Research Collection Doctoral Thesis Production and characterisation of Prosopis seed galactomannan Author(s): Cruz Alcedo, Gastón Eduardo Publication Date: 1999 Permanent Link: https://doi.org/10.3929/ethz-a-003838586 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library Diss.ETHNo. 13153 Production and characterisation of Prosopis seed galactomannan A dissertation submitted to the SWISS FEDERAL INSTITUTE OF TECHNOLOGY ZURICH For the degree of Doctor of Technical Sciences presented by Gaston Eduardo CRUZ ALCEDO Ingeniero Industrial, Universidad de Piura born June 2, 1963 citizen of Peru accepted on the recommendation of Prof. Dr. Renato Amadö, examiner Prof. Dr. Felix Escher, co-examiner Ms. Eva Arrigoni, co-examiner Zurich 1999 ACKNOWLEDGEMENTS I wish to thank Prof. Dr. Renato Amadö, my thesis director, for giving me the opportunity to work in his laboratory, for the fruitful discussions and his excellent guidance. Already in 1987 he believed in my skills and enthusiasm for the study of Prosopis fruits and permitted me to learn many analytical techniques during a stay at the ETH in Zurich. I am happy for winning his estimation. A special thanks is due also to Evi Arrigoni for her practical advice in the laboratory and for her friendly collaboration, as well as for the critical review and correction of my thesis. I am very grateful to her for agreeing to be my co-examiner. I would also like to express my gratitude to Prof. Dr. Felix Escher for agreeing to be co- examiner and for the helpful discussion on processing technologies and the rheology of gums. This work would not have been possible without the financial support of the Swiss Federal Office for Education and Science (BBW). It took on the costs of participation of the Institute of Food Science ETHZ in an international collaborative research project on Prosopis in the framework of the STD-3 Programme of the European Commission. The help of Mr. Bruno Jud, vice-director of Unipcktin AG, was invaluable for the realisation of the roasting experiments at his pilot plant. I am also grateful to him for his comments on real facts of the galactomannan industry. My sincerest thanks goes to Roberto Pompizzi, Daniel Wechsler and Georg Strasser, for the good time at the lab D24 and for their explanations and practical help during the isolation, GLC and GC-MS analyses of the gums. For performing the amino acid analyses I wish to thank Hanna Schneider, and for the linguistic support I am grateful to Berit Abt. They offered me not only their professional help but opened a part of their private lives to my family and me. I also thank Markus Burri for carrying out a great pari of the "dirty work" during the fermentation experiments. I would like to extend very special thanks to Christian Combes, Johanna Feusi, Susanna Hug-Iten, Francisca Jörger, Dr. Giuseppe Manzardo, Susan Tschäppät, Roland Wernli and all my colleagues at the ILW for the contribution in one or the other way to this work, and for the wonderful friendship. I am also grateful to my colleagues at my home university in Peru, especially to Walter Ruiz, for the help during the seed separation trials and for the continuous interest in my ideas and projects. Last but not least, I am deeply indebted to my darling Maribel and my children Valeria and Nicolas for their emotional support and the unforgettable moments spent together in Switzerland, as well as for their courage during my long absences and a lot of patience during many weekends while I was concluding the writing of this thesis. TABLE OF CONTENTS III TABLE OF CONTENTS 1 INTRODUCTION 1 2 LITERATURE REVIEW 4 2.1 Prosopis pods as food source 4 2.1.1 General description 4 2.1.2 Production, collecting and market of Prosopis pods 6 2.1.3 Traditional human food products 7 8 2.1.4 Composition of Prosop is pods 2.1.5 Processing and new food products from Prosopis pods 14 2.2 Properties and applications of galactomannans 17 2.2.1 Occurrence and structure 17 2.2.2 Galactomannans as food additives 19 2.2.3 Technology of the production of seed galactomannans 22 2.2.4 Galactomannans as dietary fibre 24 28 2.3 Prosopis seed gum: state of the art 3 EXPERIMENTAL PART 32 3.1 Plant material 32 3.2 Separation of Prosopis seeds 32 3.2.1 Separation of seeds from milled fraction 32 3.2.2 Improvement of the milling process 33 3.3 Technological processes for endosperm separation 35 3.3.1 Acid decoating process 35 3.3.2 Roasting process 35 3.3.3 Preparation of samples for characterisation 38 3.4 Isolation of Prosopis galactomaniian for structure analysis 39 3.5 Analytical methods for chemical characterisation 39 3.5.1 General methods 40 3.5.2 Determination of neutral sugars 40 3.5.3 Methylation analysis 43 3.6 Rheological measurements 45 3.6.1 Preparation of gum solutions 45 IV TABLE OF CONTENTS 3.6.2 Dynamic viscosity of gum solutions 46 3.6.3 Interaction of Prosopis gum with xanthan gum 47 3.6.4 Intrinsic viscosity 47 3.7 Enzymatic modification of Prosopis galactomannan 48 3.8 In vitro digestion and colonic fermentation of Prosopis gum 49 4 RESULTS AND DISCUSSION 53 4.1 Fractionation of Prosopis pods 53 4.2 Improvement of the seed extraction 53 4.3 Processes for endosperm separation: technological considerations 57 4.3.1 Preliminary experiments 58 4.3.2 Acid decoating process 58 4.3.3 Roasting process 59 4.3.4 Overall yield of the endosperm separation process 65 4.4 Characterisation of Prosopis galactomannan 65 4.4.1 Isolation of galactomannan 65 4.4.2 Monomelic components and impurities 67 4.4.3 Types of glycosidic linkages 71 4.4.4 Molecular weight 74 4.5 Rheological properties of Prosopis gum solutions 76 4.5.1 Flow behaviour 77 4.5.2 Development and stability of viscosity 79 4.5.3 Effect of processing on the viscosity 80 4.5.4 Viscosity as a function of concentration and temperature 82 4.5.5 Brookfield viscosity 83 4.5.6 Interaction with xanthan gum 84 4.6 Enzymatic removal of galactose from galactomannan 85 4.7 In vitro digestibility and fermentability of Prosopis gum 88 4.7.1 Effects of in vitro digestion 89 4.7.2 In vitro colonic fermentability 90 5 CONCLUSIONS 98 6 REFERENCES 103 7 APPENDIX 113 LIST OF ABBREVIATIONS V LIST OF ABBREVIATIONS Ara L-arabinose ASTM American Society for Testing and Materials acetic acid C3 propionic acid C4 butyric acid iC4 iso-butyric acid C5 valeric acid iC5 i so-val eric acid cfu colony-forming units d.m. dry matter DMSO dimethyl sulphoxide ECR effective carbon response F1-F4 fractions obtained by milling Prosopis pods FAO Food and Agriculture Organisation FID flame ionisation detector Fuc L-fucose Gal D-galactose GC-MS gas chromatography coupled with mass spectrometry GG sample of guar gum used in this study GLC gas-liquid chromatography Glu D-glucose HPAEC-PAD high performance anion exchange chromatography with pulsed amperometric detection 11-14 fractions of isolated Prosopis galactomannan IPA isopropanol JECFA Joint Expert Committee for Food Additives LB sample of carob gum used in this study LEG locust bean gum = carob gum Man D-mannose VI LIST OF ABBREVIATIONS M/G mannose to galactose ratio MS mass spectrometry NMR nuclear magnetic resonance NS neutral sugars PA sample of Prosopis gum obtained by acid decoating PMAA partially methylated alditol acetates PN solution of Prosopis gum, extracted from non-trcatcd splits PR sample of Prosopis gum obtained by roasting PRx sample of Prosopis gum obtained by roasting and optical sortin, PSp solution of Prosopis gum extracted from milled splits PSG Prosopis seed galactomannan PVDF polyvinylidene difluoride PW sample of ground Prosopis seeds R4 insoluble fraction after aqueous extraction of galactomannan R4c, R4w seed coat and a white insoluble residue respectively Rha L-rhamnose RT room temperature " of roasted seeds ül O'n' sieving fractions from splitting SCFA short chain fatty acids ss separated seeds TR sample of tara gum used in this study U units of enzyme activity UV ultra-violet WHC water holding capacity WHO World Health Organisation Xyl D-xylose SUMMARY VII SUMMARY The fruits of the "algarrobo" tree (Prosopis pallida and Prosopis juliflora) have a long tradition as food source in the arid zones of Northern Peru, in addition to their main use as animal feed. Recently, a wide range of food products has been developed on the basis of a detailed characterisation of each part of the fruit. These efforts aim to valorise the fruits as a way to avoid trees to be used for firewood only. The present work is related to the Prosopis seed gum (also referred to as mesquite seed gum), a galactomannan polysaccharide with potential applications as thickening agent in the food industry. Extraction techniques of the seed endosperm have been studied in order to develop an appropriate industrial process. Aqueous extraction of gum has been shown to be suitable for analytical purposes but not for a large-scale production. Two methods, currently used for industrial production of guar, tara and carob gum, were evaluated. Treatment with sulphuric acid and roasting of the seeds have been proven to be effective for the elimination and detachment of the seed coat, respectively. Subsequent splitting and sorting of the endosperm led to the production of two types of technical gum (PA gum = acid process and PR gum = roasting process).