Plant Gum Exudates of the World: Sources, Distribution, Properties, and Applications

PLANT GUM EXUDATES OF THE WORLD Sources, Distribution, Properties, and Applications

PLANT GUM EXUDATES OF THE WORLD Sources, Distribution, Properties, and Applications

Amos Nussinovitch

Boca Raton London New York

CRC Press is an imprint of the Taylor & Francis Group, an informa business

CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2010 by Taylor and Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed in the United States of America on acid-free paper 10 9 8 7 6 5 4 3 2 1 International Standard Book Number: 978-1-4200-5223-7 (Hardback) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http:// www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Nussinovitch, A. Plant gum exudates of the world : sources, distribution, properties, and applications / Amos Nussinovitch. p. cm. Includes bibliographical references and index. ISBN 978-1-4200-5223-7 (hardcover : alk. paper) 1. Gums and resins. I. Title. TP978.N874 2010 668’.37--dc22 Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com

2009031459

In fond memory of my classmates from the “Ohel Shem” secondary school in Ramat Gan— Mordechai (Moti) Korb, Jacob (Jack) Sofer, and Mordechai Geller—who died at a tragically young age in the Yom Kippur War and never got the opportunity to live out their dreams

Contents Preface .......................................................................................................................................xix Acknowledgments....................................................................................................................xxiii The Author ..............................................................................................................................xxv

1.

Role and Sources of Exudate Gums ................................................................................. 1 1.1 Introduction............................................................................................................. 1 1.2 Definitions............................................................................................................... 3 1.3 Gum Yields .............................................................................................................. 8 1.4 Agricultural Issues ................................................................................................... 9 1.5 Physical Properties of Gums................................................................................... 12 1.5.1 Color......................................................................................................... 12 1.5.2 Size and shape ...........................................................................................13 1.5.3 Taste and smell...........................................................................................14 1.5.4 Hardness and density.................................................................................15 1.5.5 Polarization ................................................................................................16 1.5.6 Solubility....................................................................................................16 1.5.7 Viscosity and mouthfeel.............................................................................17 1.6 Chemical Properties................................................................................................19 1.7 Commercial Assessments of Gums..........................................................................19 1.8 Industrial and Other Uses.......................................................................................19 References ........................................................................................................................ 20

2.

Physiological Aspects of Polysaccharide Formation in Plants..................................... 23 2.1 Introduction........................................................................................................... 23 2.2 Stress Factors, Ethylene and Gummosis ................................................................. 23 2.3 Borers and Gum Formation ................................................................................... 30 2.4 Gum Ducts.............................................................................................................31 2.5 Gummosis in Fruit Trees . ..................................................................................... 32 2.6 Induced Inoculation and Gum Yield...................................................................... 34 References..........................................................................................................................35

3.

Major Plant Exudates of the World .............................................................................. 39 3.1 Introduction........................................................................................................... 39 3.2 Gum Arabic and Other Acacia Gums .................................................................... 39 vii

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3.3

3.2.1 Acacia Fabaceae (subfamily: Mimosoideae)........................................... 39 3.2.1.1 Taxon: Acacia senegal (L.) Willd ................................................ 39 3.2.1.2 Taxon: Acacia seyal Delile.......................................................... 42 3.2.1.3 Taxon: Acacia abyssinica Hochst. ex Benth. subsp. calophylla Brenan....................................................................... 43 3.2.1.4 Taxon: Acacia bakeri Maiden..................................................... 43 3.2.1.5 Taxon: Acacia benthamii Meisn ................................................. 43 3.2.1.6 Taxon: Acacia binervata DC...................................................... 43 3.2.1.7 Taxon: Acacia catechu (L. f.) Willd. ........................................... 43 3.2.1.8 Taxon: Acacia dealbata Link ......................................................45 3.2.1.9 Taxon: Acacia decurrens Willd....................................................45 3.2.1.10 Taxon: Acacia drepanolobium Harms ex Y. Sjöstedt................... 46 3.2.1.11 Taxon: Acacia elata A. Cunn. ex Benth. .................................... 46 3.2.1.12 Taxon: Acacia farnesiana (L.) Willd........................................... 46 3.2.1.13 Taxon: Acacia ferruginea DC......................................................47 3.2.1.14 Taxon: Acacia harpophylla F. Muell. ex Benth.............................47 3.2.1.15 Taxon: Acacia jacquemontii Benth. ............................................47 3.2.1.16 Taxon: Acacia karroo Hayne.......................................................47 3.2.1.17 Taxon: Acacia kirkii Oliv............................................................47 3.2.1.18 Taxon: Acacia laeta R. Br. ex Benth........................................... 48 3.2.1.19 Taxon: Acacia leiophylla Benth. . ............................................... 48 3.2.1.20 Taxon: Acacia leucophloea (Roxb.) Willd.................................... 48 3.2.1.21 Taxon: Acacia maidenii F. Muell................................................ 49 3.2.1.22 Taxon: Acacia mellifera (Vahl) Benth......................................... 49 3.2.1.23 Taxon: Acacia modesta Wall....................................................... 49 3.2.1.24 Taxon: Acacia oerfota (Forssk.) Schweinf.................................... 49 3.2.1.25 Taxon: Acacia oswaldii F. Muell................................................. 50 3.2.1.26 Taxon: Acacia pendula A. Cunn. ex G. Don.............................. 50 3.2.1.27 Taxon: Acacia penninervis Sieber ex DC. ................................... 50 3.2.1.28 Taxon: Acacia pycnantha Benth. .................................................51 3.2.1.29 Taxon: Acacia retinodes Schltdl...................................................51 3.2.1.30 Taxon: Acacia salicina Lindl........................................................51 3.2.1.31 Taxon: Acacia sieberiana DC......................................................51 3.2.1.32 Taxon: Acacia stuhlmanii Taub...................................................51 3.2.1.33 Taxon: Acacia verniciflua A. Cunn  .. ..........................................52 3.2.1.34 Taxon: Acacia xanthophloea Benth..............................................52 3.2.2 Faidherbia Fabaceae (subfamily: Mimosoideae) . ....................................52 3.2.2.1 Taxon: Faidherbia albida (Delile) A. Chev..................................52 Gum Tragacanth and Similar Gums.......................................................................52 3.3.1 Astragalus Fabaceae (subfamily: Faboideae) . .........................................52 3.3.1.1 Taxon: Astragalus gummifer Labill. .........................................52 3.3.1.2 Taxon: Astragalus brachycalyx Fisch ............................................55 3.3.1.3 Taxon: Astragalus heratensis Bunge ........................................... 56 3.3.1.4 Taxon: Astragalus kurdicus Boiss................................................ 56 3.3.1.5 Taxon: Astragalus microcephalus Willd. ......................................57 3.3.1.6 Taxon: Astragalus verus Olivier ..................................................57

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3.4

3.3.2 Sterculia Malvaceae (subfamily: Sterculioideae)..................................57 3.3.2.1 Taxon: Sterculia urens Roxb........................................................57 3.3.2.2 Taxon: Sterculia foetida L. ......................................................... 60 3.3.2.3 Taxon: Sterculia guttata Roxb.....................................................61 3.3.2.4 Taxon: Sterculia quadrifida R. Br. ............................................. 62 3.3.2.5 Taxon: Sterculia scaphigera Wall. ............................................... 62 3.3.2.6 Taxon: Sterculia setigera Delile .................................................. 63 3.3.2.7 Taxon: Sterculia tragacantha Lindl. ........................................... 64 3.3.2.8 Taxon: Sterculia villosa Roxb. .................................................... 64 3.3.3 Brachychiton Malvaceae (subfamily: Sterculioideae)........................... 64 3.3.3.1 Taxon: Brachychiton acerifolius (A. Cunn. ex G. Don) Macarthur................................................................................. 64 3.3.4 Firmiana Malvaceae (subfamily: Sterculioideae) . ..............................65 3.3.4.1 Taxon: Firmiana simplex (L.) W. Wight .....................................65 3.3.5 Hildegardia Malvaceae (subfamily: Sterculioideae) ............................65 3.3.5.1 Taxon: Hildegardia barteri (Mast.) Kosterm ..............................65 3.3.6 Cochlospermum Bixaceae ..........................................................................65 3.3.6.1 Taxon: Cochlospermum religiosum (L.) Alston.............................65 Important Indian or Asiatic Gums and Their Botanical Sources............................ 66 3.4.1 Aegle Rutaceae (subfamily: Aurantioideae) ........................................ 66 3.4.1.1 Taxon: Aegle marmelos (L.) Corrêa . .......................................... 66 3.4.2 Albizia Fabaceae (subfamily: Mimosoideae) . ....................................... 68 3.4.2.1 Taxon: Albizia lebbeck (L.) Benth. ........................................... 68 3.4.2.2 Taxon: Albizia odoratissima (L. f.) Benth................................... 69 3.4.2.3 Taxon: Albizia procera (Roxb.) Benth. ..................................... 69 3.4.2.4 Taxon: Albizia chinensis (Osbeck) Merr..................................... 71 3.4.2.5 Taxon: Albizia amara (Roxb.) Boivin . ..................................... 72 3.4.3 Aleurites Euphorbiaceae (subfamily: Crotonoideae) .......................... 73 3.4.3.1 Taxon: Aleurites moluccanus (L.) Willd...................................... 73 3.4.4 Anogeissus Combretaceae .........................................................................76 3.4.4.1 Taxon: Anogeissus latifolia (Roxb. ex DC.) Wall. ex Guill. & Perr.................................................................76 3.4.5 Bauhinia Fabaceae (subfamily: Caesalpinioideae) .............................. 79 3.4.5.1 Taxon: Bauhinia purpurea L...................................................... 79 3.4.5.2 Taxon: Bauhinia roxburghiana Voigt ......................................... 80 3.4.5.3 Taxon: Bauhinia variegata L.......................................................81 3.4.6 Buchanania Anacardiaceae .................................................................... 82 3.4.6.1 Taxon: Buchanania lanzan Spreng............................................. 82 3.4.6.2 Taxon: Buchanania latifolia Roxb.............................................. 82 3.4.7 Toona Meliaceae .................................................................................... 83 3.4.7.1 Taxon: Toona ciliata M. Roem. ................................................. 83 3.4.8 Chloroxylon Rutaceae .............................................................................. 84 3.4.8.1 Taxon: Chloroxylon swietenia DC.............................................. 84 3.4.9 Delonix Fabaceae (subfamily: Caesalpinioideae) ................................ 84 3.4.9.1 Taxon: Delonix regia (Bojer ex Hook.) Raf................................ 84 3.4.10 Elaeodendron Celastraceae (subfamily: Celastroideae)..................... 86 3.4.10.1 Taxon: Elaeodendron glaucum (Rottb.) Pers............................... 86

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3.5

3.4.11 Limonia Rutaceae (subfamily: Aurantioideae) ................................... 89 3.4.11.1 Taxon: Limonia acidissima L...................................................... 89 3.4.12 Mangifera Anacardiaceae ...................................................................... 90 3.4.12.1 Taxon: Mangifera indica L......................................................... 90 3.4.13 Azadirachta Meliaceae ........................................................................... 93 3.4.13.1 Taxon: Azadirachta indica A. Juss.............................................. 93 3.4.14 Prosopis Fabaceae (subfamily: Mimosoideae) . ...................................... 95 3.4.14.1 Taxon: Prosopis cineraria (L.) Druce.......................................... 95 3.4.14.2 Taxon: Prosopis juliflora (Sw.) DC. ............................................ 95 3.4.15 Sesbania Fabaceae (subfamily: Faboideae) ............................................ 98 3.4.15.1 Taxon: Sesbania grandiflora (L.) Pers. ........................................ 98 3.4.16 Spondias Anacardiaceae ........................................................................ 98 3.4.16.1 Taxon: Spondias dulcis Sol. ex Parkinson ................................... 98 3.4.16.2 Taxon: Spondias pinnata (J. Koenig ex L. f.) Kurz ................... 100 3.4.17 Terminalia Combretaceae......................................................................101 3.4.17.1 Taxon: Terminalia bellirica (Gaertn.) Roxb. . ...........................101 Gums of The New World .....................................................................................104 3.5.1 Anacardium Anacardiaceae ..................................................................104 3.5.1.1 Taxon: Anacardium humile A. St.-Hil.......................................104 3.5.1.2 Taxon: Anacardium nanum A. St.-Hil. .....................................104 3.5.1.3 Taxon: Anacardium occidentale L. ...........................................104 3.5.2 Anadenanthera Fabaceae (subfamily: Mimosoideae) ...........................105 3.5.2.1 Taxon: Anadenanthera colubrina (Vell.) Brenan var. cebil (Griseb.) Altschul .....................................................................105 3.5.2.2 Taxon: Anadenanthera colubrina (Vell.) Brenan var. colubrina ..................................................................................106 3.5.3 Caesalpinia Fabaceae (subfamily: Caesalpinioideae) ..........................106 3.5.3.1 Taxon: Caesalpinia coriaria (Jacq.) Willd..................................106 3.5.4 Parkinsonia Fabaceae (subfamily: Caesalpinioideae) .........................107 3.5.4.1 Taxon: Parkinsonia praecox (Ruiz & Pav.) J. A. Hawkins subsp. praecox ...........................................................................107 3.5.5 Parapiptadenia Fabaceae (subfamily: Mimosoideae)...........................108 3.5.5.1 Taxon: Parapiptadenia rigida (Benth.) Brenan .........................108 3.5.6 Puya Bromeliaceae ................................................................................108 3.5.6.1 Taxon: Puya chilensis Molina....................................................108 3.5.7 Theobroma Malvaceae (subfamily: Byttnerioideae) ..........................110 3.5.7.1 Taxon: Theobroma cacao L........................................................110 3.5.8 Laguncularia Combretaceae ..................................................................110 3.5.8.1 Taxon: Laguncularia racemosa (L.) C. F. Gaertn.......................110 3.5.9 Pithecellobium Fabaceae (subfamily: Mimosoideae) ............................ 111 3.5.9.1 Taxon: Pithecellobium dulce (Roxb.) Benth............................... 111 3.5.10 Samanea Fabaceae (subfamily: Mimosoideae) ..................................... 111 3.5.10.1 Taxon: Samanea saman (Jacq.) Merr......................................... 111 3.5.11 Enterolobium Fabaceae (subfamily: Mimosoideae) ..............................113 3.5.11.1 Taxon: Enterolobium cyclocarpum (Jacq.) Griseb.......................113 3.5.12 Chloroleucon Fabaceae (subfamily: Mimosoideae) ............................... 115 3.5.12.1 Taxon: Chloroleucon mangense (Jacq.) Britton & Rose.............. 115

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3.6

3.5.13 Leucaena Fabaceae (subfamily: Mimosoideae) .................................... 115 3.5.13.1 Taxon: Leucaena collinsii Britton & Rose . ............................... 115 3.5.14 Lysiloma Fabaceae (subfamily: Mimosoideae).......................................116 3.5.14.1 Taxon: Lysiloma acapulcense (Kunth) Benth..............................116 3.5.15 Inga Fabaceae (subfamily: Mimosoideae) ............................................116 3.5.15.1 Taxon: Inga stipularis DC.........................................................116 3.5.16 Rhizophora Rhizophoraceae .................................................................117 3.5.16.1 Taxon: Rhizophora mangle L. ...................................................117 3.5.17 Melicoccus Sapindaceae (subfamily: Sapindoideae) .............................117 3.5.17.1 Taxon: Melicoccus bijugatus Jacq...............................................117 3.5.18 Ceiba Malvaceae (subfamily: Bombacoideae)......................................118 3.5.18.1 Taxon: Ceiba speciosa (A. St.-Hil.) Ravenna..............................118 3.5.19 Thespesia Malvaceae (subfamily: Malvoideae).....................................118 3.5.19.1 Taxon: Thespesia populnea (L.) Sol. ex Corrêa ..........................118 3.5.20 Cylindropuntia Cactaceae (subfamily: Opuntioideae) ....................... 120 3.5.20.1 Taxon: Cylindropuntia fulgida (Engelm.) F. M. Knuth............ 120 3.5.21 Manilkara Sapotaceae ...........................................................................121 3.5.21.1 Taxon: Manilkara zapota (L.) P. Royen ....................................121 3.5.22 Larix Pinaceae....................................................................................... 122 3.5.22.1 Taxon: Larix occidentalis Nutt................................................. 122 Miscellaneous Asiatic, African, and Australian Gums.......................................... 123 3.6.1 Actinidia Actinidiaceae  ....................................................................... 123 3.6.1.1 Taxon: Actinidia deliciosa (A. Chev.) C. F. Liang & A. R. Ferguson .................................................................... 123 3.6.2 Araucaria Araucariaceae...................................................................... 123 3.6.2.1 Taxon: Araucaria heterophylla (Salisb.) Franco......................... 123 3.6.3 Balanites Zygophyllaceae (subfamily: Tribuloideae).........................125 3.6.3.1 Taxon: Balanites aegyptiacus (L.) Delile ..................................125 3.6.4 Brabejum Proteaceae ................................................................................125 3.6.4.1 Taxon: Brabejum stellatifolium L.................................................125 3.6.5 Butea Fabaceae (subfamily: Faboideae) .............................................. 126 3.6.5.1 Taxon: Butea monosperma (Lam.) Taub................................... 126 3.6.6 Cercis Fabaceae (subfamily: Caesalpinioideae) . ............................... 127 3.6.6.1 Taxon: Cercis siliquastrum L.................................................... 127 3.6.7 Cissus Vitaceae ...................................................................................... 127 3.6.7.1 Taxon: Cissus populnea Guill. & Perr. ..................................... 127 3.6.8 Commiphora Burseraceae .....................................................................129 3.6.8.1 Taxon: Commiphora mollis (Oliv) Engl. ...................................129 3.6.9 Diospyros Ebenaceae . ............................................................................ 130 3.6.9.1 Taxon: Diospyros mespiliformis Hochst. ex A. DC......................... 130 3.6.10 Dicorynia Fabaceae (subfamily: Caesalpinioideae) ........................... 130 3.6.10.1 Taxon: Dicorynia paraensis Benth............................................... 130 3.6.11 Entandrophragma Meliaceae ................................................................ 130 3.6.11.1 Taxon: Entandrophragma angolense (Welw.) C. DC................. 130 3.6.12 Fagarta Rutaceae......................................................................................131 3.6.12.1 Taxon: Zanthoxylum zanthoxyloides (Lam.) Zepern. & Timler .................................................................................131

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3.6.13 Ferula Apiaceae.......................................................................................131 3.6.13.1 Taxon: Ferula foetida (Bunge) Regel.........................................131 3.6.14 Grevillea Proteaceae .............................................................................132 3.6.14.1 Taxon: Grevillea robusta A. Cunn. ex R. Br..............................132 3.6.15 Lophira Ochnaceae ...............................................................................133 3.6.15.1 Taxon: Lophira alata Banks ex C. F. Gaertn.............................133 3.6.16 Madhuca Sapotaceae ............................................................................ 134 3.6.16.1 Taxon: Madhuca longifolia (L.) J. F. Macbr.............................. 134 3.6.17 Millettia Fabaceae (subfamily: Faboideae)........................................... 134 3.6.17.1 Taxon: Millettia pinnata (L.) Panigrahi................................... 134 3.6.18 Mystroxylon Celastraceae (subfamily: Celastroideae).......................135 3.6.18.1 Taxon: Mystroxylon aethiopicum (Thunb.) Loes.........................135 3.6.19 Parkia Fabaceae (subfamily: Mimosoideae) ....................................... 136 3.6.19.1 Taxon: Parkia bicolor A. Chev. ................................................ 136 3.6.20 Pereskia Cactaceae (subfamily: Pereskioideae).................................. 136 3.6.20.1 Taxon: Pereskia guamacho F.A.C. Weber ................................. 136 3.6.21 Phormium Hemerocallidaceae............................................................ 136 3.6.21.1 Taxon: Phormium tenax J. R. Forst. & G. Forst....................... 136 3.6.22 Piptadeniastrum Fabaceae (subfamily: Mimosoideae)...........................137 3.6.22.1 Taxon: Piptadeniastrum africanum (Hook. f.) Brenan...............137 3.6.23 Pittosporum Pittosporaceae...................................................................137 3.6.23.1 Taxon: Pittosporum phillyreoides DC.........................................137 3.6.24 Polyscias Araliaceae (subfamily: Aralioideae) ...................................137 3.6.24.1 Taxon: Polyscias sambucifolia (Sieber ex DC.) Harms................137 3.6.24.2 Taxon: Prunus avium (L.) L........................................................138 3.6.25 Prunus Rosaceae (subfamily: Spiraeoideae) . ......................................140 3.6.25.1 Taxon: Prunus armeniaca L. ....................................................140 3.6.25.2 Taxon: Prunus domestica L. subsp. domestica ...........................141 3.6.25.3 Taxon: Prunus persica (L.) Batsch var. persica...........................143 3.6.25.4 Taxon: Prunus spinosa L............................................................143 3.6.26 Pterocarpus Fabaceae (subfamily: Faboideae)........................................144 3.6.26.1 Taxon: Pterocarpus marsupium Roxb.........................................144 3.6.27 Sapindus Sapindaceae (subfamily: Sapindoideae) ...............................145 3.6.27.1 Taxon: Sapindus trifoliatus L.....................................................145 3.6.28 Stangeria Zamiaceae  ..............................................................................145 3.6.28.1 Taxon: Stangeria eriopus (Kunze) Baill. ....................................145 3.6.29 Symphonia Clusiaceae............................................................................146 3.6.29.1 Taxon: Symphonia globulifera L. f. ............................................146 3.6.30 Talisia Sapindaceae (subfamily: Sapindoideae) . .................................147 3.6.30.1 Taxon: Talisia oliviformis (Kunth) Radlk..................................147 3.6.30.2 Taxon: Watsonia versfeldii J. W. Mathews & L. Bolus ..............147 3.6.31 Welwitschia Welwitschiaceae ..............................................................148 3.6.31.1 Taxon: Welwitschia mirabilis Hook. f........................................148 3.6.32 Ziziphus Rhamnaceae.............................................................................148 3.6.32.1 Taxon: Ziziphus jujuba Mill......................................................148 References........................................................................................................................149

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4.

Minor Plant Exudates of the World .......................................................................... 163 4.1 Introduction..........................................................................................................163 4.2 Adansonia Malvaceae (subfamily: Bombacoideae)............................................163 4.2.1 Taxon: Adansonia digitata L. ...................................................................163 4.3 Adenanthera Fabaceae (subfamily: Mimosoideae).............................................168 4.3.1 Taxon: Adenanthera pavonina L. . ............................................................168 4.4 Afzelia Fabaceae (subfamily: Caesalpinioideae)...............................................170 4.4.1 Taxon: Afzelia africana Sm. ex Pers. ........................................................170 4.5 Albizia Fabaceae .................................................................................................172 4.6 Anogeissus Combretaceae ....................................................................................173 4.6.1 Taxon: Anogeissus leiocarpus (DC.) Guill. & Perr. ....................................173 4.7 Atalaya Sapindaceae (subfamily: Sapindoideae)...............................................174 4.7.1 Taxon: Atalaya hemiglauca (F. Muell.) F. Muell. ex Benth. ......................174 4.8 Balsamocitrus Rutaceae (subfamily: Aurantioideae)........................................174 4.8.1 Taxon: Balsamocitrus dawei Stapf ............................................................174 4.9 Bauhinia Fabaceae...............................................................................................175 4.9.1 Taxon: Bauhinia carronii F. Muell............................................................175 4.9.2 Taxon: Bauhinia thonningii Schumach. & Thonn. ..................................175 4.9.3 Taxon: Tylosema fassoglense (Kotschy ex Schweinf.) Torre & Hillc............176 4.10 Julbernardia Fabaceae (subfamily: Caesalpinioideae)......................................176 4.10.1 Taxon: Julbernardia globiflora (Benth.) Troupin.......................................176 4.11 Bombax Malvaceae (subfamily: Bombacoideae)...............................................177 4.11.1 Taxon: Bombax ceiba L. ...........................................................................177 4.11.2 Taxon: Bombax insigne Wall. ...................................................................180 4.12 Borassus Arecaceae (subfamily: Coryphoideae) ...............................................180 4.12.1 Taxon: Borassus flabellifer L. ....................................................................180 4.13 Bosistoa Rutaceae (subfamily: Toddalioideae) .................................................181 4.13.1 Taxon: Bosistoa pentacocca (F. Muell.) Bail. ..............................................181 4.14 Brachystegia Fabaceae (subfamily: Caesalpinioideae).......................................181 4.14.1 Taxon: Brachystegia spiciformis Benth. . ....................................................181 4.15 Burkea Fabaceae (subfamily: Caesalpinioideae)...............................................183 4.15.1 Taxon: Burkea africana Hook. .................................................................183 4.16 Capparis Capparaceae..........................................................................................184 4.16.1 Taxon: Capparis nobilis (Endl.) F. Muell. ex Benth...................................184 4.17 Careya Lecythidaceae (subfamily: Planchonioideae).....................................185 4.17.1 Taxon: Careya arborea Roxb. ...................................................................185 4.18 Cassia Fabaceae (subfamily: Caesalpinioideae)................................................186 4.18.1 Taxon: Cassia fistula L. ............................................................................186 4.18.2 Taxon: Cassia sieberiana DC.....................................................................187 4.19 Cedrela Meliaceae ..............................................................................................189 4.19.1 Taxon: Cedrela odorata L. ........................................................................189 4.20 Ceiba Malvaceae (subfamily: Bombacoideae)...................................................190 4.20.1 Taxon: Ceiba pentandra (L.) Gaertn.........................................................190 4.21 Ceratopetalum Cunoniaceae ...............................................................................190 4.21.1 Taxon: Ceratopetalum apetalum D. Don...................................................190 4.21.2 Taxon: Ceratopetalum gummiferum Sm. . .................................................191

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4.22 Chukrasia Meliaceae...........................................................................................191 4.22.1 Taxon: Chukrasia tabularis A. Juss............................................................191 4.23 Citrus Rutaceae........................................................................................................ 193 4.24 Cocos Arecaceae (subfamily: Arecoideae) ........................................................195 4.24.1 Taxon: Cocos nucifera L. ..........................................................................195 4.25 Cola Sterculiaceae.............................................................................................197 4.25.1 Taxon: Cola cordifolia (Cav.) R. Br. . ........................................................197 4.26 Combretum Combretaceae . ...............................................................................198 4.27 Cordia Boraginaceae (subfamily: Cordioideae)............................................. 200 4.27.1 Taxon: Cordia myxa L. ........................................................................... 200 4.28 Cordyla Fabaceae (subfamily: Faboideae)..........................................................201 4.28.1 Taxon: Cordyla africana Lour. .................................................................201 4.29 Corypha Arecaceae (subfamily: Coryphoideae).............................................. 202 4.29.1 Taxon: Corypha utan Lam. ..................................................................... 202 4.30 Crataeva Capparaceae........................................................................................ 202 4.30.1 Taxon: Crataeva adansonii DC. .............................................................. 202 4.31 Cussonia Araliaceae........................................................................................... 204 4.31.1 Taxon: Cussonia arborea Hochst. ex A. Rich. . ........................................ 204 4.32 Cycas Cycadaceae............................................................................................... 204 4.32.1 Taxon: Cycas lane-poolei C. A. Gardner .................................................. 204 4.32.2 Taxon: Cycas circinalis L......................................................................... 204 4.33 Dichrostachys Fabaceae (subfamily: Mimosoideae)........................................... 207 4.33.1 Taxon: Dichrostachys cinerea (L.) Wight & Arn. . .................................... 207 4.34 Echinocarpus Elaeocarpaceae ........................................................................... 208 4.34.1 Taxon: Echinocarpus australis Benth. (now synonym of sloanea australis F. Muell., see section 4.6.2.2)............ 208 4.35 Elaeocarpus Elaeocarpaceae.............................................................................. 208 4.35.1 Taxon: Elaeocarpus grandis F. Muell. ....................................................... 208 4.35.2 Taxon: Elaeocarpus obovatus G. Don ....................................................... 208 4.35.3 Taxon: Elaeocarpus reticulatus Sm............................................................ 208 4.36 Encephalartos Zamiaceae..................................................................................... 208 4.36.1 Taxon: Encephalartos hildebrandtii A. Braun & C. D. Bouché................. 208 4.37 Entada Fabaceae (subfamily: Mimosoideae)..................................................... 209 4.37.1 Taxon: Entada africana Guill. & Perr...................................................... 209 4.38 Erythrophleum Fabaceae (subfamily: Caesalpinioideae).................................. 209 4.38.1 Taxon: Erythrophleum africanum (Welw. ex Benth.) Harms ................... 209 4.39 Flindersia Rutaceae .............................................................................................210 4.39.1 Taxon: Flindersia maculosa (Lindl.) F. Muell. ..........................................210 4.39.2 Taxon: Flindersia australis R. Br. ..............................................................211 4.40 Garuga Burseraceae ...........................................................................................211 4.40.1 Taxon: Garuga pinnata Roxb. ..................................................................211 4.41 Geijera Rutaceae . ...............................................................................................212 4.41.1 Taxon: Geijera paniculata (F. Muell.) Druce.............................................212 4.42 Geodorum Orchidaceae......................................................................................212 4.42.1 Taxon: Geodorum nutans (C. Presl) Ames ................................................212 4.43 Hakea Proteaceae..............................................................................................213 4.43.1 Taxon: Hakea gibbosa (Sm.) Cav. . ............................................................213

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4.44 Khaya Meliaceae.................................................................................................214 4.44.1 Taxon: Khaya grandifoliola C. DC. ..........................................................214 4.44.2 Taxon: Khaya madagascariensis Jum. & H. Perrier....................................214 4.44.3 Taxon: Khaya senegalensis (Desr.) A. Juss. .................................................214 4.45 Lagerstroemia Lythraceae ...................................................................................217 4.45.1 Taxon: Lagerstroemia parviflora Roxb. . ....................................................217 4.46 Lannea Anacardiaceae .......................................................................................219 4.46.1 Taxon: Lannea coromandelica (Houtt.) Merr. ...........................................219 4.47 Macrozamia Zamiaceae .......................................................................................221 4.47.1 Taxon: Macrozamia spiralis (Salisb.) Miq..................................................221 4.48 Melia Meliaceae .................................................................................................221 4.48.1 Taxon: Melia azedarach L. .......................................................................221 4.49 Melicope Rutaceae ............................................................................................. 224 4.49.1 Taxon: Bouchardatia neurococca (F. Muell.) ............................................ 224 4.50 Moringa Moringaceae . ..................................................................................... 225 4.50.1 Taxon: Moringa oleifera Lam. ................................................................. 225 4.51 Owenia Meliaceae.............................................................................................. 228 4.51.1 Taxon: Owenia venosa F. Muell. ............................................................. 228 4.52 Panax (Tieghemopanax) Araliaceae ................................................................... 228 4.52.1 Taxon: Polyscias elegans (C. Moore & F. Muell.) Harms .......................... 228 4.52.2 Taxon: Neopanax colensoi (Hook. f.) Allan .............................................. 228 4.53 Saltera Penaeaceae ............................................................................................ 228 4.53.1 Taxon: Saltera sarcocolla (L.) Bullock . .................................................... 228 4.54 Pentaceras Rutaceae ........................................................................................... 229 4.54.1 Taxon: Pentaceras australis (F. Muell.) Benth .......................................... 229 4.55 Prunus Rosaceae................................................................................................. 229 4.55.1 Taxon: Prunus dulcis (Mill.) D. A. Webb ................................................ 229 4.56 Pseudocedrela Meliaceae..................................................................................... 230 4.56.1 Taxon: Pseudocedrela kotschyi (Schweinf.) Harms. . ................................. 230 4.57 Saccopetalum Annonaceae...................................................................................231 4.57.1 Taxon: Miliusa tomentosa (Roxb.) J. Sinclaiv.............................................231 4.58 Sarcostemma Asclepiadaceae . ............................................................................231 4.58.1 Taxon: Sarcostemma brevistigma Wight & Arn.........................................231 4.59 Schefflera Araliaceae................................................................................................ 231 4.59.1 Taxon: Schefflera volkensii Harms................................................................. 231 4.60 Sclerocarya Anacardiaceae................................................................................. 232 4.60.1 Taxon: Sclerocarya birrea (A. Rich.) Hochst. ........................................... 232 4.61 Semecarpus Anacardiaceae .................................................................................233 4.61.1 Taxon: Semecarpus anacardium L. f. ........................................................233 4.62 Sloanea Elaeocarpaceae .................................................................................... 234 4.62.1 Taxon: Sloanea woollsii F. Muell.............................................................. 234 4.62.2 Taxon: Sloanea australis F. Muell. . .............................................................234 4.63 Soymida Meliaceae .............................................................................................235 4.63.1 Taxon: Soymida febrifuga (Roxb.) A. Juss. ................................................235 4.64 Tamarindus Fabaceae (subfamily: Caesalpinioideae)...................................... 236 4.64.1 Taxon: Tamarindus indica L. .................................................................. 236

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4.65 Heritiera Malvaceae ........................................................................................... 238 4.65.1 Taxon: Heritiera trifoliolata (F. Muell.) Kosterm. . .................................. 238 4.66 Terminalia Combretaceae ................................................................................. 238 4.67 Thevetia Apocynaceae . ............................................................................................ 245 4.67.1 Taxon: Thevetia peruviana (Pers.) K. Schum. ...........................................245 4.68 Virgilia Fabaceae (subfamily: Faboideae) ......................................................... 246 4.68.1 Taxon: Virgilia oroboides (P. J. Bergius) T. M. Salter ............................... 246 References........................................................................................................................247

5.

Food Applications of Plant Exudates........................................................................ 257 5.1 Introduction..........................................................................................................257 5.2 Food Uses of Gum Exudates.................................................................................258 5.2.1 Confectionery...........................................................................................258 5.2.2 Salad dressings and sauces........................................................................261 5.2.3 Frozen products....................................................................................... 262 5.2.3.1 Frozen dough .......................................................................... 263 5.2.3.2 Frozen sugar solutions ............................................................ 263 5.2.3.3 Frozen dairy products, ice pops and sherbets........................... 264 5.2.4 Spray-drying ........................................................................................... 264 5.2.4.1 Spray-drying of juices.............................................................. 264 5.2.4.2 Miscellaneous spray-dried products......................................... 266 5.2.4.3 Encapsulation via spray-drying.................................................267 5.2.5 Drum-drying ...........................................................................................267 5.2.6 Wine ....................................................................................................... 268 5.2.7 Adhesives................................................................................................. 269 5.2.8 Bakery products ...................................................................................... 269 5.2.9 Flavor fixatives and emulsifiers................................................................ 269 5.2.10 Beverages..................................................................................................270 5.2.11 Meat products ..........................................................................................270 5.2.12 Miscellaneous...........................................................................................270 5.2.13 Microencapsulation .................................................................................271 5.2.13.1 Oleoresins ................................................................................271 5.2.13.2 Linoleic acid microencapsulation .............................................274 5.2.13.3 Procyanidins ............................................................................275 5.2.14 Coacervation............................................................................................276 5.2.15 Deep-fat frying.........................................................................................276 5.2.16 Emulsions................................................................................................ 277 5.2.17 Foam....................................................................................................... 279 5.3 Gum Exudates in Animal Food . ......................................................................... 280 5.3.1 Introduction............................................................................................ 280 5.3.2 Insects..................................................................................................... 280 5.3.3 Mammals and primates............................................................................281 5.4 Health-Related Aspects ....................................................................................... 284 5.4.1 Safety ..................................................................................................... 284 5.4.2 Nutrition ................................................................................................ 285 References ...................................................................................................................... 286

Contents  ◾  xvii

6.

Gum Exudates in Water-Based Adhesives ................................................................ 293 6.1 Introduction..........................................................................................................293 6.2 Gums as Adhesives............................................................................................... 294 6.3 Industrial Uses of Exudate Glues . ....................................................................... 294 6.3.1 General . ................................................................................................. 294 6.3.2 Paper....................................................................................................... 294 6.3.3 Wood and furniture ................................................................................ 294 6.4 Biological Applications: A General Approach....................................................... 296 6.4.1 Ostomy devices ....................................................................................... 296 6.4.2 Denture fixatives ..................................................................................... 297 6.4.3 Bioelectrodes........................................................................................... 298 6.4.4 Exudate patches for transdermal drug delivery ....................................... 298 6.5 Hydrocolloid Adhesion Tests . ............................................................................. 299 6.6 Exudates as Wet Glues ......................................................................................... 302 6.7 Adhesion Mechanisms of Hydrogels .................................................................... 306 References....................................................................................................................... 308

7.

Medical, Cosmetic and Biotechnological Uses of Gum Exudates............................. 311 7.1 Introduction .........................................................................................................311 7.2 Pharmacological Applications . .............................................................................311 7.2.1 Demulcent and emollient qualities...........................................................311 7.2.2 Suspending and emulsifying agents..........................................................312 7.2.3 Laxatives . ................................................................................................314 7.2.4 Antiseptic preparations and ophthalmic infections...................................314 7.2.5 Tablets and pills . .....................................................................................314 7.2.6 Hydrophobic drug delivery.......................................................................314 7.2.7 Lycopene ................................................................................................. 315 7.2.8 Gelatin- And chitosan-gum arabic coacervates......................................... 315 7.2.9 Various medical uses . ..............................................................................317 7.2.9.1 Intravenous injections . ...........................................................317 7.2.9.2 Activity against leishmania and fungi . ...................................317 7.3 Folk Medicine ......................................................................................................318 7.4 Cosmetics and Other Products............................................................................. 320 7.4.1 General . ................................................................................................. 320 7.4.2 Different cosmetic preparations................................................................321 7.4.3 Perfume ...................................................................................................321 7.4.4 Powdered abrasive cleaners...................................................................... 322 7.5 Biotechnological Applications ............................................................................. 322 7.5.1 Recombinant plant gum ......................................................................... 322 7.5.2 Intracellular delivery................................................................................ 323 References....................................................................................................................... 323

8.

Analysis and Identification of Gum Exudates .......................................................... 327 8.1 Introduction .........................................................................................................327 8.2 Industrial Gums....................................................................................................327 8.2.1 Water solubility .......................................................................................327 8.2.2 Alcohol precipitability .............................................................................329

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8.2.3 Microscopic identification........................................................................329 8.2.4 Identification of gums in specific foods ....................................................332 8.2.5 Antibodies for the identification of gum arabic and other polysaccharides ........................................................................333 8.3 Group Analysis and Identification Schemes . ....................................................... 334 8.3.1 Characteristic reactions of gums.............................................................. 334 8.3.2 Cetavlon group identification scheme ......................................................337 8.4 Additional Analytical Methods ............................................................................338 8.4.1 IR spectroscopy........................................................................................338 8.4.2 Chromatographic techniques to identify plant gums ...............................339 8.4.3 Fourier transform-Raman spectroscopy of gum exudates ....................... 340 8.4.4 Capillary electrophoresis ......................................................................... 341 8.4.5 Other methods ....................................................................................... 342 References....................................................................................................................... 342

9.

Miscellaneous Uses of Plant Exudates . ....................................................................347 9.1 Introduction......................................................................................................... 347 9.2 Paints, Pigments and Painting.............................................................................. 347 9.3 Inks.......................................................................................................................351 9.4 Lithography...........................................................................................................354 9.5 Textiles..................................................................................................................355 9.6 Corrosion Inhibition ............................................................................................357 9.7 Immersion Plating.................................................................................................358 9.8 Drilling Fluids.......................................................................................................359 9.9 Oil-Well Cement.................................................................................................. 360 9.10 Binders and Special Coatings................................................................................361 9.10.1 Glaze binders............................................................................................361 9.10.2 Binders for insecticides.............................................................................361 9.10.3 Non-glare coatings for windshields . ........................................................361 9.11 Paper and E-Paper.................................................................................................361 9.12 Explosives............................................................................................................. 362 9.13 Ceramics.............................................................................................................. 364 9.14 Miscellaneous........................................................................................................365 9.14.1 Varnishes..................................................................................................365 9.14.2 Car polishes............................................................................................. 366 9.14.3 Cross-linked polystyrene ........................................................................ 366 9.14.4 Photoelectric determinations................................................................... 366 9.14.5 Polarographic determinations ..................................................................367 9.14.6 Abdominal ultrasound imaging and soil analyses ....................................367 9.14.7 Vinyl resin emulsions . ............................................................................ 368 References....................................................................................................................... 368

Organism Name Index ....................................................................................................... 371 General Index.....................................................................................................................383

Preface Natural gums—which exude from trees and shrubs in tear-like, striated nodules or amorphous lumps, and then dry in the sun to form hard, glassy exudates in a variety of colors—have been used for centuries in many different ways. Their use in food applications—for emulsification, thickening and stabilization, among others—dates back many years. Their use as food is well documented in the Bible: the famous “manna from heaven” that sustained the Israelites during their escape from Egypt was probably a gum exudate related to gum arabic or gum acacia. Their non-food-related uses in pharmaceuticals, cosmetics, textiles and lithography, and minor forest products can also be traced back in history. They were recognized items of trade in Biblical times, and ancient inscriptions depict the use of gum arabic—called kami by the Egyptians—in textile glues, embalming fluids, and dye dispersions. Plant exudates, both gums and resins, have also served as the basis for the creation of many new and improved gluing materials. At the Hebrew University of Jerusalem in Israel, our team has been working for the last 10 years on adhesion in general, and hydrocolloid glues and patches in particular. Part of our research has involved a thorough search in nature and in the literature for less known sources of gum exudates. In the course of this quest, we discovered that in the last 60 years many new gum exudates have been mentioned, in passing or in detail, and that their number is much higher than that first described in 1949 by Howes in his classic comprehensive monograph: Vegetable Gums and Resins. That book was devoted in its entirety to plant exudates, be they gums or resins. Many other polysaccharide/hydrocolloid books contain chapters devoted to the chemistry and industrial applications of the more common or commonly used exudates. On the other hand, there are many exudates that have never been described, nor have their applications ever been reviewed, despite that awareness of these lesser-known natural raw materials has increased in the last few years. Some have been proposed as alternatives for gum arabic, karaya, tragacanth, and ghatti as sources for novel medicines and foods, and for lesser-known industrial aims. Hence the need for a new and up-to-date book exclusively devoted to gum exudates became clear to me, and I decided to undertake this project. This book is unique in that it provides a definitive classification of gum exudates. Most, if not all, books dealing with gum exudates classify them according to country or geographic location. However, many trees are not endemic; in fact, exudate-bearing trees are distributed all over the globe, covering at least a few continents. Moreover, some of these classifications are artificial or unjustified. Other classifications have been suggested on the basis of the sugar residues comprising the internal chains of the polysaccharides’ molecular structure. This type of classification, in which one group can contain polysaccharides of diverse origins on account of their similar backbones, is not always correct and is best avoided, especially when external macromolecular xix

xx  ◾  Preface

conformations of the side chains better explain the relationships between structural and physical properties. Added to the fact that current knowledge of the detailed structures of certain gum exudates is limited, an unambiguous structural classification simply becomes unrealistic. This volume strives to eliminate the deceptive classifications found in currently available books. Here the gums are classified according to their botanical taxonomy, that is, family, genus, and species. One problem that is often encountered in the literature involves botanical names that were correct at the time of entry, but then evolved into synonyms and are now outdated, and author names that were never standardized. To avoid this pitfall, almost all of the botanical names in this volume were checked against the U.S. Department of Agriculture’s Germplasm Resources Information Network (GRIN at http://www.ars-grin.gov/), a reliable listing of names for most economic plants in which the author names have been standardized. This book contains two main chapters (3 and 4) devoted to listing the major and minor exudates of the world. Each gum is supported (wherever this information was available) with the botanical name and synonyms of the tree or shrub from which the gum is exuded, as well as a list of common and vernacular names, and information on geographic distribution, present common names for the gum, a description of the exudate’s appearance and color, information on water solubility, chemical characteristics and structural features, physical and physicochemical properties, and commercial availability. Each gum’s industrial and food applications are also mentioned and described in more detail in other chapters. The commercial and functional uses of other parts of the tree from which the gum originates are also detailed. This book is also unique in its color photographs, designed to present many of the gum exudates in their natural state as well as the relevant trees, leaves, flowers, or other plant parts. Other distinctive aspects of this book include seven additional comprehensive chapters devoted exclusively to gum exudate identification, functionality, and applications. Chapter 1 gives an overview of the roles and sources of gum exudates. This introductory chapter begins by explaining the differences between resins, oleoresins, gum resins, kino, latex, and gums. It includes a general description of selected gum-yielding plant species, delineates the role of exudates in industry, provides the history and ancient uses of these materials, describes socioeconomic aspects, lists trade and markets, names physical and chemical properties (further reviewed in Chapters 3 and 4), describes botanical aspects (including taxonomy, anatomy, production systems, harvesting, genetic resources, and breeding), and provides a brief overview of these substances’ prospects. Chapter 2 deals with the physiological aspects of polysaccharide formation in plant exudates. Gum exudates can be part of the plant’s normal metabolism, but more often than not their exudation is attributed to pathological phenomena. An understanding of the factors affecting gum formation is of fundamental importance in finding a cure for the disorder in some fruit trees, and in inducing prolific gum production for commercial purposes. Pathological exudation, or gummosis, owes its origin to a number of unrelated factors such as tissue infections caused by disease, pathogens, and parasitic invasion by microorganisms, fungi, viruses and insects; physical injury; chemicals; stress, and various climatic conditions. The chapter attempts to clearly separate the different causes of gummosis and its role as a protective function; it also expounds on the involvement of the primary cell wall in the early stages of gum formation, the interference of ethylene in the balanced biosynthesis of cell-wall polysaccharides, the role of enzymes in the transformation of cellulose, hemicelluloses, starch or pectic substances into gums, the development and ultrastructure of gum ducts, the induction of gummosis by the ethylene generator ethephon for enhanced commercial gum production, and aspects of gummosis in fruit trees.

Preface  ◾  xxi

Chapter 3 covers the world’s major plant exudates, providing a highly comprehensive list of the common gum exudates. The gums in this chapter are arranged according to the botanical taxonomy of their sources. This extensive chapter (together with Chapter 4, which covers the world’s minor exudates) makes up the major part of this book. For each tree or shrub from which gum is exuded, all available information on botanical names and their authorities, synonyms, vernacular, and common plant names is provided. In addition, information is provided on geographical distribution and common names for the gum (in an attempt to avoid duplication where different names have been given to the same gum).  The chapter also includes descriptions of exudate appearance and color, water solubility and hydrocolloidal properties, chemical and structural features, physical and physicochemical properties, commercial aspects and availability, industrial and food applications, and general uses and applications of the plant. Unique applications are covered in Chapters 5, 6, 7, and 9. For each gum, an exhaustive list of references to the literature, from the 1890s to the present, is included for the interested reader. Chapter 4 deals with world’s minor plant exudates. In a format similar to that of Chapter 3, a full list of the lesser-known, unexplored, and not previously reviewed gum exudates is provided. In some cases, this book provides the first record of a particular exudate. Note that limited sources of information for some gums permit only partial descriptions. Chapter 5 deals with food applications of plant exudates. Following their listing in Chapters 3 and 4, common industrial applications of gum exudates as well as special local, ethnic, and tribal uses are explored. It should be borne in mind that many exudates have not been given Generally Recognized as Safe (GRAS) status. Many such gums contain tannins or other ingredients that can be health hazards, and this information is covered in previous chapters. Chapter 5 traces the changes in relative importance of the currently utilized gum exudates and explains how these are influenced by changes in their value, price, or ease of collection, or by climate or other global changes. Available information on these gums from nutritional and safety standpoints is also described. This chapter is also devoted to unique applications, especially those that have prehistoric roots and have evolved into their present-day uses, and that are expected to undergo further development. Although similar chapters devoted to food applications can be found in other books, this chapter emphasizes the old versus the new, taste (providing sweetness and sensory evaluations of edible exudates), local versus international aspects, and, finally, comprehensive nutritional information on these gums. Chapter 6 describes gum exudates in water-based adhesives. Information on this issue is on the one hand most important and on the other hand quite limited. This unique chapter includes information on gum exudates as adhesive materials in medicinal products, namely, mucoadhesives, bioelectrodes, denture fixatives, ostomies, and transdermal patches; adhesive materials in the food, paper, and wood industries; mechanisms controlling adhesion of polysaccharides; testing of adhesive joints; purposes and future prospects of gum exudates in water-based adhesives; and a comprehensive comparative analysis of the adhesion properties of various gum exudates that have never before been explored and are presented for the first time in this book. Chapter 7 describes medical, cosmetic, and biotechnological uses of gum exudates. Many applications of gum exudates have a profound tradition. However, there is no doubt that a promising future for these materials is based on their medicinal, cosmetic, and biotechnological uses. This chapter describes different applications of gums in these fields, such as in bulk laxatives; in treatments for warts, ulcers, and pressure sores; for the soothing of irritated mucous membranes; as carriers in controlled-release hydrophilic matrix systems; as constituents in medicines; as binding agents in cosmetic preparations; in perfumed cachous and lozenges; in different creams and ointments; in eye cosmetics; in cough syrups; as part of intravenous injections; and in blood substitutes.

xxii  ◾  Preface

Chapter 8 deals with the analysis and identification of gum exudates. Although the analysis and identification of commercial gums is of the utmost importance, very few books discuss this topic. Since food quality has become a major issue in many countries, this chapter discusses the treatment of commercial gum samples that are usually sold in powdered form for a variety of uses in foods. This chapter attempts to bring together all of the fragmented knowledge available for as many exudates as possible. These include water-solubility properties, alcohol-precipitation characteristics, microscopic identification, and flocculation values. In addition, the chapter describes how to identify exudates in specific food products. In a few cases, the reader is supported with information on group analyses and identification schemes. A very short description of additional analytical methods is provided, although this is not the main focus of the book. In addition, the chapter briefly describes the chemical reactivities and compatibilities of different exudates. Although such information is limited, its collection under one title is expected to be highly relevant for producers of many kinds of foods, pharmaceutical products, coacervates, and more. Chapter 9 deals with miscellaneous uses of plant exudates. Although Chapters 5, 6, and 7 cover the main applications of these fascinating materials, many other, less known but nevertheless important uses exist, related to paper, photography, inhibition of corrosion, immersion plating of metals, drilling, ceramics, and binders, among many others. This book was written over a two-year period. In addition to enumerating and describing the numerous gum exudates, it describes the many traditional as well as nontraditional uses of exudates that have been developed in many hydrocolloid research and development laboratories all over the world. My hope is that this book will assist all levels of readers. It is dedicated not only to the academic community but also to the wider population of industrialists and experimenters who will find this book to be not only a source of knowledge, but also an initiator of novel ideas and inventions. In particular, this book is expected to be of interest to personnel involved in food formulation, food scientists, food technologists, industrial chemists and engineers of textiles, pharmaceutical staff and medical doctors, and those who develop cosmetics or deal with drug delivery through adhesive patches. In addition, botanists, floral experts (both professional and amateur), exudate developers and collectors, farmers, agriculturalists, and those who work on the development of arid lands are also potential readers. Finally, it is hoped that this book will find a prominent place in the traditional university and research institute libraries where food science, chemistry, agriculture, botany, and other theoretical and practical industrial topics are taught and studied.

Acknowledgments This book has been in the writing stages for the last two years. It contains a description of the world’s plant gum exudates: their sources, distribution, properties, and applications. It also includes many traditional and nontraditional uses of exudates that have been developed in our laboratory and many other hydrocolloid research and development laboratories worldwide. My hope is that this manuscript will assist all levels of readers in their search for comprehensive knowledge on the fascinating field of exudates, as well as those seeking up-to-date information on the very different current and past uses and applications of exudates in many areas. Comments and questions from these readers will be very much appreciated. I thank the publishers for giving me the opportunity to write this book. Special thanks to Stephen Zollo and David Fausel for the efficient way in which they contributed to the formation and processing of this manuscript. I wish to thank my editor, Camille Vainstein, for working shoulderto-shoulder with me when time was getting short. The help of my colleague and friend Dr. Omri Ben-Zion, who supported me with literature research, references, and good advice, is very much appreciated. The efficient help of Hanna Ben-Or in finding and rectifying the many old or inaccurate references was above and beyond the call of duty. Ben-Zion’s contribution of pictures and specimens collected in Israel for the book is much appreciated, as are the specimens collected in India by Krystal Colloids. Special thanks to Dr. Mark Nesbitt from the Royal Botanic Gardens, Kew, for a thorough reading, many corrections of Chapters 3 and 4, and help with the taxonomical information in this volume. I am grateful to Julia Steele from the Royal Botanic Gardens, Kew, who was so efficient at organizing the photography of specimens at Kew, and was welcoming, enthusiastic, and encouraging. The permissions that we obtained from publishers are warmly acknowledged. Special thanks to Forest Starr and Kim Starr, who generously provided me with so many excellent pictures of gum-exuding trees and shrubs. The generosity of Dr. Kevin C. Nixon and Sherry Vance who gave me the permission to use images from Plantsystematics.org is very much appreciated, as is the help and friendship of Dr. Madoka Hirashima and her picture-taking efforts in Japan. This list would not be complete without extending my heartfelt thanks to the many who contributed to the Web sites of USDA–GRIN and other nonprofit organizations, which made the writing of the botanical section of this book so much easier. The pictures adapted from Wikipedia are acknowledged in their turn, but I feel that it is equally appropriate here to acknowledge the many who have contributed to this gigantic educational achievement. The love and patience of my family, Varda, Ya’ara, Eran, and Yoav, who were very supportive during these last few difficult years when we were under huge pressure from many different directions. Last but not least, I thank the Hebrew University of Jerusalem for being my home and refuge for the last 18 years of very extensive research and teaching. xxiii

The Author Professor Amos Nussinovitch was born in Kibbutz Megiddo, Israel. He is the son of Holocaust survivors. Nussinovitch served as a soldier in the Yom Kippur and Lebanon wars, and both his heritage and the horrors of war deeply influenced his life, thoughts, and attitudes. He studied chemistry at the University of Tel Aviv, and food engineering and biotechnology at the Technion-Israel Institute of Technology. He has worked as an engineer in several companies and has been involved in a number of research and development projects in the United States and Israel, focusing especially on the mechanical properties of liquids, semisolids, solids, and powders. He is currently in the Biochemistry and Food Science Department of the Robert H. Smith Faculty of Agriculture, Food and Environment at the Hebrew University of Jerusalem, where he leads a large group of researchers working on theoretical and practical aspects of hydrocolloids, including: coating of cells and foods; special glues and exudate patches; water-soluble polymer uses in paper; exudate preparations in cosmetics and medicine; hydrocolloid uses in explosives, ink, and special cellular solids; and biological carriers. Nussinovitch is the author of the books Hydrocolloid Applications: Gum Technology in the Food and Other Industries and Water-Soluble Polymer Applications in Foods. He is the author or coauthor of numerous papers on hydrocolloids, physical properties of foods, and recently, the use of exudates in pharmaceutics, and he has about 30 patent applications. This book is devoted specifically to plant gum exudates of the world, their sources, distribution, properties, and applications.

xxv

Chapter 1

Role and Sources of Exudate Gums 1.1 INTRODUCTION Exudate gums have been used for centuries in a variety of fields: they have retained their importance despite the many alternative gums, with similar typical performances, which have since come into existence. Natural gums exude from trees and shrubs in tear-like, striated nodules or amorphous lumps, and then dry in the sun, forming hard, glassy exudates of different colors, from white to pale amber for gum arabic, pale gray to dark brown for karaya gum, and white to dark brown for tragacanth. Gum production increases under high temperatures and limited moisture, and yields can be increased by making incisions in the bark or stripping it from the tree or shrub. Exudate gums have been used in food applications for many years, for emulsification, thickening and stabilization, among others (Table 1.1). Gums were known and used in Biblical times: their use as food is well documented in the Bible: the famous “manna from heaven” that sustained the Israelites in their escape from Egypt was probably a gum exudate related to gum arabic or gum acacia (Glicksman, 1969). Similar acacia exudates have also been used for food. For example, in Australia, the natives eat wattle gum (Fig. 1.1), which is the exudate of the species of acacia tree known as wattle tree, in combination with fish (Maiden, 1890). In India, similar gum exudates are also quite widespread and are sold in marketplaces. The local food “laddu” and other sweetmeats (Fig. 1.2), sherbets and syrups are prepared from these materials (Glicksman, 1969). In the Australia-New Zealand region, as a result of local knowledge and widespread use of gum exudates, many picturesque gum-related colloquialisms have become part of the local language. Examples are the term “gum-sucker”, which stems from the practice in small boys of eating and chewing gum from eucalyptus or acacia, and is used loosely to refer to the natives of the area (Glicksman, 1969). Another phrase “to be up a gum tree” is used to mean being in a predicament (Partridge, 1961). Gum arabic, gum tragacanth, gum karaya and gum ghatti are safe for human consumption based on a long history of usage as well as recent toxicological studies. Tree gum exudates are also used in non-food applications, such as: pharmaceuticals, cosmetics, textiles and lithography, and minor forest products (Wang and Anderson, 1994). Gums have also long been utilized 1

2  ◾  Plant Gum Exudates of the World Table 1.1  Food Applications of Gum Arabic, Ghatti, Karaya and Tragacanth† Food Application

Gum Arabic

Gum Ghatti

Gum Karaya

Gum Tragacanth

Ice cream stabilizer

+

−

+

+

Ice milk

+

−

+

+

Milk shake

−

−

−

+

Sherbet

+

−

+

+

Ice pops and water ices

+

−

+

+

Chocolate milk drink

+

−

−

+

Cooked puddings and custards

−

−

+

−

Neufchatel-type processed cheese

−

−

+

+

Cheese spread

−

−

+

+

Whipped cream

−

−

+

−

Packageable milk or cream

+

−

−

−

Soft drinks with fruit pulp

+

−

−

−

Soft drinks

+

−

−

−

Beer foam stabilizer

+

−

−

−

Fining wines, juices and vinegar

+

−

−

−

Dry beverage mixes

+

−

−

−

Artificially sweetened beverages

+

−

−

−

Bread doughs and mixes

+

−

−

−

Cake batters and mixes

+

−

−

−

Pie filling

−

−

+

−

Doughnut glaze

+

−

−

−

Flat icing

+

−

+

−

Dairy products

Beverages

Bakery products

Role and Sources of Exudate Gums  ◾  3 Table 1.1  (Continued) Food Application

Gum Arabic

Gum Ghatti

Gum Karaya

Gum Tragacanth

French dressing

−

−

+

+

Salad dressing

−

−

+

+

Syrups and toppings

−

+

−

+

Relish

−

−

−

+

White sauces and gravies

−

−

−

+

Catsup

+

−

−

+

Caramels, nougats, taffy

+

−

−

+

Cough drops and lozenges

+

−

−

+

Gum drops, jujubes, pastilles

+

−

+

+

Dietetic syrups

+

+

−

−

Salad dressing

−

−

−

+

Prepared cereals

−

−

+

−

Processed baby food

−

−

+

−

Flavor fixative

+

−

−

−

Frozen foods

+

−

−

−

Dressings and sauces

Confectionary

Dietetic foods

Miscellaneous

†

Adopted in part from Glicksman (1969).

for many non-food-related functions, such as being recognized items of trade in Biblical times. Ancient inscriptions depict the use of gum arabic—called “kami” by the Egyptians, in textile glues, embalming fluids, and dye dispersions (Glicksman, 1969).

1.2 DEFINITIONS Exudates are fluids that ooze out of wounds in injured tress and harden upon exposure to air. This designation includes all types of natural exudates, including many water-insoluble materials such as resins, latex, chicle, etc., which accounts for the erroneous use of the term gum for many of the water-insoluble resins used in the paint and chemical industry today (Glicksman, 1969). Injury can be either a result of tapping (the removal of bark and/or wood to cause exudation) or of accidental or natural causes, such as attack by insects, animals or pathogens, or damage from

4  ◾  Plant Gum Exudates of the World

Figure 1.1  Wattle gum (Acacia pycnantha) from South Australia. Its main uses are medical and veterinary (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 58483).

drought or storms (Boer and Ella, 2000). The role of resinous exudates as a defense mechanism is described in Chapter 2. Gums exhibit great differences in their physical and chemical properties but they are all readily distinguishable from resins, oleoresins, balsams and products of a rubbery nature. Gums are

Figure 1.2  Laddu or Laddoo (Hindi:   ; Urdu: ) is an Indian, Pakistani and Bengali sweet that is often prepared to celebrate festivals or household events such as weddings. It is made of flour and other ingredients formed into balls that are dipped in sugar syrup (adapted with changes from http://commons.wikimedia.org/wiki/Image:Laddu.JPG, courtesy of Belayet Hossain).

Role and Sources of Exudate Gums  ◾  5

miscible in water and insoluble in liquids that dissolve resins, such as benzene, chloroform, ether, turpentine and fixed oils (Howes, 1949). Natural gums are capable of causing a large increase in solution viscosity, often even at low concentrations. In the food industry, they are used as thickening agents, gelling agents, emulsifiers and stabilizers. Examples include: agar (E406), alginic acid (E400), carrageenan (E407), gellan gum (E418), glucomannan (E425), guar gum (E412), gum arabic (E414), gum tragacanth (E413), karaya gum (E416), locust bean gum (E410), sodium alginate (E401), tara gum (E417) and xanthan gum (E415), among others. [The E numbers are codes for food additives and are usually found on food labels throughout the EU. The numbering scheme follows that of the International Numbering System (INS) as determined by the Codex Alimentarius committee. Only a subset of the INS additives are approved for use in the EU, as denoted by the ‘E’ prefix, which stands for Europe (http://en.wikipedia.org/wiki/E_number).] Resin is a solid to soft-semisolid amorphous, fusible, flammable substance obtained as a plant exudate or extract (Boer and Ella, 2000). The Oxford dictionary defines resin as a hydrocarbon secretion of many plants, particularly coniferous trees, valued for its chemical constituents and uses, such as in varnishes and adhesives, as an important source of raw materials for organic synthesis, or in incense and perfume. Fossilized resins are the source of amber. Amber, which is often hundreds of millions of years old, is an ancient sticky tree resin that has hardened and polymerized over the eons (Santiago-Blay and Lambert, 2007). Today, modern tools and tests such as nuclear magnetic resonance (NMR) spectroscopy can be used for sample verification. Since not all amber is the same, NMR catalogs have been created for the many different kinds. Besides helping to discern true from spurious samples, such a library has the added advantage of potentially indicating the kind of tree the amber may have come from, giving us a better idea of the prehistoric landscape (Santiago-Blay and Lambert, 2007). The term resin is not easy to define precisely. Nevertheless, resins do have some common properties. They are insoluble in water but usually dissolve readily in alcohol, ether, carbon bisulfide and certain other solvents (Howes, 1949). Natural resins are of vegetable origin, except Lac and other similar insect exudations. Plant resins are widely distributed in the vegetable kingdom and may be present in almost any organ or tissue of the plant (Howes, 1949). One example is acaroid resin or “gum accroides”, which is the product of several species of Xanthorrhoea endemic to Australia (Fig. 1.3). The term resin is also used for synthetic substances with similar properties. The on-line medical dictionary defines gum resin as the dry exudate from a number of plants, consisting of a mixture of gum and resin, the former soluble in water but not alcohol, the latter soluble in alcohol but not water. Oleoresin is defined as a natural plant product consisting of a viscous mixture of essential oils and non-volatile solids (Boer and Ella, 2000). The copals include a large group of resins that are characterized by their hardness and their relatively high melting point. They are among the best natural resins for use in varnish and paint formulations (Howes, 1949). Copals are derived from a number of different plants, mainly forest trees of the family Leguminosae that occur in various parts of the world (Howes, 1949). The name copal is probably derived from the Nahuatl copalli, meaning “resin.” When hard, copal is lustrous, varying in hue from almost colorless and transparent to a bright yellowish brown. It dissolves in alcohol or other organic solvents upon heating and is used in making varnishes and printing ink (http://www.britannica.com). Zanzibar copal, the principal commercial copal, is the fossil yielded by Hymenaea Verrucosa Gaerth. (syn. Trachylobium verrucosum); it is found embedded in the earth on the western coast of Zanzibar in tracts where not a tree is now visible. South American copals are available from Hymenaea courbaril L. and other species of trees in Brazil, Colombia, and other South American countries (http://www.britannica.com/). Kino (also keenow) gum is defined as a gum obtained from various tropical plants, and used as an astringent and in tanning. East Indian and Malabar kino are a reddish or black juice or resin from certain trees of the genus Pterocarpus and are used in medicine and tanning (Howes, 1949). Another definition of kino is any of several dark red to black tannin-containing dried juices or

6  ◾  Plant Gum Exudates of the World

Figure 1.3  An Australian resin derived from the species Xanthorrhoea preissii Endl. Its common names are: black boy and gum accroides (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 36427).

extracts obtained from various tropical trees—especially the dried juice usually obtained from the trunk of an Indian and Sri Lankan tree (Pterocarpus marsupium) as brown or black fragments and used as an astringent in diarrhea; or it is a tree that produces kino (especially P. marsupium) (http://www.britannica.com). One example of kino is produced from Butea monosperma, which is a medium-size deciduous tree with a crooked trunk that is up to 5 m in length by 60 cm in diameter, native of India, Burma and Ceylon and introduced into a few tropical countries as an ornamental, for example, Nigeria. The very light wood is white or yellowish-brown. The common names of the tree and gum are flame of the forest and Bengal kino, respectively (Fig. 1.4). Natural rubber latex comes from a liquid in tropical rubber trees (Fig. 1.5). Sapodilla (Manilkara zapota) is a long-living, evergreen tree native to the New World tropics. It is a native of Mexico and was introduced to the Philippines during the Spanish colonization. Sapodilla grows to 30 or 40 m in height. It is wind-resistant and the bark is rich in a white, gummy latex (Fig. 1.6). This liquid is processed to make many of the following rubber products, used at home and at work: balloons, rubber toys, pacifiers and baby-bottle nipples, rubber bands, adhesive tape and bandages, diapers and sanitary pads, condoms. In addition, many medical and dental supplies contain the protein latex, including gloves, urinary catheters, dental dams and material used to fill root canals, as well as tourniquets and equipment for resuscitation. Non-latex substitutes can be found for all of these latex-containing items, because this protein can cause an allergic reaction in some people. The thin, stretchy latex rubber in gloves, condoms and balloons are high in this protein. It causes more allergic reactions than products made of hard rubber (such as tires). Moreover, because some latex gloves are coated with cornstarch powder, the latex particles stick to the cornstarch and fly into the air when the gloves are taken off. In places where gloves are being put on and removed frequently, the air may contain many latex particles.

Role and Sources of Exudate Gums  ◾  7

Figure 1.4  Bengal kino of Butea monosperma (Lam.) Taub. [family Leguminosae Papilionoideae] (mag. 1.7X; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 58424).

Figure 1.5  The extraction of latex from a tree (http://en.wikipedia.org/wiki/File:Latexproduction.jpg; photo by Jan-Pieter Nap).

8  ◾  Plant Gum Exudates of the World

Figure 1.6  Air-dried latex of the sapodilla tree Manilkara zapota from the Dominican Republic (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 50872).

1.3 GUM YIELDS Many plants exude viscous, gummy liquids. Healthy Acacia tress grown under favorable climatic and soil conditions produce little or no gum. However, trees grown under adverse conditions of excessive heat, scarcity of moisture and high elevation, produce sizeable quantities of gum arabic (Fig. 1.7). The physiological aspects of polysaccharide formation in plant exudates are discussed in Chapter 2. Yields can also be increased by deliberately stripping away the bark or injuring the tree (Glicksman, 1969). It is not surprising that many studies have been aimed at examining parameters that influence yield and determining what causes plants to produce more or less exudates. A comparative study of gum arabic yield trends and peaks per tree in relation to stand management (by farmers and by researchers) and type (natural and planted) was conducted at two locations in North Kordofan, Sudan, over a 3-year period (Ballal et al., 2005a). In addition, 8-year yield trends in relation to rainfall were compared based on the 1993-2000 gum yield data from 1,440 trees. Although the gum arabic yield followed the same trend over time in all stands at both locations, the gum yield from farm stands, whether planted or natural, was 47 to 60% lower than that from research stands. Late tapping reduced the gum yield by 40 and 50% at the two different locations, respectively. Yield was highly affected by rainfall, correlating positively with annual rainfall in 6 of the 8 years of the study (Ballal et al., 2005a). It was concluded that the findings of this study should be used to improve gum arabic yield through management intervention and to predict yield in relation to stand type, management regime and rainfall. The causes of variability in gum arabic yield (from Acacia senegal) and yield trends as a basis for yield control, prediction and stability were also evaluated at an experimental site in Demokeya, Western Sudan. The effects on gum arabic yield of date and intensity of tapping, rainfall, and the

Role and Sources of Exudate Gums  ◾  9

Figure 1.7  ‘Tear drops’ of gum arabic, the dried, gummy exudate obtained from acacia trees.

minimum and maximum temperatures at tapping and gum collection were examined from 1992 to 2000 in a 12-year-old plantation (Ballal et al., 2005b). Tapping dates were found to produce roughly similar gum-production patterns across years. Yield was found to be positively correlated with tapping intensity, rainfall and the minimum and maximum temperatures at tapping time, and negatively correlated with tapping time and the minimum and maximum temperatures at gum collection (Ballal et al., 2005b). The time of tapping, tapping intensity, rainfall and maximum temperature at gum collection were found to explain 85% of the total variability in gum yield per unit area. Such studies can be helpful in understanding the causes of yield variability in gum arabic. Results can also help predict, to a certain extent, future gum yield (Ballal et al., 2005b). The question of whether inoculating mature A. senegal trees with Rhizobium has an effect on the yield of gum arabic is discussed in Chapter 2.

1.4 AGRICULTURAL ISSUES Agroforestry is an approach to land use based on the planned integration of trees with crop and/or livestock production systems (Fig. 1.8) (Young, 1989; Kang et al., 1999). It is an ancient practice, which has nevertheless benefited from methodical research and experimentation since the 1970s (ICRAF, 1997). Agroforestry can be productive, and more profitable and sustainable than other land-use systems (Kang et al., 1985; Nair, 1993), and it has the potential to offer rural households a large variety of products for trade and household use. Researchers and farmers throughout sub-Saharan Africa have developed new agroforestry practices (Franzel et al., 2001). Agroforestry manufacturing systems provide a large number of products and benefits (Huang and Xu, 1999). The net production of phytomass can be increased by the well-organized sharing of site resources among trees and other intercropping components, together with nitrogen fixation and microclimate modification (Sharrow and Ismail, 2004). About 40 years ago, a plantation of A. senegal

10  ◾  Plant Gum Exudates of the World

Figure 1.8  Maize crops growing together with Faidherbia albida (Acacia albida Delile) and palms (http://en.wikipedia.org/wiki/Image:Faidherbia_albida.JPG, photo by Marco Schmidt).

was reported to increase total nitrogen and organic carbon while having no effect on the texture, pH, available phosphorus or available potassium of a sand sheet soil. The higher nitrogen content in the topsoil may have been partially due to symbiotic fixation (Gerakis and Tsangarakis, 1970). Agroforestry can also potentially advance the water-use efficiency of systems by minimizing the non-productive part of the available soil water (Ong et al., 2002). In other words, agroforestry systems can considerably increase rainfall utilization as compared to annual cropping systems (Ong et al., 2002). Plant growth is dependent on the availability of light, water and nutrients, and manipulation of tree density in agroforestry systems can therefore modify the biomass production of component species (Eastham et al., 1990). Benefits in terms of biomass and grain yields can be expected if there is complementary resource sharing by agricultural crops and trees (Cannell et al., 1996). Tree density has a strong effect on the distribution and depth of the stand’s roots (Boswell et al., 1975). Agroforestry systems have been recognized as a tool for rehabilitating already degraded lands (Bandolin and Fisher, 1991). No less important is the fact that trees improve crop productivity by reducing wind flow, thereby reducing water loss through transpiration (Zinkhan and Mercer, 1996). Much work has already been done on studying tree-crop interactions under various tree-spacing regimes to improve the productivity of agroforestry systems (Gupta et al., 1998). The most important forest in the Sudan may be the gum arabic belt. The “belt” refers to a zone of approx. 520,000 km2 that expands across Central Sudan between latitudes 10° and 14° N, accounting for one-fifth of the country’s total area (IIED and IES, 1990). The belt accommodates ~20% of Sudan’s population and 66% of its livestock. It acts as a natural barrier, protecting over 40% of the total area of Sudan from desert encroachment, and it represents the site for most of the agriculture and animal production. This includes irrigated, mechanized rain-fed, and traditional rain-fed agriculture and forestry (Ballal, 2002). Until recently, the traditional A. senegal-based

Role and Sources of Exudate Gums  ◾  11

agroforestry system was considered one of the most successful forms of natural forest management in tropical drylands (Fries, 1990), and was regarded as sustainable in terms of its environmental, social and economic benefits (Ballal, 1991). Traditionally, the A. senegal tree is managed in temporal succession with agricultural crops such as sorghum, pearl millet, groundnut, sesame and karkadeh (Hibiscus sabdariffa L.). This agroforestry system allows a period of 10 to 15 years for reestablishment of the soil’s fertility after a short period of arable cultivation (Ballal, 2002). The cycle thus consists of a relatively short period of cultivation followed by a relatively long fallow period. The bush fallow sequence begins by clearing a 15- to 20-year-old gum garden for the cultivation of field crops. Trees are cut at 10 cm from the soil surface, and stumps are left to start vigorous coppice regrowth. The cleared area is cultivated for a period of 4 to 6 years, during which time the coppice shoot regrowth is removed to improve the establishment and growth of agricultural crops. However when the soil fertility declines, as reflected by low crop yield, crop growing ceases and the area is left fallow under A. senegal. The remaining trees are tapped for gum arabic until the age of 15 to 20 years, after which they are cleared again for crop cultivation. Therefore, the final tree stand is mainly the result of coppice regeneration, as well as some regeneration from seeds dispersed naturally or sometimes on purpose for enrichment planting (Ballal, 2002). The bush-fallow system of cultivation has proven to be a successful, sustainable farming system, particularly on the marginal lands of Kordofan. A. senegal supports the local population’s livelihood, since its gum represents a major cash crop, and in addition, fuel wood is obtained from this tree for household use and for sale (Sharawi, 1986). As an outcome of the development of a vegetable oil industry in North Kordofan in the 1940s, which strengthened the production of groundnut and sesame, there was a favorable response in terms of prices and productivity to oil seeds. However, this development occurred at the expense of the gum orchards, and the traditional rotational fallow-cultivation cycle was dramatically shortened or completely abandoned (Awouda, 1973). Consequently, the negative impact on soil and water has been considerable, to the extent that commercial agriculture is also beginning to face some problems (Ballal, 2002). Indications of system imbalance were noted decades ago and today, the area is experiencing a serious decline in fertility, as well as soil erosion and desertification. Moreover, sustainable management of the gum gardens is threatened because of severe droughts and indiscriminate clearing of A. senegal stands for firewood and charcoal production as a shortterm source of income (Elfadl et al., 1998). This has resulted in more degraded land. Accordingly, the removal of A. senegal trees and a general deterioration of the stands have resulted in a reduction in gum arabic production, by 30 to 70% between 1973 and 1984 (Bayoumi, 1996). The spread of desert-like conditions has also resulted from both physical conditions and misuse of resources (Ahlcrona, 1983; Suliman and Drag, 1983). A study of the recovery of biomass productivity in North Kordofan concluded that land degradation and the ecological imbalance associated with drought cycles and mismanagement could be reversed, if rational management practices were applied in accordance with water availability from rainfall (Yagoub et al., 1993). A. senegal is the most important component of traditional dryland agroforestry systems in the Sudan. The spatial arrangement of trees and the type of agricultural crop used influence the interaction between them (Raddad et al., 2006). The influence of different A. senegal agroforestry systems on soil water and crop yields in clay soils of the Blue Nile region in Sudan was studied (Raddade and Luukkanen, 2007). Trees were grown at 5 x 5 m or 10 x 10 m spacing, either alone or in a mixture with sorghum or sesame. Results demonstrated no significant variation in the soil water content under different agroforestry systems. Intercropping also resulted in a higher land equivalent ratio. No significant variation was found in the yields of sorghum or sesame when these crops were grown with or without trees. At an early stage of agroforestry system management,

12  ◾  Plant Gum Exudates of the World

A. senegal has no detrimental effect on agricultural crop yield. However, the pattern of resource capture by trees and crops can change as the system matures. There was little competition between trees and crops for water, suggesting that in A. senegal agroforestry systems with 4-year-old trees, the clay soil has enough water to support crop growth over a whole growing season up to maturation and harvest (Raddade and Luukkanen, 2007). In conclusion, policy has a potential role in influencing the poverty and land-degradation problems facing Africa. Both ‘good’ and ‘bad’ policies can affect the economic incentives determining poor rural households’ decisions to conserve or degrade their land (Barbier, 2000). Many plant gum exudates are known worldwide. Four of them (arabic, ghatti, karaya and tragacanth) are of importance to the food industry (Glicksman, 1969). Many other gums, which are listed and described in Chapters 3 and 4, are known and used in their local areas of availability. Sometimes these gums can serve as substitutes for others, especially if they have similar properties. In the search for gum arabic substitutes, natural gum exudations in seven South American species of Prosopis and the productivity of induced gum exudation were evaluated (Vilela and Ravetta, 2005). Prosopis is a genus of about 45 species of leguminous spiny trees and shrubs, located in subtropical and tropical regions of the Americas, Africa and southwest Asia. They often thrive in dry soil and are resistant to drought, sometimes developing extremely deep root systems. Their wood is usually hard, dense and durable. Their fruits (pods) may contain large amounts of sugar. Natural exudates were found in three species: P. flexuosa, P. chilensis and P. nigra. In the latter two, exudates were dark, liquid and bitter, while in P. flexuosa, up to 1.6 kg per tree of amber-clear gum was harvested (Vilela and Ravetta, 2005). High-productive trees were old, with very little vegetative growth, and were growing on sandy soils. To induce gum exudation, trees were wounded, and these wounds exuded plentifully for 7 months. Exudation increased during late summer and fall, after the fruits had ripened (Vilela and Ravetta, 2005).

1.5 PHYSICAL PROPERTIES OF GUMS The physical properties and appearance of natural gums are of greatest significance in determining their marketability and end use. These differ with different botanical sources. There is a considerable dissimilarity in gums from the same species collected from plants grown under different climatic conditions or even from the same plant in different seasons. Physical properties are also affected by the age of the exudate, and treatment of the gum after collection by, for example, washing, drying, sun-bleaching and storage temperatures (Glicksman, 1969).

1.5.1 Color Color is a perceptual phenomenon that depends on the observer and on the conditions under which it is observed. It is a characteristic of light, which is measurable in terms of intensity and wavelength. A material’s color only becomes visible when light from a luminous object or source illuminates or strikes the surface (Sahin and Sumnu, 2006). Color is of great importance in the commercial valuation of gums, with light-colored gums being preferred. More than 80 years ago, the claim was made that there are no completely colorless gums, but this is still open to question (Wiesner, 1927): for example, the color of the finest gum arabic in the Sudan has been described as colorless (Blunt, 1926). Commercial grades of A. senegal from Sudan include the best grade, i.e. the hand-picked, selected, cleanest and largest pieces, with the lightest color. The second-best grade includes that which remains after the hand-picked material and siftings have been removed. This grade comprises

Role and Sources of Exudate Gums  ◾  13

whole and broken lumps with a pale to dark amber color. The standard grade has a light to dark amber color (Islam et al., 1997). Another example of higher gum grades can be found with commercial gum karaya which contains less foreign matter and has a lighter color than the non-commercial gum (FAO, 1995). Gum colors depend on the plant species, climate and soil. In its solid state, gum colors vary from almost transparent white through various shades of yellow, amber and orange to dark brown. Certain gums possess a pink, red or greenish hue. Color is primarily due to the presence of impurities: it often only appears as the gum ages on the tree and may be due to substances that have washed onto the gum. There is no doubt that old trees give off a dark gum. In addition, scorching from bush or grass fires darkens gums, and tannin from the sap or tissues of the parent plant is also believed to account for some of the very dark gums yielded by certain trees (Howes, 1949).

1.5.2 Size and shape As seen or collected under natural conditions, gums are represented by a variety of shapes and forms (Howes, 1949). The fragments are generally irregularly round, drop- or pear-shaped, as is well-illustrated in the variety of commercial grades of gum arabic. Some gums are characterized by stalactitic shapes. Following collection and possible fracturing, irregular rod-shaped segments can appear, as demonstrated by cashew gum (Howes, 1949). Gum tragacanth’s name is derived from the two Greek words tragos (goat) and akantha (horn) and probably refers to the curved shape of the ribbons in the best grade of the commercial gum (Verbeken et al., 2003). The surface of most gums is perfectly smooth when fresh, but may quickly become rough or covered with minute cracks due to weathering (Howes, 1949). These fissures are not restricted to the surface, and therefore in some gums might serve to break a tear into smaller fragments. After collection, the gum is cleaned and graded. This is traditionally done by manual sorting according to the size of the lumps (FAO, 1995). The gum can be further processed into kibbled and powdered forms. Kibbling is a mechanical process which breaks up large lumps into smaller granules with a more uniform size distribution and facilitates dissolution of the gum in water. Better solubility can be obtained with powdered gum, which is usually produced by dissolving the gum in water, removing impurities and spray-drying (Verbeken et al., 2003). It is possible to specify the size of regular gum lumps, but for irregular pieces, the term size must be arbitrarily specified (McCabe et al., 1993). Size can be determined using the projected-area method: the longest dimension of the maximum projected area, the minimum diameter of the maximum projected area diameter and the shortest dimension of the minimum projected area are defined (Sahin and Sumnu, 2006). Shape can be expressed in terms of sphericity and aspect ratio. Sphericity is the volumetric ratio of the solid to a sphere that has a diameter equal to the major diameter of the object such that it can circumscribe the solid sample (Mohsenin, 1970). Sphericity was first defined ~70 years ago (Wadell, 1935). The sphericity, Ψ, of a particle is the ratio of the surface area of a sphere (with the same volume as the given particle) to the surface area of the particle:

Ψ = π 1/3 (6 Vp 2/3) / Ap

where Vp is the particle volume and Ap is its surface area. Sphericity has also been defined differently by other researchers (McCabe et al., 1993; Bayram, 2005). The aspect ratio is calculated using the length and width of a sample. It may be applied to two characteristic dimensions of a three-dimensional shape, such as the ratio of the longest to shortest axis, or for symmetrical objects that are described by just two measurements, such as the length and diameter of a rod (Maduako and Faborode, 1990). Such definitions should be entered into the shape field of the classification of collected exudates in order to render it less descriptive, and more scientific.

14  ◾  Plant Gum Exudates of the World

1.5.3 Taste and smell True gums are generally odorless, or nearly so (Howes, 1949). In contrast, resins and oleoresins have distinctive odors. For example, the gum resin opoponax is obtained by wounding the roots of opopanax chironium (L.) W.D.J. Koch (syn. Pastinaca opoponax), a native plant of the countries surrounding the Levant. It occurs in lumps that are reddish-yellow on the surface, but white within. It has a bitter and acrid taste, and a peculiar smell. Due to its exotic aroma, opoponax has long been used in perfumery. Its aroma has also been described as smooth and sweet, like a bit of toffee mixed with subtle myrrh (http://www.somaluna.com/prod/opoponax.asp). Another example is myrrh, which forms as reddish-yellow tears. It has a peculiar smell, and an aromatic bitter taste. In water, it forms a yellow opaque solution. It becomes opaque in an alcoholic solution when water is added, but there is no precipitate (Bache, 1819). In order to experience plant odors, a courtyard of senses was created in 1999 in the Montreal Botanical Garden, designed to give its visitors a whole new way of “seeing” the plant world. In the last area of the garden, one finds the common gums cistus, which is covered in a resinous secretion that sticks to the fingers, perovskia, which has a penetrating fragrance that takes the visitor by surprise if the leaves are rubbed, and the blue gum tree, which has a strong medicinal camphor smell (Turcotte, 2006). Gum resins (Fig. 1.9) denote a class of vegetable substances which are regarded by chemists as consisting of gum and resin. They are generally contained in the vessels of the plant, i.e. the root, stem, branch, leaves, flowers, or fruit. Gum resins, in their solid state, are brittle, and they generally have a strong smell, which is sometimes bitter and nauseating (Claudius, 1825). Gums may be tasteless or generally devoid of any characteristic taste (Howes, 1949). Another older reference also suggests that gum has no particular smell or taste (Lewis, 1791). Nevertheless there is evidence that some gums are slightly sweet or bitter according to their botanical origins. Some gums

Figure 1.9  Gum resin of the beef-wood tree (Grevillea striata R.Br.) collected in 1887 from New South Wales, Australia (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 44995).

Role and Sources of Exudate Gums  ◾  15

have a distinctly bitter, lingering aftertaste, and this should of course be considered when gums are used for foods (Howes, 1949).

1.5.4 Hardness and density The term hardness is widely used. Engineers and metallurgists perform hardness tests to assess the mechanical properties of metals and other engineering materials (Mohsenin, 1970). Most experts agree that hardness, as used in metals, means resistance to permanent deformation associated primarily with their plastic properties and only secondarily with their elastic properties (Mohsenin, 1970). Hardness can be measured on the Mohs scale or various other scales, and some of these, which are used for indentation hardness in engineering—Rockwell, Vickers, and Brinell—can be compared using practical conversion tables (Malzbender, 2003). The Mohs scale of mineral hardness, created in 1812 by the German mineralogist Friedrich Mohs, characterizes the resistance to scratching of various minerals based on the ability of a harder material to scratch a softer one. Attempts to classify gum hardness as with minerals in order to use hardness as a diagnostic character for gum identification have not proven at all satisfactory (Howes, 1949). Among many other things, hardness in gums depends on moisture content, which in general ranges between 12 and 16% (Howes, 1949). For example, the moisture content of the gum obtained from A. senegal ranges from 12.5 to 16.0% (Idris et al. 1998). Analytical data for exudates from the Turkish Astragalus species (Anderson and Bridgeman, 1985) demonstrate a loss upon drying of 12.7% and 9.9% weight for A. microcephalus (Fig. 1.10) and A. gummifer, respectively (Anderson and Bridgeman, 1985). Density also proves unpredictable, even in the same gum, as it depends in part on the quantity of air that may have been introduced during its formation.

Figure 1.10  A gum from Astragalus microcephalus Willd. The gum was collected in Lycia (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 60009).

16  ◾  Plant Gum Exudates of the World

1.5.5 Polarization Optical rotation or activity defines the rotation of linearly polarized light as it travels through certain materials: these can be solutions of chiral molecules, e.g. sucrose (sugar), solids with rotated crystal planes such as quartz, and spin-polarized gases of atoms or molecules. Polarization is used to measure syrup concentration, in optics to manipulate polarization, in chemistry to characterize substances in solution, and it is being developed as a method to measure blood sugar concentration in diabetics (http:// en.wikipedia.org/wiki/Optical_rotation). In aqueous solutions, gums are either levorotatory or dextrorotatory. For example, eight gum specimens from Pereskia guamacho (Cactaceae) are dextrorotatory acidic arabinogalactans and give very clear solutions of moderate viscosity (De Pinto et al., 1994). The gum from Hymenaea courbaril (Caesalpiniaceae) is soluble in water, dextrorotatory and less viscous than the gum from Cyamopsis tetragonolobus (guar gum) (Omaira et al., 2007). Samanea saman (Fig. 1.11) and Pithecellobium mangense exude clear yellow gums, both dextrorotatory (De Pinto et al., 1995). Venezuelan gum exudates from nine specimens of Parkinsonia praecox (Leguminosae) were examined. The samples, which were highly soluble in water and levorotatory, had viscosities comparable to that of gum arabic (from A. senegal) (De Pinto et al., 1993). The sugar composition and amino acid content of a gum solution influences whether gums are levorotatory or dextrorotatory. In Acacia seyal and A. senegal gums, the sugar composition and amino acids are identical but are present in different proportions, which is the main reason why A. seyal is dextrorotatory and A. senegal is levorotatory (Flindt et al., 2005).

1.5.6 Solubility A gum’s solubility may be influenced by age and the length of time it has been attached to the tree. Most gums yield a certain amount of insoluble residue when mixed with water and in general,

Figure 1.11  An exudate from Samanea saman (Jacq.) Benth. (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 59137).

Role and Sources of Exudate Gums  ◾  17

there is more of this residue with the dark-colored gums than with the pale or light-colored gums (Howes, 1949). For example, native gum karaya is insoluble and only swells in water, due to the presence of acetyl groups (Imeson, 1992). Based on their solubility in water, three fractions were distinguished in gum karaya (Le Cerf et al., 1990). Only 10% of the native gum solubilizes in cold water, but this fraction increases to 30% in hot water. After deacetylation, 90% of the native gum dissolves in water. Only lower-molecular-weight molecules are able to dissolve in cold water, while deacetylation leads to the solubilization of higher-molecular-weight material (Le Cerf et al., 1990). Better solubility can be achieved by breaking large lumps into smaller more uniform granules, and solubility can be further enhanced using spray-dried gum powder (Verbeken et al., 2003). Many macromolecules are made up of a hydrophobic portion that creates an “inside”, consisting of segments not in contact with the solvent, and an “outside”, consisting of the more hydrophilic groups that are in contact with the water (Whistler, 1973). Some electrolytes are able to stabilize macromolecular conformations in aqueous solutions (Whistler, 1973). The free energies of the macromolecule states are the sum of the individual group-solvent and group-group interactions. A change of a kilocalorie or less per mole in one of the stabilizing interactions engaged in maintaining the delicate balance is sufficient to generate a cooperative transition to a different conformation (Whistler, 1973).

1.5.7 Viscosity and mouthfeel “Viscosity” (or “absolute viscosity”) is frequently referred to as dynamic viscosity. It is the internal friction of a liquid or its tendency to resist flow (Bourne, 1982). In colloidal suspensions, viscosity is increased by the thickening of the liquid phase due to liquid absorption and resultant swelling of the dispersed colloid (Glicksman, 1969). This in turn, is accountable for functional effects such as suspension of solid particles, emulsification of oil and water phases, stabilization of liquid-solid-gas phases, and related phenomena (Glicksman, 1969). Selection of the proper hydrocolloid is crucial for an operation’s success and for the food system’s shelf stability. The viscosity of the hydrocolloid system depends on 10 factors: concentration, temperature, degree of dispersion, solvation, electrical charge, previous thermal treatment, previous mechanical treatment, presence or absence of other lyophilic colloids, age of the lyophilic sol and presence of both electrolytes and non-electrolytes (Ostwald, 1922). These factors are considered “the ten commandments of food preparation” (Lowe, 1955). Upon arrival in the importing country, the gum exudate is usually ground to a powder, with particle size varying according to the desired viscosity. Although gum arabic is highly branched, it has a compact structure (Nussinovitch, 1997). Gum arabic solutions are distinguished by their low viscosity (Table 1.2), enabling the use of high gum concentrations in various applications (Dziezak, 1991; Imeson, 1992). Solutions display Newtonian behavior at concentrations of up to 40% and become pseudoplastic at higher concentrations. Above ~30%, the hydrated molecules effectively overlap and steric interactions result in much higher solution viscosities and increasing pseudoplastic behavior (Nussinovitch, 1997). The pH of the solution is usually around 4.5 to 5.5, but maximal viscosity is found at pH 6.0 (extension of the molecule). At still higher pH, ionic strength of the solution increases until the repulsive electrostatic charges are masked, yielding a compact conformation with lower viscosity (Anderson et al., 1990; Williams et al., 1990a; Imeson, 1992). Due to gum arabic’s high water solubility, low viscosity, and emulsification properties, it is used in soups and dessert mixes (Glicksman and Farkas, 1975). The best gum tragacanth quality consists of high viscosity, good solution color and low microbial count (Nussinovitch, 1997). The viscosity of gum karaya dispersions depends on their grade (Weiping, 2000), and storage of the dry gum results in loss of viscosity (Dziezak, 1991). The viscosity of a 1% solution of gum karaya at

18  ◾  Plant Gum Exudates of the World Table 1.2  Effect of Concentration on Viscosities (cps) of Gum Exudates†‡ Exudate %

Gum Arabic

Gum Ghatti

0.5

‡

Gum Tragacanth

400

−

1.0

−

2

3,300

54

1.5

−

−

−

−

2.0

−

35

−

906

2.5

−

−

−

−

3.0

−

−

−

10,605

3.5

−

−

−

−

4.0

−

−

−

44,275

288

−

111,000

5.0

†

Gum Karaya

7.3

6.0

−

−

−

183,500

7.5

−

1,012

−

−

10.0

16.5

2,444

−

−

20.0

40.5

−

−

−

30.0

200.0

−

−

−

35.0

423.8

−

−

−

40.0

936.3

−

−

−

50.0

4162.5

−

−

−

Measured with a Brookfield Synchro-Lectric viscometer at 25°C. Results for gum arabic, karaya and tragacanth were adopted from Whistler (1973); and for gum karaya from Glicksman (1969) and Davidson (1980).

normal pH is approximately 3,300 cps (Table 1.2). Maximal viscosity is achieved at pH 8.5 (Meer Corporation, 1958). Boiling of the dispersion results in a permanently reduced viscosity (Whistler, 1973). Heating, predominantly via pressure, gives smooth, uniform, semi-transparent, colloidal dispersions, with concentrations as high as 20 to 25% being achievable in this method relative to the 3 or 4% maximal concentration obtained by non-heated water hydration (Glicksman, 1969). The viscosity of a 1% solution of the highest grade of gum tragacanth is ~3,400 cps. In cold preparations, the maximum viscosity is usually reached after 24 h, but this can be obtained in ~2 h by raising the temperature of the solution to ~50°C (Glicksman, 1969). Viscosity of food products is not necessarily correlated with their mouthfeel. For example, beverages of identical viscosity can be either slimy and coat the mouth or smooth and pleasant (Glicksman, 1969). A correlation between the organoleptic characteristics of hydrocolloid solutions and their rheological behavior has been established (Szczesniak and Farkas, 1962).

Role and Sources of Exudate Gums  ◾  19

Measurements of solution viscosities at various rates of shear showed a relationship between the shape of the curve and the degree of sliminess. This was confirmed in a work on gum-thickened sucrose solutions (Stone and Oliver, 1966). Various hydrocolloid solutions were grouped into three categories: slimy (pectin, methyl cellulose, carboxymethyl cellulose, sodium alginate, locust bean gum), slightly slimy (carrageenan, guar gum and the gum exudates karaya and tragacanth), and non-slimy (starch). This method makes it possible to select the best gums for a desired mouthfeel or texture.

1.6 CHEMICAL PROPERTIES Gums are composed of carbon, hydrogen, oxygen, small quantities of mineral matter and sometimes a little nitrogen (Howes, 1949). The pure gum may also contain small quantities of tannin. The chemical composition of the three main exudate gums is complex and varies to some extent, depending on their source and age. Therefore, it is not possible to provide defined structural formulas for these biopolymers (Verbeken et al., 2003). The chemical structures of gum arabic, gum tragacanth, gum karaya and gum ghatti are described in Chapter 3 and the structures of less known exudates are discussed, where information is available, in Chapter 4.

1.7 COMMERCIAL ASSESSMENTS OF GUMS Climatic and political constraints influence the production and provision of gums. Sudan dominates the production and trade of gum arabic, accounting for 80 to 90% of the world market (Chikamai et al., 1996). Nigeria is the world’s second largest producer and exporter of gum arabic. In recent years, production is Sudan has been estimated at ~40,000 to 50,000 ton/year (Williams et al., 1990b; Williams and Phillips, 2000). Today, prices are at about US $1,500/ton. Europe is the biggest importer of gum arabic, and the US is its second largest market. India is the largest producer and exporter of gum karaya. From the end of the 1960s to the mid-1980s, their annual export averaged 4,000 to 6,000 ton (FAO, 1995). Senegal is the biggest African producer of this gum and exports around 1,000 ton annually. Sudan exports only small amounts of gum karaya. Europe is the largest importer of gum karaya. The price of Indian gum karaya varies between US $2,250/ton and US $6,000/ton, depending on the grade. The world’s largest producer of gum tragacanth is Iran (Anderson and Grant, 1988). At present, the world market for gum tragacanth is estimated to be no more than 500 ton/year (FAO, 1995). The price of ribbons is US $3,000 to 4,000/ton for the lowest grade and up to US $22,000/ton for the highest grade.

1.8 INDUSTRIAL AND OTHER USES Exudate gums are among the oldest natural gums. About 5,000 years ago, they were already being used as thickening and stabilizing agents. The three major exudate gums are gum arabic, gum tragacanth, and gum karaya (Verbeken et al., 2003). They possess a unique range of functionalities (Phillips and Williams, 2001; and see Table 1.1 and Chapter 5). Exudate gums have been important items of international trade in the food, pharmaceutical, adhesive, paper, textile, and other industries for centuries. These are reviewed in Chapters 6, 7 and 9.

20  ◾  Plant Gum Exudates of the World

References Anderson, D. M. W., Douglas, D. M., Morrison, N. A. et al. 1990. Specifications for gum Arabic (Acacia Senegal): analytical data for samples collected between 1904 and 1989. Food Additives and Contaminants A 7:303-21. Anderson, D. M. W., and M. M. E. Bridgeman. 1985. The composition of the proteinaceous polysaccharides exuded by Astragalus microcephalus, A. gummifer and A. kurdicus—the sources of Turkish gum tragacanth. Phytochemistry 24:2301-4. Anderson, D. M. W., and D. A. D. Grant. 1988. The chemical characterization of some Astragalus gum exudates. Food Hydrocolloids 2:417-23. Awouda, H. M. 1973. Social and economic problems of the gum arabic industry. A thesis submitted for the degree of Bachelor of Letters, Oxford University. Ahlcrona, E. 1983. The impact of climate and man on land transformation in Central Sudan: Application of remote sensing. Lund, Sweden: Lund University Press. Ballal, M. E. 1991. Acacia senegal: A multi-purpose tree species for the arid and semi-arid tropics. M.Sc. thesis, University of Wales, UK. Ballal, M. E. 2002. Yield trends of gum Arabic from Acacia senegal as related to some environmental and managerial factors. PhD thesis, University of Khartoum. Ballal, M. E., El Siddig, E. A., Efadl M. A., and O. Luukkanen. 2005a. Gum arabic yield in differently managed Acacia senegal stands in western Sudan. Agroforestry Syst. 63:237-45. Ballal M. E., El Siddig, E. A., Elfadl, M. A., and O. Luukkanen. 2005b. Relationship between environmental factors, tapping dates, tapping intensity and gum arabic yield of an Acacia senegal plantation in western Sudan. J. Arid Environ. 63:379-89. Bandolin, T. H., and R. F. Fisher. 1991. Agroforestry systems in North America. Agroforestry Syst. 16:95-118. Barbier, E. B. 2000. The economic linkages between rural poverty and land degradation: Some evidence from Africa. Agri. Ecosyst. Environ. 82:355-70. Bayoumi, A. M. S. 1996. General protection of forests—Arabic version. Sudan: Khartoum University Press. Bayram, M. 2005. Determination of the sphericity of granular food materials. J. Food Eng. 68:385-90. Blunt, H. S. 1926. Gum Arabic, with special reference to its production in the Sudan. London: Oxford University Press. Boer, E., and A. B. Ella. 2000. Plant resources of South-East Asia No. 18: Plants producing exudates. Leiden: Backhuys Publishers. Boswell, S. B., McCarty, C. D., Hench, K. W., and L. N. Lewis. 1975. Effect of tree density on the first ten years of growth and production of Washington Navel orange trees. J. Am. Soc. Hort. Sci. 100:370-3. Bourne, M. C. 1982. Food texture and viscosity. New York: Academic Press. Cannell, J., Jackson, R. B., Ehleringer, J. R., Mooney, H. A., Sala, O. E., and E. D. Schulze. 1996. Maximum rooting depth of vegetation types at the global scale. Oecologia 108:583-95. Chikamai, B. N., Banks, W. B., Anderson, D. M. W., and W. Weiping. 1996. Processing of gum arabic and some new opportunities. Food Hydrocolloids 10:309-16. Claudius, J. L. 1825. An encyclopedia of agriculture. London: Longman, Hurst, Rees, Orme, Brown, and Green. Davidson, R. L. 1980. Handbook of water-soluble gums and resins. New York: McGraw-Hill Book Company. De Pinto, G. L., Demoncada, N. P., Martinez, M., Degotera, O. G., Rivas, C., and E. Ocando. 1994. Composition of Pereskia-Guamacho gum exudates. Biochem. Systematics Ecol. 22:291-5. De Pinto, G., Martinez, M., De Gutierrez, G. O., Vera, A., Rivas, C., and E. Ocando. 1995. Comparison of two Pithecellobium gum exudates. Biochem. Systematics Ecol. 23:849-53. De Pinto, G., Rodriguez, O., Martinez, M., and C. Rivas. 1993. Composition of Cercidium-Praecox gum exudates. Biochem. Systematics Ecol. 21:297-300. Dziezak, J. D. 1991. A focus on gums. Food Technol. 45:116-32. Eastham, J., Rose, C. W., Charles, E. D., Cameron, D. M., and P. Berliner. 1990. Planting density effect on water use efficiency of trees and pasture in an agroforestry experiment. New Zealand J. Forestry Sci. 20:39-53. Elfadl, M. A., Luukkanen, O., and V. Kaarakka. 1998. Environmental conservation and economic development in the Sudan: A case study of gum arabic. Conference paper presented for Finnish Society for Development Studies. Helsinki (unpublished).

Role and Sources of Exudate Gums  ◾  21 FAO. 1995. Gums, resins and latexes of plant origin (Non-wood forest products 6). Rome: FAO. Flindt, C., Al-Assaf, S., Phillips, G. O., and P. A. Williams. 2005. Studies on acacia exudate gums. Part V. Structural features of Acacia seyal. Food Hydrocolloids 19:687-701. Bache, F. 1819. System of chemistry for the use of students of medicine. Philadelphia: William Fry, Printer. Franzel, S., Coe, R., Cooper, P., Place, F., and S. J. Scherr. 2001. Assessing the adoption potential of agroforestry practices in sub-Saharan Africa. Agri. Syst. 69:37-62. Fries, J. 1990. Management of natural forests in the semi-arid areas of Africa: Present knowledge and research needs. Uppsala: IRDC, Swed. Univ. Agric. Sci. Gerakis, P. A., and C. Z. Tsangarakis. 1970. The influence of Acacia senegal on the fertility of a sand sheet (‘goz’) soil in the central Sudan. Plant Soil 33:81-6. Glicksman, M. 1969. Gum technology in the food industry. New York: Academic Press. Glicksman, M., and E. H. Farkas. 1975. Method of preventing gelation in canned gravy-based pet foods. US Patent Application 3,881,031. Gupta, G. N., Singh, G., and G. R. Kachwaha. 1998. Performance of Prosopis cineraria and associated crops under varying spacing regimes in the arid zone of India. Agroforestry Sys. 40:149-57. Howes, F. N. 1949. Vegetable gums and resins. Waltham, MA: Chronica Botanica Company. Huang, W., and Q. Xu. 1999. Overyield of Taxodium ascendens-intercrop systems. Forest Ecol. Manag. 116:33-8. ICRAF. 1997. Annual report of the International Center for Research in Agroforestry 1996, 179-92. Nairobi, Kenya: ICRAF. Idris, O. H. M., Williams, P. A., and G. O. Phillips. 1998. Characterization of gum from Acacia senegal trees of different age and location using multidetection gel permeation chromatography. Food Hydrocolloids 12:379-88 IIED & IES. 1990. Gum arabic belt rehabilitation in the republic of the Sudan: Stage 1 Report, Vol 1. London: International Institute for Environment and Development (IIED) and Institute of Environmental Studies (IES). Imeson, A. 1992. Exudate gums. In Thickening and gelling agents for food, ed. A. Imeson, 66-97. London: Chapman and Hall. Islam, A. M., Phillips, G. O., Sljivo, M. J., and P. A. Williams. 1997. A review of recent developments on the regulatory, structural and functional aspects of gum arabic. Food Hydrocolloids 11:493-505. Kang, B.T., Atta-Krah, A. N., and L. Reynolds. 1999. Alley farming. United Kingdom: Macmillan Education Ltd. Kang, B. T., Grimme, H., and T. L. Lawson. 1985. Alley cropping sequentially cropped maize and cowpea with Luecaena on a sandy soil in Southern Nigeria. Plant Soil 85:267-77. Le Cerf, D., Irinei, F., and G. Muller. 1990. Solution properties of gum exudates from Sterculia urens (karaya gum). Carbohydr. Polym.13:375-86. Lewis, W. 1791. An experimental history of the materia medica. 4th ed. London: Printed for J. Johnson in St. Paul’s Church-Yard; R. Baldwin in Pater-noster-Row; J. Sewell in Cornbill; and S. Hayes, in Oxford Street. Lowe, B. 1955. Experimental cookery from the chemical and physical standpoint. 4th ed., 16-18. New York: Wiley. Maduako, J. N., and M. O. Faborode. 1990. Some physical properties of cocoa pods in relation to primary processing. IFE J. Technol. 2:1-7. Maiden, J. H. 1890. The chemistry and commercial possibilities of wattle gum. Pharm. J. 20:869-71, 980-2. Malzbender, J. 2003. Comment on hardness definitions. J. Eur. Ceramics Soc. 1355. McCabe, W. L., Smith, J. C., and P. Harriot. 1993. Unit operations of chemical engineering, 5th ed. Singapore: McGraw-Hill. Meer Corporation. 1958. Brochure on water soluble gums. New York: Meer Corp. Mohsenin, N. N. 1970. Physical properties of plant and animal materials. New York: Gordon and Breach. Nair, P. K. R. 1993. An introduction to agroforestry. The Netherlands: Kluwer. Nussinovitch, A. 1997. Hydrocolloid applications: gum technology in the food and other industries, 125-39. London: Blackie Academic & Professional. Omaira, A., Gladys, L. D., Maritza, M., Omaira, G., and S. Lilian. 2007. Structural features of a xylogalactan isolated from Hymenaea courbaril gum. Food Hydrocolloids 21:1302-9. Ong, C. K., Wilson, J., Deans, J. D., Mulayta, J., Raussen, T., and N. Wajja-Musukwe. 2002. Tree-crop interactions: Manipulation of water use and root function. Agri. Water Manag. 53:171-86.

22  ◾  Plant Gum Exudates of the World Ostwald, W. 1922. Theoretical and applied colloid chemistry (translated by M. H. Fisher). New York: Wiley. Partridge, E. 1961. A dictionary of slang and unconventional English, 360. New York: MacMillan. Phillips, G. O., and P. A. Williams. 2001. Tree exudate gums: Natural and versatile food additives and ingredients. Food Ingred. Anal. Int. 23:26, 28. Raddade, E. Y., and O. Luukkanen. 2007. The influence of different Acacia senegal agroforestry systems on soil water and crop yields in clay soils of the Blue Nile region, Sudan. Agri. Water manag. 87:61-72. Raddad, E. Y., Luukkanen, O., Salih, A. A., Kaarakka, V., and M. A. Elfadl. 2006. Productivity and nutrient cycling in young Acacia senegal farming systems on Vertisol in the Blue Nile region, Sudan. Agroforestry Sys. 68:193-207. Sahin, S., and S. G. Sumnu. 2006. Physical properties of foods. New York: Springer. Santiago-Blay, J. A., and J. B. Lambert. 2007. Amber’s botanical origins revealed. American Scientist 95:150-7. Sharawi, H. A. 1986. Acacia senegal in the gum belt of Western Sudan: A cost benefit analysis. MSc. thesis, University College of North Wales, Bangor, UK. Sharrow, S. H., and S. Ismail. 2004. Carbon and nitrogen storage in agroforests, tree plantations, and pastures in western Oregon USA. Agroforestry Sys. 60:123-30. Stone, H., and S. Oliver. 1966. Effect of viscosity on the detection of relative sweetness intensity of sucrose solutions. J. Food Sci. 31:129-34. Suliman, M. M., and A. Drag. 1983. Desertification with special emphasis on carrying capacity and pastoral resources. In I.E.S. preassessment of natural resources in Sudan. University of Khartoum: IES. Szczesniak, A. S., and E. H. Farkas. 1962. Objective characterization of the mouthfeel of gum solutions. J. Food Sci. 27:381-5. Turcotte, D. 2006. A garden for visually impaired visitors. The nature of success: Success for nature, 1-3. Montreal Botanical Garden, Montreal, Canada. www.bgci.org/educationcongress/proceedings/ Verbeken, D., Dierckx, S., and K. Dewettinck. 2003. Exudate gums: occurrence, production, and applications. Applied Microbiology and Biotechnology 63:10-21. Vilela, A. E., and D. A. Ravetta. 2005. Gum exudation in South-American species of Prosopis L. (Mimosaceae). J. Arid Environ. 60:389-95. Wadell, H. 1935. Volume, shape and roundness of quartz particles. J. Geol. 43:250-80. Wang, W. P., and D. M. W. Anderson. 1994. Non-food applications of tree gum exudates. Chem. Ind. Forest Prod. 14:67-76. Weiping, W. 2000. Tragacanth and karaya. In Handbook of hydrocolloids, ed. G. O. Philips, and P. A. Williams, 155-68. Cambridge: Woodhead.  Whistler, R. L. 1973. Industrial gums, 2nd edition. New York: Academic Press. Wiesner, J. V. 1927. Die Rohstoffe des Pflanzenreichs (Leipzig, Engelmann). In Vegetable gums and resins, ed. F. N. Howes, 6. Waltham, MA: Chronica Botanica Company. Williams, P. A., and G. O. Phillips. 2000. Gum arabic. In Handbook of hydrocolloids, ed. G. O. Philips, and P. A. Williams, 155-68. Cambridge: Woodhead.  Williams, P. A., Phillips, G. O., and R. C. Randall. 1990a. Structure-function relationships of gum Arabic. In Gums and stabilizers for the food industry 5, ed. G. O. Phillips, D. J. Wedlock, and P. A. Williams, 25-36. Oxford: IRL Press at Oxford University Press. Williams, P. A., Phillips, G. O., and M. A. Stephen. 1990b. Spectroscopic and molecular comparison of three fractions from Acacia senegal gum. Food Hydrocolloids 4:305-11. Yagoub, A. M., Fadlalla, B., Abdalla, A., and M. A. Abdel Rahman. 1993. Indication of recovery in biomass productivity and soil organic matter of Sudan’s Sahel. A case study of northern Kordofan. National Workshop on Dry Land Husbandry in the Sudan. Adis Ababa. Young , A. 1989. Agroforestry for soil conservation. Oxon, UK: CAB and ICRAF. Zinkhan, F. C., and D. E. Mercer. 1996. An assessment of agroforestry systems in the Southern USA. Agroforestry Sys. 35:303-21.

Chapter 2

Physiological Aspects of Polysaccharide Formation in Plants 2.1 INTRODUCTION Gum exudates can be part of the plant’s normal metabolism, but in most cases they are attributed to pathological phenomena. An understanding of the factors affecting gum formation is of fundamental importance in finding a cure for the disorder in fruit trees, as well as in stimulating prolific gum production for commercial collection. Pathological exudation, or “gummosis”, owes its origin to a number of unrelated factors, such as tissue infections caused by disease, pathogens and parasitic invasion by microorganisms, fungi, viruses and insects, physical injury, chemicals, stress, and various climatic conditions. This chapter delineates the different causes of gummosis and its protective functions. It details the involvement of the primary cell wall in the early stages of gum formation, the interference of ethylene with the balanced biosynthesis of cell-wall polysaccharides, the development and ultrastructure of gum ducts, the induction of gummosis by the ethylene generator ‘ethephon’ for enhanced commercial gum production, and aspects of gummosis in fruit trees.

2.2 STRESS FACTORS, ETHYLENE AND GUMMOSIS Gummosis is the outcome of the metamorphosis of organized cell-wall materials into unrecognizable amorphous substances such as gums (polysaccharides) or resins (Fahn, 1979). Starch can also be a source for gum formation. Different views have been expressed as to the way in which gum is produced during gummosis. A number of reports credit gum formation to cellwall decomposition (Tschirch, 1889; Butler, 1911; Groom, 1926; Vander Mollen et al., 1977; Stosser, 1979). However, in Citrus and some other plants, gum production results from the activity of secretory cells, i.e. cells which eliminate the secreted substance from the cytoplasm 23

24  ◾  Plant Gum Exudates of the World

(Catesson et al., 1976; Moreau et al., 1978; Catesson and Moreau, 1985; Gedalovich and Fahn, 1985; Morrison and Polito, 1985). In extreme cases, gummosis leads to the formation of lysigenous (i.e. of or pertaining to the space formed following cell lysis) gum cavities or ducts (Butler, 1911). Gummosis can be the consequence of physiological disturbances, mechanical damage, insects or microorganisms. Resin and gum ducts develop normally in some plants, or in response to external stimuli, such as microorganisms or growth substances. Among the latter, ethylene is the most effective stimulus (Fahn, 1988). Carbohydrate mucilages and gums are synthesized by dictyosomes (also called Golgi apparatus, Golgi body or Golgi complex: this is an organelle found in most eukaryotic cells whose primary function is to process and package the macromolecules that are synthesized by the cell), but virtually every cell compartment has been suggested to play a role in the secretion of lipophilic substances (Fahn, 1988). Once eliminated from the secretory structures, the secreted materials do not normally re-enter the plant’s metabolism. Secretion may take place in specially formed cell complexes or in ordinary tissues (Fahn, 1979). The first type appears in some Prunoideae and Meliaceae species (Butler, 1911; Groom, 1926), where special groups of parenchyma cells (i.e. thin-walled ground-tissue cells that make up the bulk of most non-woody structures, although sometimes their cell walls can be lignified) are formed by the cambium (i.e. a layer or layers of tissue that are the source of cells for secondary growth), instead of the normal wood elements (Fahn, 1979). Immediately after formation of these special groups of parenchyma cells, gummosis begins in the center of these complexes and then proceeds to the periphery (Fahn, 1979). Disintegration of each cell’s walls initiates in the primary cell wall and proceeds towards the innermost lamella of the secondary cell wall (i.e. all cell walls contain two layers, the middle lamella and the primary cell wall, and many cells produce an additional layer, called the secondary wall. The middle lamella serves as a cementing layer between the primary walls of adjacent cells). The resultant cavity is filled with gum. Gummosis may also occur in the bark (i.e. the outermost layers of stems and roots of woody plants), as in the case of gum arabic of Acacia senegal and other Acacia species. In cherry, vessels (i.e. specialized cells for fluid transport) of otherwise normal wood are often filled with gum (Fahn, 1974), formed only by the lamellae of the secondary wall. When plant organs of Dianthus and Ulmus were experimentally infected with a pathogen, gum production was shown to be the result of secretion from vessel-associated parenchyma cells and not of wall lysis (Catesson et al., 1976). A particular type of traumatic duct forms kino resins. These are found in the wood of the genus Eucalyptus (Fig. 2.1). In contrast to gums, kino contains polyphenols. Kino veins are 1.5 to 5 mm in length; they are oriented longitudinally, and occur as isolated veins or in a dense anastomosing (i.e. coalescing) network (Fahn, 1979). Kino veins form in the cambial region as an outcome of injury and develop in the zone of traumatized parenchyma. At specific foci, assemblies of polyphenol-containing cells break down and form ducts into which the contents of these kino-producing cells are released. In parallel, the cells surrounding the future kino veins divide and form peripheral “cambium”. Derivatives of these latter cells grow, accumulate polyphenols, break down and enlarge the quantity of kino already present in the ducts. The final phase includes production of a layer of derivatives by the peripheral “cambium”, which in turn become suberized in the shape of a typical periderm (i.e. the innermost area of the bark, which in older stems is a living tissue) (Fahn, 1979; Skene, 1965). As stated, gummosis is the process of accumulation and exudation of gum from plants (Butler, 1911). In numerous plants, gum production represents a generalized ethylene-mediated response to aging, stress, wounding, and injury by insects and pathogens (Butler, 1911; Higgins, 1919; Smith and Montgomery, 1959; Esau, 1965; Talboys, 1968; Agrios, 1969; Martin and Nelson, 1969; Nelson, 1978; Saniewski et al., 2006). Cell lysis in immature secondary xylem and periderm

Physiological Aspects of Polysaccharide Formation in Plants  ◾  25

Figure 2.1  Kino veins in the wood of the genus Eucalyptus (courtesy of O. Ben-Zion).

of the stem can form lacunae (bearing in mind that in young stems, the tissues from the outside to the inside include: epidermis, periderm, cortex, primary phloem, secondary phloem, vascular cambium and then xylem). Lacunae are sites of gum synthesis and accumulation (Wilde and Edgerton, 1975; Stosser, 1978a,b,c; Bukovac, 1979). The plant protects itself from water loss and pathogen invasion by sealing the wounds and occluding the xylem vessels with the produced gum, while the xylem is responsible for the transport of water and soluble mineral nutrients from the roots throughout the plant. The gums frequently include phenolic compounds that may assist in plant protection (Talboys, 1968). The yellow or brown colors of the gum may be a result of the polymerization of phenolic substances to form polyphenols. Severe gummosis is associated with shoot dieback (Wilde and Edgerton, 1975). Extensive ethephon-induced gummosis and shoot dieback can occur, even when the ethephon is applied at the recommended rates, especially if trees are under stress or the ethephon application is followed by exposure to high temperature (Wilde and Edgerton, 1975; Olien and Bukovac, 1978). Material was found plugging the vessels in longitudinal sections of sweet cherry (Prunus avium L.) shoots (Fig. 2.2) in which gum production had been stimulated by treatment with ethephon (Stosser, 1978a). Gums are complexes of different substances, mostly polysaccharides with various structures. The composition of the gum polysaccharides differs from species to species and from cultivar to cultivar (Boothby, 1983; Saniewski et al., 2002, 2004a,b). However, the composition and chemical characteristics of gums are genotypic-specific (Dea, 1970; Smith and Montgomery, 1959; Keegstra

26  ◾  Plant Gum Exudates of the World

A

B

Figure 2.2  (A) Exudate of wild cherry. (B) Gummosis of sweet cherry (Prunus avium) tree. The gum from bark wounds is aromatic and can be chewed as a substitute for chewing gum (courtesy of O. Ben-Zion).

Physiological Aspects of Polysaccharide Formation in Plants  ◾  27 O Cl

P OH OH

Figure 2.3  Ethephon, a plant growth regulator. Upon metabolism by the plant, it is converted into ethylene, a potent regulator of plant growth and maturity (http://en.wikipedia.org/wiki/ Image:Ethephon.png, courtesy of Edgar 181).

et al., 1973). For example, sour cherry (Prunus cerasus L.) gum is a weakly acidic arabinogalactan (Smith and Montgomery, 1959), similar in structure to the hemicellulosic arabinogalactan of larch (Aspinall, 1969) and the pectic arabinogalactan of suspension-cultured sycamore cells (Keegstra et al., 1973). Ethylene or ethylene-releasing compounds such as ethephon (2-chloroethyl-dioxido-oxophosphorane, molar mass 142.48 g/mol, density 1.58 g/cm3, melting point 74°C) (Fig. 2.3) stimulate gum formation (Boothby, 1983) in trees and fruits of stone-fruit species of the Rosaceae family, such as almonds (Fig. 2.4) (Ryugo and Labavitch, 1978), apricots (Bradley et al., 1969), Japanese apricots (Li et al., 1995), cherries (Olien and Bukovac, 1982a,b), ornamental Japanese cherries

Figure 2.4  Exudate of the almond tree Pruaus dulcis (courtesy of O. Ben-Zion).

28  ◾  Plant Gum Exudates of the World A

B

Figure 2.5  (A) Exudate of the plum tree (Prunus domestica, the species of most “plums” and “prunes” sold as such). (B) Gummosis of plum tree (courtesy of O. Ben-Zion).

(Ueda et al., 2003), peaches (Buchanan and Biggs, 1969; Li et al., 1995) and plums (Fig. 2.5) (Bukovac et al., 1969). Ethylene is believed to be the main factor responsible for the induction of gummosis. In peaches and Japanese apricots, gummosis can also be caused by the fungi Botryosphaeria dothidea and Lasiodiplodia theobromae (syn. Botryodiplodia theobromae) (Okie and Reilly, 1983; Li et al., 1995; Beckman, 2003). In plum and cherry trees, gummosis can be caused by the bacterium Pseudomonas syringae or the fungus Chondrostereum purpureum (syn. Stereum purpureum (Boothby, 1983)). In apricot shoots, gum formation can be caused by Monilinia laxa, Monilinia fructigena, Valsaria insitiva (syn. Cytospora cincta), or by larvae of Grapholita molesta (Rosik et al., 1971, 1975). Gummosis of fungal origin significantly reduces tree growth and fruit yield in susceptible peach

Physiological Aspects of Polysaccharide Formation in Plants  ◾  29 O

O

O

Figure 2.6  Methyl jasmonate (MeJA) (http://en.wikipedia.org/wiki/File:Jasmonic_acid_structure. png, courtesy of Edgar 181).

cultivars (Beckman, 2003). This kind of gummosis is difficult to control with fungicides (Li et al., 1995, Beckman, 2003). In fact, breeding cultivars resistant to pathogens and insects may be the only effective way of limiting or eliminating gummosis. The effect of methyl jasmonate (MeJA; methyl (1R,2R)-3-oxo-2-(2Z)-2-pentenyl-cyclopentaneacetate, molecular formula C13H20O3, molar mass 224.3 g/mol, melting point Dialium guineense > Gardenia erubescens > Diospyros mespiliformis > Parkia biglobosa > Ficus sycomorus > Vitellaria paradoxa (Lamien-Meda et al., 2008). The leaves (Fig. 4.3) are rich in vitamins (especially C and A) and iron, and contain mucilage. The youngest leaves can be consumed as vegetables, but they are often dried and

166  ◾  Plant Gum Exudates of the World

A

B

Figure 4.2  (A) Boabab hanging fruit. (B) Boabab fruit on the ground (courtesy of Forest & Kim Starr). (C) Halved fruit (http://en.wikipedia.org/wiki/Image:Baobab_Frucht.jpg; courtesy of Alex Antener).

Minor Plant Exudates of the World  ◾  167

C

Figure 4.2  (Continued).

pulverized (Diop et al., 2006). Fresh young leaves have a protein content of 4%, and they are rich in vitamins A and C. Baobab leaf is an excellent source of calcium, iron, potassium, magnesium, manganese, molybdenum, phosphorus, and zinc (Yazzie et al., 1994). The mineral contents and levels of vitamins B1 and B2 were determined in dried baobab leaves from 5-yearold trees of A. digitata, A. gibbosa, Adansonia rubrostipa and Adansonia perrieri. Leaf vitamin and crude protein contents were highest in the Madagascar species, especially A. rubrostipa

Figure 4.3  Boabab leaves (courtesy of Forest & Kim Starr).

168  ◾  Plant Gum Exudates of the World

(88 mg B1/100 g leaf, 187 mg B2/100 g), protein 20.7% (dry weight) (Maranz et al., 2008). A comprehensive review on the baobab as a multipurpose tree with a promising future can be found elsewhere (Gebauer et al. 2002; Wickens, 2008).

4.3 Adenanthera Fabaceae (subfamily: Mimosoideae) 4.3.1 Taxon: Adenanthera pavonina L. Common names: coralwood, red sandalwood tree, sandalwood tree, bois de condori [French], condoribaum [German], indischer korallenbaum [German], carolina [Portuguese], árbol del coral [Spanish] (USDA, ARS, National Genetic Resources Program, 2008). Distributional range (native): ASIA, TEMPERATE-China: China. ASIA, TROPICALIndian Subcontinent: India, Sri Lanka; Indo-China: Cambodia, Laos, Myanmar, Thailand, Vietnam; Malaysia: Indonesia, Malaysia, Papua New Guinea. AUSTRALASIA-Australia: Northern Territory. PACIFIC-Southwestern Pacific: Solomon Islands. OTHER-widely cultivated in the tropics; naturalized in tropical Africa, Asia, Southeast United States, West Indies, Seychelles, Pacific Islands (USDA, ARS, National Genetic Resources Program, 2008). The tree and its uses: A. pavonina can be located in residential areas (transplanted), villages, paddy fields, and secondary forests. The tree (Fig. 4.4) is much planted for its ornamental

TARS 1207 A Adenanthera pavonina Red Sandalwood Tree

Figure 4.4  The tree and fruit of Adenanthera pavonina (computer image taken by USDA-ARS TARS).

Minor Plant Exudates of the World  ◾  169

Figure 4.5  Adenanthera pavonina leaves and flowers.

value and for its brilliant red seeds, which are used for necklaces (Howes, 1949; Lewis et al., 2003). It is also valued as firewood. The tree sprouts new branches easily and so is not damaged by harvesting for firewood. A red dye is obtained from the wood and is used by the Brahmins to make religious markings on their foreheads (Greenway, 1941; Howes, 1949). Different parts of the tree are edible. The young leaf shoots and flowers are eaten fresh or parboiled (Fig. 4.5). The seed/fruit is roasted and eaten as a snack, but is toxic when raw (Setalaphruk and Price, 2007). Chitinases have been isolated from various species and various organs of the plant, including the seeds. Thermostable chitinase from seeds of A. pavonina has been purified and characterized. A protein similar to the isolated chitinase was detected in exudates from seeds, discharged during germination (Santos et al., 2004). The seeds (Fig. 4.6) are a potential source of oil and protein in times of shortage (Ezeagu and Gowda, 2006). Analysis has shown that the seeds of A. pavonina contain appreciable amounts of protein (∼29 g/100 g of seeds), crude fat (∼18 g/100 g), and minerals, comparable to commonly consumed staples. Total sugar is low (∼8 g/100 g) while starch (42 g/100 g) constitutes the major carbohydrate. Low levels of non-digestible substances were reported, and methionine and cysteine are the most deficient amino acids. Linoleic and oleic acids make up 71% of the total fatty acids (Ezeagu et al., 2004). The oil of A. pavonina seeds was analyzed by chromatographic and instrumental means. The oil was found to be rich in neutral lipids (86.2%), and low in polar lipids (13.8%). The neutral lipids consist mainly of triacylglycerols (64.2%). Unsaturated fatty acids were found at as high as 71%, while the percentage of saturated fatty acids was only 29%. GC and GC/MS analyses revealed linoleic, oleic and lignocerotic acids to be predominant among all fatty acids in the A. pavonina oil, whereas stigmasterol was the major steroid identified in that study (Zarnowski et al., 2004). Stable formulations of submicron oil-in-water emulsions from A. pavonina seed oil, stabilized with soybean lecithin, can be formed. Non-ionic-surfactant phospholipid-based emulsions containing this edible oil may be useful as an alternative formulation matrix for pharmaceutical, nutritional or cosmetic applications of otherwise membrane-active components (Jaromin et al., 2006).

170  ◾  Plant Gum Exudates of the World

A

B

1 cm

Figure 4.6  (A) Adenanthera pavonina seeds on the ground. (B) Seeds of A. pavonina from India. U.S. National Seed Herbarium image. [Photographed by Steve Hurst for USDA-NRCS PLANTS Database. URL: http://plants.usda.gov.]

4.4 Afzelia Fabaceae (subfamily: Caesalpinioideae) 4.4.1 Taxon: Afzelia africana Sm. ex Pers. Synonyms: Intsia africana (Sm. ex Pers.) Kuntze; Pahudia africana (Sm. ex Pers.) Prain. Common name: African mahogany (Rehm, 1994). Distributional range (native): AFRICA-Northeast Tropical Africa: Chad, Sudan; East Tropical Africa: Uganda; West-Central Tropical Africa: Cameroon, Central African Republic, Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Ghana, Guinea, Guinea-Bissau, Mali, Niger, Nigeria, Senegal, Sierra Leone, Togo (Lewis et al., 2003; USDA, ARS, National Genetic Resources Program, 2008). Exudate properties: When four lesser known indigenous tropical legumes (A. africana, Brachystegia eurycoma, Detarium microcarpum and Mucuna flagellipes) were analyzed, A. africana showed

Minor Plant Exudates of the World  ◾  171

a significantly higher crude protein content of 27%, followed by M. flagellipes with a value of 20.4%. A. africana appears to have potential as a source of vegetable oil for domestic and industrial use, as it contains 32% fat (Onweluzo et al., 1994). A. africana showed about 33% total carbohydrates, about 34 to 50% of which was found to consist of a gum (water-dispersible polysaccharide). M. flagellipes gum solution showed the highest pseudoplasticity with a flow behavior index of 0.41, while in comparison to the other, lesser-known tropical legumes, A. africana was the least pseudoplastic (Onweluzo et al., 1994; Chanda et al., 1995). The gum that was extracted from A. africana was evaluated for some functional properties. At a constant shear rate, the apparent viscosity of the gum was directly proportional to the gum concentration. At 2% concentration, the gum dispersion showed an apparent viscosity of 41 cps, measured at 174 s-1 and 25°C. The gum was found to contain D-galactose as a major monosaccharide. In addition, the presence of L-rhamnose was indicated. A. africana showed significantly lower water-absorption capacity and gelation properties than D. microcarpum and M. flagellipes. The gum showed better emulsion properties at acidic vs. alkaline pH (Onweluzo et al., 1995). The tree: A. africana is a common tree in the savannah and in mixed deciduous forests that may yield gum. The tree reaches 12.2 to 18.3 m in height. It has a scaling bark and a large woody pod (Howes, 1949). Commercial and functional uses for other parts of the tree: The tree yields a valuable mahoganylike timber (Greenway, 1941; Howes, 1949; Boutelje, 1980). Afzelia species are used primarily for wood, though some species also have medicinal uses. The seeds are red and black (Fig. 4.7) and can be used as beads. The viability of seeds and the survival of seedlings under natural conditions are key factors for sexual regeneration of woody species. To grow well, the seedlings of A. africana need to be protected against fire, grazing and drought. When the seeds’ water content is about 8% (fresh weight basis), they can be stored under ambient conditions for at least 33 months after collection without significant reduction in germination rate (Bationo et al., 2001). Afzelia species are also used as cattle feed. The behavior of sheep, goats and cattle on a shrub and tree savannah in the sub-humid zone of West Africa was studied during dry, rainy and cool seasons. The plant species consumed at the highest frequency by cattle were

Figure 4.7  Afzelia africana seeds (http://commons.wikimedia.org/wiki/User:Jeffdelonge; photo by Jeffdelonge;).

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A. africana, Khaya senegalensis (Desr.) A. Juss., Pterocarpus erinaceus Poir. and Dichrostachys cinerea (L.) Wight & Arn. (Ouedraogo-Kone et al., 2006). A. africana is used in folklore remedies for the treatment of diarrhea, gastrointestinal disorders and gonorrhea, among other ailments. A crude extract of its stem bark, containing alkaloids, tannins, flavonoids and saponins, exhibited antimicrobial activity at a concentration of 25 mg/ml against 21 bacterial isolates, including both Gram-positive and Gram-negative strains. On the other hand, the extract did not show any activity against tested fungal species (Akinpelu et al., 2008).

4.5 Albizia Fabaceae A number of species of Albizia are known to yield gum. The Indian species are described in Chapter 3. Albizia gums (Fig. 4.8) can be exuded very freely, but are not of high quality: they are likely to be dark and only somewhat soluble (Howes, 1949). The generic name was misspelled as Albizzia for many years (Anderson and Morrison, 1990a). Albizia species are closely allied to, and often mistaken for

Figure 4.8  Albizia gum (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 58101).

Minor Plant Exudates of the World  ◾  173

Acacia species and vice versa (Allen and Allen, 1981). The main diagnostic taxonomic differences involve the stipules and the stamens which, in Albizia, are usually longer than in Acacia and united at the base into a tube (Anderson and Morrison, 1990a). Albizia species are a source of tannins. Saponins and fish-stupefying, insecticidal and anthelmintic compounds can be extracted from the bark of certain species for local native medicinal and other uses (Allen and Allen, 1981; Rukunga et al. 2007). No complete structure of Albizia gum has so far been proposed. A partial structure consists of a main chain of β-(1-3) D-galactose units with some β-(1-6)-linked D-galactose units (Anderson and Morrison, 1990a). Other chemical and structural features of Albizia species have also been proposed (Anderson and Dea, 1969; Anderson et al., 1996; de Paula et al., 2001; Mhinzi, 2002).

4.6 Anogeissus Combretaceae 4.6.1 Taxon: Anogeissus leiocarpus (DC.) Guill. & Perr. Synonyms: Anogeissus leiocarpa (DC.) Guill. & Perr.; Anogeissus schimperi Hochst ex Hutch. & Dalz. Common names: marke (Hausa), kane. Geographic distribution: Northern Nigeria, eastern part of Sudan (Howes, 1949). Gum (common name): marike gum (Smith and Montgomery, 1959). Exudate properties: The yellow or light brown (Smith and Montgomery, 1959) gum exudes in large or small fragments with a glassy or weathered surface (Howes, 1949). It is only partially soluble in water, swelling to a mucilaginous mass of relatively high viscosity (Greeway, 1941; Smith and Montgomery, 1959). The gum is composed of L-arabinose, D-galactose and glucuronic acid. The hydrolyzed gum has an equivalent weight of approximately 343. It contains neither proteins nor methoxyl groups (Smith and Montgomery, 1959). Leiocarpan A, the major polysaccharide component of A. leiocarpus gum, contains a backbone with alternating 4-O-substituted β-D-glucuronic acid and 2-O-substituted α-D-mannopyranose residues with terminal D-xylopyranose and L-arabinofuranose residues attached variously to the mannose residues (Aspinall and Puvanesarajha, 1983). Structural features of A. leiocarpus have been studied by several researchers (McIlroy, 1952; Aspinall and Christensen, 1961; Aspinall and McNab, 1965; Aspinall et al., 1969; Aspinall and Chaudhari, 1975). Commercial availability of the gum (pure form): In northern Nigeria and the eastern Sudan, the gum of A. leiocarpus has been reported to be chewed and eaten by the natives. It is also used for ink (Howes, 1949). Anogeissus latifolia, the source of much of the Indian ghatti gum described in Chapter 3, and Anogeissus acuminata (Roxb. ex DC.) Guill. & Perr. (formerly Anogeissus pendula Edgew.) yield a good-quality gum in India. Commercial and functional uses for other parts of the tree: A. leiocarpus is one of the most frequently used woody plants to build homes (houses, tents or huts), structures for grain storage, sheds and fences (Ganaba et al., 2004). The powdered bark is applied to wounds, sores, boils, cysts, and diabetic ulcers. It has also been mixed with green clay and applied as an unusual face mask for serious acne vulgaris (Dalziel, 1936). Extracts of A. leiocarpus have antiplasmodial, antitrypanosomal and antifungal activities. The antiplasmodial activity of methanolic extracts of 16 medicinal plants was evaluated by fluorometric assay. The most active extracts were those from A. leiocarpus and Terminalia avicennoides Guill. & Perr. None of the extracts or isolated compounds affected the integrity of human erythrocyte membranes, however, adverse effects were manifested in a concentration-dependent fashion

174  ◾  Plant Gum Exudates of the World

(Shuaibu et al., 2008a). The antitrypanosomal activity of methanolic extract of A. leiocarpus was evaluated against four strains of Trypanosoma species with a minimum inhibitory concentration range of 12.5 to 50 mg/ml. Appropriate chemical analysis revealed hydrolyzable tannins with a range of activity. On fibroblasts, the compound did not reveal any serious toxicity at moderate concentration, but again, the effect was concentration-dependent (Shuaibu et al., 2008a,b). Chloroform, ethanolic, methanolic, ethyl acetate and aqueous root extracts of A. leiocarpus were investigated for antifungal activities. The plant extract inhibited the growth of all test organisms. A. leiocarpus appears to be more effective as an antifungal agent than T. avicennoides. Ethanolic extracts of the two plant roots were more effective than the methanolic, chloroform, or aqueous extracts against all of the tested fungi (Mann et al., 2008). Another study dealt with five species of Combretaceae growing in Togo that were investigated for their antifungal activity against 20 pathogenic fungi. The five hydroethanolic extracts of Terminalia glaucescens Planch. ex Benth. and A. leiocarpus appeared to be the most active (Batawila et al., 2005). The safety and anthelmintic activity of the crude aqueous leaf extract of A. leiocarpus were investigated in sheep naturally infected with gastrointestinal nematodiasis using a fecal egg count reduction test and a controlled test. It was concluded that the crude aqueous leaf extract of A. leiocarpus could be tolerated by sheep and exhibited limited, dose-dependent anthelmintic activity (Agaie and Onyeyili, 2007).

4.7 Atalaya Sapindaceae (subfamily: Sapindoideae) 4.7.1 Taxon: Atalaya hemiglauca (F. Muell.) F. Muell. ex Benth. Synonym: Thouinia hemiglauca F. Muell. Common names: cattle brush, whitewood. Economic importance: Vertebrate poisons: mammals (Lazarides and Hince, 1993). Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Northern Territory, Queensland, South Australia, Western Australia (USDA, ARS, National Genetic Resources Program, 2008). Exudate properties: The exudate is pale, and readily dissolves in cold water (Anderson and Weiping, 1990). The gum is of chemical interest in that it has a negative specific rotation very similar to that of Acacia senegal gum, the latter regarded as having a specific rotation of -30. Care should therefore be taken to differentiate between these two gums, although Australian exudates are not usually exported. Nevertheless, clear distinctions can be made on the basis of the very low nitrogen and rhamnose contents and viscosity of Atalaya gum compared with Acacia gum, as well as the former’s low hydroxyproline and high aspartic acid and cysteine contents (Maiden, 1901; Anderson and Weiping, 1990).

4.8 Balsamocitrus Rutaceae (subfamily: Aurantioideae) 4.8.1 Taxon: Balsamocitrus dawei Stapf Common name: Uganda powder-flask fruit (Swingle and Reece, 1967). Distributional range (native): AFRICA-East Tropical Africa: Uganda (USDA, ARS, National Genetic Resources Program, 2008).

Minor Plant Exudates of the World  ◾  175

Exudate properties: The fruit of Balsamocitrus contains a gummy substance (Howes, 1949) that is quite soluble in water. This gum contains a volatile oil with a characteristic odor which prevents its use as a substitute for gum arabic (Howes, 1949). Agricultural issue: Commercially used Balsamocitrus rootstocks can all be seriously damaged by the larvae of the sugar cane root weevil, Diaprepes abbreviatus (L.), while at least seven species within the subfamily Aurantiodeae have been observed to be significantly more resistant. The species Balsamocitrus dawei was most resistant to weevil larvae, exhibiting less root damage than commonly used rootstock cultivars, as well as significantly depressed larval growth and survival (Bowman et al., 2001).

4.9 Bauhinia Fabaceae The genus is well represented in tropical and subtropical Africa (Howes, 1949). Gum-producing species with wide spreadability are Bauhinia thonningii and Bauhinia fassoglensis; however, the latter species has been reassigned to the genus Tylosema, as Tylosema fassoglense. Commercially, these gums are not important.

4.9.1 Taxon: Bauhinia carronii F. Muell. Synonym: Lysiphyllum carronii (F. Muell.) Pedley. Common names: northern bean tree, Queensland ebony, red bauhinia. Distributional range (native): AUSTRALASIA-Australia: Australia - Queensland (USDA, ARS, National Genetic Resources Program, 2008). The tree and the exudate: The endemic tree “Queensland ebony” is up to 10 m tall, commonly multistemmed, with branchlets that are usually spreading or pendulous. Its dark gray bark is furrowed and hard (Flora of Australia online; www.anbg.gov.au/abrs/abif/flora/). It is widespread in Queensland except the Cape York Peninsula, the southwest and the far southeast. It grows in sandy or rocky soil in cypress-ironbark woodland, on sandy river banks, on flood plains, in gray silty soil, in clay in Brigalow scrub and Gidgee scrub, on red clay-loam flats, and on steep slopes in vine thickets. It flowers from August to February, with fruits recorded in most months (Flora of Australia online; www.anbg.gov.au/abrs/abif/flora/). B. carronii yields a yellow, tastless gum with good tenacity (Maiden, 1901; Howes, 1949).

4.9.2 Taxon: Bauhinia thonningii Schumach. & Thonn. Synonym: Piliostigma thonningii (Schumach. & Thonn.) Milne-Redh. Common name: koa. Distributional range (native): AFRICA-Northeast Tropical Africa: Chad, Ethiopia, Sudan; East Tropical Africa: Kenya, Tanzania; West-Central Tropical Africa: Cameroon, Gabon, Zaire; West Tropical Africa: Benin, Burkina Faso, Cote D’Ivoire, Gambia, Ghana, Guinea, Guinea-Bissau, Mali, Nigeria, Senegal, Sierra Leone, Togo; South Tropical Africa: Angola, Malawi, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, Namibia, South Africa. ASIA, TEMPERATEArabian Peninsula: Yemen (USDA, ARS, National Genetic Resources Program, 2008). The shrub, exudate, products and uses: B. thonningii is a tall shrub with a twisted branched stem. It has a smooth bark that is vertically cracked and fibrous on the inner side. The wood is reddish, becoming dirty brown after exposure. The wood is simple to work, but likely to

176  ◾  Plant Gum Exudates of the World

have insect damage; it can be used for hut poles, handles and mortars. The shrub blossoms from December to June and the fruit remains on the tree for a long time. Fruits are long, wide, flat and slightly cracked pods, velvet in the premature stages. Bark fibers are used to make binding, ropes and “pagne” cloth (Baumer, 1983). The bark is rich in tannins and may be used for tanning skins. Infusions of leaves and bark are used against worms, dysentery, diarrhea and malaria (Muregi et al., 2007). They are also used against leprosy, blennorrhagoeia, hemoglobinuria, sore throat and aching gums (Baumer, 1983). Pounded, boiled and macerated bark and roots produce a red dye used for “pagne” fabric and wooden objects. A dark blue dye can be extracted from pods and seeds (Baumer, 1983). Pods and young leaves are consumed by livestock. In the Republic of Sudan, roasted seeds are consumed by humans. The inner part of the bark contains a gum, which swells in water and then hardens and is therefore used for caulking of African boats (Baumer, 1983).

4.9.3 Taxon: Tylosema fassoglense (Kotschy ex Schweinf.) Torre & Hillc. Synonyms: Bauhinia fassoglensis Kotschy ex Schweinf.; Bauhinia kirkii Oliv. Economic importance: Human food: potential as vegetable. Distributional range (native): AFRICA-Northeast Tropical Africa: Ethiopia, Sudan; East Tropical Africa: Kenya, Tanzania, Uganda; West-Central Tropical Africa: Burundi, Rwanda, Zaire; South Tropical Africa: Angola, Malawi, Mozambique, Zambia, Zimbabwe; Southern Africa: Namibia, South Africa - Natal, Transvaal, Swaziland (USDA, ARS, National Genetic Resources Program, 2008). The tree: The genus Tylosema was established in 1955 and belongs to the Leguminosae. Four species, all inhabitants of Africa, have been distinguished (Coetzer and Ross, 1977). They are stem-trailing, herbaceous geophytes, arising from a large underground tuber. T. fassoglense is widely distributed throughout East African countries from Ethiopia to the Transvaal and westward to Angola and northern Namibia. T. fassoglense develops like a tree. It is not an evergreen: during the autumn it assumes a yellow color. The adult species are large in size, reaching 17 m in height. Its beans are consumed by natives (Wilczek, 1952), and a high protein content (comparable to that of soybean) and oil level approaching that of peanuts have been reported (Malaisse and Parent, 1985): the seeds contain 240-300 g lipid/kg and 446 g protein/kg dry weight. Major fatty acids in the oil are linoleic (36-42% of the total fatty acids), oleic (32-35%) and palmitic (11.5-15.7%) acids. The proteins characteristically have high levels of lysine, proline and tyrosine. Due to their very low content, both methionine and cysteine appear to be the limiting amino acids. T. fassoglense defatted meal contains substantial amounts of trypsin inhibitors and phytates: 295 trypsin units inhibited (TUI) per mg and 35 g/kg dry weight, respectively (Dubois et al., 1995).

4.10 Julbernardia Fabaceae (subfamily: Caesalpinioideae) 4.10.1 Taxon: Julbernardia globiflora (Benth.) Troupin Synonyms: Brachystegia globiflora Benth. (USDA, ARS, National Genetic Resources Program, 2008); Berlinia eminii Taub.; Isoberlinia globiflora (Benth.) Hutch. ex Greenway (Hyde and Wursten, 2008). Common name: mnondo.

Minor Plant Exudates of the World  ◾  177

Distributional range (native): AFRICA-East Tropical Africa: Tanzania; West-Central Tropical Africa: Zaire; South Tropical Africa: Malawi, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, Namibia (USDA, ARS, National Genetic Resources Program, 2008). The tree: J. globiflora is a deciduous tree. An important constituent of miombo woodland (i.e. miombo is the Swahili word for Julbernardia, a tree genus that comprises a large number of species), often growing with Brachystegia spiciformis Benth. Its altidude range is 760 to 1660 m and it flowers from January to May (Hyde and Wursten, 2008). The mnondo is a medium-sized tree. In the northern half of its range, it is generally 15 to 16 m high, but can grow up to 18 m in height. In the southern half, it is usually smaller (12-13 m is a large specimen). Mnondo pods are concentrated at the top and sides of the tree and are readily visible in late summer. The exudate: In East Africa, J. globiflora, found in dry forest areas, yields an insoluble type of gum which has been described as a mixture of gum and kino (Howes, 1949).

4.11 Bombax Malvaceae (subfamily: Bombacoideae) 4.11.1 Taxon: Bombax ceiba L. Synonyms: Bombax malabaricum DC.; Gossampinus malabaricus (DC.) Merr.; Salmalia malabarica (DC.) Schott & Endl. Common names: Indian kapok, red cotton tree, red silk-cotton, silk-cotton tree, simal, fromager [French], bombax [French, Spanish], indischer seidenwollbaum [German]. Distributional range (native): ASIA, TEMPERATE-China: China - Fujian, Guangdong, Guangxi, Guizhou, Jiangxi, Sichuan, Yunnan; Eastern Asia: Taiwan. ASIA, TROPICALIndian Subcontinent: Bhutan, India, Nepal, Sri Lanka; Indo-China: Cambodia, Laos, Myanmar, Thailand, Vietnam; Malesia: Indonesia, Malaysia, Papua New Guinea, Philippines. AUSTRALASIA-Australia: Australia - Northern Territory, Queensland, Western Australia. OTHER-cultivated elsewhere (USDA, ARS, National Genetic Resources Program, 2008). The tree, the exudate and their uses: B. ceiba is a medium-sized deciduous tree found throughout western and southern India (Chadha, 1972). The tropical tree (Fig. 4.9A) has a straight tall trunk. Its leaves are deciduous in winter. Red flowers (Fig. 4.9B) with five petals appear in the spring before the new foliage and are one reason that the tree is widely planted. The flower is used as a common ingredient in Chinese herb tea. It produces a capsule which, when ripe, contains white fibers, like cotton (Fig. 4.9C), which has been used as a substitute for cotton. Its trunk bears spikes to deter animal attacks. Although its stout trunk suggests that it is useful for timber, its wood is too soft to be very useful. In general, its uses are ornamental, as fiber and/or wood, and for folk medicines. Phytochemical studies of this species have resulted in the isolation of several sesquiterpenoids (Seshadri et al., 1971, 1973; Sankaram et al., 1981; Puckhaber and Stipanovic, 2001; Sreeramulu et al., 2001). A new sesquiterpene lactone, together with a known naphthoquinone, were isolated from the root bark of B. ceiba. The structures of these two compounds were established by extensive oneand two-dimensional (1D and 2D) NMR spectral studies (Reddy et al., 2003). The antioxidant activity of a methanolic extract of B. ceiba was evaluated using several antioxidant assays, which tested its ability to scavenge, its action against lipid peroxidation and its effect on myeloperoxidase activity. In addition to its biological activity, the extract showed very

178  ◾  Plant Gum Exudates of the World

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Figure 4.9  (A) Bombax ceiba tree and (B) flowers. (C) Silky seed parts (courtesy of Forest & Kim Starr). (D) B. ceiba exudate (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 65260).

Minor Plant Exudates of the World  ◾  179

C

Figure 4.9  (Continued).

low toxicity to Vero cells (Vieira et al., 2009). The tree yields a dark opaque gum or gumresin. The gum is whitish when first exuded, but darkens to a dark mahogany or black color (Fig. 4.9D) upon drying (Howes, 1949). The gum is used medicinally in India as an astringent in bowel complaints (Howes, 1949), and is widely used in folk medicine as a demulcent, diuretic, aphrodisiac, emetic and for curing impotence (Kirtikar and Basu, 1975).

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4.11.2 Taxon: Bombax insigne Wall. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India; Indo-China: Laos, Myanmar, Vietnam (USDA, ARS, National Genetic Resources Program, 2008). The exudate: B. insigne is an Indian species that yields a brown gum (Howes, 1949).

4.12 Borassus Arecaceae (subfamily: Coryphoideae) 4.12.1 Taxon: Borassus flabellifer L. Common names: doub palm, palmyra palm, tala palm, toddy palm, wine palm, borasse, rônier, lontaro, palmyrapalme, broção, palmira, boraço, boraso, palma, palmira. Economic importance: Environmental: ornamental. Human food: beverage base, fruit, sugar. Materials: fiber, wood. Medicine: folk medicine (USDA, ARS, National Genetic Resources Program, 2008). Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India, Sri Lanka; Indo-China: Indochina, Myanmar, Thailand; Malesia: Indonesia, Malaysia, Papua New Guinea (USDA, ARS, National Genetic Resources Program, 2008). The tree: The palmyra palm (B. flabellifer) is a multipurpose tree of immense usefulness (Fig. 4.10). It is found extensively in India and its fruit is exploited for food (Fig. 4.11), as are its tuberous

TARS 16294 Borassus flabellifer Palmyra Palm

Figure 4.10  Palmyra palm (Borassus flabellifer), a multipurpose tree of immense usefulness (computer image taken by USDA-ARS TARS).

Minor Plant Exudates of the World  ◾  181

TARS 16294 Borassus flabellifer Palmyra Palm

Figure 4.11  Palmyra palm (Borassus flabellifer) fruit (computer image taken by USDA-ARS TARS).

seedlings; beverage and sugar are obtained from the sap, and fiber is obtained from the leaf and leaf base for brushes, cordage, weaving, and plaiting; trunk wood is used for construction and fuel, and numerous minor products (Davis and Johnson, 1987). Increasing exploitation of the palmyra palm threatens the future supply of its raw materials, which are so important to rural populations. Integrated development of palmyra products for local and export markets, as well as management/conservation measures, are needed, both to maximize the economic value of the products and to assure sustained yield from native stands (Davis and Johnson, 1987). B. flabellifer has various other uses. Peeled seedlings are eaten fresh or sun-dried, raw or cooked in various ways. They also yield starch. A fermented sweet sap (toddy), obtained by tapping the tip of the inflorescence, is a popular beverage. Roots, spadix ash, bark and sap from the flower stalk all have medicinal uses. In India, it is planted as a windbreak on the plains (Morton, 1988). Exudate properties: The exudate of B. flabellifer is vitreous (Howes, 1949) and black (Greenway, 1941). The gum swells in water and is insoluble (Howes, 1949).

4.13 Bosistoa Rutaceae (subfamily: Toddalioideae) 4.13.1 Taxon: Bosistoa pentacocca (F. Muell.) Baill. Synonyms: Bosistoa sapindiformis F. Muell. ex Benth; Euodia pentacocca F. Muell. Geographic distribution: Mullumbimby, New South Wales. The tree: B. pentacocca is confined to the rain forests of eastern Australia. No chemical work has been carried out on this species; the only thing that is known about the chemistry of this genus is the occurrence of the triterpenes taraxerol and taraxerol methyl ether (Parsons et al., 1993). Exudate properties: The exudate is pale and transparent. It is not entirely soluble in water and it resembles other Australian rutaceous gums in its physical properties (Howes, 1949).

4.14 Brachystegia Fabaceae (subfamily: Caesalpinioideae) 4.14.1 Taxon: Brachystegia spiciformis Benth. Synonym: Brachystegia randii Baker f. Common name: zebrawood (Webster’s Dictionary, 1961).

182  ◾  Plant Gum Exudates of the World

+3 C 1

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Figure 4.12  Brachystegia spiciformis (image at PlantSystematics.org; from: A. Engler. 1910. Vegetation der Erde. Vol 9. Band 1. Fig. 364; [courtesy of L.H. Bailey Hortorium ©, Cornell University (for reproduced image, not source)].

Distributional range (native): AFRICA-East Tropical Africa: Kenya, Tanzania; West-Central Tropical Africa: Zaire; South Tropical Africa: Angola, Malawi, Mozambique, Zambia, Zimbabwe (USDA, ARS, National Genetic Resources Program, 2008). The tree: B. spiciformis is a medium-sized African tree, ecologically dominant over large areas of central Africa (Fig. 4.12). Its colorful springtime foliage serves as a seasonal marker. The tree typically reaches a height of about 16 m (Dale and Greenway, 1961). It starts to lose its leaves in late May and by early August it is nearly bare. In late August (when temperatures rise again), new bright red leaves are produced. In different trees, they vary from almost purple to brownish. The color shifts to deep green over a period of 10 to 20 days. The flowers appear after the new leaves and these are followed by the pods in April. The pods split open with a loud noise and the flat seeds (∼2 cm across) (Fig. 4.13) are flung away (Dale and Greenway, 1961).

Minor Plant Exudates of the World  ◾  183

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5 mm

A

B

Figure 4.13  Brachystegia spiciformis (A) seed, (B) embryo in situ, (C) transection of seed: drawn by Lynda E. Chandler or Karen Parker [scanned by Robert J. Gibbons & Kate O’Mara; from Gunn, C.R. & C.A. Ritchie. 1988. Identification of disseminules listed in the Federal Noxious Weed Act. U.S. Department of Agriculture Technical Bulletin 1719] (courtesy of U.S. National Seed Herbarium).

Exudate properties: Brachystegias are the dominant feature of woody vegetation in many parts of Tropical Africa. They often exude gum (Howes, 1949), which is generally dark (Howes, 1949). B. spiciformis produces a deep red gum (Greenway, 1941). The dark appearance and poor quality also applies to Brachystegia floribunda Benth. (formerly Brachystegia nchangensis Greenway) and Brachystegia longifolia Benth. in northern Zimbabwe (Howes, 1949). The gum has low solubility (Anderson et al., 1984). It is an acidic polysaccharide (Anderson and Stefani, 1979), containing glucuronic acid, 4-O-methylglucuronic acid and galacturonic acid, together with galactose, minor amounts of arabinose, and relatively high proportions of rhamnose. The bark also yields high amounts of tannin (Anderson et al., 1984). The fact that Brachystegia species can also yield water-soluble gum polysaccharides is of interest, particularly because genera within the Caesalpinioideae have been recorded as sources of tannin-rich kinos, copal and dammar-type resins (Greenway, 1941). Commercial and functional uses for other parts of the tree: The wood of B. spiciformis is used for fuel (as both charcoal and firewood), and sometimes for boats and general construction. It is used as a shade tree, and for beehives. Its roots are used for medicinal applications.

4.15 Burkea Fabaceae (subfamily: Caesalpinioideae) 4.15.1 Taxon: Burkea africana Hook. Distributional range (native): AFRICA-Northeast Tropical Africa: Chad, Sudan; East Tropical Africa: Tanzania, Uganda; West-Central Tropical Africa: Cameroon, Central African Republic, Zaire; West Tropical Africa: Benin, Burkina Faso, Cote D’Ivoire, Ghana, Guinea, Mali, Niger, Nigeria, Senegal, Togo; South Tropical Africa: Angola, Malawi, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, Namibia, South Africa - Transvaal (USDA, ARS, National Genetic Resources Program, 2008). The tree: B. africana is a deciduous tree (Fig. 4.14) that occurs all over tropical Africa, chiefly in savannah forests, and extending into the Transvaal (Howes, 1949; Lewis et al., 2003). The bark is rich in tannins and alkaloids and is used for tanning leather. Due to its toxicity, pulverized bark is

184  ◾  Plant Gum Exudates of the World

H 1

/1

1/ 1

+8 D E +4

+4

B

F A

2/ 3

C

+4

G

+8

Figure 4.14  Burkea africana [image at PlantSystematics.org; from: A. Engler. 1910. Vegetation der Erde. Vol 9. Band 1. Fig. 371; courtesy of L.H. Bailey Hortorium ©, Cornell University (for reproduced image, not source)].

thrown into water to paralyze fish. The heartwood produces a dark brown to reddish-brown hardwearing, insect-resistant timber, used for parquet flooring and fine cabinet and furniture work. The gum: B. africana produces a pale yellow to reddish brown, semi-transparent, tear-like exudate (Howes, 1949).

4.16 Capparis Capparaceae 4.16.1 Taxon: Capparis nobilis (Endl.) F. Muell. ex Benth. Common names: wild lemon, devils guts, caper tree. Geographic distribution: Australia.

Minor Plant Exudates of the World  ◾  185

Exudate properties: The exudate forms small particles or vermiform tears with a horny texture. It is a semi-transparent partially soluble exudate that swells to an enormous extent in water. The exudate shows some general resemblance to gums of the Sterculiaceae. In addition to the gum, fruits of the C. nobilis tree have commercial and functional uses (Maiden and Smith, 1895; Maiden, 1901; Howes, 1949).

4.17 Careya Lecythidaceae (subfamily: Planchonioideae) 4.17.1 Taxon: Careya arborea Roxb. Common name: patana oak. Distributional range (native): ASIA, TEMPERATE-Western Asia: Afghanistan. ASIA, TROPICAL-Indian Subcontinent: India, Sri Lanka; Indo-China: Myanmar, Thailand (USDA, ARS, National Genetic Resources Program, 2008). The exudate: The exudate of C. arborea is an astringent gum (Howes, 1949). Functional uses: C. arborea (Fig. 4.15) has been used for religious and medicinal purposes since ancient times in India, but unique among the tribal and rural people of Orissa is its use for garments and for safe abortion of unwanted pregnancies (Mohanty and Rout, 1999). A methanol extract of C. arborea bark was tested for its antioxidant and hepatoprotective activities in mice with Ehrlich’s ascites carcinoma tumors (Rahman et al., 2003). Control animals inoculated with this carcinoma showed a significant alteration in antioxidant and hepatoprotective parameters. Oral administration of the extract caused a significant reversal of these biochemical changes back to normal levels in the serum, liver and kidney, indicating the

2

3 1

Figure 4.15  Careya arborea [image at PlantSystematics.org; from: Lindley, John. The Vegetable Kingdom; The Structure, Classification, and Uses of Plants. Third Edition, 1853. Fig. DIII; courtesy of L.H. Bailey Hortorium ©, Cornell University (for reproduced image, not source)].

186  ◾  Plant Gum Exudates of the World

potent antioxidant and hepatoprotective nature of the standardized extract (Senthilkumar et al., 2008). Oral administration of this extract was also reported to cause a significant reduction in percent increase in body weight, packed cell volume, and viable tumor cell count when compared to mice of the control tumor-bearing group (Natesan et al., 2007).

4.18 Cassia Fabaceae (subfamily: Caesalpinioideae) 4.18.1 Taxon: Cassia fistula L. Common names: golden shower, Indian-laburnum,  purging cassia,   bâton casse [French], canéficer [French], casse fistuleuse [French], Röhrenkassie [German], cássia fístula [Portuguese (Brazil)], cássia-imperial   [Portuguese (Brazil)], cana fístula   [Portuguese (Brazil)], chuvade-ouro  [Portuguese (Brazil)], cañafístula   [Spanish]. Geographic distribution: C. fistula (Fig. 4.16) is native to India, the Amazon and Sri-Lanka; Cassia grandis L.f. is native from Mexico to the north of South America.

Figure 4.16  Cassia fistula, the golden shower tree: flowers and pods.

Minor Plant Exudates of the World  ◾  187

Figure 4.17  Cassia fistula gum (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 59464).

Exudate properties and uses: C. fistula gum (Fig. 4.17) is dark (Howes, 1949), and slightly soluble in water (Howes, 1949). Senna nicaraguensis (Benth.) H. S. Irwin & Barneby (formerly Cassia nicaraguensis Benth.) gum solutions are said to be very viscous (Anderson et al., 1990). Cassia grandis gum is very acidic. It contains tannin and an unusually high proportion of glycine. It contains major amounts of galacturonic acid and xylose in comparison to gums from Enterolobium cyclocarpum, Lysiloma acapulcense and S. nicaraguensis (Anderson et al., 1990). C. fistula is popularly planted as an ornamental tree. The pulp of the fruit, seeds and roots is used for various medicinal applications (Duke, 1983). C. grandis is used as an ornamental tree. The fractionation of a dichloromethane extract of C. fistula fruits led to the isolation of an active isoflavone, biochanin A. This compound was effective against promastigotes of Leishmania. In addition, biochanin A exhibited activity against Trypanosoma cruzi. These results could contribute to the development of novel antiprotozoal compounds for future drug design studies (Sartorelli et al., 2009).

4.18.2 Taxon: Cassia sieberiana DC. Distributional range (native): AFRICA-Northeast Tropical Africa: Chad, Sudan; East Tropical Africa: Uganda; West-Central Tropical Africa: Cameroon, Central African Republic, Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Gambia, Ghana, Guinea, Guinea-Bissau, Liberia, Mali, Mauritania, Nigeria, Senegal, Sierra Leone, Togo (USDA, ARS, National Genetic Resources Program, 2008). The exudate: C. sieberiana is common in savannah and open forest areas throughout West Africa and extends to the eastern Sudan, Uganda and East Africa (Howes, 1949). In West Africa, the gum of C. sieberiana is mixed with the pulverized pod and may be applied

188  ◾  Plant Gum Exudates of the World A

B

Figure 4.18  Cedrela odorata (West Indian cedar) habit (A) and plant (B) (courtesy of Forest & Kim Starr).

Minor Plant Exudates of the World  ◾  189

by natives to sores (Dalziel, 1936). Further information on the chemical constituents and antimicrobial activity of several plants from Ghana, including C. sieberiana, can be found elsewhere (Asase et al., 2008).

4.19 Cedrela Meliaceae 4.19.1 Taxon: Cedrela odorata L. Synonyms: Cedrela glaziovii C. DC.; Cedrela mexicana M. Roem. Common names: Barbados cedar, cigar-box cedar, Mexican cedar, Spanish cedar, West Indian cedar (Fig. 4.18), cèdre acajou [French], cèdre des barbares, westindische zeder [German], cedro colorado [Spanish], cedro real [Spanish]. Distributional range (native): NORTH AMERICA-Mexico; SOUTH AMERICAMesoamerica: Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, Panama; Caribbean: Antigua and Barbuda, Barbados, Cayman Islands, Cuba, Dominica, Dominican Republic, Grenada, Guadeloupe, Haiti, Jamaica, Martinique, Netherlands Antilles-Curacao, Puerto Rico, St. Lucia, Trinidad and Tobago; Northern South America: French Guiana, Guyana, Suriname, Venezuela; Brazil: Brazil; Western South America: Bolivia, Ecuador, Peru; Southern South America: Argentina (USDA, ARS, National Genetic Resources Program, 2008). Gum (common names): goma de cedro [Spanish], cedro gum, cedar gum (Mantell, 1947). Exudate properties and uses: The gum is exuded in abnormally large tears (up to 15 cm in length and 5 cm in diameter; Howes, 1949). Its color is red to brown or dark amber (Mantell, 1947; Howes, 1949). The gum (Fig. 4.19) is partially soluble (25%) (Howes, 1949) and swells to form clear jellies (Mantell, 1947). In its pure form, it is used locally for cosmetics and pharmaceuticals

Figure 4.19  Cedrela odorata gum (mag. 0.75x courtesy of the Royal Botanic Gardens, Kew; Cat. No. 63005).

190  ◾  Plant Gum Exudates of the World

(Mantell, 1947). Aqueous dispersions of C. odorata gum demonstrate viscoelastic properties and may have interesting applications as stabilizers of emulsions and suspensions due to their rheological behavior (Rinchon et al., 2009). Other commercial and functional uses for other parts of the tree are in building furniture and cigar boxes. Gums are also yielded by Cedrela australis F. Muell., as well as by Toona ciliata M. Roem. (formerly Cedrela toona Roxb. ex Willd.) (Howes, 1949). C. australis also yields a gum without any trace of resin (Maiden, 1901).

4.20 Ceiba Malvaceae (subfamily: Bombacoideae) 4.20.1 Taxon: Ceiba pentandra (L.) Gaertn. Synonyms: Bombax pentandrum L.; Ceiba caribaea (DC.) A. Chev.; Ceiba casearia Medik.; Eriodendron anfractuosum DC. Common names: kapok, kapok tree, silk cottontree, white silk cottontree, capoc  [French], fromager [French], kapokier [French], kapokbaum [German], samauma [Portuguese (Brazil)], samauma-da-várzea [Portuguese (Brazil)], árbol capoc [Spanish], ceiba [Spanish], pochote [Spanish] (USDA, ARS, National Genetic Resources Program, 2008). Economic importance: Environmental: ornamental, shade/shelter. Materials: fiber, lipids (fiber for filling pillows, life preservers and mattresses, oil for soap); Medicine: folk medicine. Distributional range (native): AFRICA-Northeast Tropical Africa: Sudan; East Tropical Africa: Tanzania, Uganda; West-Central Tropical Africa: Burundi, Cameroon, Gabon, Rwanda, Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Ghana, Guinea-Bissau, Mali, Nigeria, Senegal, Sierra Leone, Togo; South Tropical Africa: Angola, Malawi, Mozambique, Zambia. NORTH AMERICA-Mexico: Northern Mexico - San Luis Potosi, Sonora, Tamaulipas; Central Mexico - Colima, Guerrero, Jalisco, Nayarit, Veracruz. SOUTH AMERICA-Mesoamerica: Belize, Costa Rica, El Salvador, Guatemala, Honduras, Mexico-Chiapas, Yucatan, Nicaragua, Panama; Caribbean: Anguilla, Antigua and Barbuda, Barbados, Cuba, Dominica, Dominican Republic, Grenada, Guadeloupe, Haiti, Jamaica, Martinique, Montserrat, Netherlands AntillesCuracao, Puerto Rico, St. Lucia, St. Vincent and Grenadines, Virgin Islands (British)-Virgin Gorda; Northern South America: French Guiana, Guyana, Suriname, Venezuela; Brazil: Acre, Maranhao, Para, Roraima; Western South America: Bolivia - Santa Cruz, Colombia, Ecuador, Peru - Huanuco, Loreto, Pasco. OTHER-naturalized in tropical Asia, native range uncertain (USDA, ARS, National Genetic Resources Program, 2008). The exudate: C. pentandra exudes an astringent dark gum. It swells in water and aside from its color, bears a resemblance to the tragacanth gums. It has been used as a replacement for katira gum in India (Howes, 1949).

4.21 Ceratopetalum Cunoniaceae 4.21.1 Taxon: Ceratopetalum apetalum D. Don Common name: coachwood. Economic importance: Materials: wood. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Queensland (USDA, ARS, National Genetic Resources Program, 2008).

Minor Plant Exudates of the World  ◾  191

Figure 4.20  Ceratopetalum gummiferum (New South Wales Christmas tree) Forest & Kim Starr).

(courtesy of

4.21.2 Taxon: Ceratopetalum gummiferum Sm. (Fig. 4.20). Common name: Christmas bush. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales (USDA, ARS, National Genetic Resources Program, 2008). Exudate properties: The gum is astringent. It is partially soluble and chemically it is presumed to be a gum-resin (Fig. 4.21). Commercial and functional uses for other parts of the tree: The tree is often used for Christmas decoration.

4.22 Chukrasia Meliaceae 4.22.1 Taxon: Chukrasia tabularis A. Juss. Synonyms: Chukrasia velutina M. Roem.; Swietenia chikrassa Roxb. Common names: chittagong tree, surian batu, chickrassy, chittagong wood, Burma almondwood, cherana puteh, repoh, suntang puteh, yinma, tawyinma, voryong nhom, nhom hin, nhom khao, siat-ka. Geographic distribution: India, Pakistan, Burma, Sri-Lanka to Indo-Malesia (De Cordemoy, 1911; Kalinganire and Pinyopusarerk, 2000). Exudate properties: Sometimes the gum reaches the market as an admixture in Indian gums. Its color is reddish to amber and it is water-soluble (Mantell, 1947). Commercial and functional uses for other parts of the tree: Polyphenols and polyphenolrich fractions of plants have been reported to have protective effects against lipid peroxidation, most probably by serving as scavengers of free radicals and/or by chelating metal ions.

192  ◾  Plant Gum Exudates of the World

Figure 4.21  (A) Ceratopetalum apetalum exudate. (B) Ceratopetalum gummiferum exudate (mag. 3x; courtesy of the Royal Botanic Gardens, Kew; Cat. No. 56964 & 56968).

Different extracts/subfractions of C. tabularis exhibited high protective activity (Kaur et al., 2009). Another study demonstrated the antioxidant activity of C. tabularis leaves, and its correlation with the phenolic content in the different fractions (Kaur et al., 2008). The wood is used for furniture, decorative veneers, paneling, carving, turnery and cooperage (Kalinganire and Pinyopusarerk, 2000).

Minor Plant Exudates of the World  ◾  193

4.23  Citrus Rutaceae Quite a few of the trees that produce the widespread citrus fruit (Fig. 4.22) yield gums on occasion (Howes, 1949). However, these gums do not appear to be of any economic importance (Howes, 1949). Certain pathological conditions of citrus that are associated with gummosis are discussed in Chapter 2. Taxa: Citrus aurantiifolia (Christm.) Swingle; Citrus limonia Osbeck (syn: Citrus limonelloides Hayata; Citrus limunum Risso; Citrus medica L. var. limonum Hook f.); Citrus maxima (Burm.) Merr. (syn: Citrus grandis Osbeck; Citrus decumana L.); Citrus sinensis (L.) Osbeck (syn: Citrus aurantium L. var. dulcis L; Citrus aurantium Risso); Citrus medica L. (syn: Citrus medica L. var. cedrata Risso; Citrus medica L. var. medica; Citrus aurantium L. var. medica Wight & Arnott; Citrus crassa Hasskarl). Common names: Chinese lemon, medicinal lemon, Canton lemon, Cantonese lemon, lemandarin, Mandarin lemon, lime (Citrus aurantiifolia), Mandarin lime, Rangpur lime (Citrus limonia), pumelo or shaddock (Citrus maxima), sweet orange (Citrus sinensis), citron, citron melon, Corsican citron, diamante citron, esrog, ethrog, etrog, Leghorn citron, preserving melon, stock melon (Citrus medica). Economic importance: Food: fruits, food additives, flavoring. Environmental: graft stock, ornamental. Medicine: folk medicine. Geographic distribution: Native to Southeast Asia, occurring from northern India to China and south through Malaysia, the East Indies and the Philippines. The trees are widely cultivated worldwide. Gum (common names): citrus gums (lemon, pumelo and orange gums). The exudate: The pale-yellow exudate appears in lumps or as a thin, shiny, brittle, solid layer on the trunk and branches. It has a characteristic aromatic odor. Symptoms of gummosis are usually found in association with injured or dead branches and caused by species of the fungal genus Phytophthora. The wood beneath the infected tissue is pink to orange. Gum pockets develop beneath the bark. Stressful growing conditions, such as freeze damage, high water table, salt accumulation, and poor cultural practices predispose trees to the disease. Citrus gum, which is soluble in water, disappears after heavy rains but is persistent on the trunk under dry conditions. Lesions spread around the circumference of the trunk, slowly girdling the tree. Badly affected trees have pale green leaves with yellow veins, a typical effect of girdling. If the lesions cease to expand or the fungus dies, the affected area is surrounded by callus tissue. Nursery and young orchard trees with small trunk circumference can be rapidly girdled and killed. Large trees may also be killed, but typically the trunks are partially girdled and the tree canopy undergoes defoliation, twig dieback, and short growth flushes. In susceptible rootstocks, lesions may occur on the crown roots below the soil line and symptoms in the canopy develop without obvious damage to the aboveground trunk (Graham and Timmer, 1994). Ethylene and gum-duct formation in citrus have been previously studied (Gedalovitch and Fahn, 1985a,b), and this is discussed in Chapter 2. Gum chemical characteristics: C. limonia gum is variously described as being composed of L-arabinose (2 parts), D-galactose (2 parts) and a mono-O-methyl-D-glucuronic acid (1 part), or of L-arabinose (2 parts), D-galactose (5 parts) and D-glucuronic acid (2 parts). The L-arabinose residues are present in the gum as end groups and some are linked through C1 and C3 (or C2). The ash-free gum shows an equivalent weight of 770-800. Analysis shows that the gum contains 4% methoxyl (Anderson et al., 1936; Connell et al., 1950; Dutton, 1956).

194  ◾  Plant Gum Exudates of the World

A

B

Figure 4.22  (A) Lime fruit (Citrus aurantiifolia) and flowers. (B) Orange fruit (Citrus sinensis) and leaves (courtesy of Forest & Kim Starr).

Minor Plant Exudates of the World  ◾  195

C. limonia and C. maxima gums have the same general structural features. It is most probable that the gum also contains 4-O-methyl-D-glucuronic acid due to the presence of 5.2% ethereal methyl groups (Connell et al., 1950).

4.24 Cocos Arecaceae (subfamily: Arecoideae) 4.24.1 Taxon: Cocos nucifera L. Common names: coconut, coconut palm (Fig. 4.23), copra, nariyal, cocotier [French], kokospalme [German], khopar [India], coqueiro [Portuguese], coco-da-bahia, coco-da-praia, coqueiro-da-bahia, coqueiro-da-praia [Portuguese (Brazil)], cocotero [Spanish]. Geographic distribution: Native to eastern tropical regions. It is grown both throughout the Asian continent (India, Sri-Lanka, Indonesia) and in Central and South America (Mexico, Brazil). In Africa, the largest producing countries are Mozambique, Tanzania and Ghana. Exudate appearance, properties and uses: Tears (Fig. 4.24) are occasionally found on the trunk of the palm, especially when there has been some sort of injury such as when a palm falls and in so doing grazes the trunk of another. The exudate color ranges from yellow to

Figure 4.23  Cocos nucifera (coconut palm).

196  ◾  Plant Gum Exudates of the World

Figure 4.24  Cocos nucifera exudate (courtesy of the Royal Botanic Gardens, Kew; Cat. No. 35457).

black. It is usually reddish-brown, clear and vitreous. The gum is mostly insoluble in water, swelling to a jelly instead. It has poor adhesive properties. Commercial and functional uses for other parts of the tree: Coconuts (Fig. 4.25) are used as whole fruits or in parts: mesocarp fibers, milk, kernel (or flesh), husk. Its leaves are used to make baskets, roofing, etc. An alcoholic drink known as a toddy or palm wine is extracted

Minor Plant Exudates of the World  ◾  197

Figure 4.25  Cocos nucifera coconuts (courtesy of Forest & Kim Starr).

from its sugar sap, tapped from the inflorescences by means of apposite cuttings (Duke, 1972). The development of anthelmintic resistance has made the search for alternative means of controlling gastrointestinal nematodes of small ruminants imperative. Among these alternatives are several medicinal plants traditionally used as anthelmintics. The efficacy of C. nucifera fruit extract on sheep gastrointestinal parasites was studied (Oliveira et al., 2009). An ethyl acetate extract was obtained from the liquid of green coconut husk fiber. The extract’s efficacy in egg hatching and larval development tests, at the highest concentrations tested, was 100% on egg hatching and 99.77% on larval development. The parameters evaluated in the controlled test were not statistically different, indicating that despite the significant results of the in-vitro tests, the ethyl acetate extract has no activity against sheep gastrointestinal nematodes (Oliveira et al., 2009).

4.25 Cola Sterculiaceae 4.25.1 Taxon: Cola cordifolia (Cav.) R. Br. Synonym: Sterculia cordifolia Cav. Common names: mandinka kola, mandingo kola, tabayer, cola ntaba (Bailleul) [French] (http://www.aluka.org/). Geographic distribution: West tropical Africa and forests of Uganda (Greenway, 1941), which are the areas in which the tree is known to yield gum (Howes, 1949). The tree: C. cordifolia is a forest tree that grows to 30 m in height. Its flowers are a uniformly dull creamy-white inside, darker yellowish tinged reddish outside, changing to orange, rich pink and red. Fruiting carpels are a light tawny brown outside, pinkish inside (http://www. aluka.org/).

198  ◾  Plant Gum Exudates of the World

4.26 Combretum Combretaceae This large genus consists of over 200 species and is well represented in Africa. There are approx. 180 different African species and about 30 different Asian species. Several of the African species are known as gum yielders (Jurasek and Phillips, 1993). Geographic distribution: West tropical Africa and East Africa, mainly in the dry forests and low rainfall areas. Other Combretum species, presumably gum yielders, are distributed in the tropics and subtrobics of both hemispheres, except for Australia and the Pacific Islands (Fig. 4.26). Gum (common names): chiriri gum (Combretum lecananthum Engl. & Diels), mumuye gum (Combretum molle R. Br. ex G. Don, formerly C. sokodense Engl., in northern Nigeria) (Howes, 1949). Exudate properties: Gum of C. molle often appears in opaque, tinged lumps, often clear and light-colored (Howes, 1949). The pale-colored nodules produced by some species are not easily distinguished from Acacia nodules if they are mixed either inadvertently or deliberately. Gums of some of the East African and Sudanese Combretum species tend to be lighter than those of West Africa (Anderson, 1978). Some Combretum gums are perfectly soluble in cold water, others only partially so. One of the least viscous Combretum gums, Combretum nigricans Lepr. ex Guill. & Perr., has a much higher viscosity than is typical for Acacia gums. The gums of Combretum adenogonium Steud. ex A. Rich. (formerly Combretum fragrans F. Hoffm.) and Combretum collinum Fresen. give high viscous solutions resembling those of karaya or tragacanth gum. These high viscosities are reflected in high molecular weights.

Figure 4.26  (A) Combretum erythrophyllum Cat. No. 56674 (mag. 2x). (B) Combretum zeyheri Sond. Cat. No. 56687 (mag. 2x). (C) Combretum glutinosum Cat. No. 56688 (mag. 3x) (courtesy of the Royal Botanic Gardens, Kew).

Minor Plant Exudates of the World  ◾  199

Figure 4.26  (Continued).

The molecular weight of C. collinum gum is 11.6 million, which is probably the highest observed for a gum exudate (Anderson and Bell, 1977). Gum chemical characteristics: The composition of Combretum gums is much more complex than that of Acacia species gums. Various Combretum gums have been found to vary in acetylation degree, reaching up to approximately 7% in Combretum psidioides Welw. (Anderson,

200  ◾  Plant Gum Exudates of the World

1978). Extensive differences in chemical and physical properties also occur within the genus Combretum (Anderson, 1978). NMR spectroscopy has shown that the rhamnose and uronic acid contents of gum combretum are located within internal polysaccharide chains. This explains the well-known difference in emulsification functionality between gum arabic, in which all rhamnose and uronic acid groups are chain-terminal, and gum combretum which is, in addition, markedly hygroscopic and characterized commercially by its tendency to ‘block up’ during transit and storage. Analytical and structural features of some Combretum gums have been widely studied (McIlroy, 1957; Anderson et al., 1959, 1986; Aspinall and Bhovanandan, 1965a,b; Anderson and Bell, 1976; Douglas et al., 1976; Anderson and Weiping, 1990; Anderson and Morrison, 1990b). Commercial availability of the gum (pure form): Poorer quality grades from different botanical sources tend to be mixed and offered for sale under a variety of names, e.g., gum Niger, Nigerian gum, West African gum or East African gum. They are also liable to be mixed with gum of Indian origin and sold as gum ghatti. This practice is more acceptable than an admixture of Combretum with Acacia gums because the main botanical source of ghatti, Anogeissus latifolia, is also a member of the Combretaceae (Anderson, 1978). Combretum adenogonium Steud. ex A. Rich. (formerly Combretum dalzielii Hutch.) has been said to provide much of the gum collected in the Niger basin, south of 14o N, although it is not tapped. Gum of Combretum nigricans var. elliotii (Engl. & Diels) Aubrév. (formerly Combretum elliotii Engl. & Diels) was believed to be the most abundant gum-yielding tree in Sokoto Province, Nigeria. The gum was used in food, by leather workers and in making ink. Gum of Combretum lecananthum has also been reported to be eaten by the natives in Nigeria, when it exudes freely in the hot season. Gum of Combretum collinum subsp. hypopilinum (Diels) Okafor (formerly Combretum hypopilinum Diels and Combretum verticillatum Engl. & Diels) is used by natives in Nigeria to plug carious teeth (Howes, 1949). The gum of Combretum nigricans has recently been suggested to be the major source of West African combretum gums (Anderson et al., 1991a). Commercial and functional uses for other parts of the tree: Combretum species are used as shade trees and to line avenues. Woods of some species are used in construction. Various parts of the tree are used for medicinal preparations.

4.27 Cordia Boraginaceae (subfamily: Cordioideae) 4.27.1 Taxon: Cordia myxa L. Common names: Assyrian plum, sapistan, sebesten plum, selu, Sudan teak. Geographic distribution: Native of tropical Asia and Africa. Found scattered throughout the mid-Himalayas up to elevations of 1,470 m. Exudate appearance, solubility and commercial availability: Records of gum exudation are from India (Howes, 1949; Khan et al., 2001). A sweet, mucilaginous, highly viscous polysaccharide from unripe fruit pulp of Cordia africana Lam. (formerly Cordia abyssinica R. Br.) was isolated from fruits from Southern Africa (Benhura and Katayi, 2000; Benhura and Chidewe, 2002). The viscosity and the solubility of the fruit gum in aqueous solution have been studied (Benhura and Chidewe, 2002). Gum of Cordia sinensis Lam. (formerly Cordia gharaf Ehrenb. ex Asch.) is astringent and in India, it has been used for gargling (Greenway, 1941). Cordia gum is used as glue because of its excellent adhesive properties

Minor Plant Exudates of the World  ◾  201

(Benhura and Chidewe, 2002). At low temperature and concentrations of at least 1.5%, the fruit gum of Cordia africana can form a gel in water (Benhura and Katayi, 2000). The fruit gum can be used beneficially in gonorrhoea (Parmar and Kaushal, 1982). Commercial and functional uses for other parts of the tree: The edible fruits have a few medicinal applications, but they are especially useful as an expectorant and are effective in treating diseases of the lungs and chronic fever. They can also be used for pasting sheets of paper, cardboard, etc. (Parmar and Kaushal, 1982). The fruit is not widely used for consumption by humans but serves as food for monkeys and other animals (Benhura and Chidewe, 2002). Leaves are useful as fodder.

4.28 Cordyla Fabaceae (subfamily: Faboideae) 4.28.1 Taxon: Cordyla africana Lour. Geographic distribution: Tropical Africa extending south to Natal. Gum (common names): chiraya gum, da gum (in Sudan) (Howes, 1949). Exudate appearance and commercial avaliability: C. africana exudes gum or resin (Fig. 4.27). Cordyla richardii Milne-Redh. exudes only gum (Greenway, 1941). The gum has been used to make a type of sizing or whitewash for houses in West Africa (Dalziel, 1936). Commercial and functional uses for other parts of the tree: The fruits are edible, and are used in sauces.

Figure 4.27  Cordyla africana exudate (mag. 2x; courtesy of the Royal Botanic Gardens, Kew; EBC No. 60171).

202  ◾  Plant Gum Exudates of the World

4.29 Corypha Arecaceae (subfamily: Coryphoideae) 4.29.1 Taxon: Corypha utan Lam. Synonyms: Corypha elata Roxb.; Corypha gebanga (Blume) Blume; Taliera gebanga Schult. & Schult. f. Common names: buri palm, gebang palm, buripalme [German]. Distributional range (native): ASIA, TROPICAL-Indian Subcontinent: India; Indo-China: Myanmar; Malesia: Indonesia, Malaysia, Papua New Guinea, Philippines. AUSTRALASIAAustralia: Australia - Northern Territory, Queensland (USDA, ARS, National Genetic Resources Program, 2008). Exudate appearance, availability and functionality: The gum of C. utan has a sweet smell and is considered rare. Its color is brownish-black (Corypha umbraculifera L.), (Fig. 4.28), or reddish-brown (C. utan). The gum is used medicinally by the Javanese and the tree is used for ornamental purposes.

4.30 Crataeva Capparaceae 4.30.1 Taxon: Crataeva adansonii DC. Common name: Gum num. Economic importance: Environmental: ornamental. A

Figure 4.28  (A) Corypha umbraculifera tree and (B) exudate (courtesy of the Royal Botanic Gardens, Kew; Cat. No.: 35306).

Minor Plant Exudates of the World  ◾  203

Figure 4.28 (Continued). 

Distributional range (native): AFRICA-Northern Africa: Egypt; Northeast Tropical Africa: Chad, Eritrea, Ethiopia, Sudan; East Tropical Africa: Kenya, Tanzania, Uganda; West-Central Tropical Africa: Cameroon, Central African Republic, Congo, Gabon, Rwanda, Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Gambia, Ghana, Guinea, Mali, Mauritania, Niger, Nigeria, Senegal; South Tropical Africa: Zimbabwe; Western Indian Ocean: Madagascar. ASIA, TEMPERATE-China: China; Eastern Asia: Taiwan. ASIA, TROPICAL-Indian Subcontinent: Bangladesh, India, Pakistan, Sri Lanka; Indo-China: Indochina, Myanmar, Thailand, Malesia, Philippines; OTHER-cultivated elsewhere (USDA, ARS, National Genetic Resources Program, 2008). The tree: The growth of C. adansonii is often stunted due to grass fires (Howes, 1949).

204  ◾  Plant Gum Exudates of the World

4.31 Cussonia Araliaceae 4.31.1 Taxon: Cussonia arborea Hochst. ex A. Rich. Synonyms: Cussonia barteri Seem.; Cussonia djalonensis A. Chev.; Cussonia nigerica Hutch.; Cussonia longissima Hutch. & Dalz.; Cussonia spicata Thunb. Common name: cabbage-wood tree. Geographic distribution: northern Nigeria (C. arborea); eastern Cape Province in South Africa and Zimbabwe (Cussonia spicata). Exudate properties: The gum of C. arborea exudes from wounded trunks and hangs in slender rods. It has a slightly irritant quality (Howes, 1949). C. spicata occasionally exudes gum from its cork-like bark (Churms and Stephen, 1971). The gum of C. arborea is clear and colorless (Howes, 1949). The gum of C. spicata is light brown (Churms and Stephen, 1971). The gum is partially water-soluble. The water-insoluble portion of the gum exudates of C. spicata may be solubilized by alkali (Churms and Stephen, 1971). In northern Nigeria, Cussonia nigerica yields a clear colorless gum when wounded, which hangs in slender pencils and is also believed to have a slightly irritant quality (Howes, 1949). Gum chemical characteristics: C. spicata gum consists of a mixture of polysaccharides that differ not only in molecular weight but also in composition. Evidence obtained for the gum exudates of C. spicata suggests a molecular core consisting of D-galactose residues, mainly β-D-(1 to 3)-linked, most of which carry a D-glucuronic acid residue, β-linked at C-6. The molecular-weight distribution pattern of the degraded polysaccharide obtained upon partial hydrolysis with acid indicates a possible repeating unit with a molecular weight of 1,200. L-arabinose residues occur as short branches, each attached to the galactan framework (at C-4), with α-L-(1 to 5)-linkages between consecutive L-arabinose units in some cases. L-rhamnopyranose end groups are also present (Churms and Stephen, 1971). Commercial and functional uses for other parts of the tree: In Zimbabwe, the bark is used in folk medicine.

4.32 Cycas Cycadaceae 4.32.1 Taxon: Cycas lane-poolei C. A. Gardner Distributional range (native): AUSTRALASIA-Australia: Australia - Western Australia. Exudate appearance: Similar to the gum mucilage of Encephalartos (De Luca et al., 1982).

4.32.2 Taxon: Cycas circinalis L. Synonym: Cycas undulata Desf. ex Gaudich. Common names: queen sago, false sago, fern palm. Geographic distribution: C. circinalis is native to equatorial Africa. The tree: C. circinalis looks like a palm tree with its featherlike leaves organized in a rosette that crowns a single trunk. It can grow up to approx. 6 m in height. The dark green pinnate leaves grow to 2.4 m in length with narrow ∼30-cm leaflets that curve gracefully downward. This species is dioecious, with male and female reproductive parts on separate plants (Fig. 4.29).

Minor Plant Exudates of the World  ◾  205

A

B

Figure 4.29  Cycas circinalis. (A) Sago palm habit. (B) Sago palm leaves. (C) Sago palm spiked stems, and (D) sago palm fruit (courtesy of Forest & Kim Starr).

206  ◾  Plant Gum Exudates of the World

C

D

Figure 4.29  (Continued).

Minor Plant Exudates of the World  ◾  207

Gum properties: Gum is produced by C. circinalis and Cycas rumphii Miq. C. circinalis gum is said to be insoluble in water but absorbing a considerable quantity of it, becomes mucilage. It is similar to tragacanth in its hydrocolloidal behavior (Greenway, 1941). Specimens of C. circinalis consist of large brown lumps (Howes, 1949). Commercial and functional uses for parts of the tree: Flour is obtained from the seeds, which must be carefully washed and processed to remove toxins. There is evidence that longterm use of this flour, even if properly prepared, can eventually result in paralysis and other neurological disorders.

4.33 Dichrostachys Fabaceae (subfamily: Mimosoideae) 4.33.1 Taxon: Dichrostachys cinerea (L.) Wight & Arn. Synonyms: Cailliea dichrostachys Guill. et al.; Cailliea nutans (Pers.) Skeels; Dichrostachys cinerea var. hirtipes Brenan & Brummitt [= Dichrostachys cinerea subsp. argillicola]; Dichrostachys cinerea subsp. lugardae (N. E. Br.) Brenan & Brummitt [= Dichrostachys cinerea subsp. africana]; Dichrostachys cinerea var. lugardiae Brenan & Brummitt [= Dichrostachys cinerea subsp. africana var. africana]; Dichrostachys forbesii Benth. [≡ Dichrostachys cinerea subsp. forbesii]; Dichrostachys glomerata (Forssk.) Chiov. [= Dichrostachys cinerea subsp. cinerea]; Dichrostachys nutans (Pers.) Benth. [= Dichrostachys cinerea subsp. cinerea]; Dichrostachys nutans var. setulosa Welw. ex Oliv. [≡ Dichrostachys cinerea subsp. africana var. setulosa]; Dichrostachys nyassana Taub. [≡ Dichrostachys cinerea subsp. nyassana]; Dichrostachys platycarpa Welw. ex W. Bull [≡ Dichrostachys cinerea subsp. platycarpa]; Mimosa cinerea L. [≡ Dichrostachys cinerea subsp. cinerea]; (=) Mimosa glomerata Forssk.; (=) Mimosa nutans Pers (USDA, ARS, National Genetic Resources Program, 2008). Common names: marabou thorn, marabou. Distributional range (native): AFRICA-Macaronesia: Cape Verde; Northeast Tropical Africa: Chad, Ethiopia, Somalia, Sudan; East Tropical Africa: Kenya, Tanzania, Uganda; WestCentral Tropical Africa: Burundi, Cameroon, Gabon, Rwanda, Zaire; West Tropical Africa: Benin, Cote D’Ivoire, Gambia, Ghana, Guinea, Guinea-Bissau, Liberia, Mali, Niger, Nigeria, Senegal, Sierra Leone, Togo; South Tropical Africa: Angola, Malawi, Mozambique, Zambia, Zimbabwe; Southern Africa: Botswana, Namibia, South Africa - Cape Province, Natal, Transvaal, Swaziland. ASIA, TEMPERATE-Arabian Peninsula: Oman, Saudi Arabia, Yemen. ASIA, TROPICAL-Indian Subcontinent: India, Sri Lanka; Indo-China: Myanmar; Malesia: Indonesia-Java, Lesser Sunda Islands. AUSTRALASIA-Australia: Australia - Northern Territory (USDA, ARS, National Genetic Resources Program, 2008). Similar gums: Presumably gum arabic (the plant is related to acacia). Commercial and functional uses for other parts of the tree: The D. cinerea tree is often a valued source of fuel. Various parts of the tree are used medicinally. Further information on additional medicinal properties of the aerial parts of D. cinerea can be found elsewhere (Abou Zeid et al., 2008).

208  ◾  Plant Gum Exudates of the World

4.34 Echinocarpus Elaeocarpaceae 4.34.1 Taxon: Echinocarpus australis Benth. (now synonym of Sloanea australis F. Muell., see section 4.6.2.2)

4.35 Elaeocarpus Elaeocarpaceae 4.35.1 Taxon: Elaeocarpus grandis F. Muell. Synonym: Elaeocarpus angustifolius Blume.

4.35.2 Taxon: Elaeocarpus obovatus G. Don Common names: blueberry ash, gray carobean, hard quandong. Economic importance: Materials: wood. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Queensland.

4.35.3 Taxon: Elaeocarpus reticulatus Sm. Common name: blueberry ash. Economic importance: Environmental: ornamental. Distributional range (native): AUSTRALASIA-Australia: Australia - New South Wales, Queensland, Tasmania, Victoria. Exudate appearance: Exudes in small quantities, and the gum is pale in color. Commercial and functional uses for other parts of the tree: Aborigines make necklaces from the seeds after eating the fruit flesh.

4.36 Encephalartos Zamiaceae 4.36.1 Taxon: Encephalartos hildebrandtii A. Braun & C. D. Bouché Distributional range (native): AFRICA-East Tropical Africa: Kenya, Tanzania. Exudate appearance: The gum of Encephalartos species is found in abundance in ducts within the stem and on the surfaces of cones were it originates in the radial canals and makes its way, in aqueous solution, between the seeds to the periphery (Stephens and Stephen, 1988). Studies on the gum of Encephalartos friderici-guilielmi Lehm. describe its exudate from cones as hard, dry nodules in older plants or as soft exudates from trees following heavy rains (Vogt and Stephen, 1993b). The exudate of E. hildebrandtii has been described as rods and tears (Howes, 1949). Incisions made in the rachis stimulate the exudation of the gum (De Luca et al., 1982). Exudate color and gum properties: The exudate of E. hildebrandtii is a clear yellow or pale brown. The gummy exudates from cones of several species of Encephalartos resemble each other in their sugar and uronic acid constituents, though the proportions vary. They are

Minor Plant Exudates of the World  ◾  209

made up of a complex acidic polysaccharide. E. friderici-guilielmi gum was found to have a (1 to 3)-D-galactan with p-cymene > cuminaldehyde > γ-terpinene (Kanakdande et al., 2007). Paprika oleoresin is extracted from the fruits of Capsicum annum L. by using organic solvents (mainly hexane) which are removed prior to use (Jarén-Galán et al., 1999). The oleoresin is composed of capsaicin (C18H27NO3, molar mass 305.4, melting point 62-65°C, boiling point 210-220°C), the main flavoring compound which gives pungency at higher concentrations, and capsanthin (C40H56O3, molecular weight 584.9 g/mol, appearance: red oil, soluble in water) and capsorubin, the main coloring compounds (among other carotenoids) (Pérez-Gálvez et al., 2003). The oleoresin and its components are used in formulating nutraceuticals, colorants and pharmaceuticals. The paprika oleoresin is microencapsulated by the traditional gelatin-gum arabic microcapsule (Fernandez-Trujillo, 2007).

5.2.13.2 Linoleic acid microencapsulation In nutrition, the term used for fats is lipids. A fatty acid is a component of the lipids in foods, usually as part of an acylglycerol (Gates, 1987). Lipid-oxidation rates can be predicted to some extent by some key factors, including the degree of fatty acid unsaturation, the distribution of fatty acids into different lipid classes, temperature, and the presence of oxygen, antioxidants, and oxidation catalysts (Lehtinen and Laakso, 2000). Saturated fatty acid is a fatty acid in which each of the carbons, except the terminal carbons, are bonded to two hydrogens (Gates, 1987). Linoleic acid is an unsaturated omega-6 fatty acid. n-6 fatty acids are a family of unsaturated fatty acids which all have a carbon-carbon double bond in the n-6 position, i.e., the sixth bond from the end of the fatty acid. The protein-rich fraction of oat reduces the oxidation rate of free linoleic acid by reducing the concentration of linoleic acid that can serve as a substrate for lipoxygenase (Lehtinen and Laakso, 2000). The mechanism underlying this behavior appears to be similar to the trapping of linoleic acid by cyclodextrin (Lopez-Nicolas et al., 1997). Another approach to reducing linoleic acid (Fig. 5.10) oxidation is microencapsulation with gum arabic using a spray-dryer with a centrifugal atomizer. The oxidation of encapsulated linoleic O HO 1

6 9

1

12

Figure 5.10  Chemical structure of linoleic acid (http://en.wikipedia. org/wiki/ Image: LAnumbering.png, courtesy of Edgar181).

Food Applications of Plant Exudates  ◾  275

acid was studied at various temperatures and at different relative humidities (Fang et al., 2005). The temperature of the dryer’s inlet air was found to have no significant effect on the moisture content of the microcapsules; hence, the oxidation process of encapsulated linoleic acid was unaffected by the inlet air temperature. However, the rotational speed of the atomizer did affect the size and moisture content of the microcapsules, which were found to be larger and higher, respectively, for microcapsules prepared at the lower rotational speed (Fang et al., 2005). Linoleic acid in a gum arabic-based microcapsule is more resistant to oxidation than that in a maltodextrinbased microcapsule. Although the size of the oil droplets in the emulsion with maltodextrin decreased and the emulsion stability improved by addition of a small-molecule emulsifier to linoleic acid, the oxidative stability of the encapsulated linoleic acid was not significantly improved. Encapsulated linoleic acid of small droplet size oxidized more slowly than that of large droplet size (Minemoto et al., 2002). The oxidation of linoleic acid in larger microcapsules proceeded more slowly. In addition, oxidation progressed more quickly at higher relative humidity, and it was suggested that the glass transition of the wall material might affect the progress of oxidation. Relative humidity was found to have little effect on the activation energy of oxidation during storage of the microcapsules (Fang et al., 2005). The oxidation processes of linoleic acid mixed with ferulic acid or the 1-pentyl, 1-hexyl and 1-heptyl ferulates, encapsulated with gum arabic or maltodextrin, were also studied. The alkyl ferulates had a higher antioxidative effect than ferulic acid, but there was no significant difference among the three alkyl ferulates (Fang et al., 2006). Suppression of oxidation by 1-hexyl ferulate or ferulic acid was more effective at higher additiveto-linoleic acid molar ratios. The suppressive effect of the alkyl ferulates was more pronounced for linoleic acid encapsulated with maltodextrin than for that encapsulated with gum arabic because of maltodextrin’s lack of antioxidative ability (Fang et al., 2006). Another approach that tackles both degradation of conjugated linoleic acid (CLA) and its acid degradation used the encapsulation of CLA in three different matrices: whey protein concentrate (WPC), gum arabic and a blend of WPC and maltodextrin 10 DE (1:1, w/w). Kinetics studies on the degradation of CLA and lipid oxidation of microcapsules were carried out at water activity values of 0.108 to 0.892, at 35 and 45°C. The highest values of CLA degradation and lipid oxidation were observed in the water-activity range of 0.103 to 0.429 for all matrices at 45°C, whereas the lowest CLA degradation and lipid oxidation were observed for WPC at a water activity of 0.743 and 35°C. WPC microcapsules exhibited the best morphology and encapsulation efficiency and the lowest CLA degradation (Jimenez et al., 2006).

5.2.13.3 Procyanidins Procyanidins, compounds commonly found in red wine, are thought to be good for our blood vessels. The endothelial cells lining our arteries are an important site of action for the vascularprotection effects of active polyphenols such as procyanidins (Corder et al., 2006). When wine is made in the traditional way, the grape fermentation period lasts 3 to 4 weeks, as opposed to the 1-week period in more modern methods. The traditional method allows for the full extraction of procyanidins from the skin and seeds. Procyanidins were extracted from grape-seed residues after oil removal. Microencapsulation of procyanidins was performed with gum arabic and maltodextrin as wall materials. After homogenization, spray-drying was used to prepare microcapsules. The microencapsulation efficiency was up to ∼89%. Analysis of the stable product showed that the procyanidin did not change during the processing and that the procyanidin microcapsule membrane was uninterrupted, maintaining fairly good integrity (Zhang et al., 2007).

276  ◾  Plant Gum Exudates of the World

5.2.14 Coacervation Coacervation is the separation of a colloid-rich layer from a lipophilic sol upon the addition of another substance (Aulton, 2002). This layer, which is present in the form of an amorphous liquid, constitutes the coacervate. Simple coacervation may be brought about by a ‘salting-out’ effect upon addition of an electrolyte or a non-solvent (Aulton, 2002). An important method of microencapsulation, employing complex coacervation, was developed by the National Cash Register Company. This method can produce capsules for use in controlled dry delivery, fragrance samplers, pesticides and cosmetic ingredients. In a complex coacervation process, gelatin with a high isoelectric point and gum arabic with many carboxyl groups are added to a core-containing suspension at relatively low pH above 35°C. The gelatin and gum arabic react to form microdroplets of polymer coacervate which separate. The wall around the core is hardened by the addition of formaldehyde or glutaraldehyde (Jason and Kalota, 1996). In the final steps, the suspension of microcapsules is cooled and the pH raised, after which the suspension is filtered leaving the microcapsules on the filter media (Jason and Kalota, 1996). Encapsulates having shells of cross-linked mixtures of proteins and polysaccharides are widely used in the food and pharmaceutical industries for controlled release of active and flavor compounds. Several analytical techniques were applied to characterize glutardialdehyde (GDA)-cross-linked encapsulates made of gelatin and gum arabic. Cross-linking occurred between GDA molecules and lysine and hydroxylysine ε-amino groups, and up to eight different types of cross-linked products could be identified. These included pyridinium ions and Schiff bases, as well as unreacted GDA condensation products (Fuquet et al., 2007). Many variations of complex coacervation are known, as well as polymer combinations. Complex coacervation is employed to encapsulate solids and liquids (Jason and Kalota, 1996). Another method of complex coacervation involves the formation of electrostatic complexes of gum arabic with chitosan. These polysaccharides are oppositely charged and optimum coacervate yield can be achieved at a gum arabic-to-chitosan ratio of 5, in a pH range of 3.5 to 5.0 (EspinosaAndrews et al., 2007). Coacervate yield was drastically decreased at pH values below 3.5 due to a low degree of ionization of gum arabic molecules, and at pH values above 5 due to low solubility of chitosan. Increasing ionic strength decreased coacervate yield due to shielding of ionized groups (Espinosa-Andrews et al., 2007). To avoid the participation of gelatin in the preparation of protein-gum arabic coacervates, complexes of pea globulin and α-gliadin proteins with gum arabic were prepared at different acidic pH values (Chourpa et al., 2006). Raman microspectrometry confirmed a higher content of β-sheets and random coils in pea globulin and dominating α-helical structures in α-gliadin. For protein-gum arabic complexes, Raman data supported the existence of specific pH conditions for optimal complex coacervation (pH 2.75 for globulin and pH 3.0 for gliadin), when pH-induced conformational perturbations of free protein structure are strongest and compensation of these perturbations by gum arabic is most pronounced (Chourpa et al., 2006).

5.2.15 Deep-fat frying Frying is a unit operation used mainly to alter the eating quality of foods (Fellows, 2000). Frying results in the thermal destruction of microorganisms and enzymes, as well as in reduced water activity at the food’s surface. During deep-fat frying, heat is transferred via convection within the hot oil and conduction to the interior of the food (Rispoli et al.,1987; Fellows, 2000). Throughout deep-fat frying, moisture loss is proportional to the square root of frying time and the oil absorption that occurs as moisture is removed from the food (Saguy and Pinthus, 1995). There are many

Food Applications of Plant Exudates  ◾  277

approaches for reducing the oil content of deep-fried foods including: pre-fry drying; blowing hot air against the freshly fried products and draining the excess oil from them; contacting the fried product with solvents such as difluorodichloromethane, and using certain additives (Annapure et al., 1999). Attempts to use hydrocolloid combinations with the goal of reducing oil content in fried foods have proven useful. Hydrocolloids at 0.25 to 2.00% (on the basis of chickpea flour weight) were screened for their ability to reduce oil uptake in a model deep-fat-fried product prepared from chickpea flour. Results indicated that the ability to reduce oil uptake in such a product decreases in the following order: gum arabic > carrageenan > gum karaya > guar gum > CMC > hydroxypropylmethyl cellulose (HPMC) (Annapure et al., 1999). Hydrocolloids such as xanthan, gum ghatti, gum tragacanth, and locust bean gum were found to be ineffective for this purpose (