made. We have the tools to visualize what is coming, but it is our dreams and vision, if not our ambitions, that inspire us to go beyond what can be viewed with mathematical models and complicated algorithms. The food industry, being one of the most conservative sectors in the food production chain, is experiencing the need for change and innovation, to a degree never encountered before. Consumers have become much more demanding, better educated in terms of food quality and nutritional aspects, forcing producers along with regulatory agencies to search for technologies that offer better products with greater safety. Scientists and avid researchers are incorporating knowledge acquired from very different and disconnected disciplines, in order to wisely blend this research pool of information with what is commonly known in food science/food engineering domains. The outcomes have been quite unexpected, though very much welxviii

come in regard to food quality and safety, and it is envisioned that this trend will persist in the years to come. Nonthermal processing of foods has essentially meant unprecedented opportunities for the industrial sector, in providing better health and wellness for the consumer, and unforeseen new food products of excellent quality without compromising safety. The challenges surrounding these emerging technologies are immense, but the long list of interested groups in support of their development is growing in an exponential fashion. Nonthermal processing technologies are being advanced and making a significant, positive impact in the food sector. This handbook covers basic information and some of the recent developments in nonthermal processing of food, and the attempts, via predicted pathways, to identify future development in the field generated from the ingenuity and creative approach of a well-trained and resourceful community. The development of nonthermal processing techniques for processing of food has resulted in an excellent balance between safety and minimal processing, between cost and superior quality, and between novel approaches and use of existing process installations to optimize resources. Nonthermal processing could be perceived as an alternative to conventional thermal processing, but this is just a small piece of the role that nonthermal processing could play in the food factory of the future. Nonthermal processing can be effectively combined with thermal processing, and interesting synergistic effects have already been identified. Other significant synergisms could

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be achieved by combining selected nonthermal technologies, as well as by combining these with other microbial stress factors, such as pH, water activity modifiers, and inclusion of antimicrobials and/or bacteriocins. At the same time, nonthermal processing facilitates the development of new products never envisioned before—a series of niche markets that will eventually receive wide attention in the years to come. The opportunities for such new products are countless, and most will have superb quality and very attractive prices. Nonthermal technologies can be used for decontamination, pasteurization and, in some cases, sterilization, but in all examples of use, one of the key attributes of the processed product is excellent quality, wherein most products have “fresh” characteristics. There is no question that the quest for technologies capable of producing optimum-quality, safe-processed products has become a top priority in the world of food science and technology. Relevant factors to consider during exploration and application of these novel technologies include the following: the kind of microorganism inactivated; number of log cycles achieved; lethal doses required for inactivation; effect on enzyme activity as related to food quality factors; finding the most attractive process combinations to maximize synergy; how quality attributes are altered; how to scale up laboratory and pilot plant results to industrial applications; reliability of a given technology; adoption costs, such as engineering the process, initial investment, operation

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of the process, maintenance, and depreciation; energy savings; environmental impact; and consumer perception of the technology and products of that technology. As a final point, the search for new approaches to processing foods should be driven, above all, to maximize safety, quality, convenience, costs, and consumer wellness; it cannot be used to force the utilization of a given technology. Any technology must fit the needs and desires of the consumer to be successfully implemented. We have worked diligently to offer a thorough and objective overview of what nonthermal processing can offer today to the consumer and the industrial sector, what needs to be investigated further, and the expected developments. We have written some chapters in this handbook, but the contributions of other authors, who come from a wide array of backgrounds and prior experience in nonthermal processing, have been instrumental in presenting a well-balanced and self-provoking document that we hope will be useful to many in academia, industry, regulatory and other governmental agencies, and foremost to all of us, the consumers, and those who interpret the impacts of science on consumers. Howard Q. Zhang Gustavo V. Barbosa-C´anovas V.M. Bala Balasubramaniam C. Patrick Dunne Daniel F. Farkas James T.C. Yuan

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Introduction Gustavo V. Barbosa-Canovas and Daniela Bermudez-Aguirre ´ ´

The focus of food engineers and food scientists in the last 20 years has been on finding alternative process and preservation technologies that are environment friendly, low in cost, and able to preserve the quality attributes of the food product. A number of novel nonthermal technologies such as high pressure and irradiation are currently under commercialization and offer many of these advantages to the consumer. These new technologies have been extensively researched worldwide from a microbiological point of view, and study of composition factors and sensorial characteristics after processing has also been conducted. The interesting fact is that they are useful not only for inactivation of bacteria or enzymes but also for the development of ingredients and finished products with novel characteristics. Final quality of such products is outstanding compared with traditional thermal methods of preservation, while there are important savings in cost, energy, and processing times as well. Here, we review some novel nonthermal technologies and their development in partnership by with industry, academia, and government, who together worked with regulatory agencies to satisfy the requirements for their use in the food industry in order to offer the consumer food products that are safe, nutritional, and tasty. The case is that some traditional regulations for pasteurization and sterilization have been modified to accommodate these emerging technologies where heat is not the main stress factor to inactivate microorganisms.

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Why Nonthermal Technologies? Thermal pasteurization and thermal sterilization are the two most common food unit operations used to process and preserve foods in the world. Heat is responsible for the microbial inactivation and reduction in enzyme activity that takes place in food products undergoing thermal treatment, and results in a safe product with longer storage life than its raw equivalent. The main purpose of thermal processing is the inactivation of pathogenic microorganisms and spores (depending on the treatment) to provide consumers with a microbiologically safe product. However, despite the benefits of thermal treatment, a number of changes take place in the product that alter its final quality, for example, flavor, color, texture, and general appearance. In the last few decades, consumers have become more demanding about what they eat and the price they pay, including concern about the safety of their food; however, most products on the market have been overprocessed to ensure consumer safety and show significant damage in sensorial and nutritional characteristics. Now, consumers are looking for fresh-like characteristics in their food, along with high sensorial quality and nutrient content. Consumers are more aware of food content and the technologies used to process their food, showing a higher preference for natural products (Evans and Cox, 2006) free of chemicals and/or additives. Thus, the need for processing alternatives that can achieve microbial inactivation, preserve food’s fresh-like

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characteristics, and provide environment-friendly products, all at a reasonable cost, has become the present challenge of numerous food scientists/ technologists around the world. Nonthermal technologies represent a novel area of food processing and are currently being explored on a global scale; research has grown rapidly in the last few years in particular. In some cases, it is very appropriate to combine preservation techniques looking for synergistic effects (hurdle technology approach). These novel technologies are very appealing to be utilized in combination, either among themselves or with traditional ones.

Food Spoilage Food is an excellent vehicle for the transport of microorganisms. Because of the presence of water and the richness of the medium, a favorable environment exists for natural bacteria to grow; there are enough nutrients for bacteria to grow and multiply to a significant degree in a very short period of time. Under warm-temperature conditions, growth of microorganisms is even faster. Moreover, if unsanitary practices are followed during handling of food products, pathogenic microorganisms can be transferred to the food from surfaces, soil, water, or animals, generating a health risk for the consumer. Thus, processing operations that can inactivate pathogenic bacteria and reduce natural flora in vegetable and animal products are essential in the food industry. The most common approach used to achieve these goals consists in thermal techniques, as applied in pasteurization and sterilization processes. Pasteurization is commonly used for high-acid food products (pH < 4.6) to inactivate target pathogenic bacteria and to extend product shelf life for a few weeks. It is also utilized for low-acid foods followed by refrigeration. The most common pasteurization method, high temperature short time, uses temperatures around 72◦ C for 15 seconds in the case of milk. Sterilization is a stronger thermal treatment used for lowacid food products (pH > 4.6); it inactivates spores, extends the shelf life of the product for months at a time, and uses temperatures around 121◦ C for several minutes (e.g., 15 minutes). Pasteurization

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and sterilization have been used to inactivate cells of pathogenic microorganisms such as Salmonella, Escherichia coli, Listeria monocytogenes, Staphylococcus aureus, and spores of Clostridium botulinum in a significant number of food products, in addition to reducing spoilage microorganisms. Enzymatic activity can also be reduced when heat is applied to food and yields a product with better stability during storage. Nevertheless, some microbial growth can be observed during food storage, for example, in pasteurized products (i.e., milk). The process does not inactivate all the microorganisms and heat-resistant spores can remain in the product after processing, and depending on storage conditions, growth of bacteria can accelerate. Some food products under specific conditions are processed to withstand long periods of storage. This is the case when manufacturing and shipping specific items from one country to another; the product must have enough shelf life to withstand being processed and consumed in two remote places. In more specific situations, such as food processed for military use or space missions, there are more strict requirements, one being product storage life in particular. For military use, the shelf life of food must be at least 3 years at room temperature. During this 3-year period, the growth of bacteria must be practically nil, or at an extremely slow rate, to avoid any spoilage. Military food is used under extreme temperature and moisture conditions, sometimes in desert environments, where food must be innocuous to soldiers and provide necessary energy and nutritive requirements. For space missions, shelf life must be longer than that required for commercial use. Food items must be microbiologically safe with adequate nutrients, taste good, and have a pleasing appearance. Although extreme temperature conditions are not considered a problem during space transportation and storage, the food must also be stable against high amounts of radiation. At present, food scientists are studying the use of new preservation factors to preserve foods and extend product shelf life, which will be especially beneficial in research of military and space foods, as well as other foods. Some of these new preservation factors belong to the nonthermal technology

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area of study, in which different physical hurdles are being explored to inactivate or delay the growth of bacteria. The main goal of these novel technologies is to process a safe product that retains the sensorial characteristics of the fresh product as closely as possible, in terms of nutrient content and sensorial properties.

Nutrient Content The microbial safety of food remains an important aspect of food processing, but because of the required conditions to inactivate microorganisms, nutrient content in some food products is detrimentally affected after processing due to thermal sensitivity of some nutrients. For example, milk, eggs, fish, meat, and other important sources of protein; once they are subjected to thermal treatment (pasteurization or sterilization), the nutrient content is affected greatly. Thus, processing technologies that can maintain original nutrient content and do not change the structure and functionality of ingredients are highly desired in the food industry. One nonthermal technology, high hydrostatic pressure (HHP), has shown a negligible effect on the nutrient content of food, for example, in processing of fruits and vegetables, where pressure has minimal effect on the anthocyanin content after processing (Tiwari et al., 2009). Anthocyanins are considered phytonutrients, and they not only are responsible for color but also have an important antioxidant effect on human health. However, anthocyanin content in juices after pulsed electric fields (PEF) treatment has shown contradictory results. Some researchers report a minimum effect on the pigment content after processing, while others show that there is degradation in anthocyanin content after pulsing (Tiwari et al., 2009). Other examples of nutrient retention in food products using nonthermal technologies are mentioned by Knorr et al. (2002), such as the minor loss of L(+) ascorbic acid in sonicated juice, better retention of ascorbic acid concentration in high pressure treated peas, complete retention of ascorbic acid in pressurized broccoli, and unchanged amino-acid content in PEF-treated grape juice (Garde-Cerd´an et al., 2007), among others.

Sensorial Quality of Food Changes in food’s sensorial characteristics are commonly observed when thermal processing is used. Temperature works as a catalyzer in some chemical reactions occurring between the pigments, mineral salts, proteins, vitamins, amino acids, fats, and other chemical species in the food, promoting a number of physical changes. Browning, oxidation, protein denaturation, coagulation or precipitation, changes in microstructure and final texture, gelation, loss of color and flavor, loss of functionality, starch retrogradation, and related chemical processes occur in food components during thermal treatment. High-pressure processing applied at room temperature yields a product with most of food’s quality attributes intact; for example, pressurization does not affect covalent bonds, avoiding any development of strange flavors in the food (Knorr et al., 2002). Some studies of orange juice processed under pressure showed no important changes compared with the fresh squeezed product, retaining the same quality during storage for as long as 3 months at 5◦ C (Knorr et al., 2002). In consumer tests, when asked to compare fresh-squeezed, thermal pasteurized, and pressurized orange juices, consumers preferred the pressurized version (Evans and Cox, 2006). In milk processing, high pressurization (>200 MPa) was found to increase casein solubility, protein and water content in curds, as well as curd yield (Knorr et al., 2002). This pressurized milk has been successfully used in cheese-making and yogurt production (Penna et al., 2007; San Mart´ın-Gonz´alez et al., 2007). Another nonthermal technology applied to milk is PEF, which allows pasteurization of milk with only minor thermal damage to milk’s properties and provides important energy and cost savings (Bolado-Rodr´ıguez et al., 2000; Bendicho et al., 2002). Ultrasound has also been used in milk pasteurization, with important results; milk shows a higher degree of homogenization, whiter color, and better stability after processing. In this method, pasteurization and homogenization are completed in a one-step process (Berm´udez-Aguirre et al., 2009). Better color in ultrasound-treated juice, better quality in pressurized strawberry jam, and better

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Figure 1. Number of high-pressure equipment units in use around the world as of 2009 (Tonello, 2009).

flavor and color in guava puree (Knorr et al., 2002) are other examples of quality enhancements experienced with nonthermal technologies. Minimal change in sensorial quality has been reported in fruit juices processed with ultrasound as well and in juices processed under dense phase carbon dioxide, showing important bacterial inactivation, which ensures microbial quality and product safety, but does not compromise the organoleptic properties (Tiwari et al., 2009).

Novel Nonthermal Technologies These new technologies for food processing are normally applied under nonthermal conditions. Although temperature could be used in combination with some of these novel technologies to enhance effectiveness, most of the research conducted is at room temperature, and due to extremely short processing times, food remains fresh-like. Scientists are exploring the use of pressure, light, different types of electromagnetic radiation, sound, and other physical hurdles to inactivate bacteria. Consumers

are gradually becoming aware of novel technologies for food processing and sometimes refer to specific nonthermal methods, such as “cold pasteurization” (Cardello et al., 2007). A more detailed list includes the following: HHP, ultrasound, PEF, oscillating magnetic fields, irradiation, ultraviolet light, cold plasma, some chemicals (e.g., ozone, dense phase carbon dioxide, chlorine dioxide, electrolyzed water, and bacteriocins), and processing methods (e.g., intelligent packaging). Some of the most explored technologies in this group are HHP and irradiation; both are currently used for commercial products and there are facilities for these technologies around the world. Figure 1 shows the growth in the number of HHP equipment in use around the world in the last 19 years. As a novel technology, development and improvement of such equipment have been based on specific requirements and needs of the food industry. Today, use of pressure (300–700 MPa) for commercial applications around the world in vessels ranging in size (35–420 L) has an annual production rate of higher than 150,000 tons (Wan et al., 2009).

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Another nonthermal technology widely used to process food is irradiation; many toxicological tests have been conducted to show that this technology is safe for foods in specific cases, such as microbial inactivation, insect disinfestation, or improvement of quality. Since the 1990s more than 40 countries around the world have established safe and appropriate facilities for irradiation of food (Molins, 2001). These facilities have begun to show consumers that irradiation technology has more advantages than disadvantages. In some countries, the name of this technology has been changed to electronic pasteurization for better acceptance by consumers (Molins, 2001). The technique is regulated both nationally and internationally by IAEA, FAO, and WHO (Morehouse and Komolprasert, 2004). FDA considers irradiation to be more of an additive than a process for food. PEF technology is probably the second most promising of the nonthermal technologies; it is already approaching industrial application. PEF application was successfully launched for fruit juices in the United States in 2006, achieving outstanding results in product quality. In the not too distant future, this technology will likely be launched by a number of European food companies for pasteurization of liquid foods, introducing all the advantages of this technology for the first time to consumers and food processors (Kempkes, 2008).

Processing Times Food scientists are also looking for more convenient processing operations. Emerging nonthermal technologies have shown important reductions in processing times compared with traditional thermal processing operations. A short processing time is characteristic of most explored novel nonthermal technologies (Wan et al., 2009). For example, using PEF for pasteurization of liquid foods reduces the total processing time to less than a second; high pressure thermal sterilization is able to inactivate spores and produce a shelf-stable product in only a few minutes (around 5 minutes, depending on the characteristics of a product). This reduction in processing time is reflected in both energy and economic savings. Another key advantage of nonthermal

technologies is the environment-friendly aspect of such energy savings, which includes minimal waste after processing. PEF technology is a good example as this technology is a waste-free process (Knorr et al., 2002). In general, most of these technologies show a significant reduction in processing time compared with traditional thermal treatment; waste is minimal or nonexistent, and savings in energy is a common characteristic in the majority of those technologies already mentioned.

A Four-Member Team Approach The development of nonthermal technologies has grown in the last several years because of the constant interaction between academia, industry, government, and the consumer, under the supervision of regulatory agencies. The first round of research was conducted by academia, but upon sharing the results with industry and government, and later on consumers, they too became interested and encouraged the continuation of this research, again under the supervision of regulatory agencies. HHP, for example, a technology that was probably looked at 20 years ago, began to be explored in labs; transfer and scaleup, from the pilot plant to industry, became a priority after viewing the encouraging results of these studies. Today, it is a commercial reality and has been adopted by industry for use in processing products with high quality and high added value, which includes processing already existing products and promoting the development of new products. Regulatory agencies such as the Food and Drug Administration have approved HHP use, first as a pasteurization alternative, and recently (February, 2009), in combination with heat, as an alternative for food sterilization known as pressure-assisted thermal sterilization (PATS) or pressure-assisted thermal processing (PATP) (NCFST, 2009).

Thermal Processing There have been some innovations in this area, but conventional equipment is still used (Mermelstein, 2001). Sterilization and pasteurization have been extensively studied over the years, and in the case of

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low-acid foods, sterilization must follow strict controls and, depending on the product, requires specific processing times to ensure that the spores of most resistant microorganisms are inactivated and beyond; this process results in loss of thermal-sensitive nutrients such as vitamins (Teixeira and Tucker, 1997). In past decades, food engineers/scientists followed a first-order kinetics or linear trend to interpret and describe thermal inactivation of bacteria. Thermal processing parameters such as D, z, and F0 values have been used extensively to calculate lethality of the process. However, it has been shown that first-order kinetics is rarely followed by bacteria during inactivation and that safety in the canning industry is based more on overprocessing operations than on kinetics models (Corradini et al., 2005). The nonisothermal conditions during thermal processing have been extensively reviewed and discussed by many authors in the last few decades (Corradini et al., 2006, 2007, 2008; Aragao et al., 2007; Smith-Simpson et al., 2007; Peleg et al., 2008). They have shown that most bacterial inactivation curves during thermal processing follow a nonlinear trend, and that alternative mathematical models can fit these curves (Aragao et al., 2007; Corradini and Peleg, 2004, 2007). Several efforts have been devoted to establishing better control during thermal processing using “intelligent systems” to monitor the process with on-line systems to optimize safety, quality, and process efficiency (Teixeira and Tucker, 1997). Local optimization algorithms (Miri et al., 2008) are used as well as comprehensive studies with time–temperature integrators (Mehauden et al., 2009), among other tools. Most of these approaches cannot be fully transferred to industry, because thermal processes (pasteurization or sterilization) must follow the established criteria, unless a variation has been successfully validated and approved by regulatory agencies. In studies of nonthermal technologies, some concerns with thermal processes are also observed, such as nonlinearity during inactivation. These issues have been addressed together with increased knowledge of emerging nonthermal technologies, as cited by many authors (Raso et al., 2000; Rodrigo et al., 2003a,

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2003b; Hassani et al., 2005); consequently, modifications resulting from these issues must be addressed in regulations and established standards by regulatory agencies.

New Definition of Pasteurization The new alternatives for pasteurization of foods have resulted in various changes that must be addressed to meet the original standards for pasteurization. For one, the definition of pasteurization should be reviewed carefully for its applicability to other technologies with the same goal of pasteurization (as sought in years past). There are a number of important factors to consider when a new technology is thought to be the equivalent of thermal pasteurization, such as the most resistant pathogenic microorganisms in a given food, the efficacy of the novel technology, the characteristics of the food product, the conditions needed for food distribution and storage, and the intended use of the food (NACMCF, 2006). The new definition of pasteurization should meet all of the above-mentioned factors so that a safe product can be offered to the consumer; at the same time, it should describe the advantages of the novel technology to the consumer and the food processor. The National Advisory Committee on Microbiological Criteria for Foods (NACMCF) adopted a new definition for pasteurization in 2004: “Any process, treatment, or combination thereof, that is applied to food to reduce the most resistant microorganism (s) of public health significance to a level that is not likely to present a public health risk under normal conditions of distribution and storage” (NACMCF, 2006). In the same document, a list of novel technologies is included as a possible alternative for thermal pasteurization. Some novel thermal technologies such as microwave and ohmic heating are cited, and most of the nonthermal technologies such as HHP, PEF, ultraviolet, irradiation, chemical treatment, pulsed light, infrared, cold plasma, oscillating magnetic fields, ultrasound, and filtration are mentioned, including their criteria for use in pasteurization according to the type of microorganism, processing conditions, and research needs.

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Additional Relevant Issues Regarding Novel Technologies The search for other food processing alternatives not only provided the required tools for microbial inactivation but during the development of some novel technologies important discoveries were also made concerning specific foods that would help improve the quality of other products or the development of new ones. Some of the advantages of novel technologies are (or will be) their use in processing specific products such as military rations or space food items that require precise and very strict regulations. Novel technologies can be used to replace some of the current military rations as well, or to process some of the excess in agricultural and farm activities, avoiding important yearly economic losses around the world.

New Ingredients, New Products The exploration of new preservation factors in food processing has not been limited to microbial and enzyme inactivation; during extensive research of nonthermal technologies, important discoveries regarding new properties in some food ingredients were observed. For example, HHP has the ability to modify the structure of proteins and polysaccharides, which allows changing the texture, functionality, and even appearance of food (Ross et al., 2003). These changes have been observed systematically according to the intensity of the applied pressure, and depending on the new use of the protein or the sugar, the changes can be modified accordingly. The possibility of having new ingredients for food processing has opened up a distinct and comprehensive world of opportunities in food research and development of new products. At the same time, new ingredients are helping to solve some quality issues in specific products. For example, during ultrasound treatment of milk, in addition to pasteurization, cavitation (which is the main effect of sonication) is responsible for breakdown of fat globules in milk and reorganization of microstructure in casein molecules and fat globules; the result is an homogenized product after processing (Berm´udez-Aguirre et al., 2008), avoiding one important step (homogenization) in the manufactur-

ing of milk by conventional methods. This new effect on milk can be “intelligently” used for some dairy products that present problems during storage, such as yogurt, in which syneresis is one of the main quality concerns; sonicating the milk prior to yogurt processing can minimize this problem.

Space Mission Food Another big challenge in food science and technology is the processing of safe and nutritious foods for storage on long space missions, where the required long storage of these foods is not the only requirement. Other important factors determine whether they are acceptable, such as the requirement that space food be of reduced volume and mass with a minimum of waste. These food items must also satisfy all dietary requirements of astronauts for maintenance of health during a space mission, not only from the perspective of physical well-being and health aspects but also to address the possible psychological effects of such food on the astronaut (Chen and Perchonok, 2008). This last aspect is important for both space mission foods and military rations, because those consuming such food are away from home and under hard conditions for long periods of time; this food must be acceptable in appearance and content, and must evoke positive feelings and comfort, giving a definite sense of being closer to home. The NASA Advanced Food Technology Project at the Johnson Space Center is the agency currently in charge of feeding systems for astronauts. At this center, state-of-the-art technologies are evaluated to achieve various required goals, and one of them is to achieve a 5-year storage life for many space mission food items. The current food technologies being investigated are retort processing, freeze-drying, irradiation, and intermediate moisture processing; for instance, thermostabilized food products, a new trend in product design for space missions, are currently replacing some of the previous retorted items (Chen and Perchonok, 2008). The ongoing intensive study of some nonthermal technologies could very possibly deliver a viable option for future space mission meals. With the recent approval of PATP as a sterilization technology, this will open new frontiers for

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food processing and the development of new food items for inclusion on space mission menus.

Military Combat Rations One area of study receiving even more attention today is research related to military combat rations. In the last several years, important investments in terms of time and money have been made to achieve a world-class feeding system for US soldiers (Natick, 2008). Recent advances in food science and the development of state-of-the-art technologies have been applied to satisfy the dietary needs of soldiers from the nutritional, safety, and quality points of view. Soldiers often endure extreme, intense physical activity requiring high-energy meals, but in addition to satisfying their high-energy demands, these foods must be of the highest quality possible and at an affordable price to the military. According to Chen and Perchonok (2008), one of the goals of the Department of Defense Combat Feeding Program by 2010 is to implement the use of nonthermal/combination technology for shelf-stable military rations. The novel technologies that have been investigated thus far (for Natick) are irradiation, PEF, high pressure, ohmic heating, microwave, and radio frequency (Cardello et al., 2007). HHP technology is the closest to being incorporated for military rations at this time. This technology has shown positive results in processing dairy products, fruits, and vegetables, potatoes, eggs, fish, and meats. According to RDECOM (2009), the product mashed potatoes in-a-pouch processed under PATS has been officially accepted for incorporation as an mealsready-to-eat (MRE) product for military use. This is indeed a giant step ahead for use of one of the first nonthermal technologies researched. Investigated in food labs 20 years ago, today PATS is a reality in commercial pasteurization as well as commercial sterilization, and generates products that require strict and rigid quality control.

World Hunger Issues Food scientists should not only focus on improving the quality and safety of foods marketed to demand-

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ing consumers in the first-world countries but should also consider areas in the world experiencing hunger and poverty. Today, approximately 1.3 billion people live in extreme poverty, surviving on less than 1 dollar a day, and nearly 2 billion people live in poverty and marginal circumstances close to these conditions (ADA, 2003). However, this does not mean that food quality is not important. Even some consumers in the first-world countries agree that they should pay extra for high added-value food, such as freeze-dried products. Yet, most consumers in underdeveloped countries just want to pay the minimum amount in dollars necessary to satisfy their basic dietary needs. Access to food is another critical issue. According to the American Dietetic Association (ADA), food security is related to a person’s access (at any given time) to adequate rations of safe, nutritious, and ethnically appropriate food (ADA, 2003). With the current level of agricultural production worldwide, food could be available to everyone on earth to feed the world’s 850 million hungry people, but only if the biological, chemical, and physical factors that commonly generate loss of food around the world could be avoided or minimized (Marsh, 2008). World hunger is by far another reason that study of novel technologies should focus on processing foods at a reasonable cost with adequate nutrient content and long shelf life; extending a technology’s commercialization in faraway and hard-to-access locations could make a huge difference. Nonthermal technologies are not going to resolve the hunger problem on a day-to-day basis; the intelligent exploration of these technologies could, however, lead to processing highly nutritious food items with longer storage life, and possibly shipping these products to remote places; this in turn could satisfy basic food supply needs in underdeveloped countries. One example is the use of PATS, to be used for military rations in 2009 based on of its demonstrated advantages, as explained previously. Some military rations are used for humanitarian daily rations, which provide a full day’s nutrition to the malnourished. These rations are designed to feed large populations of displaced people or refugees and contain ready-to-eat thermostabilized meals, similar to MRE products (Natick, 2008). Thus, the reality of feeding people

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in poverty via novel technologies in the near future is a sound possibility, and foods would have better quality and most of the original nutrients intact.

Food Science and Technology (EFFoST) to establish a world wide regulation system. Since then, GHI has made important advances in the last few years (Lelieveld, 2009).

Global Harmonization Initiative Novel nonthermal technologies have been researched in different parts of the world with important results. Thousands of references can be found on the most developed nonthermal technologies, such as HHP. A wide variety of pressurized products are mentioned in these references, including a number of ethnic food products in specific countries. Researchers found that high pressure is an excellent technology for processing ethnic foods and extending product shelf life. However, due to inconsistencies in reporting processing conditions, today, there are problems in commercializing such products outside these ethnic niches. Added to this are the problems that arise with all novel nonthermal technologies in general when conditions used in a specific country to satisfy the sanitary regulations are not legally required in another country, making processing difficult and expensive, and commercialization of these products almost impossible. Furthermore, the time-consuming activity needed to demonstrate the safety of a specific product in another country is complex and expensive, causing delays in the food processing chain (Lelieveld and Keener, 2007; Sawyer et al., 2008). Hence, a global regulation system that ensures the safety and quality of food regardless of country of origin is sorely needed. Lelieveld and Keener (2007) pointed out that, in addition to a global regulation system, there should be a governing body that regulates and monitors the enforcement of these food processing regulations. Although there are institutions that regulate food processing today, the resulting regulations often only apply to countries belonging to specific organizations (e.g., the Codex Alimentarius). Thus, the new regulations should apply to all countries and clearly show validity overseas. Meanwhile, with this goal in mind, a Global Harmonization Initiative (GHI) was launched 5 years ago by the International Division of the Institute of Food Technologists and the European Federation of

Hurdle Technology The use of novel technologies alone is often insufficient to achieve the desired processing goal, for instance, adequate microbial inactivation. Sometimes, the intelligent use of two or more preservation factors applied simultaneously, known as hurdle technology, can fulfill the requirements for a specific product. The concept of hurdle technology is not new. Processing factors have been combined in the past to extend the shelf life of food; examples include combining pH, acidity, heat, water activity, and/or antimicrobials. Today, a number of novel technologies are good candidates for use in combination with these past preservation factors, and preliminary results have shown important shelf life extension of products. Probably, the best example is the recent approval by the FDA (NCFST, 2009) of high pressure in combination with heat for commercial sterilization of food in the United States. Other technologies combined with heat to enhance their effectiveness are PEF and ultrasound. In both cases, heat is used to weaken the cells during the process and to enhance the lethal effect against bacteria. Of particular note is the test of ultrasound in three different combinations: with heat (thermosonication), pressure (manosonication), and the combined factors sound, heat, and pressure (manothermosonication). These combinations have been effective in microbial and enzyme inactivation (Knorr et al., 2002). Clearly, use of nonthermal processes in hurdle technology requires finding the right combinations of preservation factors. These factors should have a synergistic effect on cell inactivation in order to disrupt the vital functions of the microorganism; this is called a multitarget approach (Ross et al., 2003). Presently, the mechanisms of cell inactivation observed with nonthermal technologies are not all that clear. More knowledge about this topic will help determine the right combinations of preservation

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factors needed to achieve higher inactivation and more lethal treatments against bacteria.

Final Remarks Indeed, the area of nonthermal technologies is a vast world of opportunities for processing and preserving food with excellent quality. At present, there are many challenges facing food scientists, specifically those related to nonthermal technologies, although a number of these have been successfully tested in microbial inactivation. However, aspects related to mechanisms of cell inactivation and improvements in nonthermal processes and equipment are among the priorities that need to be addressed in the coming years. Currently, food scientists and engineers around the world are devoting much time to figuring out the majority of these issues. Still, other gaps in research remain, for example, the issue related to spore inactivation and the use of novel technologies to effectively inactivate vegetative cells. Results could be similar to that achieved with high pressure, which brought about the recent approval of high-pressure thermal sterilization—a result that could likewise be achieved with other technologies in the near future. In addition, several features concerning the toxicological aspects of novel products should be evaluated to test if the applied energy generated by a nonthermal technology is strong enough to inactivate microorganisms and to preserve the nutritional content of food. At the same time, a nonthermal technology should not be responsible for creating undesirable compounds or toxic substances that could be harmful to consumers. Indeed, the issues now facing researchers in promoting a technology, from the lab to regulatory approval and commercialization, are the same issues that will provide consumers with better food and new food products exhibiting outstanding characteristics.

References American Dietetic Association. 2003. Position of the American Dietetic Association: Addressing world hunger, malnutrition and food insecurity. Journal of the American Dietetic Association 103(8):1046–1057.

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Aragao, G.M.F., Corradini, M.G., Normand, M.D., and Peleg, M. 2007. Evaluation of the Weibull and log-normal distribution functions as survival models of Escherichia coli under isothermal and non-isothermal conditions. International Journal of Food Microbiology 119:243–257. Bendicho, S., Barbosa-C´anovas, G.V., and Mart´ın, O. 2002. Milk processing by high intensity pulsed electric fields. Trends in Food Science and Technology 13:195–2004. Berm´udez-Aguirre, D., Mawson, R., and Barbosa-C´anovas, G.V. 2008. Microstructure of fat globules in whole milk after thermosonication treatments. Journal of Food Science 73(7):E325– E332. Berm´udez-Aguirre, D., Mawson, R., Versteeg, K., and BarbosaC´anovas, G.V. 2009. Composition parameters, physicalchemical characteristics and shelf-life of whole milk after thermal and thermo-sonication treatments. Journal of Food Quality 32:283–302. Bolado-Rodr´ıguez, S., G´ongora-Nieto, M.M., Pothakamury, U., Barbosa-C´anovas, G.V., and Swanson, B.G. 2000. A review of nonthermal technologies. In: Trends in Food Engineering, edited by Lozano, J., A˜no´ n, M.C., Parada, E., and BarbosaC´anovas, G.V. Lancaster, PA: Technomic Publishing. Cardello, A.V., Schutz, H.G., and Lesher, L.L. 2007. Consumer perceptions of foods processed by innovative and emerging technologies: a conjoint analytic study. Innovative Food Science and Emerging Technologies 8:73–83. Chen, H. and Perchonok, M. 2008. US Governmental Interagency Programs, Opportunities and Collaboration. Food Science and Technology International 14(5):447–453. Corradini, M.G. and Peleg, M. 2004. Demonstration of the Weibull-Log logistic survival model’s applicability to non isothermal inactivation of E. coli K12 MG1655. Journal of Food Protection 67:2617–2621. Corradini, M.G. and Peleg, M. 2007. A Weibullian model of microbial injury and mortality. International Journal of Food Microbiology 119:319–329. Corradini, M.G., Normand, M.D., and Peleg, M. 2005. Calculating the efficacy of heat sterilization processes. Journal of Food Engineering 67:59–69. Corradini, M.G., Normand, M.D., and Peleg, M. 2006. On expressing the equivalence of non-isothermal and isothermal heat sterilization processes. Journal of the Science of Food and Agriculture 86:785–792. Corradini, M.G., Normand, M.D., and Peleg, M. 2007. Modeling non-isothermal heat inactivation of microorganisms having biphasic isothermal survival curves. International Journal of Food Microbiology 116:391–399. Corradini, M.G., Normand, M.D., and Peleg, M. 2008. Prediction of an organism’s inactivation patterns from three single survival ratios determined at the end of three non-isothermal heat treatments. International Journal of Food Microbiology 126:98–111. Evans, G. and Cox, D.N. 2006. Australian consumers’ antecedents of attitudes towards foods produced by novel technologies. British Food Journal 108(11):916–930.

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Garde-Cerd´an, T., Arias-Gil, M., Marsell´es-Fontanet, A.R., Anc´ın-Azpilicueta, C., and Mart´ın-Belloso, O. 2007. Effects of thermal and non-thermal processing treatments on fatty acids and free amino acids of grape juice. Food Control 18:473– 479. ´ Hassani, M., Alvarez, I., Raso, J., Cond´on, S., and Pag´an, R. 2005. Comparing predicting models for heat inactivation of Listeria monocytogenes and Pseudomonas aeruginosa at different pH. International Journal of Food Microbiology 100:213–222. Kempkes, M. 2008. Personal communication. Pullman WA. Knorr, D., Ade-Omowaye, B.I.O., and Heinz, V. 2002. Nutritional improvement of plant foods by non-thermal processing. Proceedings of the Nutrition Society 61:311–318. Lelieveld, H. 2009. Progress with the global harmonization initiative. Trends in Food Science and Technology 20:S82–S84. Lelieveld, H. and Keener, L. 2007. Global harmonization of food regulations and legislation – the Global Harmonization Initiative. Trends in Food Science and Technology 18:S15–S19. Marsh, K.S. 2008. A call to action on world hunger. Food Technology 62(3):128. Mehauden, K., Cox, P.W., Bakalis, S., Fryer, P.J., Fan, X., Parker, D.J., and Simmons, M.J.H. 2009. The flow of liquid foods in an agitated vessel using PEPT: Implications for the use of TTI to assess thermal treatment. Innovative Food Science and Emerging Technologies. doi:10.1016/j.ifset.2009.06.004 Mermelstein, N.H. 2001. High-temperature, short-time processing. Food Technology 55(6):65–66, 68, 70, 78. Miri, T., Tsoukalas, A., Bakalis, S., Pistikopoulos, E.N., Rustem, B., and Fryer, P.J. 2008. Global optimization of process conditions in batch thermal sterilization of food. Journal of Food Engineering 87:485–494. Molins, R.A. 2001. Introduction. In: Food Irradiation: Principles and Applications, edited by Molins, R.A. New York: John Wiley & Sons, pp. 1–21. Morehouse, K.M. and Komolprasert, V. 2004. Irradiation of food and packaging: an overview. In: Irradiation of Food and Packaging, edited by Komolprasert, V. and Morehouse, K.M. Washington, D.C.: American Chemical Society, pp. 1–11. Natick. 2008. Operational Rations of the Department of Defense. RDECOM. 8th edition. US Army Natick Soldier RD&E Center. National Advisory Committee on Microbiological Criteria for Foods (NACMCF). 2006. Requisite scientific parameters for establishing the equivalence of alternative methods of pasteurization. Journal of Food Protection 69(5):1190–1216. National Center for Food Safety and Technology. 2009. NFSCT receives regulatory acceptance of novel food sterilization process. Press release, February 27, 2009. Summit-Argo, IL. Peleg, M., Normand, M.D., and Corradini, M.G. 2008. Interactive software for estimating the efficacy of non-isothermal heat

preservation processes. International Journal of Food Microbiology 126:250–257. Penna, A.L.B., Gurram, S., and Barbosa-C´anovas, G.V. 2007. High hydrostatic pressure processing on microstructure of probiotic low-fat yogurt. Food Research International 40(4):510– 519. Raso, J., Alvarez, I., Cond´on, S., and Sala Trepat, F.J. 2000. Predicting inactivation of Salmonella senftenberg by pulsed electric fields. Innovative Food Science and Emerging Technologies 1(1):21–29. RDECOM. 2009. High Pressure Processing (HPP). US Army Natick, Soldier RD&E Center. Rodrigo, D., Barbosa-C´anovas, G.V., Mart´ınez, A., and Rodrigo, M. 2003a. Weibull distribution function based on an empirical mathematical model for inactivation of Escherichia coli by pulsed electric fields. Journal of Food Protection 66(6):1007– 1012. Rodrigo, D., Ru´ız, P., Barbosa-C´anovas, G.V., Mart´ınez, A., and Rodrigo, M. 2003b. Kinetic model for the inactivation of Lactobacillus plantarum by pulsed electric fields. International Journal of Food Microbiology 81:223–229. Ross, A.I.V., Griffiths, M.W., Mittal, G.S., and Deeth, H.C. 2003. Combining nonthermal technologies to control foodborne microorganisms. International Journal of Food Microbiology 89:125–138. San Mart´ın-Gonz´alez, M.F., Rodr´ıguez, J.J., Gurram, S., Clark, S., Swanson, B.G., and Barbosa-C´anovas, G.V. 2007. Yield, composition and rheological characteristics of cheddar cheese made with high pressure processed milk. LWT – Food Science and Technology 40(4):697–705. Sawyer, E.N., Kerr, W.A., and Hobbs, J.E. 2008. Consumer preferences and international harmonization of organic standards. Food Policy 33:607–615. Smith-Simpson S., Corradini, M.G., Normand, M.D., Peleg, M., and Schaffner, D.W. 2007. Estimating microbial growth parameters from non-isothermal data: A case study with Clostridium perfringens. International Journal of Food Microbiology 118:294–303. Teixeira, A.A. and Tucker, G.S. 1997. On-line retort control in thermal sterilization of canned food. Food Control 8(1): 13–20. Tiwari, B.K., O’Donnell, C.P., and Cullen, P.J. 2009. Effect of nonthermal processing technologies on the anthocyanin content of fruit juices. Trends in Food Science and Technology 20:137– 145. Wan J., Coventry, J., Swiergon, P., Sanguansri, P., and Versteeg, C. 2009. Advances in innovative processing technologies for microbial inactivation and enhancement of food safety – pulsed electric field and low-temperature plasma. Trends in Food Science and Technology. doi:10.1016/j.tifs.2009.01.050

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Plate 1. Number of high-pressure equipment units in use around the world as of 2009 (Tonello, 2009).

Plate 2. Typical small pressure vessels using a threaded closure. (Photo courtesy of Pressure Biosciences Inc.) Nonthermal Processing Technologies for Food Edited by H. Q. Zhang, G. V. Barbosa-Cánovas, V. M. Balasubramaniam, C. P. Dunne, D. F. Farkas, and J. T. C. Yuan © 2011 Blackwell Publishing Ltd. ISBN: 978-0-813-81668-5

Plate 3. Wire winding can be used for both the pressure vessel and the yoke to support the end closure force. (Photo courtesy of Avure.)

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Plate 6. A second-generation yoke-based system with a 215 L volume which operates at a pressure of 600 MPa (87,000 psi). It is vertically orientated to minimize floor space. A high power pump–intensifier is located below the loading and unloading area. (Photo courtesy of Avure.)

Plate 4. Pressure vessels, and their associated closure retaining yokes, can be operated at any desired angle of repose from horizontal to vertical. Units are available that tilt to receive product through the top opening, swing to a vertical position to engage a yoke during pressure treatment, then tilt to release treated product from their bottom opening. (Photo courtesy of Elmhurst.)

Plate 7. A third-generation 350 L volume, 600 MPa (87,000 psi) system that is capable of a 2,300 kg (5,000 pounds) per hour throughput. It is easily integrated into a horizontal product delivery subsystem. (Photo courtesy of Avure.) Plate 5. Historically, large pressure vessels have been built to operate in the vertical position and are loaded and unloaded through their top opening. (Photo courtesy of Avure.)

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50

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20

20

10

10

0

0

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–10

–20

–20

–30

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–40

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–50 Just right

Plate 8. This graph displays the results of the “ripeness” from data acquired from the “Just Right” scale. This could have been generated from naive consumers who were asked to rate their perception of how optimal the color of the fruit was or the data could have been generated from trained panelists who are rating the “ripeness” from specific criterion. The 12 treatments are seen graphically in a way that is intuitive and easy to see relative comparisons.

15

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0 Rancidity intensity

Plate 9. Bar graph results of “Rancidity intensity” for 12 different samples.

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Eggs–trained panel quality ratings (1–9 point scale). HPP experimental samples Appearance 9 8 7 6 5 4

Overall quality

Odor

3 Non HPP control HPP treatmet 1 HPP treatmet 2 HPP treatmet 3 HPP treatmet 4

2 1

Texture

Flavor

Plate 10. Spider graph display of HPP data from several treatments. The spider graph provides a visual comparison/fingerprint of products overlaying each other. In this graphic, the HPP treatment 3 is clearly the highest rated in all categories. (Note: this graph was derived from a 1- to 9-point quality scale (see Figure 7.3), not a 1- to 9-point Hedonic scale (see Figure 7.1)).

Degree of color difference

Plate 11. Degree of difference scale and results (treatments vs. control) When scales are different, it is sometimes useful to standardize the rating so that other attributes or characteristics can be viewed on the same graph. Caution should be used when multiple scales are used. Work to assure the scaling of a graph is the same as the scaling that was used to get the rating and to not create misleading information to those viewing graphs. Errors are commonly made in data acquisition and data presentation that can be misleading or confusing when multiple scales are used together to collect data and to present the data. Data Standardized to a 9-point scale—data appropriately presented (number removal simplifies understanding to an intuitive level).

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Plate 12. Distribution of energy densities as a function of the distance from the ultrasonic transducer (Saez ´ et al., 2005).

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Plate 13. 16 kW continous power ultrasound treatment system. (Courtesy of Hielscher USA, Inc.)

Plate 14. Treatment chamber examples.

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R Plate 15. 5 kW ELCRACK
technical scale system.

R R Plate 16. SteriPulse
-XL 3000 pulsed UV-light sterilization system (Xenon Corporation
, Wilmington, MA).

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Electromagnetic spectrum X-rays

Ultraviolet VacuumUV

UV-C

Visible light

UV-B

Infrared

UV-A

Wavelength (nm)

100

200

280

315

400

780

Hg-Low pressure lamp 254 nm

Plate 17. Electromagnetic spectrum. (Adapted from Anonymous, 2007b.)

Adenine Guanine Thymine Cytosine

Plate 18. UV-light effect at DNA level. (Adapted from Anonymous, 2007a.)

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Plate 19. Two UV-C assembled systems by Guerrero-Beltran, G.V. (Washington State University). ´ J.A. and Barbosa-Canovas, ´

(a)

(b)

Plate 20. Gliding arc NTP treatment of Golden Delicious apples. NTP produced using air as feed gas (300 L/minute), operating at 10 kV. Treatments pictured are of power levels 450 mA (a) and 190 mA (b). (Image courtesy B.A. Niemira, US Department of Agriculture.)

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Plate 21. A good ozone generator is an essential element to the integrated system.

Plate 22. To achieve a good mass transfer of ozone gas into the aqueous system, Venturi injector is one of solutions.

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Plate 23. Cloud stability of temperature control, room temperature control, and DPCD treated orange juice samples after 66 days of refrigerated storage at 4.4◦ C.

(a)

(b)

Plate 24. EO water generators (Hoshizaki Electric Co. Ltd, Japan).

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Plate 25. Neutralized EO water generator (MIOX Corporation, Albuquerque, NM).

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Plate 26. These electronmicroscopic photographs show clearly that PEF affects the structure of salmon cells. There is, however, no evidence that it also changes the chemical composition of the fish. (From Gudmundsson and Hafsteinsson, 2001.)

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Section I Physical Processes

Nonthermal Processing Technologies for Food Edited by H. Q. Zhang, G. V. Barbosa-Cánovas, V. M. Balasubramaniam, C. P. Dunne, D. F. Farkas, and J. T. C. Yuan © 2011 Blackwell Publishing Ltd. ISBN: 978-0-813-81668-5

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Chapter 1 Fundamentals of Food Processing Using High Pressure Loc Thai Nguyen and V.M. Balasubramaniam

1. Introduction Most processed foods are treated with heat to kill harmful bacteria, a process that often diminishes product quality. Considered one of the most important innovations in food processing in 50 years (Dunne, 2005), high-pressure processing (HPP) presents an alternative that retains food quality and natural freshness while extending microbiological shelf life (Farkas and Hoover, 2000). HPP, also commonly referred to as “high-hydrostatic pressure” processing or “ultra-high-pressure” processing, uses elevated pressures, with or without the addition of external heat, to achieve microbial inactivation or to alter food attributes. The pressures used in HPP are almost ten times greater than in the deepest oceans on earth. Common pressure units are listed in Table 1.1. Long used in the material and process engineering industry for sheet metal formation and isostatic pressing of advanced materials such as turbine components and ceramics, HPP offers many advantages to food processors. Because HPP does not break covalent bonds, it preserves food freshness (Farkas and Hoover, 2000). The technology also provides food processors with an opportunity to process heatsensitive, value-added foods with fewer additives and cleaner ingredient labels. Pressure can be applied at ambient temperature, thereby eliminating thermally induced cooked off-flavors. Finally, this technology

Nonthermal Processing Technologies for Food Edited by H. Q. Zhang, G. V. Barbosa-Cánovas, V. M. Balasubramaniam, C. P. Dunne, D. F. Farkas, and J. T. C. Yuan © 2011 Blackwell Publishing Ltd. ISBN: 978-0-813-81668-5

is efficient, as it can be used to process liquid foods in semicontinuous equipment and both liquid and solid foods in batch equipment. Table 1.2 summarizes some of the unique advantages of HPP. The applications and limitations of high-pressure food processing have been reviewed extensively (Hayashi, 1991; Cheftel, 1995; Ledward et al., 1995; Ohlsson, 1996; Karin, 1998; Kunugi and Hayashi, 1998; Smelt, 1998; Thakur and Nelson, 1998; San Martin et al., 2002; Matser et al., 2004; Hogan et al., 2005; Torres and Vel´asquez, 2005; Rastogi et al., 2007). This chapter summarizes the basic process engineering principles related to HPP of food materials and emphasizes the importance of thermal effects during this preservation process.

2. Basic Principles Governing HPP 2.1. LeChatelier’s Principle LeChatelier’s principle states that the application of pressure shifts the system equilibrium toward the state that occupies the smallest volume (Farkas and Hoover, 2000). Thus, any phenomenon (phase transition, change in molecular configuration, chemical reaction) that is accompanied by a decrease in volume is enhanced by pressure (and vice versa). This means that pressure stimulates reactions that result in a decrease in volume but opposes reactions that involve an increase in volume. For a simple chemical reaction, the kinetics of transition from A to B with intermediate state A
= can be expressed as follows (Pfister et al., 2001): A

↔

A
=

↔

B

(1.1) 3

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Table 1.1. Frequently used pressure units and conversion factors

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1.000 1.013 0.101 14.696

0.987 1.000 0.100 14.504

9.901 10.000 1.000 145.038

0.068 0.069 0.00689 1.000

relate the changes in free activation enthalpy and activation volume. V
= represents the volume of the activated system, while V A represents the volume before activation (Pfister et al., 2001). A positive
V implies a shift toward the reactants at higher pressures. Depending on the mechanism, some reactions may be accelerated or retarded by pressure.

2.2. Isostatic Principle For this reaction, the process pressure (p), temperature (T), system’s free enthalpy (
G), thermal energy (
E), volume (
V), and entropy (
S) can be related by the following:
G =
E + p
V − T
S

(1.2)

Under isothermal condition, the kinetics of this reaction can be described by Equation (1.3): 
∂
G
=
V
= = V
= − VA = ∂p T 
∂ ln k = −RT (1.3) ∂p T where k is reaction rate constant and R is universal gas constant (R = 8.314 J/mol·K).
G
= and
V
= Table 1.2. Unique advantages of high-pressure processing Description

Advantage

Pressure

Rapid and uniform distribution throughout the sample Reduced impact of thermal gradient

Thermal distribution Physical compression Product handling Process time Functionality Quality impact Reaction rate

Instant temperature increase and subsequent cooling on decompression Suitable for both particulate and pumpable foods Less dependence on product shape and size Opportunities for new process/product development Food may not undergo significant chemical changes Pressure accelerates traditional thermal inactivation kinetics

It is generally believed that at the macroscopic level, pressure is transmitted in a quasi-instantaneous manner throughout the sample volume (Pascal principle). Thus, processing time during HPP is often thought to be independent of product size and geometry (Cheftel, 1995). However, care must be taken to understand the interdependence of pressure and temperature during the HPP of food samples. Compression of the food sample results in a temperature increase (due to adiabatic heating). Water, carbohydrates, proteins, and fats are some of the basic building blocks of a complex food matrix, and each of these may respond uniquely under physical compression (Rasanayagam et al., 2003). The different rates of heating of each food matrix component under pressure may result in thermal gradients. Further, product near the vessel wall may lose heat to the environment. Traditionally, the food industry has employed modest pressure treatment (3–30 MPa; 435–4,351 psi) for the homogenization of liquid foods. During homogenization, the liquid is forced to flow under high pressure through a narrow orifice. High product velocity and high shear characterize the homogenization process (Farkas and Hoover, 2000). Product heating can be expected. On the other hand, during HPP, the product is compressed isostatically (i.e., compressed in three dimensions), held, and then decompressed. Pressure reduces the volume of water by 10% at 300 MPa (43,500 psi) and by 17% at 600 MPa (87,000 psi) (Farkas and Hoover, 2000). Little product distortion occurs at the macroscopic level in food materials with high moisture. On the other hand, if the food material contains significant amounts of air (e.g., marshmallow, strawberry, and leafy vegetable), the air will escape from the product after

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pressure treatment because of the difference in material compressibility. At HPP treatment pressures, gases in general are liquefied, if not dissolved in the liquid fraction of the food. On decompression, the gases expand and are released from the food matrix. Thus, products containing significant air may not be good candidates for pressure treatment. Similarly, dry solids form cake-like structures after pressure treatment. If food products do not contain sufficient moisture to maintain a water activity above 0.98, HPP may not provide effective microbial destruction.

the pressure on the pressure-transmitting fluid decompresses the system. A pump is used to move the free piston toward the discharge port. The treated liquid food, which is held in a sterile tank, can then be filled aseptically into sterile containers. Three batch vessels in a semicontinuous system can be connected such that while one vessel discharges the product, the second vessel is being compressed, and the third vessel is being loaded. In this way, the output is maintained in a continuous fashion (Balasubramaniam et al., 2008).

3. Typical Process Description

4. Packaging

HPP of solid foods starts with removing as much air as possible from the food and vacuum, packaging the products in flexible, high-barrier containers. Air removal is essential to ensure that a maximum number of containers can fill the pressure vessel during each cycle and that compression work will not be wasted on air in the system. The containers are loaded into a carrier basket or placed directly into the pressure vessel. Loading is similar in operation to a batch steam retort. Commercial batch vessel volumes range from 30 to 600 liters. A typical process cycle consists of loading the vessel with the prepackaged product and filling the remaining vessel void space with water, which acts as the pressure-transmitting fluid. The vessel is closed and the desired process pressure is achieved through addition of water delivered by an intensifier. After holding the product for the desired time at the target pressure, the vessel is decompressed by releasing the water (Balasubramaniam et al., 2008). Liquid foods can be processed in batch or semicontinuous mode. In the batch mode, the liquid product is prepackaged and pressure-treated as described for packaged foods. Semicontinuous pressure equipment employs two or more pressure vessels with free-floating pistons arranged to compress the liquid foods. A low-pressure transfer pump is used to fill the pressure vessel with the liquid food. After filling, the pressure vessel inlet valve is closed, and the pressure-transmitting fluid (usually water) is introduced behind the free piston to compress the liquid food. After the appropriate holding time, releasing

The packaging requirement for the HPP process varies depending on the type of equipment (batch or semicontinuous) used. Semicontinuous systems are used in the case of pumpable liquid products, which are aseptically packaged after pressure treatment. On the other hand, flexible or semirigid packaging, with at least one flexible interface, is best suited for batch processing. A variety of existing flexible packaging structures may be used (Balasubramaniam et al., 2004). Because high-moisture foods compress by 15–20% in the range of 600 MPa (87,000 psi) at ambient temperature, HPP packaging materials must be able to accommodate these reductions in volume and then return to their original volume without loss of seal integrity or barrier properties. For this reason, metal cans are generally not suited for the process. Package size and shape will influence loading efficiency of the product within the pressure chamber. The package should be designed to achieve at least 75% loading for economical processing. Chapter 3 discusses the need for optimum package design in detail. Further, the mass ratio of product to void space water, and package size and shape, can influence the heat exchange between the pressure-treated product and the surroundings and may create thermal gradients within the food. As noted previously, the air present in the package headspace should be minimized to the extent possible to further improve the loading factor. High-barrier packaging materials with oxygen- and light-impermeable properties may be desired for extended refrigerated product storage.

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This can also help preserve the fresh color and flavor attributes of many pressure-treated products (Hogan et al., 2005).

5. Pressure-Transmitting Fluids During HPP, a pressure-transmitting fluid is used to transfer pressure to the prepackaged foods uniformly and instantaneously. The choice of pressuretransmitting fluid is based on the materials used to fabricate the pressure chamber. To prevent corrosion, commercial pressure vessels use a stainless steel liner. This enables the use of water as the fluid of choice for HPP treatment of foods. It is worth noting that the compression heating behavior of water is similar to that of most food materials. This can minimize thermal gradients between the food material and the compression fluid. Water has also emerged as a pressure-transmitting fluid of choice due to its availability, nontoxicity, and low cost. Chapter 2 covers additional details on equipment design construction and operation. Castor oil, silicone oil, solutions of glycol–water mix, and sodium benzoate solutions are among the list of other pressure-transmitting fluids used in laboratory pressure equipment (Balasubramanian and Balasubramaniam, 2003). Depending on their thermal and physical properties (such as specific heat, viscosity, and compressibility), each solution may have a different rate of compression heating. For example, the heat of compression of water under pressure is 3.0◦ C per 100 MPa (14,500 psi), while that of silicone oil is about 20◦ C per 100 MPa. These differences can influence the magnitude of heat transfer among the pressure-transmitting fluid, food product, and the environment. The thermal gradient in the system subsequently could influence microbial inactivation and the quality of the processed foods (Balasubramanian and Balasubramaniam, 2003). If laboratory equipment (used for microbial or enzymatic kinetic studies) and commercial production equipment employ different pressure-transmitting fluids, the differences in respective heat transfer characteristics must be considered for reliable microbial challenge studies (Balasubramaniam et al., 2004).

6. Pressure–Temperature Response during Processing During HPP, the temperature of food materials increases, as an unavoidable thermodynamic effect of compression (Ting et al., 2002). Figure 1.1 presents the typical pressure–temperature curve for a food sample subjected to high-pressure treatment. The temperature of the food sample increases because of physical compression (Figure 1.1, p1 –p2 ). The magnitude of temperature change (Figure 1.1, T 1 –T 2 ) depends on the compressibility of the substance, thermal properties, initial temperature, and target pressure. For example, at 600 MPa (87,000 psi), the volume of a polar compound such as water is reduced by 17%. The maximum product temperature at the target process pressure is independent of the compression rate as long as heat transfer to the surroundings is negligible.

6.1. Pressure Come-Up Time The time (Figure 1.1, t1 –t2 ) required to increase the pressure of the sample from atmospheric pressure to the target process pressure is often defined as “pressure come-up time” (Farkas and Hoover, 2000). The process come-up time is primarily a function of the desired target pressure, the volume of the pressure vessel, and the horsepower of the pump–intensifier

p2

p3

T2

T3

Pressure

c01

Temperature

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p1

t1

t2

Time

t3 t4

Figure 1.1. Typical pressure–temperature response of a water-based food material undergoing high-pressure processing. Come-up time, t 1 –t 2 ; holding time, t 2 –t 3 ; decompression, t 3 –t 4 .

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employed. Typical commercial-scale high-pressure equipment is designed to have a come-up time in the range of 2–3 minutes to reach 600 MPa (87,000 psi) (see Chapters 2 and 3). Longer come-up times add to the total process time by reducing the hourly cycling rate. This affects product throughput. Variation in come-up time may also affect the inactivation kinetics of microorganisms. Therefore, consistency and awareness of these times are important in the process development of HPP (Farkas and Hoover, 2000; Ting et al., 2002; Balasubramaniam et al., 2004).

sion may be considered. The rate of decompression can be controlled by inserting a smaller venting line or by other throttling means; however, this will increase the cycle time. During decompression, the product temperature drops toward T 4, which may be lower than its initial temperature value (T 1 ). The difference between the sample initial temperature and final temperature after decompression (T 1 –T 4 ) can be indicative of the extent of heat loss from the product to the surroundings during processing (Ting et al., 2002).

6.2. Pressure-Holding Time

6.4. Cycle Time

Once the desired pressure is reached, and assuming that there is no significant pressure drop in the system as a result of heat exchange with the surroundings, no more additional energy is added to the process. Thus, pressure-holding time (Figure 1.1, t2 –t3 ) can be defined as the interval between the end of compression and the beginning of decompression. The products are held at the target pressure and temperature (if specified) for a predetermined holding time to achieve the desired microbial inactivation and/or quality. The shortest processing time (7 log10) with 4,000 pulses. At this level, the most aggressive treatment, the temperature of the juice increased by only 2.9◦ C, affirming the nonthermal nature of the treatment. This treatment combination required less than 40 seconds to implement. Interestingly, when the pulse number was held at 4,000

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0

10

20

30

40

0 –1 –2 Log (N/N0)

c20

–3 –4

1000 Hz 1500 Hz

–5

2000 Hz 2500 Hz

–6 Time (s)

Figure 20.5. Survival of E. coli on almonds following treatment with dielectric barrier discharge NTP. Voltage fixed at 25 kV, frequency range of 1.0–2.5 kHz. (Image reproduced from Deng et al. (2005), with permission.)

(9 kV), and the pulse frequency was increased, the efficacy of the process decreased, with approximately 3 log10 reductions at 200 Hz and only 1 log10 reduction in the 400–1,000 Hz range. This response of E. coli O157:H7 in apple juice to the shortened pulse interval has yet to be explained. Deng et al. (2005) treated almonds inoculated with E. coli 12,955 by placing them between the electrodes of a dielectric barrier discharge (DBD) apparatus, 20–30 kV, 1–2.5 kHz (Figure 20.1f). Studies were conducted in air. Reductions of approximately 4 log10 CFU/g were obtained for treatments of 30 seconds at 25 kV, 2 kHz. Increasing the frequency to 2.5 kHz increased the reduction to approximately 5 log10 CFU/g for the same 30 seconds of treatment (Figure 20.5). The effect on the quality of the treated almonds was negligible. The authors concluded that NTP treatment for the sanitization of almonds using the DBD apparatus was a feasible approach. Niemira et al. (2005b) treated Golden Delicious apples which were spot inoculated with L. innocua. Direct NTP discharge from a DBD apparatus (20 kV at 12 kHz) was applied to the food surfaces across

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a separation distance of 2–3 mm. Activated electrode area was approximately 2 cm2 , and the power density was approximately 1 W/cm2 , applied for intervals up to 60 seconds. The study was conducted in air. Treatment for 60 seconds was the most effective as an antimicrobial treatment, resulting in a 2.0 log10 reduction (P < 0.05). This treatment increased the temperature at the area of treatment by 9◦ C. The irregular apple surface resulted in filamentous discharges from the smooth DBD electrode. In treatments of 15 seconds and 30 seconds, these did not cause discoloration, but treatment for 60 seconds resulted in browning. During subsequent storage at 8◦ C for 10 days, the apples treated with 15 seconds or 30 seconds remained unblemished. Cantaloupe melon were inoculated with E. coli ATCC 25922 and treated using the same direct DBD system as above (Niemira et al., 2005b). As with apple, filamentous discharges were evident. A treatment of 2 minutes reduced the population by 1.0 log10 CFU and raised the temperature at the area of treatment by 6◦ C without causing noticeable damage to the melon surface. A 4-minute treatment increased the temperature by 26◦ C at the plasma contact point, but the relatively thick melon skin prevented appreciable sensory damage. As with apples, the interface of the flat DBD emitter with the irregular melon surface led to microdischarges within the plasma field. However, sensory damage to the melon surface was more limited than with apple. Eggs were also inoculated with E. coli ATCC 25922 and treated with direct DBD as part of that study (Niemira et al., 2005b). A treatment of 15 seconds significantly (P < 0.05) reduced the population by 1.0 log10 CFU. The longest treatment, 60 seconds, reduced the population by >2.0 log10 CFU (below the detectable level). The 60-second treatment increased the temperature at the area of treatment by 6◦ C. During the course of this study, trials conducted with eggs positioned on a grounded plate resulted in charge conduction across the egg surface and subsequent point discharges to ground during treatment. These point discharges caused small pinhole burns at the base of the egg, resulting from the concentration

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of electrical current and heat. In subsequent trials, the apparatus was modified such that eggs were positioned with a conductive diffuser mat interposed between the egg and the grounded plate, which eliminated the point discharges. Subsequent investigation of the inside of the shell following this modification showed no appreciable change in egg albumen.

100 80 Viability (%)

c20

60 40 20 0

0

1

2 3 Exposure time (hour)

4

5

0

1

2 3 Exposure time (hour)

4

5

5.4. General Considerations Regarding Feed Gas Composition In testing an air-based DBD system, Deng et al. (2005) repeated the most effective treatments under conditions of defined feed gases, instead of air as in the initial trials. The researchers saw no effect of substituting N2 , but processing under CO2 or Ar reduced the efficacy of the process, yielding only a ∼2 log10 reduction following a 30-second treatment. It has been suggested that an oxygen-free feed gas for the NTP would be desirable in some applications, as it precludes the possibility of ozone formation (Laroussi and Lu, 2005). Lassen et al. (2005) treated Bacillus stearothermophilus spores with NTPs derived from O2 , Ar/H2 (50/50, 15/85, 25/75, and 9/95%), O2 /H2 (50/50 and 95/5%) and O2 /CF4 (88/12%) in an RF-plasma system, operating at 100 or 400 W (13.56 MHz). The most effective feed gas for spore inactivation was Ar/H2 , 15/85%, although O2 /CF4 was seen to be more reactive with the inert substrate. Stoffels et al. (2002) showed that, where power levels were held constant, the choice of feed gas composition influenced the temperature of the resultant plasma. These results suggest that the best choice of feed gas/processing atmosphere is application-dependent, and must be optimized for individual commodities (Deng et al., 2005; Laroussi and Lu, 2005; Lassen et al., 2005; Stoffels et al., 2002). One possibility which is currently being explored in NTP research is the possibility of introducing relatively high molecular weight compounds, such as volatile oils, to enhance antimicrobial efficacy of NTP (Babko-Malyi et al., 2002). In treatments of E. coli and S. aureus, Gaunt and Hughes (2004)

100 Viability (%)

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Figure 20.6. Survival of E. coli (top) and S. aureus (bottom) following exposure to volatilized essential oils. Plasma discharge treatments are nonamended control (•), β-pinene amended (
), or orange oil amended (). Significant difference from control indicated by single asterisk (∗ ). Error bars = SE, n = 6. (Image reproduced from Gaunt et al. (2005), with permission.)

showed that the antimicrobial efficacy of an NTP discharge was enhanced by the introduction of ethyl alcohol or cinnamon oil. In contrast, volatilized tea tree oil reduced the antimicrobial efficacy of the NTP. In a later study using a thermal plasma (Figure 20.6) discharge, Gaunt et al. (2005) treated E. coli and S. aureus with volatilized β-pinene and orange oil. Both volatilized compounds were shown to be effective in reducing the viability of the bacteria following extended exposure, 1 hour in the case of S. aureus, 3 hours in the case of E. coli. Ionized products, rather than electrically neutral products, were shown to be the most effective component of the plasma discharge. These suggest that the introduction of antimicrobial chemical agents into the

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NTP feed gas could be an important area of future research.

6. Plasma Treatment of Food Contact Surfaces: Materials Processing Conventional plasmas have been used to improve the characteristics of a variety of materials, through vapor deposition of specific compounds, ablation, etching, and other processes. For the food industry, plasma treatment of food contact surfaces and packaging materials using advanced plasma systems may provide benefits for safety, quality, and profitability in food processing and at point-of-sale food distribution. It should be noted that, although researchers in this field of materials processing refer to “cold plasma,” this process of plasma treatment can be conducted at 150◦ C (Wang et al., 2003), well beyond the range of “nonthermal” as it is defined in this chapter. However, a brief overview of this field is warranted; additional information may be obtained via the following references, and the literature cited therein. Treatment of stainless steel coupons with di(ethylene glycol) vinyl ether in an RF-driven plasma system resulted in the deposition of a poly(ethylene glycol)-like layer (Wang et al., 2003). This protective layer reduced the ability of Listeria monocytogenes to adhere and form biofilms. Related work by Dong et al. (2005) describes the antifouling properties of the poly(ethylene glycol)-like coating on plasma-treated stainless steel specifically within the context of food contact surfaces. These researchers observe that the plasma treatment system is suitable for application to polymers, rubber, ceramics, and other materials as well as steel. Jiang et al. (2004) used RF-driven plasma to deposit silver nanoparticles on silicone rubber, which were then inoculated with L. monocytogenes. After 12 hours, no viable cells were recoverable from the plasma-treated material, a reduction of 4.5 log10 CFU relative to the untreated control. Plasma modification of food packaging polymers results in improved performance, durability and antimicrobial properties (Ozdemir et al., 1999).

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7. Economic Analysis Given the very early stage of development of NTP, estimates of the cost of implementation are necessarily based on preliminary data. The significant differences in technology and intended application between NTP and conventional thermal plasmas mean that one cannot meaningfully relate their expected capital costs and operational expenses. Deng et al. (2005) refers to the low equipment and operational cost of NTP processing as advantages of this technology, but does not provide an economic analysis with this assessment. Lee et al. (2005) described a microwave-induced NTP system as “low-cost and reliable,” but does not elaborate on this description. Adler et al. (1998) determined that low-temperature plasma sterilization was more cost-effective than chemical sterilization of delicate medical devices. Pilot- or commercial scale NTP food processing systems will necessarily present a higher level of capital cost than the laboratory bench-scale devices that have been developed to date. How capital costs will scale for application to food processing will be influenced by the specific NTP technology used, and the intended application of the NTP, although details remain unclear. Operational costs specific to NTP equipment will be based on power consumption of the NTP emitters and associated equipment (power and control electronics, monitoring, cooling, etc.), the nature and flow rate of the gas used, wear and tear on electrodes, and other factors. Systems which use air as the feed gas will be less expensive than those which use a pure gas (Ar, He, etc.), or a defined gas mixture. Bench-scale systems have widely varying power consumptions, depending on the scale of the system and the NTP technology used. For air-based systems, a minimum voltage of approximately 3 kV is required to achieve ionization. Reported values for experimental systems range from ∼15 W for a plasma plume approximately 0.1 cm in diameter by 5 cm long (Laroussi and Lu, 2005), ∼500 W for a glow discharge reactor with a pair of 18 cm × 15 cm electrodes (270 cm2 , operating at “less than a few watts/cm2 ”) (Montie et al., 2000) to ∼1 kW for a

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gliding arc system producing a plasma discharge approximately 12 cm × 15 cm by 1 cm thick (Niemira et al., 2005a). Depending on the intended application, the potential exists for multiple plasma emitters, perhaps using several different NTP technologies in combination, to be deployed as part of a given food processing system, with consequently increased gas flow, power consumption, etc. Other ancillary costs such as installation, training, maintenance, etc., will be related to the novelty and complexity of the equipment, costs which typically decline as technology matures.

8. Key Areas for Future Research The technology to produce NTP is developing rapidly, driven by the potential benefits of NTP in a variety of applications. From the standpoint of the food processing industry, a number of important questions must be addressed with NTP research to identify the most appropriate applications for this technology. Some of these key areas for future research are summarized below:

r Influence of complex surfaces, and the efficacy

r r r r

r r r r

against protected or subsurface contaminants (e.g., chicken skin, apple stem and/or scar area, seed coats) NTP processing in high-moisture environments Applicability of “chemical-free” NTP to highvalue commodities (e.g., organic foods) Volatile antimicrobial compounds within NTP feed gas Control of feed gas composition to control UV production, potential for utilization for antimicrobial efficacy, and sensory impact of NTP processing on foods Efficacy against biofilm-associated microorganisms Sensory impact of NTP on meats, seafood, or produce Potential for application to beverages or liquids Applicability of newer NTP technologies (e.g., microwave-driven, GHz-rate RF, magnetically guided gliding arc)

r Regulatory methods—approval of medical devices for food, confirmation of toxicological safety of NTP-treated foods, etc. r Economics—scale-up, capital costs, commercialscale throughput, etc.

9. Conclusions NTPs, and the wide range of devices used to create them, represent a diverse, innovative and flexible group of rapidly evolving tools for sanitizing surfaces. This promising technology will continue to be investigated for potential use in food processing, to address important questions regarding antimicrobial efficacy, food sensory impact, and the technical issues of integration of NTP into food processing systems.

Acknowledgments The authors would like to thank Drs. E. Stoffels and D. Geveke for their thoughtful reviews of this manuscript, M.E. Niemira for valuable discussion and L. Cheung for technical assistance in its preparation. The authors gratefully acknowledge the assistance and cooperation of various authors and publishers, identified in the text, for permissions related to reproduced images and figures.

References Adler, S., Scherrer, M., and Dascher, F.D. 1998. Costs of low-temperature plasma sterilization compared with other sterilization methods. Journal of Hospital Infection 40:125– 134. Anonymous. 2003. Code of Federal Regulations, Title 21, Part 110 (21 CFR 110): Current Good Manufacturing Practice in Manufacturing, Packing, Or Holding Human Food. Available at: www.access.gpo.gov/nara/cfr/waisidx 03/21cfr110 03.html (accessed May 17, 2006). Babko-Malyi, S., Crowe, R., and Yu, N. 2002. Effect of additives on sterilization rates of surfaces using atmospheric pressure nonthermal plasma. In: The Eighth International Conference on Advanced Oxidation Technologies for Water and Air Remediation (AOTs-8), Toronto, Ontario, Canada; November 17–21. Chirokov, A., Gutsol, A., and Fridman, A. 2005. Atmospheric pressure plasma of dielectric barrier discharges. Pure and Applied Chemistry 77:487–495.

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Deng, S., Ruan, R., Mok, C.K., Huang, G., Mok, C.K., and Chen, P. 2005. Nonthermal plasma disinfection of Escherichia coli on almond. Paper #056149, ASAE Ann. Mtg., Tampa, FL; July 2005. Dong, B.Y., Manolache, S., Somers, E.B. Wong, A.C.L., and Denes, F.S. 2005. Generation of antifouling layers on stainless steel surfaces by plasma-enhanced crosslinking of polyethylene glycol. Journal of Applied Polymer Science 97(2):485– 497. Fridman, A., Chirokov, A., and Gutsol, A. 2005. Non-thermal atmospheric pressure discharges. Journal of Physics D: Applied Physics 38:R1–R24. Fridman, A. and Kennedy, L. 2004. Plasma Physics and Engineering. New York: Taylor & Francis. Fridman, G., Peddinghaus, M., Ayan, H., Fridman, A., Balasubramanian, M., Gutsol, A., Brooks, A., and Friedman, G. 2006. Blood coagulation and living tissue sterilization by floatingelectrode dielectric barrier discharge in air. Plasma Chemistry and Plasma Processing 26(4):425–442. Gadri, R.B., Roth, J.R., Montie, T.C., Kelly-Wintenberg, K., Tsai, P., Helfritch, D.J., Feldman, P., Sherman, D.M., Karakaya, F., and Chen, Z. 2000. Sterliization and plasma processing of room temperature surfaces with a one atmosphere uniform glow discharge plasma (OAUGDP). Surface and Coatings Technology 131:528–542. Garate, E., Evans, K., Gornostaeva, O., Alexeff, I., Kang, W., Rader, M., and Wood, T.K. 1998. Atmospheric plasma induced sterilization and chemical neutralization. Proceedings IEEE International Conference on Plasma Science, Raleigh, NC p. 183. Institute of Electrical and Electronics Engineers, New York, NY. Gaunt, L.F., Higgins, S.C., and Hughes, J.F. 2005. Interaction of air ions and bactericidal vapours to control micro-organisms. Journal of Applied Microbiology 99:1324–1329. Gaunt, L.F. and Hughes, J.F. 2004. Use of volatile additives to increase the antimicrobial efficacy of a corona discharge. Proceedings of IEJ-ESA Joint Symposium on Electrostatics. pp. 273–280. Jiang, H., Manolache, S., Wong, A.C.L., and Denes, F.S. 2004. Plasma-enhanced deposition of silver nanoparticles onto polymer and metal surfaces for the generation of antimicrobial characteristics. Journal of Applied Polymer Science 93:1411– 1422. Kelly-Wintenberg, K., Hodge, A., Montie, T.C., Eleanu, L.D., Sherman, D., Roth, J.R., Tsai, P., and Wadsworth, L. 1999. Use of a one atmosphere uniform glow discharge plasma to kill a broad spectrum of microorganisms. Journal of Vacuum Science & Technology A 17(4):1539–1544. Laroussi, M. and Lu, X. 2005. Room-temperature atmospheric pressure plasma plume for biomedical applications. Applied Physics Letters 87:113902. Laroussi, M., Mendis, D.A., and Rosenberg, M. 2003. Plasma interaction with microbes. New Journal of Physics 5:41.1– 41.10. Lassen, K.S., Nordby, B., and Grun, R. 2005. The dependence of the sporicidal effects on the power and pressure of RF-generated

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plasma processes. Journal of Biomedical Materials Research Part B: Applied Biomaterials 74B:553–559. Lee, K.Y., Park, B.J., Lee, D.H., Lee, I.S., Hyun, S.O., Chung, K.H., and Park, J.C. 2005. Sterilization of Escherichia coli and MRSA using microwave-induced argon plasma at atmospheric pressure. Surface and Coatings Technology 193:35–38. Lieberman, M.A. and Lichtenberg, A.J. 2005. Principles of Plasma Discharges and Materials Processing. Hoboken, NJ: Wiley-Interscience. McDonald, K.F., Curry, R.D., Clevenger, R.E., Brazos, B.J., Unklesbay, K., Eisenstark, A., Baker, S., Golden, J., and Morgan, R. 2000. The development of photosensitized pulsed and continuous ultraviolet decontamination techniques for surface and solutions. IEEE Transactions on Plasma Science 28; 89–96. Moisan, M., Barbeau, J., Crevier, M., Pelletier, J., Phillip, N., and Saoudi, B. 2002. Plasma sterilization. Methods and mechanisms. Pure and Applied Chemistry 74:349–358. Moisan, M., Barbeau, J., Moreau, S., Pelletier, J., Tabrizian, M., and Yahia, L.H. 2001. Low-temperature sterilization using gas plasmas: a review of the experiments and an analysis of the inactivation mechanisms. International Journal of Pharmaceutics 226:1–21. Montenegro, J., Ruan, R., Ma, H., and Chen, P. 2002. Inactivation of E. coli O157:H7 using a pulsed nonthermal plasma system. Journal of Food Sciences 67:646–648. Montie, T.C., Kelly-Wintenberg, K., and Roth, J.R. 2000. An overview of research using the one atmosphere uniform flow discharge plasma (OAUGDP) for sterilization of surfaces and materials. IEEE Transactions on Plasma Science 28: 41–50. Niemira, B.A., Alvarez, I., Annous, B.A., Gutsol, A., and Fridman, A. 2005b. Antimicrobial efficacy of cold atmospheric pressure plasma applied to inoculated food surfaces. P2. Institute of Food Technologists Nonthermal Processing Division Meeting, Wyndmoor, PA; September 2005. Niemira, B.A., Gutsol, A., and Fridman, A. 2005a. Cold, atmospheric pressure plasma reduces Listeria innocua on the surface of apples. Poster Abstract P2–40. International Association for Food Protection Annual Meeting, Baltimore, MD; August 2005. Ozdemir, M., Yurteri, C.U., and Sadikoglu, H. 1999. Physical polymer surface modification methods and applications in food packaging polymers. Critical Reviews in Food Science and Nutrition 39:457–477. Polak, L.S. and Lebedev, Y.A. 1999. Plasma Chemistry. England: Cambridge. Ponomarev, A.N., Maksimov, A.I., Vasilets, V.N., and Menagarishvily, V.M. 1989. Photo-oxidation of polyethylene and polyvinyl chloride in the process of simultaneous action of ultraviolet and active oxygen. High Energy Chemistry 23(3):231–232. Raizer, Y.P. 1991. Gas Discharge Physics. Berlin: Springer. Sharma, A.K., Josephson, G.B., Camaioni, D.M., and Goheen, S.C. 2000. Destruction of pentachlorophenol using glow

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discharge plasma process. Environmental Science and Technology 34:2267–2272. Sladek, R.E.J. and Stoeffels, E. 2005. Deactivation of Escherichia coli by the plasma needle. Journal of Physics D: Applied Physics 38:1716–1721. Stoffels, E., Flikweert, A.J., Stoffels, W.W., and Kroesen, G.M.W. 2002. Plasma needle: a non-destructive atmospheric plasma

source for fine surface treatment of (bio)materials. Plasma Sources Science & Technology 11:383–388. Wang, Y., Somers, E.B., Manolache, S., Denes, F.S., and Wong, A.C.L. 2003. Cold plasma synthesis of poly(ethylene glycol)like layers on stainless steel surfaces to reduce attachment and biofilm formation by Listeria monocytogenes. Journal of Food Sciences 68:2772–2779.

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Nonthermal Processing Technologies for Food Edited by H. Q. Zhang, G. V. Barbosa-Cánovas, V. M. Balasubramaniam, C. P. Dunne, D. F. Farkas, and J. T. C. Yuan © 2011 Blackwell Publishing Ltd. ISBN: 978-0-813-81668-5

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Chapter 21 Basics of Ozone Sanitization and Food Applications Ahmed E. Yousef, Mustafa Vurma, and Luis A. Rodriguez-Romo

1. Introduction Interest in ozone use in food production and processing has been increasing steadily. This trend is driven by industry’s need for potent antimicrobial agents and the news about recent successful implementations of this sanitizer. Ozone has been effectively used in the production of bottled drinking water. Additionally, many water treatment plants currently use ozone as a better alternative to chlorine. Processors of fresh-cut produce who are considering ozone use in their facility are encouraged by the positive experience of few small companies that have already integrated ozone into their production lines. Costs of implementing ozone in food processing are not excessively prohibitive and removal of excess sanitizer does not represent a disposal hurdle. In spite of these successes, many food processors are carefully analyzing the economic benefits and risks associated with ozone implementation. Compared to other sanitizers, the gas has limited solubility in water and, thus, aqueous applications require efficient gas injection systems and closed treatment vessels. Careful monitoring of ozone dissolution and residues in processing water and the potential for offgassing may add technical complexities to processing lines. Corrosiveness of ozone makes it difficult to use with old pieces of equipment (e.g., pumps) in an ozone-upgraded facility. Interestingly, some of the ozone properties that are considered undesirable in a given application make Nonthermal Processing Technologies for Food Edited by H. Q. Zhang, G. V. Barbosa-Cánovas, V. M. Balasubramaniam, C. P. Dunne, D. F. Farkas, and J. T. C. Yuan © 2011 Blackwell Publishing Ltd. ISBN: 978-0-813-81668-5

the sanitizer suitable for other applications. The limited solubility of ozone in water can be advantageous, and the gaseous state of the sanitizer may have beneficial implementations in food processing. Additionally, some of the drawbacks (e.g., corrosivity) correlate with the potency of ozone as an effective sanitizer. This chapter covers the science and technology of ozone sanitization. The authors emphasize the antimicrobial properties of ozone and potential uses to control spoilage and pathogenic microorganisms in food. Advantages and limitations of ozone use in food processing are also addressed.

2. Ozone Chemistry and Physics Ozone is a triatomic molecule (O3 ) and a very reactive form of oxygen. It is commonly produced in nature by interactions of molecular oxygen (O2 ) with chemicals, electric discharges during lightning, or short ultraviolet (UV) radiation from the sun (Figure 21.1). These interactions cause rearrangements of atomic oxygen and the formation of the triatomic molecule of ozone. The gas has a characteristic pungent odor that is readily detectable by the human nose at concentrations as low as 0.02 mg/L. Gaseous ozone is colorless at low concentrations and has a bluish color at high concentrations (Rice et al., 1981). In the stratosphere, small amounts of ozone (0.05 mg/L) are formed at 15–50 km of altitude by photochemical reactions involving the action of solar UV radiation (2.0 >2.0 6.1 1.3

5 5 1 1

0.12 2.29 11 11

>4.5

20

0.32

Water Water Spore suspension Aqueous ozone mix Water

Farooq and Akhlaque (1983) Broadwater et al. (1973) Khadre and Yousef (2001b)

>2.0

19

2.2

Raw waste water

Listeria monocytogenes Shigella sonnei S. sonnei Yersinia enterocolitica

Salmonella enteritidis Salmonella enteritidis Salmonella typhimirium Bacillus cereus B. cereus (spores) B. cereus B. stearothermophilus Legionella pneumophila Fecal streptocci

degree of inactivation is also affected by the physiological status of treated bacterium. Cells in their exponential phase were more sensitive to ozone than cells in their stationary phase (da Silva et al., 1998; Kim et al., 2003).

5.2. Inactivation of Fungi Ozone in aqueous and gaseous states is a potent antifungal agent and its fungicidal action varies among species (Table 21.3). Beuchat et al. (1999) investigated the susceptibility of conidia of aflatoxigenic aspergilli to ozone. Aspergillus flavus and Aspergillus parasiticus conidia were treated with 1.74 ppm ozone in phosphate buffer at pH 5.5 and 7.0. The authors reported that the D-values were 1.7

Selma et al. (2006)

Ramirez et al. (1994)

Edelstein et al. (1982) Joret et al. (1982)

and 1.5 minutes for A. flavus and 2.1 and 1.7 minutes for A. parasiticus at pH 5.5 and 7.0, respectively. The antimycotic effect of aqueous ozone against Candida parapsilosis was studied by Farooq and Akhlaque (1983). Treatment of C. parapsilosis with ozonated water at 0.23 to 0.26 mg/L for 1.67 minutes decreased the population of this microorganism by 2 log units. Kawamura et al. (1986) reported that the counts of Candida tropicalis decreased by 2 log units when the yeast cells were treated with aqueous ozone at 0.02 mg/L for 20 seconds or at 1 mg/L for 5 seconds. In another study, ozonated water containing ∼0.19 mg/L ozone instantaneously decreased Cistus albanicus and Zygosaccharomyces bailii populations by 4.5 log units, but the same concentration

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Table 21.3. Inactivation of fungi by ozone Treatment Conditions

Fungi Aspergillus flavus (conidia) A. parasiticus (conidia) A. niger (spores) Candida parapsilosis C. tropicalis C. albanicus Zygosaccharomyces bailii

Inactivation (log10 CFU units)

Time (minutes)

Concentration (mg/L)

Medium/Food

1.0 1.0 1.0 1.0 4.5 >4.5

0.30–0.08 Immediate Immediate

0.02–1.0 0.188 0.188

Water Water Water

decreased Aspergillus niger spores by 1 log with ozone treatment for 5 hours at low temperature; however, this treatment did not affect the microbial counts of other tested yeasts. The author reported that the fungicidal effect of ozone was enhanced with increasing treatment temperature, humidity, and time. Mycelial growth of Botrytis cinerea was slower when this plant pathogen was inoculated on potato dextrose agar and stored at 2◦ C in

References

Beuchat et al. (1999) Restaino et al. (1995) Farooq and Akhlaque (1983) Kawamura et al. (1986) Restaino et al. (1995) Restaino et al. (1995)

ozone-enriched (1.5 µg/L) environment (Nadas et al., 2003).

5.3. Inactivation of Protozoa Protozoan parasites such as Giardia, Cryptosporidium, and Cyclospora have been implicated in a number of waterborne disease outbreaks worldwide (Clark et al., 2002; Erickson and Ortega, 2006). According to Clark et al. (2002), ozone is a more effective chemical disinfectant than chlorine or chlorine dioxide against protozoan parasites in water systems. Selected studies describing inactivation of protozoa by ozone are summarized in Table 21.4. Widmer et al. (2002) investigated the effect of ozone on Giardia lamblia cysts in gerbils using an infectivity assay and by scanning electron microscopy, immunoblotting, and flow cytometry techniques. Cysts were treated with ozone at 1.5 mg/L for 0, 30, 60, and 120 seconds. The authors reported that ozone exposure for 60 seconds or longer effectively inactivated cysts of G. lamblia and the treatments caused extensive protein degradation and profound structural modifications to the cyst wall. Differences in resistance of cysts and oocysts of protozoan parasites to ozone treatments have been reported (Erickson and Ortega, 2006). According to Wickramanayake et al. (1984), cysts of Naegleria

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Table 21.4. Inactivation of protozoa by ozone Treatment Conditions

Protozoa

Inactivation (log10 CFU units)

Time (minutes)

Concentration (mg/L)

Medium/Food

References

Giardia lamblia

2.0

1.1

0.7

Water

G. lamblia G. lamblia

>3.0 >3.0 >4.0

1.0 2.0 5.0

1.5 1.7 1.9

Water Buffer (pH 6.85) Buffer (pH 6.85)

Wickramanayake et al. (1984) Widmer et al. (2002) Finch et al. (1993)

G. muris

2.0

2.8

0.5

Water

G. muris Cryptosporidium parvum Naegleria gruberi

∼4.0 >1.0

5.0 5.0

0.6 1.0

Buffer (pH 6.70) Water

2.0

2.1

2.0

Water

gruberi were more resistant to ozone than were Giardia muris cysts. The author reported that ozone treatment at 0.2 mg/L for 7.5 minutes inactivated 2 log units whereas only 1.05 minutes was sufficient to achieve similar inactivation for the cysts of G. muris. The population of Cryptosporidium parvum oocysts decreased >1 log when the parasite was exposed to 1 mg/L ozone for 5 minutes (Korich et al., 1990). The researchers also reported that C. parvum oocysts were 30 times more resistant to ozone than were Giardia cysts when these parasites were treated under the same conditions.

5.4. Inactivation of Viruses Ozone is an effective virucide. This is evident from results of selected studies on inactivation of viruses including bacteriophages and human/animal viruses as summarized in Table 21.5. Ozone at low concentration levels and short contact times is generally sufficient for inactivation of viruses when present in low ozone demand media. When the ozone demand of the medium is high (e.g., in wastewater), long contact time and high ozone concentration are required to inactivate viruses (Kim et al., 1999). Variation in viruses susceptibility to ozone has been reported (Khadre et al., 2001). It appears that

Wickramanayake et al. (1984) Finch et al. (1993) Korich et al. (1990) Wickramanayake et al. (1984)

bacteriophages such as f2, MS2 are the most susceptible viruses to ozone. Resistance of viruses to ozone was greater for hepatitis A than for poliovirus (Herbold et al., 1989). Susceptibility of human rotavirus to ozone was tested (Khadre and Yousef, 2002). A rotavirus suspension at high titer (∼1011 TCID50 /mL) was treated with ozone at 5.2–25 mg/L for 1 minute. These treatments decreased the infectivity of these microorganisms by 2–8 log units TCID50 /mL. Poliovirus type 1 (Mahoney) was treated with 0.25 mg/L of ozone for 5 minutes and this exposure yielded 2-log inactivation (Harakeh and Butler, 1985). Farooq and Akhlaque (1983) reported 2.5-log reduction of poliovirus type 1 (Mahoney) when the virus suspension was ozonated at 0.23–0.26 mg/L for 1.67 minutes.

6. Ozone and Food Applications 6.1. Food Properties and Ozone Applicability Reactivity, solubility, and disinfection efficacy of ozone are affected by many factors such as temperature, pH, humidity, and presence of ozonedemanding materials in the treated medium. In addition, microbicidal effect of ozone is highly dependent on its accessibility to target microorganisms without

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Table 21.5. Inactivation of viruses by ozone Treatment Conditions

Viruses

Inactivation (log10 CFU units)

Time (minutes)

Concentration (mg/L)

Medium/Food

References

Bacteriophage f2 Bacteriophage MS2

2.0 to 7.0 2.96

0.08 1.0

0.09 to 0.8 0.6

Water Phosphate buffer

Kim et al. (1980) Finch and Fairbairn (1991)

Bacteriophage MS2 Norwalk Poliovirus type 1 Poliovirus type 1

>3.0 >3.0 >3.0 2.5 to 3.0

0.17 0.17 0.17 1.67

0.37 0.37 0.37 0.23 to 0.26

Water Water

Poliovirus type 3

1.63

1.0

0.6

Phosphate buffer

Shin and Sobsey (2003) Farooq and Akhlaque (1983) Finch and Fairbairn (1991)

∼1.0 2.7 >2.8% 3.9 3.0 3.0

0.80 0.02 0.08 6.0 6.0–8.0

0.10 0.25 0.38 0.3 to 0.4 0.1 to 0.3 0.1 to 0.25

Up to 1.0

1.0

2.1 to 4.2

Up to 5.0

1.0

1.9 to 15.9

>1.7 2.0 4.0

0.16 2.0 2.5

0.035 0.32 0.40

Hepatitis A Hepatitis A Rotavirus human Rotavirus SA 11 simian Rotavirus Wa human ATCC Rotavirus Wa human Wooster Coxsackie virus A9 Coxsackie virus B5

interacting with the food components (Figure 21.6). Microorganisms are generally not found in readily accessible location in food as they are in pure water. Microorganisms that are strongly attached, internalized, or organized as a biofilm on food surfaces or those embedded in the food matrix are not readily inactivated by ozone treatments. Achen and Yousef (2001) reported that washing with aqueous ozone was more effective in inactivating microorganisms on the surface of apples than in decontaminating the calyx and stem areas. The authors also pointed out that the ozone efficacy was reduced when E. coli O157:H7 was allowed to attach to the apple surface. Readily available high-ozone-demand compounds may compete with microorganisms for ozone. High-fat-containing foods such as meat require higher ozone concentration than low-fat

Phosphate buffer Phosphate buffer Phosphate buffer

Herbold et al. (1989) Hall and Sobsey (1993) Vaughn et al. (1987)

Water

Khadre et al. (2001)

Water Sludge effluent

Boyce et al. (1981) Harakeh and Butler (1985)

foods such as fruits and vegetables (Kim et al., 2003). The ability of ozone to reduce microbial load in the presence of whipping cream, locust bean gum, soluble starch, and sodium caseinate was investigated (Guzel-Seydim et al., 2004a). The authors pointed out that the food components had influenced the bactericidal action of ozone against the treated microorganisms. Compared to control buffer, starch did not provide any protective effect against microbial inactivation of ozone while moderate or strong protective effects were observed in the presence of other tested components. Similarly, Restaino et al. (1995) reported that ozone inactivation of microorganisms was not affected by the presence of soluble starch in the treatment medium while addition of bovine serum albumin (BSA) reduced the microbial inactivation. Achen (2000) demonstrated

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Limited accessibility .. Limited ozone efficacy Entrapped microbial cells

Ozone-demanding contaminants in media

Least ozone efficacy

Diminished ozone efficacy

O3

Competing food surface components

Free microbial cell High ozone efficacy

Smooth matrix surface

Figure 21.6. Schematic representation of accessibility of ozone to target microorganisms as related to the efficacy of the sanitizer.

that the inactivation of bacteria with ozone was dependent on the concentration of BSA added to the medium.

6.2. Ozone as an Alternative Sanitizer in Food Processing Ozone was introduced as a disinfectant in the treatment of drinking water for the first time in 1893 at Oudshourn, Netherlands (Rice et al., 1981). Subsequently, ozone was used for water disinfection in many European countries (Bryant et al., 1992). Ozone may be used in the gaseous or aqueous state in food processing. In general, gaseous ozone is applied for storage applications whereas the aqueous form is used for surface decontamination of foods, equipment, or packaging materials.

6.3. Ozone Treatment System Ozone can be applied in gaseous or aqueous states for food applications. Sanitization of fresh or fresh-

cut vegetables is an example of processes that can make use of both forms of ozone. Figure 21.7 shows conceptual aqueous and gaseous ozone systems that may be applicable to fresh produce treatments. Essential components for an ozone treatment system for food applications include:

r A gas feed system r An ozone generator with electrical power supply r An ozone contactor for aqueous ozone applications, or a treatment vessel for gaseous ozone treatments r Ozone measurement devices r An ozone off-gas destruct system High-purity oxygen or dry air can be used to generate ozone. Commonly, corona discharge generators are used to produce ozone for food applications, and these generators require a high-voltage electric supply units. Gaseous ozone should be dissolved into water for aqueous ozone treatments of foods. Transfer efficiency of ozone from gaseous state to liquid

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Raw product

O2

Oxygen tank

Destruct

Ozonated water

Ozone generator Venturi

Processed product

Pump Circulation pump

(a)

303

O3 OFF GAS

O3 gas

Ozone-water contactor O 3 Monitor

Raw product

O2

Excess O3 gas

O3 gas

Oxygen tank

c21

Destruct

Ozone generator O3 Monitor

Cooling/humidity control

Processed product (b) Figure 21.7. Conceptual (a) aqueous and (b) gaseous ozone treatment systems that may be relevant to food applications.

form is an important factor that could affect the process feasibility. There are several ozone dissolution methods for increasing transfer efficiency of this gas into water; these include conventional fine bubble diffusers, turbine mixers, injectors, packed columns, spray chambers, porous plate diffuser contactors, and submerged static radial turbine contactors (Bellamy et al., 1991). Ozone and the matrix (e.g., food) to be treated are brought together in a treatment vessel. This vessel should be leak proof and equipped with monitoring devices and an excess gas destruction unit. The treatment vessel should be designed to permit efficient contact between ozone and the matrix. Automatic control units can be used in conjunction with process flow meters and monitors to maintain the target ozone concentration in the process and control ozone generation. There are thermal and catalytic destruction units commercially available to convert excess ozone to oxygen prior to its release in the at-

mosphere. Ozone detectors should be employed in the working environment to routinely monitor the concentration of this gas for employees’ safety. Concentration of ozone and time of exposure are critical parameters that determine ozone efficacy during the treatment. For water applications, efficacy of the treatment is commonly expressed as ozone concentration (mg/L) and contact time (minutes) that are sufficient to inactivate a given microbial population (e.g., 2 log decrease). The product of multiplication of these two parameters is termed Ct value. Interaction of ozone with processing equipment and packaging material should be considered for efficacy of the treatment as well as the corrosion stability of the materials used. Ozone’s corrosive effect is most pronounced at high concentrations commonly found inside the ozone generator or in the ozone-to-water contacting system. Materials most frequently used in the food processing industry are

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resistant to ozone at moderate concentrations. The materials with high resistance to corrosion by ozone include austenitic (300 series) stainless steel, glass, PTFE (Teflon), hypalon, and concrete. In addition, plastics commonly used in food industry, such as polyvinylchloride (PVC) and polyethylene (PE), are generally resistant to low ozone concentrations. The use of copper alloys and natural rubber should be avoided because they are prone to oxidation and rapid disintegration, respectively. When designing and manufacturing a treatment system, all equipment materials, including the seals, gaskets, and lubricants that come into contact with this sanitizer should be selected from materials of high ozone resistance (Kim et al., 2003).

7. Selected Food Applications Potential applications of ozone as an antimicrobial agent in food industry have been extensively studied (Kim et al., 1999; Khadre et al., 2001; Kim et al., 2003). Ozone has been tested on food products such as meat, poultry, fish, fruits and vegetables, and cheese. Other ozone applications tested include the decontamination of food packaging materials, food contact surfaces, and removal of residual pesticides on fruits. Ozone has the advantage of decomposing spontaneously to a nontoxic product, that is, O2 .

7.1. Fruits and Vegetables Fresh fruits and vegetables are susceptible to contamination with pathogenic and spoilage microorganisms, beginning with the preharvesting stage thoroughout postprocessing. Food-borne disease outbreaks linked to minimally processed fruits and vegetables have increased during the past few decades (Sivapalasingam et al., 2004). Microbial contamination of fresh fruits and vegetables not only poses significant risks to public health but also affects the industry financially by decreasing product shelf life. Ozone has been explored for treating agricultural commodities because it provides more disinfecting power than other sanitizers (e.g., chlorine) and removes a myriad of contaminants including microorganisms resistant to chlorine treatment

(Graham, 1997). Sanitation of fresh produce is one of the most promising applications of ozone. The food industry is strongly interested in using this sanitizer to enhance the shelf life and safety of these perishable products and in exploring new applications of the sanitizer. Efficacy of ozone against natural microflora on lettuce was tested (Kim et al., 1999). Mesophilic and psychrotrophic natural contaminants of shredded lettuce were inactivated by 1.4 and 1.8 log units, respectively, when aqueous ozone was applied at 1.3 mM for 3 minutes. When the ozonation time was increased to 5 minutes, the counts of these microorganisms decreased by 3.9 and 4.6 log units, respectively. The authors suggested that bubbling gaseous ozone into wash water was necessary to increase the efficacy of ozone against microorganisms on lettuce. In a more recent study, Beltran et al. (2005) concluded that sanitization of fresh-cut lettuce using ozonated water was a good alternative to chlorine treatment. Washing shredded lettuce with ozonated water and storing the treated produce under modified atmosphere packaging reduced its microbial populations and extended its shelf life. Ozone delivery method affects ozone efficacy against microorganisms on fruit surfaces. Achen and Yousef (2001) investigated the inactivation of E. coli O157:H7 on apple surfaces by bubbling ozone during washing or by dipping in preozonated water. Counts of E. coli O157:H7 decreased by 3.7 and 2.6 log units when the apples were ozone-washed by bubbling and dipping, respectively. When the pathogen was inoculated in the stem-calyx region of apples,