Emerging natural hydrocolloids : rheology and functions [First edition.] 9781119418665, 1119418666

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Emerging Natural Hydrocolloids

Emerging Natural Hydrocolloids Rheology and Functions

Edited by Seyed M.A. Razavi Food Hydrocolloids Research Center Department of Food Science and Technology Ferdowsi University of Mashhad Mashhad Iran

This edition first published 2019 © 2019 John Wiley & Sons Ltd All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions. The right of Seyed M.A. Razavi to be identified as the author of the editorial material in this work has been asserted in accordance with law. Registered Offices John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK Editorial Office 9600 Garsington Road, Oxford, OX4 2DQ, UK For details of our global editorial offices, customer services, and more information about Wiley products visit us at www.wiley.com. Wiley also publishes its books in a variety of electronic formats and by print-on-demand. Some content that appears in standard print versions of this book may not be available in other formats. Limit of Liability/Disclaimer of Warranty While the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials or promotional statements for this work. The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the information or services the organization, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. Library of Congress Cataloging-in-Publication Data Names: Razavi, Seyed M.A., 1967- editor. Title: Emerging natural hydrocolloids : rheology and functions / edited by Seyed M.A. Razavi, Food Hydrocolloids Research Center, Department of Food Science and Technology, Ferdowsi University of Mashhad, Mashhad, Iran. Description: First edition. | Hoboken, NJ, USA : John Wiley & Sons, Inc., 2019. | Includes bibliographical references and index. | Identifiers: LCCN 2018037728 (print) | LCCN 2018038293 (ebook) | ISBN 9781119418559 (Adobe PDF) | ISBN 9781119418542 (ePub) | ISBN 9781119418665 (hardcover) Subjects: LCSH: Hydrocolloids–Industrial applications. | Hydrocolloids–Abrasion resistance. | Food–Composition. Classification: LCC TP456.H93 (ebook) | LCC TP456.H93 E44 2019 (print) | DDC 664/.2–dc23 LC record available at https://lccn.loc.gov/2018037728 Cover Design: Wiley Cover Images: © Anna Hoychuk / Shutterstock,© photowind / Shutterstock, Image of sage seed mucilage: © Seyed M.A. Razavi, Image of graph courtesy of Seyed M.A. Razavi Set in 10/12pt WarnockPro by SPi Global, Chennai, India

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This book is dedicated with love and affection to my wife, Reyhane, and my children, Parniyan, Narges, and Ali.

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Contents About the Editor xxi List of Contributors xxiii Preface xxvii 1

Introduction to Emerging Natural Hydrocolloids 1 Seyed M.A. Razavi

1.1 1.2 1.3 1.3.1 1.4 1.5 1.5.1 1.5.2

Introduction 1 World Market of Hydrocolloids 2 Hydrocolloids Classification 4 Natural Hydrocolloids 6 Functions of Hydrocolloids 8 Overview of the Chapters 13 Chapter 2: Dilute Solution Properties of Emerging Hydrocolloids 13 Chapter 3: Steady Shear Rheological Properties of Emerging Hydrocolloids 13 Chapter 4: Transient and Dynamic Rheological Properties of Emerging Hydrocolloids 17 Chapter 5: Hydrocolloids Interaction Elaboration Based on Rheological Properties 17 Chapter 6: Sage (Salvia macrosiphon) Seed Gum 17 Chapter 7: Balangu (Lallemantia royleana) Seed Gum 18 Chapter 8: Qodume Shirazi (Alyssum homolocarpum) Seed Gum 18 Chapter 9: Espina Corona (Gleditsia amorphoides) Seed Gum 18 Chapter 10: Qodume Shahri (Lepidium perfoliatum) Seed Gum 19 Chapter 11: Persian Gum (Amygdalus scoparia Spach) 19 Chapter 12: Gum Tragacanth (Astragalus gummifer Labillardiere) 19 Chapter 13: Cashew Tree (Anarcadium Occidentale L.) Exudate Gum 20 Chapter 14: Brea Tree (Cercidium praecox) Exudate Gum 20 Chapter 15: Chubak (Acanthophyllum glandulosum) Root Gum 20 Chapter 16: Marshmallow (Althaea officinalis) Flower Gum 21 Chapter 17: Opuntia Ficus Indica Mucilage 21 Chapter 18: Emerging Technologies for Isolation of Natural Hydrocolloids from Mucilaginous Seeds 21 Chapter 19: Purification and Fractionation of Novel Natural Hydrocolloids 22

1.5.3 1.5.4 1.5.5 1.5.6 1.5.7 1.5.8 1.5.9 1.5.10 1.5.11 1.5.12 1.5.13 1.5.14 1.5.15 1.5.16 1.5.17 1.5.18

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Contents

1.5.19 1.5.20 1.5.21 1.5.22 1.5.23 1.6

Chapter 20: Improving Texture of Foods using Emerging Hydrocolloids 22 Chapter 21: New Hydrocolloids in Ice Cream 23 Chapter 22: Novel Hydrocolloids for Future Progress in Nanotechnology 23 Chapter 23: Edible/Biodegradable Films and Coatings from Natural Hydrocolloids 24 Chapter 24: Healthy Aspects of Novel Hydrocolloids 24 Conclusion 24 References 25

2

Dilute Solution Properties of Emerging Hydrocolloids 53 Ali R. Yousefi and Seyed M.A. Razavi

2.1 2.2 2.3 2.4 2.5 2.5.1 2.6 2.7 2.8 2.9 2.10 2.11 2.12

Introduction 53 Partial Specific Volume 54 Hydrogel Content 55 Molecular Weight 57 Intrinsic Viscosity 59 Huggins Constant 64 Coil Overlap Parameter and Molecular Conformation 65 Chain Flexibility Parameter 67 Stiffness Parameter 68 Coil Radius and Volume 69 Voluminosity and Shape Factor 70 Hydration Parameter 71 Conclusion and Future Trends 72 References 73

3

Steady Shear Rheological Properties of Emerging Hydrocolloids 81 Fataneh Behrouzian and Seyed M.A. Razavi

3.1 3.2 3.3 3.3.1 3.3.2 3.3.3 3.3.4 3.4 3.4.1 3.4.2 3.5 3.6

Introduction 81 Time-Independent Rheological Properties 83 Time-Dependent Rheological Properties 87 Hysteresis Loop 87 Single Shear Stress Decay 88 In-Shear Structural Recovery Measurements 90 Time Dependency of Steady Shear Properties 91 Yield Stress 92 Static Yield Stress 92 Dynamic Yield Stress 92 Cluster Analysis 94 Conclusion and Future Trend 97 References 97

4

Transient and Dynamic Rheological Properties of Emerging Hydrocolloids 101 Ali Alghooneh and Seyed M.A. Razavi

4.1 4.2

Introduction 101 Viscoelastic Characteristics 103

Contents

4.2.1 4.2.1.1 4.2.1.2 4.2.2 4.2.2.1 4.2.2.2 4.2.3 4.2.4 4.3 4.4

Oscillatory Properties 103 Strain Sweep 103 Frequency Sweep 112 Transient Properties 117 Creep Test 117 Stress Relaxation Test 120 Comparison of Dynamic Rheology and Steady Shear: The Cox–Merz Rule 121 Yield Stress 124 Cluster Analysis 125 Conclusion and Future Trends 129 References 131

5

Hydrocolloids Interaction Elaboration Based on Rheological Properties 135 Ali Alghooneh, Fataneh Behrouzian, and Seyed M.A. Razavi

5.1 5.2 5.3 5.3.1 5.3.2 5.3.3 5.3.3.1 5.3.3.2 5.3.4 5.3.4.1 5.3.4.2 5.3.4.3 5.3.4.4 5.3.5 5.3.6 5.4 5.5 5.5.1 5.5.2 5.5.3 5.6

Introduction 135 Dilute Regime 136 Concentrated Regime 137 Steady Rheological Behavior 137 Transient Rheological Behavior 138 Dynamic Rheological Behavior 139 Amplitude Sweep Properties 139 Frequency Sweep Properties 139 Temperature Effect 142 Temperature Effect in an Isothermal Condition 142 Temperature Effect in a Non-isothermal Condition 145 Kinetics of Biopolymer Interaction 148 Time–Temperature Superposition Principle 150 Effect of Salts 150 Effect of pH 151 Thermodynamic 151 Miscibility 152 Interaction Coefficient 152 Cole-Cole Plot 153 Han Curve 153 Conclusions and Future Trends 154 References 154

6

Sage (Salvia macrosiphon) Seed Gum 159 Seyed M.A. Razavi, Ali Alghooneh, and Fataneh Behrouzian

6.1 6.2 6.2.1 6.2.2 6.3 6.3.1

Introduction 159 Salvia macrosiphon Seed Mucilage 160 Mucilage Extraction Optimization 161 Physicochemical Properties 161 Rheological Properties 163 Dilute Solution Properties 163

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6.3.1.1 6.3.1.2 6.3.2 6.3.2.1 6.3.2.2 6.3.3 6.3.3.1 6.3.4 6.3.4.1 6.3.4.2 6.3.4.3 6.3.4.4 6.3.5 6.3.6 6.3.6.1 6.3.6.2 6.4 6.5 6.5.1 6.5.2 6.5.3 6.5.4 6.6

Influence of Salts 163 Influence of Temperature 163 Viscoelastic Properties 164 Oscillatory Properties 164 Creep Properties 169 Steady Shear Properties 170 Flow Behavior 170 Thixotropy 172 Hysteresis Loop 172 Single Shear Decay 172 In-Shear Structural Recovery 174 Extent of Time Dependence in Small Deformation 174 Yield Stress 175 Steady and Oscillatory Shear Rheological Properties Comparison 175 Cox–Merz Rule 176 Shear-Thinning Phenomena 177 Textural Properties 177 Applications 177 D-Limonene-in-Water Emulsions 177 Edible Film 178 Yogurt 178 Sauces 178 Summary 179 References 179

7

Balangu (Lallemantia royleana) Seed Gum 183 Asad Mohammad Amini

7.1 7.2 7.3 7.4 7.4.1 7.4.2 7.4.3 7.4.4 7.5 7.5.1 7.5.2 7.5.3 7.5.4 7.5.5 7.5.6 7.6

Introduction 183 Extraction and Purification 184 Physicochemical and Structural Properties 185 Rheological Properties 187 Dilute Solution Properties 187 Steady Shear Properties 188 Dynamic Shear Properties 192 Textural Properties 192 Functional Properties 194 Stabilizing 194 Fat Replacement 196 Emulsifying 197 Foaming 197 Edible Films 198 Other Applications 199 Conclusions and Future Trends 199 References 200

8

Qodume Shirazi (Alyssum homolocarpum) Seed Gum 205 Arash Koocheki and Mohammad Ali Hesarinejad

8.1

Introduction 205

Contents

8.2 8.3 8.3.1 8.3.2 8.3.3 8.3.4 8.3.5 8.3.6 8.4 8.4.1 8.4.2 8.4.2.1 8.4.2.2 8.4.2.3 8.4.2.4 8.4.3 8.4.4 8.5 8.6 8.6.1 8.6.2 8.6.3 8.6.4 8.6.5 8.7

Gum Extraction Optimization 205 Physicochemical Properties 207 Composition 207 Fourier Transform Infrared Spectroscopy (FTIR) 207 Chain Flexibility 208 Shape, Swollen Volume, and Hydration Parameters 208 Coil Radius and Volume 209 Partial Specific Volume 209 Rheological Properties 209 Intrinsic Viscosity 209 Steady Shear Rheological Properties 210 Effect of Temperature 210 Effect of pH 211 Effect of Salt 211 Effect of Sucrose 211 Time Dependency (Thixotropy) 212 Dynamic Rheological Properties 212 Biological Activity 212 Applications 213 Emulsions 213 Encapsulation 215 Edible Film 215 Application in Dairy Products 218 Application in Bakery Products 218 Conclusion and Future Trends 219 References 219

9

Espina Corona (Gleditsia amorphoides) Seed Gum 225 María J. Spotti, Martina Perduca, Paula Loyeau, Amelia Rubiolo, and Carlos Carrara

9.1 9.2 9.3 9.3.1 9.3.2 9.3.3 9.3.4 9.3.4.1 9.4 9.5 9.5.1 9.5.2 9.5.3 9.5.3.1 9.5.3.2 9.5.3.3 9.5.4 9.6

Introduction 225 Purification and Composition 226 Flow Behavior 227 Effect of Concentration 228 Effect of Temperature 229 Effect of Ionic Strength 230 Effect of pH 230 Effect of ECG Addition on Viscosity of Yogurts 230 Viscoelasticity 231 Applications of ECG in Colloidal Systems 233 Emulsions 233 Foams 235 Gels and Structured Systems 235 Interaction between ECG and Xanthan Gum 236 Interaction between ECG and Carrageenan 238 Interaction between ECG and Proteins 241 ECG Microspheres 243 Conclusions and Future Trends 244 References 245

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10

Qodume Shahri (Lepidium perfoliatum) Seed Gum 251 Arash Koocheki and Mohammad A. Hesarinejad

10.1 10.2 10.3 10.4 10.5 10.5.1 10.5.1.1 10.5.1.2 10.5.1.3 10.5.1.4 10.5.2 10.5.2.1 10.5.2.2 10.5.2.3 10.6 10.6.1 10.6.2 10.6.3 10.6.4 10.6.5 10.6.6 10.7

Introduction 251 Gum Extraction Optimization 252 Chemical Compositions 253 Functional Properties 253 Rheological Properties 253 Flow Properties 253 Effect of Concentration 253 Effect of Temperature 255 Effect of Salt 255 Effect of pH 256 Dynamic Rheological Properties 256 Strain Sweep Measurements 256 Frequency Sweep Measurements 257 Temperature Sweep Measurements 258 Applications 259 Emulsions 259 Edible Film 262 Dairy Products 266 Bakery Products 266 Coating of Osmotic Dehydrated Apple 267 Batter in Deep Frying 267 Conclusions and Future Trends 267 References 268

11

Persian Gum (Amygdalus scoparia Spach) 273 Soleiman Abbasi

11.1 11.2 11.3 11.4 11.5 11.5.1 11.5.2 11.5.3 11.5.4 11.6 11.7 11.7.1 11.7.2 11.7.2.1 11.7.2.2 11.7.2.3 11.7.2.4 11.8 11.9

Botanical Aspects and Importance 273 General Specifications 275 Production, Collection, and Processing 277 Physicochemical Properties 278 Structural Characteristics 279 Monosaccharide Composition 280 Chemical Structure 281 Functional Chemical Groups 282 Molecular Weight 283 Rheological Properties 284 Interaction with Other Macromolecules 286 Polysaccharides 286 Proteins 287 Gelatin 287 Whey Protein Isolate 287 Casein 288 β-Lactoglobulin 289 Surface Activity and Emulsifying Properties 290 Thermal Characteristics 291

Contents

11.10 11.11

Potential Applications 291 Concluding Remarks 292 References 293

12

Gum Tragacanth (Astragalus gummifer Labillardiere) 299 Zahra Emam-Djomeh, Morteza Fathi, and Gholamreza Askari

12.1 Introduction 299 12.2 Structure 300 12.3 Thermal Properties 306 12.4 Functional Properties 306 12.4.1 Rheological Behavior 306 12.4.1.1 Steady Shear Rheological Properties 306 12.4.1.2 Dynamic Rheological Properties 309 12.4.2 Surface Activity 310 12.4.3 Solubility 310 12.4.4 Emulsification Ability 311 12.5 Biological Activity 312 12.6 Antibacterial Activity 312 12.7 Effect of Pre-treatment on GT: Physicochemical Properties 313 12.7.1 Irradiation 313 12.7.2 Heat Treatment 314 12.7.3 High Shear Rate 314 12.8 Food Applications 314 12.8.1 Ice Cream 314 12.8.2 Doogh 315 12.8.3 Yogurt 315 12.8.4 Cheese 315 12.8.5 Kashk 316 12.8.6 Flavored Milk Drink 316 12.8.7 Pasta 316 12.8.8 Ketchup 317 12.8.9 Use of GT as Coating Material 317 12.8.10 Use of GT as Delivery Carrier 318 12.8.10.1Complexation and Coacervation 318 12.8.10.2Encapsulation of Phytochemicals using Coacervation Technique 318 12.9 Conclusions and Future Trends 319 References 320 13

Cashew Tree (Anarcadium occidentale L.) Exudate Gum Esther Gyedu-Akoto, Frank M. Amoah, and Ibok Oduro

13.1 13.2 13.2.1 13.2.2 13.2.3 13.2.4 13.2.5

Introduction 327 Cashew Tree Gum 328 Production of Cashew Gum 328 Chemical Structure 329 Organoleptic Properties of Cashew Gum 330 Physicochemical Properties of Cashew Gum 330 Rheological Properties of Cashew Gum 332

327

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13.2.6 13.2.7 13.3 13.3.1 13.3.2 13.3.3 13.3.4 13.3.5 13.4 13.4.1 13.4.2 13.5 13.6

Toxicity and Microbial Determination of Cashew Gum 334 Modification of Cashew Gum 336 Application of Cashew Gum in Foods 336 Cashew Gum as an Encapsulating Agent 337 Cashew Gum as a Coating Agent (Film-Former) 337 Cashew Gum as a Gelling Agent 338 Cashew Gum as a Clarifying Agent 338 Cashew Gum as a Fat-Replacing Agent 338 Application of Cashew Gum in the Pharmaceutical Industry 339 Cashew Gum as an Excipient 339 Pharmacological Studies on Cashew Gum 340 Conclusion 342 Future Trends 342 References 343

14

Brea Tree (Cercidium praecox) Exudate Gum 347 María A. Bertuzzi and Aníbal M. Slavutsky

14.1 14.2 14.2.1 14.2.2 14.2.3 14.3 14.3.1 14.3.2 14.3.3 14.3.4 14.3.5 14.4 14.4.1 14.4.2 14.4.3 14.4.4 14.4.5 14.5 14.6

Introduction 347 Physicochemical Characteristics 349 Compositions 349 Color 351 Density 352 Functional Properties 352 Solubility 353 Surface Properties 353 Rheological Properties 354 Foaming Properties 355 Emulsifying Properties 357 Applications 358 Edible Film 358 Encapsulation 361 Hydrogels 362 Bread Additive 363 Medium for Fungal Culture 364 Conclusions 364 Future Trends 365 Acknowledgments 365 References 366

15

Chubak (Acanthophyllum glandulosum) Root Gum 371 Hojjat Karazhiyan

15.1 15.2 15.3 15.3.1 15.3.2 15.3.3

Introduction 371 Chubak Root Extract (CRE) 372 Applications of CRE in Foods 374 Doughnut 374 Yogurt 376 Ketchup 379

Contents

15.3.4 15.3.5 15.3.6 15.3.7 15.3.8 15.4

Non-alcoholic Beer 380 Muffin Cake 381 Sponge Cake 384 Mayonnaise 386 Grape Juice 388 Conclusions and Future Trends 388 References 389

16

Marshmallow (Althaea officinalis) Flower Gum 397 Seyedeh Fatemeh Mousavi, Seyed M.A. Razavi, and Arash Koocheki

16.1 16.2 16.2.1 16.2.2 16.2.3 16.2.4 16.2.5 16.2.6 16.2.7 16.3 16.4 16.5 16.6 16.7 16.7.1 16.7.1.1 16.7.1.2 16.7.1.3 16.7.2 16.8 16.9

Introduction 397 Extraction Optimization using RSM 398 Fitting Models 398 Effect of Extraction Conditions on Yield 399 Effect of Extraction Conditions on Consistency Coefficient 399 Effect of Extraction Conditions on L* 405 Effect of Extraction Condition on Foam Stability Index 406 Effect of Extraction Conditions on Emulsion Stability Index 406 Optimization and Verification of Models 407 Chemical Compositions 407 FT-IR 408 Differential Scanning Calorimetry (DSC) 409 DPPH Radical-Scavenging Activity 409 Steady Shear Rheological Properties 411 Flow Behavior 411 Effect of Concentration 411 Effect of Temperature 413 Effect of pH 414 Thixotropy 415 Intrinsic Viscosity 416 Conclusions and Future Trends 417 References 418

17

Opuntia ficus-indica Mucilage 425 Elnaz Salehi, Zahra Emam-Djomeh, Morteza Fathi, and Gholamreza Askari

17.1 17.2 17.2.1 17.2.2 17.3 17.3.1 17.3.2 17.3.3 17.3.4 17.4 17.4.1 17.4.2

Introduction 425 Opuntia ficus-indica Plant Parts 428 Cladodes 428 Fruit 429 Opuntia ficus-indica Mucilage 431 Extraction Yield 431 Chemical Composition 432 Structural Characteristics 436 Rheological Properties 437 Food Applications 441 Coatings and Edible Films 441 Encapsulation Agent 442

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Contents

17.4.3 17.4.4 17.5

Wastewater Treatment 443 Other Uses 443 Conclusion and Future Trends 443 References 444

18

Emerging Technologies for Isolation of Natural Hydrocolloids from Mucilaginous Seeds 451 Asgar Farahnaky, Mahsa Majzoobi, and Shaahin Bakhshizadeh-Shirazi

18.1 18.2 18.3 18.3.1 18.3.2 18.3.3 18.3.3.1 18.3.3.2 18.3.4 18.3.5

Introduction 451 Mucilaginous Seeds 451 Mucilage Isolation using Conventional Methods 452 Pre-treatments Prior to Mucilage Isolation 452 Milling Mucilaginous Seeds 452 Conventional Methods for Isolation of Seed Mucilage 457 Wet Isolation Method 457 Dry Isolation Method 459 Purification of Isolated Mucilage 460 Main Challenges of Isolating Mucilage Gums using the Conventional Methods 460 Emerging Mucilage Isolation Technologies 461 Ultrasound Waves and Its Applications 461 Ultrasound-Assisted Isolation of Mucilage From Wild Sage and Quince Seeds 461 Ultrasound-Assisted Isolation of Mucilage from Basil Seed 462 Preparation of Hydrated Seeds and Ultrasound Application 463 Mucilage Yield and Chemical Composition of Mucilage Obtained by Ultrasound-Assisted Isolation 464 Lightness of Mucilage Powders 466 Rheological Properties of Mucilage Solutions 466 Conclusions and Future Trends 469 References 469

18.4 18.4.1 18.4.2 18.4.3 18.4.3.1 18.4.3.2 18.4.3.3 18.4.3.4 18.5

19

Purification and Fractionation of Novel Natural Hydrocolloids 473 Somayeh Razmkhah

19.1 19.2 19.2.1 19.2.2 19.2.3 19.2.4 19.2.5 19.2.6 19.2.6.1 19.2.6.2 19.2.6.3 19.2.6.4 19.3

Introduction 473 Purification of New Natural Hydrocolloids 474 Chemical Composition 474 Molecular Weight (Mw) 475 Intrinsic Viscosity 475 Dynamic Shear Rheological Properties 475 Steady Shear Rheological Properties 476 Functional Characteristics 479 Solubility and Water-Holding Capacity 479 Surface Tension 481 Emulsifying Properties 481 Foaming Properties 482 Fractionation of New Natural Hydrocolloids 482

Contents

19.3.1 19.3.2 19.3.3 19.3.4 19.3.5 19.3.6 19.3.6.1 19.3.6.2 19.3.6.3 19.4

Chemical Compositions 482 Molecular Weight 483 Intrinsic Viscosity 483 Dynamic Shear Rheological Properties 484 Steady Shear Rheological Properties 487 Functional Characteristics 490 Surface Tension 490 Emulsifying Properties 491 Foaming Properties 492 Conclusions and Future Trends 494 References 496

20

Improving Texture of Foods using Emerging Hydrocolloids 499 Ali Rafe

20.1 20.2 20.3 20.4 20.5 20.6 20.6.1 20.6.2 20.6.3 20.7 20.8

Introduction 499 Influence of Hydrocolloids on Food Structure 499 Textural Attributes 502 Tribology (Body–Texture Interaction) 506 Consumer Perceptions of Food Hydrocolloids 510 Fractal Analysis 511 Concepts and Theory 511 Scaling Behavior and Fractal Analysis of BSG Gels 513 Scaling Behavior and Fractal Analysis of 𝜅-Carrageenan 514 Microstructure of BSG 515 Conclusions and Future Trends 517 References 518

21

New Hydrocolloids in Ice Cream 525 Fatemeh Javidi and Seyed M.A. Razavi

21.1 21.2 21.2.1 21.2.2 21.2.3 21.2.4 21.2.5 21.2.6 21.2.7 21.2.8 21.2.9 21.2.10 21.2.11 21.2.12 21.3 21.3.1 21.3.1.1 21.3.1.2

Introduction 525 New Sources of Hydrocolloids in Ice Cream 526 Lallemantia royleana Seed Gum 527 Ocimum basilicum Seed Gum 527 Salvia hispanica Seed Gum 527 Lepidium sativum Seed Gum 527 Linum usitatissimum Seed Gum 528 Gundelia tournefortii Gum 528 Plantago ovate Seed Gum 528 Abelmoschus esculentus Gum 529 Lepidium perfoliatum Seed Gum 529 Salvia macrosiphon Seed Gum 529 Salep Glucomannan 529 Gum Tragacanth 530 Functions of New Hydrocolloids in Ice Cream 530 Stabilizing 530 Rheological Properties 530 Textural Attributes 532

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21.3.1.3 21.3.1.4 21.3.1.5 21.3.2 21.3.2.1 21.3.2.2 21.3.2.3 21.3.2.4 21.3.2.5 21.3.3 21.4 21.5

Overrun 532 Melting Resistance 533 Sensory Characteristics 534 Fat Replacement 534 Rheological Properties 534 Textural Attributes 536 Overrun 536 Melting Resistance 537 Sensory Characteristics 537 Cryoprotection 538 Conclusions 541 Future Trends 542 References 543

22

Novel Hydrocolloids for Future Progress in Nanotechnology 549 Sara Naji-Tabasi

22.1 22.2 22.3 22.3.1 22.3.1.1 22.3.1.2 22.3.1.3 22.3.1.4 22.3.2 22.3.2.1 22.3.2.2 22.3.2.3 22.3.2.4 22.3.2.5 22.3.2.6 22.3.2.7 22.3.2.8 22.3.2.9 22.4

Introduction 549 Importance of Finding New Material Sources in Nanotechnology 550 Nanomaterials 550 Nanofiber 551 Basil (Ocimum bacilicum L.) Seed Gum 551 Almond (Amygdalus communis L.) Tree Exudate Gum 552 Cress (Lepidium sativum) Seed Gum 553 Ficus-indica Mucilage 553 Nanoparticles 554 Cress Seed Gum 554 Basil Seed Gum 557 Cashew (Anacardium occidentale) Tree Exudate Gum 558 Chichá (Sterculia striata) Gum 559 Angico (Anadenanthera macrocarpa) Gum 559 Ghodome Shirazi (Alyssum homolocarpum) Seed Gum 560 Chia (Salvia hispanica L.) Seed Mucilage 561 Kondagogu (Cochlospermum gossypium) Exudate Gum 562 Angelica sinensis Polysaccharides 563 Conclusions and Future Trends 563 References 564

23

Edible/Biodegradable Films and Coatings from Natural Hydrocolloids 571 Younes Zahedi

23.1 23.2 23.3 23.3.1 23.3.2 23.3.2.1 23.3.2.2

Introduction 571 Film Preparation 572 Film Characteristics 573 Thickness 573 Permeability 576 Water Vapor Permeability (WVP) 576 Oxygen Permeability (OP) 577

Contents

23.3.3 23.3.4 23.3.4.1 23.3.4.2 23.3.4.3 23.3.4.4 23.3.5 23.3.6 23.3.7 23.4 23.5

Density 578 Water-Related Properties 581 Moisture Content 581 Water Solubility 581 Water Contact Angle 582 Moisture Uptake and Moisture Sorption Isotherm 585 Mechanical Properties 587 Visual Characteristics 588 Scanning Electron Microscopy (SEM) 593 Applications 593 Conclusions and Future Trends 594 References 595

24

Health Aspects of Novel Hydrocolloids Jafar M. Milani and Abdolkhalegh Golkar

24.1 24.2 24.2.1 24.2.2 24.2.3 24.2.4 24.2.5 24.2.6

601

Introduction 601 Health Benefits of Hydrocolloids 602 Anti-diabetic Effects 602 Antioxidant Activity and Cancer Prevention 607 Immunostimulant Activity 608 Antimicrobial Activity 608 Anti-obesity 609 Blood Pressure and Cholesterol-Lowering Effects (Cardiovascular Health) 610 24.2.7 Mineral Absorption Effect 611 24.2.8 Prebiotic Effects 612 24.2.9 Biomedical Applications 612 24.2.10 Other Benefits 613 24.3 Conclusions and Recommendations 614 References 615 Index 623

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About the Editor Seyed M.A. Razavi is currently a Professor at the Department of Food Science and Technology, Ferdowsi University of Mashhad (FUM), Iran. He received the BSc degree in Food Science & Technology from the Ferdowsi University of Mashhad, MSc degree in Food Process Engineering from the University of Tehran, and PhD degree in Food Physics & Engineering from the Ferdowsi University of Mashhad in collaboration with the University of Wales, Swansea. His research interests are mainly focused on food rheology and hydrocolloids with an emphasis on the biopolymers’ functional properties, structure-function relationships, and product formulation engineering. He is the founder and director of Food Hydrocolloids Research Center (FHRC) at FUM. He has authored or co-authored over 250 peer-reviewed papers, 6 book chapters, and 3 edited books. He is editor-in-chief of the Iranian Food Science and Technology Research Journal (IFSTRJ) and also serves as editor for several scientific journals. Prof. Razavi was named a highly cited author (top 1% globally) in Agricultural Sciences (2015, 2016, 2017, Web of Science) by ISI-Thomson Reuters Scientific and has received several awards for his achievements in research, teaching, and scholarly works. Other details are available at http://profsite.um.ac.ir/~s.razavi/index.htm.

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List of Contributors S. Abbasi

S. Bakhshizadeh-Shirazi

Food Colloids and Rheology Laboratory Department of Food Science and Technology Faculty of Agriculture Tarbiat Modares University Tehran Iran

Department of Food Science and Technology School of Agriculture Shiraz University Shiraz Iran F. Behrouzian

A. Alghooneh

Food Hydrocolloids Research Center Department of Food Science and Technology Ferdowsi University of Mashhad Mashhad Iran

Food Hydrocolloids Research Center Department of Food Science and Technology Ferdowsi University of Mashhad Mashhad Iran M.A. Bertuzzi

F.M. Amoah

Cocoa Research Institute of Ghana Akim-Tafo Ghana

Instituto de Investigaciones para la Industria Química Universidad Nacional de Salta Salta Argentina

G. Askari

Transfer Phenomena Laboratory (TPL) Control Release Center Department of Food Science Engineering and Technology College of Agriculture and Natural Resources University of Tehran Karaj Iran

C. Carrara

Food Technology Institute Chemical Engineering Department National University of Litoral Santa Fe Argentina

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List of Contributors

Z. Emam-Djomeh

M.A. Hesarinejad

Transfer Phenomena Laboratory (TPL) Control Release Center Department of Food Science Engineering and Technology College of Agriculture and Natural Resources University of Tehran Karaj Iran

Department of Food Processing Research Institute of Food Science and Technology (RIFST) Mashhad Iran

A. Farahnaky

School of Science RMIT University Bundoora West Campus Melbourne Australia M. Fathi

Transfer Phenomena Laboratory (TPL) Control Release Center Department of Food Science Engineering and Technology College of Agriculture and Natural Resources University of Tehran Karaj Iran

F. Javidi

Food Hydrocolloids Research Center Department of Food Science and Technology Ferdowsi University of Mashhad Mashhad Iran H. Karazhiyan

Department of Food Science & Technology Torbat-e Heydarieh Branch Islamic Azad University Torbat-e Heydarieh Iran A. Koocheki

Department of Food Science and Technology Ferdowsi University of Mashhad Iran

A. Golkar

P. Loyeau

Department of Food Science & Technology Sari Agricultural Sciences and Natural Resources University (SANRU) Sari Iran

Food Technology Institute Chemical Engineering Department National University of Litoral Santa Fe Argentina M. Majzoobi

E. Gyedu-Akoto

Cocoa Research Institute of Ghana Akim-Tafo Ghana

Department of Primary Industries Wagga Wagga Agricultural Institute and Graham Centre for Agricultural Innovation Wagga Wagga NSW Australia

List of Contributors

J.M. Milani

A. Rafe

Department of Food Science & Technology Sari Agricultural Sciences and Natural Resources University (SANRU) Sari Iran

Department of Food Processing Research Institute of Food Science and Technology (RIFST) Mashhad Iran Seyed M.A. Razavi

A. Mohammad Amini

Department of Food Science and Technology Faculty of Agriculture University of Kurdistan (UOK) Sanandaj Iran

Food Hydrocolloids Research Center Department of Food Science and Technology Ferdowsi University of Mashhad Mashhad Iran S. Razmkhah

S.F. Mousavi

Food Hydrocolloids Research Centre Department of Food Science and Technology Ferdowsi University of Mashhad (FUM) Mashhad Iran S. Naji-Tabasi

Department of Food Nanotechnology, Research Institute of Food Science and Technology (RIFST) Mashhad Iran I. Oduro

Kwame Nkrumah University of Science and Technology Kumasi Ghana M. Perduca

Engineering and Technological Faculty Scientific Research Institute Universidad de la Cuenca del Plata Corrientes Argentina

GUM Group Knowledge Base Company Technology Development Center Ferdowsi University of Mashhad Iran A. Rubiolo

Food Technology Institute Chemical Engineering Department National University of Litoral Santa Fe Argentina E. Salehi

Transfer Phenomena Laboratory (TPL) Department of Food Science Technology and Engineering Faculty of Agricultural Engineering and Technology Agricultural Campus of the University of Tehran Karadj Iran

xxv

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List of Contributors

A.M. Slavutsky

A.R. Yousefi

Instituto de Investigaciones para la Industria Química Universidad Nacional de Salta Salta Argentina

Department of Chemical Engineering Faculty of Engineering University of Bonab Bonab Iran

M.J. Spotti

Y. Zahedi

Food Technology Institute Chemical Engineering Department National University of Litoral Santa Fe Argentina

Department of Food Science and Technology Faculty of Agriculture and Natural Resources University of Mohaghegh Ardabili Ardabil Iran

xxvii

Preface Hydrocolloids are finely divided particles dispersed in water with long-chained polymeric systems. Depending on the quantity of the medium, namely, water, hydrocolloids exist as sols or as gels. Hydrocolloids are versatile ingredients with a wide range of functions and applications, especially in modifying the rheology and texture of complex fluids. Natural hydrocolloids, as biological macromolecules (mainly polysaccharides and proteins), are frequently used in various industries as stabilizing, thickening, fat replacing, flavor and bioactive encapsulating, edible coating/film, plasticizing, emulsifying, carrier, binding, and gelling agents. Compared to synthetic and semi-synthetic hydrocolloids, natural hydrocolloids have distinct advantages, such as being nontoxic, sustainable, renewable, biodegradable, biocompatible, eco-friendly, cost-effective, readily available, and capable of chemical modifications. Moreover, the demand for natural products is increasing among health-conscious consumers. For example, the growing demand for functional foods and increasing public awareness about the importance of fiber in diet have increased the consumption of various biopolymers in food products. This has resulted in the tremendous growth of the global hydrocolloids market in different industry sectors. In recent years, an ever-growing interest has been devoted to finding new sources of natural hydrocolloid with interesting functions in the product matrix. Therefore, an extensive range of studies has focused on the characterization of new sources (mainly plant gum exudates and seed gums) of hydrocolloids, which could be potential substitutes for commercial gums. In fact, scientists, technologists, and industries over the world have paid special attention to emerging hydrocolloids, especially the natural ones, owing to their functional and nutraceutical properties. Since the aim is to replace the existing commercial (semi-synthetic and synthetic) hydrocolloids by the natural ones for various applications, one needs to find novel hydrocolloids that perform certain unique functions for this purpose. In order to introduce the potential and applicability of novel hydrocolloids in industries, it is necessary to explore emerging hydrocolloids with the desired properties. So, in this book, the recent scientific papers, theses, and research works about emerging hydrocolloids have been reviewed in detail. This book contains 24 chapters prepared by outstanding scientists who have made a significant impact on the field of emerging natural hydrocolloids. This comprehensive set provides an updated and highly structured material for researchers in food, paper,

xxviii

Preface

oil, textile, paint, and pharmaceutical fields. It is also a valuable compendium of recent scientific progress, along with the best-known applications of hydrocolloids in the food industry, to be used by researchers and technologists. Moreover, novel opportunities and ideas for developing the emerging hydrocolloids are highlighted. I sincerely hope that this comprehensive compilation of studies on emerging natural hydrocolloids in book form is useful to researchers in the field, and I welcome any suggestions to improve the book and additional information on this subject. Seyed M.A. Razavi

1

1 Introduction to Emerging Natural Hydrocolloids Seyed M.A. Razavi Food Hydrocolloids Research Center, Department of Food Science and Technology, Ferdowsi University of Mashhad, PO Box: 91775-1163, Mashhad, Iran

1.1 Introduction Hydrocolloids, also known as gums, are a diverse group of long-chain and hydrophilic polymers with high molecular weight which are readily dispersive, fully or partially soluble, and prone to swell in water, thus producing colloidal systems of different structures. Therefore, a hydrocolloid is a highly water-soluble (or water-dispersible) material that readily dissolves (or disperses) to form highly hydrated entities of colloidal dimensions (1–1000 nm) [1, 2]. Hydrocolloids generally produce a dispersion, which is intermediate between a true solution and a suspension, and exhibit the properties of a colloid [3]. Each dissolved polymer molecule of a hydrocolloid ingredient is deemed to interact strongly via hydrogen bonding with its surrounding water molecules as well as with any neighboring hydrocolloid molecules. Due to the tendency of these large hydrophilic macromolecules to overlap and join together into entangled networks and macroscopic gels, most hydrocolloids have the capability to function as viscosity modifiers and thickeners in aqueous media at relatively low concentrations [4]. The presence of many hydroxyl groups in their structures conspicuously increases the affinity for binding water, rendering them hydrophilic. At sufficiently high concentrations, the hydrocolloids become entangled with each other, forming loose networks (gel) that change their rheological properties [5]. The term food hydrocolloid includes all the polysaccharides and proteins that are widely used in a variety of food processing sectors to control and regulate such a colloidal state. Food hydrocolloids are from various natural sources: agar and carrageenan are from seaweeds, guar gum and locust bean gum from plant seeds, pectin from citrus or apple peels, xanthan gum and gellan gum from microorganisms, and chitin and chitosan from animals [1]. Food hydrocolloids exhibit multiple functions in foods, including thickening, gelling, water holding, dispersing, stabilizing, film forming, and foaming, and have been used as a texture modifier in almost every kind of food product. Because of their interesting properties, food hydrocolloids are widely used as food additives to obtain particular functional properties [3]. In fact, food hydrocolloids are important parts of our daily diet in food systems such as yogurt, ice cream, cheese, mayonnaise and salad dressing, dessert jellies, bakery Emerging Natural Hydrocolloids: Rheology and Functions, First Edition. Edited by Seyed M.A. Razavi. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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1 Introduction to Emerging Natural Hydrocolloids

products, and so on [2, 6]. The food industry especially has been using a large number of hydrocolloids in recent years as ingredients. Although they are often applied at low concentration (less than 1% of the final product), they significantly influence the textural, rheological, and sensory properties of the final products. These substances are best known as powerful thickeners but perform an extraordinary number of other functions essential to food quality. They impart food texture and structure, and they play a role in flavor release, appearance, and shelf stability [7, 8]. They are actually not emulsifiers, because they lack the characteristic lipophilic and hydrophilic linkage in the molecular structure [9]. However, they can stabilize emulsions by increasing the viscosity of the continuous phase or by interaction with surface-active substances. In recent years, food hydrocolloids have been recognized as healthy sources of fiber as well [10]. In general, hydrocolloids are natural-origin biopolymers, but this does not mean that one cannot produce hydrocolloids through synthetic means. All kinds of hydrocolloids can be obtained from both renewable and non-renewable resources. For many reasons, preference is being given to the renewable hydrocolloids. Due to the recent trends in the demand for all-natural products by consumers, the aim is to replace the existing non-renewable and synthetic hydrocolloids by renewable ones for different applications in industry, so we need to find novel natural hydrocolloids to provide certain unique features for the purpose. In order to introduce the novel hydrocolloids’ potential and applicability in industries, it is necessary to explore the emerging natural hydrocolloids with the desired properties. In this chapter, some aspects of the hydrocolloids including hydrocolloid classification and functions are highlighted. In addition, a brief review of the chapters is presented at the end of this chapter.

1.2 World Market of Hydrocolloids The global hydrocolloids market has been growing tremendously due to the increasing demand for healthy and natural products by health-conscious consumers. Hydrocolloids are used in different industries, such as oil, food, paper, paint, textiles, and pharmaceuticals. The extensive range of functions exhibited by hydrocolloids in the industry is an important driving force in the market. The main reason for the widespread use of hydrocolloids in industry is their functions as stabilizing, thickening, binding, emulsifying, and gelling agents [11]. The world hydrocolloids market was valued at about 2100 MT (US$5.5 billion) in 2014. The value increased to about US$5.70 billion in 2015. The global market for hydrocolloids is projected to reach $7.9 billion by 2019 [12] and a value of US$8.5 billion by 2022 with a growing compound annual growth rate (CAGR) of 5.8% [11]. The base year considered for the study is 2014, and the forecast period is from 2015 to 2020. In 2013, the market was dominated by North America, followed by Europe. The Asia-Pacific market is projected to grow at the highest CAGR with rapid growth in the food and beverage industries in developing countries, such as India and China. Increasing consumer awareness of health, diet, nutrition, and natural products is driving the market. The market has been segmented on the basis of types, sources, functions, applications, and regions. The major types of hydrocolloids are gelatin, pectin, xanthan gum, and guar gum. On the basis of the hydrocolloid type, gelatin held the largest share in

1.2 World Market of Hydrocolloids

the food hydrocolloids market as it is widely used as a gelling agent in confectionary, meat, poultry, and dairy products. The market has been divided on the basis of natural sources, such as plant, seaweed, animal, microbial, and synthetic sources. On the basis of function, hydrocolloids have been segmented into thickeners, gelling agents, stabilizers, fat replacers, and coating materials. Dairy products have the largest food hydrocolloid applications. Hydrocolloids are extensively used in dairy and frozen products such as ice creams, milkshakes, and creams to maintain stability and increase the shelf life. The multifunctional characteristics of hydrocolloids, coupled with the growth in demand from the food and beverage industries, drive the hydrocolloids market. The market has also been divided on the basis of geographies, such as North America, Europe, Asia-Pacific, and Rest of the World (RoW). Key participants in the supply chain of the hydrocolloids market are the manufacturers, end-use industries, and raw material suppliers. The leading players involved in the hydrocolloids market include Cargill Incorporated (United States), Ingredion Incorporated (United States), E. I. du Pont de Nemours and Company (United States), Darling Ingredients Inc. (United States), Kerry Group plc (Ireland), CP Kelco (United States), Ashland Inc. (United States), DuPont (United States), Hawkins Watts (Australia), Royal DSM (the Netherlands), Archer Daniels Midland Co. (United States), Fuerst Day Lawson Limited (United Kingdom), E.I. Dupont De Nemours and Company (United States), Lucid Colloids Ltd. (India), and Danisco A/S company (Denmark). These market players have been focusing on the expansion of new facilities and launching new products [11, 12]. According to an IHS Markit report, native (unmodified) and modified starches account for the great majority (95%) of the market by weight; smaller-volume, higher-priced materials such as gelatin, guar gum, casein, xanthan gum, gum Arabic, and carrageenan make up the remainder [13]. The world consumption of hydrocolloids, including starches in 2015, is shown in Figure 1.1. As is seen, Asia was responsible for 60% of total hydrocolloid consumption, with China alone accounting for almost half (46%) of the demand. In contrast, the Americas and EMEA (Europe, the Middle East,

India

4.1 5.71

Japan Central/South America

8.96

Other Asia/Oceania

16.18

North America

31.32

EMEA

33.75 0

5

10 15 20 25 30 Hydrocolloids consumption (%)

35

40

Figure 1.1 World consumption of hydrocolloids in 2015 (EMEA means Europe, the Middle East, and Africa regions).

3

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1 Introduction to Emerging Natural Hydrocolloids

and Africa) accounted for the bulk of consumption in the (much smaller) non-starch hydrocolloid market. Together, the Americas and EMEA consumed 60% of non-starch hydrocolloids. China will drive future market growth. In 2020, China is expected to account for 70%–75% of the increase over 2015 market volumes. Chinese hydrocolloid consumption is expected to rise by 5.0% per year through 2020, exceeding the world average annual growth rate of just over 3%. All other regions expect slower growth. In North America, Central and South America, EMEA, and Japan, consumption will increase at low rates (0.4%–2.0% per year); in India and Other Asia and Oceania, consumption will grow at a moderate pace (2.4%–3.0% per year). Paper and board production is the largest end use for starches. They serve as binders, sizing, and coating agents in the paper-making process; starch-based adhesives are essential to the manufacture of corrugated cardboard, paper bags, and envelopes. Food applications are second in importance for starches, but they represent the single most important end use for many other hydrocolloids. Pectin serves as a gelling agent in jams, jellies, and marmalades; gum Arabic inhibits sugar crystallization in soft drinks; locust bean gum maintains ice cream’s creamy texture by controlling ice crystal formation, to give just a few examples. The hydrocolloid market has a reputation for volatility, but this is somewhat undeserved. Raw materials for various hydrocolloids are periodically in short supply as a result of weather or political disruptions, but only guar gum has experienced major fluctuations in supply and demand in recent years. In this case, demand for guar gum surged because of the dramatic expansion of hydraulic fracking activity in the United States. The collapse of crude oil prices at the end of 2014 led to a reduction in drilling activity and lower consumption of guar gum. Additionally, in the food sector, processors have reformulated many products, replacing guar gum with other hydrocolloids. In the energy sector, the use of guar-free slickwater fluids as cost-effective alternatives to guar-thickened fracking fluids is increasing. The overall demand for hydrocolloids will track growth in major end-use industries, including paper, food, oil and gas production, and pharmaceuticals [13].

1.3 Hydrocolloids Classification Hydrocolloids could be categorized according to their origins, chemical structure and composition, chemical nature (ionic and non-ionic), and functional properties. Hydrocolloids, depending on their origin, may be classified as natural, semi-synthetic, and synthetic. The natural hydrocolloids are hydrophilic biopolymers of plant, animal, and microbial origin. The plant-derived hydrocolloids are mainly used to stabilize oil-in-water emulsions, but the animal-derived hydrocolloids generally form water in oil emulsions. They are quite likely to cause allergies and are susceptible to microbial growth and rancidity. The semi-synthetic hydrocolloids are those synthesized by modification of naturally occurring hydrocolloids. Starch and cellulose derivatives such as methylcellulose (MC), carboxymethylcellulose (CMC), hydroxypropyl methylcellulose (HPMC), microcrystalline cellulose (MCC), acetylated starch (AS), phosphorylated starch (PS), and hydroxypropylated starch (HPS) are the examples of the semi-synthetic hydrocolloids. The semi-synthetic hydrocolloids are stronger emulsifiers, are non-toxic, and less likely to undergo microbial growth. Synthetic hydrocolloids are the ones that are completely synthesized in industries starting with petroleum-derived base materials.

1.3 Hydrocolloids Classification

These are basically derived from chemical combinations to give a product having a structure similar to the natural polysaccharides. The acrylate copolymers, carboxyvinyl polymers (Carbopol), polyethylene oxide polymers (Polyox), and polyvinylpyrrolidone (PVP) are examples of synthetic hydrocolloids [2, 5, 14]. The synthetic hydrocolloids are the strongest emulsifiers, and they do not support microbial growth, but their cost may be prohibitive. The synthetic hydrocolloids are mainly limited to use as oil-in-water emulsifiers. Semi-synthetic hydrocolloids are preferred to the purely synthetic gums. The literature has shown that the synthetic hydrocolloids are far more inefficient and have the following inherent disadvantages: • • • • • •

High cost Toxicity to the body and other animal life Environmental pollution during the manufacturing process Non-renewable sources Acute and chronic adverse effects on the skin in some cases Poor biocompatibility compared to the natural gums

Synthetic hydrocolloids offer certain advantages over their natural counterparts, such as increased potency, resistance to microbial degradation, and solution clarity. Compared to synthetic and semi-synthetic polymers, the natural hydrocolloids are the most preferred in all the industries due to the following distinct advantages: Cost-effective and inexpensive. Readily available, easy to handle, and they are also easier to extract. Biodegradable; they are renewable sources which are easily biodegradable. Biocompatible. Capable of physical and chemical modifications. Non-toxic to the body. Sustainable, eco-friendly, and easily available in nature. They have more public acceptance due to their numerous health benefits, and they are also extracted from edible sources. • In pharmaceutical applications, there is less chance of side effects to patients compared to synthetic hydrocolloids. • • • • • • • •

On the other hand, the growing demand for ready-made meals and increasingly public awareness about the importance of fiber in the diet has increased the consumption of various biopolymers in food products. However, the naturally occurring plant hydrocolloids have the disadvantages of being required in large quantities to be effective as emulsifiers (compared to semi-synthetic or synthetic ones) and are susceptible to microbial growth. With all these advantages and disadvantages, the natural hydrocolloids are gradually replacing synthetic gums in industrial applications. Another classification of food hydrocolloids is based on their chemical structure. For example, guar gum, tara gum, locust bean gum, and fenugreek gum are galactomannan. Other structure-based groups are glucan (starch, curdlan, and so on), fructan (inulin), xylan, rhamnan, glucomannan (alginate), arabinoxylan (flaxseed gum), galactan (agar, carrageenan), arabinogalactan (gum Arabic), galacturonan (pectin), glycano-rhamnogalacturonan, glycano-glycosaminoglycans, glucosamine polymer (chitin, chitosan), and protein (gelatin).

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1 Introduction to Emerging Natural Hydrocolloids

1.3.1

Natural Hydrocolloids

The natural hydrocolloids may originate from proteins or carbohydrates as they are the two main macromolecules that are naturally available. These two macromolecules are the major foods for human beings and are consumed every day. Human beings mainly derive their food from the plants, as various parts of a plant (seed, stem, root, leave, flower, fruit, etc.) are edible. The classification of hydrocolloids into proteins and carbohydrates is the classification based on their chemistry but in fact, the natural hydrocolloids are categorized based on their origin. As shown in Figure 1.2, the classification of commercially important hydrocolloids is (1) botanical, (2) algae, (3) microbial, and (4) animal sources [1, 15]. Cellulose (trees origin), gum Arabic, gum karaya, gum ghatti, gum tragacanth (exudate gums), starch, pectin, cellulose (plants source), guar gum, locust bean gum, tara gum, (seed endosperm flour), konjac gum (extracted from tubers), fenugreek seed gum, mustard seed gum, and flaxseed gum (mucilage) are overall grouped under botanical sources. Agar, carrageenan (red seaweeds), and alginate (brown seaweeds) are classified as of algal origin. Microbial sources are included as xanthan gum, curdlan, dextran, gellan gum, and cellulose. Gelatin, caseinate, whey proteins, and chitosan are natural hydrocolloids belonged to

Microorganism (Xanthan, Gellan etc)

Seeds (Locust bean gum etc) Fruits (Pectin etc) Seeds (Soy soluble polysaccharide, Guar etc) Tree exudates (Gum arabic etc)

Tree pulps (Cellulose etc)

Animals (Chitin, Chitosan)

Root (Starch, Konjac etc) Seaweeds (Agar, Carrageenan etc)

Figure 1.2 Source of natural hydrocolloids in nature. Source: Adapted from Funami [2011] with permission from Elsevier.

1.3 Hydrocolloids Classification

the animal group. Nowadays, the demand for hydrocolloids from plants (e.g., plant cell walls, tree exudates, seeds, seaweeds) is greater than those from animals (hyaluronan, chitin, chondroitin sulfate) because of more benefits and a consumer-friendly image. Hydrocolloids from seeds are the major source of natural gums. In general, seed gums are derived from ground endosperm of seeds. They are highly viscous at low concentrations [16]. Collection and processing of seed gums include the drying and crushing of harvested pods to separate seeds from pod husk. The seeds are dehulled, and the germ is separated from the endosperm. The pieces of endosperm are then ground to the required particle size to furnish the gum. Further processing involves either chemical modification of the gum or blending with other gums to produce a final product (food additive) with a range of physical and functional properties designed to suit end-user requirements. One of the most promising sources of plant hydrocolloids is mucilaginous substances. Mucilage is a heterogeneous branched and hydrophilic polysaccharide which forms a thick and sticky solution when dissolved in water. Mucilage is generally produced in the seeds, buds, and leaves of many plants. In seeds, it is presumed that the mucilage is located in the outer cells that form the seed coat, called mucilaginous cells, and can be easily removed after hydration. The seed coat or testa is composed of three layers: an outer layer, formed by rectangular thin-walled cells, where presumably the mucilage is localized; a scleroid layer of long and thin cells resembling fibers, and the endocarp, a thin and inner layer. Tamarind seed, mustard seed, chia seed, fenugreek seed, and flaxseed are the well-known sources of seed mucilage. When this seed is hydrated, the mucilage is exudated, and spiral filaments (mucilage fibers) become apparent. These filaments begin to expand until fully stretched to achieve maximum hydration, and new structures on the seed surface become apparent. These new structures, called columella, have a “volcano-shaped” conformation and are uniformly distributed on the surface. When the mucilage is fully hydrated, it forms a transparent “capsule” surrounding the seed that adheres to it with great tenacity, and when many seeds are hydrated in water, a highly viscous solution is formed. The mucilage hydrocolloids have attractive functional properties such as stabilizing, thickening, water absorption capacity, emulsifying and foaming properties, and high solubility in cold and hot water and show promise for incorporation into different food formulations. Plant/tree exudates from various plant species are obtained as a result of tree bark injury. They are normally collected as air-dried droplets with diameters from 2 to 7 cm. Plant exudates are generally excreted from tree species belonging to families of Burseraceae, Mimosaceae, and Sterculiaceae, which grow in the wild. Almost all the existing gum-bearing trees grow naturally in the wild under arid, warm or hot, unorganized, and rugged topographic conditions. This type of gum includes gum Arabic, karaya, tragacanth, and cashew gum [17]. Exudates from the stem and branches of a tree are produced as large nodules during a process called gummosis to seal wounds in the bark of the tree. The major commercial processes involved in the production of these plant exudates are collection, sorting, processing, quality control, and end-user marketing [18]. They are mostly not processed in countries of production but are exported to overseas markets for processing. Gums are produced by exudation from trees resulting from natural damage on the trees by natural agents or individuals and animals on a casual basis [17]. Several techniques are now being used to produce gum artificially to guarantee viability and improvement of the quality of the commercial product. These

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techniques involve systematically controlled tapping and collection procedures. Exudate gums could be graded physically based on their color, size, and brightness. They could also be graded in terms of solubility, viscosity, bark and foreign matter (BFOM) and total ash content [19]. All this grading could be done when the gum is in its natural as well as powdered forms. The quality of gum is usually assessed by its moisture content, optical rotation, and the level of foreign matter. Gum Arabic, for instance, must have a moisture content between 12% and 14%, optical rotation between −25 and −35, and foreign matter must be less than 3%–5%. Also, the microbiological count for Salmonella, Escherichia coli, and Staphylococcus aureus must be negative [20]. Seaweed gums are gelatinous products isolated from seaweed, mainly red and brown algae, by hot water or an alkali extraction process followed by drying or isolate precipitation. Industrial gums extracted from seaweeds fall into three categories: alginates (derivatives of alginic acid), agars, and carrageenans. The first is extracted solely from brown seaweeds, while the last two are extracted only from red seaweeds. There are a number of artificial products reputed to be suitable replacements for seaweed gums, but none have the exact gelling and viscosifying properties of seaweed gums, and it is very unlikely that seaweeds will be replaced as the source of these polysaccharides in the near future [21]. Microbial hydrocolloids are extracellular polysaccharides which originate from microorganisms produced from nutritive media. The major types of microbial hydrocolloids include xanthan gum, which accounts for over 90% of the overall microbial hydrocolloids market. Other types of microbial hydrocolloids include pullulan and gellan gums. Xanthan gum is one of the microbial gums permitted for use in foods. It has many interesting properties such as high viscosity at low shear rates and yield stress [21]. Animal hydrocolloids commonly originate from the bones and skins of animals such as swine and cattle. The major types of animal hydrocolloids include gelatin, which accounts for approximately 99% of the overall animal hydrocolloids market. Other animal hydrocolloids include chitin, chitosan, whey proteins, and caseins. Semi-synthetic hydrocolloids, also known as chemically modified hydrocolloids, include sodium caseinate and derivatives of several other types of animal hydrocolloids.

1.4 Functions of Hydrocolloids Natural hydrocolloids as biological macromolecules are frequently applied in food and pharmaceutical industries due to their excellent functional properties. Hydrocolloids perform various interesting functions in a formulation including thickening and gelling aqueous solutions; stabilizing/emulsifying foams, emulsions, and dispersions; inhibiting ice and sugar crystal formation; controlled release of flavors; flocculation; film formation, plasticization, fat replacement, biological active encapsulation, edible coating formation, carrier, and binding [1, 22–24]. The most used commercial hydrocolloids in the food industry, as well as their functions, are listed in Table 1.1. It can be seen that these compounds are usually used in food systems depending on their functional properties, for example, as thickener (soups, gravies, salad dressing, and topping), gelling agent (puddings and jellies), emulsifier (ice cream, yogurt, and butter), stabilizer (ice cream, mayonnaise, and sauces), fat replacer (meat and dairy products), clarifying agent (beer

Table 1.1 Functions of hydrocolloids in food and non-food systems. Example Function

Hydrocolloid

Product

Reference

Gelling agent

Agar, alginate, κ-carrageenan, gelatin, low and high methoxy pectin, hydroxypropyl methyl cellulose (HPMC)

Puddings, desserts, confectionary, jellies, dairy desserts, bakery products, tofu, milk shakes, whipped topping, glazes, cheese, acidified milk, wastewater treatment, immobilization of enzyme, milk drinks, aerogel, emulsion-filled gels

[25–33]

Emulsifier

Gum arabic, starch nanocrystals

Salad dressing, ketchup, mayonnaise, soft drink emulsion

[34–37]

Thickener

Carboxymethylcellulose (CMC), xanthan, guar gum, gum karaya, gum ghatti, locust bean gum, gum tragacanth, tara gum, konjac mannan, carrageenan

Ice cream, yogurt, sauces, jams, pie fillings, soups, gravies, salad dressings, cake batters, noodles, milk drinks

[38–45]

Thickener/emulsifier

Hydroxypropylcellulose (HPC), fenugreek gum, λ-carrageenan, sugar beet pectin

Processed cheeses, spray-dried milk powder, yogurt, ketchup tomato sauce, nanoemulsion

[46–49]

Thickener/emulsifier/gelling agent

Methylcellulose (MC)

Baked cakes, drug carriers, calcium phosphate cement

[50–52]

Thickener/gelling agent

Microcrystalline cellulose, starch and modified starches

Fried beef patties, dairy desserts, dissert sauces, snack foods

[53–57]

Emulsion/foam stabilizer

Xanthan, guar gum, propylene glycol alginate, agar

Whipped toppings, whipped cream, ice cream, beer, orange beverage emulsion

[58–61]

Thickening/ forming films agent

Cellulose gum

Lotions, shower gels, toothpaste

[5]

Thickening/ stabilizing/forming gels/films agent

Carrageenan

Lotions, shampoos, shave gels, toothpaste

[5]

Suspending/ stabilizing/forming gels/films agent

Gellan

Sprayable sunscreens, body washes, toothpaste

[5] (Continued)

Table 1.1 (Continued) Example Function

Hydrocolloid

Product

Reference

Thickening/skin feel/pH buffering agent

Pectin

Lotions, aftershave creams, gels

[5]

Thickening/suspending/stabilizing agent

Xanthan

Lotions, sunscreens, mascara, body washes, toothpastes

[5]

Adhesive

Starch and modified starches, alginate

Glazes, icings, frostings, mucoadhesive paste, wood adhesive

[62, 63]

Binding agent

λ-Carrageenan, gelatin

Pet foods, almond cystatin, aroma compounds

[64, 65]

Whipping agent

Starch, soya bean protein

Toppings, marshmallows, gluten-free breads

[66, 67]

Crystallization inhibitor

κ-Carrageenan, guar

Ice cream, sugar syrups, frozen foods

[68, 69]

Clarifying agent

chitosan, gelatin

Beer, wine, fruits, vegetables juice

[70, 71]

Clouding agent

Xanthan, pectin

Fruit drinks, beverages

[72, 73]

Coating agent

Aloe Vera, chitosan, pectin, gellan, gum arabic

Confectionary, fabricated onion rings, carrots, Fuji apples, fresh fruit

[74–76]

Dietary fiber

Inulin, beta glucan, hydroxypropylmethylcellulose, gum arabic

Cereals, breads, yogurts, gluten-free rice dough, cake

[77–80]

Film former

Gelatin, pectin, chitosan, agar, κ-carrageenan, starch

Sausage casings, protective coatings, packaging films

[81–84]

Molding

Starch

Gum drops, jelly candies

[85, 86]

Suspending agent

κ-Carrageenan, gellan

Chocolate milk

[5, 87]

Swelling agent

Carrageenan

Processed milk products

[30]

Syneresis inhibitor

Carrageenan, gellan, methylcellulose

Cheese, yogurt, frozen foods, peanut butter, tofu, turkey meat sausages, dough, a yogurt-based Iranian drink, fried seafood

[88–91]

Encapsulating agent

Alginate, agar, κ-carrageenan, pectin, starch, gelatin

Microencapsulation of flavors, fish oil, essential oil, enzymes d-limonene and minerals, drug, asphalt mastic, filled gel

[92–98]

Pore-former

κ-Carrageenan

membrane

[99]

Compressive and tensile strength enhancer

Carrageenan

Adobe constructions

[100]

Color stability

Carrageenan

Beef steaks

[101]

Fat substitutes

Carrageenan, pectin, starch

Frankfurters, mayonnaise, salad dressing

[102–104]

Predust agents

Hydroxypropylmethylcellulose (HPMC)

Battered fish nuggets

[105]

12

1 Introduction to Emerging Natural Hydrocolloids

and wine), flocculating agent (wine), clouding agent (juice and soft drinks), whipping agent (beer, whipped cream, and cake), coating agent (confectionary and fried foods), suspending agent (chocolate milk), anti-staling agent (breads and batters), water binding agent (gluten-free foods), encapsulating agent (powders’ flavors), and crystallization inhibitors (ice cream and sugar syrups) [1, 2]. From the viewpoint of compatibility, some hydrocolloids may be used in combination for obtaining better properties. Also, some hydrocolloids have a synergistic effect in mixture form with other hydrocolloids (e.g., xanthan gum in combination with galactomannans such as locust bean gum). The functional characteristics of natural hydrocolloids considerably depend on their physicochemical properties such as molecular weight, chemical composition, the sequence of monosaccharide, conformation, configuration, the position of glycoside linkage, particle size, hydrodynamic volume (intrinsic viscosity), and so on [106, 107]. Hydrocolloids can dramatically alter the viscosity of many times their own weight of water due to their interactions with the water molecules through hydrogen bonding. There are two rheological properties which are of major importance in hydrocolloid science and technology: gel (viscoelasticity and texture) and flow (shear thinning and thixotropy) properties. A clear understanding of the rheological behavior of hydrocolloids has emerged over the last 20 years, which has led in turn to the exploitation of commercial hydrocolloids in various industries. The viscosity of a biopolymer solution shows a marked increase at a critical polymer concentration, commonly referred to as the critical concentration (C*). This corresponds to the transition from the “dilute region,” where the polymer molecules are free to move independently in solution without interpenetration, to the “semi-dilute region,” where molecular crowding occurs which gives rise to the overlapping of polymer coils, thus causing interpenetration. The structural characteristics of hydrocolloids and their interaction with water (solvent) affect the rheology of hydrocolloids, leading to thickening, gelling, and so on. It is generally found that [14]: ➢ The hydrodynamic size of biopolymer molecules in solution is significantly influenced by its molecular structure. Linear and stiff molecules have a much larger hydrodynamic size than highly branched flexible polymers with the same molecular mass, and thus they give rise to higher viscosity values. ➢ Hydrocolloids stabilize emulsions primarily by increasing the viscosity of the system. They also act as emulsifiers, wherein the emulsification ability is reported to be mainly due to accompanying protein moieties. ➢ Hydrocolloids form gels when the intra- or intermolecular hydrogen bonding is favored over hydrogen bonding to water. ➢ The charged polymers or polyelectrolytes exhibit very high viscosity as compared to the non-ionic polymers of similar molecular mass. On the whole, it can be concluded that the rheological properties of hydrocolloids form the basis for their wide functions and applications in industries and also that the unique rheological behavior of the hydrocolloids can be attributed to the presence of a large number of hydroxyl groups in their structure, which leads to their H-bonding interactions in aqueous systems. During the last decades, the search for new sources of natural hydrocolloids and their characterization have been the subject of invaluable studies due to the need for novel and/or improved functional properties. So, in recent years, several important studies have been published on the characterization and functional properties of emerging hydrocolloids for application in various food systems. On

1.5 Overview of the Chapters

the basis of recently published works, some of the emerging natural hydrocolloids and their functions in the food and non-food systems are addressed in Table 1.2.

1.5 Overview of the Chapters In this book, recent papers, theses, and research works about some emerging hydrocolloids have been reviewed in detail. The following paragraphs aim to provide a brief overview of the chapters for the readers. 1.5.1

Chapter 2: Dilute Solution Properties of Emerging Hydrocolloids

In this chapter, the dilute solution properties of novel hydrocolloids have been discussed. The viscosity behavior of macromolecular substances in the dilute regime is one of the most frequently used approaches to determine its specification. In dilute solution, it is assumed that macromolecule chains are separated without intermolecular interactions. Investigation of molecular properties such as macromolecule–solvent interaction, macromolecule–macromolecule interaction, molecular weight, molecular shape, and conformation seems to be useful for understanding and controlling the behavior of a hydrocolloid in dilute solution under different conditions. Intrinsic viscosity [η] is a measure of the capability of a polymer in solution to increase the viscosity of the solution. Much information on the fundamental properties of a solute and its interaction with a specific solvent can be obtained by determination of the intrinsic viscosity. In this chapter, the dilute solution properties of some emerging natural hydrocolloids like basil (Ocimum basilicum L.) seed gum, cress (Lepidium sativum) seed gum, sage (Salvia macrosiphon) seed gum, Balangu (Lallemantia royleana) seed gum, Qodume Shirazi (Alyssum homalocarpum) seed gum, Qodume Shahri (Lepidium perfoliatum) seed gum, chia seed gum, canary seed starch, hsian-Tsao leaf gum, and so on, under various conditions (temperature, pH, salts, sugars) have been investigated. Finding interactions between hydrocolloids and solvent/cosolutes helps food researchers and manufacturers to understand the functional properties of these hydrocolloids in different food systems. 1.5.2 Chapter 3: Steady Shear Rheological Properties of Emerging Hydrocolloids This chapter aims to give an idea about how to use steady shear rheological measurements to identify the important structure-related characteristics of biopolymers and enables the reader to compare the rheological properties of various hydrocolloids and select the most appropriate hydrocolloid for their specific usage. For this purpose, a number of rheological tests were applied in the steady shear mode to describe the flow characteristics of two novel gums (sage seed gum [SSG] and cress seed gum) and three commercial gums (xanthan gum, guar gum, and pectin) dispersions. Various methods were used to quantify the thixotropic behavior of the selected gums, that is, hysteresis loop, shear stress decay, in-shear structural recovery, and time-dependency of steady shear properties. In addition, the static yield stress, dynamic yield stress, difference between yield stress at short and long time scales, and the corresponding time

13

Table 1.2 Some emerging hydrocolloids and their functions (2007–2017). Origin

Name

Principle function

Reference

Hylocereus undatus

Thickener and stabilizer

[108]

Hsian-Tsao (Mesona chinensis)

Emulsifier and gelling agent

[109–114]

Pereskia aculeate Miller

Coating, thickener, and emulsion stabilizer

Botanical • Plant

• Tree and shrub exudates

[115]

Cordia abyssinica

Emulsifier and gelling agent

[116–122]

Cissus populnea

Emulsifier, stabilizer and binder

[123–125]

Marshmallow (Althaea officinalis)

Thickener, emulsion and foam stabilizer

[126]

Nopal (Opuntia ficus indica)

Thickener, turbidity remover in contaminated water, antioxidants, emulsifier and coating

[127–137]

Aloe vera (Aloe vera barbadensis Miller)

Thickener and stabilizer

[138, 139]

Kondagogu (Cochlospermum gossypium DC.)

Emulsifier and stabilizer

[140–145]

Black tree fern (Cyathea medullaris)

Thickener

[146]

Persian (Amygdalus scoparia Spach)

Thickener and emulsifier

[147–149]

Tragacanth (Astragalus gummifer Labil)

Disintegrant

[150–156]

Brea (Cercidium praecox) gum

Emulsifier and stabilizer

[157–161]

Cashew (Anacardium occidentale L.)

Thickener and emulsifier

[162–165]

Apricot (Prunus armeniaca L.)

Thickening agent and emulsifier

[22, 166, 167]

Damson plum (Prunus domestica, Prunus insitia)

Thickening agent

[166]

Cherry (Prunus cerasus, Prunus cerusoides, and Prunus virginiana)

Antioxidant and emulsifier

[107, 168–171]

Almond (Prunus dulcis, syn. Prunus amygdalus)

Fat replacers, carrier, emulsifier, and coating

[172–187]

Peach (de-excitation rosaceae)

Thickener, emulsion stabilizer and surfactant

[188]

• Seed mucilage and extract

Basil (Ocimum bacilicum L.)

Stabilizer, thickener, emulsifier, foaming agent, gelling agent, fat replacer, disintegrant, binder, and crystal growth inhibitor

[189–223]

Cress (Lepidium sativum)

Stabilizer, thickener, emulsifying/foaming agent, fat replacer, disintegrant, and binder

[224–242]

Sage (Salvia macrosiphon)

Stabilizer, thickener, and fat replacer

[243–263]

Balangu (Lallemantia royleana)

Stabilizer, thickener, fat replacer, and crystal growth inhibitor

[38, 264–276]

Qodume Shahri (Lepidium perfoliatum)

Thickener and stabilizer

[277–282]

Qodume Shirazi (Alyssum homolocarpum)

Thickener, stabilizer and bioactive encapsulation

[23, 283–292]

Sophora alopecuroides L.

Thickener, stabilizer and gelling agent

[293–296]

Chinese Quince (Chaenomeles sinensis)

Gelling agent and emulsifier

[297–300]

Quince (Cydonia vulgaris Pers.)

Superdisintegrant and binder

[301, 302]

Quince (Cydonia oblonga Miller)

Thickener, water-based lubricant, emulsifier, emulsion stabilizer, and gelling agent

[303–308]

Espina Corona (Gleditsia amorphoides)

Thickener and stabilizer

[309–313]

Gleditsia triacanthos

Antioxidant, emulsifying and foaming capacities, stabilizer of foams and emulsions

[314–318]

Barhang (Plantago major L.)

Emulsion stabilizer and foam stabilizer

[319–323]

Delonix regia

Gelling agent, controlled delivery system, and foaming agent

[324–330]

Chia Salvia hispanica L.

Stabilizing, thickening agent, and emulsifier

[331–340]

Eruca sativa

Thickener and stabilizer

[341]

Tamarind (Tamarindus indica L.)

Thickener, emulsifier, stabilizer, gelling agent, and binder

[342–345]

Fenugreek (Trigonella foenum-graecum)

Thickener and binder

[346] (Continued)

Table 1.2 (Continued) Origin

• Starch

Name

Principle function

Reference

Flixweed (Descurainia sophia)

Thickener and stabilizer agent

[347–349]

Sophora japonica galactomannan

Thickener, film, and gelling agent

[350–353]

Mesona Blumes

Fat substitute, binder, and gelling agent

[354–363]

Roselle (Hibiscus sabdariffa)

Stabilizer and gelling agent

[364–368] [369–375]

Plantago (psyllium & ovata)

Gelling agents and stabilizer

Brachystegia eurycoma

Thickener

[376–378]

Leucaena leucocephala

Thickener

[379, 380]

Schizolobium parahybae galactomannan

Emulsifier and carrier

[381, 382]

Quinoa

Thickener and fat replacer

[383, 384]

Litchi chinensis

Thickener and bulking agent

[385, 386]

Mango (Mangifera indica L.)

Thickener and bulking agent

[385, 386]

Tamarind (Tamarindus indica L.)

Thickener and bulking agent

[387, 388]

Persian acorn (Quercus brantii Lindle.)

Thickener and stabilizer

[389, 390]

Canary (Phalaris canariensis)

Thickener and stabilizer

[391–395]

• Tuber

Chubak (Acanthophyllum glandulosum)

Emulsifier and emulsion stabilizer

[396–400]

• Wood Algal

Spruce galactoglucomannans

Emulsifier and stabilizer

[401–410]

Gracilaria grevill

Gelling agent and thickener

[411]

Ulva fasciata

Nature moisturizer, emulsifying agent, and stabilizer

[412–417]

Agrobacterium sp. ZX09

Thickener

[418]

Bacillus amyloliquefaciens LPL061

Emulsification activity

[419]

Rhizobium sp. strain ((LBMP-C01, LBMP-C02, LBMP-C03, and LBMP-C04)

Emulsification activity

[420]

Pseudomonas stutzeri AS22

Thickener, gelling agent, and emulsifier

[421]

Microbial

1.5 Overview of the Chapters

intervals were investigated. In order to categorize the hydrocolloids, the hierarchical clustering technique (HCT) and principal component analysis (PCA) were employed in serial mode. These data allow researchers to know the most critical parameter in the clustering of hydrocolloids. 1.5.3 Chapter 4: Transient and Dynamic Rheological Properties of Emerging Hydrocolloids In a steady shear flow test, the flow properties of all fluids, regardless of whether or not they exhibit elastic behavior, are a concern. However, much of the rheological behavior of food products cannot be described by viscosity function alone, and elastic behavior must also be taken into consideration. Experiments involving the application of unsteady state deformations, such as transient and oscillatory tests, are implemented to generate data that reflect both the elastic and viscous characters of materials. These tests can be implemented in linear and nonlinear regions. This chapter focuses on a number of new viscoelastic parameters beside some commonly used viscoelastic parameters to compare the dynamic and transient rheological characteristics of two novel gum dispersions, SSG and cress seed gum, and three commercial hydrocolloids, guar gum, xanthan gum, and pectin. 1.5.4 Chapter 5: Hydrocolloids Interaction Elaboration Based on Rheological Properties The study of synergistic polysaccharide–polysaccharide interactions remains a very attractive research area. The literature has proved that some novel gums could serve as alternatives to some of the commercial hydrocolloids in gum blend formulations as a stabilizer, thickener, binder, and gelling agents and could be used in food, cosmetics, and pharmaceutical systems. This chapter is invaluable for blends characterization regarding thermos-rheology, thermodynamic, and the kinetics of the interaction behavior of biopolymers. It reviews studies on new gums and some conventional gum mixtures and reports their rheological properties and the effect of temperature, salts, and pH on these characteristics to provide an assessment of the potential of these gums for influencing the structure of food products. The chapter enables the reader to compare the properties of different sources and aids in the eventual utilization of novel gums in blend systems for their specific usage. 1.5.5

Chapter 6: Sage (Salvia macrosiphon) Seed Gum

Sage (Salvia macrosiphon) is a pharmaceutical plant distributed worldwide. The literature has proved that SSG could be an interesting alternative to some of the commercial gums as a stabilizer, thickener, binder, and as fat-replacing and gelling agents in food, cosmetics, and pharmaceutical systems. Besides the SSG properties themselves, food ingredients and processing conditions affect its function. This chapter focuses on the very latest researches on the rheological properties of SSG and reviews the effect of some processing conditions, especially temperature, and other food components to provide an assessment of the potential of this novel biopolymer for influencing the structure of food products. In the end, some of the potential applications of SSG within foods,

17

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1 Introduction to Emerging Natural Hydrocolloids

such as ice cream, sauce, yogurt, d-limonene-in-water emulsions, and edible film, are highlighted. 1.5.6

Chapter 7: Balangu (Lallemantia royleana) Seed Gum

Balangu (Lallemantia royleana) seed has been recently investigated for its potential as a novel source of hydrocolloid for its superior thickening, stabilizing, and fat-replacing characteristics. Furthermore, the chemical and structural properties of Balangu seed gum (BSG) have been studied, which revealed the presence of arabinose, galactose, and rhamnose as the major monosaccharides with strong shear-thinning properties and high intrinsic viscosity comparable to those of commercial hydrocolloids. This chapter aims to review the structural, physicochemical, functional, and rheological properties of the gum extracted from Balangu seeds. Additionally, the research trends and prospects of BSG are discussed by specifically considering the potential applications in food systems. 1.5.7

Chapter 8: Qodume Shirazi (Alyssum homolocarpum) Seed Gum

Alyssum homolocarpum seed gum (AHSG) is a carbohydrate with a small number of uronic acids. This gum is a rhamnogalactan polysaccharide with a random coil structure and has an average molecular weight compared to other hydrocolloids. The aqueous dispersions of AHSG exhibit shear-thinning behavior, making it a good candidate for a thickening agent. AHSG solution exhibits high viscosity at low shear rates, and hence AHSG nano-capsules could be used as a wall material for encapsulation of bioactive compounds. This gum provides a relatively strong biopolymer gel and has a solid-like behavior. Moreover, AHSG has great emulsion stabilizing capacity, and with the incorporation of AHSG into O/W emulsion, the stability of the emulsion against flocculation, coalescence, and gravitational phase separation improves. On the other hand, AHSG has low surface activity due to its high hydrophilic nature and low molecular flexibility. The biodegradable film could also be prepared from AHSG with suitable mechanical characteristics and low oxygen permeability, making this film a great source for packaging materials. On the basis of the prominently reported references, this chapter provides a review of the extraction optimization, chemical constituents, functional properties, and applications of AHSG. 1.5.8

Chapter 9: Espina Corona (Gleditsia amorphoides) Seed Gum

Espina Corona gum (ECG) is extracted from the seeds of Gleditsia amorphoides trees that grow in South American countries. This gum is approved by the Argentinean food code. It is a galactomannan with an approximate molecular weight of 1.39 × 106 Da, consisting of 71.4% D-mannose and 28.6% D-galactose with a mannose/galactose (M/G) ratio of 2.5. The mannose forms a linear chain of (1 → 4) β-mannopyranose units with one molecule of d-galactopyranose linked at position 6 every three units of mannose. Structurally, ECG is similar to guar gum (GG), which has an M/G ratio of 2.0. ECG solutions exhibit shear-thinning behavior. The viscosity of ECG presents good stability during heating and to the addition of salts and acids. At 1% w/w, ECG exhibits the viscoelastic behavior of a weak gel, with light frequency dependence. Moreover, ECG

1.5 Overview of the Chapters

shows very good stabilizing properties in colloid systems by increasing the viscosity of the continuous phase and thus delaying the creaming and coalescence in emulsions, and the drainage, disproportionation, and coalescence in foams. In gels and films, ECG also presents synergistic effects with xanthan gum and improves the mechanical properties of carrageenans/K+ and whey protein systems. This chapter shows this gum is a promising hydrocolloid with great potential use in food and pharmaceutical applications. 1.5.9

Chapter 10: Qodume Shahri (Lepidium perfoliatum) Seed Gum

Lepidium perfoliatum seed gum (LPSG), with 88.23% total carbohydrate, exhibits interesting shear-thinning behavior with a consistency coefficient higher than pectin, starch, and locust bean gum. This gum can bind and immobilize a large amount of water and increase the viscosity and modify the texture of food products. LPSG can add texture to formulations and stabilize the dispersions and emulsions. LPSG has the ability to reduce the surface and interfacial tensions due to the presence of proteinaceous moiety being present either as an inherent part of the molecular structure or as impurities when extracting this gum. Since LPSG has a weak gel-like property in aqueous systems, this gum could be an excellent new source of polysaccharides for the formation of films and coatings. LPSG is highly compatible with legume proteins such as grass pea protein isolate and forms homogeneous single-phase blends. This ability enables LPSG to improve the quality of foods prepared from legume seeds. Addition of LPSG could reduce the amount of oil absorbed by fried food and improves the quality of the final products. In addition, LPSG has the potential to be used as a fat replacer and can act as a binder in food. Most of LPSG functional properties in food are due to the thickening action of this gum in aqueous systems. In this chapter, the rheological and functional properties, as well as the effect of LPSG on the structure and quality of food products, are discussed. 1.5.10

Chapter 11: Persian Gum (Amygdalus scoparia Spach)

Persian gum is one of the emerging potential emerging hydrocolloids which has been introduced and studied during the past decade. This chapter will first discuss our present understanding of the botanical source of the wild almond tree (Amygdalus scoparia Spach) alongside one of its by-products, “Persian gum.” Then, the following subsections will deal with how it is harvested and processed, its physicochemical characteristics, structure, rheology, interaction with other macromolecules, surface activity, thermal properties as well as potential applications. In the last subsection, the major challenges with reference to characterization and expansion of its applicability will be addressed. 1.5.11

Chapter 12: Gum Tragacanth (Astragalus gummifer Labillardiere)

Gum tragacanth (Astragalus) (GT) is a plant gum exuded from the stems and branches of various species of Astragalus with a branched heterogeneous anionic structure, containing carboxylic acid groups. There are various species of GT which have different physicochemical and rheological properties. All species of GT are made up of two distinct fractions: tragacanthin, which is the water-soluble part, and bassorin, which is water swellable. The objective of this chapter is to review safety assessments, structural, rheological, and functional properties of various species of this gum for exploration of their potential applications as a natural pharmaceutical and food agent.

19

20

1 Introduction to Emerging Natural Hydrocolloids

1.5.12

Chapter 13: Cashew Tree (Anarcadium Occidentale L.) Exudate Gum

The cashew tree gum is seen as a promising plant exudate for the food industry; however, there is a lack of understanding of its basic physicochemical, rheological, and toxicological properties, thus preventing its utilization in foods. The best long-term strategy for promoting the use of cashew gum in the food industry is, therefore, to understand and exploit the agricultural production, harvesting, physicochemical, and rheological properties of the gum. Cashew gum is similar to gum arabic and can be used as a liquid glue substitute for paper, in the pharmaceutical and cosmetic industries as an agglutinant for capsules and pills, and in the food industry as a stabilizer of juices. The production and physicochemical properties of cashew gum can be influenced by the environment within which the trees are found and the age of the trees. Studies on cashew gum have shown that it has good physicochemical, rheological, and functional properties. Cashew gum has been found to be safe for consumption, with a median lethal dose (LD50 ) of more than 30 g kg−1 b.w., and its application in the production of pineapple jam and chocolate pebbles and as a fat replacer in baked doughnuts as well as an excipient in drug formulation has been studied. In this chapter, the role of this gum in food formulations and product development has been discussed along with examples and methods of characterization to indicate the increasing use of cashew gum. 1.5.13

Chapter 14: Brea Tree (Cercidium praecox) Exudate Gum

Brea gum is the exudate from the Brea tree (Cercidium praecox) that is widespread in arid and semiarid regions of the American continent. The Brea tree grows in poor soils and can help with degraded environment restoration. Brea gum is obtained through cuts or incisions on the bark. Its chemical composition is based on a β-(1 → 4) xylan backbone heavily substituted by short branch chains containing neutral sugars and uronic acids and their ethers. In an aqueous solution, the molecules acquire a spherical form and exhibit high solubility and a rheological behavior practically Newtonian with a moderate viscosity at high concentrations. Brea gum contains 4%–10% of proteins that influence its functional properties. The gum is suitable as a stabilizer for systems containing high insoluble solids. It acts as a good emulsifier and stabilizer of oil-in-water emulsions and favors foam formation and stabilization. Besides, Brea gum forms dense edible films with high water solubility, and hence their mechanical and barrier properties are strongly affected by the ambient relative humidity. Clay nanoparticle incorporation into the film matrix reinforces the structure and reduces the effect of humidity on the film properties. In bread making, an addition of 0.5% of Brea gum to wheat flour increases the moisture of the crumb. The food safety of this hydrocolloid has been demonstrated, and it was approved as a food additive. According to its physicochemical and rheological properties discussed in this chapter, Brea gum could be used as a substitute for gum arabic or similar gums in several applications. 1.5.14

Chapter 15: Chubak (Acanthophyllum glandulosum) Root Gum

A new natural hydrocolloid can be isolated from the roots of Acanthophyllum glandulosum, popularly called “Chubak” in Iran. The gum has a high total content of carbohydrate (84.3%), and its uronic acid content is 10.3%, which is consistent with the acidic nature

1.5 Overview of the Chapters

of the polysaccharide in gum. The Chubak root extract (CRE) has a high superficial and interfacial activity due to its saponin and hydrocolloid components; thus, it is known as a natural emulsifier and aerating agent because it enables formation of a stable foam. Its use in food systems has been recommended to improve foaming properties or, in other words, aeration. In this chapter, the extraction methods of CRE and its applications in different products such as doughnut, yogurt, ketchup, non-alcoholic beer, muffin cake, sponge cake, mayonnaise, and grape juice have been discussed. In sum, this chapter demonstrates that CRE can serve as a natural emulsifier and an aerating agent with valuable pharmaceutical properties and a unique taste. 1.5.15

Chapter 16: Marshmallow (Althaea officinalis) Flower Gum

In this chapter, the effect of extraction variables including pH (5–9), temperature (25–65 ∘ C), and water-powder (W/P) ratio (40:1–80:1 v/w) on yield, consistency coefficient (k), emulsion stability index (ESI), foam stability index (FSI), and color component value (L* parameter) of marshmallow flower gum (MFG) are optimized using response surface methodology (RSM). In addition, some physicochemical properties and biological activity of the optimized MFG, including chemical compositions, average molecular weight, monosaccharides, uronic acids, thermal analysis, and antioxidant potential (DPPH), are characterized. The chapter suggests that MFG could potentially be used as a new source of hydrocolloid whose functional properties are comparable with commercial ones. Also, the influence of different temperatures (5, 25, 45, and 65 ∘ C), pH (5, 7, 9, and 11), and concentration (0.25, 0.5, 1.0, and 2.0 w/v) on the steady shear rheological properties and intrinsic viscosity of MFG were evaluated. The results revealed that the power-law model satisfactorily described the rheological behavior of the mucilage solutions, and all the MFG solutions exhibited shear-thinning behavior and non-dependence on shearing time at all temperatures, pH, and concentrations tested. 1.5.16

Chapter 17: Opuntia Ficus Indica Mucilage

The present chapter aims to summarize the research on the chemical compositions, molecular structure, functional properties, and rheological behavior (steady shear and dynamic rheology) of the mucilages extracted from different parts of Opuntia ficus indica to find their potential applications in food, pharmaceutical, and other systems. It has been suggested that Opuntia ficus indica mucilage is a rhamnogalacturonan polysaccharide mainly composed of xylose, rhamnose, and galactose. It also has been reported that the mucilage from Opuntia ficus can be used as an appropriate edible coating to extend the shelf life of vegetables and fruits. Furthermore, the positive effect of the mucilages of Opuntia ficus indica on encapsulation of phytochemicals and wastewater treatment has been demonstrated in this chapter. 1.5.17 Chapter 18: Emerging Technologies for Isolation of Natural Hydrocolloids from Mucilaginous Seeds Many mucilaginous seeds around the world have been introduced for use as accessible, cost-effective, and natural sources. These hydrocolloids are used as thickener, gel

21

22

1 Introduction to Emerging Natural Hydrocolloids

former, and as foam and emulsion stabilizing agents in a wide range of foods and pharmaceuticals. Due to the high stickiness between mucilaginous layers and seed cores, a severe mechanical stress is required for quick separation of mucilaginous layers from seed cores. The conventional method for isolating/extracting hydrocolloids from mucilaginous seeds includes hydration processes, followed by the application of a severe mechanical shear stress by high-speed mixers or stirrers with rotating blade plates. Therefore, a heterogeneous mixture of crushed seeds and mucilage may be produced. Several stages of time-consuming centrifugation are required to separate the crushed seeds’ parts and impurities, which are followed by drying and grinding the derived gum. This leads to high level of damage and crushing of the seed cores, which, on the one hand, makes the use of centrifuge force inevitable and on the other hand results in a large amount of impurities from crushed seeds entering the isolated hydrocolloids. In recent years, attempts have been made to use emerging technologies and new methods for extraction of seeds gums aiming at improving the extraction process of seed gums. This chapter aims to review conventional and emerging extraction methodologies and provides an overview of the current state of hydrocolloid extraction techniques with comparisons of their advantages and disadvantages. 1.5.18 Chapter 19: Purification and Fractionation of Novel Natural Hydrocolloids Purification of polysaccharides removes unacceptable flavors of the crude gums, and the purified gums give more stable solutions. Physicochemical, rheological, and functional properties of the crude gum improve after purification. In fractionation, the major polymer will be subdivided into fractions with different molecular weights and structures. Therefore, different physicochemical, rheological, functional, and application areas are expected for the fractions. Fractionation, physicochemical, rheological, and functional properties of the fractions and the effect of purification methods on the characteristics of some new hydrocolloids such as durian seed gum, chia seed gum, basil seed gum, and cress seed gum are reviewed in this chapter. 1.5.19 Chapter 20: Improving Texture of Foods using Emerging Hydrocolloids Foods would never be foods if humans do not feel happiness and satisfaction during eating. From this perspective, palatability is the most important attribute of foods and differentiates them from medicines. Food palatability is determined by some organoleptic attributes, including flavor, texture, appearance, sound, and temperature, and flavor and texture are the two major factors determining food palatability. Texture sensing is primarily the responsibility of the tactile senses to physical stimuli which result from contact between some part of the body and the food. The tactile sense (touch) is the primary method for sensing texture, but kinesthetic (sense of movement and position) and some sight (degree of a slump, the rate of flow) and sound (associated with crisp, crunchy, and crackly textures) are also used to evaluate texture. Texture properties are perceived by human senses. To understand texture, it is critical to know how the human body interacts with food. Mastication is the process in which pieces of food are ground into a fine state, mixed with saliva, and brought to body temperature in readiness for

1.5 Overview of the Chapters

transfer to the stomach, where most of the digestion occurs. Pulverization of food is the main function of mastication, but it also imparts pleasurable sensations that fill a basic human need. Mastication usually reduces particle size by two to three orders of magnitude before passage of the food to the stomach, where another approximately 20 orders of magnitude of size reduction is accomplished by chemical and biochemical action. Since texture is perceived by the human senses, one needs to understand how the body interacts with different foods, because this is the foundation on which is built an understanding of what is needed in objective and subjective tests for texture. In addition, the influence of thermal processing on hydrocolloids is important in some processes such as heating and freezing that are used to prepare many foods. Thus, this chapter is devoted to the effect of hydrocolloids on texture from the standpoint of oral processing, eating psychology, and fractal analysis of some studied hydrocolloids. 1.5.20

Chapter 21: New Hydrocolloids in Ice Cream

Ice cream is a complex colloidal system consists mainly of fat globules, air bubbles, and ice crystals dispersed in a highly viscous aqueous phase. The quality of ice cream largely depends on its formulation. The viscosity of the ice cream mix affects the body, texture, air incorporation, and melting resistance of ice cream. The most important factor which is responsible for enhancing the viscosity of the ice cream mix is stabilizers such as hydrocolloids added to this system. The final quality of ice cream is also influenced by ice crystals. Hydrocolloids are able to reduce ice crystal growth due to high water retention and viscosity enhancement capability. Therefore, they increase the stability of ice cream during storage by providing thickness and cryoprotection. On the other hand, health-conscious consumers are attracted by fat-replaced ice cream to prevent obesity and coronary heart diseases. For this reason, the food industry is looking for new alternatives to fat in ice cream. The majority of fat replacers are hydrocolloids whose functionalities allow them to mimic the mouthfeel, texture, and flow properties in a similar manner to fat. In this chapter, the effect of some new hydrocolloids on the ice cream characteristics and their functions as stabilizer, fat replacer, and cryoprotector agents are reviewed. 1.5.21 Chapter 22: Novel Hydrocolloids for Future Progress in Nanotechnology Hydrocolloids are suitable as building blocks of nanosystems. They can offer a wide diversity in structure and properties due to their wide range of molecular weight and chemical composition. The main advantage of hydrocolloids as natural biomaterial carriers is their availability in nature and low cost of processing. Furthermore, the presence of hydrophilic groups in their structure enhance bio-adhesion with biological tissues like epithelial and mucous membranes in delivery systems. Hydrocolloids can be obtained from several resources, including plants, algae, animals, and microbes. Though the use of commercial gums has continued, a new source of gum potential has been investigated to develop more nanosystems with a novel structure. Recently, new research has been conducted to evaluate novel gum potential in nanotechnology. Therefore, the advantage and limitation of various types of novel sources of hydrocolloids used as the nanostructure systems have been discussed in this chapter.

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1.5.22 Chapter 23: Edible/Biodegradable Films and Coatings from Natural Hydrocolloids In recent decades, fabrication of edible/biodegradable films and coatings from renewable resources has received much attention for reducing the environmental risks caused by the use of synthetic films in the packaging industry. Edible films are mostly prepared from natural polymers, that is, polysaccharides, proteins, and their composites, derived from plants or animals. These natural hydrocolloids demonstrate good film-making capability. Evaluation of the novel films’ properties reveal that they are comparable with most of the commercial biopolymer-based films. Despite some modifications, additional works are required to further improve the performance and achieve film properties closer to synthetic ones. In brief, different environmental and health issues of petroleum-based films, and fossil oil non-renewability have led researchers to seriously think about designing eco-friendly packaging from renewable resources; therefore, gum-based films and coatings show promise for large-scale production and commercial use. This chapter comprehensively focuses on the film preparation process from some emerging natural hydrocolloids, besides comparing their physical, mechanical, and thermal characteristics with films from commercial polysaccharides, and finally, evaluates their food applications. 1.5.23

Chapter 24: Healthy Aspects of Novel Hydrocolloids

Hydrocolloids have been recognized mainly for their rheological and structural functionalities in food industries. From a physiological perspective, hydrocolloids (particularly dietary fiber) have many important functions. Cholesterol lowering, weight regulation, cancer prevention, short-chain fatty acid production, positive modulation of colonic microflora, anti-diabetic properties, and so on, are the main biological functions that hydrocolloids perform as dietary fiber. Recently, other healthy properties of hydrocolloids such as antioxidant properties, prebiotic effects, immune modulating activity, antiviral activity, antiglycation, antiangiogenic activity, anticoagulant activity, stimulation of minerals, and biomedical applications have been considered. This chapter describes the abovementioned properties as well as its structural dependence for novel hydrocolloids.

1.6 Conclusion Hydrocolloids are hydrophilic polymers dispersed in water. Hydrocolloids, on the basis of their origin, are classified as natural, semi-synthetic, and synthetic. Compared to synthetic and semi-synthetic polymers, natural hydrocolloids have distinct advantages, such as being non-toxic, sustainable, eco-friendly, cost-effective, readily available, biodegradable, biocompatible, and capable of chemical modification. Hydrocolloids are valuable additives that have many interesting functions in various products despite their low usage level. Natural hydrocolloids, as biological macromolecules, are frequently used in food and pharmaceutical systems as thickening, emulsifying, stabilizing, fat replacing, flavor encapsulating, edible coating, plasticizing, binding, and gelling agents. Over the past few decades, there has been a growing demand for new sources of natural

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2 Dilute Solution Properties of Emerging Hydrocolloids Ali R. Yousefi 1 and Seyed M.A. Razavi 2 1

Department of Chemical Engineering, Faculty of Engineering, University of Bonab, Bonab, Iran Food Hydrocolloids Research Center, Department of Food Science and Technology, Ferdowsi University of Mashhad, POBox: 91775-1163, Mashhad, Iran 2

2.1 Introduction Hydrocolloids are broadly applied in food systems to enhance their quality by influencing their physical and organoleptic properties as thickening and gelling agents, stabilizers, and texture modifiers [1–4]. Nowadays, the demand for hydrocolloids from plants (e.g., plant cell walls, tree exudates, seeds, and seaweeds) is greater than those from animals (hyaluronan, chitin, gelatin, and chondroitin sulfate) because of greater benefits and a more consumer-friendly image [5, 6]. In addition to the common and commercial hydrocolloids like xanthan, locust bean, guar, dextran, pectin, and so on, nowadays novel hydrocolloids have been introduced by researchers which represent specific characteristics to some extent. Here, some of these novel hydrocolloids are briefly introduced. Hsian-tsao (Mesona procumbens Hemsl) leaf gum is found to be used as a thickener, and it is reported that it strongly interacts with starch to form thermos-reversible resilient gels [7]. Lepidium sativum seed gum (cress seed gum) is an annual herb from the Cruciferae family growing in Middle East countries, Europe, and the United States. This hydrocolloid is a culinary herb and has some health-promoting properties [8]. Cress seeds have been used in traditional medicine for a long time to treat asthma, hypertension, hepatotoxicity, hyperglycemia, enuresis, and fractures [9]. Lallemantia royleana (Benth. in Walla.) is a folk medicinal plant of the Labiatae family, which grows naturally in Asia, Europe, and the Middle East, especially in various regions of Iran. Its common Persian name is Balangu–Shirazi [10]. The mucilage extracted from its seeds shows promise as an emerging source of hydrocolloids, according to recent reports [11]. Alyssum homolocarpum (Qodume Shirazi) is a member of the Cruciferae family, which has many traditional applications. Qodume is native to some Middle East countries including Egypt, Iraq, Iran, and Pakistan. Its mucilage has pharmaceutical applications and has recently been examined as a novel source of hydrocolloids [12]. Wild sage (Salvia macrosiphon) is one Iran’s endemic plants, and its seed mucilage is a promising alternative to some commercial gums [13]. Basil (Ocimum basilicum) seed gum is one of the emerging hydrocolloids; it can be isolated from the seeds of basil herb and has recently found many applications in food formulations as a stabilizer, emulsifier, thickener, and gelling agent [14]. Canary seed is an annual cereal crop produced Emerging Natural Hydrocolloids: Rheology and Functions, First Edition. Edited by Seyed M.A. Razavi. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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primarily in Canada and Argentina. The distinctive composition and characteristics of this crop make it a favorable cereal for food and industrial applications. Two varieties of hairless canary seed, including CDC Maria and C05041, are currently registered in Canada and have received GRAS (Generally Recognized as Safe) status [15]. Hydrocolloids indicate various functional attributes in the food system because of the physicochemical mechanism underlying their behaviors in a solution, such as their interactions with solvent molecules. Solubility, viscosity enhancing, binding, and many other characteristics are the most important thermodynamically controlled macromolecule–solvent interactions. As an easy and interesting approach, viscosity measurements in dilute domains can be applied to characterize the behavior of hydrocolloids [16]. In a dilute solution, the macromolecular chains are at an adequate distance from each other, and there are no notable interactions between the chains. Therefore, each isolated molecule occupies a discrete hydrodynamic volume within the solution and contributes individually to the bulk properties of the system almost independently [11]. An intense increase in viscosity upon dissolution in an aqueous solution is one of the hallmarks of macromolecules. When a few hydrocolloids dissolve in an aqueous solution, the intrinsic viscosity parameter can be extensively used for their analysis or characterization [17, 18]. The limiting viscosity number or intrinsic viscosity is a molecular parameter that indicates the hydrodynamic volume occupied by a unit mass of macromolecule and depends primarily on the molecular size, conformation, and molecular weight as well as solvent quality [19, 20]. On the basis of this definition, the intrinsic viscosity concept gives deep insight into the principal molecular attributes of macromolecules in solution. For a particular hydrocolloid, the attractive and repulsive interactions between chain segments can be altered by changing the solvent quality and/or electrostatic repulsion between chains elements via commonly used additives. Basically, it can be expected that any change in the intrinsic viscosity can cause changes in the molecular hydrodynamic volume, conformation, and macromolecular associations [11, 13, 20]. On the other hand, the mentioned interaction between solvent and cosolutes can reveal the functional properties of hydrocolloids. The objective of this chapter is to address the dilute solution properties of the aforementioned emerging hydrocolloids and to investigate their structural and morphological characteristics to shed some light on their behavior in the concentrate and gel regimes.

2.2 Partial Specific Volume The study of the partial specific volume (υ) of polymers in dilute solution has recently attracted some attention as a means of gaining information about polymer–solvent interactions. The partial specific volume can be determined with a pycnometer or densimeter. This parameter is very much affected by the molecular weight and concentration of the polymer as well as by the quality of the solvent. This value can be measured by calculating the slope of the (ρ-ρ0 ) versus concentration plot, where 𝜌 and 𝜌0 are the densities of the solution and solvent, respectively. Amini and Razavi [11] calculated the υ value of Balangu seed gum solution in deionized water from density measurements at 20 ∘ C (Table 2.1). This parameter was obtained to be 0.61 ml g−1 , which was similar to the value of 0.63 ml g−1 reported for high-methoxyl pectin [25]

2.3 Hydrogel Content

Table 2.1 Partial specific volume (υ) for some hydrocolloids.

Hydrocolloid

Partial specific volume (ml g−1 )

Reference

Alyssum homolocarpum

0.44

[21]

Balangu seed gum

0.61

[11]

Basil seed gum

0.62

[14]

Carboxymethyl chitins

0.47

[22]

Chitosan

0.58

[23]

Citrus pectin

0.57

[24]

High-methoxyl pectin

0.63

[25]

Hyaluronan

0.56

[26]

Guar and Locust bean gums

0.61

[17]

Konjac glucomannan

0.63

[27]

Sage seed gum

0.48

[13]

Xanthan

0.60

[28]

and Konjac mannan [27], and the value of 0.61 ml g−1 reported for guar and locust bean gums [17], but higher than the value reported for hyaluronan (0.56 ml g−1 ) by Cowman and Matsuoka [26]. Yousefi et al. [13] found a value of 0.48 ml g−1 for sage seed gum, which was similar to the value obtained for carboxymethyl chitins [22], but lower than for citrus pectin (0.57 ml g−1 ) [24], xanthan (0.60 ml g−1 ) [28], and Balangu seed gum (0.61 ml g−1 ) [11]. The buoyancy of particles in food systems is an important factor that affects the sedimentation phenomenon. The buoyancy of a specific particle increases with the increase in the partial specific volume, and therefore the higher the partial specific volume for a polymer, the less the sedimentation [28]. Durchschlag [29] reported that the partial specific volume of native conjugated proteins in aqueous solution varies in the range 0.59–1.05 ml g−1 . For another novel hydrocolloid, A. homolocarpum seed gum, a value of 0.44 ml g−1 was reported by Hesarinejad et al. [21], which is comparable to those determined for the sage seed gum (0.48 ml g−1 ) and carboxymethyl chitins (0.47 ml g−1 ). In another study, the partial specific volume of basil seed gum found to be about 0.62 ml g−1 , which decreased upon increasing the temperature [14]. This value is very close to those reported for some hydrocolloids such as Balangu seed gum, high-methoxyl pectin, guar, and locust bean gums, but higher than that for hyaluronan and chitosan.

2.3 Hydrogel Content So far, researchers have defined hydrogels in many different ways. The most common of these is that a hydrogel is a water-swollen, cross-linked polymeric network produced by the simple reaction of one or more monomers. It is also defined as a polymeric material that represents the ability to swell and retain a significant fraction of water

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2 Dilute Solution Properties of Emerging Hydrocolloids

Physical stimuli response

Temperature Electric field

Chemical stimuli response

56

pH

Magnetic field Light Pressure Sound

Ionic strength

Unswollen hydrogel

Swollen hydrogel

Solvent composition Molecular species

Figure 2.1 Stimuli response of swelling hydrogel. Source: Adapted from Ahmed [30] with permission from Elsevier.

within its structure without dissolving in water [30]. Hydrogels have received much attention in the past 50 years, due to their exceptional promise in a wide range of applications [31, 32]. The water absorption ability of hydrogels is associated with hydrophilic functional groups attached to the polymeric backbone, whereas their resistance to dissolution is due to cross-links between network chains. Hydrogels can be designed with controllable responses such as shrinkage or expansion with changes in external environmental conditions [30]. They may exhibit dramatic volume transitions in response to a variety of physical and chemical stimuli, where the physical stimuli include temperature, electric or magnetic field, light, pressure, and sound, while the chemical stimuli include pH, solvent composition, ionic strength, and molecular species (Figure 2.1). Biopolymer-based hydrogels have attracted increasing attention due to their biocompatibility, biodegradability, and tissue-mimicking consistency. It has been demonstrated that biopolymer-based hydrogels are used in varied fields such as agriculture [33, 34], hygiene, biomedical materials [35, 36], pollutant adsorbents [37–39], biosensors [40], and so on. So far, various natural polymers or their salts such as sodium alginate, starch, protein, gelatin, hyaluronate, hemicelluloses, lignin, cellulose, chitin, and their derivatives have been applied to fabricate biopolymer-based hydrogels [41]. The hydrogel content of hydrocolloids can be determined using the filtration method defined by Karazhiyan et al. [18]. In this method, a prepared solution of hydrocolloid is filtered under vacuum via filter paper. The filtrate is discarded, and the insoluble hydrogel is dried in an oven at 105 ∘ C until a constant weight achieved. Then, the hydrogel content of hydrocolloid can be estimated as follows: m − m2 × 100 (2.1) Hydrogel content (%) = 3 m1 where m1 , m2 , and m3 are the sample weight, initial weight, and final weight of the filter paper, respectively. The hydrogel content of several novel hydrocolloids has been reported. The hydrogel content of Balangu seed gum solution in deionized water was

2.4 Molecular Weight

determined to be about 46% insoluble [11]. The hydrogel content of basil seed gum was obtained as 73.6% [14], which is near to that of L. sativum seed gum (76%) [18]. It is found that the type and concentration of the cosolute can significantly affect the amount of hydrogel content. Accordingly, an increase in ionic strength or concentration of ions drastically increases the hydrogel content. In this case, divalent cations like Ca2+ are more effective in increasing the hydrogel content rather than monovalent cations like Na+ . In this case, Amini and Razavi [11] stated that as a result of the increase in ionic strength, the hydrogel content of Balangu seed gum solutions at all levels of ion concentrations was observed to increase drastically, and the Ca2+ was more effective than the Na+ . On the other hand, the hydrogel content of Balangu seed gum is enhanced by the presence of sugars (sucrose and lactose) compared to sugar-free solution, and in most cases, it is not influenced significantly by increasing the sugar concentration. The hydrogel, from the physical standpoint, probably indicates that the molecular species form large aggregates in solution so that their overall sizes exceed the pore size of the filter paper, making it impossible for them to pass through it. If this assumption is valid, it could be inferred that the hydrogel content would be used as a sensitive measure of molecular species aggregation in response to any alteration in solvent conditions [11].

2.4 Molecular Weight The same polymer from different sources may have different molecular weights. All common synthetic polymers and most natural polymers (except proteins) have a distribution in molecular weights. Therefore, some molecules in a given sample of a hydrocolloid are larger than others. The two most important molecular weight averages are the number-average molecular weight, Mn , and the weight-average molecular weight, Mw , as follows: ∑n i=1 Ni Mi Mn = ∑ (2.2) n i=1 Ni ∑n 2 i=1 Ni Mi (2.3) Mw = ∑ n i=1 Ni Mi where N i is the number of molecules of molecular weight Mi . For single-peaked distributions, Mn is usually near the peak. The weight-average molecular weight is always larger than number-average molecular weight. For simple distributions, Mw may be 1.5–2.0 times Mn . The ratio Mn /Mw , sometimes called the polydispersity index, provides a simple definition of the molecular weight distribution [42]. There are different methods for molecular weight determination of polymers. These techniques can be classified as osmometry techniques (membrane and vapor pressure osmometry) [43], end group analysis (this method is important particularly in the determination of the average molecular weight of step-growth polymers) [44], light-scattering technique (this technique thus relies on the measurement of light scattered at an angle to the incident ray as it passes through the target), sedimentation technique (this instrument measures sample concentration with respect to position from the center of a rapidly rotating cell) [43], and gel permeation chromatography (GPC) (the separation mechanism is essentially based on the differences in the size

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of polymer materials) [45]. The light scattering and GPC techniques are rather more common than the others as reported in the literature. In the case of the light-scattering technique, the weight-average molecular weight (Mw ) and the second virial coefficient (A2 ) can be obtained from the scattered light intensities using a plot of the excess Rayleigh factor (R𝜃 ) at the scattering angle (θ = 90∘ ) as a function of polymer concentration (c) which is in the dilute solution regime. The following equations allow determination of Mw [11]: Kc∕R𝜃 = (1∕Mw ) + 2A2 c

(2.4)

K = (2𝜋 2 ∕𝜆40 NA ) (1 + cos2 𝜃) n2 (dn∕dc)2

(2.5)

R𝜃 = R𝜃,solution − R𝜃,solvent

(2.6)

where λ0 is the beam wavelength, K is a calibration constant, N A is Avogadro’s number, n is the refractive index of solvent, and dn/dc is the specific refractive index increment. After constructing the Kc/R𝜃 versus curve at different concentrations, A2 and Mw can be calculated from the slope and the reciprocal of the intercept, respectively. According to the Zimm plot, the key equations at the limit of the zero angle (Eq. (2.4)) and zero concentration (Eq. (2.7)), respectively, relating the light-scattering intensity to the weight-average molecular weight Mw and the z-average radius of gyration Rg are [ ) ] ( ( ) 1 1 4𝜋 2 2 2 𝜃 c = R sin 1+ + … (2.7) K g R(𝜃) c=0 Mw 3 𝜆′ 2 where λ′ is the wavelength of the light in solution (λ0 /n0 ), and Rg is the gyration radius. To construct a Zimm plot, Eqs. (2.4) and (2.7) are added. To make a more aesthetic plot, the concentration term is usually multiplied by an arbitrary factor. Thus three quantities of interest can be determined from the same experiment: the weight-average molecular weight, the z-average radius of gyration, and the second virial coefficient. A useful practical equation for the determination of Rg from a plot of K[c/R(θ)] versus sin2 θ/2 is [42] R2g =

3𝜆′2 (slope) 16𝜋12 (intercept)

(2.8)

Equations (2.4) and (2.7) show the function K[c/R(θ)] in the limit of θ = 0 and c = 0, respectively. Three important pieces of information can be extracted from this experiment: the weight-average molecular weight, z-average radius of gyration, and the second virial coefficient [42]. A most powerful advance was the introduction of the Zimm plot, which enabled the radius of gyration, the molecular weight, and the second virial coefficient to be calculated from a single master figure, by plotting K[c/R(θ)] versus a function of both the angle and concentration (Figure 2.2). Amini and Razavi [11] used the Debye plot (it is not capable of determining the z-averaged square of the radius of gyration) rather than the Zimm plot one to determine the Mw and A2 of Balangu seed gum. Their results in the temperature range 30–50 ∘ C showed that Mw decreased significantly with increasing temperature from 30 to 50 ∘ C. This reduction in Mw may probably indicate that Balangu seed gum has been degraded or debranched at temperatures higher than 30 ∘ C. Also, A2 decreased with an increase

2.5 Intrinsic Viscosity

Kc/Rθ × 106

6 5 Kc/Rθ × 106

Figure 2.2 Zimm plots of a bacterial polysaccharide in 0.1 M NaCl obtained with the static light scattering technique. λ0 = 488 nm, dn/dc = 0.145 cm3 g−m . Static light-scattering yields Rg , Mw , and A2 . Source: Adapted from Dentini et al. [46] with permission from American Chemical Society.

4 3

static

2 1 0

0

2

4

6 8 10 12 (q2 + kc) × 1010/cm–2

14

16

in temperature, demonstrating that the solvent quality has been decreased. In contrast, for some hydrocolloids like pullulan, it is observed that A2 does not change with temperature [47]. Similar results were found in the case of the influence of temperature on Mw by Axelos and Branger [48] for pectin and by Morris et al. [25] for high-methoxyl pectin. According to the literature, it has been reported that the Mw of pullulan is not affected by temperature, and it seems that only the temperatures above 35 ∘ C decrease this value slightly [47]. Mirabolhassani et al. [14] applied a dilute solution of basil seed gum with a concentration in the range of 0.0025–0.01 g ml−1 to measure Mw using the light-scattering method. Their results indicate that basil seed gum has a small molecular weight (3.66 × 105 Da). Using the same method, Razavi et al. [49] reported that the Mw of sage seed gum was found to be 4.33 × 105 Da. These values of Mw for the novel hydrocolloids were lower than those reported for guar gum (1.3 × 106 Da), locust bean gum (1.2 × 106 Da), mesquite gum (1.2 × 106 Da), and fenugreek gum (1.4 × 106 Da) [50–52].

2.5 Intrinsic Viscosity The hydrodynamic volume occupied by a given polymer mass is defined as its intrinsic viscosity, [𝜂], which is a parameter that can be measured by dilute solution viscosity measurement [53]. This parameter is a measure of the interaction of the molecular structure with the solution. In dilute solution domains, due to the separation of polymer chains, this parameter is closely in associated with the size and conformation of macromolecular chains in a specific solvent [19]. According to the literature, several theories in polymer physics relate the intrinsic viscosity to the molecular properties of polymers such as the molecular weight, overlap concentration, radius of gyration, and pore size of the concentrated polymers [54]. The intrinsic viscosity values are also important in determining the solubility parameters of polymers with a linear structure in different solvents [55]. Finally, the intrinsic viscosity values are important for probing the biological macromolecular structure and interaction with a solution [56]. The intrinsic viscosity is evaluated by measuring the viscosity of the polymer solution over a range of concentrations. The intrinsic viscosity is determined by either timing the flow of the solution through a capillary tube or by measuring the force required to rotate two concentric surfaces separated by the solution. The intrinsic viscosity [𝜂] can be determined by measuring the viscosity of very-low-concentration solutions by calculating the

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following viscosities: 𝜂 𝜂rel = 𝜂s 𝜂sp = 𝜂rel − 1

(2.9) (2.10)

𝜂sp ln𝜂rel = lim (2.11) c→0 c→0 C C where 𝜂 is the solution viscosity, 𝜂 s is the solvent viscosity, 𝜂 rel is the relative viscosity, and 𝜂 sp is the specific viscosity. Several equations have been developed to determine the intrinsic viscosity. According to the Huggins model [57] (Eq. (2.12)), the intrinsic viscosity [𝜂] is obtained simply by extrapolating 𝜂 sp /C data to zero concentration through a linear regression: [𝜂] = lim

𝜂sp

(2.12) = [𝜂] + k′ [𝜂]2 C C where k′ is the Huggins constant. Kraemer [58] reported that the intrinsic viscosity [𝜂] could be obtained by extrapolating ln𝜂 rel /C values to zero concentration (Eq. (2.13)): ln𝜂rel (2.13) = [𝜂] + k ′′ [𝜂]2 C C where k′′ is the Kraemer constant. It is demonstrated that the methods that calculate the intrinsic viscosity on the basis of the slopes of plots had higher correlation coefficient and lower standard errors in comparison with methods that employ the intercepts of plots [59, 60]. From this finding, the following three equations are shown to determine the intrinsic viscosity of the solutions on the basis of the slope of plots: Tanglertpaibul and Rao model [61]: 𝜂rel = 1 + [𝜂]C

(2.14)

Higiro et al. models [19]: 𝜂rel = e[𝜂]C 𝜂rel =

1 1 − [𝜂]C

(2.15) (2.16)

It should be noted that in addition to the capillary viscometer method, differential viscometer and light scattering and imaging techniques can be used to determine the intrinsic viscosity. The differential viscometer technique is based on a fluid analog of the Wheatstone bridge electrical circuit. The differential pressure across a bridge of four fluid capillaries is measured to evaluate the relative viscosity of the polymer solution [53]. The mean square displacement of the scattering (imaging) particles in the polymer solution is calculated using scattered intensity or particle position data. In the light scattering and imaging technique, the intrinsic viscosity of the solution is then evaluated using the Stokes–Einstein equation, which relates diffusivity and viscosity [62]. Amini and Razavi [11] observed good linear extrapolations for both Huggins and Kraemer plots (R2 > 0.97) in the case of determination of the intrinsic viscosity of Balangu seed gum in different solvent/cosolutes and temperatures. The intrinsic viscosity of Balangu seed gum at 20 ∘ C in deionized water was observed to be 72.36 dl g−1 (Figure 2.3).

2.5 Intrinsic Viscosity

11 Huggins plot Kraemer plot

ηsp/c, Ln(ηrel)/c × 103 (ml/g)

10 9 8 7 6 5 0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Concentration ×10–4 (g/ml)

Figure 2.3 Typical dual Huggins–Kraemer plot of Balangu seed gum in deionized water at 20 ∘ C. Source: Adapted from Amini and Razavi [11] with permission from Elsevier.

Mirabolhassani et al. [14] reported that all the aforementioned models (Eqs. (2.12)– (2.16)) can be utilized for estimation of the intrinsic viscosity of basil seed gum at different temperatures and in the presence of different cosolutes; however, among them, the Higiro model showed the best fitting results (R2 > 0.98). They found that the intrinsic viscosity of basil seed gum solution in deionized water was 11.38 dl g−1 at 25 ∘ C. According to the results reported by Yousefi et al. [13], the obtained intrinsic viscosity from the models in which this value is calculated through the slopes of plots had a higher determination coefficient (R2 ) and lower root mean square error (RMSE) than the intrinsic viscosity obtained from the intercepts of plots. Similar results were reported by McMillan [60], Razavi et al. [59], and Behrouzian et al. [8]. Their results demonstrate that the Higiro model (Eq. (2.15)) is the most suitable model for determination of the intrinsic viscosity of sage seed gum, which had the highest R2 in the range 0.993–0.999 and the lowest RMSE in the range 0.002–0.041. Accordingly, the value of the intrinsic viscosity of sage seed gum in deionized water at 25 ∘ C was found to be 10.11 dl g−1 . Razavi et al. [59] reported that Tanglertpaibul and Rao’s model is the best model to estimate the intrinsic viscosity of sage seed gum at 20, 30, and 40 ∘ C, but in agreement with the results of Yousefi et al. [13], the Higiro model (Eq. (2.15)) is the best model to determine the intrinsic viscosity value of sage seed gum at different concentrations of NaCl and CaCl2 (0.5, 20, 50 mM). The results obtained by Irani et al. [63] showed that the Higiro model is the best among the models (Eqs. (2.12)–(2.16)) for intrinsic viscosity determination of both canary seed starch and wheat starch. They found that the intrinsic viscosity of canary seed varieties (C05041and CDC Maria) and wheat starches were 1.42, 1.46, and 1.70 dl g−1 , respectively. Lai and Chiang [7] used the Huggins model to determine the intrinsic viscosity of hsian-tsao leaf gum. The results obtained by Timilsena et al. [64] revealed that the intrinsic viscosity of chia seed gum can be precisely (R2 > 0.950) determined by extrapolating the experimental data to infinite dilution using the Huggins and Kraemer models at 20 ∘ C. The

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2 Dilute Solution Properties of Emerging Hydrocolloids

estimated intrinsic viscosity of chia seed gum in deionized water was in the range 16.34–16.63 dl g−1 . These models (Huggins and Kraemer) also have been reported to be suitable (R2 > 0.950) for determination of the intrinsic viscosity of A. homolocarpum seed gum [21]. Accordingly, the intrinsic value obtained for A. homolocarpum seed gum solution in deionized water at 25 ∘ C was 18.34 dl g−1 . For cress seed gum, it is found that the intrinsic viscosity attained by Tanglertpaibul and Rao model is the most accurate value (R2 = 0.995) in comparison with the other models. The intrinsic viscosity obtained for this hydrocolloid in deionized water at 25 ∘ C is about 3.92 dl g−1 [8]. Many studies on the dilute solution properties of hydrocolloids have underscored the fact that the intrinsic viscosity is highly sensitive to the solution temperature and concentration of the cosolutes. The intrinsic viscosity decreases with increasing temperature, possibly due to the increased kinetic energy and phase separation [13]. On the basis of thermodynamic principles, low temperatures are suitable for polymer–solvent interactions, which provide a negative enthalpy of polymer–solvent mixing. Phase separation takes place with increasing temperature because of the more unfavorable entropy contribution to the free entropy. Therefore, it can be concluded that the solvent quality decreases as the temperature increases [65]. By increasing the temperature from 25 to 65 ∘ C, the intrinsic viscosity of sage seed gum decreased from 10.11 to 2.96 dl g−1 . Similar results have been reported regarding the influence of temperature on the intrinsic viscosity of some conventional hydrocolloids such as pectin [25], dextran [66], L. sativum [18], chitosan [23], pullulan [47], gellan [67], hydroxypropyl cellulose [65], and hyaluronan [68]. In contrast, it has been shown that intrinsic viscosity of mesquite gum is not affected by ionic strength variation from 0.05 to 2.0 M [69]. Moreover, divalent cations (Mg2+ and Ca2+ ) had a more effective reduction in the intrinsic viscosity value of sage seed gum compared with the monovalent cations (Na+ and K+ ) when the salt concentration rose to 200 mM [13] (Figure 2.4). The intrinsic viscosity of Balangu seed gum decreased from 72.36 to 50.04 dl g−1 when the temperature was increased from 20 to 50 ∘ C. In disagreement with these results, Stivala and Bahary [70] found that the intrinsic viscosity of levan was increased as the 8 7 6 [η] (dl/g)

62

NaCI

5

KCI

4

MgCI2 3

CaCI2

2 1 0 0

2

4

6

8

10

12

I–0.5

Figure 2.4 Intrinsic viscosity of sage seed gum as a function of the inverse square root of ionic strength at 25 ∘ C. Source: Adapted from Yousefi, Razavi, and Khodabakhsh Aghdam [13] with permission from Elsevier.

2.5 Intrinsic Viscosity

temperature increased from 25 to 57 ∘ C. Also, it has been reported that temperature has little impact on alginate’s intrinsic viscosity [71]. Lai and Chiang [7] found that the intrinsic viscosity of hsian-tsao leaf gum is not affected by temperature, so that with increasing temperature from 20 to 40 ∘ C, the intrinsic viscosity only decreased from 2.93 to 2.37 dl g−1 . The hydrodynamic behavior (intrinsic viscosity) of hsian-tsao leaf gum was found to be strongly affected by ion types (Na+ , K+ , Ca2+ , and Mg2+ ) and ionic strength [7]. Although no research has been done on the influence of salts on the intrinsic viscosity of A. homolocarpum seed gum, it is observed that the apparent viscosity of this hydrocolloid decreases with addition of Na+ , K+ , Ca2+ ( lactose > sucrose. It was concluded that the ions are more effective than the sugars and/or temperature in decreasing the coil dimensions. Similar results were reported for dextran by Antoniou et al. [66]. According to the results obtained for basil seed gum by Mirabolhassani et al. [14], Rcoil was almost not influenced by a temperature increment, although at 65 ∘ C, this value decreased and contraction of basil seed gum coil was observed. They reported that this may be related to the increase in the instability of the hydrogen bonds between basil seed gum and water molecules and the relative increase in stability of intramolecular interactions among the polymer Vcoil =

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segments of basil seed gum [96]. In the case of canary seed starches, Heydari et al. [15] found that the starch obtained from CDC Maria variety had higher Rcoil (4.00 nm) and V coil (267.5 nm3 ) values rather than that of C05041. Overall, the Rcoil and V coil values of canary seed starches are rather smaller than those of several hydrocolloids such as sage seed gum (6.23 nm and 1012.35 nm3 ), Balangu seed gum (9.95 nm and 4121.3 nm3 ), and wheat starch (4.467 nm and 378.37 nm3 ). Also, by adding sugars and increasing their concentrations, the coil radius and coil volume were decreased significantly. The results of Hesarinejad et al. [21] revealed that the Rcoil of A. homolocarpum seed gum was reduced slightly as the temperature increased from 25 to 55 ∘ C; however, a small increase accompanied a subsequent increase in temperature to 65 ∘ C. In addition, in the case of the effect of cosolutes, it was found that as sucrose and lactose concentrations increase, the Rcoil of A. homolocarpum seed gum decreases. The V coil of A. homolocarpum seed gum decreased with an increase in the sugar concentration as well. The variations were more pronounced in the presence of sucrose rather than of lactose [102]. It is reported that salt concentration and salt type (mono or divalent) have a pronounced influence on the Rcoil and V coil values of sage seed gum macromolecules [13]. In divalent solutions and higher concentrations regardless of the salt type, these values reduce to a greater extent. The obtained Rcoil value for sage seed gum in 50 mM NaCl solution (4.96 nm) was similar to that for Balangu seed gum (4.60 nm), while it was different at the same concentration in CaCl2 solution (4.37 nm for SSG and 3.77 nm for Balangu seed gum) [11]. Antoniou et al. [66] found that the Rcoil value for dextran T500 in single and binary good + bad solvents at 20 ∘ C was between 13.7 and 19.7 nm, which was much higher than the obtained Rcoil value for sage seed gum.

2.10 Voluminosity and Shape Factor The voluminosity or swollen specific volume parameter (V E ) is a measure of the volume of a solvated polymer molecule, which could be obtained from the intercept of the plot of the Y value (as shown in Eq. (2.23)) versus C (concentration) [59]: Y =

0.5 𝜂rel −1 0.5 C(1.35𝜂rel − 0.1)

(2.23)

V E exhibits the conformation of a polymer in different solvent conditions. Eq. (2.24) reveals the relationship between V E and intrinsic viscosity through another parameter, which is known as the shape factor (𝜐v) or the viscosity increment: [𝜂] = 𝜐.VE

(2.24)

The shape of the polymer’s particles in a solution can be estimated through the shape factor. It is believed that the solvent association causes an anhydrous macromolecule to expand when suspended or dissolved in solution, so V E can be considered as a measure of the solvent associated with the macromolecule; or by definition, it is the volume of macromolecule in solution per its unit anhydrous mass. The viscosity increment (𝜐) is called the “universal shape function,” since unlike intrinsic viscosity, it can be directly related to the shape of a particle independent of its volume [56]. From experimental observations, the physical meaning of 𝜐 can be summarized as follows: (1) a value of 2.5

2.11 Hydration Parameter

for 𝜐 indicates a spherical shape, (2) a higher value is associated with an ellipsoidal shape, and (3) different values of 𝜐 suggest an oblate or prolate shape for a polymer coil [66]. For Balangu seed gum, with increasing temperature and in the presence of ions, the values of V E and 𝜐 decreased significantly. The results of the shape function suggested that the effective molecular shape of Balangu seed gum approaches a sphere-like configuration (𝜐 = 2.5) as the temperature increases, showing a greater contraction at higher temperatures. Similar results have been reported by Antoniou et al. [66] regarding the effect of temperature on the shape function of dextran. Also, in the case of sugars, an increase in the concentration of sucrose caused the V E and 𝜐 of Balangu seed gum to decrease; however, lactose did not follow a definite trend. Yousefi et al. [13] have stated that the shape factor of sage seed gum macromolecule at temperatures of 25–65 ∘ C is an oblate or prolate, whereas, in the presence of slats, the shape is found to be roughly ellipsoidal. They observed that with increasing temperature from 25 to 65 ∘ C, the shape factor value increased from 2.19 to 2.46, indicating the lesser flexibility of sage seed gum macromolecules at higher temperatures. In a poor solvent, the monomers of individual polymers effectively attract each other to minimize their contacts with the solvent molecules, so a roughly spherical or ellipsoidal shape forms which has less flexibility [103]. For basil seed gum, the values of V E and 𝜐 were not affected by temperature; however, a remarkable reduction was seen for the 𝜐 parameter at 65 ∘ C. The results obtained for the 𝜐 parameter indicated that the effective molecular shape of basil seed gum approaches a sphere-like configuration (𝜐 = 2.5) as the temperature increases, showing more contraction at higher temperatures. By increasing the sucrose or lactose concentration, the V E value of basil seed gum increased, whereas the 𝜐 value decreased [14]. In the case of canary seed starch, it is reported that by raising the temperature, the V E value declined, indicating that the coil dimension of canary seed starches and/or the solvent power decreased. Canary seed starches had a 𝜐 value of around 2.5 at 25 ∘ C, indicating that the shape factor of the samples at this temperature was spherical. With increasing temperature, the 𝜐 value increased, showing that the higher the temperatures, the less the flexibility of canary starches. In addition, at 25 ∘ C, the shape factor value of canary seed starches decreased slightly in the presence of sugars, although it did not obey a regular trend in some cases [15]. Hesarinejad et al. [21] have stated that V E and 𝜐 of A. homolocarpum seed gum diminish slightly up to 55 ∘ C. The results obtained for the shape function indicate that as the temperature increases, the influential molecular shape of A. homolocarpum seed gum approaches a sphere-like configuration, depicting more contraction at higher temperatures. In another study, Hesarinejad et al. [102] reported that the V E value of A. homolocarpum seed gum decreased with increasing sucrose and lactose concentration, which demonstrates the negative influence of these sugars on the volume of A. homolocarpum seed gum molecules. The value of 𝜐 in deionized water was less than 2.5, showing the spherical shape of the molecule, while this value was more than 2.5 in sucrose and lactose solutions, indicating that the molecules tended to be ellipsoidal in shape.

2.11 Hydration Parameter The associated solvent with the macromolecule in solution can be regarded as that which is either chemically attached through hydrogen bonds or physically absorbed by the

71

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macromolecule, and its extent could be represented by the hydration parameter (𝛿). This parameter is considered as the level to which aqueous solvent can be added to a dry macromolecule beyond which there is no change in a macromolecular property other than dilution of the sample. It is possible to assign a value for 𝛿 (dimensionless) from viscosity measurements by the following relation [56]: 𝛿 = 𝜌s (VE − ν)

(2.25)

where 𝜌s is the density (g dl−1 ), V E is the swollen specific volume or voluminosity (dl g−1 ), and υ is the partial specific volume (dl g−1 ). It was observed by Hesarinejad et al. [21] that the value of 𝛿 for A. homolocarpum seed gum decreases by increasing the temperature up to 55 ∘ C. The results obtained regarding the A. homolocarpum seed gum hydration parameter at 65 ∘ C suggest the plausible reduction in the associated solvent through hydrogen bonds and/or physical entrainment, leading to an enhancement in the intermolecular interactions (i.e., aggregation) between unsolvated chains. Similar results have been obtained for basil seed gum at 65 ∘ C [14]. The value of 𝛿 for Balangu seed gum was found to decrease with rising temperature and ionic strength, although the reduction in the 𝛿 parameter affected by ionic strength was more pronounced [14]. They reported that the 𝛿 parameter was not influenced by sucrose concentration, while this value decreased slightly with an increase in lactose concentration. In the case of canary seed starches, the 𝛿 value of CDC Maria variety was more influenced by lactose concentration rather than by sucrose concentration, while its value for the C05041 variety diminished further upon increasing the concentration of sucrose [15]. Sugars might compact the molecules by penetrating into the amorphous regions of the starch molecules and create bridges, thereby decreasing the hydration volume and as a result, reducing viscosity [104].

2.12 Conclusion and Future Trends In this chapter, the dilute solution properties of some emerging natural hydrocolloids under various conditions were investigated. Among the emerging natural hydrocolloids, the partial specific volumes of Balangu seed gum (0.61 ml g−1 ) and basil seed gum (0.62 ml g−1 ) were found to be greater than those of others which were almost close to the values reported for xanthan (0.60 ml g−1 ) and pectin (0.57 ml g−1 ). The hydrogel content of basil seed gum (73.6%) in deionized water was near to that of L. sativum seed gum (76%), and these values were greater than that of Balangu seed gum (46%). The hydrogel content of novel hydrocolloids was strongly affected by the type and concentration of cosolutes in the solutions. In the case of the molecular weight (Mw ), it was found that Balangu seed gum had higher Mw (3.65 × 106 g mol−1 ) than other emerging hydrocolloids and also many other common hydrocolloids as well. The intrinsic viscosity of emerging hydrocolloids can be classified into (1) hydrocolloids with high intrinsic viscosity value (Balangu seed gum), (2) hydrocolloids with medium value of intrinsic viscosity (A. homolocarpum seed gum, chia seed gum, basil seed gum, sage seed gum), and (3) hydrocolloids with low intrinsic viscosity value (canary seed starch, hsian-tsao leaf gum, cress seed gum), as compared with the intrinsic viscosity values reported for common hydrocolloids. The reported results clearly demonstrated that the intrinsic viscosity of emerging hydrocolloids is remarkably influenced by

References

the type and concentration of cosolutes such as salts and sugars in solutions and by temperature as well. The Berry number value reported for novel hydrocolloids in the dilute solution regime indicated that their molecular conformations were between the random coil and rod-like. The obtained values of the chain flexibility parameter (Ea /RT) and activation energy (Ea ) for sage seed gum were 3046.45 and 2.53 × 107 J kg−1 mol−1 , respectively, which were greater than those of other emerging hydrocolloids. The stiffness parameter (S) values of Balangu seed gum and sage seed gum were found to be almost similar, especially in the presence of monovalent cations, but were much lower than that of hsian-tsao leaf gum. The coil radius and volume of the emerging hydrocolloids were diminished in the presence of salts and sugars, and Balangu seed gum was found to have a greater Rcoil (9.95 nm) and V coil (4121.3 nm3 ) than others. The voluminosity and shape factor of novel hydrocolloids were influenced by temperature and the type of cosolutes in solutions. For Balangu seed gum and A. homolocarpum seed gum, the value of the hydration parameter (𝛿) was found to decrease with increasing temperature and ionic strength, but the reduction in the 𝛿 parameter affected by ionic strength was more pronounced. The various properties and characteristics of emerging natural hydrocolloids reported in this chapter show that they have good potential to be used as thickening, stabilizing, and gelling agents as compared with commercial ones. Although hydrocolloids have historically been used in food systems to control rheological properties and texture, consumers are being made increasingly aware of their nutritional benefits. Most of the emerging natural hydrocolloids investigated in this chapter have nutritional and pharmaceutical benefits. In addition, owing to safety, availability, low processing costs, and good functionality, it seems that emerging natural hydrocolloids have excellent potential for application as additives for various food, cosmetics, and pharmaceutical systems. Moreover, due to the distinctive characteristics, it is hoped that in many cases emerging natural hydrocolloids will be easily used as a substitute for common hydrocolloids.

References 1 Yousefi, A.R., Eivazlou, R., and Razavi, S.M.A. (2016). Steady shear flow behavior

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of sage seed gum affected by various salts and sugars: time-independent properties. International Journal of Biological Macromolecules 91: 1018–1024. Yousefi, A.R. and Razavi, S.M.A. (2016). Steady shear flow behavior and thixotropy of wheat starch gel: impact of chemical modification, concentration and saliva addition. Journal of Food Process Engineering 39: 31–43. Yousefi, A.R. and Razavi, S.M.A. (2015). Dynamic rheological properties of wheat starch gels as affected by chemical modification and concentration. Starch-Stärke 67: 567–576. Yousefi, A.R., Razavi, S.M.A., and Norouzy, A. (2015). In vitro gastrointestinal digestibility of native, hydroxypropylated and cross-linked wheat starches. Food & Function 6: 3126–3134. Yousefi, A.R. and Razavi, S.M.A. (2017). Modeling of glucose release from native and modified wheat starch gels during in vitro gastrointestinal digestion using artificial intelligence methods. International Journal of Biological Macromolecules 97: 752–760.

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6 Moosavi-Nasab, M. and Yousefi, A.R. (2011). Biotechnological production of cel-

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3 Steady Shear Rheological Properties of Emerging Hydrocolloids Fataneh Behrouzian and Seyed M.A. Razavi Food Hydrocolloids Research Center, Department of Food Science and Technology, Ferdowsi University of Mashhad, PO Box: 91775-1163, Mashhad, Iran

3.1 Introduction Application of new hydrocolloids is very limited, which may be attributed to the necessity for further investigation of their rheological properties. Today, there is a great interest in combining low cost with proper functionality and, especially, well-characterized natural hydrocolloids. To meet the demand for these ingredients, significant efforts have been devoted to find new structure-functionality relationships [1]. Rheology of materials may be described as the study of their deformation and flow when exposed to a stress or strain. The flow properties of a fluid can be defined using the relationship between shear stress (𝜏) and shear rate (𝛾) ̇ in a steady shear laminar flow [2]. Rheological experiments measure properties that can be related to structural elements in materials. Understanding of flow behavior is essential for optimizing product development, processing conditions, and product quality [3]. The rheological behavior of hydrocolloids can be significantly affected by variables such as shear rate, shear history, and time of shearing [4]. Under flow conditions, the network of hydrocolloids is disrupted into smaller structures or aggregates, and structural viscosity is the major characteristic reflecting its rheological behavior [5]. Some hydrocolloids have found their place in the market and have been used in many food formulations. The choice of hydrocolloids in food systems is based on their functions, which are determined by their molecular characteristics (e.g., molecular weight, conformation, flexibility, polarity, hydrophobicity, and interactions) and are associated with their rheological behaviors. So, introducing the novel hydrocolloids and their similarity to the generally used hydrocolloids on the basis of some specific rheological properties could be beneficial to rationally designed structural features in food systems. Clustering is a part of pattern recognition theory, which aims to summarize information by grouping data in categories or classes. The members are as similar as possible in each class, while being as different as possible from other class members. The hierarchical clustering algorithm is one of the clustering techniques and is classified into agglomerative hierarchical and divisive hierarchical methods [6]. Agglomerative hierarchical clustering is suitable for representing the original data set in the feature space at Emerging Natural Hydrocolloids: Rheology and Functions, First Edition. Edited by Seyed M.A. Razavi. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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multiple levels of abstraction since each clustering level results in an abstract representation of the original data set [6]. Clustering has been successfully applied in different fields of the food industry [6–8]. Guar gum (GG), pectin (PE), and xanthan gum (XG) are three frequently used hydrocolloids in food systems. GG, which is obtained from guar (Cyamopsis tetragonoloba) seeds, contains linear chains of d-mannopyranosyl units with a d-galactopyranose substituent protruding by (1 → 6) linkages. It has the specific structure of galactomannans with 1.3 × 103 kDa molecular weight and 12.5 dl g−1 intrinsic viscosity [9]. XG, with 4.05 × 103 kDa molecular weight, is an extracellular polysaccharide extracted from Xanthomonas campestris. This gum consists of a cellulose backbone attached with a charged trisaccharide side chain composed of a glucuronic acid residue between two mannose residues [10]. Using the Tanglertpaibul and Rao equation, Higiro et al. [10] reported 214.21 dl g−1 intrinsic viscosity for XG. PE with a heteropolysaccharides structure originates in most plant tissues. It consists of α-(1–4)-d-galacturonic acid units, interrupted by the insertion of rhamnose units and with side chains of neutral sugars attached to the backbone. Natural PEs are usually highly methoxylated (HM) with more than 50% of the esterified carboxyl groups. The intrinsic viscosity of HM PE was reported as 15 dl g−1 [11]. Many studies reported a slightly stiff conformation for the PE macromolecules [12]. The literature has established the high potential of sage seed gum (SSG) and cress seed gum (CSG) as emerging hydrocolloids to be used in food formulations. Sage seed (Salvia macrosiphon) swells in water and produces mucilage. The weight-average molecular weight of SSG polysaccharides ranges from 4 × 102 to 1.5 × 103 kDa [13, 14]. It is a polyelectrolyte galactomannan hydrocolloid (1.78–1.93:1 mannose/galactose ratio and 28.2%–32.2% uronic acids) with 22.55 dl g−1 intrinsic viscosity [14]. CSG exists in the outer layer of the garden cress plant seed (Lepidium sativum L.). The macromolecular component has a molecular weight of 540 kDa and possesses a semi-rigid chain conformation [15]. This polyelectrolyte galactomannan (8.2 mannose/galactose ratio and 15% uronic acids and 13.3 dl g−1 intrinsic viscosity) has been introduced as novel thickening, gelling, and emulsifying agent [16–19]. In this chapter, initially, flow patterns were evaluated for all gum dispersions. Then, the power-law and Moore models were applied to understand the flow properties of SSG and CSG and compare them with three commercially used food biopolymers of XG, PE, and GG. To illustrate how structure and flow properties are related with time, we applied four procedures: hysteresis loop, shear stress decay, in-shear structural recovery, and the time dependency of steady shear properties measurements. Two types of yield stress, which are related to the two types of structure in a thixotropic fluid, that is, static and dynamic yield stresses (DYSs), were determined and discussed. Besides, the range of short and long time scales yields stresses, and the corresponding time intervals were compared among different gum systems. Finally, to categorize all hydrocolloids, the similarity of the rheological properties of gums was investigated using the hierarchical clustering technique and principal component analysis (PCA) in a serial mode. These comprehensive steady shear rheological measurements of SSG and CSG, and their comparison with commercialized food hydrocolloids, help us to better decide on the final usage of the former hydrocolloids. Despite much progress on SSG and CSG, as hydrocolloids are still limited to only several types, it is necessary to achieve a more complete understanding of their rheological properties to meet the food industry demands.

3.2 Time-Independent Rheological Properties

3.2 Time-Independent Rheological Properties The steady shear flow behavior of selected gum dispersions (1%) was evaluated at constant temperature (20 ∘ C) using a Physica MCR 301 rheometer (Anton Paar, GmbH, Graz, Austria) equipped with cone-plate geometry (4∘ cone angle, 50 mm of diameter, and 1 mm gap). The shear stress was measured at a logarithmically increasing scale of shear rate from 0.01 to 700 s−1 . Also, the apparent viscosity at a given shear rate was calculated as the ratio of the shear stress to the shear rate [20]. Except GG, other gum dispersions exhibited a three-stage apparent viscosity versus shear rate response when sheared over a wide shear rate range. According to Table 3.1, shear-thinning behavior was observed for all tested dispersions. This behavior has been reported for many hydrocolloid solutions, due to the formation of a dispersion of aggregated polymers and their high molecular weight [21]. At lower shear rates, the apparent viscosity exhibits a Newtonian plateau, and except for GG, with a further decrease in the shear rate, the shear-thickening region appeared. The length of each region was quite different for all gum dispersions. XG showed the highest length of the shear-thickening region among all gum dispersions. It is well known that the thickening behavior could be the result of a stiffer inner structure due to the formation of entanglements of polymer coils and the increase in intermolecular interactions with an increase in the shear rate [22]. Liu et al. [23] stated that “flow-induced formation of macromolecular associations” were the mechanism for the shear-thickening behavior. On the other hand, GG showed the highest length of the Newtonian region among all gum dispersions, from 0.01 to 1.268 s−1 . In the low-shear Newtonian stage, there is little rearrangement of the polymer chains and replacement of disrupted entanglements by new entanglements, whereas in the shear-thinning stage, the chains undergo continuing rearrangement with an increase in the shear rate, which is caused by the disentanglement of the polymer coils in solution or alignment of the polymer coils in the flow direction [24]. Shear thinning begins when the rate of disentanglement becomes greater than the rate of their reformation, and consequently the viscosity is reduced [25]. The critical shear rate (𝛾̇ c , the shear rate at which the shear stress starts to decrease with an increase in the shear rate) of gum dispersions was on the order of GG > CSG > XG > Pe > SSG (Table 3.1). It has been accepted that when a small-particle-sized dispersion encounters shearing, the effect of Brownian motion lasts longer along the shear rate axis, and higher values of shear rate are required to initiate the shear-thinning stage [26]. In the shear-thinning region, the effect of the shear rate ranges on the decreasing order and decreasing ratio of the apparent viscosity for different gum dispersions was investigated, and the results are illustrated in Figures 3.1 and 3.2, respectively. It can be seen that, except for GG, the highest extent of viscosity reduction for all gum dispersions occurred at 0.01–0.1 s−1 . At this range, PE with 81.07% and 6.19 times viscosity reduction showed the highest shear-thinning behavior. More than 94% of the total shear-thinning behavior of SSG, XG, and PE was occurred in the range 0.01–1 s−1 , while this value was 44.75% for GG and 81.73% for CSG. GG showed almost uniform viscosity reduction at all shear rate ranges, suggesting it has the least shear-thinning behavior among other gums. In the largest shear rate range (0.01–700 s−1 ), SSG, XG, and PE showed a higher ratio of apparent viscosity reduction in comparison with CSG and GG. Above the critical shear rate, shear stress-shear rate data were fitted using a well-known power-law model, Eq. (3.1) [20]. Also, the Moore model was selected to fit

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Table 3.1 Three different shear rate ranges observed in the steady shear flow behavior of sage seed gum (SSG), cress seed gum (CSG), xanthan gum (XG), pectin (PE), and guar gum (GG) (1%, 20 ∘ C, and 0.1–700 s−1 ).

Gum

Shear thickening (s−1 )

Newtonian (s−1 )

Shear thinning (s−1 )

Critical shear strain (s−1 )

XG

0.010–0.025

0.025–0.030

0.030–700

0.030

GG

—

0.010–1.268

1.268–700

1.268

PE

0.010–0.013

0.013–0.020

0.020–700

0.020

SSG

0.010–0.013

0.013–0.017

0.017–700

0.017

CSG

0.010–0.019

0.019–0.070

0.070–700

0.070

Decreasing order of shear viscosity

84

0.01–0.1 (s–1)

0.1–1 (s–1)

XG

GG

1–10 (s–1)

10–100 (s–1)

100–700 (s–1)

100

10

1

0.1 Pe

SSG

CSG

Figure 3.1 Effect of shear rate range on the decreasing order of shear viscosity of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG) (1%, 20 ∘ C, and 0.1–700 s−1 ).

the apparent viscosity-shear rate data, Eq. (3.2) [24]: τ = kP (𝛾) ̇ nP

(3.1)

where 𝜏 is the shear stress (Pa), 𝛾̇ is the shear rate (s ), kP is the power-law consistency coefficient (Pa sn ), and np is the power-law flow behavior index (dimensionless) 𝜂 − 𝜂∞M (3.2) 𝜂 = 𝜂∞M + 0M 1 + (𝜆 × 𝛾) ̇ −1

where 𝜆 is the Moore relaxation time (s), 𝜂 0M is the limiting zero-shear viscosity (Pa s), and 𝜂 ∞M is the limiting infinite-shear viscosity (Pa s). The magnitudes of parameters that obtained from the Moore model (𝜂 0M , 𝜂 ∞M , and 𝜆) are shown in Table 3.2, and the kP , nP trends are depicted in Figure 3.3. Power-law and Moore models adequately fitted the shear stress versus shear rate and shear viscosity versus shear rate data for each hydrocolloid, respectively (R2 = 0.85–0.93 and RMSE = 0.05–0.18). As seen in Figure 3.3, the flow behavior index of all samples ranged between 0.124 and 0.382, confirming a strong shear-thinning behavior of the selected gums. As compared to other hydrocolloids, XG and PE with the lowest flow behavior indexes showed the

3.2 Time-Independent Rheological Properties

Table 3.2 The rheological parameters of the Moore model determined for sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG) (1%, 20 ∘ C, and 0.1–700 s−1 ). Moore model Gum

𝜼0M (Pa s)

𝜼∞M (Pa s)

𝝀 (s)

XG

962.46a ± 17.73

0.07c ± 0.01

53.46a ± 12.23

d

18.83 ± 0.51

GG

bc

0.76c ± 0.12

a

0.36 ± 0.06

b

PE

439.57 ± 96.49

1.41 ± 0.77

65.29a ± 4.09

SSG

116.91c ± 28.59

0.42b ± 0.23

73.88a ± 27.92

d

c

16.90 ± 0.99

CSG

14.81b ± 2.94

0.07 ± 0.05

Decreasing ratio of apparent viscosity

a–d: Means followed by the same letters in the same column are not significantly different (P > 0.05).

XG

10000

GG

PE

SSG

CSG

1000

100

10

1

0.01–0.1

0.01–1

0.01–10 Shear rate range

0.01–100

0.01–700

Figure 3.2 Effect of shear rate range on the decreasing ratio of shear viscosity of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG) (1%, 20 ∘ C, and 0.1–700 s−1 ).

highest shear-thinning behavior, whereas CSG and GG showed the highest nP values. This result confirmed that XG and PE were mostly affected by the shear rate, and SSG showed the most pronounced pseudoplasticity compared to other galactomannans (GG and CSG). The noticeably strong shear-thinning behavior of SSG compared with GG and CSG might be attributed to the enhanced macromolecular entanglement due to the relatively rigid chain conformation of SSG [14], while GG showed a random coil conformation [27] and CSG demonstrated a semi-rigid structure [16]. The shear thinning in the steady shear test, under a large deformation, can occur when rod-like particles align in the flow direction and lose their junctions in polymer solutions, which results in the breakdown of polymers agglomerates [25]. More shear-thinning behavior leads to easier pumping and desirable texture and mouth feel [28]. PE with the highest kP value demonstrated the highest viscosity and strength of the network structure, whereas CSG showed the lowest consistency coefficient value. The Moore model was employed in this study because all the experimental data depicted zero-shear viscosity and infinite-shear viscosity. CSG and GG showed the lowest limiting zero-shear viscosity, while XG showed the highest value of this parameter

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3 Steady Shear Rheological Properties of Emerging Hydrocolloids

K (Pa.sn)

K′ (Pa.sn)

n

n′ 1

n & n′

100

K & K′ (Pa.sn)

86

10

1

XG

GG

PE

SSG

CSG

0.1

Figure 3.3 Power-law flow behavior parameters of presheared (k and n) and unpresheared (k′ and n′ ) samples of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG) (1%, 20 ∘ C, and 0.1–700 s−1 ).

(Table 3.2). The magnitude of the zero-shear viscosity indicates the microstructural behavior of the biopolymer during storage [14]. A higher 𝜂 0M value reveals a greater number of linkages among macromolecules [14]. The greater 𝜂 0M of SSG compared to GG may be attributed to its polyelectrolyte nature, in which the coil dimensions may be expanded by long-range electrostatic repulsions, resulting in a higher zero-shear viscosity. The higher molecular weight of SSG might be another reason for the higher 𝜂 0M value of SSG compared to CSG as a polyelectrolyte hydrocolloid. Once a food system completes processing, the material should either stop flowing or flow sufficiently slowly under the low stresses that the product might still be subjected to such as gravity. In some cases, the high zero-shear viscosity serves to prevent sedimentation of heavier particles or droplets throughout storage [29]. According to Table 3.2, XG and CSG showed the lowest 𝜂 ∞M values among all, whereas PE exhibited the highest (1.41 Pa s) limiting infinite-shear viscosity. This parameter is a measure of the consistency of the materials during processing such as pumping, mixing, and spraying and conveys the energy required for processing [14]. In nearly all applications of food suspensions, a relatively low viscosity is essential at high shear rates in order to process or apply the product properly and/or easily [29]. Except for GG, with the lowest time constant of the Moore model (0.76 s) followed by CSG (14.81 s), other gum dispersions did not show significant differences in relaxation time (Table 3.2). A higher 𝜆 value produces a faster breakdown of the structure and/or of agglomerates due to the lower opposition to flow because of the higher development of an ordered structure, so could be associated with the formation of greater intermolecular aggregates [14]. These results indicated that the mean lifetime of the junction zones in SSG, XG, and PE entanglements might be higher than those of GG and CSG, the consequence being an increase in the time required for new entanglements to replace those disrupted by an externally imposed deformation [24].

3.3 Time-Dependent Rheological Properties

The intrinsic viscosities of CSG and GG are almost the same and are far smaller than those of the three other gum dispersions, which could explain the closeness and the lowest magnitude of 𝜂 0M and 𝜆 of these two galactomannans. XG with the highest intrinsic viscosity among other gum samples resulted in the lowest flexibility and hence a more expanded coil geometry, which in turn produced higher zero-shear viscosity and 𝜆 values.

3.3 Time-Dependent Rheological Properties Up to now, a variety of methods have been utilized to demonstrate the existence of associations between polymer chains, including static and dynamic light scattering, fluorescence spectroscopy, and thixotropic measurements [30]. The characterization of the time-dependent rheological properties (thixotropy and rheopexy) of food products is important in both providing information on how structure and flow properties are related with time and how physical parameters correlate with sensory properties during storage [28]. The time-dependent behavior of the rheological parameters is associated with the changes occurring in the inner structure of the fluid due to particle interaction forces, which result in the formation of aggregates [22]. Various methods are available to quantify thixotropic behavior such as hysteresis loop, shear stress decay, and in-shear structural recovery measurements [15, 31]. In addition, a comparison of the steady shear flow parameters of presheared (time-independent) and unpresheared (time-dependent) samples could provide additional insight into thixotropic behavior. Thixotropic properties provide a range of desirable characteristics appropriate for products such as dairy desserts, salad dressing, and mayonnaise [31]. In the food industry, the products which flow during processing but stiffen afterward are very important. [29]. 3.3.1

Hysteresis Loop

The hysteresis loop experiment consists of an alternately increasing and decreasing shear stress which involves the determination of the area enclosed between the up and down curves. The hysteresis loop area is the difference between the energy required for structural breakdown and buildup, which is regarded as an estimate of the degree of thixotropy [22]. Strongly thixotropic suspensions should exhibit large hysteresis areas since the kinetic process of breakdown or buildup is time consuming, and measured viscosities are further from the steady state [5]. The experimental protocol for this test consisted of a three-step operation: An increasing shear rate ramp from 0.01 to 700 s−1 (upward flow curve), followed by a plateau of 700 s−1 for 60 s (peak hold), and thereafter the ramp was reversed to 0.01 s−1 . The percentage of relative hysteresis area was calculated as follows: (Aup − Adown ) Hystersis(%) = × 100 (3.3) (Aup ) where Aup is the area under the upstream data points, and Adown is the area under the downstream data points. In addition, viscous flow behavior data in the forward and backward curves were described by power-law model, Eq. (3.1) [20].

87

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Table 3.3 Viscous flow behavior parameters in forward and backward curves and hysteresis area of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG) (1%, 20 ∘ C, and 0.1–700 s−1 ). Forward

Backward ′′

nP ′′

Hysteresis (%)

12.26a B ± 0.36

0.36c B ± 0.02

3.82a ± 0.06

1.23d A ± 0.10

0.49b A ± 0.02

1.68c ± 0.02

Gum

kP

nP

kP

XG

17.19a A ± 0.78

0.13d A ± 0.01

GG

1.34d A ± 0.17

0.49b A ± 0.02

PE

A

14.16b ± 0.85

0.15d ± 0.01

7.53b ± 0.66

0.35c ± 0.01

1.98b ± 0.05

SSG

6.41c A ± 0.38

0.28c A ± 0.02

4.99c B ± 0.23

0.58a B ± 0.01

3.75a ± 0.03

CSG

0.24e A ± 0.04

0.57a A ± 0.03

0.19e A ± 0.01

0.6a A ± 0.01

1.25d ± 0.01

A

B

B

a–d: Means followed by the same lowercase letters in the same column are not significantly different (P > 0.05). A–B: kP and kP′′ or nP and nP′′ followed by the same uppercase letters in the same row are not significantly different (P > 0.05).

The upward and downward flow curves are superimposed for a time-independent sample, whereas they are not the same in the case of a time-dependent liquid [22]. According to Table 3.3, the hysteresis area appeared for all gum dispersions, indicating that the rate of the disentanglement of the macromolecules by shearing was higher than that of re-entanglement [22]. The highest area was determined for XG (3.82%) and SSG (3.75%), and the lowest area for CSG (1.25%), indicating more sensitivity to shear history and the stronger thixotropic properties of the former gums. It is noteworthy that the hysteresis area represents both reversible and irreversible changes in the samples’ microstructure [29]. In the ascending curves, the kP parameter was higher and the np parameter was lower than those in descending curves (kP ′′ and nP ′′ ) for SSG, XG, and PE, whereas there were no significant differences between these parameters in the two curves for GG and CSG, suggesting that the structure responsible for thixotropy was destroyed through the forward test for the former gums group. The highest consistency coefficient and the lowest flow behavior index in both forward and backward curves were obtained for XG, whereas CSG showed the lowest kP and kP ′′ and the highest nP and nP ′′ among other dispersions. These results suggested that XG has the strongest structure among the other dispersions. It is noteworthy that the shear rate and time of shearing are coupled in this experiment, which makes the test less suitable for separating the effect of these two parameters; besides, the hysteresis area does not generally reflect the state of the internal structure [5, 29]. 3.3.2

Single Shear Stress Decay

The transient rheological approach can be combined with a structural kinetics model to analyze the thixotropic behavior of a dispersion. The structural parameter in this experiment represents the fraction of the unbroken network links in a solution, so the thixotropy of a polymer solution is considered as the breakdown of the network links formed by associations between polymer chains under shear [30]. In contrast with the hysteresis loop test, single shear stress decay enables us to study the effect of time alone.

3.3 Time-Dependent Rheological Properties

In this experiment, samples were sheared at a constant shear rate (50 s−1 ), and the shear stress (𝜏, Pa) was recorded as a function of the shearing time (t, min) until the shear stress reached steady state. The transient viscosity profile is fitted by a structural kinetics model as follows [32]: ] [ 𝜂 − 𝜂∞ 1−n = (n − 1) × kt + 1 (3.4) 𝜂0 − 𝜂∞ where 𝜂 0 (Pa s) is the initial apparent viscosity at t = 0 (structured state), and 𝜂 ∞ (Pa s) is the steady-state apparent viscosity at t → ∞ (non-structured state). n and k are the orders of the structural breakdown reaction and the breakdown rate constant, respectively. This model attempts to elucidate the complicated phenomena occurring during the internal structure’s breakdown and buildup by formulating equations of state, called the constitutive equations, and kinetic equations, which consider the time dependence of viscosity under constant shear rate conditions [5]. In this chapter, the second order (n = 2) was used to describe the structural breakdown kinetic of samples. For all gum dispersions, this model adequately fitted the transient apparent viscosity data (R2 = 0.89–93 and RMSE = 0.05–0.12). The structural kinetic model parameters of all gum dispersions are shown in Figure 3.4. The rate of time dependency (k parameter) was the highest for XG (2.847 s−1 ) and the lowest for CSG (0.135 s−1 ) and GG (0.161 s−1 ), while other gums showed the intermediate magnitudes. This behavior may be due to the highest static yield stress (SYS) of XG, which is discussed in Section 3.4.1. In thixotropic fluids, the yield stress is a function of structure and therefore of time [28]. In addition, it may be attributed to the greater strength of the XG structure and confirms that the timescale of segment–segment interaction in CSG and GG chains is shorter than the lifetime of physical entanglements of XG, PE, and SSG, which leads to a higher rate of thixotropic breakdown of the cross-linked gum structure for the latter gums. The larger amount of thixotropy of SSG compared to that of CSG may be due to the higher SYS of SSG (Section 3.4.1), related to the greater rigidity with more entanglement of SSG. Both initial and steady-state apparent viscosities were the highest for PE and the lowest for CSG among gum dispersions. As compared to other hydrocolloids, 𝜂 0 /𝜂 ∞ (a relative measure of the amount of structure breakdown, or in other words, a relative measure of the extent η0 (Pa.s)

ηinf (Pa.s)

Rate of decay (s–1) 10.000

1.000 1.000 0.100

0.010

XG

GG

PE

SSG

CSG

0.100

Figure 3.4 Structural kinetic model parameters of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG).

Rate of decay(s–1)

η0 & ηinf (Pa.s)

10.000

89

90

3 Steady Shear Rheological Properties of Emerging Hydrocolloids

of thixotropy) were the highest for SSG (2.250) followed by XG (2.165) and PE (1.889) and the lowest for GG (1.191) and CSG (1.185) (data not shown). 3.3.3

In-Shear Structural Recovery Measurements

In-shear structural recovery measurement concerns the time-dependent behavior of material in storage periods after large deformation. In-shear structural recovery of the samples is determined based on the Mezger procedure [33]. The samples are subjected to a three-step shear flow test as follows: (1) a constant shear rate of 1 s−1 for 120 s (with pre-shear at 1 s−1 for 30 s), (2) a constant shear rate of 300 s−1 for 60 s, and (3) a constant shear rate of 1 s−1 for 120 s. The percentage ratio of the average apparent viscosity during the first 120 s in step 3 to the average apparent viscosity in step 1 is termed the extent of recovery (Rr , %). Moreover, to provide more structural features from the time-dependent behavior of samples; we employed a four-parameter model (Eq. (3.5)), which was fitted on the shear stress (𝜏) data of step 3 versus time (t) as follows [34]: 1

𝜏(t) = 𝜏∞ − ((𝜏0 − 𝜏∞ ) × [(p − 1) × 𝛼r × t + 1)] (1−p)

(3.5)

where 𝜏 0 (Pa) indicates the instantaneous recovered structure, and 𝜏 ∞ (Pa) indicates the structural stability of the recovered material. p and 𝛼 r are the orders of the structure recovery reaction and the recovery rate constant, respectively. The recovery reaction order (p) was the same for all gum dispersions equal to two. In thixotropic materials, physical change can cause irreversible changes including rupture or strong aggregation of particles [29]. The recovery parameter (Rr , %), which is a general indicator of the recovered structure after high shear exposure, did not show any significant differences between three commercial hydrocolloids, while it was lower for SSG, specially for CSG (Table 3.4). This reversibility is related to particle rearrangements or to the slow microstructure rebuilding at rest. When a gel slowly develops its structure, the particulate structure becomes gradually more rigid in time, resulting in slower reversible or irreversible changes in the microstructure. Sometimes a fast thixotropic recovery is advantageous, and sometimes a slow thixotropic recovery is required during the low-shear period following application at high shear rates, for example, wet Table 3.4 Extent of recovery parameter (Rr ) and the exponential four-parameter model parameters (𝜏 0 (instantaneous recovered structure), 𝜏 ∞ (the structural stability of recovered material), and 𝛼 r (the recovery rate constant)) of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG). Four-parameter model parameters Gum

𝝉 0 (Pa)

𝝉 ∞ (Pa)

𝜶 r (s−1 )

Rr (%)

XG

9.999b ± 0.272

16.453a ± 0.015

0.198b ± 0.009

0.886a

GG

5.341d ± 0.339

6.291c ± 0.022

0.016d ± 0.001

0.889a

PE

a

a

SSG CSG

12.197 ± 0.065 c

6.064 ± 0.389 e

0.133 ± 0.008

15.590 ± 0.030 b

9.597 ± 0.235 d

0.262 ± 0.002

a

0.861a

c

0.625b

d

0.453c

0.261 ± 0.031 0.099 ± 0.002 0.029 ± 0.003

a–d: Means followed by the same letters in the same column are not significantly different (P > 0.05).

3.3 Time-Dependent Rheological Properties

paint film on a vertical wall [29]. The values of 𝜏 0 , 𝜏 ∞ , and 𝛼 r of all gum dispersions are summarized in Table 3.4. Thixotropic materials can display elastic effects [29]. The highest value of the instantaneous recovered stress (𝜏 0 ), which indicates the extent of the elastic component of samples in high deformation, was obtained for PE followed by XG. The highest value of stress at the equilibrium plateau (𝜏 ∞ ), which shows the restructuring behavior of samples after recovery of the structure, was obtained for PE and XG. CSG exhibited the lowest value of both these parameters. The highest recovery rate (𝛼 r ) value was obtained for PE (0.261 s−1 ) followed by XG (0.198 s−1 ). Mao and Chen [30] studied the thixotropic behavior of galactomannans and stated that the interchain association occurs in the unsubstituted regions of the mannan backbone of the polymer chains. They reported that galactomannans with a higher mannose-to-galactose (M:G) ratio had a stronger tendency to form associations, whereas galactomannans with a lower M:G ratio were free of chain associations in solutions. The M:G of CSG, GG, and SSG was reported as 4:1 [15], 1.59:1 [30], and 1.78–1.93:1 [14], respectively, which contradicted the results of Mao and Chen [30]. It seems that some other more important structural features exist in SSG, resulting in the greater structural strength. 3.3.4

Time Dependency of Steady Shear Properties

As in the steady shear rheological experiments, the time and shear responses of materials are recorded, simultaneously; the obtained parameters are not an indicator of only the shear effect. No framework has been introduced so far to compare the time-dependent and time-independent flow behavior power-law model parameters. Therefore, it is essential to find a test to accurately determine the time effects on the steady shear rheological properties of materials. To get a general idea of the time dependency of steady shear parameters, we used the following procedure. One batch of sample was divided into two samples to avoid the error of sampling. One of them was sheared without pre-shearing in the range 0.01–700 s−1 . The other sample was first presheared for 15 min at 100 s−1 (to remove any time dependency), and then sheared in the range 0.01–700 s−1 . At the end, the rheological data were analyzed, and the ratio of the power-law model parameters for samples without pre-shearing to the presheared samples was evaluated. As shown in Figure 3.3, the flow behavior indexes of all unpresheared gum dispersions were lower than those of their presheared counterparts. The value of n-n′ subtraction was the highest for XG followed by PE, whereas it was lowest for CSG, which suggested that the share of time dependency in the steady shear flow behavior parameters of unsheared XG and PE was far greater than that of the galactomannans. An almost similar trend was observed for the consistency coefficient of presheared and unpresheared samples, which showed the lowest differences between k and k′ for CSG followed by GG. As for the flow behavior index of gums, these differences are attributed to the share of time dependency in the consistency coefficient magnitudes of each gum. The complex rheological behavior of thixotropic materials can be understood on the basis of their microstructure [29]. In a polymer solution, the microstructure can mean alignment of fibers, entanglement density, or molecular association, and the maximum microstructure is seen when the alignment and spatial distribution are random and the entanglement density is higher [25]. Samples with higher thixotropic characteristics lost their hydrogel network after

91

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pre-shearing, so they exhibited lower shear-thinning behavior, which was more obvious than what occurred on the less thixotropic hydrocolloid dispersions.

3.4 Yield Stress The yield stress is generally defined as the transition stress at which materials behave in an elastic solid-like or viscous liquid-like manner [35]. The yield stress can be utilized in different food products to prevent the sedimentation of dispersed particles in beverages [36]. Although the yield stress has practical importance for engineering, the absolute yield stress is an elusive property [20]. Two types of yield stresses, related to two types of structure, are the SYS (associated with a structure that is sensitive to the shear rate and forms over a certain period of time when the sample is at rest) and the DYS (insensitive to the shear rate and related to the amount of stress needed to maintain/stop the flow of a test material) [35]. Here, the SYS was obtained by applying a linear shear stress ramp (0.1–15 Pa) to the samples (𝜏 0SR ), and the DYS was determined by the extrapolation of stress in the limit 𝛾̇ → 0 with the Bingham (𝜏 0B ), Vocadlo (𝜏 0V ), Casson (𝜏 0C ), Herschel–Bulkley (𝜏 0H − B ), and Moore (𝜏 0M ) models. An alternative procedure to determine the DYS is the extrapolation of the reverse of the apparent viscosity versus shear stress curve to the infinite apparent viscosity, 𝜏 0E [36]. 3.4.1

Static Yield Stress

To determine the SYS, the stress was ramped linearly from 0.1 to 15 Pa over 120 s. The viscosity–stress curve was drawn, and the stress at the peak of the viscosity curve was presented as the yield stress [37]. The yield stress achieved from the stress ramp was the highest for PE (8.52 Pa) followed by XG (6.38 Pa) and the lowest for GG (0.14 Pa) (Table 3.5). Other gum dispersions showed intermediate values. Tipvarakarnkoon and Senge [38] reported that XG is able to form intermolecular associations in solutions, so the formation of a complex network of weakly bound molecules resulted in the yield stress phenomena; however, in GG, yield stress is not observed. The network created by GG had a higher consistency than that created by SSG (Figure 3.3) but upon application of a proportional shear stress, the network broke suddenly, the particles lost their inter-particle connections, and the product acquired the characteristics of a fluid material more than the latter gum. For all gum dispersions, the structure insensitive to shear rate was higher than the sensitive structure. Some researchers also reported a lower 𝜏 0SR than those calculated by the rheological models [37, 39]. Some of the applications of the SYS in foods are controlling the thickness of the coating layer (chocolate on ice cream, glazing on cakes), settling of particles in dispersions (spices in salad dressing, chocolate in chocolate milk), spreadability (cream cheese, mayonnaise), and mouthfeel (creaminess of yoghurt) [40]. 3.4.2

Dynamic Yield Stress

As shown in Table 3.5, the intercepts of the various rheological models differed among dispersions; whereas CSG showed the lowest yield stress estimated by all models, XG and PE showed the greatest yield stresses values. It is known that the intercept point is

Table 3.5 Static yield stress (SYS (stress ramp, 𝝉 0SR )) and dynamic yield stress (DYS (Bingham (𝝉 0B ), Casson (𝝉 0C ), and Moore models (𝝉 0M ), and stress-viscosity extrapolation (𝝉 0E ))) of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG). SYS

DYS

Gum

𝝉 0SR (Pa)

𝝉 0E (Pa)

𝝉 0H − B (Pa)

𝝉 0V (Pa)

𝝉 0B (Pa)

𝝉 0C (Pa)

𝝉 0M (Pa)

XG

6.38b ± 0.42

17.27a ± 1.75

–

13.84a ± 1.85

17.97b ± 1.87

14.81a ± 1.80

18.62b ± 4.09

GG

0.14e ± 0.01

5.49 b ± 0.55

–

–

3.01d ± 0.67

4.20c ± 0.07

1.64c ± 0.25

PE

8.52a ± 0.28

14.48a ± 2.45

4.25a ± 1.40

7.86b ± 0.59

20.86a ± 4.49

11.91a ± 2.21

26.31a ± 2.47

SSG

3.67c ± 0.15

7.66b ± 0.32

1.23b ± 0.16

–

15.58c ± 1.02

7.92b ± 0.44

17.78b ± 0.84

CSG

0.43d ± 0.02

0.13c ± 0.04

0.31c ± 0.06

0.43c ± 0.08

0.68e ± 0.16

0.33d ± 0.05

0.91c ± 0.06

a–d: Means followed by the same letters in the same column are not significantly different (P > 0.05).

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3 Steady Shear Rheological Properties of Emerging Hydrocolloids

dependent on the range of the shear rate and the model employed for extrapolating the data [37]. The yield stresses obtained by extrapolating the reverse of the apparent viscosity versus shear stress curve to the infinite apparent viscosity for two novel hydrocolloids were lower than for the commercial ones. The Herschel–Bulkley model was not able to determine the yield stress of XG and GG, the Vocadlo model was not able to determine the yield stress of GG and SSG, and the yield stresses of the Heinz and Heinz–Casson models were negative for all gum dispersions, confirming the inappropriateness of these models. The main usage of DYS in foods is in process design calculations and pipeline design (flow and velocity profiles through transportation) [40].

3.5 Cluster Analysis Clustering, one of the most important unsupervised learning problems, is a common procedure for statistical data analysis which is used in many fields such as machine learning, data mining, pattern recognition, image analysis, and bioinformatics. It is a method of grouping similar objects into various groups, or more precisely, the partitioning of a data set into subsets according to some defined distance measure [41]. Data clustering algorithms can be hierarchical or partitional. Hierarchical clustering finds successive clusters using previously established clusters. To investigate the similarity of the time-dependent and time-independent steady shear rheological properties of two novel gums (SSG and CSG) with three commercialized biopolymers (GG, XG, and PE), we employed the hierarchical clustering technique and PCA in a serial mode. Hierarchical algorithms can be agglomerative (bottom-up) or divisive (top-down). In this research, we used the agglomerative algorithm, which begins with each element as a separate cluster and merges them in successively larger clusters. A key step in hierarchical clustering is to select a distance measure. Here, the Euclidean distance, computed by finding the square of the distance between each variable, summing the squares, and finding the square root of that sum, was used [41]. PCA is a statistical procedure which uses sophisticated underlying mathematical principles to transform a number of possibly correlated variables into a smaller number of linearly uncorrelated variables called principal components. It should be mentioned that distance correlation was used for hierarchical clustering. The rheological properties of five gum dispersions were given by 25 parameters. As a large number of rheological parameters were introduced in this study, to use PCA for clustering, we employed a screening filter. In this way, first, the 25 parameters were classified into four categories with more than 60% similarity indexes in each group by agglomerative hierarchical clustering (Table 3.6). Generally, the first group contained variables related to the initial structure of material (no destruction), the second group contained parameters related to the manner of structure destruction, the third group variables were associated with the structure of matter in the absence of a shear field, and the fourth group contained parameters determined after destruction of the structure in the shear field. Then, one parameter was randomly selected for clustering from each of the four groups, which represented one of the rheological aspects of matter (boldfaced parameter). These four parameters were the Moore zero-shear viscosity, extent of hysteresis, yield stress obtained from stress-viscosity extrapolation, and the power-law model consistency coefficient in the absence of a time-dependent structure, respectively. Using these parameters and the PCA technique, the novel and commercialized hydrocolloids

3.5 Cluster Analysis

Table 3.6 Clustering of steady shear and time-dependent rheological parameters of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG). A (similarity index = 65.65)

B (similarity index = 71.15)

C (similarity index = 63.55)

D (similarity index = 75.65)

K (equilibrium consistency coefficientunpresheared)

Hysteresis area

𝜂 ∞ (steady-state apparent viscosity from single shear stress decay)

K′ (equilibrium consistency coefficientpresheared)

𝜏 0 (indicator of instantaneous recovered structure)

k (decay rate from single shear stress decay test)

𝜏 0E (yield stress from apparent viscosity versus shear stress curve)

n′ (equilibrium flow behavior index-presheared)

𝛼 r (recovery rate from single shear stress decay)

𝜆 (relaxation time from Moore model)

𝜏 0c (yield stress by Casson model)

K p ′′ (hysteresis loop test)

𝜏 0SR (yield stress by stress ramp test)

𝜂 0 (single shear stress decay test)

𝝉 0B (yield stress by Bingham model)

np ′′ (hysteresis loop test)

𝜏 0M (yieldstress by Moore model)

𝜂 ∞ (single shear stress decay test)

—

𝜂 0∞ (limiting infinite-shear viscosity by Moore model)

𝜼0M (zero-shear viscosity by Moore modele)

K p (consistency coefficient from hysteresis loop test)

—

—

n (equilibrium flow behavior index-unpresheared)

np (flow behavior index from hysteresis loop test)

—

—

Rr % (recovery from in-shear structural recovery)

—

—

—

Bolded parameters were randomly selected for clustering

were clustered. A Scree plot showed that just two components can evaluate more than 91% of variances in the data (data not shown), so they were used for the clustering analysis. As shown in Figure 3.5, the score plot for the two first components demonstrated that from the standpoint of the rheological characteristics (steady shear and time dependent), CSG is more similar to GG, and SSG has the greatest similarity to XG and after that to PE dispersions. Investigating the most effective rheological parameter in hydrocolloids clustering analysis showed that the zero-shear viscosity, which is related to the structure of the gums, showed the most influential effect (0.771 coefficient for PC1), and the consistency coefficient in the absence of structure demonstrated the least influential effect (0.084 coefficient for PC1) on hydrocolloids clustering (data not shown). Table 3.7 demonstrated the Euclidean distance between different gums in the score plot. The formula for the Euclidean distance measurement between a point X (X1, X2, etc.) and a point Y (Y1, Y2, etc.) is [41] √ (3.6) dij = (Xi − Xj )2 + (Yi − Yj )2

95

3 Steady Shear Rheological Properties of Emerging Hydrocolloids

CSG

GG

PE

SSG

XG

1

2

2.5 2 1.5 1 Second component

96

0.5 –5

–4

–3

–2

0

–1

0

3

4

5

–0.5 –1 –1.5 –2 –2.5 First component

Figure 3.5 Distribution and correlation between the studied hydrocolloids in vector space. Table 3.7 Euclidean distance between sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG) in the vector space. Euclidean distance from: Gum

XG

GG

PE

SSG

8.14c ± 0.14

2.64a ± 0.13

XG

0.00

GG

c

0.00

b

b

0.00

c

b

PE

8.14 ± 0.14 2.64 ± 0.13 a

7.04 ± 0.15

c

7.04 ± 0.15

CSG

0.70a ± 0.08

9.15c ± 0.13

c

1.26a ± 0.41

b

3.29 ± 0.32

8.41b ± 0.41

7.95 ± 0.21

SSG

0.70 ± 0.08

7.95 ± 0.21

3.29 ± 0.32

0.00

8.70b ± 0.08

CSG

9.15d ± 0.13

1.26a ± 0.41

8.41d ± 0.41

8.70d ± 0.08

0.00

a–d: Means followed by the same letters in the same column are not significantly different (P > 0.05).

According to Table 3.7, among different commercialized hydrocolloids, SSG showed the lowest Euclidean distance with XG (0.70) and the highest distance with GG (8.14); in contrast, CSG showed the lowest Euclidean distance with GG (1.26) and the highest distance with XG (9.15). It is noteworthy that, among galactomannans, SSG showed the highest similarity with PE with the lowest Euclidean distance magnitude. Although both SSG and GG are galactomannans with almost the same molecular weight (≈103 kDa for GG [9] and 4 × 102 –1.5 × 103 kDa for SSG [13, 14], the lack of similarity between SSG with GG could be related to the anionic nature of SSG and the neutrality of the GG chains, which is reflected in the higher intrinsic viscosity of SSG (22.55 dl g−1 [13]) compared to GG (12.5 dl g−1 [9]). On the other hand, it is expected that the behavior of CSG, a polyelectrolyte galactomannan, would be similar to that of SSG rheologically, whereas its behavior was surprisingly similar to that of GG. This behavior could be attributed to the lower molecular weight of CSG (540 kDa, almost half of GG’s molecular weight [15], which is demonstrated in their almost similar intrinsic viscosity values (13.3 dl g−1 for CSG [15]) and seems to compensate for the positive effect of the CSG polyelectrolyte nature to some extent. The highest similarity of SSG to XG may be attributed to the

References

likeness of their conformation (rigid conformation of SSG and XG). Although the intrinsic viscosity of XG (214.21 dl g−1 [10]) is much higher than that of SSG, the literature proves that SSG exhibits a higher storage modulus, loss modulus, complex modulus, extent of elastic component temperature dependency, the slope of double logarithmic complex viscosity–frequency plots at different temperatures of 10–90 ∘ C (1%w/w, f = 1 Hz), complex viscosity (1 Hz, 50 ∘ C) [42], and departure value from the Cox–Merz rule and lower complex compliance (1/Pa, 0.01–10 Hz) than XG [31].

3.6 Conclusion and Future Trend The rheological characteristics of three generally used and two novel hydrocolloids were investigated. Except GG, which did not show shear-thickening behavior, other gums showed a specific three-stage apparent viscosity versus shear rate response when sheared over a wide shear rate range. As compared to other hydrocolloids, GG showed the highest critical shear rate. XG was found to be the most pseudoplastic gum with the lowest power-law flow behavior index, especially in the range of 0.01–0.1 s−1 (67.3% viscosity reduction). The Moore and power-law models could describe the flow behavior of hydrocolloid solutions. XG and SSG with the highest hysteresis area among all selected gums showed the highest sensitivity to shear history. Using the structural kinetic model, XG exhibited the highest breakdown rate constant. In addition, the relative measure of the extent of thixotropy was the highest for XG and SSG and the lowest for CSG and GG. The recovery parameter (Rr , %) obtained from in-shear structural recovery measurements did not show any significant differences between XG, GG, and PE, while it was the lowest for CSG. PE showed an intermediate behavior as compared to other dispersions with respect to the limiting zero-shear viscosity from the Moore model and the consistency coefficient of the power-law model. PE exhibited the highest SYS among all the hydrocolloids. The hierarchical clustering technique with PCA showed the highest similarity of SSG with XG and CSG with GG. In addition, the zero-shear viscosity was determined as the most effective rheological parameter in hydrocolloids clustering analysis, whereas the consistency coefficient in the absence of structure demonstrated the least influential effect. Using the aforementioned results, one can decide on the final usage of SSG and CSG in various food formulations, based on their steady shear rheological behavior similarity to the commercialized hydrocolloids, XG, GG, and PE. Choosing hydrocolloids in food systems on the basis of their functions enables us to rationally design structural features. In this way, combining the results of multiple tests provides a better insight into their structure-function relationship. So, it seems beneficial to employ the aforementioned framework by using the hierarchical clustering technique and PCA to investigate the similarity of different emerging hydrocolloids with generally used gums regarding their physicochemical, textural, and microstructural characteristics besides their bioactivity. This information is invaluable in the design of biopolymer blends with a specific extent of compatibility for a specific functionality.

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emulsions as affected by xanthan gum, guar gum and carboxymethyl cellulose interactions studied by a mixture regression modeling. Food Hydrocolloids 53: 199–208.

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101

4 Transient and Dynamic Rheological Properties of Emerging Hydrocolloids Ali Alghooneh and Seyed M.A. Razavi Food Hydrocolloids Research Center, Department of Food Science and Technology, Ferdowsi University of Mashhad, Mashhad, Iran

4.1 Introduction Exploring novel hydrocolloids provides additional flexibility in the design of new products that may have a lower cost. In this way, there is great interest in well-characterized natural hydrocolloids with appropriate functionality. Fundamental rheological properties include elasticity, viscosity, and viscoelasticity, which are related to the composition, structure, and the strength of interaction within the structural elements of hydrocolloids [1]. Steady shear flow tests concern the flow properties of all fluids, regardless of whether or not they exhibit elastic behavior. Nevertheless, many rheological characteristics of hydrocolloids cannot be described by viscosity alone, and elastic function must also be taken into account. Experiments based on unsteady state deformations, such as oscillatory and transient tests, are implemented to generate data that reflect both the elastic and viscous characters of materials [2]. These tests can be performed in linear and nonlinear regions. In any industry, the choice of hydrocolloids is based on their functions, which are associated with their molecular characteristics (e.g., molecular weight, conformation, flexibility, polarity, and hydrophobicity) and so with their rheological behaviors. Thus, introducing the rheological properties of novel hydrocolloids and questioning their similarity to the generally used hydrocolloids based on some specific rheological parameters could be beneficial to rationally design structural features in food systems and to give insight into the structure–function relationship between them. However, a definitive scheme does not exist to characterize biopolymers on the basis of their important structural properties obtained from dynamic and transient rheological measurements and to discover their similarity. Clustering is a part of pattern recognition theory. It helps to summarize information by grouping data in categories in which the members are as similar as possible to each other in the same group and as different as possible from members of other categories.

Emerging Natural Hydrocolloids: Rheology and Functions, First Edition. Edited by Seyed M.A. Razavi. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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4 Transient and Dynamic Rheological Properties of Emerging Hydrocolloids

The hierarchical algorithm is one of the clustering techniques and is classified into agglomerative hierarchical and divisive hierarchical methods [3]. Agglomerative hierarchical clustering is appropriate to represent the original data set in the feature space at multiple levels of abstraction because of each clustering level produces an abstract representation of the original data set [3]. Clustering has been successfully applied in various fields of the food industry [3–5]. Guar gum (GG), pectin (PE), and xanthan gum (XG) are three generally used hydrocolloids in food formulations. GG is obtained from guar (Cyamopsis tetragonoloba) seeds. It contains linear chains of d-mannopyranosyl units with a d-galactopyranose substituent protruding by (1 → 6) linkages and has the specific structure of galactomannans with 1.3 × 103 kDa molecular weight and 12.5 dl g−1 intrinsic viscosity [6]. XG is a high-molecular-weight exopolysaccharide (4.05 × 103 kDa) produced by the bacterium Xanthomonas compestirs and consists of a cellulose backbone with an attached charged trisaccharide side chain composed of a glucuronic acid residue between two mannose residues [7]. Higiro et al. [7] reported 214.21 dl g−1 intrinsic viscosity for XG by using the Tanglertpaibul and Rao equation. PE, with a heteropolysaccharide structure, originates in most plant tissues, with α-(1–4)-d-galacturonic acid units as the principal component, which interrupted by the insertion of rhamnose units and with side chains of neutral sugars attached to the backbone. Naturally, PE is highly methoxylated (HM) with more than 50% of the esterified carboxyl groups. The intrinsic viscosity of HM PE is 15 dl g−1 [8]. It has been reported that PE macromolecules adopt a slightly stiff conformation [9]. The literature establishes the high capability of both sage seed gum (SSG) and cress seed gum (CSG) for use in food formulations. SSG is extracted from Salvia macrosiphon seeds. The weight average molecular weight of SSG polysaccharides is 4 × 102 –1.5 × 103 kDa [10, 11]. It is a polyelectrolyte galactomannan (1.78–1.93:1 mannose/galactose ratio and 28.2%–32.2% uronic acids) with 22.55 dl g−1 intrinsic viscosity [11]. CSG exists in the outer layer of the garden cress plant seed (Lepidium sativum L.). CSG, with a molecular weight of 540 kDa, possesses a semi-rigid chain conformation [12]. This polyelectrolyte galactomannan (8.2 mannose/galactose ratio, 15% uronic acids, and 13.3 dl g−1 intrinsic viscosity) is known as a novel thickening, gelling, and emulsifying agent [13–16]. To the best of our knowledge, there is no similar published work regarding the characterization of the biopolymers structure that widely addresses dynamic and transient rheological behaviors. Therefore, the aims of the present study were, broadly, investigation of three commercialized (GG, PE, and XG) and two novel hydrocolloids’ (CSG and SSG) dynamic oscillatory rheological properties (small amplitude strain sweep, large amplitude strain sweep, frequency sweep, time sweep), transient rheological properties (creep and stress relaxation) and the Cox–Merz rule, yield stress, and finally, probing the similarity of these five hydrocolloids based on the aforementioned rheological properties using the hierarchical clustering technique and principal component analysis (PCA) in a serial mode. Such a comprehensive rheological investigation is critical to decide on the hydrocolloids on the basis of their specific usage in food formulations and other industries, to adjust processing parameters and is important from the fundamental point of view.

4.2 Viscoelastic Characteristics

4.2 Viscoelastic Characteristics 4.2.1

Oscillatory Properties

4.2.1.1

Strain Sweep

Rheological measurements were carried out using a Physica MCR 301 rheometer (Anton Paar, GmbH, Graz, Austria) equipped with cone-plate geometry (4∘ cone angle, 50 mm of diameter, and 1 mm gap). The temperature was fixed using a Peltier system at 20 ∘ C, and then each sample was equilibrated for at least 5 min before the rheological test and was coated around their periphery with light silicone oil to minimize loss of water. Strain sweep tests in oscillatory shear were performed in the range 0.01%–250% in the controlled shear rate mode at 20 ∘ C and a constant frequency of 1 Hz. Then, data in the linear viscoelastic region, LVE, and in the nonlinear viscoelastic region, NLVE, were analyzed. 4.2.1.1.1

Small Amplitude Oscillatory Shear Test

The storage modulus (G′ LVE ), complex modulus (G* LVE ), loss tangent (tan 𝛿) in LVE, limiting value of strain (𝛾 c ) and stress (𝜏 c ), the slope of loss tangent after flow point (tan 𝛿 AF ), the extent of strain overshoot (G′′ p /G′′ LVE ), fracture strain (𝛾 Fr ), fracture stress (𝜏 Fr ), and degree of ductility ((𝛾 Fr -𝛾 L )/ 𝛾 Fr )) were determined by the amplitude sweep measurements [17]. These parameters of five selected hydrocolloids are presented in Table 4.1. With an increase in strain, two different regions were observed (data not shown): (1) LVE, where G′ and G′′ were approximately constant, while G′ was greater than G′′ and (2) NLVE, in which G′ and G′′ started to decline. At LVE, the highest and lowest values of the elastic moduli of PE and CSG were 158.00 and 7.40 Pa, respectively. This parameter demonstrates the rigidity of the sample [18]. The complex modulus, G* LVE (comprising both elastic and viscose components), showed a similar trend with G′ LVE for all gums, indicated that the total structural strength of PE was at the highest extent. Tan (𝛿)LVE , which indicates the physical behavior of a system (the ratio of G′′ LVE to G′ LVE ), of all samples was less than 1, although GG, with the highest value of this parameter, showed the most liquid-like behavior, followed by CSG, while there were not any significant differences between PE, XG, and SSG, which suggested a more pronounced solid-like behavior for them. The critical strain (𝛾 c , the strain in which G′ sharply decreases with an increase in strain) of GG was the highest (33.00%), followed by CSG (9.10%), whereas PE exhibited the lowest value of this parameter among all (0.95%). On the other hand, 𝛾 c did not show any significant difference between SSG and XG. Γc depends on the molecular architecture of the biopolymers [19] and the deformability of the gel samples [20]. This result suggested that the timescale of interaction in PE chains is much longer than those in GG, which increases the time required for a new entanglement to replace those disrupted by an externally imposed small deformation in the amplitude oscillatory test. The magnitude of the stress at the limiting strain, 𝜏 c (the nonlinear region immediately begins after this stress), which is considered as the starting point of the weakening of the gel strength, was in the order of PE > XG > SSG > GG ≈ CSG. With the increase in the strain being higher than the critical strain, the G′ of all gum dispersions decreased consistently. The G′′ of GG and CSG showed a similar behavior with

103

Table 4.1 Storage modulus (G′ LVE ), complex modulus (G*LVE ), limiting value of strain (𝛾 c ), limiting value of stress (𝜏 c ), and loss tangent (Tan (𝛿)LVE ) in the linear viscoelastic region, besides extent of loss modulus overshoot G′′ p /G′′ LVE , fracture stress (𝜏 Fr ), fracture strain (𝛾 Fr ), reversible extensibility ahead of fracture ((𝛾 Fr -𝛾 L )/𝛾 Fr ), the slope of loss tangent after flow point (Tan (𝛿)AF ) for sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG) as determined by amplitude sweep tests (1 Hz, 20 ∘ C). Gum

G′ LVE (Pa)

G*LVE (Pa)

𝜸 c (%)

𝝉 c (Pa)

Tan (𝜹)LVE (−)

G′′ p /G′′ LVE (−)

XG

75.90b ± 0.76

77.10b ± 0.91

7.14bc ± 0.41

6.85b ± 0.51

0.18c ± 0.01

GG

25.00d ± 1.02

31.50d ± 0.96

33.00a ± 1.40

1.52d ± 0.25

0.74a ± 0.02

—

0.003d ± 0.00

PE

158.00a ± 1.75

160.00a ± 1.79

0.95d ± 0.07

8.57a ± 0.28

0.16c ± 0.01

2.01a ± 0.03

10.00c ± 0.21

72.70b ± 0.82

25.70a ± 1.57

0.35a ± 0.01

SSG

55.80c ± 0.56

56.70c ± 0.67

5.25c ± 0.30

3.75c ± 0.28

0.18c ± 0.01

1.57b ± 0.06

27.40b ± 1.75

80.90a ± 0.14

15.40c ± 0.60

0.19c ± 0.01

CSG

7.40e ± 0.19

7.83e ± 0.12

9.10b ± 0.49

1.75d ± 0.21

0.34b ± 0.04

—

0.01d ± 0.00

1.88a ± 0.07 —

—

a–d: Means followed by the same letters in the same column are not significantly different (P > 0.05).

𝜸 Fr (−)

(𝜸 Fr -𝜸 L )/ 𝜸 Fr (%)

𝝉 Fr (Pa)

37.30a ± 2.38

80.90a ± 0.12

20.90b ± 0.81

—

—

—

—

Tan (𝜹)AF (−) 0.26b ± 0.01

4.2 Viscoelastic Characteristics

G′ , whereas in XG, PE, and SSG, G′′ showed overshoot. This suggests that the structures formed with the CSG and GG were weaker than those formed with XG, SSG, and PE [21]. Hyun [22] reported that at least four types of large-amplitude oscillatory shear (LAOS) behavior exist depending on the interactions between the microstructures: type I, strain thinning (G′ , G′′ decreasing); type II, strain hardening (G′ ,G′′ increasing); type III, weak strain overshoot (G′ decreasing, G′′ increasing followed by decreasing); type IV, strong strain overshoot (G′ ,G′′ increasing followed by decreasing). On the basis of this classification, XG, PE, and SSG showed weak strain overshoot behavior, whereas CSG and GG demonstrated strain thinning behavior. The former behavior, which has the same origin as shear-thinning behavior, is most easily observed in polymer solutions and melts. With an increase in strain, polymer chains disentangle and align with the flow field. This response becomes more significant in anisotropic systems which flow more readily, and both moduli afterward decrease further [22]. On the other hand, a highly extended biopolymer with a polyelectrolyte nature such as SSG, XG, and PE align and associate (partly due to hydrogen bonding) to form a weakly structured material in solution. These complex structures resist deformation up to a certain strain where G′′ increases to its highest value. This peak in G′′ denotes the maximum energy dissipation (viscous response) and has been reported in soft glassy materials [23, 24]. Then, this shear-induced structure is destroyed by a larger deformation, after which the polymer chains align with the flow field, and G′′ decreases. G′′ p /G′′ LVE , which shows the extent of G′′ overshoot and is an index of structural resistance against deformation, was lower for SSG than for two other hydrocolloids with weak strain overshoot behavior, while no significant difference was observed between XG and PE. After 𝛾 c , when the material yields and/or fractures, G′ decreased rapidly. One method to determine fracture strain or stress is by plotting the product of the elastic modulus and strain (G′ .𝛾) against the dynamic strain and looking for a maximum, which corresponds to the fracture point. As shown in Table 4.1, only systems with G′′ max exhibited fracture stress and strain. Among them, XG showed the highest fracture strain (𝛾 Fr ), while PE showed the lowest value of this parameter. On the other hand, the order of fracture stress (𝜏 Fr ) of hydrocolloids dispersions was PE > XG > SSG. Fracture properties are important in food systems as they mimic the response of foods to chewing and biting. Fracture takes place at the weakest parts of the gel network [25]. This result shows that the sensitivity of entanglement to deformation for the three hydrocolloids was in the order XG < SSG < PE, whereas the strength of the structure at fracture was in the order SSG < XG < PE. From the comparison of 𝜏 Fr and 𝜏 c , one can conclude that microscopic fracture of the three gum dispersions showed the same order as for macroscopic fracture. Also, results showed a higher reversible extensibility ahead of fracture for XG and SSG than for PE, whose higher (𝛾 Fr −𝛾 L )/ 𝛾 Fr value suggested the highest brittleness for PE. It has been shown that the magnitude of the flow point stress (when G′ = G′′ ), which is related to the yield stress characteristic, is strongly correlated with the spreadability of many food products. Beyond the flow point, materials change from viscoelastic to elastoviscous behavior, where the materials display irrecoverable deformation [26]. Since it seems that spreadability is a kinetic property that manifests from the yield point, it should not be defined by just the yield stress value. Therefore, we defined the slope of the loss tangent, which corresponds to the rate of change of the viscous to elastic behavior, after the flow point stress (tan 𝛿 AF ) of different hydrocolloids as a representative parameter of the spreadability characteristic. According to Table 4.1, PE showed

105

106

4 Transient and Dynamic Rheological Properties of Emerging Hydrocolloids

the highest value of tan 𝛿 AF , while the lowest spreadability was observed for both GG and CSG. 4.2.1.1.2

LAOS Test

Small amplitude oscillatory tests use a small strain amplitude and so have a limited resolution for distinguishing complex fluids with structural differences. Steady simple shear rate experiments provide little information about the microstructure. Unlike these tests, the LAOS test provides valuable information with high resolution which is useful to connect quantitative nonlinear measures with microstructure and to provide useful information about the behavior of materials during processing operations in which a large deformation for short time is encountered and the material does not reach steady state [23]. With the transformation from the LVE to the NLVE range, the physical interpretation of dynamic properties is no longer the same as those in the LVE range because of the generation of the nonlinear response stress, which is not a perfect sinusoid and, consequently, the viscoelastic moduli are not uniquely defined. Different nonlinear material coefficients can be extracted from LAOS tests depending on the employed method (Lissajous curves, Fourier transform rheology, stress decomposition, decomposition of characteristic waveforms, and analysis of parameters related to Fourier transform rheology) and the chosen frame of reference (i.e., time domain or deformation domain) [23, 27]. The methods which have been used to calculate viscoelastic moduli can be grouped into two categories: full cycle methods and local methods. A full cycle method allows the average elasticity and dissipated energy at each imposed pair of LAOS coordinates (𝛾 0 , 𝜔) to be calculated from the first-order Fourier or Chebyshev coefficients (intercycle nonlinearities). On the other hand, local methods allow the viscoelastic moduli at an instantaneous strain to be calculated (intracycle nonlinearities). Here, first, LAOS flow was qualitatively investigated via waveform analysis by using elastic and viscous Lissajous–Bowditch plots (also called Lissajous plots) in which the ̇ 𝛾̇ 0 , respectively. To quantitatively detertotal stress (𝜏/𝜏 0 ) was plotted versus 𝛾/𝛾 0 and 𝛾∕ mine the extent of nonlinearity, we used the G ′′ 3 /G ′′ 1 and G′ 3 /G′ 1 ratios calculated from the Fourier transform analysis in the time domain. The type of nonlinearity – intracycle strain softening and intracycle strain stiffening (in the strain domain) and intracycle shear thinning and shear thickening (in the strain rate domain) –was determined using the Ewolt et al. [28] local method. Besides, intercycle nonlinearities (intercycle strain softening, intercycle strain stiffening, intercycle shear thinning, and intercycle shear thickening) were determined by Fourier transform analysis to better distinguish the LAOS behavior of different hydrocolloids. In addition, on the basis of the Ewolt et al. [29] procedure, the perfect plastic dissipation ratio is used for identifying plastic behavior and quantifying how close a measured material response corresponds to rigid, perfect plastic yield stress behavior. The Lissajous plots of GG, CSG, SSG, XG, and PE at 100% strain are shown in Figure 4.1. For all the samples at strains of 0.1% and 1% and for GG and CSG at these strains as well as 10% strain (i.e., within the LVR), the shape of the elastic and viscous Lissajous plots were perfectly elliptical, indicating ideal viscoelastic behavior. With an increase in strain at 10% and 100% strains for SSG, XG, and PE, and at 100% strain for GG and CSG, the shape of the elastic Lissajous plots changed from an ellipse to a parallelogram and the area encompassed by the plots increased, indicating the shift from elastic to viscous-dominated behavior. Although, XG, SSG, and PE solutions at

–1.5

–1

1.5 1 0.5 0 –0.5–0.5 0 –1 –1.5

0.5

1

1.5

Normalized stress

Normalized stress

4.2 Viscoelastic Characteristics

1.5 1 0.5 0 –1.5

–1

–1

0.5

1

1.5

Normalized strain

0.5 0 –0.5

0

0.5

1

1.5

–1 –1.5

Normalized stress

Normalized stress

1

–0.5

–1.5

–1

1.5 1 0.5 0 –0.5–0.5 0 –1 –1.5

0

0.5

1

1.5

–2

–1.5

–1

Normalized stress

0 –1

–1.5

–1

1.5 1 0.5 0 –0.5–0.5 0 –1 –1.5

0.5

1.5

1

1.5

1 0.5 0 –1.5

–1

–0.5

–0.5

0

0.5

(h)

Normalized strain (i)

1

1.5

1.5

–1

Normalized shear rate

0.5

1

–1.5

(g) 1.5 1 0.5 0 –0.5–0.5 0 –1 –1.5

1

1.5

Normalized strain

Normalized stress

Normalized stress Normalized stress

1 –0.5

0.5

Normalized shear rate (f)

2

–1

1.5

Normalized shear rate

Normalized strain (e)

–1.5

1

(d)

1.5

-1

0.5

–1.5

(c)

–1.5

0

Normalized shear rate (b) Normalized stress

Normalized stress

–1.5

–0.5 –1

Normalized strain (a) 1.5 1 0.5 0 –0.5 –0.5 0 –1 –1.5

–0.5

–1.5

–1

1.5 1 0.5 0 –0.5–0.5 0 –1 –1.5

0.5

1

1.5

Normalized shear rate (j)

Figure 4.1 Elastic and viscous Lissajous plots of SSG, (a, b) CSG, (c, d) GG, (e, f ) PE, (g, h) and XG, (i, j) respectively, at 100% strain (1%-1 Hz).

107

108

4 Transient and Dynamic Rheological Properties of Emerging Hydrocolloids

10% and 100% strains displayed strain-hardening behavior, the shapes of the nonlinear stress waveforms were markedly different, which originated from different microstructures. Particular shapes of the Lissajous plot relate to different microstructural features and correspond to borderline different rheological behaviors [24]. This behavior may be attributed to the stronger gel network structure of SSG, XG, and PE than CSG and GG achieved through their polyelectrolyte moiety and rigid conformation, resulting in less flexibility of the network and greater structural damage under large strains, which is reflected by the start of nonlinearity at the lower strain compared with CSG and GG. The inability of the structure to adapt to large strains would result in permanent structural deformation and the appearance of viscous-like behavior [24]. While visual investigations of Lissajous plots are helpful to give an overview of nonlinear viscoelastic responses, quantitative methods are also necessary for analyzing the nonlinear shear stress responses. To determine the extent of nonlinearity and the behavioral shifts of Lissajous plots, the stress response to an oscillatory strain input was written as a Fourier series to determine the third viscoelastic moduli (G3′ and G3′′ ) [30]. Then, the ratio of the third harmonic viscoelastic moduli to the first harmonic viscoelastic moduli, G1′ and G1′′ , were investigated. Values of G3′ ∕G1′ > 0.01 or G3′′ ∕G1′′ > 0.01 reflect nonlinear viscoelastic behavior. G3′ ∕G1′ and G3′′ ∕G1′′ ratios were greater than 0.01 for XG, SSG, PE, and CSG at 10% and 100% strains, while this occurred only at 100% strain for GG, indicating nonlinear behavior at these strains (Table 4.2). For all hydrocolloids, when the samples showed nonlinearity, the extent of nonlinear viscoelastic behavior increased with an increase in strain, as reflected by the greater values of these ratios at higher strain. The highest G3′′ ∕G1′′ and G3′ ∕G1′ ratios at 10% and 100% were obtained for PE. The G3′ ∕G1′ ratio did not show any significant differences between SSG and XG at both 10% and 100% strains. In addition, with an increase in strain, the differences between these ratios for CSG and GG vanished (Table 4.2). The type of intracycle nonlinear behavior was identified by using two viscoelastic ′ (the minimum strain modulus), and two moduli, GL′ (the largest strain modulus) and GM instantaneous viscosities, 𝜂L′ (the instantaneous viscosity at the largest strain rates) and ′ (the instantaneous viscosity at the smallest strain rates) parameters defined by Ewoldt 𝜂M ′ ′ and 𝜂L′ ∕𝜂M are the measures of elastic-related nonlinear behavior and et al. [28]. GL′ ∕GM viscous-related nonlinear behavior, respectively. These parameters for all hydrocolloids ′ – higher than 1, are depicted in Table 4.2. The magnitudes of the ratio of GL′ ∕GM less than 1, and equal to unity – are indicative of strain-stiffening, strain-softening, ′ = 1 indicates a linear and linear elastic behaviors, respectively. Furthermore, 𝜂L′ ∕𝜂M ′ ′ < 1 represents shear-thinning behavior, and 𝜂L′ ∕𝜂M > 1 indicates regime, 𝜂L′ ∕𝜂M shear-thickening behavior [28]. On the basis of these classifications, XG, PE, and SSG behaved similarly, with strain and their elastic components showing linear elastic behavior at 0.1% and 1% strains, while demonstrating strain-stiffening behavior at 10% and 100%. Also, the amount of strain stiffening was greater at higher strains. At 10% and 100% strains, PE displayed the greatest amount of strain-hardening behavior among the hydrocolloids. On the other hand, the elastic component of CSG and GG showed linear elastic behavior at 0.1%, 1%, and 10% strains, whereas they showed strain-softening ′ was almost equal to unity for XG, SSG, and PE at 0.1% behavior at 100% strain. 𝜂L′ ∕𝜂M and 1% strains, indicating linear viscous behavior of their viscose component. This ′ ratio was less behavior was shown for CSG and GG at 0.1%, 1%, and 10% strains. 𝜂L′ ∕𝜂M than unity for XG, SSG, and PE at 10% and 100% and for CSG and GG at 100% strain.

4.2 Viscoelastic Characteristics

Table 4.2 Elastic and viscous parameters of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gums (GG) at different strains in LAOS domain. Elastic parameters

Viscous parameters

Gum

Strain

G′L ∕G′M

XG

0.1

0.981c 1 ± 0.022

0.001c 1 ± 0.000

0.943a 1 ± 0.028

0.009c 1 ± 0.000

1

0.971c 1 ± 0.036

0.001c 1 ± 0.000

0.984a 1 ± 0.047

0.004c 1 ± 0.000

10 100 GG

6.480a ± 0.209 1

3

0.084b ± 0.004 2

0.204a ± 0.013

0.053b 3 ± 0.005

2

0.186a 2 ± 0.012

1

0.741b ± 0.063 0.481c ± 0.038 0.941a ± 0.028

0.001b 1 ± 0.000

1

0.968a 1 ± 0.036

0.002b 1 ± 0.000

0.968a 1 ± 0.046

0.000b 1 ± 0.000

1

0.969a ± 0.043 1

0.797b ± 0.052

1

0.001b ± 0.000 1

0.046a ± 0.003

0.005b 1 ± 0.000

4

0.036a 1 ± 0.002

1

0.965a ± 0.082 0.876b ± 0.053

0.983c ± 0.032

0.001c ± 0.000

0.990a ± 0.030

0.003c 1 ± 0.000

1

0.974c 1 ± 0.036

0.002c 1 ± 0.000

0.967a 1 ± 0.046

0.002c 1 ± 0.000

3

4.291b ± 0.084 4

8.591a ± 0.426

3

0.135b ± 0.006 3

0.260a ± 0.017

0.115b 4 ± 0.010

1

0.493a 3 ± 0.032

1

0.534b ± 0.045 0.182c ± 0.012

0.984c ± 0.012

0.002c ± 0.000

1.057a ± 0.032

0.002c 1 ± 0.001

1

1.062c 1 ± 0.040

0.003c 1 ± 0.000

0.947a 1 ± 0.043

0.004c 1 ± 0.001

100 0.1

2

3.514b ± 0.068 2

5.485a ± 0.161 1

0.942a ± 0.031

3

0.096b ± 0.004 2

0.174a ± 0.011 1

0.001b ± 0.000

0.043b 3 ± 0.004

2

0.081a 1 ± 0.005

1

0.001b 1 ± 0.000

1

0.780b ± 0.066 0.577c ± 0.045 0.924a ± 0.028

0.965a ± 0.036

0.002b ± 0.000

0.894a ± 0.042

0.002b 1 ± 0.001

10

0.933a 1 ± 0.042

0.012b 2 ± 0.000

0.861a 2 ± 0.073

0.022b 2 ± 0.002

1

0.702b ± 0.045

1

2

1 100

1

1

1

0.1 10

1

1

3

0.1

100

1

1

2

0.001b ± 0.000

10

CSG

3

G′′ ∕G′′ 3 1

0.943a ± 0.046

100

SSG

3.426b ± 0.064

𝜼′L ∕𝜼′M

0.1 10

PE

2

G′3 ∕G′1

1

0.080a ± 0.005

3

0.776b ± 0.050

0.052a 1 ± 0.003

1–5: Means followed by the same number in the same column denote that the corresponding parameter for each column is not significantly different among hydrocolloids at the same strain (P > 0.05). a–d: Means followed by the same letter in the same column denote that the corresponding parameter for each column is not significantly different for each gum at various strains (P > 0.05).

The lowest values of these ratios were obtained for PE at both 10% and 100% strains, whereas the lowest shear-thinning behavior at 10% strain was obtained for GG followed by CSG and at 100% for SSG and XG without any significant differences. These results indicated the higher sensitivity of SSG and XG, and especially PE gels, structure to a large deformation than the other two galactomannans [24]. To gain a deeper insight into the rheological and structural behaviors of the selected hydrocolloids, the average elasticity and dissipated energy in the material response were determined by means of the full cycle method using Fourier series, and the results are shown in Figures 4.2 and 4.3, respectively. At 0.1%–1% strain, the elastic component of all hydrocolloids showed linear elastic behavior, reflected by the strain independency of the first harmonic elastic modulus (G1′ ). With an increase in strain in the range 0.1%–10% and 0.1%–100%, the elastic modulus decreased with an increase in strain, indicating an intercycle strain-softening behavior for all the studied systems. With an increase in the

109

4 Transient and Dynamic Rheological Properties of Emerging Hydrocolloids

XG

SSG

CSG

GG

PE

1000

G′1 (Pa)

100

10

1 0.1

1

10

100

Strain

Figure 4.2 Strain independency of first harmonic elastic modulus (G′1 ) of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG). PE

XG

GG

SSG

CSG

10

1 η′1 (Pa.s)

110

0.1

0.01 0.005

0.05

0.5

5

50

Shear rate (rad/s)

Figure 4.3 Strain independency of first harmonic viscose component (𝜂1′ ) of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG).

strain range at 0.1%–10%, the G1′ reduction ratios of SSG, XG, and PE were not significantly different; similarly, CSG and GG did not show any significant differences in the G1′ reduction ratio, although the former group showed a much higher reduction ratio than the latter one. Finally, at 0.1%–100%, the order of the G1′ reduction ratio was PE > XG ≈ SSG > CSG ≈ GG. Regarding the first harmonic viscous component behavior of different hydrocolloids, except GG and CSG, other gum dispersions exhibited a three-stage first-order dynamic viscosity versus shear rate response when sheared over a wide shear rate range. The intercycle shear-thinning behavior was observed for all tested dispersions, which may be attributed to the formation of aggregated polymers dispersions and their high molecular weight [31]. With the exception of CSG and GG, at a lower strain rate, a shear-thickening region appeared. This behavior was followed by the Newtonian plateau at the lowest strain rate range for all gum dispersions.

4.2 Viscoelastic Characteristics

The length of each region was quite different for all gum dispersions. PE showed the highest length of the shear-thickening region, while XG showed the highest extent of shear-thickening behavior. It is assumed that the shear-thickening behavior could be the result of a stiffer inner structure with formation of entanglements of polymer coils as the shear rate increases [32]. This result suggested a greater effect of the shear rate on the thickening of PE and XG and the greater resistance of these hydrocolloids against the shear rate. Besides, different structure formation was exhibited with shear for PE and XG at low shear rates. On the other hand, CSG exhibited the highest length of Newtonian region among all gum dispersions, from 0.006 to 1.453 s−1 . In the low-shear Newtonian stage, the disrupted entanglement under deformation is replaced by new ones, whereas in the shear-thinning stage, the chains undergo continuing rearrangement as the shear rate increases [33]. Shear thinning begins when the rate of disentanglement becomes greater than the rate of re-formation [34]. This occurred at the same shear rate for PE and GG while they showed the highest value of this parameter. The extent of intercycle shear thinning was in the order PE > XG > SSG > CSG > GG, which confirmed the highest effect of shear on PE entanglement disruption at high shear rates. It is well known that when a small-particle-sized dispersion encountered shearing, the effect of Brownian motion lasts longer along the shear rate axis, and higher values of the shear rate are needed to initiate the shear-thinning stage [35]. An abrupt G1′ reduction occurred at 50% strain for PE, and this abrupt change occurred for 𝜂1′ reduction of XG (1.45 s−1 ) and PE (8.06 s−1 ) too, suggesting that these hydrocolloids assumed a more complicated structure. GG and CSG showed almost uniform G1′ reduction at all strain ranges, suggested the least intercycle strain-softening behavior among other gums. Rigid, perfectly plastic behavior is an idealized approximation for a material which exhibits slight elastic strains in comparison with large plastic deformations. This behavior can originate from strong short-range interparticle forces which maintain a percolated solid phase and is observed for many “apparent yield stress fluids” [29]. To compare the energy dissipated in a single LAOS cycle to the energy which would be dissipated in a perfect plastic response, we employed the 𝜑 parameter as follows: } 𝜋 × 𝛾0 × G1′′ { Ed 𝜋 𝜙≡ 1(Perfect plastic) ⋅ (Newtonian).0 (Puerly elastic) = (Ed )pp 4 × 𝜎max 4 (4.1) where Ed is the energy dissipated per unit volume in a single LAOS cycle, visualized by the area enclosed by the Lissajous curve of stress versus strain, (Ed )pp is the energy dissipated per cycle by the perfect plastic in LAOS, and 𝜎 max is the maximum stress. With an increase in strain, the 𝜑 values of SSG, XG, and PE approach the yield stress limit 𝜑 → 1, while for CSG and GG, they almost were close to the Newtonian fluid reference value 𝜑 ≈ 𝜋/4 ≈ 0.785 (data not shown). The highest 𝜑 value was obtained for PE at 100% strain, which showed the closest response to that of a perfect plastic under LAOS deformations. At 100% deformation, 𝜑 did not show any significant differences between SSG and XG and also between CSG and GG. We analyzed the correlation between the loss tangent after flow point (tan 𝛿 AF ) data and plastic dissipation index (𝜑) data. These two parameters exhibited a significant linear positive correlation with each other (p < 0.05), indicating that a possible trend observed in one of these parameters can be estimated by the other. The presented data demonstrate that the analysis of the nonlinear behaviors of hydrocolloids may be successfully carried out with the use of the LAOS techniques.

111

112

4 Transient and Dynamic Rheological Properties of Emerging Hydrocolloids

4.2.1.2

Frequency Sweep

Dynamic measurements were performed over the frequency range 0.01–10 Hz within the LVE range (strain amplitude 0.50%). In this frequency range, except for GG, the G′ dominating over the G′′ with weak frequency dependence and the mechanical spectra did not show any crossover points for all the hydrocolloids. The frequency at which G′ becomes equal to G′′ is called the crossover frequency (f*) and is considered as the beginning of the elastic plateau. f* was 5.130 Hz for GG. To investigate the possible crossover points outside the experimental frequency range for other gum dispersions, we asymptote two lines from the end of G′ and G′′ versus the frequency curves. PE showed the lowest f*, followed by SSG and XG without any significant differences (Table 4.3). When the frequency is so high that translational movements are no longer feasible, they start behaving like the weak gels, with G′ greater than G′′ and exhibiting little change with frequency [36]. This result suggested the lowest entanglement density for GG and the strongest associated network for PE among all the hydrocolloids. The effect of frequency ranges on the decreasing percentage and decreasing ratio of the dynamic viscosity (𝜂 ′ ) of different gum dispersions was investigated to find out the pseudoplasticity of hydrocolloids in the dynamic shear rheological test in the small deformation mode (data not shown). It was found that, except for GG, which showed the highest percentage of viscosity reduction at both 0.628–6.280 and 6.280–62.800 rad s−1 , for all other gum dispersions this phenomenon occurred at 0.0628–0.6280 rad s−1 . At the lowest angular frequency range (0.0628–0.6280 rad s−1 ), the 𝜂 ′ reduction percentage did not show any significant difference between SSG, XG, and PE; besides, these hydrocolloids showed a higher 𝜂 ′ reduction percentage than GG and CSG. In addition, PE with the highest 𝜂 ′ ratio reduction at all three angular frequency ranges (0.0628–0.6280, 0.0628–6.2800, and 0.0628–62.800 rad s−1 ) represented the highest shear-thinning behavior, while there were no significant differences between GG and CSG, the gums least influenced by shear at all these ranges. Shear thinning as an important rheological behavior of biopolymers is found to be broadly different in steady and dynamic shear tests [37]. In contrast to the steady shear test (under a large deformation), in which shear thinning occurs when rod-like particles are aligned in the flow direction and have lost their junctions in polymer solutions, in the dynamic test at high frequency when the time interval is not large enough for the broken inter- and intramolecular bonds to re-form, permanent disentanglement of long-chain polymers occurs, causing a decrease in 𝜂 ′ . Therefore, this result shows that the timescale of segment–segment interaction in PE chains must be long in comparison with the lifetime of the physical entanglements of other hydrocolloids, which consequently leads to an increase in the time required for a new entanglement to replace those disentangled by the externally imposed deformation in the dynamic shear test. The power-law model (Eqs. (4.2) and (4.3)) was used to estimate the frequency dependence of G′ and G′′ from a double logarithmic plot of G′ and G′′ against frequency as follows: G ′ = k ′ × 𝜔n

′

G′′ = k ′′ × 𝜔n

(4.2) ′′

(4.3)

Table 4.3 Frequency dependency of the elastic (k′ and n′ ), loss (k′′ and n′′ ) and complex (A and z) moduli, the complex viscosity slope (𝜂*s ), the molecular weight between crosslinks (Mc ), degree of crosslinking (X c ), number density of crosslinks (𝜐), the distance between sequential crosslinking points (𝜉), elastic active network chain (EANC) concentration, and the crossover frequency (f*) (1% w/w, 0.5% strain). Gum k′

n′

k′′

n′′

k′′ /k′

𝜼*s

A

z

Mc

Xc

XG

52.01b ± 1.07

0.15c ± 0.01

11.31b ± 0.11

0.08c ± 0.01

0.22c ± 0.00

−0.82c ± 0.02

54.10b ± 0.17

6.41c ± 0.17

52848.3c ± 205.7

1.88 × 10−5 b 1.74 × 1022 b ± 7.33 × 10−8 ± 6.76 × 1019

GG

4.79d ± 0.17

0.72a ± 0.04

8.32c ± 0.10

0.47a ± 0.02

1.67a ± 0.04

−0.46a ± 0.02

—

—

—

𝝊

—

𝝃

— −5

EANC

— 22

f*

3.85 × 10−8 c 0.027b 0.002c ± 1.50 × 10−10 ± 0.002 ± 0.000 —

5.130a ± 0.143

−8

18.29a ± 0.39

0.07c ± 0.01

0.15d ± 0.00

−0.87d 131.42a 9.30a ± 0.03 ± 1.27 ± 0.06

27100.7d ± 145.2

3.66 × 10 a 3.53 × 10 a ± 1.96 × 10−7 ± 1.89 × 1020

3.03 × 10 d 0.055a 0.000d ± 1.63 × 10−10 ± 0.053 ± 0.000

SSG 36.47c ± 0.75

0.11c ± 0.00

8.05c ± 0.08

0.13c ± 0.01

0.22c ± 0.00

−0.85c ± 0.02

39.79c ± 0.47

7.31b ± 0.29

90283.5b ± 413.7

1.10 × 10−5 c 9.69 × 1021 c ± 5.04 × 10−8 ± 4.44 × 1019

4.67 × 10−8 b 0.016b 0.002c ± 2.14 × 10−10 ± 0.002 ± 0.000

CSG 4.65d ± 0.18

0.40b ± 0.03

1.94d ± 0.06

0.30b ± 0.01

0.42b ± 0.03

−0.63b ± 0.01

4.88d ± 0.05

2.67d ± 0.06

142588.4a 6.91 × 10−6 d 6.04 × 1021 d ± 1491.0 ± 7.23 × 10−8 ± 6.32 × 1019

5.44 × 10−8 a 0.010c 0.038b ± 5.69 × 10−10 ± 0.000 ± 0.002

PE

120.43a 0.12c ± 1.27 ± 0.01

a–d: Means followed by the same letters in the same column are not significantly different (P > 0.05).

114

4 Transient and Dynamic Rheological Properties of Emerging Hydrocolloids

where k′ (Pa sn ) and k′′ (Pa sn ) are intercepts, n′ and n′′ are exponents or slopes of frequency dependence of G′ and G′′ , respectively, and 𝜔 is the angular frequency (rad s−1 ). The correlation (R2 value) between frequency and G′ or G′′ was high for all gum dispersions (0.891–0.953). It was found that all gums displayed gel-like behavior because the slopes (n′ = 0.110–0.725 and n′′ = 0.694–0.469) were positive and were much lower than those reported for a Maxwell fluid (G′ ∞ 𝜔2 and G′′ ∞ 𝜔). A similar trend was observed for both n′ and n′′ with respect to the gum type, in which GG showed the highest and SSG, XG, and PE, without any significant differences among them, showed the lowest values of both parameters. A low n′ value indicates elastic gel behavior, while for n′ values close to 1, the system behaves as a viscous gel [37]. This result suggests the general tendency of all dispersions to elastic gel, except for GG with a n′ of 0.725. The highest and lowest values for both k′ and k′′ parameters were obtained for PE and CSG, respectively. This parameter represents the stiffness of the continuous phase due to the thickening effect of the hydrocolloid. The magnitudes of k′ were much higher than k′′ for all gums, confirming the gel-like behavior of these systems, except for GG, which showed the opposite trend, as reflected by the k′ /k′′ ratio of 1.674. Based on a double logarithmic scale, the complex dynamic viscosity (𝜂*) of all gum samples decreased linearly with increasing frequency, indicating a non-Newtonian shear-thinning flow behavior. The highest value of the complex viscosity slope (𝜂* s ) was observed for PE (−0.867). Such behavior has been reported for XG, which creates a “weak-gel” network by the tenuous association of rigid, ordered molecular structures in solution [38, 39]. In a similar way, the 𝜂* s value for SSG and XG was substantially steeper than the maximum value of −0.76 which Morris [38] used to describe the “weak gel” characteristics of a polysaccharide gel formed by overlapping and entangled flexible random coil chains, whereas this parameter was −0.632 and −0.465 for CSG and GG, respectively. This result suggested strong shear-thinning flow behavior for PE, XG, and SSG, which can be explained in terms of higher entanglement formation as they take on a rigid conformation in solution [6, 7, 9], while GG and CSG adopt random coil and semi-rigid conformations, respectively, with a less entangled polymer solution [10, 11]. Except for GG, which showed concentrated solution rheological behavior, the network parameters of other hydrogel-forming hydrocolloids were determined and reported in Table 4.3. In this way, the molecular weight between crosslinks, Mc , the degree of crosslinking, X c , the number density of crosslinks, 𝜐, and the distance between sequential crosslinking points, 𝜉, can be calculated according to the following equations, using the frequency sweep data [40]: Mc =

𝜌RT Gp′

(4.4)

Xc =

M 1 ≈ Mc Mc

(4.5)

υ= 𝜉=

Gp′ NA RT (√ )−1 3 𝜐

(4.6) (4.7)

4.2 Viscoelastic Characteristics

where 𝜌 is the density (kg m−3 ), R is the gas constant (J mol−1 K−1 ), T is the temperature (K), G′p is the plateau storage modulus (Pa), N A is the Avogadro number (atoms/mole), and M is the molecular weight (g mol−1 ). CSG showed the highest Mc and 𝜉 values, whereas PE showed the lowest values of these parameters. On the other hand, the X c and 𝜐 of these two gums showed the opposite trend. Other hydrocolloids showed intermediate values for these parameters. The 𝜐 of the semi-crystalline and amorphous hydrogels vary, because semi-crystalline gels had additional net points by crystallite formation, which resulted in a greater distance between sequential crosslinking points [41]. These results suggested the highest gel strength for PE occurs with the highest number density of crosslinks and degree of crosslinking and the lowest distance occurs between sequential crosslinking points. To understand the strength of the network and the network extension, dynamic data were explained by a power-law relationship between the dynamic complex modulus (G*, Pa) and the frequency (𝜔, rad s−1 ) as follows [42]: 1

G∗ (𝜔) = A × 𝜔 Z

(4.8)

where z is the network extension, related to the number of interacting rheological units within the network (a higher z value corresponds to a more extended network), and A is the strength of the interactions (Pa s1/z ). Except for GG, which did not have a weak gel structure, the z and A parameters of other hydrocolloids were calculated, and the results are depicted in Table 4.3. PE and CSG showed the highest and the lowest values of the z parameter, respectively. The A parameter of different gum systems showed a similar trend as the X c and 𝜐 parameters, suggesting that the strength of the interactions and the number of interacting rheological units increased along with the number and density of subunits groups contributing to crosslinking and vice versa. The pseudo-equilibrium modulus, Ge , is a numerical measure of the structural contribution of the mechanical modulus. Ge is defined as follows [43]: ( ) 𝜌 Ge = g 𝜐e RT = g RT (4.9) Me where g is a numerical factor, 𝜐e is the moles of network stands per unit volume, 𝜌 is the density, Me is the average molecular weight between crosslinks, R is the universal gas constant, and T is the absolute temperature. 𝜐e , which is called the elastic active network chain (EANC) concentration, is directly proportional to the equilibrium modulus, and it quantitatively represents the structural contribution to the mechanical modulus. Generally, the numerical factor (g) is supposed to be unity. Then, from the plateau region of the frequency spectrum, Ge and 𝜐e (EANC) are estimated [43]. The EANC parameter was not accessible for GG, since this hydrocolloid did not demonstrate gel-like behavior. The highest value of EANC was observed for PE, followed by SSG and XG without any significant differences between the latter gums (Table 4.3). 4.2.1.2.1

Continuous Relaxation Spectrum

Timescales of various molecular motions can be plotted on a relaxation spectrum that describes chain dynamics [44]. The Generalized Maxwell model assumes that instead of a single relaxation time, the fluid has a distribution of relaxation times. If the number of elements in the Generalized Maxwell model is increased to infinity, a continuous

115

116

4 Transient and Dynamic Rheological Properties of Emerging Hydrocolloids

spectrum is obtained as follows [45]: +∞

G′ =

H𝜆2 𝜔2 d(ln(𝜆)) ∫−∞ 1 + 𝜆2 𝜔2

(4.10)

+∞

G′′ =

H𝜆𝜔 d(ln(𝜆)) ∫−∞ 1 + 𝜆2 𝜔2

(4.11)

where H (𝜆) is the continuous relaxation spectrum. The Tschoegl method was used to solve Eqs. (4.10) and (4.11) [46]. As the ±∞ limits of frequency were not accessible, the relaxation spectrum was determined in the operational frequency range of this study (0.01–10 Hz). Table 4.4 represents a number of valuable parameters obtained from the relaxation spectra of different gum dispersions. Macromolecular motion, also called structural relaxation, is accompanied by a reduction in chain stiffness, and thus mechanical network strength [44]. The relaxation time function of all gum dispersions slightly decreased with the increase in relaxation time up to a critical relaxation time point, C p (t), which marks the passage to a short-time behavior and usually indicated the onset of the glassy state [44], followed by an abrupt reduction in the relaxation time function in which the discrepancies in spectral decay are distinguished well. This parameter was the highest for PE (2.492 s) and the lowest for GG (0.086 s), while other hydrocolloids showed intermediate C p values (Table 4.4). A similar trend was obtained for 𝜆min with respect to the gum type. The structure corresponding to solid-like behavior is responsible for the short relaxation times (𝜆min ). It is theorized that the microstructural features of the gel network that are responsible for the short relaxation times include the suprafibers, and the relaxation processes taking place in the junctions will correspond to longer relaxation times [45]. In the other words, slow movements (at long relaxation times) are due to the repetition of the entire chain along its contour [44]. Other valuable parameters which could be obtained from the relaxation spectra are the proportion of the relaxation strengths at long relaxation times (𝜆max ) to the relaxation strengths at short relaxation times (𝜆min ), (H𝜆max /H𝜆min ), which shows the extent of network strength change; and d(H𝜆)/d𝜆, which represents the rate of mechanical network strength change with relaxation time. SSG and XG showed the lowest d(H𝜆)/d𝜆 value, while PE showed the highest d(H𝜆)/d𝜆 parameter, which demonstrated that although PE had the highest EANC and the lowest distance between sequential crosslinking points (𝜉) (Table 4.3), the stiffness of its network is more unstable and decreases at a greater Table 4.4 Relaxation spectrum and fracture parameters of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG). d(H𝝀)/d𝝀 (Pa s−1 )

Gum

H(𝝀min ) (Pa)

C p (Pa)

XG

11.157b ± 0.568

2.630d ± 0.133

0.724b ± 0.036

0.725a ± 0.037

GG

10.518b ± 0.378

4.564c ± 0.072

0.199d ± 0.016

0.053c ± 0.002 0.499b ± 0.018

H𝝀max /H𝝀min

PE

35.665a ± 0.205

12.099a ± 0.359

2.492a ± 0.030

SSG

8.520c ± 0.057

2.233d ± 0.083

0.596c ± 0.022

0.575b ± 0.019

CSG

10.518b ± 0.378

4.564c ± 0.072

0.199d ± 0.016

0.053c ± 0.002

a–d: Means followed by the same letters in the same column are not significantly different (P > 0.05).

4.2 Viscoelastic Characteristics

rate than SSG and XG. On the other hand, d(H𝜆)/d𝜆 was the highest for XG and the lowest for GG and CSG (without any significant differences between them). These results showed that the relaxation strengths at short relaxation times, the extent of network strength, and the kinetic parameters of network strength change (C p and d(H𝜆)/d𝜆) differ with respect to the gum type, which suggests different spatial arrangements (aligned or non-aligned hydrocolloids chains).

4.2.2 4.2.2.1

Transient Properties Creep Test

The creep test was carried out at 0.1 Pa (the minimum stress for the linear viscoelastic domain) for 400 s, and the shear strain (𝛾) ̇ was recorded for a further 600 s during the recovery procedure. It is worth mentioning that the lower limit of the stress to achieve the linear viscoelastic domain in the creep compared to the dynamic rheology test (0.5 Pa) may be attributed to the different time frames of the dynamic and transient rheological tests. The creep and recovery compliances (J C and J R ) were fitted by means of the four-component Burger model (Eq. (4.12)) and an empirical model (Eq. (4.13)) for creep and recovery phases, respectively, as follows [47]: [ ( )] t t JC = J0C + J1C 1 − exp − (4.12) + 𝜆ret 𝜂0 JR = J∞ + [J1R . exp(−at b )]

(4.13)

where J 0C is the instantaneous elastic compliance (Pa−1 ) of the Maxwell spring, J 1C is the elastic compliance (Pa−1 ) of the Kelvin–Voigt unit, 𝜆ret is the retardation time (in seconds) of the Kelvin–Voigt component, and 𝜂 0 is the Newtonian viscosity (Pa s) of the Maxwell dashpot. b is the order of reaction, and a is the parameter that defines the recovery speed of the system. J ∞ and J 1R are the recovery compliances of the Maxwell dashpot and Kelvin–Voigt elements, respectively. When t → 0, J R is equal to J ∞ + J 1R , which corresponds to the maximum deformation of the dashpots in the Burger model. For t → ∞, J R is equal to J ∞ , as it corresponds to the irreversible sliding of the Maxwell dashpot. The initial shear compliance, J 0R , was obtained by Eq. (4.14) as follows [48]: J0R = Jmax − (J∞ + J1R )

(4.14)

where J max is the maximum compliance for the longest time (300 s) in the creep transient analysis. Full mechanical characterization of a system can be established by calculating the contribution of the compliances in Eqs. (4.12) and (4.13) to the maximum deformation to which the system is subjected. The percentage deformation of each element of the system can be calculated by Je∗ =

Je JMax

× 100

(4.15)

where J e is the corresponding compliance: J 0C , J 1C , J 0R , J 1R, , and J ∞ . In this chapter, the percentage deformation of 𝜂 0 was also determined by the following relationship: ∗ ∗ ∗ = 100 − (J0c + J1c ) J2c

(4.16)

117

118

4 Transient and Dynamic Rheological Properties of Emerging Hydrocolloids

In addition, the final percentage recovery (%R) of the entire system was calculated by the following equation [48]: ] [ Jmax− J∞ × 100 (4.17) %R = Jmax When the stress was applied, there was an instantaneous increase in strain, followed by a gradual increase over time for all samples, which can be attributed to the rearrangement of the network structure. The initial recovery corresponds to the spring of the Maxwell element (J 0R ), while the gradual increase in strain is the recovery due to the Kelvin–Voigt element (J 1R ). In the end, a residual or permanent deformation due to the irreversibility of the Maxwell dashpot sliding is depicted [49]. Compliance curves for creep and recovery phases of all hydrocolloids were successfully fitted with the Burger model (R2 ≥ 0.821 and RMSE ≤ 0.881) and the empirical model (R2 ≥ 0.89 and RMSE ≤ 0.05), respectively, and the resultant parameters are summarized in Table 4.5. GG showed the highest maximum compliance (J max ), whereas PE and XG showed the lowest value of this parameter, indicating the greatest strength of the structure for the latter hydrocolloids. The most important contribution of the Maxwell ∗ ≈ 35.40%), were those spring to deformation, at creep (J 0C ≈ 30.40%) and recovery (J0R corresponding to the PE, while GG showed the lowest value of these parameters (Table 4.5). J 0C represents the value of the instantaneous shear creep compliance at the initial time, and it may be related to the undisturbed hydrocolloid network structure and gel rigidity [50]. This is in agreement with the results earlier observed for the G′ LVE behavior, in which PE showed the highest value of this parameter (Table 4.1). 𝜂 0 , which represents the Newtonian flow viscosity, was the lowest for GG (38 Pa s) followed by CSG (569 Pa s) and the highest for PE (11730 Pa s). The contribution of the Maxwell ∗ ) were the highest dashpot to deformation at the creep (J 2C * ) and recovery stages (J2R for GG followed by CSG and SSG, indicating the lowest resistance to flow at longer times for GG [51]. Also, the viscosity flow deformation percentage in creep/recovery ∗ ) played the most important role for GG among other compliprocesses (J 2C * and J2R ances. The retarded compliance (J 1C ) represents the component of the viscoelastic behavior. So, the highest value of this parameter in the creep/recovery processes for PE and the lowest values for GG are associated with a greater elasticity of the Kelvin–Voigt ∗ were element in the former and latter systems, respectively. In addition, J 1C and J1R the most important compliances for PE at the creep and recovery stages, respectively. There were no significant differences among XG, PE, SSG, and CSG, while GG showed a higher value of the retardation time (𝜆ret ). The Voigt unit represents an orientation of intermeshed macromolecules during which secondary bonds are breaking and re-forming [52]. GG takes on a random coli conformation with less chain stiffness than XG, PE, SSG (rigid), and CSG (semi-rigid) [6, 7, 9, 10, 12], which leads to a less entangled macromolecule with a shorter timescale of segment–segment interaction than other gums. This structure requires a shorter time for new entanglements to replace those disrupted by an externally imposed deformation, which results in a higher retardation time. This also implies that retardation time is inversely related to network viscoelasticity; that is, the lower the level of 𝜆ret , the higher the elastic character of the sample [11]. The order of the recovery reaction (b parameter) was almost the same for all gums, while the speed of the recovery phase (a parameter) was the highest for PE and the lowest for GG, while other hydrocolloids showed intermediate values of

Table 4.5 Maximum compliance and the creep/recovery normalized parameters obtained for sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG). Creep Paramete r XG

Recovery

SSG

PE

GG

CSG

0.01e 1 ± 0.00

0.16d 1 ± 0.01

∗ J0C (−)

0.25b 1 ± 0.01

0.21c 1 ± 0.01

0.30a 2 ± 0.01

XG

SSG

PE

GG

CSG

∗ J0R (−)

0.25b 1 ± 0.01

0.31c 1 ± 0.01

0.35a 2 ± 0.01

0.01e 1 ± 0.00

0.17d 1 ± 0.01

0.47a 3 ± 0.02

∗ (−) J1C

0.50b 2 ± 0.01

0.47b 3 ± 0.02

0.56a 3 ± 0.04

0.18d 2 ± 0.03

0.40c 2 ± 0.00

∗ J1R (−)

0.42ab 2 ± 0.01 0.30c 1 ± 0.01

∗ (−) J2C

0.25c 1 ± 0.01

0.32bc 2 ± 0.02 0.14d 1 ± 0.06

0.81a 3 ± 0.03

0.42b 2 ± 0.05

∗ J2R (−)

0.27c 1 ± 0.00

0.39b 2 ± 0.00 0.17c 1 ± 0.03

0.80a 3 ± 0.08

𝜂 0 (Pa s)

8773b ± 751

2432c ± 389

569d ± 88

a

0.09b ± 0.02

0.08b ± 0.01

0.14a ± 0.01

0.01d ± 0.00

0.05c ± 0.01

𝜆ret (s)

18.04b ± 3.85 13.76b ± 0.85

11.44b ± 1.07

115.57a ± 15.75 24.05b ± 0.56 b

0.62a ± 0.03

0.62a ± 0.02

0.63a ± 0.03

0.67a ± 0.02

0.66a ± 0.03

11730a ± 1600 38e ± 1

0.19d 2 ± 0.08 0.36c 2 ± 0.04 0.47b 3 ± 0.04

JMax (1 Pa−1 ) 0.07d ± 0.00

0.33c ± 0.00

0.07d ± 0.00

12.50a ± 0.57

1.55b ± 0.06

%R

73.10b ± 0.05

61.10c ± 0.15 82.81a ± 2.63 14.79e ± 8.54 46.72d ± 1.32

R2 adj

0.967

0.930

0.972

0.999

0.950

R2 adj

0.998

0.999

0.999

0.821

0.999

RMSE

0.003

0.026

0.003

0.040

0.083

RMSE 0.000

0.001

0.002

0.881

0.002

a–d: Means followed by the same letters in the same column are not significantly different (P > 0.05).

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4 Transient and Dynamic Rheological Properties of Emerging Hydrocolloids

the a parameter. The final percentage recovery behaved similarly to the a parameter. The higher the final percentage recovery value (%R), the higher the viscoelastic solid property of the sample [53]. In PE with the highest %R, only 17.19% of the links were irreversibly broken during the creep test. 4.2.2.2

Stress Relaxation Test

The rheological properties which are determined by the stress relaxation test are related to the properties of crosslinking in gel networks [54]. The stress relaxation test was made at a constant strain of 0.3%, and 25 ∘ C, and the stress was recorded for 400 s. In order to predict the different patterns of viscoelasticity, the stress relaxation data were reduced to viscoelastic parameters by fitting an appropriate model to the stress-time experimental data. Three common viscoelastic models, that is, the Generalized Maxwell (Eq. (4.18)), Peleg (Eq. (4.19)), and Nussinovitch (Eq. (4.20)) were used as follows [47]: ( ) n ∑ t 𝜎t = 𝜎e + 𝜎i exp − (4.18) 𝜏i i=1 where 𝜎 t is the time-dependent stress, 𝜎 e is the stress in the elastic element, 𝜎 i is the stress in the combined viscous-elastic elements, t is time, and 𝜏 i is the relaxation time of the combined viscous-elastic elements. The Nussinovitch model is a simplified Generalized Maxwell model which assumes 10, 100, and 1000 as the relaxation times of the first, second, and third dashpot elements in the model. This model has been formulated for three viscous elements as follows [55]: ) )) ( ( ) ( ( −t −t −t 𝜎t = 𝜎0 A1 + A2 exp + A3 exp + A4 exp (4.19) 10 100 1000 where 𝜎 0 is the initial stress, t is time, and A1 , A2 , A3 are constants. Peleg [56] proposed an empirical model as follows: 𝜎0 t (4.20) = k1 + k2 t 𝜎0 − 𝜎(t) where the equilibrium stress, 𝜎 e , is calculated as ( ) 1 (4.21) 𝜎e = 𝜎0 1 − k2 The constants k1 and k2 are obtained by linear regression. The advantages of this model are that if the data follow the linear relationship shown in Eq. (4.20), constants k1 and k2 will be independent of the test duration; also, this model predicts the complex behavior of materials (nonlinearity) well [57]. The Peleg model is the best approach for all the hydrocolloids (R2 = 0.912–0.976 and RMSE = 0.015–0.065) employed for data modeling of stress relaxation data, and the corresponding data are represented in Table 4.6. The stress relaxation rate, that is, the initial decay rate, is represented by the constant 1/k1 values. The initial decaying rate was the highest for GG followed by CSG, while there were no significant differences between the other three hydrocolloids. The physical significance of the k1 value ought to be interpreted with caution since many materials initially relax fast; in addition, the shape of the very initial part of the recorded relaxation curves is strongly influenced by the deformation history of the sample. On the other hand, the value of k2 is more indicative of the general rheological characteristics of materials. 1/k2 differed among hydrocolloids in the following order: GG ≈ CSG > SSG > XG ≈ PE. It is reported that k2 represented the degree of solidity,

4.2 Viscoelastic Characteristics

Table 4.6 Pleg model parameters and Deborah number (De ) of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG). Gum

1/k1 (1 s−1 )

1/k2 (–)

𝝀 (s)

XG

0.45c ± 0.03

0.73c ± 0.04

11.75b ± 2.32

21.17a ± 1.99

0.029ab ± 0.009

GG

8.11a ± 0.73

0.97a ± 0.03

0.42d ± 0.02

0.01d ± 0.00

0.001c ± 0.000

PE

0.19c ± 0.02

0.73c ± 0.02

26.58a ± 2.85

24.64a ± 1.92

0.066a ± 0.018

SSG

1.51c ± 0.35

0.81b ± 0.01

2.02c ± 0.56

13.40b ± 0.30

0.005b ± 0.001

CSG

3.30b ± 0.24

0.88ab ± 0.01

0.78d ± 0.03

2.32c ± 0.03

0.002c ± 0.000

𝝈 e (Pa)

De (−)

a–d: Means followed by the same letters in the same column are not significantly different (P > 0.05).

and it varies between the value of k2 = 1 for a material that is truly a liquid (i.e., all the stress relaxes) to k2 → ∞ for an ideal elastic solid where the stress does not relax at all [57]. The reciprocal of k2 denotes the asymptotic value of the relaxed portion of the initial stress and represents the portion of the stress that would have remained unrelaxed at equilibrium [56]. This result suggests more solid-like behavior for PE and XG, whereas GG and CSG showed liquid-like behavior in the stress relaxation test time scale. According to Table 4.6, 𝜎 e was the highest for XG and PE, whereas it was the lowest for GG. The equilibrium stress following relaxation is positively related to gel strength and reflects the degree of crosslinking in the polymer network [54]. It was reported that the relaxation time is the time required for the viscoelastic material to dissipate its force to about 36.8% (1/e) of the original applied force [58]. Accordingly, we supposed that when the stress reached the 1/e value of 𝜎 0 , the materials yielded, and this time was reported as the relaxation time (𝜆). This parameter differed from the 1/k1 parameter, as the latter parameter concerns just the time dependency at t = 0, while the former one shows the total time dependency of the samples’ structure during the test and is a measure of how fast the structure relaxes. The 𝜆 parameter varied among hydrocolloids in the following order: PE > XG > SSG > GG ≈ CSG. It was also reported that the softness of the gel samples and the lower polysaccharide entanglement resulted in fast dissipation of the force [59], and higher values of 𝜆 show that the sample is firmer and more elastic [60]. The relaxation time is an important index since it can be used for calculation of the Deborah number [61], which is the ratio of the relaxation time to the observation time, which is 400 s in this study. The Deborah number is used to determine the viscoelastic behavior of the material. De ≪ 1 indicates viscous fluid behavior, De ≫ 1 indicates an elastic character, and De ≈ 1 indicates viscoelastic behavior [61]. As seen in Table 4.6, De values are lower than 1, indicating the dominant viscous behavior of all hydrocolloids in the relaxation stress test. 4.2.3 Comparison of Dynamic Rheology and Steady Shear: The Cox–Merz Rule According to linear viscoelasticity theory, the dynamic viscosity can be represented as follows [62]: 𝜆rel (4.22) 𝜂 ′ (𝜔) = G (1 + (𝜔 × 𝜆rel )2 )

121

122

4 Transient and Dynamic Rheological Properties of Emerging Hydrocolloids

where G is the shear modulus (Pa), and 𝜆rel is the relaxation time. As the relaxation time 𝜂 is the ratio of the viscosity to the shear modulus ( Ga ), we can rewrite Eq. (4.22) on the basis of the relationship between the dynamic and shear viscosity as follows: 𝜂a (4.23) 𝜂 ′ (𝜔) = (1 + (𝜔 × 𝜆rel )2 ) Then, in the linear viscoelastic limit for a material, the dynamic viscosity is related to the zero shear rate viscosity as follows: ̇ ∣ 𝛾̇ → 0) 𝜂 ′ (𝜔 → 0) ≈ (𝜂a (𝛾)

(4.24)

′

When the dynamic viscosity (𝜂 ) dominates the material response, and the viscosity contribution from the “elastic–plastic” region 𝜂 ′ can be neglected, the magnitude of complex viscosity (𝜂 * ) and the value of 𝜂 ′ are almost equal. For this condition, Eq. (4.24) changes to ̇ ∣ 𝛾̇ → 0) 𝜂 ∗ (𝜔 → 0) ≈ (𝜂a (𝛾)

(4.25)

Equation (4.25) is valid in the LVE, but for some materials, this rule can be extended into the nonlinear response regime when the frequency and shear rate are equal, provided that the shear-thinning behavior under small and large deformations is almost the same, which is known as the Cox–Merz rule. ̇ ∣ 𝛾̇ = 𝜔) 𝜂 ∗ (𝜔) = (𝜂a (𝛾)

(4.26)

Also, the materials can obey the generalized Cox–Merz rule when a shift factor is introduced to give the following form [63]: ̇ ∣ 𝜔 = c𝛾) ̇ |𝜂 ∗ |(𝜔) = (𝜂(a𝛾)

(4.27)

where a is the shift factor. In this study, the correlation between the complex and apparent viscosity was compared using the generalized Cox–Merz rule at the shear rate and frequency ranges of 0.01–700 s−1 and 0.01–10 Hz, respectively, and the shift factors are shown in Figure 4.4. Only GG obeyed the Cox–Merz rule, while other hydrocolloids obeyed the generalized Cox–Merz rule. The extent of departure from the Cox–Merz rule was studied by measuring the ̇ and the complex viscosity area between the apparent viscosity (𝜂 a )–shear rate (𝛾) (𝜂 * )–angular frequency (𝜔) curves. This area was calculated by the difference between the integrals of the area for 𝜂 a -𝛾̇ and 𝜂 * -𝜔 measurements: ) ( 𝝎 𝛾̇ abs ∫𝝎 𝜂 ∗ d𝜔 − ∫𝛾̇ 𝜂a d𝛾̇ 𝟎 𝟎 %𝛽 = × 100 (4.28) 𝝎 ∗ ∫𝝎 𝜂 d𝜔 𝟎

Departures from the Cox–Merz rule are attributed to the presence of high-density entanglements resulting from very specific polymer–polymer interactions. Except for GG, which showed a negligible departure value (𝛽), for other gum dispersions, 𝜂* was higher than 𝜂 a , which is explained by structure decay due to the effect of deformation exerted on the system. This effect is low in oscillatory shear, but is high enough in steady shear to break down intermolecular associations. So, in this situation, the complex viscosity is usually higher than the apparent viscosity [13, 64]. The extent of departure (𝛽) from the Cox–Merz rule was the highest for PE (85.35) followed by SSG (71.73). A similar trend was observed for the shift factor value of the generalized Cox–Merz rule, 𝛼,

4.2 Viscoelastic Characteristics

with respect to the gum type (Figure 4.4). It is well known that for solutions of entanglement systems, the magnitude of the complex viscosity and the apparent viscosity are closely superimposed at equivalent values of the deformation rate. So, higher departures from the Cox–Merz rule demonstrated the characteristics of a weak gel to a greater degree. The pseudoplasticity in the large and small deformation modes was compared between different hydrocolloids by comparing the 𝜂 ′ /𝜂 a (dynamic viscosity at small deformation to apparent viscosity at large deformation) at various frequencies/shear rates. On the basis of the Eq. (4.24), at small magnitude of frequencies/shear rates, the values of 𝜂 ′ and 𝜂 a are equal, and the 𝜂 ′ /𝜂 a ratio shifts to unity. A decrease in 𝜂 ′ /𝜂 a with an increase in the strain rate, which occurred for SSG and CSG, suggested greater shear-thinning behavior in the small deformation mode, whereas the opposite behavior of XG and PE suggested greater shear-thinning behavior in the large deformation mode. The shear-thinning behavior under small and large deformations was almost the same for GG, which was reflected by an unchanged 𝜂 ′ /𝜂 a with shear rate/frequency. These behaviors are associated with different shear-thinning mechanisms in small and large deformation modes of various hydrocolloids (Table 4.7).

%φ

100

100

10

10

1

CSG

PE

SSG

GG

XG

Shift factor

Shift factor

%φ

1

Figure 4.4 Shift factor (a) and the extent of departure (𝛽) from the Cox–Merz rule (𝜑) of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG). Table 4.7 Magnitude of apparent viscosity to dynamic viscosity (ηa /η′ ) of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG) at various angular frequencies. Frequency (rad s−1 )

XG

GG

PE

SSG

CSG

0.0628

1.122c ± 0.096

1.009a ± 0.019

0.816d ± 0.015

1.032a ± 0.015

0.89a ± 0.014

0.6280

1.555b ± 0.035

1.098a ± 0.005

1.420c ± 0.050

0.818b ± 0.019

0.545b ± 0.049

6.2800

1.705a ± 0.035

1.124a ± 0.026

1.679b ± 0.008

0.487c ± 0.036

0.360c ± 0.014

62.8000

1.74a ± 0.028

1.082a ± 0.039

2.075a ± 0.035

0.425c ± 0.035

0.335c ± 0.035

a–d: Means followed by the same letters in the same column are not significantly different (P > 0.05).

123

4 Transient and Dynamic Rheological Properties of Emerging Hydrocolloids

4.2.4

Yield Stress

It is known that any material has a range of yield stress that depends on how they are measured [65]. Dynamic mechanical measurement is a valuable technique for the determination of the yield stress. The crossover stress (𝜏 f at G′ = G′′ ) is a good indicator of the yield stress when the structure ruptures and the flow behavior starts [66]. As the time frame of yield measurement is a key parameter, in our previous study [17], we obtained the yield stress under large deformation as a crossover point in the amplitude sweep test, which represented the yield stress over a short time scale (𝜏 0s ), and the yield stress under small deformation as a crossover point in the frequency sweep test (using the Cole–Davidson model) which occurred over a long time scale (𝜏 0l ). To obtain these parameters for the five mentioned hydrocolloids, strain sweep tests were conducted in the range of 0.01%–100% strain at a constant frequency of 1 Hz, and the frequency sweep measurements were performed within the LVE range over a frequency range of 0.01–100 Hz. The extent of shift (Es ) in the crossover points (the difference between the yield stresses over short and long time scales) was calculated as follows [17]: √ (4.29) Es = ((t0s − t0l )2 + (𝜏0s − 𝜏0l )2 ) where t0l is the time of observation in the small deformation domain (the reciprocal of the frequency at the crossover point in the frequency sweep test), t0s is the time of observation in the large deformation domain (the reciprocal of the frequency at the crossover point in the amplitude sweep test). As shown in Figure 4.5, PE showed the highest 𝜏 0s value among all gums (35.76 Pa), while GG showed the lowest value of this parameter (0.30 Pa), and the other gums showed intermediate values. The yield stress is correlated with the strength of the coherent network structure throughout the volume of the material [26]. This result confirmed the greatest strength of PE and the weakest structure for GG. In addition, we determined the reciprocal of the frequency at the crossover points that represented the time at which each shear stress was observed. For all gum dispersions, the longer the observation period, the lower the yield stress measured, which confirmed that the yield stress is a time-dependent property [65]. As strain XG

Guar

PE

SSG

CSG

100.00

Yield stress (Pa)

124

10.00

1.00

0.10 0.10

1.00

10.00

100.00

1000.00

Time of observation (s)

Figure 4.5 Time length of observation between the yield stress over short and long time scales of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG).

4.3 Cluster Analysis

sweep tests were performed at a constant frequency of 1 Hz for all gum systems, the time at which 𝜏 0s occurred was the same for all gum dispersions. The highest time interval between 𝜏 0l and 𝜏 0s was obtained for PE, while the shortest distance was for GG. As the observation time of t0l varied among different gums, one can conclude that PE demonstrated the longest-lasting structure under small deformation. It is worth mentioning that in the time interval between t0l and t0s , the magnitudes of 𝜏 0l and 𝜏 0s of SSG were surprisingly close to those of XG (Figure 4.5). The distances between crossover points in the amplitude sweep and frequency sweep tests (Es ) were calculated in Cartesian space. Results showed that the extent of yield stress shift was the highest for PE (223.29), while this parameter was the lowest for GG (0.81). This behavior confirmed the highest rigidity of PE chains and the random coil conformation of GG.

4.3 Cluster Analysis One of the most important unsupervised learning problems is clustering. This procedure is used for statistical data analysis in many fields, such as data mining. There are many clustering methods, such as the hierarchical clustering method. The agglomerative hierarchical method is a subclass of hierarchical clustering. Hierarchical clustering finds successive clusters using previously established clusters and merges them until the desired cluster structure is obtained [3]. PCA is a statistical method which uses sophisticated underlying mathematical principles to transform a number of possibly correlated variables into a smaller number of linearly uncorrelated variables called principal components [67]. Here, the similarity of the dynamic and transient shear rheological properties of two novel gums (SSG and CSG) with three commercialized biopolymers (GG, XG, and PE) were investigated by using the agglomerative hierarchical clustering technique (bottom-up) and the PCA in a serial mode. In addition, the Euclidean distance, computed by finding the square of the distance between each variable, summing the squares, and finding the square root of that sum, was used as a distance measure [68]. The dynamic and transient shear rheological properties of five hydrocolloid dispersions were given by 52 parameters. As a high number of rheological parameters are introduced in this chapter, to use PCA for clustering, we applied a screening filter. Initially, the 52 parameters were classified into 5 categories with more than 65% similarity indexes in each group using agglomerative hierarchical clustering (Table 4.8). The first to fifth groups contained those variables associated with the elastic component, viscous component, viscoelastic component, plasticity, and conformation of hydrocolloids, respectively. Then, from each group, only one parameter, which represented one of the rheological aspects of matter (boldfaced parameter), was randomly selected for clustering. These five parameters were EANC concentration, the power-law model’s exponent of the double logarithmic plot of G′′ against frequency (n′′ ), the ratio of the power-law model’s intercepts of the double logarithmic plot of G′ and G′′ against the frequency (k′ /k′′ ), plastic dissipation index (𝜑), and the slope of the double logarithmic scale plot of complex viscosity versus frequency (𝜂* s ). The Scree plot indicated that just two components can evaluate more than 90% of variances in the data (data not shown), and thus they were used for clustering analysis. According to Figure 4.6, the score plot for the first two components verified that

125

Table 4.8 Clustering of dynamic and transient rheological parameters of sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG) based on similarity index (S.I). A (S.I: 84.75)

B (S.I: 75.45)

D (S.I: 75.65)

E (S.I: 81.25)

K′ (intercept of elastic modulus vs. frequency curve’s power-law model)

n′′ (slope of viscous modulus vs. frequency curve’s power-law model)

J 1R (recovery due to the Kelvin–Voigt element)

C (S.I: 65.63)

a (speed of recovery phase)

Tan (𝛿)AF (slope of loss tangent after flow point)

𝜼* s (slope of complex viscosity vs. frequency curve’s power-law model)

G′ LVE (elastic modulus at the LVE)

J max (maximum compliance)

J 1C (retarded compliance)

λ (time for reaching 1/e G0 )

(𝛾 Fr -𝛾 L )/ 𝛾 Fr % (Ductility)

d(H𝜆) (the rate of d𝜆 mechanical network strength change with relaxation time)

Xc (degree of crosslinking)

J 2C * (contribution of the Maxwell dashpot to deformation at creep)

𝜎 e (equilibrium stresses)

f * (crossover frequency)

𝝋 (plastic dissipation index)

Extent of shear thinning

EANC (elastic active network chain concentration)

∗ (contribution of the J2R Maxwell dashpot to deformation at recovery)

A (intercept of complex modulus vs. frequency curve’s power-law model)

Tan (𝛿)LVE (loss tangent at the LVE)

′ 𝜂L′ ∕𝜂M (10) (viscous-related nonlinear behavior at 100% strain)

𝜐 (number density of crosslinks)

𝜉 (the distance between sequential crosslinking points)

1/k2 (asymptotic value of the relaxed portion of the initial stress)

max (ratio of H𝜆min relaxation strengths at long relaxation time to short relaxation time)

H𝜆

G′′ p /G′′ LVE (extent of viscous modulus overshoot)

J 0C % (instantaneous elastic compliance)

𝜂 0 (Newtonian flow viscosity)

Db (Debora number)

H𝜆min (relaxation strengths at short relaxation time)

—

′ (100) 𝜂L′ ∕𝜂M (viscous-related nonlinear behavior at 100% strain)

J 0R % (initial recovery compliance)

K′′ (intercept of G′′ vs. frequency curve’s power-law model

1/k1 (decay rate)

C p (critical relaxation time point)

—

𝛽 (extent of departure from Cox–Merz rule)

𝜏 Fr (Fracture stress)

—

z (network extension)

K′′ /K′ (the ratio of power-law model’s intercepts of the double logarithmic plot of G′ and G′′ against frequency)

—

′ GL′ ∕GM (10) (elastic-related nonlinear behavior at 10% strain)

𝜆ret (retardation time)

′ GL′ ∕GM (100) (elastic-related nonlinear behavior at 100% strain)

G1′ reduction ratio α (shift factor) Extent of shear thickening b (order of recovery reaction) Es (extent of shift in crossover points) Bolded parameters were randomly selected for clustering.

4 Transient and Dynamic Rheological Properties of Emerging Hydrocolloids

CSG

SSG

XG

GG

PE

3 2 Second component

128

1

–3

–2

0

–1

0

1

2

3

–1 –2 –3 First component

Figure 4.6 Distribution and correlation between the studied hydrocolloids in a vector space.

from the rheological characteristics point of view (dynamic and transient shear rheological properties), CSG and SSG are more similar to GG and XG, respectively. The most effective rheological parameters in hydrocolloids clustering analysis were 𝜂* s , a conformation-related parameter (0.58 coefficient for PC1 ) and 𝜑,, which is related to the structure of hydrocolloids (0.55 coefficient for PC1 ), whereas n′′ demonstrated the least influence (0.29 coefficient for PC1 ) on hydrocolloids clustering (data not shown). Euclidean distances were calculated to quantitatively represent the similarity of different gums in the score plot as follows [68]: √ dij = (Xi − Xj )2 + (Yi − Yj )2 (4.30) where dij is the Euclidean distance between a point X (X1, X2, etc.) and a point Y (Y1, Y2, etc.). According to Table 4.9, among the different commercialized hydrocolloids, SSG showed the lowest Euclidean distance with XG (0.63) and the highest distance with GG (2.42) and PE (2.07); in contrast, CSG showed the lowest Euclidean distance with GG (1.44) and the highest distance with XG (2.92). Besides, among galactomannans, Table 4.9 Euclidean distance between sage seed gum (SSG), cress seed gum (CSG), xanthan (XG), pectin (PE), and guar gum (GG) in the vector space. Gum

XG

GG

PE

SSG

CSG

XG

0.00

3.19b ± 0.10

1.80d ± 0.04

0.63c ± 0.06

2.49b ± 0.05

GG

3.19a ± 0.10

0.00

4.28a ± 0.06

2.42a ± 0.24

1.44d ± 0.07

PE SSG CSG

c

1.80 ± 0.04 d

0.63 ± 0.06 b

2.49 ± 0.05

a

0.00

c

4.28 ± 0.06 2.42 ± 0.24 d

1.44 ± 0.07

ab

2.07 ± 0.05

2.92a ± 0.06

c

0.00

1.84c ± 0.07

b

b

2.07 ± 0.05 2.92 ± 0.06

1.84 ± 0.07

0.00

a–d: Means followed by the same letters in the same column are not significantly different (P > 0.05).

4.4 Conclusion and Future Trends

SSG showed the highest similarity with PE with the lowest Euclidean distance magnitude. The variation in SSG and GG rheological behaviors could be related to the fact that although SSG and GG are galactomannans with approximately the same molecular weight (≈103 kDa for GG [6] and 4 × 102 –1.5 × 103 kDa for SSG [10, 11]), SSG is a polyelectrolyte hydrocolloid whereas GG is a neutral polysaccharide. These physicochemical properties are reflected by the higher intrinsic viscosity of SSG (22.55 dl g−1 [10]) compared to that of GG (12.5 dl g−1 [6]). Also, it was expected that CSG, a polyelectrolyte galactomannan, would be similar to SSG rheologically, whereas it was similar to GG, which could be attributed to the lower molecular weight of CSG (540 kDa) compared with SSG. On the other hand, the polyelectrolyte nature of CSG could compensate for its negative effect of the lower molecular weight in comparison with GG, resulting in the greater similarity with GG, which is reflected in the similar intrinsic viscosity of CSG (13.3 dl g−1 [12]). The lowest Euclidean distance between SSG and XG may be attributed to the likeness of their conformation (rigid conformation of SSG and XG) [7, 10].

4.4 Conclusion and Future Trends To better understand the elastic, viscous, and viscoelastic characters behavior of two novel hydrocolloids, SSG and CSG, and compare them with three generally used hydrocolloids, GG, XG, and PE, experiments based on unsteady state deformations, that is, oscillatory (in linear and nonlinear regions) and transient tests (in the linear region), were employed, and the similarity of these five hydrocolloids were investigated using the agglomerative hierarchical clustering technique and PCA. PE showed the highest storage modulus, complex modulus, limiting value of stress, fracture stress, and the slope of the loss tangent after the flow point and the lowest limiting value of strain, loss tangent, fracture strain, and reversible extensibility ahead of fracture among other hydrocolloids in the small deformation strain sweep test. XG, PE, and SSG showed G′′ overshoot and were categorized as weak strain overshoot, whereas GG and CSG demonstrated strain thinning behavior. Only hydrocolloids which showed overshoot in G′′ showed fracture properties. PE showed the highest, and GG, as well as CSG, showed the lowest values of spreadability, which were determined on the basis of the slope of the loss tangent after flow point stress (tan 𝛿 AF ). Qualitative investigation of LAOS flow revealed ideal viscoelastic behavior for XG, PE and SSG up to 1% and for GG and CSG up to 10% strain. These results were quantitatively confirmed by G3′ ∕G1′ and G3′′ ∕G1′′ > 0.01 for XG, PE, and SSG at 10% and 100% and GG at 100% strain. Using the Ewolt (2008) procedure, XG, PE and SSG showed intracycle strain-stiffening behavior and GG showed strain-softening behavior in their nonlinear strain domains. A full cycle study by Fourier series showed intercycle strain-softening behavior for all the hydrocolloids at the 0.1%–10% and 0.1–100% strains, although XG, PE, and SSG showed greater first harmonic elastic modulus (G1′ ) reduction than did GG and CSG. In addition, except for GG, which did not show intercycle shear-thickening behavior, the first harmonic viscous component of other gum dispersions showed different three-stage dynamic viscosity versus shear rate responses with the Newtonian, shear-thickening, and shear-thinning behaviors in order. Among different parameters, intercycle nonlinearities were the most distinguishing parameters for different

129

130

4 Transient and Dynamic Rheological Properties of Emerging Hydrocolloids

hydrocolloids. With an increase in strain, the plastic dissipation index (𝜑) values of SSG, XG, and PE approached the perfect plastic limit 𝜑 → 1, while it approached to the Newtonian fluid reference value (𝜑 ≈ 𝜋/4 ≈ 0.785) for CSG and GG. There was great correlation between 𝜑 and tan 𝛿 AF , which suggests the applicability of the 𝜑 parameter to determine the spreadability of materials. Over the frequency range 0.01–10 Hz, only GG showed the crossover frequency, while other hydrocolloids behaved as weak gels. The highest pseudoplasticity of PE in the dynamic shear rheological test in the small deformation mode is reflected by the highest 𝜂 ′ ratio reduction and the complex viscosity versus frequency slope (−0.867). Also, PE showed the highest gel strength, the highest number density of crosslinks, degree of crosslinking, EANC concentration, and the lowest distance between sequential crosslinking points among different hydrocolloids. Different relaxation spectra of hydrocolloids were investigated, and the results showed that the relaxation strengths at a short relaxation time, the extent of network strength, and the kinetic parameters of network strength change (C p and d(H𝜆)/d𝜆) differed with respect to the gum types, which suggested different spatial arrangements. The most important contribution of the Maxwell spring to ∗ ≈ 35.40%), were those cordeformation, at creep (J 0C ≈ 30.40%) and recovery (J0R responding to PE, while GG showed the lowest value of these parameters. PE also had the highest recovery percentage during the creep/recovery test. The transient rheological behavior of hydrocolloids was investigated by using three well-known viscoelastic models to fit the experimental data, where the Peleg model described the viscoelastic characteristics of all hydrocolloids appropriately, as compared to the Generalized Maxwell and Nussinovitch models. The Pleg model data suggested greater solid-like behavior for PE and XG, whereas GG and CSG showed liquid-like behavior in the stress relaxation test time scale. Except for GG, other hydrocolloids exhibited departure from the Cox–Merz rule, while PE showed the highest departure (85.35) followed by SSG (71.73). The yield stresses over a short time scale (𝜏 0s ) and over a long time scale (𝜏 0l ) were determined. PE showed the highest 𝜏 0s value (35.76 Pa), while GG showed the lowest value of this parameter (0.30 Pa). In addition, the highest time interval between 𝜏 0l and 𝜏 0s was obtained for PE, while the shortest distance was for GG, which confirmed the highest rigidity of PE chains among the hydrocolloids. The hierarchical clustering technique with PCA indicated the highest similarity of SSG with XG and CSG with GG. In addition, the plastic dissipation index (𝜑) and the slope of the double logarithmic scale plot of complex viscosity versus frequency (𝜂* s ) were determined as the most effective rheological parameter in hydrocolloids clustering analysis. These results can help the manufacturer decide on the final usage of SSG and CSG in various food formulations on the basis of the similarity of their oscillatory and transient rheological behaviors to the commercialized hydrocolloids, XG, GG, and PE. The approach presented in this chapter will help food scientists to gain a better insight into the structure–function relationship between hydrocolloids. In addition, the similarity of other physicochemical and structural properties of novel hydrocolloids could be investigated using the hierarchical clustering technique and PCA. Further work in this area is necessary for assessing the applicability and limitations of the emerging hydrocolloids in food and pharmaceutical systems.

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rate dependence of viscosity in random coil polysaccharide solutions. Carbohydrate Polymer 1: 5–21. Barnes, H.A. (2000). A Handbook of Elementary Rheology. Aberystwyth: University of Wales, Institute of Non-Newtonian Fluid Mechanics. Ross-Murphy, S.B. (1988). Small deformation measurements. In: Food Structure-Its Creation and Evaluation (ed. J.M.V. Blanshard and J.R. Mitchell). London: Butterworth Publishing Co. Alghooneh, A., Razavi, S.M.A., and Behrouzian, F. (2016). Flow behavior, thixotropy and viscoelastic characterization of biopolymer blends: sage seed gum-xanthan gum blends as a case study. Food Hydrocolloids 57 (21): 9609–9621. Morris, E.R. (1990). Shear-thinning of ‘random coil’ polysaccharides: characterisation by two parameters from a simple linear plot. Carbohydrate Polymer 13: 85–96. Rafe, A. and Razavi, S.M.A. (2013). Dynamic viscoelastic study on the gelation of basil seed gum. International Journal of Science and Technology 48: 556–563. Balaghi, S., Edelby, Y., and Senge, B. (2014). AIP Conference Proceedings 1593, The Polymer Processing Society Nuremberg, Germany. Balk, M., Behl, M., Nöchel, U., and Lendlein, A. (2012). Shape-memory hydrogels with switching segments based on oligo (ε-pentadecalactone). Macromolecular Materials and Engineering 297: 1184–1192. Gabriele, D.G., Migliori, M., Sanzo, R.D. et al. (2009). Characterization of dairy emulsions by NMR and rheological techniques. Food Hydrocolloids 23: 619–628. Yoon, W.B. and Gunasekaran, S. (2007). Effect of temperature and concentration on rheological behavior of xanthan-carob mixed gels. Biotechnology and Bioprocess Engineering 12 (3): 295–301. Kontogiorgos, V. and Kasapis, S. (2016). Modeling and fundamental aspects of structural relaxation in high solid hydrocolloid systems. Food Hydrocolloids 68: 232–237. Labropoulos, C.K., Rangarajan, S., Niesz, D.E., and Danforth, S.C. (2001). Dynamic rheology of agar cell based aqueous binders. Journal of the American Ceramic Society 84 (6): 1217–1224. Ferry, J.D. (ed.) (1980). Viscoelastic Properties of Polymers. New York: Wiley. Steffe, J.F. (ed.) (1996). Rheological Methods in Food Process Engineering. Michigan: Freeman Press. Dolz, M., Hernandez, M.J., and Delegido, J. (2008). Creep and recovery experimental investigation of low oil content food emulsions. Food Hydrocolloids 22: 421–427. Banville, V., Power, N., Pouliot, Y., and Britten, M. (2015). Relationship between baked-cheese sensory properties and melted-cheese physical characteristics. Journal of Texture Study 46: 321–334. Petroci´c, J., Fi´ste´s, A., Raki´c, D. et al. (2015). Effect of defatted wheat germ content and its particle size on the rheological and textural properties of the cookie dough. Journal of Texture Study 46: 374–384. Kuo, M.I., Wang, Y.C., and Gunasekaran, S. (2000). A viscoelasticity index for cheese meltability evaluation. Journal of Dairy Science 82: 412–417. Kramer, A. and Szczesniak, A.S. (eds.) (1973). Texture Measurements of Foods: Psychophysical Fundamentals; Sensory, Mechanical, and Chemical Procedures and Their Interrelationships. Boston: D. Reidel Publishing, Co.

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53 Razavi, S.M.A., Taheri, H., and Sunchez, R. (2013). Viscoelastic characterization of

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wild sage (Salvia macrosiphon) seed gum as a function of concentration. International Journal of Food Properties 16: 1604–1619. Tang, J., Tung, M., and Zeng, A.Y. (1998). Characterization of gellan gels using stress relaxation. Journal of Food Engineering 38: 279–295. Nussinovitch, A., Peleg, M., and Normand, M.D. (1989). A modified Maxwell and a nonexponential model for characterization of the stress relaxation of agar and alginate gels. Journal of Food Science 54 (4): 1013–1016. Peleg, M. (1980). Linearization of relaxation and creep curves of solid biological materials. Journal of Rheology 24 (4): 451–463. Peleg, M. and Normand, M.D. (1983). Comparison of two methods for stress relaxation data presentation of solid foods. Rheologica Acta 22: 108–113. Mohsenin, N.N. (ed.) (1986). Physical Properties of Plant and Animal Materials. Structure, Physical Characteristics and Mechanical Properties. New York: Gordon and Breach Science Publishers, Inc. Kajuna, S.T.A.R., Bilanski, W.K., and Mittal, G.S. (1998). Effect of ripening on the parameters of three stress relaxation models for banana and plantain. Applied Engineering in Agriculture 14 (1): 55–61. Herrero, A.M., Heia, K., and Careche, M. (2004). Stress relaxation test for monitoring postmortem changes of ice-stored cod (Gadus morua L.). Journal of Food Science 69 (4): 178–182. Sozer, N. and Dalgic, A.C. (2007). Modelling of rheological characteristics of various spaghetti types. European Food Research and Technology 225: 183–190. Li, S.-P., Zhao, G., and Chen, H.-Y. (2005). The relationship between steady shear viscosity and complex viscosity. Journal of Dispersion Science and Technology 26 (4): 415–419. Cox, W.P. and Merz, E.H. (1958). Correlation of dynamic and steady flow viscosities. Journal of Polymer Science 28: 619–622. Shatwell, K.P., Sutherland, I.W., Ross-Murphy, S.B., and Dea, I.C.M. (1991). Influence of the acetyl substituent on the interaction of xanthan with plant polysaccharides – II. Xanthan-guar gum systems. Carbohydrate Polymers 14: 115–130. Cheng, D.C.-H. (1986). Yield stress: a time-dependent property and how to measure it. Rheologica Acta 25: 542–554. Mysore, S.S. and Rudrapatnam, T.N. (2015). Modulation in the rheological behaviour of porcine pepsin treated guar galactomannan on admixture with κ–carrageenan. Carbohydrate Polymers 115: 253–259. Lardy, F., Vennat, B., Pouget, M.P., and Pourrat, A. (2000). Functionalization of hydrocolloids: principal component analysis applied to the study of correlations between parameters describing the consistency of hydrogels. Drug Development and Industrial Pharmacy 26 (7): 715–721. Madhulatha, T.S. (2012). An overview on clustering methods. IOSR Journal of Engineering 2 (4): 719–725.

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5 Hydrocolloids Interaction Elaboration Based on Rheological Properties Ali Alghooneh, Fataneh Behrouzian, and Seyed M.A. Razavi Food Hydrocolloids Research Center, Department of Food Science and Technology, Ferdowsi University of Mashhad, PO Box 91775-1163, Mashhad, Iran

5.1 Introduction Binary mixtures of polysaccharides have been thoroughly studied for the purpose of gaining a fundamental understanding, and also to discover industrial applications, especially in food systems to improve some properties of each component [1]. The literature has established that some novel gums could be alternatives to some of the commercial hydrocolloids in blend formulations as stabilizer, thickener, binder, and gelling agents and could be used in food, cosmetics, and pharmaceutical systems. Apart from blends’ functional properties, food ingredients and processing conditions such as salts, pH, and temperature affect their functions. This chapter reviews studies on new gum blends and reports their rheological properties and the effect of food ingredients and processing conditions on these characteristics. In addition, the interaction behavior of biopolymers is investigated from both thermodynamic and kinetic viewpoints based on rheological properties. Some researchers have described the interaction between xanthan gum (XG) and galactomannans as incompatibility [2]. Nevertheless, some evidence supports intermolecular binding between XG and galactomannans [3] and suggests that destabilization of the XG helix facilitates binding between XG and galactomannan [4]. So, knowledge of the thermodynamic functions of mixing and inter-chain association in the binary polymer blends is of great significance for both fundamental science and practical applications. On the other hand, understanding the specific interactions and/or phase separation conditions is still a challenge that usually involves the establishment of a phase diagram, which is highly time consuming and requires large quantities of raw materials which are not always available, especially when working with purified polysaccharides. Gibbs free energy is a thermodynamic function useful in probing the compatibility of biopolymers in blends which can be taken only from experimental thermodynamics. However, experimental studies on Gibbs energy of polymer blends are quite rare [5]. To overcome these major drawbacks, alternative strategies recently emerged, one of them being rheology, which this chapter deals with in both dilute and concentrated regimes. On the other hand, dynamic rheology can probe the inter-chain association in which the viscoelastic characteristic of hydrocolloids could be determined without alteration of the sample’s structure [6]. The Emerging Natural Hydrocolloids: Rheology and Functions, First Edition. Edited by Seyed M.A. Razavi. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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present chapter enables the reader to compare the properties between different sources and aids in the eventual utilization of novel gums in blend systems for their specific usage and to broaden the application of novel hydrocolloids in different industries.

5.2 Dilute Regime The viscosity measurement of binary blends in the dilute solution domain has been a very useful approach to understanding how molecules behave and interact in solution [7] and allows the determination of intrinsic viscosity, [𝜂], and other molecular characteristics of polymers under given thermodynamic conditions [8]. Arthur et al. [9] investigated the interaction between Khaya senegalensis (KS gum) and Acacia senegal (AS or gum arabic) using the Ubbelohde viscometer. The Huggins equation was applied to a ternary polymer–polymer–solvent dilute solution as follows: √ √ (5.1) 𝛼 = bm − ( b 1 W 1 + b 2 W 2 ) 2 bm = bm1 + bm2 + bm3 ≈ bm1 + bm3

(5.2)

where bm , b1 , and b2 are the Huggins coefficients for blend, gum 1, and gum 2, respectively. W 1 and W 2 are the weight fractions of polymers 1 and 2, respectively. bm1 represents the long-range hydrodynamic interaction of pairs of single molecules, bm2 indicates the formation of double molecules or attraction between blend components, and bm3 shows the intermolecular attraction or repulsion. By measuring bm from the Huggins equation for a polymer blend solvent solution, 𝛼 is calculated, and the interaction is characterized, where 𝛼 ≥ 0 denotes attraction, and 𝛼 < 0 denotes repulsion. The 20% AS–80% KS blend exhibits the strongest attraction between KS and AS molecules since the blend has the highest value of the intrinsic viscosity value, while the 60% AS–40% KS blend has the least attraction as evidenced by the polymer miscibility coefficient (𝛼), but these interactions vanish as salts (KCl, KBr, and AlCl3 at a concentration of 10 g dm−3 or 1 g dl−1 ) are added. The specific viscosity decreases as the temperature increases (the least viscosity is at 70 ∘ C, followed by a slightly increase up to 90 ∘ C), the concentration of the blends decreases, and the concentrations of KBr, KCl, or AlCl3 increase in an aqueous medium. In each of the gum blends, the trivalent ions from AlCl3 show a more pronounced effect on the specific viscosity compared with the monovalent ions of KCl and KBr. The hydrodynamic interaction value, bm1 , indicates that the blends become more soluble in water when a greater concentration of gum arabic is added to the blends. The power-law coefficient of the specific viscosity versus concentration shows an inverse relationship with an increase in KS fraction in the blends, suggesting a more flexible AS-KS complex dependent on KS [9]. The rheological interaction of sage seed gum (SSG) with XG in the dilute region at five blending ratios (100:0, 75:25, 50:50, 25:75, and 0:100) and three temperatures (25, 40, and 55 ∘ C) was investigated [10]. The higher slope of the master curve (double logarithmic plots of 𝜂 sp against C[𝜂]) at 40 ∘ C compared to the slope at 25 ∘ C indicates the greater rigidity of blends at the former temperature. In addition, the slope of the master curve of the blends is slightly lower than the slopes of either XG or SSG alone. Comparing the intrinsic viscosity calculated with five models of Kraemer, Huggins, Tanglertpaibul & Rao, and Higiro, the Tanglertpaibul & Rao model shows a better fit, with a higher

5.3 Concentrated Regime

correlation (R2 ) value for all blends. At 25 and 40 ∘ C, the intrinsic viscosity of XG-SSG blends is lower than the calculated intrinsic viscosity from the weight averages of the two individually, whereas at 55 ∘ C the opposite behavior is observed, indicating that molecular binding occurs between XG and SSG only at 55 ∘ C. Among the gum blends, the 75% XG–25% SSG blend shows the largest intrinsic viscosity [10].

5.3 Concentrated Regime 5.3.1

Steady Rheological Behavior

Steady shear measurement is employed to follow the breakdown of the structure at different rates of shear [11]. The synergistic behavior of xanthan and galactomannans from Brazilian seeds (Mimosa scabrella Bentham and Schizolobium parahybum (Veil) Blake), with mannose/galactose ratios of l.l:l and 3:l, respectively, were examined [12]. Viscometric determinations were performed at 20 ∘ C over a range of polymer conceṅ 350 s−1 ). A stronger interaction exists between xanthan-S. trations of 0.1–2 g l−1 (10 < 𝛾< parahybum galactomannan in water at 1 and 2 g l−1 , with a stronger increase in viscosity compared with that of the galactomannan from M. scabrella, and a maximum in synergistic effect in water exists when the mixing ratio of xanthan to galactomannan is 1:l. The maximum viscosity (70 s−1 ) for the xanthan-M. scabrella galactomannan occurs at the ratio 4:1. 0.01 M NaCl addition decreases the synergistic effect, compared with the result obtained in water. When the xanthan-galactomannan of the M. scabrella mixture is prepared at 25 ∘ C, the system shows less synergism than when prepared at 80 ∘ C in water (both tested at 20 ∘ C), as indicated by the lower specific viscosity at 70 s−1 [12]. The interaction between Mimosa scabrella galactomannan polysaccharide (G) -sodium caseinate (NaC) mixtures using 10 and 20 g l−1 galactomannan concentration and 10–100 g l−1 of NaC was investigated. The steady shear experiments of G (10 g l−1 )/NaC give rise to an increase of viscosity with the increase of NaC at the lower shear rate (10−3 –100 s−1 ), suggesting a probable interaction between these blends [13]. The steady shear rheological behavior of konjac glucomannan (KGM)-spruce galactoglucomannan (GGM, a wood-derived polysaccharide) mixtures shows that spruce GGM has a very low viscosity compared to KGM, and with the increase in the ratio of KGM in the mixtures, shear thinning become more dramatic [14]. Feng et al. [15] studied the effect of Mesona Blumes gum (MBG) at 0%, 0.1%, 0.35%, 0.5%, and 0.7% (w/w, d.b.) on the rheological properties of rice starch (RS) paste (6% w/w). Using the Herschel–Bulkley model, RS–MBG mixtures show pseudoplastic flow behavior (0.17 ≤ n ≤ 0.24). The flow behavior index (n) value initially decreases to 0.17 with the MBG concentration increasing to 0.35%, followed by stable n values with the MBG concentration increasing to 0.7%. The values of 𝜂 50 (apparent viscosity at 50 s−1 ) and k (consistency coefficient) of RS–MBG mixtures are also much higher than those of RS paste without MBG, which explains the synergistic interaction between RS and MBG. The effect of temperature (25–65 ∘ C) on 𝜂 50 is described by the Arrhenius equation. Activation energy values (16.8–22.3 kJ mol−1 ) of RS–MBG mixtures vary considerably, indicating a strong temperature dependence. On the other hand, according to Marcotte et al. [16], when the Ea value is more than 3.03 × 104 J mol−1 , the system viscosity is more prone to the temperature effect. Thus, the starch–MBG gel mixtures are relatively thermostable [15].

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The flow behavior of mixed solutions of xanthan and galactomannan isolated from Delonix regia seeds at different shear rates (1.19–95.03 s−1 ) are determined with a rheogoniometer. Keeping the total concentration constant at 0.1% at 45 ∘ C, the flow curves of mixed solutions of native xanthan and galactomannan show plastic behavior except for xanthan and galactomannan alone, which indicates that synergistic interaction occurs between xanthan and galactomannan molecules [17]. Razavi et al. [18] studied the rheological interaction of various SSG and GG (guar gum) blends at 3:1, 1:1, and 1:3 ratios (20 ∘ C). As the SSG fraction increases, the extent of viscosity reduction in the range 0.01–316 s−1 increases from 58.68 for GG to 832.73 times for SSG, which is not the same at different ranges of the shear rate, indicating augmentation of shear thinning with increasing SSG fraction. The power-law and Moore models adequately fit the shear stress versus shear rate and shear viscosity versus shear rate data, respectively (R2 = 0.93–0.99). Using the Moore model, the zero-shear viscosity and the time constant increase when the SSG fraction is increased. The reciprocal time constant (1/𝜏), which gives the critical shear rate for the beginning of shear thinning, decreases appreciably when the SSG fraction increases. This result suggests an increase in the time required for new entanglement to replace those disrupted by an externally imposed deformation as the SSG fraction increases in blends [18]. In another study, Gleditsia triacanthos (Gt) gum (0.1%, 0.4%, 0.7%, and 1.0%, w/v) and tapioca starch (2.5%, w/v) were combined, and rheological characterization of the binary mixture was evaluated [19]. The power-law model describes the shear rate effect on the apparent viscosity values of samples (1–100 s−1 shear rate at 25 ∘ C). An increase in the Gt level increases the apparent viscosity and consistency coefficient of the samples. All the mixtures show non-Newtonian shear-thinning behavior. The results suggest that Gt gum and tapioca starch show good interaction and synergism [19]. Alghooneh et al. [11] investigated the flow behavior of SSG–XG at three different ratios of 1:3, 1:1 and 3:1in the range 0.01 to 300 s−1 . The apparent viscosity-shear rate data were fitted using the power-law equation. The strong shear-thinning behavior for all blends is characterized by flow behavior index values less than 0.30. The flow behavior index increases with an increase in the SSG fraction, while the consistency coefficient shows a decreasing trend [1]. The effect of SSG at different concentrations (0%, 0.1%, 0.25%, and 0.5% w/w) on the steady shear flow behavior of wheat starch dispersion (2% w/w) was evaluated [20]. The apparent viscosity increases with increasing SSG concentration, and all the samples exhibit shear-thinning flow behavior. Addition of SSG up to 0.5% results in an approximately twofold increase in the limiting viscosity at a high shear rate, and a 251-fold increase in the consistency coefficient, but a 19% decrease in the flow behavior index values of wheat starch dispersion using Sisko’s model [20]. 5.3.2

Transient Rheological Behavior

The use of creep and recovery tests has been suggested to assess the most likely internal structure of a system [21]. Perissutti et al. [13] studied the creep and recovery behavior of M. scabrella galactomannan polysaccharide (G)-sodium caseinate (NaC) mixtures. A decrease in the compliance parameter (J) was observed with an increase in NaC concentration, indicating a more viscoelastic solution in comparison with the galactomannan in aqueous solution, with J values of 60 and 54 Pa−1 for the G (10 and 20 g l−1 )/NaC (50 g l−1 ) mixtures, respectively, and 52 and 36 Pa−1 for G (10 and 20 g l−1 )/NaC (100 g l−1 ) mixtures, respectively.

5.3 Concentrated Regime

5.3.3 5.3.3.1

Dynamic Rheological Behavior Amplitude Sweep Properties

Many useful rheological properties could be obtained from the amplitude sweep data, such as the elastic modulus (G′ LVE ), viscous modulus (G′′ LVE ), loss tangent (tan 𝛿), the limiting value of strain (𝛾 C ) at the LVE region, the slope of the storage modulus and loss tangent at the start of the n-LVE (nonlinear viscoelastic) region, yield stress at the limit of the LVE range (𝜏 y ), and flow-point stress (𝜏 f ). Razavi et al. [18] investigated the interaction behavior of different SSG–GG ratios (1:3, 1:1, and 3:1) in the LVE region. SSG–GG blends show higher G′ values than G′′ values at 1:1 and 3:1 ratios, whereas the 1:3 SSG–GG sample shows the reverse behavior. Both moduli increase with increase in the SSG fraction. The loss tangent of blends at 1:1 and 3:1 ratios is less than 1, while this parameter is 1.32 for the 1:3 SSG–GG. The critical strain (𝛾 c ) and loss tangent increase with increasing GG fraction. Except 1:3SSG–GG, for all samples exceeding the critical strain amplitude, beyond the LVE, G′ can cross G′′ (crossover). 𝜏 f (the stress at the crossover point) increases when the SSG fraction is increased from 50% to 100%, showing a greater tendency to flow for 1:1 SSG–GG. In addition, the amplitude dependency of G′ increased with the SSG fraction [18]. 5.3.3.2

Frequency Sweep Properties

Frequency sweep measurements within the LVE range provide some valuable rheological parameters that are helpful for elaborating the interaction behavior. The mechanical spectra could be characterized by the storage modulus (G′ ), loss modulus (G′′ ), complex modulus (G*), complex viscosity (𝜂*), and the loss tangent (tan 𝛿) as a function of frequency (Hz). The frequency dependencies of G′ (Eq. (5.3)), G′′ (Eq. (5.4)), and 𝜂* (Eq. (5.5)), for any dispersion, could be approximated by the power-law model as follows [11]: G′ = k ′ × 𝜔n′ G′′ = k ′′ × 𝜔n

(5.3) ′′

(5.4)

𝜂 ∗ = k ∗ 𝜔(n −1) ∗

′

n

′′

(5.5) n

*

n

′

′′

*

where k (Pa s ), k (Pa s ) and k (Pa s ) are constants; n , n , and n are viscoelastic exponents; and 𝜔 is the angular velocity (rad s−1 ). Mixed gels of κ-carrageenan from Hypnea musciformis (κ-car) and galactomannans from Cassia javanica (CJ) and locust bean gum (LBG) were compared using dynamic viscoelastic measurements [22]. Mixed gels at 5 g l−1 of total polymer concentration in 0.1 M KCl show a synergistic maximum in viscoelastic measurements for κ-car/CJ and κ-car/LBG at 2:1 and 4:1 ratios, respectively. The plot of log 𝜂* versus log ω is linear with a slope of −1 for all blends, as expected for true gels. However, the values of 𝜂* are higher for the mixtures than for κ-car alone. An enhancement in the G′ and G′′ is observed in the mechanical spectra of the mixtures in relation to κ-car. The proportionally higher increase in G′′ compared with G′ , as indicated by the values of the loss tangent (tan δ), suggests that the galactomannans adhere non-specifically to the κ-car network [22]. Different ratios of starch and decolorized Hsian-tsao leaf gum (dHG) composite gels with starch/gum 3:3, 4:2, and 5:1 show the higher G′ and G′′ values compared to those of starch or dHG alone, due to the constructive interactions between starch and dHG. In addition, rheologically, these composite gels can be classified as weak to strong gels due

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to the fact that the G′ values are much greater than the G′′ values, and the tan δ values are much less than 1 [23]. Perissutti et al. [13] reported that M. scabrella galactomannan polysaccharide (G)-sodium caseinate (NaC) at 10 and 20 g l−1 galactomannan concentration and 10–100 g l−1 of NaC show a viscous behavior, and an increase in viscoelasticity accompanying an increase in galactomannan and NaC concentrations. Azero and Andrade [24] investigated the frequency dependence of G′ and G′′ for κ-carrageenan solutions at 1.0 and 1.2 g l−1 and for 3:1 κ-carrageenan/Prosopis juliflora seed gum mixed solutions at 1.0 g l−1 total polymer concentration. For the mixed solution, no synergy is observed. On the other hand, self-supporting gels obtained by mixing κ-carrageenan and Prosopis juliflora seed gum or GG in 0.25 mol L−1 KCl at 10 g l−1 total polymer concentration show similar mechanical properties. Xu et al. [14] investigated the storage modulus of spruce GGM-konjac glucomannan (GGM/KGM) mixtures with respect to the polysaccharide ratio. The storage modulus is significantly lower when the GGM ratio increases in the mixtures. This indicates that no synergistic interaction occurs in the applied conditions (total polysaccharide concentration 0.5 wt%, 1 Hz, 25 ∘ C). Mixtures of GGM and GG, LBG, and carrageenan show a significant reduction in the storage modulus G′ . The mixture of GGM and xanthan shows a different behavior from other polysaccharides. It has a relatively high value of G′ , which indicates that synergistic interaction might exist in this mixture [14]. MBG (0%, 0.1%, 0.35%, 0.5%, 0.7% w/w, d.b.)- RS (6% w/w) mixtures’ rheological behavior (6.3–63 rad/s, 1% strain and 25 ∘ C) was investigated, and the results were modeled by the natural logarithm of the storage modulus (Eq. (5.3)), loss modulus (Eq. (5.4)), and angular frequency. The RS–MBG pastes display true gel-like behavior, with much higher G′ values than G′′ values, showing a small dependence on frequency (n′ = 0.057–0.094). The magnitudes of k ′ also increase with an increase in the MBG concentration from 0.1% to 0.7% [15]. Mixed solutions of xanthan and galactomannan isolated from seeds of Delonix regia at 0.1% total gums at room temperature (25 ∘ C) make a gel with the maximum elastic modulus at the ratio of xanthan (native, de-pyruvated, and deacetylated) to galactomannan of 2:1. The largest elastic modulus is observed in the mixture solution of deacetylated xanthan. However, a small elastic modulus is obtained in the mixture with de-pyruvated xanthan. These results suggest the pyruvate groups may take part in the intermolecular interaction with galactomannan [17]. The synergistic interactions of two nonconventional galactomannans (G. triacanthos galactomannan (mannose/galactose ratio [M/G] = 2.82) and Sophora japonica galactomannan (M/G = 5.75)) with κ-carrageenan and xanthan were quantified (0.1–100 rad s−1 range at 25 ∘ C and strain amplitude of 5%) and compared with GG and LBG with the same polysaccharides [25]. The mechanical spectra of the mixed polysaccharide gels are characterized by a modest dependency of the shear storage modulus over the entire range of frequencies (G′ is almost independent of the frequency for ω > 1 rad s−1 ). For κ-carrageenan/galactomannans mixtures, the synergistic interactions are stronger for mixtures of 60:40 (% w/w) κ-carrageenan/LBG, 60:40 (% w/w) κ-carrageenan/S. japonica galactomannan, 80:20 (% w/w) κ-carrageenan/GG, and 60:40 (% w/w) κ-carrageenan/G. triacanthos galactomannan. For all xanthan/galactomannans systems, the maximum synergy is observed for a ratio of 20:80 (% w/w) [25]. Comparing the elastic modulus of mixtures containing 6% (d.b.) RS and 0.5% (d.b.) of various hydrocolloids (xanthan, MBG gum, carrageenan, gelatin, carboxylmethylcellulose, gum arabic, and konjac), the RS–MBG mixture shows the highest values of both moduli

5.3 Concentrated Regime

(G′ and G′′ ) and the lowest tan δ among other RS–hydrocolloid blends, indicating that the elasticity and viscosity of gels formed by RS and MBG are larger than those of RS and other gums (1% strain, frequency range 1–10 Hz, 25 ∘ C). G′ changes slightly with frequency in the range of the sweeping frequency, suggesting that the gel formed by RS–MBG belong to a strong gel. The tan δ of RS–MBG gel (around 0.1519–0.157) is higher than RS alone in the low-frequency range (1 < ω < 6 Hz), but they are roughly equivalent in the high-frequency range (6 < ω < 10 Hz) [26]. Sorghum (Sorghum saccharatum) starch and cactus (Opuntia ficus-indica) mucilage blends with the ratios of 90:10 and 95:5 (g:g) are characterized by the frequency sweep test (0.1 to 100 rad/s, at a stress of 3 Pa). Both blends show the character of a physical gel since there is a predominance of the storage modulus over the applied frequency range (G′ > G′′ ). The storage modulus (G′ ) and loss modulus (G′′ ) in samples with 90:10 starch: mucilage mixture are about three times and twice those at the starch mechanical spectra alone, respectively, suggesting a rearrangement in the starch–mucilage system structure. A decrease in the frequency dependence of gel moduli values is observed with mucilage addition in a concentration-dependent fashion, determined by a decrease in the slope’s value (n′ and n′′ ) from 0.1 to 0.05 for log G′ and from 0.19 to 0.13 for log G′′ in the frequency sweep profiles [27]. Frequency sweep data for Gleditsia triacanthos (Gt) gum-tapioca starch blends (0.1–10 Hz, 0.2 Pa in LVE) show that G′ and G′′ of the blends increase as Gt gum in the mixtures increases [19]. SSG–GG at 1:3exhibits the behavior of entangled polymer solutions with two crossover point at low frequency (0.35 and 7.12 Hz), whereas at 1:1 and 3:11 ratios it behaves as a typical gel [18]. The frequency dependence of G′ decreases as the SSG fraction in mixtures increases, as indicates by the decreasing value of the power-law index (n′ ) (Eq. (5.3)). The elastic character is less pronounced in the case of 1:3SSG–GG (tan δ > 1) than that of other ratios (tan δ < 1). The slope of the complex viscosity with increasing frequency on a double logarithmic scale decreases with as the GG fraction increases, suggesting the transition to an entangled polymer solution. The difference between the complex and dynamic viscosities increases as the SSG fraction increases, which again confirms a higher elasticity for the component as the SSG fraction in the mixture is increased. The generalized Maxwell models (Eqs. (5.6) and (5.7)) are commonly used to estimate the relaxation time in dynamic tests in biological materials [18]: G′ = G′′ =

n ∑

Gi

2 2 i=1 1 + (𝜔 × 𝜆irel ) n ∑ Gi i=1

1 + (𝜔2 × 𝜆2irel )

(5.6) (5.7)

where the subscripts refer to the different mechanical elements in the system, G is the relaxation modulus (Pa), and 𝜆rel is the relaxation time (s). Also, the strength of the network and the number of interactions between the biopolymers, at all gum ratios, are assessed by using the material stiffness parameter, Aa (Pa rad−𝛼 s𝛼 ), and the order of the relaxation function, 𝛼 (dimensionless), respectively, obtained from the Friedrich and Heymann [28] model parameters: √ √ 2 ∗ α (5.8) s 𝜔 = Aα 𝜔α G∗ = G′ (𝜔)2 + G′′ (𝜔)2 ≅ 𝜋 α

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5 Hydrocolloids Interaction Elaboration Based on Rheological Properties

As the GG fraction in SSG–GG blends increases, the values of G, 𝜆rel , and Aa decrease, whereas the relaxation function (𝛼) increases [18]. SSG–XG at 1:3, 1:1, and 3:1 ratios (1% w/w) shows strong shear-thinning behavior characterized by values less than 0.26 for the power index of the complex viscosity, which increases as the SSG fraction of blends increases [11]. The viscoelastic functions (G′ and G′′ ) of SSG–XG blends obey power-law frequency dependence. In regard to the n′ (Eq. (5.3)) value, the general tendency of all blends to exhibit elastic gel behavior at any frequency range (0.01–0.1, 0.1–1, and 1–10 Hz) is found. At middle and high-frequency ranges (0.1–1 and 1–10 Hz), the lowest frequency dependence of G′ is observed for 3–1 SSG–XG among other blends. tan (δ) for all samples is less than 1, confirming solid-like behavior, and it decreases with as the SSG fraction increases, especially in the range 1–10 Hz, indicating a greater influence of SSG gum on the elasticity property than on the viscosity property of the blend systems relative to XG. tan (δ) values of all blends decrease with frequency, indicating the systems are in a pre-gel regime [29]. The 𝜂*/𝜂 ′ , which represents the extent of the elastic component that sustained small deformation in small amplitude oscillatory shear (SAOS), increases with increasing SSG ratio in mixed gum dispersions. With decreasing SSG fraction, the magnitudes of Aa decrease. The lowest and highest values of the relaxation function are found for 3:1 SSG–XG (0.11) and 1:1 SSG–XG (0.17), respectively, which confirms the highest shear thinning in SAOS for 3:1 SSG–XG [11]. 5.3.4 5.3.4.1

Temperature Effect Temperature Effect in an Isothermal Condition

The effect of temperature on the interaction of biopolymers was probed by a number of rheological tests such as the stress/strain sweep, frequency sweep, and creep/recovery test in the isothermal mode. Rafe et al. [30] studied the frequency sweep of β-lactoglobulin-basil seed gum mixtures (BLG–BSG) after heating to 90 ∘ C. The mixtures develop a relatively weak gel at different heating rates; however, this property is more pronounced when BSG is added (the higher ′ the BSG concentration, the lower the n value of Eq. (5.3)). The addition of BSG) to BLG solution reduces the phase angle and strengthens the BLG gel. The transient viscoelastic rheological behaviors of the SSG–XG blends at various ratios (1:3, 1:1, and 3:1 SSG–XG) and temperatures (10, 30, and 50 ∘ C) were investigated using creep and recovery analyses at 1 Pa during 300 s at each stage in the linear viscoelastic range [31]. Compliance experimental data were fitted by means of the four-component Burger model (Eq. (5.9)) and an empirical model (Eq. (5.10)) for creep and recovery phases, respectively, as follows [31]: [ ( )] t t (5.9) JC = J0C + J1C 1 − exp − + 𝜆ret 𝜂0 JR = J∞ + [J1R .exp(−t C )]

(5.10) −1

where J 0C is the instantaneous elastic compliance (Pa ) of the Maxwell spring, J 1C is the elastic compliance (Pa−1 ) of the Kelvin–Voigt unit, 𝜆ret is the retardation time (s) of the Kelvin–Voigt component, and 𝜂 0 is the Newtonian viscosity (Pa s) of the Maxwell dashpot. C is the parameter that defines the recovery speed of the system. J ∞ and J 1R are the recovery compliance of the Maxwell dashpot and the Kelvin–Voigt element,

5.3 Concentrated Regime

Compliance (10°C)

Compliance (30°C)

Compliance (50°C)

0.8 Compliance (1/Pa)

0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0

50

100

150 Time (s)

200

250

300

Figure 5.1 Compliance versus time curves in the creep test, fitted by the Burger model for 1:1 SSG-XG at 10, 30, and 50 ∘ C. Source: Adapted from Razavi et al. [31] with permission from John Wiley and Sons.

respectively. When t → 0, J R is equal to J ∞ + J 1R , which corresponds to the maximum deformation of the dashpots in the Burger model. For t → ∞, J R is equal to J ∞ , as it corresponds to the irreversible sliding of the Maxwell dashpot [31]. In addition, the final percentage recovery (%R) of the entire system can be calculated by the following equation [31]: ] [ J J (5.11) %R = max− ∞ × 100 Jmax where Jmax is the maximum compliance value for the longest time (300 s) in the creep test. Typical compliance curves, fitted by Burger model for 1:1 SSG–XG at 10, 30, and 50 ∘ C, are presented in Figure 5.1. For 3:1 SSG–XG, the maximum compliance (J max ), retardation time (𝜆ret ), contribution of viscous flow compliance to deformation (J 2C * ), relaxation exponent (n), contribution of retarded creep compliance to deformation (J 1C * ), retarded recovery compliance (J 1R ), residual compliance (J ∞ ), and the percentage participation of the residual compliance to deformation (J ∞ * ) reduce as the temperature increases from 10 to 50 ∘ C, while the reverse behavior is found for the other ratios, which could be attributed to the immiscibility of the 1:1 and 1:3 SSG–XG mixtures. On the other hand, the instantaneous creep elastic compliance percentage (J 0C * ), the percentage deformations of the instantaneous recovery elastic element (J 0R * ), 𝜂 0 , C, and %R, for 3:1 SSG–XG decrease as temperature increases, while other gum blends show the opposite trend [31]. The temperature effect on the interaction behavior of SSG–XG at the temperature levels of 10, 30, 50, 70, and 90 ∘ C was investigated using strain sweep tests [32]. With increasing SSG fraction, the effective range of the applied temperature on G′ LVE shifts to a higher temperature, which is the most effective temperature range for SSG dispersion, and the average value of G′ s(n-LVE) increases. As temperature increases from 10 to 90 ∘ C, the G′ LVE , and 𝜏 f of 3:1 SSG–XG increases from 21.89 to 34.08 Pa and 4.52 to 8.98 Pa, respectively, whereas the 𝜏 f of 1:3SSG–XG decreases from 7.50 to 5.35 Pa in the similar temperature range. Among the various ratios, 1:3 SSG–XG shows the highest value of tan (𝛿)LVE up to 50 ∘ C, and 3:1 SSG–XG shows the highest value of the tan (𝛿) s(n-LVE) parameter at 50 ∘ C among the other blends and temperatures. Behrouzian et al. [32]

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Table 5.1 Storage modulus (G′ ), loss modulus (G′′ ), complex modulus (G*), and loss tangent (tan 𝛿) for various sage seed gum:xanthan ratios and temperatures, as determined by frequency sweep tests (f = 1 Hz, 1% w/w, 𝛾 = 0.01%). SSG–XG

T (∘ C)

G′ (Pa)

G′′ (Pa)

G* (Pa)

tan (𝜹)

1:0

10

27.42 ± 3.24

14.08 ± 1.46

30.82 ± 3.55

0.51 ± 0.01

3:1

10

19.77 ± 4.44

9.34 ± 0.93

20.85 ± 4.44

0.23 ± 0.02

1:1

10

25.47 ± 1.11

11.30 ± 0.13

27.49 ± 1.08

0.37 ± 0.01

1:3

10

20.12 ± 3.56

6.62 ± 1.02

21.18 ± 3.70

0.32 ± 0.03

0:1

10

32.14 ± 0.91

8.24 ± 0.10

33.18 ± 0.86

0.25 ± 0.01

1:0

30

60.92 ± 2.47

9.90 ± 0.54

61.72 ± 2.52

0.16 ± 0.02

3:1

30

57.21 ± 5.09

11.26 ± 3.46

62.31 ± 4.38

0.19 ± 0.07

1:1

30

32.63 ± 1.05

11.85 ± 0.13

34.71 ± 0.91

0.36 ± 0.01

1:3

30

30.11 ± 3.91

9.50 ± 1.53

32.53 ± 4.19

0.30 ± 0.02

0:1

30

26.42 ± 1.29

7.43 ± 0.38

27.44 ± 1.35

0.28 ± 0.01 0.18 ± 0.05

1:0

50

44.19 ± 3.43

8.35 ± 1.87

46.75 ± 3.04

3:1

50

31.62 ± 5.85

7.31 ± 0.69

32.46 ± 5.86

0.23 ± 0.02

1:1

50

40.17 ± 1.86

13.03 ± 0.68

43.18 ± 1.98

0.32 ± 0.01

1:3

50

9.60 ± 0.98

4.21 ± 0.15

10.48 ± 0.95

0.44 ± 0.03

0:1

50

21.15 ± 2.69

6.78 ± 0.58

22.21 ± 2.73

0.31 ± 0.01

1:0

70

58.79 ± 4.39

6.37 ± 0.11

59.13 ± 4.38

0.11 ± 0.01

3:1

70

35.82 ± 5.42

7.11 ± 0.54

36.54 ± 5.20

0.20 ± 0.04

1:1

70

21.69 ± 0.64

8.94 ± 0.11

23.45 ± 0.64

0.41 ± 0.04

1:3

70

8.89 ± 0.52

10.28 ± 1.33

13.61 ± 0.67

1.28 ± 0.03

0:1

70

18.59 ± 0.30

6.91 ± 0.08

19.37 ± 0.31

0.38 ± 0.01

1:0

90

90.89 ± 4.87

10.84 ± 0.07

91.53 ± 4.74

0.12 ± 0.01

3:1

90

54.59 ± 1.43

11.97 ± 1.11

55.90 ± 1.16

0.22 ± 0.03

1:1

90

38.16 ± 3.47

13.29 ± 1.80

40.40 ± 3.87

0.35 ± 0.02

1:3

90

8.01 ± 0.62

10.07 ± 0.26

12.88 ± 0.18

1.13 ± 0.02

0:1

90

18.10 ± 2.01

7.51 ± 0.25

20.05 ± 1.95

0.41 ± 0.06

Source: Adapted from Behrouzian et al. [32] with permission from John Wiley and Sons.

performed frequency sweep measurements within the LVE range over the frequency range 0.01–10 Hz and at various temperatures (10–90 ∘ C) on different SSG–XG ratios (1:3, 1:1, and 3:1). Table 5.1 demonstrates G′ , G′′ , G* , and tan 𝛿 at a frequency of 1 Hz for different mixtures at different temperatures. The mechanical spectra for 1:3SSG–XG at 70 and 90 ∘ C show the behavior of an entangled polymer solution, with G′ dominating over G′′ in the high-frequency range and crossover points at the frequencies of 0.90 Hz and 2.84 Hz at 70 and 90 ∘ C, respectively. Other blends do not show crossover at any temperature. G′ 1Hz for 3:1 SSG–XG increases from 19.77 Pa at 10 ∘ C to 54.59 Pa at 90 ∘ C, whereas the 1:3blend decreases from 20.12 to 8.01 Pa in this range of temperature. G′′ 1Hz of all blends increase with temperature from 10 to 90 ∘ C. All blends display gel-like behavior because the slopes of the double logarithmic plots of G′ and G′′ against frequency (Eqs. (5.3) and (5.4)) are positive (n = 0.08–0.43 and n′′ = 0.07–0.43)

5.3 Concentrated Regime

and much lower than those reported for a Maxwell fluid (G′ ∞ 𝜔2 and G′′ ∞ 𝜔). The magnitudes of k ′ are much higher than k′′ at any temperature and gum ratio, confirming the gel-like behavior of these systems, whereas the exception is 1:3SSG–XG at 70 and 90 ∘ C, which shows a reverse trend. Generally, the k ′ /k′′ ratio noticeably increases as the temperature increases from 10 to 90 ∘ C for dispersions with a high SSG fraction (3:1 and 1:1 SSG–XG), indicating an increase in the number of physically active bonds. tan 𝛿 (1 Hz) exceeds unity for 1:3SSG–XG at 70 and 90 ∘ C, confirming the predominantly viscous behavior. On the other hand, the value of this parameter is within the range of 0.11–0.51 for the other blends and temperatures, indicating more elastic behavior. Based on a double logarithmic scale, the complex viscosity (𝜂*) of any gum sample at various temperatures decreases linearly with increasing frequency, indicating a non-Newtonian shear-thinning flow behavior. 3:1 and 1:3SSG–XG dispersions show the lowest shear-thinning properties at 10 ∘ C (n* of Eq. (5.5) equal to −0.70) and 90 ∘ C (n* of Eq. (5.5) equal to −0.56), respectively. Figure 5.2 represents the dependence of the dynamic viscosity (𝜂 ′ ) and complex viscosity (𝜂*) with gum ratios at the frequency of 1 Hz and 50 ∘ C. As the SSG fraction of the blends increases, the difference between 𝜂* and 𝜂 ′ increases, with the highest and lowest differences being for SSG and 1:3SSG–XG, respectively, which show the developed elastic component with an increase in the SSG fraction and the least elastic component for 1:3SSG–XG at 50 ∘ C. The relaxation time of 3:1 SSG–XG increases from 10.17 Pa at 10 ∘ C to 13.63 Pa at 90 ∘ C, while it decreases from 8.40 to 4.34 Pa for 1:3SSG–XG. The increase in relaxation time of 3:1 SSG–XG could be associated with the formation of intermolecular aggregates, which is facilitated by temperature for SSG [32]. 5.3.4.2

Temperature Effect in a Non-isothermal Condition

The effect of temperature on the interaction of biopolymers could be probed by temperature table sweep in the non-isothermal mode, using different temperature programs such as the linear temperature program (temperature gradient sweep (TGS)) and 60 η′ (Pa.s)

η* & η′ (Pa s)

50

η* (Pa.s)

40 30 20 10 0 (1–0)

(3–1)

(1–1)

(1–3)

(0–1)

Sage seed gum-xanthan gum ratio

Figure 5.2 Dynamic viscosity (𝜂 ′ ) and complex viscosity (𝜂*) of sage seed gum, xanthan gum, and their blends (1 Hz and 50 ∘ C). Source: Adapted from Behrouzian et al. [32] with permission from John Wiley and Sons.

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nonlinear temperature program (e.g., table temperature sweep (TTS) and temperature profile sweep (TPS)), which are discussed in this section. To study the rheological properties of mixtures of κ-carrageenan (κ-car) from H. musciformis and galactomannan from CJ at a total polysaccharide concentration of 5 g l−1 , Andrade et al. [22] first performed a temperature sweep experiment from 85 to 15 ∘ C at the rate of 1 ∘ C min−1 and a constant frequency of 6.28 rad/s, followed by a time sweep experiment at the same frequency and a frequency sweep, both at 5 ∘ C. Then, the temperature was raised to 25 ∘ C at a constant rate of 1 ∘ C min−1 , and new time sweep and mechanical spectrum experiments were performed. Finally, the temperature was increased to 85 ∘ C at the rate of 1 ∘ C min−1 . The gelation temperature, T g (the temperature at which a definitive and sharp increase in G′ is observed), is 55 ∘ C for κ-car, 60 ∘ C for κ-car/LBG, and 72 ∘ C for κ-car: CJ, which shows that galactomannan addition to κ-car increases T g . The effect is more pronounced for CJ than for LBG in the above conditions. Also, when the cured gels are heated from 25 to 85 ∘ C, the melting temperature, T m , is 74–75 ∘ C for κ-car and higher than 85 ∘ C for the mixed systems. The thermal hysteresis is higher for the κ-car/Gal mixtures than for κ-car alone [22]. The rheological behavior of GGM/KGM mixtures in the 1:1 ratio with a total polysaccharide concentration of 0.5 wt% at 1 Hz by controlling the temperature from 80 to 5 ∘ C shows that, like GGM and KGM on their own, the G′ and G′′ of the mixtures increase upon cooling. G′ is below G′′ throughout the cooling process from 80 to 5 ∘ C, showing the solution to be a viscous system. The difference between G′ and G′′ is smaller when the temperature is lower [14]. The effect of temperature on the elastic modulus of a mixed solution of xanthan and Delonix regia seed galactomannan was investigated over the temperature range 0–45 ∘ C and raised stepwise at the rate of 1 ∘ C min−1 [17]. A mixture of xanthan to galactomannan in the ratio of 1:2 exhibited a large elastic modulus. G′ decreased a little with an increase in temperature up to 25 ∘ C, which was estimated to be a transition temperature, then decreased rapidly. The transition temperature was also observed in mixing ratios of 3:1 and 4:1 at 25 and 30 ∘ C, respectively. A hardly changeable elastic modulus was observed in the mixing ratio of 1:4 as in xanthan alone, a phenomenon which might be attributed to intramolecular hydrogen bonding and van der Waals interaction within the xanthan molecule. The effect of temperature on the dynamic viscoelasticity of the xanthan–Delonix regia seed galactomannan mixed solution (0.1%) at a mixing ratio of 1:2 was compared with those for 4 M urea-added (is known as a hydrogen bonding breaker) or CaCl2 -added (6.8 mM) dispersions. The elastic modulus and dynamic viscosity of the mixed solution with urea or CaCl2 are lower than those with polysaccharide alone, which suggests that hydrogen bonding is involved in the interaction and dissociates above the transition temperature. It also suggests that the side chains of the xanthan molecules take part in the interaction because the small dynamic viscoelasticity should be attributed to the formation of Ca2+ bridges between the carboxyl groups of the glucuronic acid residues of the intermediate side chain of xanthan on different molecules [17]. The synergistic interactions of G. triacanthos galactomannan and Sophora japonica galactomannan with κ-carrageenan and xanthan on temperature sweep behavior were quantified and compared with GG and LBG by Pinheiro et al. [25]. To perform the temperature sweeps, each sample was heated to 70 ∘ C, equilibrated for 5 min, and then cooled from 70 to 25 ∘ C (for systems with xanthan) or 20 ∘ C (for systems with κ-carrageenan). A time sweep of 90 min was then performed, and the system

5.3 Concentrated Regime

was heated back to 70 ∘ C. A rate of 2 ∘ C min−1 was used at a constant frequency of 6.279 rad s−1 . For κ-carrageenan/galactomannan systems, T m seems to be dependent on the galactomannan present in the blend: the highest values are obtained for LBG and S. japonica galactomannan, and the lowest value is obtained for G. triacanthos galactomannan followed by GG. These systems are thermally reversible, and a significant (p < 0.05) thermal hysteresis is observed between melting and gelation in accordance with previous findings. For XG, no thermal hysteresis is detected between melting and gelation. This behavior is a consequence of the full reversibility of the disorder–order transition of xanthan. These results show that the gelation and melting temperatures of these systems are related (although not directly) to the galactomannan M/G ratio, among other characteristics such as the fine structure and molecular weight of galactomannans [25]. The effects of the heating rate (0.5, 1, 5, and 10 ∘ C min−1 ) on the rheological behavior of BSG- β-lactoglobulin (BLG) gel at different ratios (20:1, 10 : 1, 5 : 1, and 2:1) were studied using the TGS program for a temperature increase from 20 to 90 ∘ C. The gelation temperature of BLG reduces by when the heating rate decreases and the BSG ratio increases. The maximum G′ at the end of the heating period is greatly decreased by decreasing the BLG:BSG ratio. Addition of BSG to 10% BLG solution leads to the formation of a separated phase network in which increasing the BSG content induces a very fine stranded protein structure [30]. In another study, Rafe et al. [33] employed TGS at a scan rate of 1 ∘ C min−1 from 20 to 90 ∘ C, and samples were set at 90 ∘ C for 30 min. The effect of heating on the elastic modulus of BSG-BLG mixed gels containing four different ratios is shown in Figure 5.3. Upon heating–cooling time of BLG–BSG mixtures and returning to the original temperature, mixed gels exhibit a biphasic profile: the first phase is characterized by a sharp increase in the storage modulus in which gelation of BLG occurs, and the second phase exhibits an increase in the storage modulus corresponding to the build-up of a BSG network. The biphasic profile of mixed gels suggests that phase separation of the polymers occurs. During cooling, the presence of BSG has a synergistic effect on gel-forming and the rebuilding of new structures [33]. 1–2

2–1

5–1

10–1

80

10000

70 1000 60 50

100

40 10

Temperature (˚C)

Storage modulus (Pa)

90

30 1

0

1000

2000

3000 4000 Time (s)

5000

6000

20 7000

Figure 5.3 Storage modulus (G′ ) development for different ratios of basil seed gum- β-lactoglobulin as a result of heating from 20 to 90 ∘ C at 1 ∘ C min−1 and holding for 30 min (frequency 1 Hz; strain 0.5%). Source: Adapted from Rafe et al. [33] with permission from Elsevier.

147

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Razavi et al. [34] investigated three different temperature programs on the interaction behavior of SSG–XG blends at different ratios (1:3, 1:1, and 3:1) in the range 10 to 90 ∘ C. During TGS, the temperature was steadily (linear sweep) increased/decreased at a heating/cooling rate of 1 ∘ C min−1 . In TPS, the temperature was programmed to increase (at the rate of 11 ∘ C min−1 ), decrease (at the rate of −11 ∘ C min−1 ), and hold (at 90 ∘ C for 5 min). In this mode, the temperature was steadily changed by setting eight steps (time at each step = 1 min). In TTS, the temperature was steadily increased/decreased at a heating/cooling rate of 36 ∘ C min−1 in 17 linearly distributed steps (time at each step = 16 s). The results of the temperature sweep rheological tests show that during heating and cooling, G* increases as the SSG fraction increases. In addition, the G* of 3:1 SSG–XG increases as the temperature increases, especially in the range of 70–90 ∘ C, in the heating stages of all used temperature sweep modes (TSMs), except in the range 10–50 ∘ C, in which the G* of 3:1 SSG–XG is almost unchanged. On the other hand, the G* values of 1:3and 1:1 SSG–XG reduce as the temperature increases, mainly in the range of 50–70 ∘ C, except for 1:1 (obtained from TGS and TTS) and 1:3SSG–XG (obtained from TGS and TPS) in the range 70–90 ∘ C. The percentage change in G* per degree Celsius from TTS for all SSG fractions is far less than the two other TSMs at both heating and cooling stages due to the higher heating rate at TTS (36 ∘ C min−1 ), indicating the lower capacity of TTS to impact the strength of the gum network. In addition, all samples show strong thermal hysteresis, which increases as the SSG fraction increases. It is worth mentioning that the temperature profile sweep is the only temperature program with the capability to describe the time dependency of samples. In this way, the Weltman model was applied to describe the time-dependent complex modulus properties of SSG–XG dispersions during heating and cooling stages at 10, 30, 50 and 70 ∘ C and the holding stage at 90 ∘ C. The values of Weltman’s coefficient of thixotropic breakdown (B) of 3:1 SSG–XG, which indicates the extent of thixotropy, increase as the temperature increases. By contrast, the B parameter of the 1:1 and 1:3SSG–XG samples decreases as the temperature increases. When cooling, all gum samples show the increasing trend of time dependence [34]. 5.3.4.3

Kinetics of Biopolymer Interaction

The main objective of kinetic studies is to develop a mathematical model to describe the reaction rate as a function of experimental variables such as temperature. This can be done under both isothermal and non-isothermal conditions, each of which has its own merits and demerits [35]. 5.3.4.3.1

Kinetics of Biopolymer Interaction in Isothermal Condition

The rate equation is usually determined for isothermal conditions [35]. The temperature dependence of the rate constant is then determined from the Arrhenius equation. The temperature dependence of some characteristics mentioned in Section 5.3.4.1 could be described by an Arrhenius-type equation [32]: ) ( C (5.12) B = A exp RT where A is the proportionality constant, C is the temperature dependence parameter (kJ mol−1 ), R is the universal gas constant (kJ mol−1 K−1 ), and T is the absolute temperature (K). Among the gum ratios (1:3, 1:1, and 3:1), 3:1 SSG–XG shows the lowest

5.3 Concentrated Regime

temperature dependence of all rheological parameters, except G′ s(n-LVE) , which suggests at this ratio, SSG makes the influence of temperature on the rheological behaviors less effective. The highest temperature dependence of G′ LVE and G′′ LVE for the 3:1 blend is in the range 70–90 ∘ C. Among all parameters, 3:1, 1:1, and 1:3SSG:XG ratios show the highest C value of G′ s(n-LVE) , 𝜏 y , and 𝜏 f , respectively, and the lowest C value of G′ LVE , G′′ LVE , and tan (𝛿)LVE , respectively. 3:1 and 1:1 SSG–XG show the least temperature sensitivity of k’ (Eq. (5.3)) and k′′ (Eq. (5.4)), respectively. The highest C (tan (𝛿)1Hz ) is found for 1:3SSG–XG (133.27 kJ mol−1 ), while 1:1 SSG–XG shows the lowest C (tan (𝛿)1Hz ) value (4.37 kJ mol−1 ). For all gum ratios and frequencies in the range 0.01–10 Hz, C (𝜂*) is higher than C (𝜂 ′ ), which shows a lower temperature tolerance of the elastic component than the viscous one. At 0.01–10 Hz, the least difference between C (𝜂*) and C (𝜂 ′ ) is observed for 3:1 SSG–XG, which indicates the lowest temperature sensitivity of the elastic component for 3–1 SSG–XG. In the frequency range 0.01–10 Hz, the highest C (𝜂 ′ ) is found for 1:3SSG–XG, and the lowest C (𝜂 ′ ) is achieved for 3–1 SSG–XG. 1:3SSG–XG shows the highest C (𝜆t ), while 3–1 SSG–XG exhibits the lowest value [32]. Razavi et al. [34] studied the temperature dependence of the time-dependent parameter (C (B)) from the temperature profile mode of the dynamic temperature sweep (DTS) test at both heating and cooling stages for all gum blends. At both stages, C (B) increases with the SSG fraction, indicating the increased temperature sensitivity of the structure. 5.3.4.3.2

Kinetics of Biopolymer Interaction in Non-isothermal Condition

Investigation of kinetics based on the isothermal method has several drawbacks, especially at high temperatures. Since instantaneous heating or cooling of the sample to the desired temperature cannot be achieved in kinetic experiments, thermal lag correction may be required. A non-isothermal method can overcome the problem associated with thermal lag in kinetic studies and simplify the collection of data [35]. A number of thermal analysis techniques using non-isothermal temperature programs have been developed, such as the DTS tests. Structure development or degradation of samples could be characterized by the non-isothermal kinetic analysis proposed by Rhim et al. [35] based on a combination of the classic rate equation, Arrhenius equation, and time–temperature relationship. The general form of non-isothermal kinetics based on the complex modulus (G*) from DTS data yields the following: ( ) ) ( Ea 1 dG∗ 1 × = ln k0 + × (5.13) ln G∗m dt R T where m is the reaction rate order, t (s) is time, k 0 is the Arrhenius pre-exponential or frequency factor, Ea is the activation energy (kJ mol−1 ), R is the universal gas constant (kJ mol−1 K−1 ), and T is the absolute temperature (K). In this way, three different temperature sweeps, which are defined in Section 5.3.3.2, could be employed. Razavi et al. [34] studied the activation energy using Eq. (5.13) for SSG–XG at different ratios (3:1, 1:1, and 1:3) in three different temperature sweep modes. Ea at the heating stage increases as the SSG fraction increases, with the highest and lowest Ea values for 3:1 and 1:3 SSG–XG, respectively, which shows that the former blend’s network is more sensitive to temperature than the latter blend’s. On the other hand, Ea decreases as the SSG fraction increases during the cooling stage in TTS. The m parameter indicates the dependence between the rate of structure development or degradation and structure in the material [36]. The m value of all blends is 2 in TGS

149

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and TPS, as well as in 1:3SSG–XG in TTS at both heating and cooling stages; however, 3:1 and 1:1 SSG–XG are first order in TTS during these stages [32]. 5.3.4.4

Time–Temperature Superposition Principle

The well-known time–temperature superposition principle (TTSp ) is applied to determine either the temperature dependence of the rheological behavior of a biopolymer or to expand the time or frequency regime at a given temperature [37]. Razavi et al. [34] tested TTSp for G′ and G′′ in the frequency sweep test (0.01–10 Hz). The rheological parameters obtained in the temperature range 10–90 ∘ C were tentatively reduced to an arbitrary reference temperature (50 ∘ C), using TTSp [38]. TTSp cannot be applied to the superposition of G′ and G′′ (ω) for 1:3and 1:1 SSG–XG dispersions; in contrast, it is applied successfully for the dynamic shear test data of 3:1 SSG–XG. Good superposability of TTSp suggests that 3:1 SSG–XG is thermorheologically simple during the dynamic shear test; whereas lack of superposability of the isothermal frequency curves indicates that the other dispersions are thermorheologically complex [34]. Generally, immiscible blends will not obey TTSp due to the different temperature dependences of both components [37], which are observed for 1:3and 1:1 SSG–XG blends [34]. However, the strong interaction between the components plays a role which may result in single-temperature dependence [39], as observed for 3:1 SSG–XG, which has the lowest incompatibility among other mixtures as shown by the lowest incompatibility parameter (𝜓, see Section 5.4). aT is the ratio of the maximum relaxation time at different temperatures to the maximum relaxation time at the reference temperature (T r ), and bT is a temperature-density Tr 𝜌0 correction factor ( T𝜌 ) [40]. The aT value of 3:1 SSG–XG almost decreases with increase in temperature. The Arrhenius equation adequately describes the temperature dependence of the shift factors (R2 ≥ 0.91 and RMSE ≤0.05). The Ea values of 3:1 SSG–XG and SSG are 39.39 and 102.03 (kJ mol−1 ), respectively, which suggests that an almost three times higher relaxation energy is required for 3:1 SSG–XG. Furthermore, TTSp helps obtain rheological information over a wider range of frequency of 0.002–20 Hz for 3:1 SSG–XG than what is obtainable by the normal instrumental methods of measurement (0.01–10 Hz) [34]. 5.3.5

Effect of Salts

The interaction behavior of GGM/KGM was assessed by the addition of 0.05 M NaCl to the mixtures. The G′ values do not change at low frequencies but decrease dramatically at higher frequencies. Further addition of NaCl to 0.5 M NaCl does not affect the mixture more. Both purified GGM and GGM/KGM at 1:1 ratio with the addition of salt show a viscous character, while KGM with the addition of salt shows an elastic character with the storage modulus G′ being greater than the loss modulus G′′ throughout the frequency range [14]. The effect of Ca2+ (0.01–0.5 M) on the gelation of mixed systems of 10% BLG and 1% BSG was investigated [41]. When the Ca2+ concentration increases, the storage moduli of BLG and BSG gels increase BLG gel and BSG network formation, suggesting that phase-separated gels are formed. In addition, higher strength is obtained for the BLG–BSG mixture at higher Ca2+ concentrations. Rheological tests on a mixture of 10% BLG–1% BSG were carried out at different Ca2+ concentrations in the time sweep mode. The gelling point temperature at 0.01 CaCl2 is less than two other concentrations,

5.4 Thermodynamic

and this is the optimum Ca2+ ion for gel formation. At 0.1 M CaCl2 , the storage modulus is greater than the other concentrations [41]. 5.3.6

Effect of pH

In the BLG–BSG mixture, BSG has a strong synergistic effect on G′ , and its presence causes the effect of pH on gelation to be opposite of when only protein is in solution. The gelling point of the 10% BLG–1% BSG mixed gel is strongly pH-dependent, and stiffer gels form at higher pH. The storage modulus of the mixture decreases when the pH increases from 4.5 to 7.5, but the pH value 5.5 is an exception, in that the mixture shows the highest elasticity. At this pH, the highest G′ for 10% BLG and 1% BSG is about 197 and 43.7 kPa, respectively; however, the highest G′ for mixed gel is about 264 kPa, indicating the synergistic effect BSG on the stiffness of mixed gel [41].

5.4 Thermodynamic The performance of polymer mixtures depends on how they are arranged in space. The spatial arrangement is controlled by the thermodynamics [42]. Arthur et al. [9] studied the thermodynamic parameters of K. senegalensis (KS gum) and A. senegal (AS gum) blends in dilute solution by using the Frenkel–Eyring equation: ( ) ΔSv ΔHv ln𝜂 = lnA − + (5.14) R RT The activation energy and enthalpy change of gum flow are accounted for using the Frenkel–Eyring and Arrhenius–Frenkel models, respectively. The enthalpy change (ΔH) and activation energy of gum flow (Ea ) for blends do not show a trend, although these parameters for gum blends are within those for each gum individually. Thermodynamic incompatibility, that is, the limited miscibility of biopolymers at the molecular level, leads to separation and concentration of biopolymers within the different coexisting phases and is responsible for the functional mixing of food biopolymers, their antagonism, or synergism effects [42]. This phenomenon can be probed by investigating the Gibbs free energy, enthalpy, and entropy [5]. Razavi et al. [34] proposed a new method based on DTS data to determine the thermodynamic status of biopolymers’ reaction. In this method, they supposed that biopolymer interaction is a kind of equilibrium reaction: w1 ⋅ A + w2 ⋅ B ⇌ w3 ⋅ (AB)

(5.15)

where w1 and w2 are the weight fractions of polymers in the blend (A and B), and w3 is the weight fraction of the blend (AB). As a result, the equilibrium constant (K eq ) is calculated from G* as follows: (G∗AB )w3 Keq = (5.16) [(G∗A )w1 × (G∗B )w2 ] The equilibrium constant (K eq ) can be related to the standard Gibbs free energy change (ΔG∘ ) in a reaction by [43]: ∘ (5.17) ΔG = −RT ln(Keq )

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The entropy change and enthalpy change of the reactions are calculated on the basis of Eqs. (5.18) and (5.19), respectively [44]: ) ( Ko × NA × h (5.18) ΔS = R × ln 2.72RT ΔH = ΔG + TΔS

(5.19)

ΔS is the entropy change (J mol−1 K−1 ), K0 is the frequency factor, NA is the Avogadro constant (mol−1 ), h is the Planck constant (J s), and ΔH is the enthalpy change (J mol−1 ). The ΔG∘ values of sage seed gum–xanthan gum blends (SSG–XG) at different ratios (3:1, 1:1, and 1:3) using the aforementioned method are positive and increase as the XG fraction increases at 25 ∘ C, which indicates that the interaction between SSG and XG is a non-spontaneous reaction and cannot occur without the progressive increasing input of work from an external source as the XG fraction increases. All blends show a negative ΔS, which decreases as the XG fraction increases. Thermodynamic incompatibility of macromolecules arises from the low entropy of their mixing [45]. The enthalpy of mixing is strongly endothermic for all the blends and decreases as the XG fraction increases in blends. Miscibility can only be achieved when ΔH is negative [5]. These results confirm the immiscibility of SSG–XG blends that increase with the XG fraction [34]. Since ΔG∘ has a specific definition, for elaborating the thermodynamic incompatibility of biopolymers in a temperature sweep test, Razavi et al. [34] proposed the 𝜓 parameter (−ln (K eq )) as a representative of the Gibbs free energy change. The thermodynamic incompatibility parameter of SSG–XG, 𝜓, increases during heating (10–90 ∘ C) and decreases with the decrease in temperature during the cooling stages for 3:1 SSG–XG, whereas 1:1 and 1:3SSG–XG show a reverse trend. The absolute values of 𝜓, ΔH, ΔS, and ΔG parameters at cooling stages are higher than those at heating stages using three different temperature sweep modes (TTS, TGS, and TPS), which could be attributed to the fact that during cooling, when the molecules form a fluctuating network, higher occupancy of a mixed solution phase occurs, result in greater phase separation [46]. The results suggest that the interaction of incompatible SSG and XG is mainly due to the excluded volume effect, which is dependent upon the conformations of macromolecules [34].

5.5 Miscibility There are numerous methods to elaborate the synergistic/antagonistic interaction behavior of biopolymers. Some of them are as follows. 5.5.1

Interaction Coefficient

For a ternary system (polymer–polymer–solvent), the interaction coefficient (𝛼, %) could be calculated as follows [18]: 𝛼 (%) =

Exerimental dataAB − [(w1 × Exerimental dataA ) + (w2 × Exerimental dataB )] Exerimental dataAB (5.20)

5.5 Miscibility

where w1 is the weight average of the A component, and w2 is the weight average of the B component. Among different SSG–GG mixtures (1:3, 1:1, and 3:1), 1:1 SSG–GG shows the highest %α of consistency coefficient and the flow behavior index followed by the 3:1 ratio [18]. In addition, an antagonistic interaction of the zero-shear viscosity and time constant is present between SSG and GG at all ratios, which is the least for 3:1 SSG–GG. 1:3SSG–GG shows the highest antagonistic effect of G′ , G′′ , and G*, whereas the highest value of Aa is found for 3:1 SSG–GG (10.22 Pa rad−𝛼 s𝛼 ) with the 17.55% synergism percentage, indicating that in this mixture the highest molecular binding occurs between GG and SSG [18]. Razavi et al. [31] reported that the G*LVE and Aa of SSG–XG blends are lower than the values of these parameters calculated from the weight averages of the single-component systems, confirming that no synergy is present between SSG and XG at any proportions, except for 3:1 and 1:1 SSG–XG at 50 ∘ C, which shows the synergy of the Aa parameter. At 30 ∘ C, the storage modulus, static and dynamic yield stresses, and recovery time parameters obtained from the in-shear structural recovery test of XG and SSG blends are lower than the values of these parameters calculated from weight averages of the single-component systems, confirming that no synergy of these parameters is present between SSG and XG at any proportion, whereas the loss modulus, loss tangent, and power index of the complex viscosity of all gum ratios show the synergy behavior [11]. For 1:1 SSG–XG and 1:3SSG–XG, the %𝛼 of maximum compliance (J max ) and retardation time (𝜆ret ) increase, whereas the %𝛼 of gel strength (S) decreases with the increase in temperature; on the other hand, 3:1 SSG–XG shows a reverse trend [31]. The G* values of SSG–XG blends (1:3, 1:1, and 3:1) are lower than the value of this parameter calculated from the weight averages of the single-component systems, confirming that no synergy is present between SSG and XG at any proportion. 3:1 SSG–XG at 50 ∘ C shows the lowest antagonistic effect (lowest %𝛼) of G* among the other gum blends and temperatures (10 to 90 ∘ C) [34]. Studies by Razavi’s team [11, 18, 31, 32, 34] conclude that 3:1 SSG–GG and 3:1 SSG–XG are the best synergist mixtures among the different blends of SSG with guar gum or xanthan, respectively. 5.5.2

Cole-Cole Plot

Another method used for analyzing the antagonism/synergism effects is Cole-Cole plots, which represent the relationship between the imaginary viscosity (𝜂 ′′ ) and dynamic viscosity (𝜂 ′ ). This empirical method has been widely used to analyze the miscibility of polymer blends [46]. A smooth, semicircular shape of the plotted curves suggests good miscibility, and any deviation from this shape shows a heterogeneous dispersion and a poorer compatibility of the constituents of the blend. To investigate the deviation from the semicircular shape in the Cole-Cole plots of different SSG–XG ratio dispersions, the power-law model was fitted to all curves by Razavi et al. [11]. The power-law index for 3:1, 1:1, and 1:3SSG–XG are 0.52, 0.97, and 0.93, respectively, which in turn shows that the semicircularity is only present for the 3:1 SSG–XG curve, while the curves of the other two blends are significantly different from this shape [11]. 5.5.3

Han Curve

The Han curve method, which represents the relationship between the storage modulus (G′ ) and loss modulus (G′′ ) in the log scale, has often been used to detect phase separation due to differences in structural units [47]. For a homogeneous polymer system, the

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Han curve is not dependent on the temperature and is generally linear. Razavi et al. [31] investigated the interaction behavior of SSG–XG using Han curves at 10, 30, and 50 ∘ C. 3:1 SSG–XG exhibits single-phase behavior since the plots are generally linear and not dependent on the temperature; thus, it is believed that 3:1 SSG–XG is miscible, or at least the XG fraction is finely dispersed in the SSG fraction. On the other hand, the Han curves of log G′ versus log G′′ at different temperatures for 1:1 and 1:3 SSG–XG are not superimposed, confirming the immiscibility of these systems.

5.6 Conclusions and Future Trends In this chapter, we presented a summary of findings on the rheological behavior of systems consisting of blends of novel biopolymers. The literature verifies that some emerging gums could be alternatives to some of the commercial hydrocolloids in blend formulations due to the specific properties that they impart. Comparisons of the rheological behavior of these novel blends with some of the commercial ones help the reader decide on the particular hydrocolloid among different new hydrocolloids for their specific usage and expand the applications of the emerging hydrocolloids in food and pharmaceutical systems. In addition, the thermodynamics and kinetics of biopolymer blends are described in detail to introduce a new methodology for the elaboration of biopolymer interaction, which is so important from the fundamental science point of view. Having an idea of the potential of a biopolymer blend for use in a food formulation, the preference depends on the best-known types of blends. Therefore, before using the aforementioned gum blends in food formulation or other gum-related industries, more needs to be known about their microstructure and physicochemical and thermal properties, which will be the subject of future works.

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6 Sage (Salvia macrosiphon) Seed Gum Seyed M.A. Razavi, Ali Alghooneh, and Fataneh Behrouzian Food Hydrocolloids Research Center, Department of Food Science and Technology, Ferdowsi University of Mashhad, PO Box 91775-1163, Mashhad, Iran

6.1 Introduction Sage (Salvia macrosiphon) is an endemic plant belonging to the genus Salvia (Figure 6.1a). The genus Salvia (Labiatae) contains more than 700 species, of which about 200 are found in Iran and distributed worldwide. S. macrosiphon Boiss is a perennial, herbaceous, strongly aromatic, lemon-scented, and pale yellowish green plant [1]. There is evidence that plants belonging to this genus are pharmacologically active, and they have been used in traditional medicine as a diuretic agent, tonic, anti-rheumatoid agent and to relieve chronic pain, antimicrobial agent, carminative agent, and for flavor as spices since antiquity all around the world [2]. Javidnia et al. [3] investigated the composition of the essential oil of S. macrosiphon and characterized 64 components, representing 93.3% of the oil, the main constituents being linalool (26.3%), hexyl hexanoate (9.6%), hexyl isovalerate (9.3%), hexyl-2-methyl-butanoate (8.9%), sclareol (7.2%), and hexyl octanoate (6.1%). The aerial parts of S. macrosiphon contain flavonoids of salvigenin, eupatorin, and 13-epi-manoyl oxide [4]. Furthermore, Gohari et al. [5] isolated four flavonoids plus a steroid compound from ethyl acetate and methanol extracts of the aerial parts of this plant. Some physical and mechanical properties of sage seeds were measured by a computer vision system and/or experimental methods including the projected area, sphericity, roundness, surface area, unit mass, 1000 grain mass, volume, true density, bulk density, porosity, static coefficient of friction, filling and emptying angles of repose, terminal velocity, rupture force, hardness, and absorbed energy [6]. Wild sage seed (S. macrosiphon) readily swells in water to give mucilage [6] (Figure 6.1b,c). The sage seed gum (SSG) conformation was elaborated in aqueous solution [7]. SSG dispersion exhibits a higher extent of departure from the Cox–Merz rule, yield stress values, amplitude dependence of the storage modulus at the start of the nonlinear viscoelastic range (n-LVE), relaxation modulus, relaxation time (obtained from the mechanical spectra), material stiffness parameter [8], zero-shear viscosity, shear-thinning behavior [9], time scale of junction zones, and a lower order of relaxation function than guar gum (GG) [8]. In addition, SSG shows higher temperature tolerance of many rheological parameters in amplitude sweep (storage modulus, loss Emerging Natural Hydrocolloids: Rheology and Functions, First Edition. Edited by Seyed M.A. Razavi. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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(a)

(b)

(c)

Figure 6.1 A pictorial view of (a) Salvia macrosiphon plant, (b) sage seeds, and (c) the seeds soaked in water.

modulus, loss tangent, yield stress at the limit of the LVE range, flow point stress, with the corresponding modulus, slope of the storage modulus and loss tangent at the start of n-LVE), higher storage modulus, loss modulus, complex modulus, extent of elastic component temperature dependency, the slope of double logarithmic complex viscosity- frequency plots at different temperatures of 10–90 ∘ C (1% w/w, f = 1 Hz), complex viscosity (1 Hz, 50 ∘ C) [10], the time dependence of the yield stress at small and large deformations [11], and departure value from the Cox–Merz rule, and lower complex compliance (1 Pa−1 , 0.01–10 Hz) than xanthan gum (XG) [12]. Such positive effects make SSG excellent stabilizing, thickening, emulsifying, fat replacing, and binding agents in food, cosmetics, and pharmaceutical systems. Herein, we review the rheological properties of SSG and their relationship with its functional properties.

6.2 Salvia macrosiphon Seed Mucilage People generally use plant extracts for the treatment of various diseases and for minimizing the effects of the chemotherapeutic agent. Amirghofran et al. [13] investigated S. macrosiphon extract for a possible anti-cancer effect. The extract showed a strong inhibitory effect on Raji lymphoma tumor cell line (IC50 = 77 ± 1 μg ml−1 ). The effect of S. macrosiphon aerial part extract on morphine dependence was investigated in mice. The methanolic extract of S. macrosiphon can suppress the morphine withdrawal

6.2 Salvia macrosiphon Seed Mucilage

syndrome [14]. The seeds consist of 9.97%–12% mucilage, depending on their origin and extraction procedure, which comprise uronic acid containing polysaccharides [15, 16]. The average molecular weight of associated carbohydrate polymer chains ranges from 4 × 105 to 1.5 × 106 Da [7, 17]. 6.2.1

Mucilage Extraction Optimization

The extraction of galactomannans from seed involves milling, extraction with cold and hot water, and precipitation with an alcohol. By means of the water extraction procedure, the flow behavior index, consistency coefficient, and apparent viscosity (46.16 s−1 ) under different extraction conditions of temperature, that is (25–80 ∘ C), water-to-seed ratio (25:1 to 85:1), and pH (3–9), range from 0.317 to 0.374, 4.455 to 9.435 Pa sn , and 373 to 694 Pa s, respectively. The extraction conditions were optimized by the response surface method (RSM). Optimum conditions for the water extraction procedure of crude hydrocolloid from sage seed, using the quadratic model for maximizing the responses of the yield, apparent viscosity, and emulsion stability index, are a temperature of 25 ∘ C, a water-to-seed ratio of 51:1, and a pH of 5.5. At these conditions, the yield, apparent viscosity (122 s−1 ), and emulsion stability of SSG (1% w/w and 25 ∘ C) are 10.1%, 312 mPa s, and 403 min, respectively. At these ranges of treatments, the highest value of yield is 12.2%, obtained at the highest temperature (80 ∘ C), a water-to-seed ratio of 55:1, and a pH of 6.00 [15]. In addition, water extraction following the alcoholic precipitation (ethanol 96%: hydrocolloid of 3:1 % v/v ratio) of SSG at the water-to-seed ratio of 30:1 w/v% and different hydration times (15, 30, 60, and 120 min) and temperatures (25 and 65 ∘ C) show the optimum hydration time at 30 min and temperature of 25 ∘ C for the maximum extraction yield of 12% [16]. The kinetics of SSG water extraction is represented by the first-order mass transfer model. The extraction process is spontaneous, irreversible, and endothermic. The enthalpy change (ΔH), entropy change (ΔS), and Gibbs free energy change (ΔG) values are 0.52–14.99 kJ mol−1 , 6.3–52.2 J mol−1 K−1 , and 0.14–2.44 kJ mol−1 , respectively. A mathematical model of mass transport fits the experimental data. The volumetric mass transfer coefficient values are in the range 4.7–16.9 (h−1 ) [18]. Investigating the effect of different drying methods in the SSG extraction procedure, that is, oven drying (40–80 ∘ C), freeze drying (−40 ∘ C), and vacuum oven drying (100 mbar, 50 ∘ C) on the color of SSG shows that different drying methods cause various degradation of color parameters. The rise in temperature has a negative effect on the color (high color change) and brightness (low brightness) of gum solution. In comparison with the other drying procedures, the freeze-drying process results in the best color quality and the highest viscosity for SSG [19]. 6.2.2

Physicochemical Properties

The chemical compositions of SSG under optimal extraction conditions were determined by Bostan et al. [15]. In addition, the physicochemical properties of two SSG species (SSG1 and SSG2 ), were broadly investigated and shown in Table 6.1 [7]. Total sugar determined via the DuBois method is in the range 69.96%–71.05%. SSG contains 28.2%–32.2% total uronic acid, reflecting the polyelectrolyte nature of gum. Monosaccharide analysis by high-performance anion exchange chromatography (HPAEC) demonstrates the presence of mannose (M) and galactose (G) as the

161

162

6 Sage (Salvia macrosiphon) Seed Gum

Table 6.1 Chemical composition of sage seed gum. Composition (%)b)

SSG1

Moisture

14.40 ± 0.00a) 8.08 ± 0.16

Ash

9.33 ± 0.12

9.07 ± 0.63

Protein

2.58 ± 0.01

1.59 ± 0.08

Carbohydrate

69.96 ± 0.80 71.05 ± 2.52

SSG2

Minerals

Minerals

SSG1

SSG2

Macroelements

Sodium

0.192 ± 0.032

0.122 ± 0.010

Potassium

2.968 ± 0.095

2.699 ± 0.049

Calcium

0.962 ± 0.033

0.908 ± 0.036

Magnesium

0.873 ± 0.023

0.778 ± 0.022

Phosphorus

0.030 ± 0.006

0.026 ± 0.000

Iron

0.022 ± 0.006

0.034 ± 0.000

Sulfur

0.130 ± 0.006

0.059 ± 0.000

Cadmium

sucrose > temperature [19]. 7.4.2

Steady Shear Properties

The steady shear flow behavior of BSG solutions has been investigated in some studies [4, 11, 15, 20, 21]. Generally, it has been concluded on the basis of fitting time-independent models on shear rate–shear stress data that BSG exhibits a pronounced pseudoplastic or shear-thinning behavior, characterized by small values of the flow behavior index along with a high consistency coefficient determined by the power-law and Herschel–Bulkley models (Table 7.3). Surprisingly, the values determined for BSG are comparable to those of commercial hydrocolloids under similar conditions. The strong pseudoplasticity of BSG solutions has been attributed to its rather semi-rigid chain conformation that gives rise to a highly entangled macromolecular solution and the presence of a gel-like structure, which is related to the tendency of molecular association [4]. By fitting viscoplastic models on BSG rheological data, it has been shown that there is a yield stress (Table 7.3) indicating a cross-linked or an interactive structure with intermolecular associations which must be broken down before hydrocolloid solution can flow appropriately. It is believed that the yield stress is a useful characteristic when binding, stabilizing, and fat-replacing applications are needed [4]. In this regard, different direct and indirect methods of determining the yield stress have been assessed, and it has been concluded that BSG solutions exhibit yield stress. The indirect method, that is, viscometry, seemed inappropriate for yield stress measurements because it has not detected the concentration dependence of the yield stress of BSG over the range 1%–1.4%. On the other hand, the inclined plane and cylindrical penetrometer methods showed significant differences between the yield values of BSG at different concentrations [21].

7.4 Rheological Properties

Table 7.3 Steady shear flow properties of 1% aqueous solution of BSG at 20 ∘ C and shear rate range of 0.01–1000s−1 . Modela)

𝝉 0 (Pa)

𝜼 (Pa s)

0.29

—

—

0.35

1.64

—

—

—

5.66

0.044

—

—

4.6

0.019

k (Pa sn )

n (−)

Power-law: 𝜏 = k 𝛾̇ n

4.2

Herschel–Bulkley: 𝜏 = k 𝛾̇ n + 𝜏0

2.8

Bingham: 𝜏 = 𝜂 𝛾̇ + 𝜏0 Casson: 𝜏 0.5 = 𝜂 𝛾̇ 0.5 + 𝜏0 0.5

a) 𝜏, k, n, 𝜏 0 , and 𝜂 are shear stress, consistency coefficient, flow behavior index, yield stress, and plastic viscosity, respectively. Source: Reproduced from Razavi et al. [4] with permission from Elsevier.

Table 7.4 Parameters of shear-thinning models for 1% solution of BSG at 20 ∘ C and shear rate range of 0.01–1000 s−1 . Modela)

𝜼0 (Pa s)

𝜼∞ (Pa s)

k (s−1 )

Carreau: 𝜂 = 𝜂∞ + (𝜂0 − 𝜂∞ ∕1 + (k 𝛾) ̇ 2)

67.21

0.64

14.47

0.61

̇ m) Cross: 𝜂 = 𝜂∞ + (𝜂0 − 𝜂∞ ∕1 + (k 𝛾)

67.44

1.31

9.53

0.84

̇ m) Williamson: 𝜂 = (𝜂0 ∕1 + (k 𝛾)

68.09

—

6.69

0.69

m (−)

a) 𝜂 0 , 𝜂 ∞ , k, and m are zero-shear viscosity, infinite-shear viscosity, relaxation time, and power index, respectively. Source: Reproduced from Razavi et al. [4] with permission from Elsevier.

The viscosity profile of BSG has been described by different shear-thinning models by determining the zero-shear and infinite-shear viscosities (Table 7.4). The value of the zero-shear viscosity for BSG has been observed to be higher than that of commercial galactomannans like locust bean gum and guar. The higher the zero-shear viscosity, as an indicator of the microstructural nature of BSG during storage, the greater the number of linkages between the macromolecules. On the other hand, the infinite-shear viscosity indicates the consistency of the hydrocolloid during processing, so that a greater value shows that a greater energy is required for processing [4]. Estimation of the relaxation time (k), which is an indicator of the rate of breakdown of macromolecules in a shear environment, showed that BSG exhibits a higher gel strength compared to that of the galactomannans (Table 7.4). The lower the value of the relaxation time, the higher the resistance of the macromolecule to the applied shear. In addition, on the basis of the parameter m obtained by the Cross and Williamson models, it has been observed that BSG tends to form shear-thinning rather than Newtonian-like solutions, as indicated by m tending to unity [4]. The time-dependent rheological characteristics of BSG solutions (4%), characterized by the forward–backward shear method, revealed that thixotropic behavior appeared at concentrations of 4% or higher. Alternatively, assessing the time-dependent properties of BSG by the constant shear method revealed thixotropic behavior. From the results of fitting time-dependent models, it has been observed that the first-order stress decay model with a nonzero equilibrium stress value is more appropriate compared to models

189

7 Balangu (Lallemantia royleana) Seed Gum

such as the Weltman model, structural kinetic model, and first-order stress decay model with zero equilibrium stress [20]. The flow behavior of BSG mixtures with xanthan, guar gum, and locust bean gum has been evaluated at 1:3, 1:1, and 3:1 blending ratios to describe the interactions through steady shear and relative viscosities. It was shown that there were no significant differences between the consistency coefficient of guar and locust bean solutions and their blends at 1:3 ratio (25% substitution). Also, from a comparison of the apparent viscosity (at 293 s−1 ), it has been concluded that the investigated commercial gums can be substituted by 25% and 50% BSG to provide the same consistency [22]. The influence of drying methods (air drying, freeze drying, and vacuum air drying) applied to extracted BSG on the apparent viscosity has been investigated, and it has been reported that the drying process generally decreased the viscosity, and that the most drastic decrease was caused by the air drying method at 80 ∘ C (Figure 7.2). The viscosity reduction has been attributed to the substantial impact of the drying process on the chemical composition of BSG, altering the balance of the soluble and insoluble fractions of the macromolecule [15]. In another study, the influence of different sugars (sucrose, glucose, fructose, and lactose) and salts (NaCl and CaCl2 ) at 1%–4% concentrations on the flow behavior and apparent viscosity of BSG solutions (1%) has been investigated. It has been concluded that the apparent viscosity of BSG solutions has been improved in the presence of different sugars, with the lowest viscosity enhancement being observed for fructose. On the other hand, the addition of salts and increase of their concentration decreased the apparent viscosity of BSG solutions, in which the presence of NaCl with concentrations higher than 0.25% had a small additional effect on reducing the viscosity [15]. This is in accordance with the results of Mohammad Amini and Razavi [19], which investigated the influence of sugars and salts on the intrinsic viscosity of BSG. The viscosity reduction of BSG solutions containing salts may be attributed to the reduction of the intermolecular repulsions in presence of counterions, thus inhibiting the macromolecules of BSG from forming an expanded structure. 0.3

Apparent viscosity (Pa.s)

190

0.25 0.2 0.15 0.1 0.05 0 CS

AD-40°C AD-50°C AD-60°C AD-70°C AD-80°C

FD

VO

Figure 7.2 Apparent viscosity of Balangu seed gum (BSG) at shear rate of 60 s−1 as affected by air drying (AD), freeze drying (FD), and vacuum oven drying (VO) methods in comparison with non-dried (CS) BSG. Source: Adapted from Salehi and Kashaninejad [15] with permission from Taylor & Francis.

7.4 Rheological Properties

On the basis of the power-law model, it has been reported that the consistency coefficient (k) of BSG solutions has been enhanced by the addition of sugars, whereas the presence of salts did not have an obvious impact on k. On the other hand, sucrose, fructose, and lactose did not induce a significant change in the flow behavior index (n), except glucose, which increased it. The presence of salts, in contrast, decreased the value of n, indicating an improvement in the pseudoplasticity of BSG solutions [23]. In another work, the influence of multiple freeze–thaw cycles (up to three times) at −18 ∘ C and − 30 ∘ C on the steady shear rheological properties of BSG has been studied. Similarly, pseudoplastic flow behavior has been observed for BSG solutions: the consistency coefficient and yield stress increased when the concentration was increased, whereas the flow behavior index decreased, showing a stronger shear-thinning behavior at higher concentrations. On the basis of the Herschel–Bulkley model, it has been reported that the yield stress of BSG solutions increased slightly when the number of repeated freeze–thaw cycles was increased, which was more pronounced at a lower temperature (−30 ∘ C) compared to −18 ∘ C (Table 7.5). On the other hand, no specific change in the flow behavior index and consistency coefficient of BSG has been Table 7.5 Rheological parameters of BSG as a function of freeze–thaw cycles at different temperatures and concentrations.

Concentration (%)

Temperature (∘ C)

Freeze–thaw cycle

𝝉0 (Pa)a

k (Pa sn )a

n (−)a

Relative hysteresis (%)

0.25

Control

—

0.66

0.15

0.60

7.22

st

1

0.71

0.24

0.56

10.32

2nd

0.70

0.21

0.60

10.89

3rd

0.73

0.23

0.60

11.80

1st

0.78

0.18

0.60

10.95

2nd

0.80

0.17

0.61

11.04 13.02

−18

−30

0.50

3rd

0.89

0.17

0.60

Control

—

1.38

1.07

0.46

13.42

−18

1st

1.64

0.99

0.47

11.65

2nd

1.60

1.13

0.45

15.44

3rd

2.19

1.00

0.48

17.34

1st

1.60

0.98

0.45

12.75

2nd

1.68

1.26

0.43

15.19

3rd

1.90

1.16

0.47

16.56

Control

—

4.06

1.87

0.44

13.97

−18

1st

4.14

2.56

0.41

14.88

−30

0.75

−30

2nd

4.91

2.70

0.42

17.81

3rd

4.44

2.79

0.41

17.95 14.15

1st

3.65

2.41

0.40

2nd

5.09

2.52

0.43

17.13

3rd

5.15

2.57

0.42

18.46

a) 𝜏 0 , k, and n denote yield stress, consistency coefficient, and flow behavior index, respectively. Source: Reproduced from Khodaei et al. [24] with permission from Elsevier.

191

192

7 Balangu (Lallemantia royleana) Seed Gum

observed in regard to the increased number of freeze–thaw cycles. Overall, the rheological parameters of BSG solutions, regardless of their concentration, remained almost unchanged, and the freeze–thaw process had no pronounced destructive influence. Using the hysteresis loop method, the time-dependent rheological characteristics of BSG solutions in the concentration range 0.25%–0.75% has been shown; an increase in the concentration and number of cycles of the freeze–thaw process increased the relative hysteresis, which was more pronounced at −30 ∘ C (Table 7.5). The constant shearing (50 s−1 , 25 ∘ C) method and modeling of the first-order stress decay with the nonzero equilibrium model showed that 1% BSG solutions exhibited thixotropic behavior in which application of multiple freeze–thaw cycles increased the initial and equilibrium stress values, whereas the decay rate constant was not affected. This has been attributed to the exclusion of BSG polymer chains from the growing ice crystals during the freezing, resulting in polymer-rich regions within the unfrozen concentrated phase that promote chain association, thus enhancing thixotropic behavior [24]. 7.4.3

Dynamic Shear Properties

The limiting or critical strain, which determines the maximum applicable deformation for a system before structural failure occurs, has been obtained through the strain sweep test. It has been observed that the storage modulus (G′ ) is independent of the strain amplitude up to 5%, which corresponds to the critical strain for BSG solution (Figure 7.3a). As a measure of the yield stress, the stress value at the crossover point of G′ and loss modulus (G′′ ), where the material behavior changes from solid to viscous, has been determined to be 2.15 Pa, which seems close to the value of the yield stress estimated using steady shear data (Table 7.3). Also, it has been demonstrated that BSG exhibits a gel structure at 1% concentration on the basis of the ratio of G′ to G′′ (1.38–1.63) in the linear viscoelastic region [4]. The results of the frequency sweep test have shown that BSG behaves like a weak gel, which can be inferred from the parallel curves of G′ and G′′ over a wide range of frequency with G′ > G′′ , a linear reduction in the complex viscosity in the logarithmic scale, and a lower-than-unity loss tangent (tan 𝛿) (Figure 7.3b). On the basis of the Cox–Merz relationship, which relates the dynamic viscosity and shear viscosity (Figure 7.3c), it has been revealed that BSG exhibits a flexible and ordered conformation between random coil and semi-rigid- chain (refer to Section 7.3), showing strong inter-chain association and pseudoplastic flow behavior [4]. 7.4.4

Textural Properties

Large-deformation texture analysis has established that BSG solutions with 4% concentration had the lowest hardness value in comparison with xanthan, guar gum, and locust bean gum according to penetration, back extrusion, and texture profile analysis (TPA) tests. The penetration test showed that substitution of guar gum with 25% BSG decreased the hardness, while replacing locust bean gum and xanthan with 25%–75% BSG improved the hardness. In the back extrusion test, the hardness of the xanthan and locust bean gum mixed gels was increased with an increase in BSG concentration, whereas the highest values were observed in guar and locust bean gum mixtures with 50% substitution level of BSG. On the basis of the TPA test, the hardness of mixed gels

7.4 Rheological Properties

(a)

100

100

1

1

100 G′ (Pa), G″ (Pa), G* (Pa), η′ (Pa.s)

Tan delta

10

0.1

1

G′ (Pa)

100

10 Strain (%)

G″ (Pa)

Tan (d)

0.1 1000

η′ (Pa)

10

1

0.1 0.001

(c)

G* (Pa)

10

0.1 0.01

(b)

G″ (Pa)

Tan delta

Modulus (Pa)

G′ (Pa)

100.00

0.01

0.1

Complex viscosity (Pa.s)

1

10

100

Shear viscosity (Pa.s)

ηa, η* (Pa.s)

10.00

1.00

0.10

0.01 0.00

0.01

0.10 1.00 10.00 100.00 1000.00 10000.00 Frequency (rad/s), shear rate (1/s)

Figure 7.3 Mechanical spectra of 1% Balangu seed gum solution determined at 20 ∘ C: (a) strain sweep test (1 Hz frequency) and (b) frequency sweep at 0.5% strain, and (c) Cox–Merz plot. Source: Adopted from Razavi et al. [4] with permission from Elsevier.

193

194

7 Balangu (Lallemantia royleana) Seed Gum

Table 7.6 Influence of drying methods on textural characteristics of 3% BSG solutions. Drying methoda)

Hardness (g)

Stickiness (g)

Consistency (g s)

Adhesiveness (g s)

AD-40 ∘ C AD-50 ∘ C

39.6

11.2

386.3

91.7

40.4

11.4

364.8

91.6

AD-60 ∘ C

34.4

10.1

324.2

69.9

AD-70 ∘ C AD-80 ∘ C

33.1

10.7

284.7

69.1

33.6

9.9

245.3

64.1

FD

46.9

14.6

487.8

130.8

VO

46.6

12.3

426.8

95.4

a) AD, FD, and VO denote air drying, freeze drying, and vacuum oven drying, respectively. Source: Adopted from Salehi and Kashaninejad [15] with permission from Taylor & Francis.

decreased significantly at all substitution levels of BSG. On the other hand, the value of the apparent modulus of elasticity, cohesiveness, and gumminess did not change with BSG replacement. The springiness of xanthan and guar gum exhibited an increase in the presence of BSG, whereas it did not change for locust bean gum mixed gels. Although the chewiness of xanthan was not affected by BSG substitution, the presence of BSG in guar gum and locust bean gum mixed gels increased and decreased the chewiness, respectively [25]. In another study, textural parameters have been investigated with the penetration test for BSG gels with 3% concentration as a function of gum drying method (Table 7.6). It has been reported that the lowest hardness, stickiness, consistency, and adhesiveness values were exhibited by air-dried BSG at elevated temperatures, while freeze- and vacuum-dried gums exhibited the highest values [15]. By investigating the influence of multiple freeze–thaw cycles on the textural parameters of 1% BSG gels at 25 ∘ C using the TPA test, Khodaei et al. [24] reported that hardness, stiffness, cohesiveness, springiness, and gumminess have been increased slightly, more profoundly at lower temperatures (−30 ∘ C). The authors attributed the high resistance of BSG gels to the freeze–thaw process to the weak gel characteristics, and therefore they concluded that BSG has excellent potential for controlling texture and reducing the destructive effects of ice crystals during temperature fluctuations of food systems.

7.5 Functional Properties 7.5.1

Stabilizing

The potential of replacing commercial hydrocolloids (palmate-tuber Salep (PTS) and carboxymethylcellulose (CMC)) with BSG as a stabilizer in hardened ice cream formulation has been studied. It has been reported that the presence of BSG in formulation increased the viscosity of ice cream mix so that the highest values were observed in the case of 75% replacement of CMC and 50% substitution of PTS with BSG. The higher viscosity of ice cream mix is believed to be an important factor for its melting resistance and smoothness. In contrast, the presence of BSG caused a significant reduction in ice cream overrun, due to the increased viscosity of the mixture, while the sensory

7.5 Functional Properties

0.8

BSG

CMC

PTS

a

0.7 0.6 Viscosity (Pa.s)

Figure 7.4 Viscosity of soft ice cream mix as a function of stabilizer type and level. Source: Adapted from Bahramparvar et al. [28] with permission from Wiley. CMC, carboxymethylcellulose; BSG, Balangu seed gum; PTS, palmate-tuber Salep.

b

b

0.5 0.4 0.3 0.2

c

c d

0.1

c d

e

0 0.30

0.40 Stabilisers (%)

0.50

attributes of ice cream containing BSG, whether alone or in combination with PTS and CMC, were improved or at least not changed compared to the control [26, 27]. In another study, the influence of different concentrations of BSG as a stabilizer for soft ice cream compared to PTS and CMC gums has been investigated. It has been reported that the viscosity of ice cream increased as the level of stabilizer increased from 0.3% to 0.5%, and viscosity enhancement followed this order: CMC > BSG > PTS (Figure 7.4). Similarly, BSG reduced the overrun value of ice cream as its concentration increased, and it also caused greater reduction in overrun compared to other gums. The results of sensory attributes have established that ice creams containing BSG were acceptable at all addition levels [28, 29]. In a similar study, it has been found that soft ice cream mixes containing BSG behaved as a pseudoplastic fluid, and on the basis of the power-law model, the apparent viscosity and the consistency coefficient increased, while the flow behavior index decreased in response to increasing addition levels. Comparing the flow properties, BSG enhanced the rheological properties of ice cream mix to a greater extent than CMC and Salep. This, in turn, will guarantee a better mouthfeel, which is desirable in ice creams. The sensory analysis showed that BSG acts as a very suitable ice cream stabilizer, which is comparable with CMC, a well-known commercial stabilizer [29, 30]. In another study, the influence of BSG as yogurt stabilizer at 0.15%–0.25% concentration has been assessed in comparison with gelatin. It has been reported that incorporating BSG in yogurt formulation has led to acceptable physicochemical characteristics (pH, titratable acidity, syneresis, water-holding capacity, hardness, and viscosity) and sensory perception with lower concentrations compared to gelatin (0.5%). Microbiological examinations showed that the microbial count was affected by incorporation of BSG, with minimum count and negative test results for coliforms during storage being observed. The best results for physicochemical parameters have been achieved at 0.25% concentration, while the highest sensory scores were obtained at 0.20% concentration [31]. The stabilizing effect of 0.15%–0.30% BSG was recently investigated in an oil-in-water emulsion containing whey protein. It was established that increasing the BSG concentration resulted in higher viscosity, zeta potential, and polydispersity index (PDI) while decreasing the mean droplet diameter and creaming rate, resulting in an overall

195

7 Balangu (Lallemantia royleana) Seed Gum

enhancement of emulsion stability during two days of storage. The optimum BSG concentration is suggested to be 0.15% or less because of the depletion flocculation phenomenon [32, 33]. 7.5.2

Fat Replacement

The incorporation of BSG as a fat replacer (at least 25% fat replacement) along with different sweeteners in low-calorie pistachio butter (isomalt and sucrose) has been compared to basil seed gum and xanthan on the basis of steady shear rheological properties. Pseudoplastic behavior has been reported for pistachio butter containing BSG so that increasing the gum level from 0.01% to 0.04% increased the consistency coefficient and yield stress while decreasing the flow behavior index [34]. Alternatively, time-dependent rheological parameters have been investigated through the forward–backward shearing method for the same system and similar BSG levels in pistachio butter formulation, which revealed thixotropic behavior, decreasing the magnitude of the hysteresis loop with increasing gum level and emulsion stability for three-month storage [35]. In another study, dynamic shear and large-deformation rheological measurements at 5–65 ∘ C on reduced-fat pistachio butter containing 0.136% BSG have been performed by comparing formulations containing 0.4% xanthan and 0.092% basil seed gum. From dynamic spectra, a viscoelastic solid structure has been reported for pistachio butter containing gums. It has been revealed by the temperature sweep test that raising the temperature changed the elastic structure of pistachio butter to viscous behavior, characterized by an increase in the loss tangent. From the time sweep test, it has been observed that the complex modulus diminishes as the temperature rises, where the value of the complex modulus remains almost constant over time at 45 and 65 ∘ C but shows an increasing trend at room temperature (Figure 7.5). For TPA test, the highest hardness and adhesiveness values have been reported for pistachio butter samples containing BSG [36]. The results of steady shear rheological measurements at 5–65 ∘ C revealed that the apparent viscosity and consistency of reduced-fat pistachio butter containing BSG 100000 Complex modulus (Pa)

196

10000

1000

100 0

100

200

300

400 500 Time (s)

600

700

800

Figure 7.5 Complex modulus as a function of time for low-calorie pistachio butter containing Balangu seed gum: (○) 25 ∘ C, (◽) 45 ∘ C, and (Δ) 65 ∘ C. Source: Adopted from Emadzadeh et al. [36] with permission from Taylor and Francis.

7.5 Functional Properties

declined when the test temperature was increased, but remained higher than the values determined for formulations containing xanthan. Also, the structural recovery evaluations proved weak thixotropic behavior [37]. In another work, the potentials of BSG at 0.3%–0.5% concentration as a fat replacer in model O/W emulsions with 25%–35% fat content has been studied. The mean particle size of emulsions containing BSG ranged from 2.19 to 2.75 μm so that when the gum concentration was increased, the mean particle size decreased at all fat content levels. When the BSG concentration was increased, the specific surface area of the emulsions increased at all fat content levels, indicating an increase in emulsion stability. The steady shear rheological assessment of emulsions indicated a pseudoplastic behavior in which the pseudoplasticity decreased with increasing gum concentration, while the apparent viscosity, consistency coefficient, and yield stress increased. On the basis of dynamic rheological characterizations, it has been shown that emulsions exhibit weak gel structure with loss tangent values higher than 0.1, while the loss tangent decreases with increasing gum concentration and fat content. The sensory evaluations revealed that by when the BSG concentration was increased, the sensory consistency and oiliness increased, while the smoothness of the emulsions remained unchanged. The visual assessment of emulsions revealed that they were stable for up to three weeks when stored at 4 and 25 ∘ C without any phase separation, except at the lower BSG concentrations, while the emulsions containing the highest concentration of BSG were stable for at least 40 days. The authors related the observations to viscosity enhancement, the existence of yield stress, and strong steric layers in boundaries caused by the presence of BSG and increasing BSG concentration [38]. Recently, the fat-replacing potential of BSG at 0.1%–0.3% concentration has been assessed in Iranian white cheese and compared to full-fat (3.8%) cheese. It has been concluded that BSG improved the texture of cheese so that adding 0.2% BSG showed the most likeness to full-fat cheese, which gained the highest acceptance based on sensory evaluation [39]. 7.5.3

Emulsifying

The emulsifying properties of BSG solution at 0.1%–0.5% concentration has been studied [24]. It has been established that the emulsification capacity and emulsion stability were increased with increasing concentration; also, they were improved to some extent by applying repeated freeze–thaw cycles. The results of the emulsification potential of BSG are in accordance with the measurements of surface tension performed by Razavi et al. [4]. It is believed that an increase in emulsion stability could be attributed to the inter-chain association and concentration of polymer chains in the non-frozen phase of the solution, which prevented oil droplets from aggregating. Also, the stabilization of the emulsion has been related to the presence of protein in BSG along with the large molecular size of its polymer chains, which can form a thick layer to protect oil droplets against aggregation [24]. 7.5.4

Foaming

The foaming potential of BSG has been evaluated in comparison with xanthan, Qodume Shahri (Lepidium perfoliatum) seed gum, basil seed gum, and cress (Lepidium sativum)

197

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7 Balangu (Lallemantia royleana) Seed Gum

seed gum in the white button mushroom puree. It has been revealed that foam density and foam stability increased when the gum level was raised from 0.1% to 0.9% in foam formulations. While low concentrations of BSG have been reported to be less effective on foam stability, greater effects have been observed at higher concentrations [40]. In another work, the foaming capacity and foam stability of BSG at 0.5%–1% concentration was studied. It was reported that BSG cannot form stable foams at concentrations below 0.5%, but at higher concentrations, foaming capacity enhanced by increasing the BSG concentration. On the other hand, it was observed that the presence of BSG increases the stability of foam after applying multiple freeze–thaw cycles, more significantly at a lower temperature (−30 ∘ C) [24]. 7.5.5

Edible Films

The properties of a new edible film prepared from 0.4% to 1.6% BSG solutions containing 10%–60% glycerol as plasticizer have been recently studied. It has been reported that increasing the plasticizer concentration increases the water solubility of films, while increasing the concentration of BSG decreased it. On the other hand, the lowest water vapor permeability (WVP) has been observed for BSG films with 1.2% concentration, and increasing glycerol caused an increase in WVP. The higher solubility and WVP of films has been attributed to the integrity disruption caused by the inclusion of low-molecular-weight plasticizer, resulting in a porous structure in the films. Also, a higher concentration of BSG made fabricated films more permeable to water vapor (Figure 7.6). The transparency and whiteness index of films decreased as the BSG concentration increased, while tensile strength and elongation at break enhanced with increasing the concentration of BSG up to 1.2%, but higher concentration decreased them. This behavior has been explained in terms of increased molecular chain interactions resulting in greater inhomogeneity in the film structure. The glass transition temperature of BSG films decreased with increasing glycerol concentration, and its value has been reported to be higher than for commercial films like high-density polyethylene. It was concluded that the optimal BSG and glycerol concentrations for fabricating BSG edible film are 1.2% and 35%, respectively. The

(a)

(b)

(c)

Figure 7.6 Micrographs of the cross-section of films containing 35% glycerol fabricated with (a) 0.4% BSG, (b) 1.2% BSG, and (c) 1.6% BSG. Source: Adopted from Sadeghi-Varkani et al. [41] with permissions from Elsevier.

7.6 Conclusions and Future Trends

Figure 7.7 Images of bread samples containing Balangu seed gum [12].

oxygen permeability (50% relative humidity for 24 h) of BSG film has been reported to be 6.25 cm3 μm m−2 kPa. Overall, the conclusion was that BSG films exhibit mechanical, oxygen permeability, and WVP properties that are comparable to those of some polysaccharide-based edible films [41]. 7.5.6

Other Applications

The influence of the BSG at 0.25% and 0.5% concentrations on the rheological properties of wheat flour dough and quality attributes of loaf bread have been investigated. It has been shown from farinograph and extensograph examinations that water absorption, stability, resistance to mixing, strength, and extensibility of dough are enhanced by adding BSG. Further, the water activity, firmness, porosity (Figure 7.7), anti-staling, and organoleptic properties of bread are improved [11]. The stability of 1% BSG gel over multiple freeze–thaw cycles has been investigated by measuring syneresis. It has been observed that BSG gel can strongly withstand multiple freeze–thaw cycles without any syneresis, indicating strong water-holding capacity. Therefore, BSG has been suggested for use as a gelling agent in frozen dairy and bakery products [24]. Recently, the influence of BSG concentration (0.3% and 0.6%) in sponge cake formulations was determined. It was concluded that the moisture content and lightness of cake increased as a result of BSG. The formulation containing 0.3% BSG had the highest amount of specific volume, porosity, and sensory scores; also, BSG had anti-staling and texture-softening properties [42].

7.6 Conclusions and Future Trends The extracted gum from Balangu (L. royleana) seeds, that is, BSG, has been the subject of important studies in the past few years. As a novel hydrocolloid, BSG is mainly composed of arabinose, galactose, and rhamnose with semi-rigid conformation, high

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7 Balangu (Lallemantia royleana) Seed Gum

intrinsic viscosity, strong pseudoplastic flow behavior and high shear viscosity, and a weak gel structure, which are comparable to most commercial hydrocolloids. On the basis of the knowledge that is available to date, BSG can be viewed as an interesting option for food and pharmaceutical applications. Although different chemical, rheological, and technological features of BSG have been assessed, further investigations on the molecular structure of its polysaccharides and some other potential functionalities like emulsifying and foaming properties for broader applications are required.

References 1 Naghibi, F., Mosaddegh, M., Mohammadi Motamed, S. et al. (2005). Labiatae fam-

2

3 4

5 6 7

8

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12

ily in folk medicine in Iran: from ethnobotany to pharmacology. Iranian Journal of Pharmaceutical Research 2 (2): 63–79. Mahmood, S., Hayat, M.Q., Sadiq, A. et al. (2013). Antibacterial activity of Lallemantia royleana (Benth.) indigenous to Pakistan. African Journal of Microbiology Research 7 (31): 4006–4009. Khare, C.P. (2007). Indian Medicinal Plants: An Illustrated Dictionary. New York: Springer-Verlag, Ltd. Razavi, S.M.A., Cui, S.W., and Ding, H. (2016). Structural and physicochemical characteristics of a novel water-soluble gum from Lallemantia royleana seed. International Journal of Biological Macromolecules 83: 142–151. Bozorgi, M. and Vazirian, M. (2016). Antioxidant activity of Lallemantia royleana (Benth.) seed extract. Traditional and integrative Medicine 1 (4): 147–150. Jasmine, F. (2016). Antioxidant properties and phytochemical analysis of some medicinal plants. Ph.D. thesis. Integral University. Jasmine, F., Shazia, M., Ali, S.M. et al. (2016). Phyto-chemical analysis, in-vitro antioxidant potential and GC-MS of Lallemantia royleana seeds. International Journal of Scientific and Research Publications 6 (2): 407–411. Ghannadi, A., Movahedian, A., and Jannesary, Z. (2015). Hypocholesterolemic effects of Balangu (Lallemantia royleana) seeds in the rabbits fed on a cholesterol-containing diet. Avicenna Journal of Phytomedicine 5 (3): 167–173. Atabaki, R. and Hassanpour-ezatti, M. (2014). Improvement of lidocaine local anesthetic action using Lallemantia royleana seed mucilage as an excipient. Iranian Journal of Pharmaceutical Research 13 (4): 1431–1436. Razavi, S.M.A., Mohammadi Moghaddam, T., and Mohammad Amini, A. (2008). Physico-mechanic properties and chemical composition of Balangu (Lellemantia royleana (Benth. In Walla.)) seed. International Journal of Food Engineering 4 (5): 1–10. Mohammad Amini, A. (2007). Optimization of the Lallemantia royleana gum extraction and investigation into its effects on rheological and organoleptic properties of bread in comparison with xanthan gum. Master thesis. Ferdowsi University of Mashhad. Mohammad Amini, A., (2007). Modeling and optimization of mucilage extraction from Lallemantia royleana: a response surface-genetic algorithm approach. Poster presented at the EFFOST/EHEDG Joint Conference, Lisbon, November 14–16, 2007.

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13 Emadzadeh, B., Razavi, S.M.A., Mohammad Amini, A. (2008) Evaluation of the

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hydrocolloid extraction of Lallemantia royleana seed by image analysis method. Poster presented at the 9th International Hydrocolloids Conference (9th IHC), Singapore, June 15–19, 2008. Salehi, F. and Kashaninejad, M. (2013). Modelling gum extraction from Balangu (Lallemantia royleana) seed. Innovative Food Technologies (JIFT) 1 (1): 13–20. (in Persian). Salehi, F. and Kashaninejad, M. (2014). Effect of different drying methods on rheological and textural properties of Balangu seed gum. Drying Technology 32: 720–727. Ali, S., Parvez, N., and Sharma, P.K. (2016). Extraction and evaluation of Lallemantia royleana seed mucilage. World Journal of Pharmacy and Pharmaceutical Sciences 5 (6): 1056–1066. Piazza, L., Bertini, S., and Milany, J. (2010). Extraction and structural characterization of the polysaccharide fraction of Launaea acanthodes gum. Carbohydrate Polymers 79: 449–454. Farhadi, N. (2017). Structural elucidation of a water-soluble polysaccharide isolated from Balangu Shirazi (Lallemantia royleana) seeds. Food Hydrocolloids 72: 263–270. Mohammad Amini, A. and Razavi, S.M.A. (2012). Dilute solution properties of Balangu (Lallemantia royleana) seed gum: effect of temperature, salt, and sugar. International Journal of Biological Macromolecules 51: 235–243. Razavi, S.M.A. and Karazhiyan, H. (2009). Flow properties and thixotropy of selected hydrocolloids: experimental and modeling studies. Food Hydrocolloids 23 (3): 908–912. Razavi, S.M.A., Emadzadeh, B., and Zahedi, Y. (2011). Direct and indirect methods to evaluate the yield stress of selected food hydrocolloids. EJEAFChe 10 (11): 3132–3142. Moahammadi Moghadam, T., Razavi, S.M.A., and Emadzadeh, B. (2011). Rheological interactions of Lallemantia royleana seed extract with selected food hydrocolloids. Journal of the Science of Food and Agriculture 91: 1083–1088. Salehi, F., Kashaninejad, M., and Behshad, V. (2014). Effect of sugars and salts on rheological properties of Balangu seed (Lallemantia royleana) gum. International Journal of Biological Macromolecules 67: 16–21. Khodaei, D., Razavi, S.M.A., and Haddad Khodaparast, M.H. (2014). Functional properties of Balangu seed gum over multiple freeze-thaw cycles. Food Research International 66: 58–68. Razavi, S.M.A. and Mohammadi Moghadam, T. (2011). Influence of different substitution levels of Balangu seed gum on textural characteristics of selected hydrocolloids. EJEAFChe 10 (9): 2826–2837. Bahramparvar, M., Haddad Khodaparast, M.H., and Mohammad Amini, A. (2008). Effect of substitution of carboxymethylcellulose and salep gums with Lallemantia royleana hydrocolloid on ice cream properties. Iranian Food Science and Technology Research Journal 4 (1): 37–47. (in Persian). Bahramparvar, M., et al. (2010) Substitution of carboxymethylcellulose and salep gums with Lallemantia royleana hydrocolloid in ice cream formulation. Poster presented at the 10th International Hydrocolloids Conference (10th IHC), Shanghai, June 20–24, 2010.

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28 Bahram Parvar, M., Haddad Khodaparast, M.H., and Razavi, S.M.A. (2009). The

29 30

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33

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effect of Lallemantia royleana (Balangu) seed, palmate-tuber Salep and carboxymethylcellulose gums on the physicochemical and sensory properties of typical soft ice cream. International Journal of Dairy Technology 62 (4): 571–576. Bahramparvar, M. and Mazaheri Tehrani, M. (2011). Application and functions of stabilizers in ice cream. Food Reviews International 27: 389–407. Bahram Parvar, M., Razavi, S.M.A., and Haddad Khodaparast, M.H. (2010). Rheological characterization and sensory evaluation of typical soft ice cream made with selected food hydrocolloids. Food Science and Technology International 16 (1): 79–88. Sohail, B., Huma, N., Mehmood, A. et al. (2014). Use of tukhm-e-balangu (Lallemantia royleana) as a stabilizer in set type yogurt. Journal of Agroalimentary Processes and Technologies 20 (3): 247–256. Hosseini, V.S., Najaf Najafi, M., Mohammadi Sani, A. et al. (2013). Effect of Lallemantia royleana seed gum and whey protein concentrate on stability of oil-in-water emulsion. Journal of Research and Innovation in Food Science and Technology 2 (2): 109–120. Najaf Najafi, M., Hosaini, V., Mohammadi-Sani, A. et al. (2016). Physical stability, flow properties and droplets characteristics of Balangu (Lallemantia royleana) seed gum/whey protein stabilized submicron emulsions. Food Hydrocolloids 59: 2–8. Emadzadeh, B., Razavi, S.M.A., and Hashemi, M. (2011). Viscous flow behavior of low-calorie pistachio butter: a response surface methodology. International Journal of Nuts and Related Sciences 2 (1): 37–47. Emadzadeh, B., Razavi, S.M.A., and Nassiri Mahallati, M. (2012). Effects of fat replacers and sweeteners on the time-dependent rheological characteristics and emulsion stability of low-calorie pistachio butter: a response surface methodology. Food and Bioprocess Technology 5: 1581–1591. Emadzadeh, B., Razavi, S.M.A., and Schleining, G. (2013). Dynamic rheological and textural characteristics of low-calorie pistachio butter. International Journal of Food Properties 16: 512–526. Emadzadeh, B., Razavi, S.M.A., Rezvani, E. et al. (2015). Steady shear rheological behavior and thixotropy of low-calorie pistachio butter. International Journal of Food Properties 18 (1): 137–148. Razavi, S.M.A., Emadzadeh, B., Mohammad Amini, A. (2012) Investigation on potentials of some Iranian endemic seed gums as fat replacers. Research project report, Ferdowsi University of Mashhad. Rahmani, B.H. and Najaf Najafi, M. (2017). Effect of Lallemantia royleana (Balangu) seed gum on chemical, physical and sensory attributes of low fat cheese. Iranian Journal of Food Science and Technology 14: 173–183. (in Persian). Pasban, A., Mohebbi, M., Pourazarang, H. et al. (2014). Effects of endemic hydrocolloids and xanthan gum on foaming properties of white button mushroom puree studied by cluster analysis: a comparative study. Journal of Taibah University for Science 8: 31–38.

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41 Sadeghi-Varkani, A., Emam-Djomeh, Z., and Askari, G. (2018). Physicochemical

and microstructural properties of a novel edible film synthesized from Balangu seed mucilage. International Journal of Biological Macromolecules 108: 1110–1119. 42 Sheikholeslami, Z., Karimi, M., Davoodi, G. et al. (2017). Evaluation of qualitative, visual and sensory properties of cake containing native gum and natural emulsifier. Journal of Food Science and Technology 14: 237–249.

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8 Qodume Shirazi (Alyssum homolocarpum) Seed Gum Arash Koocheki 1 and Mohammad Ali Hesarinejad 2 1 Department of Food Science and Technology, Ferdowsi University of Mashhad (FUM), PO Box 91775-1163, Mashhad, Iran 2 Department of Food Processing, Research Institute of Food Science and Technology (RIFST), PO Box 91735-147, Mashhad, Iran

8.1 Introduction Alyssum, a famous genus of Brassicaceae, the mustard family, is native to the Middle East, especially Iran, Iraq, and Pakistan, and comprises 100–170 related species [1]. Alyssum homolocarpum is well known to Iranian practitioners and folk healers [2]. The plant is traditionally known as Qodume Shirazi or Toodari in Persian, and it is administered for various ailments such as topical inflammation and swellings. It was also reported to be beneficial in respiratory complications, sexual dysfunction, and some neurological disorders [3–5]. As seen in Figure 8.1a, A. homolocarpum comprises annual herbaceous plants clothed with stellate, white hairs, growing to 10–20 cm tall, with oblanceolate, or oblong-linear, leaves, and white flowers. Each locule of this plant has two broad, round pale pink margined seeds with length 1.5–2.5 mm [1]. Alyssum homolocarpum seeds have been used as a traditional medicine for hundreds of years (Figure 8.1b). It has been used to cure a dry cough, whooping cough, asthma, pneumonia, and kidney stones in Iranian traditional medicine [6]. The application of plant extracts for the treatment of several diseases and for minimizing the impact of the chemotherapeutic agent is growing [7]. There is evidence that A. homolocarpum seed extract has antioxidant properties [8]. A. homolocarpum is planted mainly for its mucilage, and the outer layer of seeds absorbs moisture rapidly when immersed in water and produces a viscid, turbid, and insipid liquid (Figure 8.1c). The seeds are known to have plenty of mucilaginous substance [1]. Plant mucilages are applied for thickening, binding, disintegrating, emulsifying, suspending, and stabilizing, and as gelling agents [9]. These properties are relevant to their structural properties and metabolic functions in food, pharmaceutical, and biomedical products [10]. Here, we review these characteristics.

8.2 Gum Extraction Optimization Response surface methodology (RSM) is applied to optimize the effect of different extraction conditions on the extraction yield and functional properties Emerging Natural Hydrocolloids: Rheology and Functions, First Edition. Edited by Seyed M.A. Razavi. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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8 Qodume Shirazi (Alyssum homolocarpum) Seed Gum

(a)

(b)

(c)

Figure 8.1 Pictorial view of (a) Alyssum homolocarpum plant, (b) seeds, and (c) the seeds soaked in water.

of A. homolocarpum seed gum (AHSG) [1]. In order to extract mucilage from A. homolocarpum seeds, whole seeds are dispersed in deionized water (water:seed of 30:1) at pH 8. The pH is monitored continuously and adjusted by 0.1 mol l−1 NaOH and HCl, while the temperature of the adjustable water bath is set on 48 ± 1.0 ∘ C. Water is preheated before the seeds are added. The seed–water slurry is mixed with an electric stirring paddle throughout the whole extraction period (1.5 h). Separation of the seed from the liquid is performed using a 27 cm basket centrifuge lined with a

8.3 Physicochemical Properties

1 mm mesh. The seed slurry is poured into the basket while the centrifuge is running at approximately 1200 rpm. The mucilage is regained from the extract via precipitation in three volumes of 95% ethanol. The precipitates are collected, dispersed in deionized water, and dried overnight in a vacuum oven [1]. Independent extraction variables including temperature, pH, and water:seed ratio have significant effects on the yield, purity, and viscosity of AHSG. Applying the desirability function method, optimum extraction conditions are found to be a temperature of 36.3 ∘ C, pH of 4, and the water:seed ratio of 40:1. At this optimum extraction condition, the consistency coefficient, flow behavior index, extraction yield, and protein content are 8.27 (Pa sn ), 0.29, 287.3 (g kg−1 ), 1.27 (%), respectively. Furthermore, the apparent viscosity of AHSG (3%) is 855.9 (mPa s) at a shear rate of 46.16 s−1 and 25 ∘ C [1].

8.3 Physicochemical Properties 8.3.1

Composition

AHSG has high total carbohydrate content (85.33 ± 0.89, w/w%), which reveals the relatively high purity of the extracted gum [11]. The gum consists of a small amount of uronic acids (5.63 ± 0.18, w/w%), illustrating its weak polyelectrolyte nature [11]. This polysaccharide is mainly composed of galactose (82.97 ± 0.64), glucose (5.70 ± 0.06), rhamnose (5.04 ± 0.29), mannose (3.04 ± 0.37), xylose (2.72 ± 0.07), and arabinose (0.53 ± 0.01), which is different from most other gums and is probably a galactan-type polysaccharide and not a galactomannan or glucomannan type [11]. The zeta potential (𝜉) of AHSG solution (0.1% w/w) is −25.81 ± 0.04 mV at neutral pH, meaning that AHSG has a negative charge and so is an anionic hydrocolloid. The polysaccharide backbone composes chiefly of 1,2-rhamnose, 1,3- and 1,3,6- galactose glycosidic linkages [12]. Measuring the molecular weight (Mw ) at room temperature (25 ∘ C) indicates that AHSG has a small molecular weight (3.66 × 105 Da) compared to other gums [11]. AHSG (0.1%) has an average particle size of 225.36 ± 31.06 (nm). A smaller particle size can lead to a more stable suspension, showing that AHSG solutions might be more stable than those of other hydrocolloids [11, 13]. 8.3.2

Fourier Transform Infrared Spectroscopy (FTIR)

The main absorption peaks of AHSG and their tentative assignments are summarized in Table 8.1 [11]. The Fourier transform infrared spectroscopy (FTIR) spectrum of AHSG is dominated by a broad band at about 895 cm−1 , resulting from the presence of β-D-mannopyranose units. The absorptions at the wavenumber range of 950–1150 cm−1 are ascribed to vibrations of C—O, C—O—C glycosidic, and C—O—H bonds. The peak at 1621 cm−1 is because of the asymmetrical —COO stretching vibration, while the band at 1426 cm−1 is caused by the symmetrical —COO stretching vibration [14, 15]. The 3000–2800 cm−1 wavenumber range is related to the stretching modes of the C—H bonds of ethyl groups (—CH3 ). The bands around 2900–2950 cm−1 refer to C—H absorption including CH, CH2 , and CH3 stretching and bending vibrations, symmetric, asymmetric, and occasionally double overlapping with O—H [16].

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Table 8.1 The main absorption peaks and their tentative assignments of FTIR spectrum of purified Alyssum homolocarpum seed gum. Wavenumber (cm−1 )

Fragment

3460.27

Hydroxyl (—OH) stretching

2902.71

—CH stretching of CH2 and CH3 groups

2369.74

Alkynes C=C Stretch or C≡C terminal alkynes

1621.34

COO— asymmetrical stretching of the hydrogen-bonded carboxylic groups

1426.57

C—H deformations/COO— symmetrical stretching of carboxylic groups

1066.03

C—O, C—O—C glycosidic and C—O—H bonds =CH out of plane =CH out of plane

895.10 777.62

Source: Adapted from Hesarinejad et al. [11] with permission from Elsevier.

8.3.3

Chain Flexibility

The value of the Huggins constant (KH ) shows the polymer–polymer interactions in a dilute regime and is related to the molecular architecture and the extent of polymer coil expansion. The KH value of AHSG in deionized water at 25 ∘ C is 0.301, which approximated its value in good solvents (0.3). In addition, when the temperature is increased from 25 to 65 ∘ C, the KH value decreases, indicating weaker intermolecular polymer–polymer interactions or deterioration of the solvent quality at high temperature [11, 17]. The chain flexibility parameter (Ea /R) and activation energy (Ea ) for AHSG are 618.54 and 0.51 × 107 J (kg mol)−1 , respectively. These results indicate that the flexibility of the AHSG chain is relatively low compared to some stiff chain hydrocolloids like chitosan, xanthan, and sage seed gum [11, 18]. 8.3.4

Shape, Swollen Volume, and Hydration Parameters

Some molecular parameters of AHSG are summarized in Table 8.2. The shape function (ν) is used with an anhydrous macromolecule which essentially expands when suspended or dissolved in solution because of its associations with the solvent. The swollen specific volume (νs ) is a measure of a (aqueous) solvent associated with the Table 8.2 Some molecular parameters of Alyssum homolocarpum seed gum. Temperature (∘ C)

𝛎s (dl g−1 )

𝛎 (−)

𝛅 (−)

Rcoil (nm)

Vcoil (nm3 )

25

7.21

2.55

6.55

11.10

5732.50

35

6.98

2.53

6.32

10.77

5231.69

45

6.80

2.30

6.14

10.56

4935.10

55

6.89

2.48

6.20

10.44

4777.08

65

6.96

2.61

6.26

10.57

4956.98

νs : swollen specific volume; ν: shape function; δ: hydration parameters; Rcoil : coil radius; Vcoil : coil volume. Source: Adapted from Hesarinejad et al. [11] with permission from Elsevier.

8.4 Rheological Properties

macromolecule and is defined as the volume of the macromolecule in solution per unit anhydrous mass of macromolecules. The hydration parameter (δ) is considered as the level to which an aqueous solvent can be added to a dry macromolecule beyond which there is no change in a macromolecular property other than dilution of the sample. The shape of the AHSG macromolecules is spherical at temperatures between 25 and 65 ∘ C, and it has a universal shape function. It is further observed that the hydration value of AHSG is temperature dependent and decreases when the temperature is increased up to 55 ∘ C. Results relating to the AHSG hydration parameter suggest the plausible reduction in the associated solvent through hydrogen bonds and/or physical entrainment, leading to an enhancement in the intermolecular interactions (i.e., aggregation) between unsolved chains [11]. 8.3.5

Coil Radius and Volume

The hydrodynamic coil radius is based on the Einstein viscosity relation, and the coil volume depends on the assumption that the shape of the AHSG coil is sphere-like. The alterations in the hydrodynamic coil radius (Rcoil ) and thereby in the corresponding volume (Vcoil ) of AHSG are caused by the temperature rise (Table 8.2). The temperature could depress the coil dimensions; however, a small increase is observed by a subsequent increase in temperature to 65 ∘ C. The decrease in the AHSG coil dimensions by heating could be attributed to the reduced stability of the hydrogen bonds between AHSG and solvent molecules and a small increase in the stability of the intramolecular interactions between the polymer segments of AHSG. The values obtained for the AHSG coil radius and volume at 25 ∘ C are 11.10 nm and 5732.50 nm3 , respectively [11]. 8.3.6

Partial Specific Volume

A particle’s buoyancy in food systems is an influential factor that affects the sedimentation phenomenon. As the partial specific volume (υ) increases, the buoyancy of a specific particle is increased, and therefore the greater the partial specific volume of a polymer, the less the sedimentation [19]. The partial specific volume of AHSG is 0.44 ml g−1 , which is smaller than that of most gums [11].

8.4 Rheological Properties 8.4.1

Intrinsic Viscosity

The intrinsic viscosity [η] is calculated by measurement of the solution viscosity at very low concentrations. The result of the AHSG intrinsic viscosity [η], calculated using five models (Huggins, Kraemer, Tanglertpaibul and Rao, Higiro 1, and Higiro 2) at different temperatures (25–65 ∘ C), shows that the Tanglertpaibul and Rao model gives the highest determination coefficient. It is also observed that on the basis of this model, the intrinsic viscosity diminishes from 23.11 to 19.65 dl g−1 when the temperature is increased from 25 to 55 ∘ C. Increasing the temperature may result in decreasing hydrogen-bonded hydration water of glucose, dextran, and so on. The decrease in hydrogen-bonded hydration water may decrease the specific volume, and therefore the

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intrinsic viscosity decreases. The intrinsic viscosity of AHSG at a temperature of 65 ∘ C increases to 20.39 dl g−1 , which could be attributed to the increased chain dimensions of AHSG [11]. The solutions of sucrose and lactose are poor solvents for AHSG as indicated by a decrease in the intrinsic viscosity. As the sucrose and lactose concentrations increase, the coil radius of AHSG decreases. The reduction in the shape and swollen volume parameters in the presence of sucrose and lactose, as compared to the sugar-free solution, indicates the negative effect of the chosen sugars on the molecular volume of AHSG. Evaluations of the dilute solution properties of this gum in sucrose and lactose solutions reveal the existence of a conformation which tends to an ellipsoidal shape and the probability of a random coil conformation with no molecular entanglements in AHSG solutions [20]. 8.4.2

Steady Shear Rheological Properties

AHSG exhibits a non-Newtonian shear-thinning behavior. The rheological behavior of AHSG solutions is well described by the power-law model with a high coefficient of determination. Increasing the gum concentration decreases the flow behavior index values while increasing the consistency coefficient. The values of the consistency coefficient (k) vary between 1.48 and 29.80 Pa sn for upward and between 1.47 and 31.07 Pa sn for downward curves as the gum concentration increases from 1.5% to 4% [21]. The increase in k values is probably related to the increase in the water binding capacity [22]. The apparent viscosity of AHSG decreases with increasing shear rate, and it has a direct dependency on the gum concentration too [21]. The flow behavior of AHSG shows that after a sharp reduction, the viscosity change is smoothened at high shear rates. Shear thinning is the result of an orientation effect. As the shear rate is increased, the long chain of polymer molecules and randomly positioned chains become increasingly aligned in the direction of flow, resulting in less interaction between adjacent polymer chains [21]. The concentration of AHSG in solution is known to affect the apparent viscosity and the degree of pseudoplasticity [23]. Increasing the AHSG concentration increases its apparent viscosity. This is due to the presence of higher solids content, which generally cause an increase in the viscosity owing to mainly molecular movements and interfacial film formation [21]. 8.4.2.1

Effect of Temperature

The examination of flow properties as a function of the shear rate designates the non-Newtonian behaviors of AHSG at different temperatures. The values of the flow behavior index are less than 1, indicating the pseudoplastic (shear-thinning) nature of the gum at different temperatures. By increasing the temperature, the flow behavior index increases, and the consistency coefficient decreases. Furthermore, no differences are found between the flow behaviors indices of the upward and downward curves. The effect of temperature on the flow behavior index (n) is negligible until 45 ∘ C at gum concentrations of 1.5% and 2%. The concentrated solution of AHSG (4%) at 5 ∘ C is the most pseudoplastic among the other concentrations of AHSG (1.5%–4%). A decrease in the consistency coefficient is observed with increasing temperature, which indicates a decrease in the apparent viscosity at higher temperatures [24]. AHSG has lower k values compare to carrageenan and xanthan at similar concentrations and higher values compare to that of pectin, starch, and the rounded-tuber salep [25, 26].

8.4 Rheological Properties

The apparent viscosity of AHSG decreases with increasing temperature [24]. This effect is reversible and is due to the interactions of the molecules in solution which become weaker at a higher temperature [27]. Viscosity is a function of the intermolecular forces and water solute interactions that restrict the molecular motion. Therefore, as temperature increases, the thermal energy of the molecules increases, and the intermolecular distances increase as a result of thermal expansion [24, 28]. The temperature dependence of the viscosity is assessed by applying the Arrhenius-type model. The activation energy for AHSG decreases when the gum’s concentration increases from 1.5% to 4% (from 8229.81 J mol−1 to 4520.57 J mol−1 ), indicating that the solution with lower concentration has the greater viscosity sensitivity to temperature. A higher activation energy value signifies a more rapid change in viscosity. Therefore, temperature control is more critical when 1.5% AHSG is used [24]. 8.4.2.2

Effect of pH

AHSG is sensitive to pH. Increasing the pH of the AHSG solution from three to seven augments the pseudoplasticity and the consistency coefficient. These effects have been explained by the induction of electrostatic repulsion by functional groups, which tend to keep the molecules in an extended form, thus producing a highly viscous solution, and therefore the consistency coefficient values increase [29, 30]. In the vicinity of pH 7, at the point where the carboxyl groups are ionized to a degree that the consistency index reaches a maximum, its molecular chains in the solution are in rod conformation [21]. The apparent viscosity of AHSG also increases when the pH is increased to 7. For pHs above 7, the viscosity values do not change. The pH has relatively little effect on the apparent viscosity over the range 7–9 [21]. This could be explained by the ionization of the mucilage carboxyl groups for pHs above 7. 8.4.2.3

Effect of Salt

Since the gum extracted from AHSG behaves as a polyelectrolyte, the solution viscosity is affected by the addition of salt. If no intermolecular interaction occurs, the viscosity of a dilute gum solution decreases due to the screening of charge and contraction of the macromolecule in presence of the counterions. In a more concentrated solution, the presence of multivalent ions may promote interactions between chains, resulting in an increase in the viscosity [21]. The values of the flow behavior index increase progressively when the salt concentration is increased from 0.035 to 0.172 M for NaCl and KCl. Addition of CaCl2 at 0.01 M and MgCl2 at 0.039 M augments the flow behavior index, but decreases afterward and remains constant at higher salt concentrations. The consistency coefficient of AHSG decreases with the addition of NaCl and KCl. Also, increases in CaCl2 concentration from 0 to 0.01 M and in MgCl2 concentrations from 0 to 0.039 M decrease the consistency coefficient value. The results of surveying the effects of some edible salts on the flow behavior of AHSG confirm that KCl can decrease the apparent viscosity of AHSG more than other salts [21]. 8.4.2.4

Effect of Sucrose

The values of the consistency coefficient and flow behavior index of AHSG are influenced by sucrose concentrations. The consistency coefficient value of AHSG increases in the presence of sucrose, while the flow behavior index value decreases. The lower flow behavior index indicates that at higher concentration of sucrose, the solutions are less pseudoplastic [21].

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8.4.3

Time Dependency (Thixotropy)

The thixotropy and rheopexy of a polymer solution are interpreted as the continuous breakdown or rearrangement of network links formed by the associations between polymer chains during shearing, respectively [24]. The hysteresis loop between the upward and downward curves indicates time dependency. The extent of thixotropy increases with increasing AHSG concentration and decreases with increasing temperature and shear rate [24]. Three models are generally used to predict time-dependent rheological behavior, namely, the first-order shear stress decay, second-order structural kinetic, and Weltman models. The AHSG concentration has a considerable effect on the degree of the thixotropic behavior. On the other hand, the solution becomes somewhat less thixotropic at high temperatures. The rupture rate of AHSG association increases at high shear rates, temperatures, and concentrations. Among the three models used, the thixotropic behavior of AHSG is well described by the first-order shear stress decay [24]. 8.4.4

Dynamic Rheological Properties

AHSG dispersions exhibit viscoelastic properties at any given temperature (5∘ –85∘ ). The storage modulus (G′ ) is always higher than the loss modulus (G′′ ) at all concentrations and temperatures. The mechanical spectra of AHSG are classified as weak gels on the basis of the frequency sweep, complex viscosity, and loss tangent results. The frequency sweep test reveals that viscoelastic moduli have a very low-frequency dependency, indicating that AHSG is a cross-linked network. At higher concentrations (3%) and a heating-cooling rate of 1 ∘ C min−1 , AHSG forms a gel during cooling. At high gum concentrations (2.5%–3%), as the temperature increases from 50 to 85 ∘ C, the storage modulus starts to increase, whereas for low AHSG concentrations, an increase in temperature has no significant effect on the storage modulus [31, 32].

8.5 Biological Activity Antioxidants are vital substances which possess the ability to protect the body from the damage caused by free-radical-induced oxidative stress [33]. A variety of free-radical-scavenging antioxidants are found in dietary sources like fruits, vegetables, and tea. The characteristics of A. homolocarpum and the inhibitory effects of its methanolic extracts on linoleic acid peroxidation are expressed as IC50. Considering the IC50 values (94.25 μg ml−1 ), the antioxidant activity of A. homolocarpum is low (IC50 > 75 μg ml−1 ). The phenolic content of A. homolocarpum, calculated as the gallic acid equivalent, is 165.68 mg/100 g of the dry weight, which is moderate (100–300 mg) according to Souri et al. [33]. The cytotoxic activity of ethanolic extracts of A. homolocarpum is studied against three different cancer cell lines: colon carcinoma (HT-29), colorectal adenocarcinoma (Caco-2), and breast ductal carcinoma (T47D). In addition, Swiss mouse embryo fibroblasts (NIH 3T3) are used as normal nonmalignant cells. The MTT assay (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) is utilized for calculating the cytotoxicity of extracts on cell lines [34]. The anti-proliferative effects of the ethanolic extract of A. homolocarpum are found to have no cytotoxic activity on colon, colorectal, and breast cancer cell lines [8].

8.6 Applications

8.6 Applications Gum extracted from AHSG can be used as thickening, fat replacing, and stabilizing agents [1, 21, 35]. In the following sections, the applications of AHSG in the formulation of different food products are reviewed. 8.6.1

Emulsions

AHSG could be used as a potential stabilizing agent for food emulsions, although it does not show any noticeable emulsifying property or surface activity [35]. On the other hand, AHSG is a poor emulsifier owing to its high hydrophilic nature, low molecular flexibility, and consequently low surface activity. However, it may contribute to the stability of O/W emulsion by increasing the medium viscosity, forming a network in which oil droplets are entrapped and thus reducing the mobility of droplets and delaying their coalescence [35–38]. Increasing the gum concentration enhances the stabilizing capacity and improves the heat stability of ultrasonically prepared corn oil-in-water emulsions. A low degree of droplet polydispersity is observed when higher concentrations of AHSG are used. The negligible surface activity observed for this gum can be attributed to the proteins co-extracted from the seed that are not completely removed during the gum purification process [35]. The number of large droplets present in these emulsions increases during storage. These alterations are more pronounced in the emulsion containing 0.25% AHSG over the first 3 weeks, and thereafter no significant changes occur. In general, emulsions made with higher concentrations of AHSG (>0.5%) are stable during the storage period of 4 weeks, and the size distribution of droplets does not show any remarkable variation [35]. The droplet diameter of AHSG stabilized emulsions varies over a wide range of sizes from 0.39 to 6.04 μm for the fresh emulsion and 0.39–15.81 μm for the sample stored for 4 weeks. During storage, the median diameter increases from 2.14 to 2.48 μm within the first 2 weeks and remains unchanged afterward [35]. For the freshly prepared emulsion, the Sauter diameter (D32 ) decreases gradually from about 1.92 to 1.59 μm when the concentration of gum increases from 0.25% to 0.75% [35]. The stability of emulsions against creaming and phase separation can be enhanced by increasing the AHSG concentration. At lower concentrations of gum (0.25% and 0.5%), distinctive creaming is observed within 7 days. On the other hand, at higher concentrations (0.75% and 1%), no visual changes are observed, and the emulsions retain their initial integrity during storage. This is due to the increase in the viscosity of the aqueous phase as well as the small size of droplets at higher proportions of the gum that drastically reduce the mobility of the oil droplets and hence their upward movement. The cream layer in the emulsion with 0.25% gum is evidently more compact, indicating free mobility of droplets and a higher degree of their interactions with each other due to weak forces in the aqueous phase. The emulsions stabilized with 0.75%–1% AHSG; on the other hand, they show no distinguishable serum separation during 28 days of storage [35]. Briefly, the incorporation of AHSG in an O/W emulsion greatly enhances the stability against flocculation, coalescence, and gravitational phase separation. In addition to its beneficial effect on the emulsification stage, it also reduces the droplet–droplet interactions during the storage of emulsion and thus delays the occurrence of destabilizing

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Boundary lines

Figure 8.2 Overall appearance of emulsion samples containing different levels of Alyssum homolocarpum seed gum after storage for four weeks. From right to left: 0.25%, 0.5%, 0.75%, and 1% AHSG, respectively. Source: Adapted from Koocheki et al. [35] with permission from Elsevier.

phenomena. These effects are found to be all dependent on the concentration of gum. AHSG with 0.75% concentration is more effective for producing small droplets during ultrasonic homogenization. However, energy input considerations should be taken into account when higher levels of the gum are to be used. Considering the excellent stability of emulsions against phase separation as well as their improved texture and consistency, AHSG could be accounted as a potential stabilizer for O/W emulsions [35]. Figure 8.2 illustrates changes in the overall appearance of emulsion samples after 4 weeks [35]. AHSG and emulsifier (Tween 80) and NaCl greatly affect the quality attributes of an O/W emulsion and its overall stability during storage. The contribution of AHSG, however, seems to be more prominent than that of the emulsifier once the droplets form. At higher AHSG content, the addition of salt up to 1% has no effect on the physical properties of the emulsion, except for the viscosity, which is slightly influenced. Taking into account the nature of the surfactant and the behavior of the gum, the changes observed in the presence of salt are postulated to be mainly due to the competition between gum and NaCl for water. The optimum emulsion formulation for the maximum specific surface area and viscosity as well as the minimum D32 , span, and creaming index are achieved by setting the AHSG concentration, Tween 80 content, and NaCl content at 1%, 0.96%, and 0%, respectively. This emulsion is greatly stable against flocculation and gravitational phase separation. It shows pseudoplastic behavior (n < 1) with no significant changes in the flow behavior index and consistency coefficient during storage [39]. For emulsions stabilized with an AHSG–whey protein concentrate mixture, increasing the gum content increases particle size, the negative charge on the droplet surface, the consistency coefficient, yield stress, and hysteresis between the forward and the backward flow diagrams. The particle size distribution curve is monomodal, and emulsions stabilized with this mixture show non-Newtonian shear-thinning behavior. No creaming phenomenon is observed in these emulsions [40].

8.6 Applications

8.6.2

Encapsulation

Studies on the nano-encapsulation of bioactive compounds are taken into consideration because of the unique properties of materials at the nanometer length scale. Nanostructures exhibit a greater surface area to volume ratio, which improves encapsulation efficiency, solubility, bioavailability, and controlled release of the encapsulated compounds [41]. AHSG could also be used for fabrication of nanocapsules containing d-limonene through the electrospraying process. However, the morphology of these nanostructures is mainly affected by the physical properties of AHSG solution, particularly its rheological behavior, surface tension, and electrical conductivity. AHSG solution (0.5% w/w) produces aggregated structures with a wide size range owing to its high surface tension and high electrical conductivity. Addition of 10% and 20% d-limonene and 0.1% Tween 20 increases the solution apparent viscosity, while it decreases the surface tension and conductivity of the solution, allowing the formation of round and smooth capsules. The size of these particles, ranging from 35 to 90 nm, increases with increasing d-limonene content. The transition from particles to fibers occurs for 30% d-limonene emulsion, due to its low storage modulus (G′ ), high loss modulus (G′′ ), and very low surface tension. High encapsulation efficiency (around 87%–93%) and the low surface of d-limonene reveal the stability of 10% and 20% d-limonene emulsions, which do not separate during the electrospraying process. d-limonene-loaded nanocapsules have a fully amorphous structure. The increased thermal stability of d-limonene after encapsulation holds promise for the protection of sensitive bioactive compounds in thermally processed food [41]. 8.6.3

Edible Film

AHSG has great potential to be used as a new source of biodegradable film due to its proper thickening/gelling function [42]. AHSG can produce films with excellent appearance and can easily be cast with satisfactory mechanical properties. The films formulated without plasticizer or with plasticizer content lower than 25% (w/w) are brittle and difficult to handle and remove from the casting plate. An increase in plasticizer concentration increases the transparency, flexibility, and homogeneity of the films, as well as producing smooth surfaces without pores or cracks. An over 50% (w/w) increase in glycerol concentration makes AHSG films very soft and sticky [43]. The density of AHSG films decreases upon adding the plasticizer, and a slight variation is evident. In this condition, the moisture content of the films increases, and this rise is likely caused by the water-holding capacity of glycerol [44]. The increase in moisture content is consistent with the increase in film thickness. Increasing the moisture and glycerol contents decreases the contact angle and density. Given the hydrophilic nature of glycerol, reducing the hydrophobicity would consequently decrease the contact angle of AHSG films [43, 45]. Increasing the glycerol content from 25% to 45% augments the film solubility. These are directly related to the hydrophilic nature of glycerol in the AHSG films. If the packaged film would be consumed simultaneously with food, then a high degree of solubility would be acceptable [43]. A significant increase in both water vapor permeability (WVP) and oxygen permeability (OP) is observed after adding glycerol. The predominantly hydrophilic behavior of biopolymers, such as polysaccharides, results in poor water barrier characteristics. The WVP of films is a characteristic that depends on the diffusion rate and solubility of

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water in the film. Thus, the WVP of plasticized AHSG film would increase by adding a plasticizer to the film matrix. Increasing the glycerol concentration decreases the intermolecular forces among the biopolymer chains, and increases the segmental motions and free volume, allowing water molecules to diffuse more easily and providing a higher WVP [43, 45, 46]. Given the significance of oxygen in the oxidation of food, the OP of food packaging materials is very important in food preservation. The oxygen and aroma permeability of polysaccharide-based films are very low because of large amounts of hydrogen bonds. The biopolymer chain structure and plasticizer distribution within the biopolymer matrix are important in the permeability of films. Increasing the glycerol levels from 25% to 45% augments the OP values of AHSG film drastically. This finding could be attributed to an increase in chain mobility of the AHSG and the creation of void spaces in the film matrix [45]. The OP of AHSG films at 50% RH is 67.36–102.27 (cm3 μm m−2 d atm) [43]. Incorporating glycerol into the AHSG films mostly increases the lightness index (L*) [43]. One of the most important parameters required for food packaging is the mechanical stability of films during shipping, handling, and storage [47]. Thus, these properties are critical for the evaluation of the industrial biodegradable film. Tensile strength (TS), Young’s modulus (YM), and elongation at break (EB) are the most common parameters used to evaluate the mechanical properties of films [48, 49]. The TS and YM of the plasticized AHSG films decrease when the plasticizer content increases from 25% (19.39 MPa and 0.438 GPa) to 45% (11.87 MPa, 0.279 GPa), respectively. In addition, by adding glycerol, the EB of such film increases from 25% to 43%. Therefore, the increase in glycerol concentration in AHSG films weakens the films but enhances their flexibility [43]. The glass transition temperature (Tg ) of the AHSG film is around 43–58 ∘ C. The addition of glycerol increases the moisture content of films and then decreases the Tg of films from 58 to 43 ∘ C. The AHSG films surface without plasticizer appears smooth, but that of the plasticized AHSG films exhibits certain differences in terms of the surface microstructure. This is caused by the high moisture content absorbed by glycerol, which is hydrophilic in nature. Increasing the concentration of glycerol from 25% to 45% results in a rougher film surface compared with that of control films. The pores on the film surface could be the binding site for water during moisture uptake. This qualitative result may explain the increase in gas permeability and moisture content of AHSG films containing plasticizers [43]. To improve the physical, mechanical, barrier, thermal and optical properties of AHSG film, Marvdashti et al. [42] blended AHSG with polyvinyl alcohol (PVA). They investigated the interactions among two polymers and their effect on the properties of blend films. Films made from AHSG have poor mechanical and barrier (to oxygen) properties. The addition of PVA to this film significantly increases the moisture content, solubility, EB, and transparency, while it decreases the density, OP, Chroma, water contact angle, and Young modulus. The films with higher AHSG to PVA ratios have a lower WVP. The light barrier measurements present low values of transparency at 600 nm for PVA/AHSG films, indicating that films are very transparent while they have excellent barrier properties against UV light. The moisture content of these blend films is affected by the PVA to AHSG ratios. Since PVA is a polar polymer containing many hydroxyl groups, it can impart higher hydrophilicity to the film. Therefore, as the PVA to gum ratio increases in PVA/AHSG films, the number of possible hydrogen bonds that

8.6 Applications

interact with water molecules increases. The moisture content of the film negatively correlates with their density. The moisture content of these films affects their permeability to water and gas; therefore, a film with high moisture content cannot act as a good barrier against water vapor and gases. The moisture sorption of pure AHSG films at 0.9 aw is 2.7 times lower than that for pure PVA films. As the AHSG ratio increases in PVA/AHSG blend films, their water sorption ability decreases. Due to the higher hydrophilic property of PVA, any increase in the AHSG content enhances the water resistance of the blended films. The hydroxyl groups of PVA can form hydrogen bonds with hydroxyl and/or carboxyl groups of AHSG, which might decrease the free hydroxyl groups and reduce the number of hydroxyl groups available for binding with water molecules in the blend films. AHSG film has the lowest solubility; therefore, with the addition of PVA to AHSG film, the water solubility increases. This might be due to the distribution of hydroxyl groups and their higher density in AHSG film. Pure AHSG film has a smooth surface and reveals a homogeneous structure, where polysaccharide chains aggregate to form a continuous and dense network. AHSG film shows a surface with no obvious phase separation, crack, or pores. Incorporation of PVA into AHSG film forms a homogeneous structure, due to the high compatibility of both polymers [42]. AHSG film has a rough cross section due to its brittle structure, which fractures when liquid nitrogen is used for the preparation of film for the scanning electron microscopy (SEM) test. SEM analysis shows that at higher PVA to AHSG ratios, complex networks with high homogeneity are formed. The color parameters of films, including lightness (L*), redness or greenness (a*) and yellowness or blueness (b*), the total color difference (E), Chroma (C), yellowness index (YI), and whiteness index (WI), significantly change when the AHSG/PVA ratio increases. Chroma values decrease with the addition of PVA to AHSG film, probably due to the reduction of film compactness. The E and YI of AHSG/PVA blend films decrease with increasing PVA content, while their WI increases. These trends might be due to the variation of L* and b* with the addition of PVA. The lowest OP is observed for PVA film, while AHSG film has the highest OP. The oxygen permeability of the blended films decreases with increasing PVA to AHSG ratios. The oxygen permeability value of these films is below 10 cm3 μm−2 d−1 kPa−1 . The WVP of AHSG film can be changed by the integrity of the film, the hydrophilic-hydrophobic ratio, and the water vapor diffusivity rate [50]. Pure AHSG film has the lowest WVP. On the other hand, AHSG film resists water molecule transfer through its matrix; therefore, AHSG could reduce the WVP of PVA-AHSG films. The water contact angles (WCAs) of AHSG/PVA blend films lie between 30∘ and 90∘ . The WCA of AHSG film is 74.6∘ . Addition of PVA to AHSG film decreases the WCA of the blend films. A conceivable reason for this phenomenon might be the difference in the nature and chemical structure of film-forming materials which leads to diverse WCA films [42]. The glass transition temperatures of PVA/AHSG blend films are in the range −78.52 to −67.6 ∘ C. Tg increases when the PVA to AHSG ratios decrease. This increase indicates that the mobility of PVA film decreases with the addition of AHSG. This trend could be due to the higher molecular weight of AHSG in the blend matrix, which increases the interactions among polymer chains and hence Tg [51]. The thermal stability verifies due to the difference in interactions between AHSG and PVA polymers. This result indicates that more intermolecular interactions through hydrogen bonding between PVA and AHSG improve the thermal stability of the final films. AHSG film has a significantly higher YM (3526.5 MPa) and TS (37.23 MPa), but a lower EB (1.4%) compared

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with PVA film. The higher elongation indicates that the film is more flexible when subjected to tension and mechanical stresses [52]. The high TS and low EB of AHSG film are probably due to the presence of higher intermolecular interactions along the polysaccharide chains (SEM), solubility, density, and moisture content. Intermolecular interactions and hydrogen bonds between polymer chains make a rigid and brittle matrix with low elongation. An increase in the number of intermolecular crosslinks and decrease in the intermolecular distance in AHSG film increase its TS but decrease the EB. The results of FTIR show a clear interaction between PVA and AHSG, forming a new material. These results indicate that PVA/AHSG blend films have good compatibility [53]. Film transparency provides information about its ability to protect the packaged material from the disadvantages of light, especially UV radiation. Ultraviolet light is a powerful oxidative agent, so light transmission resistance of films can determine their application for different conditions. The light barrier properties of films are controlled by the amount of AHSG in the final blend. Transparency values tend to decrease in films with higher PVA to AHSG ratios compared to AHSG film. Transparency and opacity are inversely related, so high transparency leads to low opacity [47]. High AHSG content in films produces high opacity values. The transparency of PVA/AHSG blend films is high, so these blend films are clear enough to be selected and used as a see-through packaging material [42]. 8.6.4

Application in Dairy Products

AHSG has been considered as a substitute for fat in ultrafiltrated Iranian white cheese (UF cheese). By decreasing the fat content, the moisture content increases, and protein plays a more effective role in cheese texture. These changes affect the sensory, functional, microbial, and chemical properties of cheese. AHSG can technically be a good replacer for fat in Iranian white cheese. Increasing the AHSG concentration enhances the moisture content of cheese, and thus the texture softness increases. The most acceptable concentration of AHSG is found to be 0.3%, while the texture of samples containing 0.4% AHSG is too soft and have an undesirable mouthfeel [54]. AHSG can be also used as a natural stabilizer in yogurt drink. Addition of AHSG to yogurt drink changes its flow behavior from a Newtonian fluid to a shear-thinning one, and the apparent viscosity increases from 4.5 to 8.8 cP. Adding AHSG causes stabilization in yogurt drink. The highest stability is observed for the sample containing 0.3% AHSG, while sensory evaluations show that 0.2% AHSG is the most desirable concentration [55]. 8.6.5

Application in Bakery Products

Sponge cake is a bakery product with an approximate shelf life of four week. Retarding the staling rate of baked goods is one of the biggest issues and is of nutritional and economic importance. The application of AHSG in bakery products increases the shelf life and postpones its staling. The addition of AHSG up to 0.75% improves the characteristics of the sponge cake in terms of sensory, shelf life, cake batter specific gravity, volume, and apparent density. During the storage time, the highest moisture content and the lowest firmness are observed in sponge cake containing 0.75% AHSG [56].

References

The addition of AHSG can improve the rheological properties of wheat flour and increase the quality of bread. The gelatinization temperature of flour containing this gum is reduced. AHSG ameliorates the properties of bread and its softness and therefore can be added as a natural supplement to wheat flour to improve its quality [4].

8.7 Conclusion and Future Trends The physicochemical properties of A. homolocarpum seed gum have been reviewed in this chapter. The benefits of AHSG solutions depend on their extraction methods (temperature, pH, and seed to water ratio) and the measurement conditions (concentration, temperature, shear, pH, and the attendance of additives such as salts and sugars). The biological activity, physicochemical, functional, and rheological attributes of A. homolocarpum seed gum demonstrate a potential for their usage as a novel food hydrocolloid and herbal medicine sources. The cost of commercial gums is steadily increasing due to drought and unexpected increase in demand. Therefore, their usage by food manufacturers will be very limited. In this situation, if a new replacement is found, the new gum will be welcomed. Also, the food industry will always substitute new texturizing gums to the old ones. AHSG can be applied because of its unique properties in the food industry, such as dairy, bakery, and other food processing industries. Middle East countries can help to export AHSG in the future to support the productivity in the food industry. Subsequently, AHSG can affect the global economy gradually. It can be one of the importing commodities in the world market. Future and options for AHSG application can be high in the coming years.

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24 Koocheki, A. and Razavi, S.M.A. (2009). Effect of concentration and temperature on

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flow properties of Alyssum homolocarpum seed gum solutions: assessment of time dependency and thixotropy. Food Biophysics 4 (4): 353–364. Marcotte, M., Hoshahili, A.R.T., and Ramaswamy, H.S. (2001). Rheological properties of selected hydrocolloids as a function of concentration and temperature. Food Research International 34 (8): 695–703. Farhoosh, R. and Riazi, A. (2007). A compositional study on two current types of salep in Iran and their rheological properties as a function of concentration and temperature. Food Hydrocolloids 21 (4): 660–666. Garcia-Ochoa, F. and Casas, J.A. (1992). Viscosity of locust bean (Ceratonia siliqua) gum solutions. Journal of the Science of Food and Agriculture 59 (1): 97–100. Hassan, B.H. and Hobani, A.I. (1998). Flow properties of Roselle (Hibiscus sabdariffa L.) extract. Journal of Food Engineering 35 (4): 459–470. Launay, B., Doublier, J.L., and Cuvelier, G. (1985). Flow properties of aqueous solutions and dispersions of polysaccharides. In: Functional Properties of Food Macromolecules (ed. J.R. Mitchell and D.A. Ledward), 1–78. Onweluzo, J.C., Obanu, Z.A., and Onuoha, K.C. (1994). Viscosity studies on the flour of some lesser known tropical legumes. Nigerian Food Journal 12: 1–10. Hesarinejad, M.A., Razavi, S.M.A., and Koocheki, A. (2015). The viscoelastic and thermal properties of Qodume Shirazi seed gum (Alyssum homolocarpum). Iranian Food Science and Technology Research Journal 11 (2): 116–128. (In the Persian Language). Alaeddini, B., Koocheki, A., Mohammadzadeh Milani, J. et al. (2017). Steady and dynamic shear rheological behavior of semi dilute Alyssum homolocarpum seed gum solutions: influence of concentration, temperature and heating–cooling rate. Journal of the Science of Food and Agriculture, 98 (7): 2713–2720. Souri, E., Amin, G., and Farsam, H. (2008). Screening of antioxidant activity and phenolic content of 24 medicinal plant extracts. DARU Journal of Pharmaceutical Sciences 16 (2): 83–87. (In the Persian Language). Emami, S.A., Sahebkar, A., Tayarani-Najaran, N. et al. (2012). Cancer and its treatment in main ancient books of Islamic Iranian traditional medicine (7th to 14th century AD). Iranian Red Crescent Medical Journal 14 (12): 747–757. (In the Persian Language). Koocheki, A., Kadkhodaee, R., Mortazavi, S.A. et al. (2009). Influence of Alyssum homolocarpum seed gum on the stability and flow properties of O/W emulsion prepared by high intensity ultrasound. Food Hydrocolloids 23 (8): 2416–2424. Dickinson, E. and Stainsby, G. (1982). Colloids in Food. London: Applied Science Publishers, Ltd. Darling, D.F. and Birkett, R.J. (1987). Food colloids in practice. In: Food Emulsions and Foams, 1–29. London: Royal Society of Chemistry. Gaonkar, A.G. (1991). Surface and interfacial activities and emulsion characteristics of some food hydrocolloids. Food Hydrocolloids 5 (4): 329–337. Koocheki, A. and Kadkhodaee, R. (2011). Effect of Alyssum homolocarpum seed gum, tween 80 and NaCl on droplets characteristics, flow properties and physical stability of ultrasonically prepared corn oil-in-water emulsions. Food Hydrocolloids 25 (5): 1149–1157.

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40 Alipour, A., Koocheki, A., Kadkhodaee, R. et al. (2015). The effect of Alyssum

41

42

43

44

45

46 47 48 49

50

51

52

53

54

homolocarpum seed gum-whey protein concentrate on stability of oil-in-water emulsion. Journal of Food Science and Technology 12 (48): 163–174. Khoshakhlagh, K., Koocheki, A., Mohebbi, M. et al. (2017). Development and characterization of electrosprayed Alyssum homolocarpum seed gum nanoparticles for encapsulation of d-limonene. Journal of Colloid and Interface Science 490: 562–575. Marvdashti, L.M., Koocheki, A., and Yavarmanesh, M. (2017). Alyssum homolocarpum seed gum-polyvinyl alcohol biodegradable composite film: physicochemical, mechanical, thermal and barrier properties. Carbohydrate Polymers 155: 280–293. Nafchi, A.M., Olfat, A., Bagheri, M. et al. (2017). Preparation and characterization of a novel edible film based on Alyssum homolocarpum seed gum. Journal of Food Science and Technology 54 (6): 1703–1710. Cheng, L.H., Karim, A.A., and Seow, C.C. (2006). Effects of water-glycerol and water-sorbitol interactions on the physical properties of konjac glucomannan films. Journal of Food Science 71 (2): 62–67. Jouki, M., Yazdi, F.T., Mortazavi, S.A. et al. (2013). Physical, barrier and antioxidant properties of a novel plasticized edible film from quince seed mucilage. International Journal of Biological Macromolecules 62: 500–507. Sothornvit, R. and Krochta, J.M. (2001). Plasticizer effect on mechanical properties of β-lactoglobulin films. Journal of Food Engineering 50 (3): 149–155. Kanatt, S.R., Rao, M.S., Chawla, S.P. et al. (2012). Active chitosan–polyvinyl alcohol films with natural extracts. Food Hydrocolloids 29 (2): 290–297. Dufresne, A. and Vignon, M.R. (1998). Improvement of starch film performances using cellulose microfibrils. Macromolecules 31 (8): 2693–2696. Finkenstadt, V.L., Liu, C.K., Cooke, P.H. et al. (2008). Mechanical property characterization of plasticized sugar beet pulp and poly (lactic acid) green composites using acoustic emission and confocal microscopy. Journal of Polymers and the Environment 16 (1): 19–26. Souza, B.W., Cerqueira, M.A., Teixeira, J.A. et al. (2010). The use of electric fields for edible coatings and films development and production: a review. Food Engineering Reviews 2 (4): 244–255. Ghanbarzadeh, B., Almasi, H., and Entezami, A.A. (2010). Physical properties of edible modified starch/carboxymethylcellulose films. Innovative Food Science and Emerging Technologies 11 (4): 697–702. Garcia, M.A., Pinotti, A., and Zaritzky, N.E. (2006). Physicochemical, water vapor barrier and mechanical properties of cornstarch and chitosan composite films. Starch-Stärke 58 (9): 453–463. Monjazeb, M.L., Yavarmanesh, M., and Koocheki, A. (2017). The effect of different concentrations of glycerol on properties of blend films based on polyvinyl alcohol-Alyssum homolocarpum seed gum. Iranian Food Science and Technology Research Journal 12 (5): 663–677. (In the Persian Language). Azarnia, F., Nasiraii, L. R., Alaeddini, B., et al. (2014). Effect of Alyssum homolocarpum gum as fat replacer on chemical and sensory properties of ultra-filtrated Iranian white cheese. 1st International Conference on Natural Food Hydrocolloids, Mashhad, Iran.

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55 Pure, A.E., Shojaei, M., Tadbiri, S. (2016). Alyssum homolocarpum gum as stabilizer

in yogurt drink (Doogh). 3rd international conference on research in engineering, science and technology, Batumi, Georgia. 56 Beikzadeh, S., Peighambardoust, S.H., Beikzadeh, M. et al. (2017). Effect of qodume shirazi seed mucilage on physical, sensory and staling properties of sponge cake. Journal of Food Science and Technology 14 (63): 209–220. (In the Persian Language).

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9 Espina Corona (Gleditsia amorphoides) Seed Gum María J. Spotti 1 , Martina Perduca 2 , Paula Loyeau 1 , Amelia Rubiolo 1,3 , and Carlos Carrara 1 1 National University of Litoral, Food Technology Institute, Chemical Engineering Department, 1 de Mayo 3250, 3000, Santa Fe, Argentina 2 Universidad de la Cuenca del Plata, Engineering and Technological Faculty, Scientific Research Institute, Lavalle 50, 3400, Corrientes, Argentina 3 Instituto de Desarrollo Tecnológico para la Industria Química, Biotechnology and Food Engineering department, RN 168, Km 0 3000, Santa Fe, Argentina

9.1 Introduction Espina Corona gum (ECG) is a galactomannan extracted from the seeds of Espina Corona (Gleditsia amorphoides), a leguminous tree native of Latin America. The area where it grows is in the north and center of Argentina, in the provinces of Salta, Jujuy, Chaco, Corrientes, Entre Ríos, Santa Fe, Misiones, and Formosa. The tree also grows in neighboring countries like Brazil, Paraguay, and Uruguay [1]. The genus is Gleditsia, and the family is Fabaceae (Caesalpinioideae). In Argentina, two species of Gleditsia exist: (1) the Gleditsia amorphoides, which grows spontaneously in the north of Argentina, better known as Espina Corona, which means “thorn crown” in English, and (2) Gleditsia triacanthos, which was imported from the United States, better known as “black acacia.” The Gleditsia amorphoides tree was named after the thorn crown placed on Christ’s head, the assumption being that the crown was made with the thorns of this tree. Other common names for this tree are Coronillo, quillai, quillar, caranchí, ivopé, and ivapó, among others. The several uses of the tree include constructions in general: carpentry, braces, floors, rods, walls, roof structures, ornamental sheets, and so on. It is a meso-xerophilous tree that is 15 m tall, with a straight trunk and cylindrical base, with branches having ramified thorns 8 cm long with pinnate and bipinnate leaf arrangements. It has leaflets narrowly elliptic to lanceolate or oblong-lanceolate up to 3 cm long and 1 cm wide, small green flowers gathered in clusters, and indehiscent pod fruits of glossy black color that at maturity are 5–10 cm long by 2–3.5 cm wide. In Figure 9.1, the tree, its trunk, leafs, and fruits are shown [1]. The fruits enclose the seeds from which the gum is extracted, similar to locust bean gum (LBG), which comes from the seed of the European carob tree (Ceratonia silicua). Despite the rich flora biodiversity and the favorable climate for their production, galactomannans from Latin American sources are not well known [2]. The degree of purity of commercial ECG is generally not very high, lowering the value of the product and Emerging Natural Hydrocolloids: Rheology and Functions, First Edition. Edited by Seyed M.A. Razavi. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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9 Espina Corona (Gleditsia amorphoides) Seed Gum

Figure 9.1 Espina corona gum tree, trunk, leafs, and fruits. Source: Adapted from the website: http:// arbolesdelchaco.blogspot.com.ar/2016/01/espina-corona-camba-nambi-coronillo.html [1].

its applications in food formulations. Although there is scientific information about this gum, international publications focused on the study of its rheological properties and its relation with other gums are scarce. The study of these topics could promote and consolidate the technological applications of ECG on the national and international market. In this chapter, the rheological properties of this novel gum as a function of temperature, ionic strength, and pH as well as its interaction with some commercial hydrocolloids have comprehensively been reviewed. In addition, applications of ECG in different food systems like emulsions, foams, and gels have been addressed.

9.2 Purification and Composition The usual ECG purification process includes its extraction from the seeds’ flour using water as a solvent, followed by filtration or centrifugation. In the Argentinian market, the gum is not often commercially available in a purified form and contains significant amounts of insoluble fraction, visible as black spots from the tegument residues that cover the seed’s endosperm. These black spots are generated in the roasting procedure used to remove the tegument. This insoluble fraction reduces the product value since it cannot be used in food formulations that need clear or light colors. Different purification procedures in both laboratory and pilot plant scales were studied to determine the soluble and insoluble fractions of ECG [3]. The soluble fraction that was translucent and without tegument residues was subjected to precipitation by alcohols and then drying by an appropriate method like spray drying. Using precipitation by alcohols, it

9.3 Flow Behavior

OH OH H

O

H HO

1 OH α

H H 4

OH

H

H

H

H

O

O HO H

H

H

H

1 β H

HO O 4 OH H OH

H O

H 1 β

H

4

δ

OH

O

O HO

O

H H

H

1 β

O

H

Figure 9.2 Espina Corona gum (ECG) structure.

was observed that the greater the volume of alcohol, the higher the percentage of solids of the precipitate, its aspect being white and fibrous. On the other hand, a fraction of purified gum was concentrated by spray-drying on a pilot plant [3]. As a consequence of the purification, the ECG resulted in an additive that can be applied to any type of food because of its suitable visual characteristics. The color of purified ECG was compared with that of commercial guar gum (GG) and was found to be very similar. Regarding the chemical composition, the ECG extracted from Gleditsia amorphoidesis contains more than 80% of polysaccharides, about 2% of proteins, and low concentrations of lipids and fiber, being similar to the gums extracted from other species. The chemical composition of ECG was postulated by Cerezo in 1965 as a galactomannan composed of 71.4% d-mannose and 28.6% d-galactose with a mannose-to-galactose (M/G) ratio of 2.5 [4]. The mannose forms a linear chain of (1 → 4) β-mannopyranose units with one molecule of d-galactopyranose linked at position 6 every 3 units of mannose (Figure 9.2). This relation is very similar to that of other galactomannans such as GG, with 1 galactose every 2 units of mannose and an M/G ratio of 2.0 [5]. ECG has an approximate molecular weight of 1.39 × 106 Da [6].

9.3 Flow Behavior The steady shear rheological properties of hydrocolloids have a significant role in food processing as they govern the product development, process design, and analysis of the present process [7]. The common property of gums is that they impart high viscosity or thickening properties to aqueous solutions or dispersions at very low concentrations. The viscosifying power depends on the type of gum and the level of concentration. The rheology of gums can be correlated with the sensory properties of the solution and, thereby, the acceptability of the products. Since the rheological properties of gums could be a useful tool to formulate specific foods, it is essential to analyze their flow behavior. The rheology of ECG was investigated at different concentrations and temperatures [6]. Also, the flow behavior of ECG solutions upon heating, addition of NaCl, and pH decrease is discussed in the following sections.

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9 Espina Corona (Gleditsia amorphoides) Seed Gum

1 ηap (Pa s)

228

ECG % (w/w) 1.50% 0.1

1.00% 0.75% 0.50%

0.01

0.25% 10

100 · –1 γ (s )

1000

Figure 9.3 Flow behavior of Espina Corona gum ECG solution at 0.25% w/w, 0.50% w/w, 0.75% w/w, 1.00% w/w, and 1.50% w/w. Source: Adapted from Perduca et al. [6] with permission from Elsevier.

9.3.1

Effect of Concentration

The flow curves of ECG solutions as a function of concentration were obtained at 0.25, 0.50, 0.75, 1.00, and 1.50%, w/w, using a rotational rheometer (HAAKE RS80-Rheo stress, Haake Mess-Technik GmbH, Germany). As shown in Figure 9.3, all ECG solutions exhibited non-Newtonian shear-thinning behavior. The shear-thinning behavior is generally found in many high-molecular-weight polysaccharides [8], and it is due to the fact that when the molecules are at rest, they are arranged in no particular order, which causes a great internal resistance to flow. As the shear rate increases, the molecules orient toward the flow, which decreases the slip resistance and therefore the apparent viscosity. The values of the flow behavior index (n) and consistency coefficient (k) determined by fitting the power-law model are shown in Table 9.1. It can be seen that an increase in ECG concentration raises both pseudoplasticity and viscosity, which increases k and Table 9.1 Power-law rheological parameters of Espina Corona gum (ECG) in comparison with guar gum (GG).

Sample

Concentration % (w/w)

ECG

0.25

25

0.25 ± 0.03

0.44 ± 0.02

0.897

0.50

25

0.41 ± 0.03

0.57 ± 0.02

0.981

0.75

25

0.65 ± 0.07

0.58 ± 0.00

0.994

1.00

10

2.75 ± 0.02

0.49 ± 0.00

0.989

25

1.57 ± 0.02

0.55 ± 0.00

0.991

GG

Temperature (∘ C)

Consistency coefficient (Pa.sn )

Flow behavior index(-)

R2

40

1.09 ± 0.02

0.58 ± 0.01

0.995

60

0.69 ± 0.00

0.61 ± 0.00

0.978 0.988

1.50

25

20.72 ± 1.14

0.32 ± 0.06

0.50

25

1.83 ± 0.06

0.38 ± 0.00

0.999

1.00

25

50.60 ± 6.22

0.14 ± 0.00

0.999

9.3 Flow Behavior

decreases n. In addition, by comparing the flow behavior of ECG with GG, it was found that GG has higher consistency coefficient and lower flow behavior index values than ECG at equal concentration and temperature [6]. This would be associated with the higher molecular weight of GG as compared with that of ECG (1.81 × 106 vs. 1.39 × 106 Da, respectively) [6]. 9.3.2

Effect of Temperature

The influence of different temperatures (10, 25, 40, and 60 ∘ C) on the apparent viscosity of ECG solution (1.0% w/w) is shown in Figure 9.4A [6]. It can be seen that the apparent viscosity decreases when the temperature is increased from 10 to 60 ∘ C, confirmed

η (Pa s)

1

0.1

0.01 10

100 · γ (s–1)

1000

10

(A)

100 · γ (s–1)

1000

(B)

η (Pa s)

1

0.1

0.01 10

100 · γ (s–1) (C)

1000

10

100 · γ (s–1)

1000

(D)

Figure 9.4 A: Flow behavior of Espina Corona gum (ECG) solution (1.00% w/w) at different temperatures: (◾) 10 ∘ C, (•) 25 ∘ C, ( ) 40 ∘ C, and ( ) 60 ∘ C; B: Apparent viscosity of ECG solutions (0.5% w/w, 25 ∘ C) after heating treatment at different temperatures: (◾) without heating, and after heating at: ( ) 60 ∘ C, (▴) 75 ∘ C, and (⧫) 90 ∘ C. C: Effect of NaCl concentration on apparent viscosity of ECG solution (0.5% w/w, 25 ∘ C): (◾) 0 mM, ( ) 30 mM, ( ) 60 mM, and ( ) 90 mM; and D: Effect of glucono-δ-lactone (GDL) addition on apparent viscosity of ECG solution (0.5% w/w, 25 ∘ C) heated at 75 ∘ C for 30 min: (◾) 0% GDL (pH = 6.60), (•) 0.05% GDL (pH = 4.70), ( ) 0.15% GDL (pH = 4.34), ( ) 0.30% GDL (pH = 4.03), and ( ) 0.60% GDL (pH = 3.20). Source: Adapted from Perduca et al [6] and Perduca [3] with permission from Elsevier.

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by lower k value at a higher temperature (Table 9.1). In general, these galactomannan solutions show a decrease by 50% of the apparent viscosity values when the temperature increases from 25 to 80 ∘ C [9]. In addition, the effect of heating treatment on the ECG stability was studied. In order to perform this treatment, the solutions of ECG were heated in a water bath at different temperatures (60, 75, and 90 ∘ C) for a period of 30 min and then were cooled down until 25 ∘ C. Then, the samples were tested for rheological properties at 25 ∘ C. As observed in Figure 9.4B, the flow curves are the same at different heating temperatures, so the ECG structure was not affected by the thermal treatment. These results suggest that ECG could be used in the food products that require stability upon heating. Other commonly used hydrocolloids such as GG and xanthan gum (XG) also exhibit thermic stability [10]. 9.3.3

Effect of Ionic Strength

The effect of NaCl addition on the ECG solution viscosity was studied [6]. Charged polymers exhibit higher viscosity than uncharged polymers because the molecular chains can be expanded due to the electrostatic repulsion of intermolecular charges. However, the galactomannan viscosity, like GG or algarroba, is not influenced by electrolytes. Electrolyte addition reduces the dissociation degree of charged groups, which normally leads to chain compaction and a significant drop in viscosity [11]. As shown in Figure 9.4C, the apparent viscosity of ECG (0.5%, 25 ∘ C) was not changed significantly by increasing the concentration of NaCl from 30 to 90 mM, indicating the stability of ECG viscosity in the presence of salts. 9.3.4

Effect of pH

The effect of pH on hydrocolloid viscosity can vary according to the hydrocolloid species. XG maintains its viscosity, and it is stable at low pHs [12]; however, carboxymethylcellulose (CMC) and some galactomannans exhibit a decrease in viscosity with decreasing pH [13]. The effect of lowering pH as well as heating (75 ∘ C, 30 min) on the flow behavior of ECG was investigated [6]. In order to evaluate the effect of varying pH, glucono-δ-lactone (GDL) was added to the ECG solutions. GDL is a salt that is hydrolyzed in water, giving δ-lactone and gluconic acid, which slowly decrease the pH of the solution. The pH of ECG solution (0.5% w/w, 25 ∘ C) before GDL addition was 6.6. The different concentrations of GDL – 0.05%, 0.15%, 0.30%, and 0.60% – led to a final pH of 4.70, 4.34, 4.03, and 3.20, respectively. As shown in Figure 9.4D, the decrease in pH from 6.6 to 3.2 did not alter the apparent viscosity of the ECG solutions, not even after heating. The literature shows that galactomannans can be degraded at very low pH or low pHs along with heating [11]. However, this behavior was not observed for ECG solutions, which maintain the same viscosity after heating at 75 ∘ C for 30 minutes at low pH. These observations are very important for the ECG applications since they reveal that this gum is not affected by salt addition, heating, or acidic pH. 9.3.4.1

Effect of ECG Addition on Viscosity of Yogurts

The effects of ECG along with gelatin (G) on the rheological, physical, and sensory properties of the cholesterol-reduced probiotic set (firm texture) and stirred yogurts were studied by Pavón et al. [14]. These authors measured the rheological properties of the

9.4 Viscoelasticity

probiotic yogurts and applied the modified Casson and Herschel–Bulkley models in order to obtain the values of the consistency index (K) and flow behavior index (n). They found that all yogurt samples exhibited non-Newtonian shear-thinning behavior (n < 1), indicating the viscosity dependence on shear rate. As expected, the consistency index increases with increasing hydrocolloid dosage, resulting in a firmer coagulum with more consistency and viscosity; meanwhile the flow behavior index decreased. The hysteresis area was larger for those samples manufactured with the addition of both thickeners (G mainly). These differences between the areas were more noticeable after 25 days of storage, probably due to non-covalent bond formation that promotes thixotropy. ECG and G are hydrophilic hydrocolloids, which significantly increases the system viscosity and improves texture. The authors stated that ECG probably acts as a filler between the network of milk proteins, establishing hydrogen bonds, principally, because it is a neutral polysaccharide [15]. Therefore, yogurt samples with a higher content of both hydrocolloids were more susceptible to structural breakdown due to the application of a shear stress. Sensory evaluation is also important, since yogurt with a high degree of grittiness and astringency is not accepted by consumers, while a creamy product is related to high-fat content, dairy flavor, and a viscous, slippery, greasy, and mouth-coating texture [16]; hence, it is important that the use of hydrocolloids results in desirable changes in terms of texture or mouthfeel [17]. Pavón et al. [14] have seen an increase in scores of texture attributes during storage that might depend on the water-holding capacity of proteins added to probiotic yogurts (like whey proteins and thickeners agents) as was described by Akalın et al. [18] and Marafon et al. [19]. They also have shown that the acid taste was less detected in those samples with more G and ECG, while the creamy taste was significantly higher in samples with more ECG content. ECG proved to be useful in low-fat formulations because it can improve the lubricity and flow control, which helps to provide a perception of fat-like properties (e.g., creamy mouthfeel). Pavón et al. [14] also studied the effect of ECG and G on the syneresis of yogurts, and they found that ECG and G decreased the syneresis, since these hydrocolloids have high water-binding capacity and may act synergistically in retaining water in the gel structure [20]. So, the addition of ECG and G achieved greater clot stability, which is a relevant quality parameter because whey separation is an undesirable defect in dairy products. Increased syneresis with storage time is usually associated with casein network rearrangements that promote whey expulsion [21]. In summary, Pavón et al. [14] found that the optimum formulations were 0.49% G–0.41% ECG to obtain set yogurts and 0.01% G–0.43% ECG for stirred yogurts, with desirable sensory, rheological, and stability characteristics.

9.4 Viscoelasticity The study of viscoelastic behavior is important since almost all foods exhibit some viscous and some elastic behavior simultaneously. Viscoelastic properties can be determined by dynamic methods applying a small sinusoidal strain (or stress) and measuring the resulting stress (or strain). Rheological studies of model systems are usually performed in the small deformation limit, for example, the linear viscoelastic region. There are a number of good practical reasons to do so: such deformations are easier to describe

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9 Espina Corona (Gleditsia amorphoides) Seed Gum

theoretically and therefore more readily interpretable in terms of a model; data are usually quite reproducible; and the method is non-destructive, which makes it easier to study the time evolution of specific rheological characteristics of a material. However, the small deformation regime is not always the most relevant one. For example, many model studies on food structuring agents are performed in the small deformation regime, whereas the breaking properties of these materials are much more important [22]. Oscillatory tests express the results with two parameters: (1) the storage modulus G′ , which represents the solid part of the material, that is, the energy spent in deform an elastic solid that is stored, and (2) the loss moduli G′′ , which represents the resistant to the flux of the sample, that is, the energy spent in introducing the flow [23]. The commonly used test in oscillatory rheology for characterizing structures is the G′ and G′′ dependency with the frequency applied, which is denominated as mechanical spectra. The viscoelastic behavior of ECG solutions at 0.5% w/v and 1% w/v concentration were evaluated by the frequency seep test at a constant strain amplitude (4%) and temperature (25 ∘ C) [6]. In the dilute solutions, G′′ is higher than G′ in a large portion of the frequency range where intermolecular disorder does not take place [11]. As shown in Figure 9.5, at the highest concentration and at low frequencies of oscillation, the viscous modulus was higher than the elastic modulus up to a point where this behavior was reversed (the crossing point) [6]. This is a typical behavior of macromolecules in solution known as a concentrated solution [14, 24]. It can also be observed that the higher the hydrocolloid concentration, the less the difference in G′ and G′′ values. These results were compared with the same concentrations of GG solutions. The mechanical spectra of both gums at 0.5 and 1.0% w/v concentrations are shown in Figure 9.5. In comparison, the crossing point of G′ and G′′ occurred at lower frequencies for GG. This may be due to the higher molecular weight of GG, which exhibits a more elastic behavior than ECG [6]. 1.0 % (w/w)

0.5 % (w/w)

102 101

G′/G″ (Pa) η* (Pa s)

232

100 10–1 10–2 10–3 10–4 0.01

0.1 (a)

1

0.01 Frequency (Hz)

0.1

1

(b)

Figure 9.5 Mechanical spectra of Espina Corona gum solutions at (a) 0.5% w/w and (b) 1.0% w/w (𝛾 = 4%, T = 25 ∘ C), G′ ( ) being the elastic modulus, G′′ ( ) the viscous modulus, and 𝜂* ( ) the complex viscosity. Source: Adapted from Perduca et al. [6] with permission from Elsevier.

9.5 Applications of ECG in Colloidal Systems

9.5 Applications of ECG in Colloidal Systems Food colloids are multi-phase systems containing particles or other structures with characteristic spatial dimensions in the colloidal size range [25]. The term colloid can be applied to particulate dispersions, foams, gels, and emulsions (oil-in-water, water-in-oil, and water-in-water systems). Therefore, many foods can be classified as food colloids, and hydrocolloids are added as ingredients in order to control the stability and rheological properties of these systems. In the following sections, the rheological behavior of ECG in different colloidal systems is presented. 9.5.1

Emulsions

Emulsions are dispersed systems which comprise two immiscible liquids [26]. Many natural and processed foods consist either partly or wholly of an emulsion, or have been in an emulsified state during processing, including milk, cream, beverages, dressings, mayonnaise, and so on [26]. These systems are thermodynamically unstable since liquid phases are non-miscible and the density difference between them leads to fast phase separation if there are no kinetic factors to prevent it; thus, they are formulated with different macromolecules to improve their stability and shelf life. Destabilization is due to the action of forces of various ranges: gravitational force, interparticle repulsive and attractive forces, flow forces, and molecular forces. To a differing degree, these are responsible for the action of destabilization mechanisms. The processes leading to instability are creaming, flocculation, and coalescence, and sometimes emulsion phase inversion and Ostwald ripening [27]. It was observed that ECG alone is not a good emulsifier, probably because it is not an amphiphilic molecule, but it was used as a stabilizing agent in whey protein/sunflower oil systems [3]. The difference between having the emulsifying capacity and being an emulsifying stabilizer is that most of the emulsifiers produce emulsions, whereas the stabilizers help prevent the destabilization process. In order to study the stabilizing capacity of ECG, we have formulated oil-in-water emulsions with whey protein isolate as an emulsifying agent and studied the influence of different concentrations of ECG in the prevention of a destabilization process [3]. First, the minimum protein concentration (% w/w) to coat the oil globules without observing free oil after subjecting the emulsions to centrifugation was determined. The emulsions were prepared at whey protein isolate (WPI) concentrations of 1%, 3%, and 5% w/w, with 20% of sunflower oil and produced by blending at 20 000 rpm for 30 s. The minimum concentration of WPI for producing the emulsion was found to be 1%. After that, ECG was added to the emulsion in the following concentrations: 0.5%, 1.0%, and 1.5% w/w, and 30 s additional blending was applied to the systems. Finally, the emulsion rheology and stability were studied [3]. As shown in Figure 9.6, the creaming index significantly decreased with increasing ECG concentration. In addition, the flow curves of ECG emulsions presented shear-thinning behavior, meaning the apparent viscosity decreased as the shear rate increased. The flow behaviors were modeled with the power-law model. It was found that the consistency coefficient and flow behavior index increased with increasing concentration of ECG (data not shown). Oscillatory tests of the emulsions were also performed in the linear viscoelastic range, recording the elastic and viscous modulus versus frequency. As observed in Figure 9.7,

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9 Espina Corona (Gleditsia amorphoides) Seed Gum

101 0.5%, 1.0 and 1.5% w/w ECG ηap (Pa s)

100

WPI 1% ECG 0.0% ECG 0.5% ECG 1.0% ECG 1.5%

10–1

10–2

WPI 0% ECG 1.0%

10–3 10–2

10–1

100

101 · –1 γ (s )

102

103

Figure 9.6 Flow behavior of oil-in-water emulsions prepared by whey protein isolate (WPI, 1% w/w) and different concentrations of Espina Corona gum (ECG, 0.0, 0.5, 1.0, and 1.5% w/w). Source: Adapted from Perduca [3] with permission. Figure 9.7 Mechanical spectra of the O/W emulsions prepared by whey protein isolate (WPI, 1% w/w) and different concentrations of Espina Corona gum (ECG, 0.5, 1.0, and 1.5%). Source: Adapted from Perduca [3]) with permission.

103 102 G′ / G″ (Pa)

234

101 100 G′ G′ G′

10–1

G″ ECG 0.5% G″ ECG 1.0% G″ ECG 1.5%

10–2 0.1

1 Frequency (Hz)

10

G′′ was greater than G′ in the frequency range studied up to a critical frequency at which the curves showed a crossover [3]. The increment in the hydrocolloid content produced an increase in elastic and viscous moduli, but there was no change in the emulsion structure in the concentration range studied. When the ECG concentration increased from 0.5% to 1.5% w/w, the critical frequency where the curves of the moduli exhibited a crossover increased from 0.15 to 4 Hz. The hydrocolloid addition to oil-in-water emulsions improved stability against creaming because the initial velocity of creaming in emulsions stored for 30 days decreased (data not shown). Coalescence phenomena were not observed in dispersed systems stabilized by ECG. ECG also produced a lower tendency to flocculation that could be due to the viscosity increment in the dispersed phase. These results indicated that dispersed systems of oil-in-water emulsions with ECG addition are more stable against the destabilization effects, allowing stable emulsions to be obtained.

9.5 Applications of ECG in Colloidal Systems

9.5.2

Foams

Foams are dispersions of gas bubbles in a continuous liquid or semisolid phase [28]. Proteins are one of the main foaming agents used in food products, but they may have certain deficiencies if long-term foam stability is required. Long-term stability is much more difficult to achieve for aerated systems as foam than it is for emulsions. Hence, the incorporation of colloidal particles as a possible way of enhancing foam stability is a matter of great technological and commercial significance, because the aerated structure provides the essential textural characteristics of highly popular foods such as ice cream [29]. Therefore, we have studied the foam stability properties of ECG along with whey proteins comparing two methods: bubbling and stirring [3]. The stirring method proved to be better than bubbling, producing more stables foams with smaller bubble sizes. The flow behavior of the foam continuous phase with the addition of different ECG concentrations is shown in Figure 9.8. Higher ECG concentrations (ECG 0.5%–1.0% w/w) show strong pseudoplastic behavior, while lower concentrations exhibit a decrease in the apparent viscosity, indicating that the increment in ECG concentration increased the pseudoplasticity and the viscosity of the foam continuous phase. The power-law model was applied, and it was found that the consistency coefficient (k), and the flux behavior index (n) increased with increasing ECG concentration (data not shown). Along with these studies, the disproportionation of the air bubbles of all the formulations has been studied [3]. ECG has been shown to be a good stabilizer that prolonged the drainage time, making the drainage slower. This was possible because the ECG increased the viscosity of the continuous phase, retarding the disproportionation of air bubbles. 9.5.3

Gels and Structured Systems

Gelation is a very important functional property of hydrocolloids since gelling agents are extensively used in products like jam, jelly, marmalade, restructured foods, and WPI 1% GEC 0.00% GEC 0.10% GEC 0.25% GEC 0.50% GEC 0.75% GEC 1.00%

ηap (Pa s)

1

0.1

0.01

101

102 · γ (s–1)

103

Figure 9.8 Flow behavior of foams continuous phase of whey protein isolate (WPI, 1% w/w) at different Espina Corona gum (ECG) concentrations. Source: Adapted from Perduca [3]) with permission.

235

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9 Espina Corona (Gleditsia amorphoides) Seed Gum

low-sugar/low-calorie gels [30]. When we describe a gel, it is important to note that it is a viscoelastic material, which means that it has the properties of both liquid and solid. These properties can be measured by applying a stress: if a force is applied to an elastic solid, the shape changes, and the deformation is proportional to the applied stress; when that stress is removed, the material returns to the initial shape, and most of the force used for the deformation is recovered. On the contrary, when a force is applied to a liquid, it responds by flowing, and the flow speed is proportional to the applied force. A gel has both properties, so this viscoelastic behavior is the main characteristic of the gel state [23, 31]. Although galactomannans do not have the ability to form real gels when used singly, they form structured systems or weak gels or can act as a filler in the presence of other gelling biopolymers. The mixture of XG and galactomannan is one of the oldest and most extensively studied synergistic gelling systems [32]. The synergistic interactions can lead to an increase in viscosity and/or gel formation depending on the mannose-galactose ratio of the galactomannan [33]. The viscoelastic properties of the mixed systems depend on the food system conditions, such as ionic strength, nature of salt added, processing temperature, and so on. The synergistic interactions between different polysaccharides are attractive in the food industry; they can confer different textures and rheological characteristics, and hence, they can reduce costs. In the following section, the interactions of ECG with other biopolymers for obtaining gel systems are reviewed. 9.5.3.1

Interaction between ECG and Xanthan Gum

XG and galactomannans can interact in solution, significantly increasing the viscosity and producing a gel structure [34–36]. XG is an exocellular polysaccharide produced by the bacterium Xanthomonas campestris and is nowadays very widely used in a broad range of products, including foods, pharmaceuticals, cosmetics, personal care, drilling muds, and so on, because of its unique rheological properties [11]. Essentially, XG solutions exhibit a very high viscosity at low shear rates, and a strong pseudoplastic behavior because of the weak intermolecular association of the polysaccharide chains [37]. The XG structure consists of β-d-mannose, (1,4)-β-d-glucuronic acid, and (1,2)-α-d-mannose, with side branch chains linked at position 3. The inner mannose may be acetylated, and the terminal mannose may be pyruvated. It has been clearly demonstrated by a range of techniques that the molecules undergo a conformational transition in solution to form a more flexible disordered state, which is favored at high temperature and low ionic strength [11]. These conformational changes are responsible for the interaction with galactomannan molecules, such as LBG and Tara gum, leading to the formation of thermoreversible gels [11, 38]. These gels are optically clear and highly elastic and have considerable commercial importance. A common feature of galactomannans with respect to their interaction with XG is that they adopt an extended conformation in solution. Many studies have proposed that the synergic interaction between XG and the galactomannans is based on a cooperative interaction that depends on the structure of the galactomannan [35]. This association is produced between the main and ordered chain of the XG and the unsubstituted regions of the galactomannan, forming junction zones [39, 40]. This interaction depends on the galactose/mannose ratio of the galactomannan structure. The galactomannans with fewer lateral branches of galactose and more unsubstituted regions can establish more

9.5 Applications of ECG in Colloidal Systems

interactions. The amount of galactose depends on the species from which the galactomannan was extracted. So, LBG, which has a mannose/galactose ratio of 3.5:1, reacts more strongly with XG than GG, which has an M/G ratio of 2:1 [11]. ECG has an M/G ratio of 2.5:1, so the expected behavior is between these two gums. The interaction of XG with ECG also depends on the ratio of the two hydrocolloids in the mixture, pH, and ionic strength. Generally, the synergic interaction with galactomannans is at their maximum with deionized water at neutral pH, and it is reduced at high salt concentration and low pH [11]. The literature suggests that xanthan and galactomannans may interact by two distinct mechanisms. One takes place at room temperature, gives weak elastic gels, and has little dependence upon the galactose content of the galactomannan, while the second requires significant heating of the polysaccharide mixture, gives stronger gels, and is highly dependent upon galactomannan composition [41]. Khouryieh et al. [40] have reported that mixed systems of XG and GG exhibited the maximum synergic interaction when the mixture is heated at 80 ∘ C and is then cooled to 25 ∘ C, because the interaction is improved. We have studied the interaction between XG and ECG in the following XG:ECG ratios: 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100 [3]. After mixing, the mechanical spectra of the mixtures at 0.25% w/w polysaccharides with the addition of 0.1 M of KCl were evaluated. ECG (XG:ECG 0 : 100) exhibited the typical behavior of a viscous solution, with an elastic modulus G′ lower than the viscous modulus G′′ , whereas XG (XG:ECG 100:0) exhibited weak gel behavior, with G′ higher than G′′ over the entire range frequency (data not shown) [3]. As seen in Figure 9.9, the mechanical spectra of XG:ECG 80:20 and 60:40 are shown with respect to XG alone (black lines). The system XG:ECG 80:20 exhibited higher values of G′ and G′′ moduli with respect to XG alone, which indicates that addition of ECG produced an increase in the solid character of the systems. In these conditions, the maximum synergism is produced. A higher XG:ECG ratio (60:40) produced an increase in G′ while G′′ did not show significant differences. However, when the ECG concentration in the mixture is higher than 50% of the total concentration of the polysaccharides, a decrease in both moduli G′ and G′′ is produced (data not shown) [3].

101

GX:ECG 80:20 G′ G″

G′/G″ (Pa)

Figure 9.9 Mechanical spectra representative for mixed systems of xanthan: Espina Corona gum (GX/ECG) with a total concentration 0.25% w/w and with the addition of 0.1 M KCl. (Reference: GX:ECG 100:0 (−) G′ , (−-) G′′ ). Source: Adapted from Perduca [3]) with permission.

GX:ECG 60:40 G′ G″

100

10–1 0.1

1

0.1 10 Frequency (Hz)

1

10

237

238

9 Espina Corona (Gleditsia amorphoides) Seed Gum

We have also compared the XG/ECG systems with XG/GG systems [3]. Some authors described the interaction between XG with GG as compatible [42]. According to several studies, the lower proportion of mannose/galactose in GG (2:1) relative to ECG (2.5:1) should produce a weaker synergism between XG and GG [43, 44]. As previously mentioned, the mechanism of intermolecular association between XG and galactomannans is still controversial [40], although it is known that the galactose-to-mannose content strongly influences the interaction between galactomannans and XG. In order to study this interaction and compare the results with ECG, systems with different XG:GG ratios were prepared: 100:0, 80:20, 40:60, 60:40, 20:80, and 0:100. According to our results, no synergic interaction was found between XG and GG. Not only the viscous modulus (G′′ ) but also the elastic modulus (G′ ) decreased with the incorporation of GG into the mixed system [3]. Because XG is an anionic polysaccharide and its conformation changes according to the ionic strength of the media in which is solubilized, we also studied the effect of electrolytes (monovalent (NaCl) and divalent (CaCl2 ) salts) on the viscoelastic properties of XG/ECG mixed systems [3]. The maximum elastic modulus was obtained for XG:ECG 40:60 ratio in the presence of 0.1 M CaCl2 . The addition of NaCl increased the elastic modulus linearly with the increase in the ECG ratio in the system [45]. The interaction of XG/GG systems in different-ionic-strength media was also studied. It was found that the addition of NaCl at a concentration higher than 0.001 M or CaCl2 at a concentration higher than 0.0005 M decreased the interaction significantly. Calcium has a deeper impact on decreasing the synergism between these polysaccharides when compared with monovalent ions like sodium. This is possibly due to the electrostatic interaction that occurs between the XG and calcium, resulting in higher molecular contraction, inhibiting the interaction with the galactomannan [46]. Clark [47] found that the decrease in the synergism with the addition of ions is related to the conformational change in the XG molecule from disordered to ordered, induced by the presence of the ions. According to this study, the conformation of the xanthan molecule controls the interaction. The ionic strength favors the ordered conformation of XG, limiting the synergism with galactomannans like ECG at high salt concentrations [45]. However, Goycoolea et al. [48] showed that XG in any conformation can develop synergic properties with galactomannans. 9.5.3.2

Interaction between ECG and Carrageenan

Galactomannans can also interact synergistically with kappa-carrageenan. Many mixed systems formed by galactomannans and κ-carrageenan already find extensive applications in the food industry [49]. Carrageenan is the sulfated linear polysaccharides of d-galactose and 3,6-anhydro-d-galactose extracted from certain red seaweeds of the Rhodophyceae class [50]. They have been extensively used in the food industry as thickening, gelling, and protein-suspending agents, and more recently by the pharmaceutical industry as an excipient in pills and tablets. The importance of carrageenans in the food industry derives mainly from the ability of kappa- and iota-carrageenan to form elastic gels in the presence of certain cations (K+ and Ca2+ are the usual counterions in kappaand iota-carrageenan gels, respectively). Despite extensive research, the molecular basis for the conformational transitions in a solution that result in aggregation and gelation is as yet imperfectly understood. Carrageenans are able to form aqueous gels because of the association of the molecular chains into double helices, which then aggregate to form

9.5 Applications of ECG in Colloidal Systems

a network capable of immobilizing water [51], so gelation is achieved through junction zones formed by the helices, leading to a three-dimensional network [52]. In general, the carrageenans produce rigid but fragile gels with syneresis. They slowly release water when stored, and also in the freezing and thawing process. A modification is required in the formulation of these systems in order to improve resilience, cohesiveness, and water retention [53]. Kappa-carrageenan and some galactomannans, when mixed together, form a network whose strength depends on the preparation temperature and on the weight ratio between the two components [49]. Possibly, kappa-carrageenan could interact through hydrogen bonding with unbranched smooth segments of the d-mannose backbone of galactomannan molecules. Due to this interaction, mixed gels can be obtained at lower concentrations in respect of carrageenan alone. In comparison with carrageenan gels at the same concentration, the mixed systems with galactomannans exhibit an increase in gel strength and elasticity, with a reduced tendency to syneresis. In order to study the influence of ECG on the rheological and mechanical properties of carrageenan gels (4% w/w), different concentrations of ECG (0.00%, 0.35%, and 0.70% w/w) and KCl (0.010, 0.105, and 0.200 M) were studied [3]. The uniaxial compression test and texture profile analysis (TPA) were carried out on these samples. Large deformation tests have generally been used for studying the mechanical properties of the hydrocolloid gels. These measurements are characterized by (1) the nonlinear elastic response of the material and (2) the failure of the material at a certain critical strain, the breaking strain. Both phenomena are accessible in a single experiment by plotting the stress–strain curve of the material [22]. This type of study is important since, during manufacturing, food products are subjected to large strains that may cause severe deformation or even final fracture, affecting their structural integrity. Moreover, large deformations and fracture processes are involved in biting and mastication, and therefore, they are linked to consumer acceptance and preference. Determination of mechanical properties is of great importance for food scientists and technologists since the mechanical response affects food processing, handling, and consumption [54]. In a typical uniaxial compression test, some of the calculated parameters are the true or Hencky stress (𝜎 H ), and Hencky strain (𝜀H ), which can be defined as 𝜎H = F(t) × H(t)∕(H0 − A0 )

(9.1)

𝜀H = ln(H(t)∕H0 )

(9.2)

where F(t) and H(t) are the force and the height at a given time t, and A0 and H0 are the initial area and initial height of the gel, respectively [55]. The parameters calculated from the compression data were the maximum stress (𝜎 M ), which is the maximum value of 𝜎 H until rupture, calculated from Eq. (9.1); maximum strain (𝜀M ), which is the maximum value until rupture, calculated with Eq. (9.2); and Young’s modulus (E), which is calculated as the slope of the linear and initial region of the curve 𝜎 H versus 𝜀H (5% strain) [56]. In Figure 9.10, the images of carrageenan/ECG gels and the uniaxial compression curves obtained in our study are shown [3]. In general, all the analyzed properties exhibited a maximum value at KCl concentrations of 0.105 mM and increased with increasing ECG concentration. These results indicate that there is an optimum in the KCl concentration, and the addition of ECG reinforces the gel resistance to rupture by increasing the maximum stress. At the same concentration of KCl (0.105 mM), the deformation

239

9 Espina Corona (Gleditsia amorphoides) Seed Gum

(a)

ECG 0.00 % (b)

0.35%

0.70%

40 35 30

σH (kPa)

240

25 20 15 GEC 0.00% GEC 0.35% GEC 0.70%

10 5 0 0.00

0.05

0.10

0.15 εH

0.20

0.25

0.30

Figure 9.10 Image of carrageenan gels at 4.0 (%w/w) with Espina Corona gum (ECG) addition of 0.35 and 0.70% w/w (a); and (b) uniaxial compression curves of those gels. Source: Adapted from Perduca [3]) with permission.

values and Young’s modulus are the same for gels without ECG or with 0.35% and 0.70% w/w ECG addition. TPA was also carried out in the carrageenan/ECG mixed gels. The mechanical properties of solids and viscoelastic materials are described in terms of hardness, strength, deformability, fragility, rigidity, plasticity, elasticity, and ductility, among others. These mechanical and structural properties are related to the food texture that consumers can perceive as physical characteristics specific to each food. These macroscopic properties reflect molecular interactions. Several parameters are calculated from the TPA plot [57]: (1) Fracturability (originally called brittleness) is “the force at the first significant break in the curve.” As a break is a visible phenomenon related to the macrostructure of the sample, it must be identified as a change in the inflection of the curve whose magnitude must be defined. (2) Hardness is “the peak force during the first compression cycle” (this force is related to the first bite during chewing”). (3) Cohesiveness is “the ratio of the positive force area during the second compression portion to that during the first compression (Area 2/Area l), excluding the areas under the decompression portion in each cycle.” (4) Adhesiveness is defined as “the negative force area in the first cycle.”

9.5 Applications of ECG in Colloidal Systems

Table 9.2 Parameters of texture profile analysis (TPA) determined for carrageenan/Espina Corona gum (ECG) gels as a function of ECG and KCl concentration. ECG (% w/w)

KCl (mM)

Hardness (N)

Adhesiveness (N.s)

Cohesiveness (−)

Gumminess (N)

0.0

0.01

9.60 ± 1.37

0.65 ± 0.45

0.12 ± 0.32

1.17 ± 0.19

0.35

0.01

16.26 ± 1.55

0.28 ± 0.22

0.06 ± 0.14

1.05 ± 0.31

0.7

0.01

13.45 ± 4.78

2.89 ± 1.81

0.08 ± 0.05

1.12 ± 0.67

0.0

0.105

37.08 ± 6.77

0.21 ± 0.29

0.06 ± 0.013

2.14 ± 0.1

0.35

0.105

45.19 ± 1.49

0.44 ± 0.17

0.07 ± 0.14

2.99 ± 0.72

0.7

0.105

42.76 ± 4.66

0.55 ± 0.30

0.08 ± 0.01

3.35 ± 0.45

0.0

0.2

25.44 ± 1.34

1.28 ± 0.01

0.08 ± 0.00

2.05 ± 0.13

0.35

0.2

29.38 ± 3.59

0.26 ± 0.08

0.09 ± 0.01

2.85 ± 0.70

0.7

0.2

34.63 ± 3.27

0.17 ± 0.01

0.1 ± 0.00

3.43 ± 0.10

(5) Springiness (originally called elasticity) is “the height that the food sample recovers during the time that elapses between the end of the first cycle and the start of the second cycle.” (6) Gumminess is “the product of hardness and cohesiveness.” (7) Chewiness is defined as “the product of gumminess and springiness” (which is equivalent to hardness × cohesiveness × springiness). These parameters obtained from TPA curves of carrageenan gels at 4% w/w with the addition of different concentrations of KCl and ECG are presented in Table 9.2. At the same concentration of ECG, the hardness is higher for the mixture containing 0.105 mM KCl, and the maximum hardness is exhibited by 0.105 mM KCl and 0.35% (w/w) ECG. Cohesiveness values are low because the gels lost their physical structure with the first compression. Something similar happened with adhesiveness (the gels were not adhesive). The maximum chewiness value is obtained at 0.2 mM KCl and 0.7%w/w ECG [3]. 9.5.3.3 9.5.3.3.1

Interaction between ECG and Proteins ECG and WPI Mixture

Since proteins and polysaccharides are the major components of food systems and they play an essential role in their structure, texture, and stability, the study of mixed system properties is important to the food industry development. Among all food proteins, whey proteins have been extensively studied because of their important functional and nutritional properties. One important functional property is their ability to form gels. The gelation of whey proteins has been studied in the presence of a wide variety of polysaccharides [58–60]. Different types of mixed gels can be obtained according to the relative concentration of each macromolecule, their nature (neutral or ionic), and environmental conditions (temperature, pH, and ionic strength) [61]. The textural, mechanical, and sensory properties of these gels are a consequence of their microstructure, and this depends on the type and degree of protein–protein and protein–polysaccharide interactions, among other things [62]. Our group studied the interactions and the rheological properties of WPI/ECG mixed gels [15]. The WPI concentration was 12% w/w, and ECG was added at 0.12, 0.36, and

241

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9 Espina Corona (Gleditsia amorphoides) Seed Gum

0.60% (w/w), leading to final ratios of 1:0.01, 1:0.03, and 1:0.05 [15]. On the basis of the results of the uniaxial compression test, the increment in ECG concentration led to an increase in the maximum stress (σM ), this being significant from 0.36% of ECG onward. The maximum Hencky strain (εM ) of the gels was not affected by the ECG concentration (p > 0.05). Similar results were obtained by Fitzsimons et al. [38] in WPI/GG mixed gels. By means of confocal laser microscopy, it could be observed that WPI/ECG mixed systems exhibited phase separation. This phase separation could be the reason for the higher maximum strength in WPI/ECG gels when compared with WPI alone and lower pore size, since ECG could create micro-areas with higher protein concentration, reinforcing the network cross-linking. The addition of polysaccharide might cause protein molecules to approach each other, probably acting as a filler [63]. However, there are other protein–polysaccharide interactions that could be considered in the gel formation, such as hydrogen bonds among certain groups of polysaccharide and proteins. Electrostatic interactions between WPI and ECG should be underestimated because ECG is a neutral polysaccharide [15]. 9.5.3.3.2

ECG and Sodium Caseinate Mixture

The influence of ECG addition on sodium caseinate’s (NaCAS) properties was studied by López et al. [64]. NaCAS is derived from micellar casein and is composed of a soluble mixture of four proteins (α-s1 , α-s2 , β-, and κ-caseins), excluding the phosphate and calcium components. In solution, NaCAS is a mixture of monomeric or small aggregated particles [65]. They studied the aqueous interaction in diluted and concentrated systems by zeta potential, size distribution, and viscosity measurements. They found that the zeta potential of NaCAS was not affected by ECG at the different concentrations studied, suggesting that there was no modification in the surface charge of the NaCAS particles in the presence of ECG. The authors also found an increase in NaCAS particle size due to the addition of ECG, suggesting that the presence of ECG favors NaCAS self-aggregation. Moreover, they found an increase in the size of the protein particles after 24 h incubation, which suggests that ECG affects not only the aggregation of NaCAS but also its stability in solution [66]. Other systems composed of galactomannans and caseins also showed phase separation [67]. Each system has a different concentration in which the phase separation occurs, so it is important to determine that biopolymer concentration. A relatively low concentration of ECG is needed to induce phase separation in NaCAS systems. However, even lower concentrations of GG were needed to induce phase separation in NaCAS/GG mixtures [68], which can be explained by taking into account that ECG has a lower molecular weight than GG [6]. Regarding the effect of ECG on viscosity, the authors have found a synergism between ECG and NaCAS that could be due to changes in the NaCAS structure in solution as a result of the presence of ECG. Comparing their results with those obtained by Bourriot et al. [69] in GG/casein micelles systems, it could be concluded that the flocculation of NaCAS as a result of the exclusion of the ECG from the protein surface is responsible for the observed behavior. In conclusion, the authors found that ECG and NaCAS did not interact effectively since the results would indicate that ECG is excluded from the protein surface, but it is likely to favor the aggregation of NaCAS. The results also suggested that the presence of ECG may induce the formation of NaCAS aggregates, whose sizes depend on the ECG concentration. The authors proposed that ECG addition

9.5 Applications of ECG in Colloidal Systems

causes NaCAS aggregation through depletion-flocculation since the galactomannan is excluded from the NaCAS surface. The same authors studied the effect of ECG on the aggregation and gelation of NaCAS and the physical characteristics of the derived acid-induced gels [70]. NaCAS can produce a gel by acidification. The unfolded proteins solution first leads to protein aggregation, and when the amount of aggregated protein exceeds a critical concentration, a gel protein network can be formed by the association among these protein aggregates, for example, by inhibiting the electrostatic repulsion among aggregates. The gel properties depend strongly on the structure of the protein aggregates and their association into a three-dimensional network [71]. Acidification of NaCAS can be carried out by microbial fermentation or by the chemical method through hydrolysis of GDL into gluconic acid [72]. First, López et al. [70] carried out the aggregation process, which consists of the removal of the electrostatic repulsion of the negative surface charges of NaCAS by means of GDL hydrolysis into gluconic acid. While the aggregation was under way, there was a decrease in the pH until the equilibrium gluconate/gluconic acid was established. ECG did not change the net amount of protonable groups exposed by NaCAS but affected the acidification rate, extending the time required to reach the aggregation pH as the ECG concentration increased. The presence of ECG did not modify the aggregation pH, which is the pH value at which gels are formed; in this case, it was 5.00 ± 0.02 and was not influenced by the addition of ECG. The gels containing ECG exhibited lower water-holding capacity, maybe due to a phase separation through a depletion-flocculation mechanism as seen in the previous study [70]. The mechanical properties with 0.1% (w/w) of ECG presented a similar penetrometer profile to those obtained for the NaCAS gels in the absence of ECG. Although firmness was not affected, the gel broke at a lower deformation rate than it did in the absence of ECG, the fracture force also being lower. On the other hand, the addition of 0.2% (w/w) ECG produced fewer firm gels that fracture at less penetration, thus being less deformable. The presence of the highest ECG concentration (0.3%, w/w) dramatically affected the mechanical properties of the system, reducing firmness significantly and making it impossible to determine the fracture point. Even though phase separation was not observed macroscopically, it was confirmed by confocal microscopy images analysis. The effect of ECG on the size distribution of the protein aggregates is not clear. However, the size of the pores in NaCAS acid-induced gels is smaller and their distribution is narrower in the presence of ECG, which are similar results to those obtained by Spotti et al. [73] in the WPI/ECG heat set gels described in the previous section. 9.5.4

ECG Microspheres

The possibility of using biodegradable polymers as drug carriers attracted the attention of many researchers since biodegradable polymers have several advantages: biocompatibility, low dosage, and reduced side effects are some reasons why using biodegradable microspheres have gained in popularity. The drug and polymer may be combined in a number of different ways depending upon the application of interest. Microparticulate formulations have the widest applicability to the widest variety of formulation needs: oral delivery, intramuscular injection, subcutaneous injection, and targeted delivery. The use of ECG for synthesizing microspheres for use in the transport of pharmaceutical drugs was compared with GG, and ECG-XG and GG-XG mixed systems [74]. The

243

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9 Espina Corona (Gleditsia amorphoides) Seed Gum

microspheres were prepared using the emulsion solvent evaporation/extraction method with glutaraldehyde (GA) as a cross-linker. The chemical reaction between an excess of cross-linker and the polymeric chains leads to the formation of a network [75]. According to the chemical structure of the repeating units of galactomannans, such as ECG and GG, and owing to the fact that the reaction of GA occurs only with the vicinal diols, the network formed in the presence of an excess of GA could exhibit a high degree of cross-linking [75]. In order to prepare the spheres, the aqueous phase (AP) was prepared by dissolving ECG, GG, ECG-XG, and GG-XG solutions (3%, w/w) with Tween 80 (0.2%, w/w) and GA at 2% (w/w) under continuous and moderate stirring while the pH was decreased to 2 with 2 N HCl (to protonate the hydroxyl groups of the polymer) [74]. The oil phase (OP) was prepared using castor oil with Span 80 (5%, w/w). Both Tween 80 and Span 80 are emulsifiers; the former is soluble in the AP and the latter in the OP. Both phases, OP and AP, were mixed with a Baring Blender homogenizer (United States) to generate the water-in-oil emulsion. After stirring, the emulsion was mixed with ethanol to dehydrate the particles. OP was eliminated, the microspheres were sieved, and the GA was removed. The microspheres were dehydrated using acetone washes and dried. To analyze the absorption and retention of drugs, theophylline (THF) was used as a model molecule. THF is a bronchus-dilator drug, but its use in the treatment of asthma has been restricted due to its short half-life. One way to minimize this limitation is to encapsulate THF in an appropriate vehicle. The microspheres were allowed to soak up in a 0.67% (w/w) THF solution. The process was carried out at room temperature with moderate stirring. Since THF is insoluble in acetone, the microspheres were washed with this solvent and dried. To analyze the THF desorption process, the UV–Vis absorption spectrum of THF was obtained (Perkin Elmer, United States), the maximum absorption value occurring at 271 nm. The desorption process of THF was carried out at pH 6.8 and 37 ∘ C with moderate stirring. Samples were taken at different times, and the absorption at 271 nm was determined [74]. It was found that after 2 h, GG and ECG systems released 8.48 ± 0.05% and 8.36 ± 0.05% THF, whereas GG-XG and ECG-XG released 15.51 ± 0.03% and 10.84 ± 0.09% THF, respectively. Sandolo et al. [75] have studied also the release of THF from GG hydrogels cross-linked with GA and found that 97% of the charge was released in 8 h.

9.6 Conclusions and Future Trends ECG exhibits shear-thinning behavior, being influenced by the temperature but being stable after heating, salt addition, and pH decrease. ECG exhibits less viscosity and less pseudoplastic behavior than GG at the same concentration, probably because of its lower molecular weight. The stabilizing capacity of ECG for thermodynamically unstable systems such as foams and emulsions shows that oil-in-water emulsions prepared by ECG exhibit stability against the destabilization process because the gum increases the viscosity of the continuous phase, which produces a decrease in the creaming rate. In regard to the addition of ECG in foam systems, the gum exhibits the same effect as in emulsions, and thus the foams formulated with this gum are more stable to the disproportion phenomena and the draining time increase. ECG in combination with different biopolymers exhibits synergic interactions with other polysaccharides, such as XG and

References

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10 Qodume Shahri (Lepidium perfoliatum) Seed Gum Arash Koocheki 1 and Mohammad A. Hesarinejad 2 1

Department of Food Science and Technology, Ferdowsi University of Mashhad (FUM), PO Box 91775-1163, Mashhad, Iran Department of Food Processing, Research Institute of Food Science and Technology (RIFST), PO Box 91735-147, Mashhad, Iran 2

10.1 Introduction Lepidium perfoliatum is locally called Qodume Shahri in Iran. The seeds of this plant have been used for hundreds of years in traditional Iranian medicinal prescriptions because of their pharmacological effects [1]. In traditional medicine, mucilage extracts from L. perfoliatum seeds are widely employed as a demulcent for the treatment of dry coughs, whooping cough, and lung infections [2]. Any of the 230 species of herbs constituting the genus Lepidium of the Cruciferae family are distributed throughout the world, and it is native to Egypt, Arabia, Iraq, Iran, and Pakistan. Many, such as L. perfoliatum, are lawn and field weeds, but some are useful salad plants. Most species have long taproots, broad basal leaves differing from the narrow leaves on the flowering stalks, and spike-like arrangements of small, greenish or whitish, four-petaled flowers (Figure 10.1a). Lepidium perfoliatum seeds are 2 mm long, flat, rounded, ovate-oblong with reddish brown color and narrowly winged all around (Figure 10.1b). Lepidium perfoliatum seed gum (LPSG) is mainly formed in the outer layer of seeds. When the shell contacts with water, it quickly produces a viscid, turbid, and insipid liquid. The dried LPSG has a brownish-yellow color (Figure 10.1c). Considering the cost, availability, and functional characteristics of common commercial stabilizers, studies are increasingly being done on the production of new polysaccharides from local sources. Natural plant-based gums are widely utilized in food industries as thickening, binding, disintegrating, emulsifying, suspending, stabilizing, and gelling agents [3]. Among them, LPSG has shown promise to be considered as a potential novel food thickening agent and is effective for food emulsions [1, 4]. Therefore, the objective of this chapter is to highlight the unknown potential of LPSG for use in food industries and provide holistic information on its wide spectrum of uses and prospects.

Emerging Natural Hydrocolloids: Rheology and Functions, First Edition. Edited by Seyed M.A. Razavi. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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(a)

(b)

(c)

Figure 10.1 Pictorial view of (a) Lepidium perfoliatum plant, (b) seeds, and (c) gum powder.

10.2 Gum Extraction Optimization LPSG occurs mainly in the outermost layer of the hull. This hull is able to release mucilaginous material easily when soaked in water. Therefore, aqueous extraction is one of the most common techniques applied for the extraction of the seed mucilaginous material [1]. The most common method used for the extraction of seed mucilaginous material is the aqueous extraction technique [5–9]. Conventional hot-water treatment has been used for the extraction of polysaccharides, which is a time-temperature-dependent method. The effects of process variables including temperature, time, pH, and the water-to-seed ratio are important for extraction of LPSG [1]. LPSG is extracted from whole seeds using deionized water at a water-to-seed ratio of 30:1 and pH of 8. The pH is monitored continuously and adjusted by addition of 0.1 mol l−1 NaOH. The water bath temperature is set at 48 ± 1.0 ∘ C during the extraction process. Water is preheated to the desired temperature before the seeds are added. The seed-water slurry is stirred with an electric mixing paddle throughout the entire extraction period (1.5 h). The mucilage of seeds is discarded, and ultimately the dispersion is dried in a conventional oven (overnight at 45 ∘ C), milled, and sieved using a mesh 18 sifter [1]. This optimum extraction condition is found for maximizing extraction yield, viscosity, hue, and emulsion stability as well as obtaining minimum protein content. While increasing the extraction temperature increases the extraction yield and the protein content of the mucilage, it decreases the viscosity, hue, and stabilizing effect of the gum. Lower pH at the higher water-to-seed ratio seems to reduce the apparent viscosity and emulsion stability of the hydrocolloid, but it has no effect on the extraction yield. However, at the higher water-to-seed ratio, an increase in pH decreases the hue value. The extraction yield, hue, and protein content of gum increase with an increase in the water-to-seed ratio from 30:1 to 60:1, whereas the viscosity and emulsion stability decrease with increase in this variable [1]. Different drying methods affect the apparent viscosity and gelling properties of LPSG. Drying methods for mucilage affect the rigidity and adhesion of LPSG gel. Vacuum oven drying exhibits the highest viscosity reduction. The viscosity of LPSG is not affected by hot air and freeze drying methods. Since the hot air drying requires lower cost, it is preferable to use this process for the production of LPSG with higher viscosity [10].

10.5 Rheological Properties

10.3 Chemical Compositions LPSG has a high total carbohydrate content (88.23 w/w%) [4], showing that the extracted gum is relatively pure. This polysaccharide is mainly composed of xylose (44.66 ± 0.37), arabinose (31.99 ± 0.48), galactose (12.77 ± 0.01), glucose (7.15 ± 0.33), and rhamnose (3.40 ± 0.21), which is different from most other seed mucilages and is probably an arabinoxylan-type polysaccharide [11]. The composition of LPSG is similar to that of flaxseed mucilage, which has a mixture of neutral arabinoxylans and strongly acidic rhamnose-containing polymers [12]. Plantago ovata seed mucilage (also called psyllium) is also an arabinoxylan polysaccharide [13]. Aspinall [14] also stated that the cress seed mucilage contains a xyloarabinan and an acidic polysaccharide in association with cellulose. Arabinoxylans constitute the main part of plant cell walls [15, 16]. Arabinoxylans are prebiotic carbohydrates with promising health-promoting properties that stimulate the activity of specific colon bacteria, particularly bifidobacteria [17]. In other words, they are very important for human nutrition as readily fermentable substrates for gut microbiota [18].

10.4 Functional Properties The water absorption capacity (WAC) of LPSG (∼20 g/g) is lower than that of guar and locust bean gum, but it is almost similar to that of xanthan. Different WACs could arise due to the differing levels of the polar hydroxyl groups in gums and hence their extent of hydrodynamic interactions. Therefore, a low WAC of an LPSG might be due to the strong chain-to-chain interactions among the polysaccharides, and hence their lower interactions with water [4]. LPSG shows lower solubility compared to xanthan, guar, and locust bean gums at temperatures from 30 to 90 ∘ C. The low solubility might be due to the low degree of substitution, which allows the polysaccharide to be more compact. The solubility of LPSG increases as the temperature increases. The solubility of LPSG does not exceed 25%, which is related to the particle size and the impurity of the sample [4].

10.5 Rheological Properties 10.5.1

Flow Properties

In general, LPSG dispersions exhibit non-Newtonian shear-thinning behavior at different concentrations and temperatures. LPSG has a great potential as a thickening and stabilizing agent in food systems [4, 19, 20]. Steady shear flow properties show that LPSG has high viscosity, yield stress, and strong shear-thinning characteristics [4]. This gum is able to bind and immobilize a large amount of water, thus increasing the viscosity, modifying the texture, and stabilizing the product consistency. 10.5.1.1

Effect of Concentration

Figure 10.2 illustrates the effect of different LPSG concentrations on the apparent viscosity at 25 ∘ C and the on consistency coefficient at different temperatures. It can be seen

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10 Qodume Shahri (Lepidium perfoliatum) Seed Gum

3.10 Apparent viscosity (Pa.s)

0.5%

1%

1.5%

2%

2.48 1.86 1.24 0.62 0.00 60

0

120 180 Shear rate (1/s) (a)

240

300

2.00

2.50

30 Consistency coefficient (Pa.sn )

254

5°C

25°C

45°C

65°C

25 20 15 10 5 0 0.00

0.50

1.00 1.50 Gum concentration (%) (b)

Figure 10.2 Effect of gum concentration on (a) the apparent viscosity at 25 ∘ C and (b) the consistency coefficient at different temperatures of LPSG. Source: Adapted from Koocheki et al. [4] with permission from Elsevier.

that the apparent viscosity of LPSG decreases with increasing shear rate (Figure 10.2a). The reduction in viscosity is sharp at the beginning and smoothened at high shear rates. At low shear rates, the gum molecules are disarranged and only partially aligned, resulting in a higher viscosity. As the shear rate is increased, the molecules become completely oriented and aligned, thus decreasing the inner friction and lowering the viscosity. A comparison of the apparent viscosity of LPSG with that of other commercial gums shows that at identical applied shear rates, the viscosity of this gum is lower than that of guar gum, almost similar to that of xanthan gum, and higher than that of locust bean gum [4]. Increasing the concentration of LPSG increases the apparent viscosity of the solution [4]. LPSG can maintain its stabilizing and thickening effect during slow or fast freezing (slow and fast conditions). The apparent viscosity of LPSG increases insignificantly after the fast freezing condition [21]. Since the main mechanism of emulsion stability by hydrocolloids is the increase in solution viscosity, it is expected that emulsion stability will be preserved by the addition of LPSG under fast freezing conditions [21]. As seen in Figure 10.2b, the consistency coefficient (k) of LPSG, obtained by the power-law model, increases nonlinearly as the gum concentration increases. The

10.5 Rheological Properties

increase in the k value with gum concentration might be due to the increase in the water-binding capacity of LPSG [4]. A power-law equation (k = aC b ) is successful in describing the concentration dependency of the LPSG consistency coefficient. When the LPSG concentration increases, both “a” and “b” parameters increase. An increase in the “b” value indicates a higher dependency of k on concentration [4, 22]. The flow behavior index, n, also decreases progressively as the gum concentration increases, indicating its increasing tendency toward pseudoplastic behavior [4]. While non-Newtonian behavior is observed for the LPSG solution (n < 1), a solution containing 0.5% LPSG is found to be less pseudoplastic at 65 ∘ C (n = 0.82). The shear-thinning behavior (pseudoplasticity) of the LPSG solution represents an irreversible structural breakdown and the molecular alignment which takes place within such substance. Solutions containing 1%–2% LPSG at selected temperatures (5, 25, 45, and 65 ∘ C) and 0.5% gum solution at temperatures below 25 ∘ C demonstrate a flow behavior index less than 0.6, which is an important factor for sensory properties and food formulation [4]. The pseudoplastic nature of the gum and the onset of entanglement result in the shear-thinning becoming progressively more pronounced as the concentration is increased. Magnitudes of the yield stress from the Mizrahi–Berk model for LPSG solutions are also dependent on the concentration of the gum. At higher LPSG concentrations, a higher yield stress is obtained [4]. 10.5.1.2

Effect of Temperature

10.5.1.3

Effect of Salt

As temperature increases from 5 to 65 ∘ C, the apparent viscosity of LPSG decreases. This decrease may be related to the decrease in the intermolecular interactions, which in turn decreases the energy needed for the flow and thus decreases the interference of the hydrodynamic domains [4, 23, 24]. The LPSG solutions are less pseudoplastic (higher n values) when the temperature is higher. As seen in Figure 10.2b, a decrease in the consistency coefficient is observed when the temperature is increased at all levels of solid concentration, indicating the temperature dependency of the apparent viscosity of LPSG [4]. The yield stress value obtained from the Mizrahi–Berk model for LPSG decreases with temperature, since the stress level in the fluid increases and the structure responsible for the yield stress is destroyed [4]. The activation energy, estimated by an Arrhenius-type model for LPSG, decreases from 31.61 kJ mol−1 at 0.5% concentration to 11.43 kJ mol−1 for 2% concentration. The decrease in activation energy, as a result of the increase in concentration, shows the lower sensitivity of LPSG to temperature at higher concentrations and can be interpreted by the Eyring theory. The Eyring theory postulates that the activation energy of a flow process is due to the formation of some extra space becoming available for molecular flow. As the concentration increases, the space available for molecular flow decreases, thus decreasing the activation energy [4, 25].

The effect of ion concentration on viscosity is important for the determination of the polyelectrolytic behavior of mucilage and estimation of the functional and rheological properties [4]. The LPSG solutions show a rapid reduction in viscosity values when 0.2% of NaCl, KCl, CaCl2 , and MgCl2 are added. The decreasing effect is more pronounced for solutions containing higher salt concentrations (Figure 10.3). However, NaCl concentrations higher than 0.6% have little additional effect on the reduction of mucilage

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Figure 10.3 Effect of different NaCl, KCl, MgCl2 , and CaCl2 concentrations on the apparent viscosity of 1% (w/w) LPSG solution at the shear rate of 46.16 s−1 and 25 ∘ C. Source: Adapted from Koocheki et al. [4] with permission from Elsevier.

viscosity. Divalent salts have more ability to decrease the apparent viscosity of LPSG solutions than other tested salts [4]. LPSG has a negative charge at pH 7, and the measured zeta potential in aqueous suspension is −43.7 ± 2.68 mV [20]. When the hydrocolloid is consists of negatively charged polyelectrolyte molecules, the addition of positive ions reduces the repulsion forces and molecular expansion, which significantly reduces the viscosity [26]. Data suggest that the affinity of LPSG for metal ions depends on the charge/ion-radius ratios, and small ions with high charge have a stronger affinity to chain binding sites [4, 27, 28]. 10.5.1.4

Effect of pH

At low pH levels (3–5), charge suppression results in a smaller conformation of the polymer chains because the acidic components exist in the free acid form [4]. At shear rates lower than 60 s−1 , the maximum viscosity of LPSG is maintained over the pH range 7–9 (Figure 10.4). This occurrence is, presumably, due to the ionization of carboxyl groups in the LPSG structure which increases its viscosity [4]. The viscosity will be at its maximum when the LPSG molecular chains are in a state close to the rod conformation in the solution [27]. In other words, as the pH rises, the functional groups in LPSG chains induce electrostatic repulsion that tends to keep the molecules in an extended form and therefore produce a highly viscous solution [29]. Conversely, in the more alkaline regions (pH 11), the solution viscosity drops at 0.5%–2% concentrations. At a high pH (11), the decrease in viscosity may be related to the alkaline depolymerization reactions [30]. At higher shear rates (over 60 s−1 ), changes in pH values do not have a considerable influence on the viscosity. 10.5.2

Dynamic Rheological Properties

Dynamic rheology is one of the most extensively used methods to assess the viscoelastic behavior of polysaccharide solutions, dispersions, and gels [31]. 10.5.2.1

Strain Sweep Measurements

At low gum concentrations (1.5%–2.5%), the elastic modulus (G′ ) remains constant at strains of up to about 1%. As the gum concentration increases, the strain at which the

10.5 Rheological Properties

1.00 Apparent viscosity (Pa.s)

3 5 7

9 11

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60

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Figure 10.4 Effect of different pHs on viscosity of 1% LPSG at 25 ∘ C. Source: Adapted from Koocheki et al. [4] with permission from Elsevier.

elastic modulus decreases, increases to more than 1%. The values of the elastic and loss moduli (G′ and G′′ ) at the linear viscoelastic (LVE) region also increase with increasing LPSG concentration. This indicates that increasing LPSG concentration increases the strength of the system and makes it more rigid. The increase in temperature has the same effect as a concentration increase. As the temperature is raised from 5 to 85 ∘ C, the limiting values of the strain are also increased. This value is high for 3% LPSG at 85 ∘ C, implying higher stability of the viscoelastic material under the strain amplitude [31]. Accordingly, raising the temperature from 5 to 85 ∘ C increases the structural strength (G′ at LVE) of the gum solution at constant concentrations [31]. Increasing gum concentration increases the yield stress values at the flow point, meaning that the gel network formed by LPSG becomes stronger. The yield stress values for LPSG decrease with temperature increase, which might be due to the increase in the stress level in the fluid and the destruction of the structure responsible for the yield stress [31]. 10.5.2.2

Frequency Sweep Measurements

The LPSG solution has a typical weak gel-like behavior where the magnitudes of G′ and G′′ slightly increase with a small frequency dependency when the frequency is increased from 0.0628 to 62.8 rad s−1 . The storage modulus for LPSG is always higher than its loss modulus within the experimental range of frequencies (0.01–10 Hz) with no crossover point. Therefore, LPSG behaves more like a solid; that is, the deformations will be essentially elastic and recoverable [31]. At 85 ∘ C, the G′ and G′′ values for 2.5% LPSG concentration are lower than that of 2% LPSG, showing that the elastic properties can be decreased at the special concentration. The reason for this phenomenon is unknown. Increasing the temperature from 5 to 85 ∘ C increases the elastic modulus and decreases the viscous modulus for LPSG solutions. However, at both temperatures, G′ is always greater than G′′ throughout the frequency range covered (Figure 10.5). This means that LPSG solutions can show a weak gel behavior even at high temperatures, and their structure is not highly sensitive to temperature change [31]. The loss factor (tan 𝛿) values for LPSG solutions lie between 0.1 and 0.5 (tan 𝛿 < 1) within the experimental frequency range (0.0628–62.8 rad s−1 ), with a weak dependence

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Figure 10.5 Effect of LPSG concentration on storage (G′ ) and loss (G′′ ) moduli as functions of frequency at (a) 5 ∘ C and (b) 85 ∘ C. Source: Adapted from Hesarinejad et al. [31] with permission from Elsevier.

on frequency for all the samples, indicating that the mixtures are more elastic than viscous [31]. The complex viscosity (G* ) increases as the LPSG concentration increases from 1.5% to 3%. These results confirm the high potential of this hydrocolloid as a thickener or stabilizer in increasing the consistency of food systems. The complex viscosity of LPSG is also affected by temperature, so that an increase in the complex viscosity is observed when the temperature is increased from 5 to 85 ∘ C [31]. 10.5.2.3

Temperature Sweep Measurements

The LPSG shows a higher storage modulus than the loss modulus, in the entire range of temperatures from 5 to 85 ∘ C. There is no crossover point for G′ and G′′ , which

10.6 Applications

means that the LPSG solution behavior is predominantly elastic and remains in the solid-like state at all temperatures. During the initial heating from 40 to 50 ∘ C, G′ decreases slowly as temperature increases, reaching to its minimum at around 50 ∘ C [31]. The initial decrease in G′ can be related to the increase in fluidity with increasing temperature. This decrease may also be attributed to the energy dissipation movement of the molecules and decrease in the intermolecular interactions, which in turn decrease the energy needed for flow [23, 24]. The increasing trend for G′ depends on the concentration of LPSG. As the temperature increases from 50 to 85 ∘ C, the loss modulus for higher gum concentrations (2.5%–3%) starts to increase with a uniform trend [31]. However, for low LPSG concentrations, an increase in temperature has no significant effect on the storage modulus. The increase in G′ can be related to the formation of a three-dimensional network structure and to the conversion of the sol fraction into a gel. In LPSG solutions, the increase in G′ during heating may also be caused by the thickening effect of the gums, which restricts the mobility of fluids. Keeping the samples at 85 ∘ C has no further effect on G′ [31] (Figure 10.6). A hysteresis in the rheological measurements between the heating and cooling curves is found for LPSG solutions. The storage modulus of LPSG increases during cooling, which indicates that hydrogen bonds are formed, and the network becomes stronger. The increase in G′ during cooling is due to the strengthened hydrophobic interactions. The effect of the cooling process on the storage modulus is more pronounced for 3% LPSG, and G′ is much larger than those obtained during the heating process. Such a greater increase in G′ can be attributed to the formation of a three-dimensional network structure due to the strong interactions in LPSG solutions. This fact seems to show that structural change occurs during cooling of 3% LPSG solution. G′ also decreases by increasing the heating–cooling rates, which indicates that the molecules of LPSG do not have enough time to develop a firm network. The effect of the heating–cooling rate on the gelling characteristics of LPSG solutions is observed especially during cooling; an increase in G′ during cooling of 3% LPSG after heating is much higher for samples with a 1 ∘ C min−1 cooling rate [31]. It increases rapidly and shows a peak of 1 ∘ C min−1 cooling rate due to the formation of a thermo-irreversible network structure, while G′ curves for all LPSG solutions (1.5%–3%) show an almost plateau region at heating–cooling rates of 5 and 10 ∘ C min−1 . Results suggest that the heating–cooling rate dependence of G′ is negligible for 1.5%–2.5% LPSG. Therefore, we can propose a critical concentration of 3% LPSG for gel formation, because at this concentration, a thermo-irreversible network structure will be formed, and the structural strength will be increased at low heating–cooling rates.

10.6 Applications 10.6.1

Emulsions

The incorporation of LPSG into oil-water emulsions greatly enhances the stability against phase separation [4]. When the LPSG concentration increases from 0.5% to 0.75%, the stability of these emulsions slightly increases, but remains constant at concentrations higher than 0.75% [4]. Stoke’s law states that the velocity of a moving

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Figure 10.6 Variation of storage modulus at different LPSG concentrations and heating-cooling rate of (a) 1 ∘ C min−1 , (b) 5 ∘ C min−1 , and (c) 10 ∘ C min−1 . Source: Adapted from Hesarinejad et al. [31] with permission from Elsevier.

10.6 Applications

droplet is inversely related to the viscosity of the solution. Thus, by increasing the viscosity of the emulsion through the addition of LPSG, the stability of the emulsion to gravitational separation can be increased [32]. At low concentrations (0.5%–0.75%), LPSG also has a higher emulsion stabilizing effect than locust bean gum; nevertheless, these values are lower than those for guar and xanthan gums. Comparatively, the emulsion stability of LPSG is almost similar to that of guar gum at 1%; however, the stabilizing property of LPSG is lower than that of xanthan and locust bean gums at this concentration. For the LPSG-stabilized emulsion, when the concentration increases from 0.5% to 0.75%, the stability slightly increases due to the increase in the emulsion viscosity, but remains constant at 1% LPSG [4]. Oil dispersions are well stabilized in the aqueous phase by whey protein concentrate (WPC) and LPSG [19]. It is found that the LPSG concentration should be considered as a primary factor for the stabilization of corn oil-in-water emulsion. The LPSG concentration significantly reduces the creaming in corn oil-in-water emulsions [19]. The effective size of the droplets also decreases because of the high viscosity of the aqueous phase. However, the addition of 0.4% LPSG to WPC emulsions promotes droplet flocculation through a depletion mechanism. Furthermore, this process leads to faster coalescence of droplets within the flocculated emulsion [19]. At neutral pH, the addition of a very low level of LPSG (0.2%) to emulsions made with WPC causes the droplet’s flocculation, which leads to rapid creaming and phase separation. The flocculation could be assumed to occur by a depletion mechanism. However, at higher gum concentrations beyond this value, the creaming rate and the droplet size are lowered because of the high viscosity of the aqueous phase. This effect is more pronounced for emulsions stored at 4 ∘ C. The emulsions containing LPSG are relatively stable against droplet aggregation or growth during storage at 4 ∘ C compared to the ambient temperature. As far as the rheological properties of the emulsions are concerned, the consistency coefficient and yield stress are found to be very low in the absence of gum. Following gum addition, the consistency coefficient and yield stress of emulsions increase considerably. Addition of LPSG has no significant effect on the zeta potential values of such emulsions, and the content remains at −33.15 ± 6.15 mV. This shows that LPSG has high acidic fractions. The surface and interfacial tension increases with the addition of LPSG to WPC-coated oil droplets. Therefore, for emulsions stabilized with WPC, there is no or very little adsorption of LPSG at the interface [20]. Increasing the oil volume fraction in O/W emulsions stabilized by LPSG increases the droplet size of the emulsion. In addition, at high oil volume fractions, the high viscosity caused by the increase in the packing fraction can limit the motion of the oil droplets and hence decrease the creaming rate [19]. It can be concluded that LPSG and WPC can be used to produce low-fat emulsions with good stability during storage [19]. Corn oil-in-water emulsions stabilized with WPC in the presence of LPSG have a small droplet size under ultrasound treatment, meaning that ultrasonic waves have the ability to reduce the emulsion’s droplet size [33]. Adding LPSG to the emulsion during homogenization can increase the adsorption and coverage of oil droplet surfaces by a protein, which effectively inhibits droplet aggregation or coalescence and enhances the formation of small particles in the emulsion. This is due to the increase in the viscosity of the continuous phase, giving enough time to the protein to be absorbed on the surface of the oil. The viscosity of the emulsions increases as the LPSG content increases. The presence of high amounts of high-molecular-weight molecules increases the resistance to flow

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and prevents the creaming of oil droplets. As the concentration of LPSG is increased, the yield stress of the emulsion also increases [33]. The high yield stress is a beneficial property for the gum when it is applied as a binder because it prevents the material from undergoing phase separation, sedimentation, or aggregation [34]. Different processing treatments such as freezing, pasteurization, and sterilization affect the oil droplet size, creaming, flow properties, and stability of O/W emulsions prepared by WPC and stabilized by LPSG. The shear-thinning behavior for emulsions at all thermal treatments is also observed. Increasing the LPSG concentration decreases the flow behavior index at all thermal processing. This indicates that the shear-thinning behavior of the emulsions increases when the LPSG concentration is increased [35]. Also, with increasing LPSG concentration, the consistency coefficient of the emulsions increases in all treatments [35]. The addition of LPSG to WPC emulsions in pasteurization and sterilization treatments causes flocculation of oil droplets, which results in a marked increase in particle size and the creaming rate. However, at higher LPSG concentrations, the particle size remains constant, apparently because of the high viscosity of the aqueous phase [35]. It should also be noted that freezing conditions (slow and fast conditions) have no significant effect on the LPSG emulsion particle size [21, 35]. The results show that adding LPSG to the emulsion can produce a product which tolerates the thermal processes and create a relatively stable system [35]. 10.6.2

Edible Film

LPSG can be a new potential source for the manufacture of films and coatings with modified properties. LPSG-based films can be produced by adjusting the glycerol content as a plasticizer [36]. The density of films ranged between 0.88 and 0.93 g cm−3 . However, no significant decrease is observed by increasing the glycerol concentration. Increasing glycerol concentration has also no significant effect on the thickness of the film. Therefore, any changes in film density and thickness are not due to the presence of glycerol [36]. Images taken from electron scanning microscopy indicate that LPSG film has a uniform surface comprising compact sheets with no holes or fracture in its structure [36]. The moisture content of LPSG film increases as the glycerol concentration increases. Since glycerol acts as a water-holding agent [37], increasing the glycerol concentration makes the film more hydrophilic. Therefore, the moisture content of LPSG films can be changed due to the formation of glycerol–gum and glycerol–water interactions [36]. Increasing the glycerol content from 40% to 50% does not change LPSG film moisture adsorption, while further increase substantially increases this property. This is due to the high water absorption tendency of glycerol [36]. Glycerol, being a small molecule, can be placed between polymer chains more easily as compared to larger plasticizer molecules, to interrupt the formation of polymer-polymer hydrogen bonds. At high plasticizer content, glycerol-rich domains can form within the polymer matrix [38, 39]. Therefore, the glycerol might facilitate moisture permeation into LPSG-based film in high-moisture atmospheres [36]. Generally, when the water solubility of a film is high, it cannot protect food from moisture or from water loss. Increasing glycerol concentration significantly alters the water solubility of LPSG-based film. The highest solubility is achieved when a higher concentration of glycerol (70%, w/w) is incorporated [36]. Plasticizers can reduce the crosslinks between biopolymer molecules and thus increase the solubility of the film [40]. Because

10.6 Applications

glycerol is highly hygroscopic, this may explain why glycerol-plasticized blend films have high water solubility [41]. The water vapor barrier properties of LPSG films are significantly affected by glycerol concentration. Increasing the glycerol content increases the water vapor permeability (WVP) and water vapor transmission rate (WVTR) of the LPSG films. High WVP values in LPSG films can be attributed to the developing hydrophilic nature of the films as the glycerol level increases. This is supported by the differences between the moisture absorptions of LPSG films with different glycerol concentrations [36]. Addition of a plasticizer modifies the properties of the edible film by reducing the intermolecular bonds between the polymer chains, thus increasing the WVP and WVTR of the film. In addition, glycerol as a low-molecular-weight substance can probably penetrate into the LPSG network, thereby effectively disrupting the intermolecular interactions among polysaccharide chains [36]. Consequently, there would be greater space for water and other molecules to migrate through the film structure [42]. Increasing the glycerol concentration slightly reduces the water contact angle of LPSG films, which is due to the hydrophilic nature of this plasticizer. The values of the contact angles of LPSG films (>30∘ ) indicate that they would wet, at least partially, the surface of the product [36]. Wettability is one of the most important properties when evaluating the capacity of a solution to coat a surface where higher values of wettability (lower contact angles) are considered the most suitable to coat the surface. An increase in contact angle is known to lower the wetting (relatively higher hydrophobicity) property of the film surface [36]. Measuring the contact angle is a way to specify the surface hydrophilicity of a film. It is well known that a small contact angle below 30∘ indicates a hydrophilic surface. In other words, films with higher moisture contents have lower contact angles, indicating a greater ability to absorb water and thus higher hydrophilicity [36]. Optical properties are needed to define the ability of films to be applied over the surface of the food since these affect the appearance of the covered product, which is an important quality factor [43]. Among these properties, color attributes are of prime importance because they directly influence consumer acceptability [44]. The color parameters (a* and b*) of LPSG films, with the exception of the L* value, significantly change when the glycerol concentration increases. Incorporation of glycerol into the LPSG film matrix is able to increase the b* value and decrease the a* value. In other words, greenness and yellowness increase with increasing glycerol content [36]. Opacity and transparency are inversely correlated. A higher value of opacity means lower transparency. The transmission of light through the resulting LPSG films does not change with plasticizer concentration [36]. These findings are important since film transparency or opacity are critical properties in various film applications, particularly if the film will be used as a surface food coating or for improving product appearance [45]. In many applications, an increased opacity is desirable; for example, some applications need to provide protection against reactions of deterioration produced by the effect of light, offering some advantage to this type of film. An increase in plasticizer concentration in LPSG-based film exerts a great influence over elongation at break values. When the glycerol content increases, the elongation at the break value increases. As the glycerol concentration increases to up to 50%, the tensile strength decreases, and at higher plasticizer concentrations, it will be constant. Moreover, the modulus of elasticity as an index of stiffness also shows a general decrease

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as the glycerol content increases [36]. Films with low tensile strength and high elongation at break tend to be less brittle. As a result, LPSG films plasticized with glycerol exhibit great flexibility and hence undergo fracture in a slow and sustained pace. Furthermore, the higher the glycerol content, the lower the brittleness and the higher the flexibility of LPSG films. This most likely arises from the penetration of glycerol in the polymer matrix and reduction of inter-chain interactions, which finally alters the mechanical properties of LPSG-based film [36]. Generally, plasticizers interfere with polymer chains where, by decreasing intermolecular forces, they soften the rigidity of the film’s structure and increase the polymer mobility; this decreases the tensile strength and increases the elongation at break [46]. The variation in the glass transition temperature (Tg ) is another effective indicator of the compatibility of polymers. Glycerol is compatible with LPSG, and the effectiveness of plasticization is confirmed since only one Tg is observed. Tg decreases as the glycerol content increases [36]. The increase in glycerol concentration leads to an increase in the free volume and mobility of the polymer network, changing the physical structure of the LPSG film, which is in agreement with the decrease in the Tg values [47]. Tg is the temperature at which the material undergoes a structural transition from the glassy state to a rubbery state [48]. Below Tg , films are rigid and brittle, whereas above it films become flexible and pliable. Tg values for LPSG films are below −61.58 ∘ C and depend on the glycerol concentration of the film. The low Tg values of LPSG films can be attributed to their inherent structural characteristics (high chain mobility) and to their relatively high hydrophilicity, which lets them absorb more water molecules than less hydrophilic films. Tg values are inversely associated with the moisture content of LPSG-based films; in fact, water acts as a plasticizer and increases the molecular mobility (0.6% w/w), the tannins either need to be removed (by chemical, enzymatic, or filtration methods), or PG should be utilized in non-food industries, for example, textiles, papers, chemical, leather, and ink [3, 28, 34, 39]. Considering the negligible content of lipids and proteins and taking into account the ash and tannin contents, it can be obviously concluded that the major fraction of the dry matter of PG should be carbohydrates, particularly polysaccharides. On a wet basis, PG contains 82%–90% w/w polysaccharides. In addition, 98% of polysaccharides are composed of sugars (arabinose, galactose, mannose, xylose, and rhamnose), of which 2%–10% w/w as uronic acids (e.g., galacturonic) on the basis of the existing reports [3, 28, 35, 37, 39, 41]. The minimum gelation concentration (MGC) and water absorption capacity (WAC) are around 11% w/w with diverse correlation with color: the darker the gum, the lower the MGC and the higher the WAC. It should be noted that PG is not capable of converting to a true gel, as takes place, for instance, in pectin or tragacanth. As with most other hydrocolloids, the dispersibility and solubility of PG are strongly temperature dependent, as upon heating, its solubility could significantly improve, from 45% in cold water (30 ∘ C) to almost 75% in hot water (90 ∘ C), with a profound effect on the insoluble fraction. Furthermore, around 94% of PG precipitates in alcohol, which implies that only one third of the soluble fraction (SFPG) is soluble in alcohol comprising mono-, di-, or oligosaccharides [28, 32, 37, 39].

11.5 Structural Characteristics Generally speaking, there is a direct relation between the functional properties of polysaccharides (gelling, stabilizing, texturizing, emulsifying, and binding) and their chemical structures and molecular weights. Therefore, the structural elucidation is a very crucial step to understand their behaviors under different circumstances. There are several techniques to qualify and quantify the constituent monosaccharides (chromatographic methods, e.g., high performance liquid chromatography, HPLC, or gas chromatography, GC), the chemical groups (Fourier transform infrared spectroscopy, FTIR), bondings (nuclear magnetic resonance, NMR), molecular weight (e.g., sedimentation, gel permeation chromatography, gel electrophoresis, and dynamic light scattering) as well as other properties [43–46], and ideally a combination of these techniques needs to be used in the case of any unknown hydrocolloid. It needs to be emphasized that due to the complexity and inclusion of various oligo- and polysaccharides of different molecular weight and structure, any unknown hydrocolloid (e.g., PG) should be fractionated prior to any further characterization via these techniques [43, 44]. Otherwise, the collected data could be too confusing and misleading. Considering these criteria and for the sake of the readers, the available data related to characterization of the structural features of PG and its fractions will be discussed

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in the following subsections. Most of these data could be also found in the previous reports and reviews written by the author [3, 28, 34]. 11.5.1

Monosaccharide Composition

Using qualitative HPLC measurements, the presence of galactose, arabinose, and rhamnose as the major monosaccharides of whole PG has been confirmed [3, 28, 39]. Its water (WE) and alkaline (0.1, 0.5, and 1 M NaOH) extracts (AE) and final residues (RES) as well as their Smith degradation products have also been analyzed [28, 39]. The uronic acid content is around 10% w/w, distributed in 2, 2, 1, 1, and 4% w/w in the WE, AE0.1, AE0.5, AE1, and RES fractions, respectively. No uronic acid was detected in their Smith degradation products except for RES (2% w/w). This implies that the majority of uronic acid was not located in the backbone, since they were removed by chemical degradation. The total sugar content of the alkaline extracts was 10%–15% w/w, higher than that of their Smith degradation products, owing to the removal of the low-molecular-weight components and oligomeric species by dialysis during Smith degradation [3, 28, 39]. In another study [35], GC/MS was employed to investigate the monosaccharide’s composition. It is not clear from the report whether they examined the soluble fraction or the whole gum, but it is likely that they analyzed the soluble fraction. Apart from this ambiguity, they also detected arabinose (Ara) and galactose (Gal) with an Ara:Gal ratio of 2:1 along with some other monosaccharides, namely, xylose, rhamnose, and mannose (6.8, 1.1, 0.3 mol%). The sum of galacturonic acid and 4-ortho-methyl-galacturonic acid was 2.3 mol%, which is much less than what was reported earlier [28, 39]. On the basis of this evidence, it was concluded that PG can be considered to be an arabinogalactan, like most of the exudate gums from Prunus genus as well as gum arabic. However, the adverse ratio of Ara:Gal, the low protein content, and the existence of xylose and mannose were highlighted as a distinguishing feature compared to gum arabic. It is noteworthy that owing to the high price of gum arabic and the competitive lower price of PG, there are serious concerns regarding the adulteration of gum arabic with PG. On this basis, it is suggested that these differences could likely employed as potential clues to verify any adulterations or contaminations; however, this is not confirmed yet [35]. In a very recent report [41], the soluble fraction of PG (SFPG) was first extracted by hot water. Then the alcohol-precipitated fraction (alcohol-insoluble fraction of SFPG) was purified with DEAE-cellulose A52 and Sephacryl S-400 HR columns. The monosaccharide composition was analyzed by GC-MS, and the chromatograms indicated that the alcohol-insoluble fraction of SFPG was an arabinogalactan containing arabinose, galactose, xylose, and rhamnose with a relative molar ratio of 20.0:17.9:5.2:1.1. The uronic acid content of the fraction was about 6%. Considering the differences in preparation and fractionation methods and the analysis techniques utilized in the abovementioned reports, it can be concluded that arabinose and galactose are the major constituent monosaccharides in the chemical structure of PG, and its soluble (SFPG) and insoluble (IFPG) fractions as well as the alcohol-insoluble fraction of SFPG; therefore, they can be classified as an arabinogalactan. However, a distinct and comprehensive compositional analysis on various fractions (water, alcohol, acid- and alkaline-soluble and insoluble fractions) is necessary to obtain a clear picture of their structures.

11.5 Structural Characteristics

11.5.2

Chemical Structure

1

The H–NMR spectra of the aforementioned fractions (WE, AE0.1, AE0.5, AE1, and RES) showed high numbers of β–anomeric protons (δ 4–5 ppm) and a fine chemical shift signal over the range 1.0–1.1 ppm attributable to the methyl group protons of rhamnose. The existence of a large number of β-anomeric carbons (δ 100–105 ppm) in the 13 C–NMR spectra also confirmed the dominance of β links among the building blocks of PG. It was also shown that rhamnose is most likely located in the backbone, since its corresponding signal was detected (signal at 16.5–17.5 ppm) in the 13 C–NMR spectra of all fractions, including Smith degradation products. A comparison of the chemical shifts of 13 C–NMR spectra with other polysaccharides suggested the existence of β-D–Galp-(1 → 3) and (1 → 6), α-L–Araf -(1 → 3). It was concluded that the backbone of PG is most likely constructed from (1 → 3) linked β-D-Galp and rhamnose residues, whereas the branches are composed of (1 → 6) linked 𝛽-D-Galp, (1 → 3) linked α-L-Araf , and terminal α-L-Araf . On the basis of these findings, a tentative chemical structure is proposed as depicted in Figure 11.4a [39]. The deuterium-exchanged 1 H NMR and 1 H-1 H COSY spectra of SFPG also showed the anomeric region of t-α-Araf and variously linked α -Araf residues, t- α -Galp, t-β-GlcA, and 4-OMe-β-GlcA resonances. The anomeric signal of α -L-Rha residue was not distinguished due to signal overlap, but the chemical shift of methyl proton of Rha and its correlation with H5 of Rha were easily identified. The authors concluded that Ara and Gal accounted 54–62 and 27–31 mol% of SFPG, respectively. Chemical shifts of t-β-GlcA and 4-O-Me-β-GlcA residues were tentatively assigned from the NMR spectra [35]. On the basis of another NMR study [41], the alcohol-insoluble fraction of SFPG (only one third of SFPG is soluble in alcohol, and two third is considered insoluble in alcohol; α-L-Araf(1→3)—

α-L-Araf(1→3)-α-L-Araf(1→3)—

β-D-Galp(3→1)-β-D-Galp(3→1)-β-D-Galp(6→1)-β-D-Galp(3→1)-β-D-Galp(3→1)-β-D-Galp(3→1))-β-D-Galp(6→1)-β-D-Galp(3→1)-β-D-Galp

(a) β-D-GlepA-(1→6)-β-D-Galp

-(1→3)-

-(1→6)-

β-D-Xylp-(1→3)-α-L-Araf-(1→3)-α-L-Araf

-(6←1)-

→6)-β-D-Galp-(1→3)-β-D-Galp-(1→3)-β-D-Galp-(1→3)-α-L-Araf-(1→3)-β-D-Galp(1→ 5 5 10 3 α-L-Rhap-(1→6)-β-D-Galp (b)

Figure 11.4 Representation of chemical structure of the soluble fraction of Persian gum (SFPG). Source: (a) Proposed by Rahimi [47] and (b) Molaei and Jahanbin [41]; adapted with permission.

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see Ref [32]) is classified as an acidic branched polysaccharide with a backbone consisting of →3,6)-𝛽-d-Galp-(1→, →3)-𝛽-d-Galp-(1→ and →3)-𝛼-l-Araf -(1 → residues with side chains attached to the O-3 and O-6 positions of 1,3,6-linked 𝛽-d-Galp. The side chains consist of 𝛽-d-Xylp-(1 → 3)-𝛼-l-Araf -(1 → 3)-𝛼-l-Araf -(1→), α-l-Rhap-(1 → 6)𝛽-d-Galp-(1→), and 𝛽-d-GlcAp-(1 → 6)-𝛽-d-Galp-(1→). This report also proposed a different chemical structure (Figure 11.4b). It seems that the researcher did not consider the partial solubility of SFPG in alcohol; consequently, the fraction precipitated by alcohol has been reported as the soluble fraction, which is misleading [41]. From a review of these findings, it is obvious that there is no good agreement between these reports, and extensive investigations need to be conducted by an expert group of researchers in a well-equipped laboratory on various fractions of PG with special attention to details. Otherwise, these findings cannot be considered as a solid platform for describing its functions under various conditions. 11.5.3

Functional Chemical Groups

In the field of carbohydrate analysis, FTIR spectra are usually used to determine their major organic functional groups. The full spectra of PG and its soluble (SFPG) and insoluble (IFPG) fractions have been already considered by researchers [3, 28, 39, 41, 47–49]. Despite some differences, five distinct peaks could be highlighted in all the examined samples regardless of their differences (i.e., source, solubility, insolubility, measuring device, and resolution levels). For instance, the spectral bands falling between 1427 and 1448 cm−1 are attributed to the CH3 bonding vibration or to the presence of COOH as the carboxylic group of uronic acids. Peaks at 1614–1633 cm−1 were also attributed to carboxyl groups, anhydride components produced via carboxyl groups, or the presence of bound water. Moreover, peaks over the wave numbers of 2920–2935 cm−1 were indicated as clues to the symmetric and asymmetric stretching of C—H bonds, overlapping of the double bonds with O—H, as well as the existence of asymmetric CH2 functional groups. The two other peaks (2140–2146 and 3424–3441 cm−1 ) were not clearly described. In a very recent report [41] on the characterization of the alcohol-insoluble fraction of SFPG, apart from peaks at 3433, 2925, and 1637, other peaks were detected at 1736, 1379, 1144, 1080, and 1033 cm−1 , and some others at lower wave numbers. Therefore, it seems the FTIR spectra of PG and its fractions were not very well described by the authors for further elucidation of their structural features; however, this technique has demonstrated its effectiveness for monitoring any structural or chemical changes or interactions which happen due to chemical or enzymatic treatment [47, 48, 50]. In terms of gum modification, in an interesting study based on response surface methodology (RSM), using acryl amide, the solubility of the insoluble fraction (IFPG) was improved for utilization in broader applications. A significant increase in the FTIR spectra intensity at 1100–1300 cm−1 and the presence of a peak at 1575 cm−1 were attributed to the formation of etheric (C–O–C) bonds as well as to the stretching and bending vibrations of C=O and N—H bonds in the esterified structure (IFPG–O–CH2 –CH2 –CONH2 ), respectively. The latter peak did not exist in the original IFPG. Using the FTIR spectra alongside the molecular weight and intrinsic viscosity measurements, the occurrence of esterification was approved [48]. In order to improve the emulsifying capability of PG, the influence of octenyl succinic anhydride (OSA), gum concentration, pH, temperature, and reaction time on the

11.5 Structural Characteristics

esterification of PG, SFPG, and IFPG was investigated. On the basis of the FTIR spectra, an absorption peak emerged at 1726 cm−1 , indicating ester carbonyl bond formation in OSA-PG and OSA-SFPG but not in IFPG, due to its insolubility. The absorption peak at 1569 cm−1 was also attributed to the asymmetric stretching vibration of carboxylate ions (RCOO–) as indicative of the esterification reaction [47]. FTIR spectra have been also employed to investigate the incidence of the Maillard reaction or covalent linkage in wet-heated complexes of β-lactoglobulin and PG conjugates [50]. The peaks at 3311 and 2923 cm−1 were attributed to the hydroxyl stretching vibration and C—H stretching and bending vibrations in PG, respectively. In addition, the normal peaks of amide II and III were shifted to higher wavelengths upon wet heating without any considerable change in the amide I peak. In addition, the fall in spectra between 3600 and 3200 cm−1 corresponded to the hydroxyl stretching vibration, and the one at 1031−1 indicated a hydroxyl-bending vibration in the wet-heated complex. These FTIR spectra, as evidence of β-lactoglobulin–PG conjugation, were supported by SDS-PAGE chromatograms. 11.5.4

Molecular Weight

The molecular weight (Mw ) of a definite polysaccharide is another parameter which could affect its interactions with neighboring, like or unlike, macromolecules or ions, and hence the rheological properties, functionalities, and applications. Therefore, over the past few years, the Mw and dispersity index of PG and its fractions have been investigated. For instance, it was attempted [35] to separate SFPG of various color groups (white W, yellow Y, and red R) by centrifugation followed by freeze drying. The freeze-dried powders were then dissolved in 0.1 M NaCl and filtrated (1 μm filter), and the permeate was analyzed with a GPC-MALLS system. An inverse correlation was found between the color of PG powder and the Mw : the darker the color, the smaller the Mw . It was concluded that the white PG consisted of high Mw and homogenous molecules, while yellow and red ones were composed of very heterogeneous polysaccharides with lower Mw . The average Mw of the soluble fraction of the white PG was estimated as 4.74 × 106 Da. However, in a recent report from the same researchers on similar samples [51], the molecular weights were quite different (3.14, 2.72, and 1.66 × 106 Da for white, yellow, and red color groups, respectively). In another study [40], a similar procedure with minor modifications was employed for molecular weight investigation. The PG was initially dissolved in 0.2 M NaCl, centrifuged, and the supernatant was filtrated (0.22 μm filter). It was noticed that the dry matter content of the SFPG filtrate was only 7% w/w, indicating that PG is mainly composed of large water-insoluble particles (93% w/w). The weight-average molecular mass Mw (2.82 × 106 –5.11 × 106 Da), number-average molecular mass Mn (0.43 × 106 –2.01 × 106 Da), and dispersity index Mw /Mn (2.54–6.64) of the SFPG filtrate were relatively high. Using a capillary viscometer, the intrinsic viscosity of various fractions (WE, AE0.1, AE0.5, AE1) of PG at distinct concentrations (0.2 g dL−1 ) was also determined [39]. The approximate intrinsic viscosities for these fractions were 7.08, 9.22, 11.33, and 13.33 dL g−1 , respectively. It was concluded that these viscosities are directly correlated with solubility: the smaller the intrinsic viscosity, the higher the solubility. Similar measurements [48] were conducted on various concentrations (0.18, 0.018, 0.0018,

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and 0.00018 g dL−1 ) of the ordinary SFPG and the SFPG, which were separated from chemically modified (esterified by acryl amide) IFPG. Their molecular weights were also examined using static light scattering. The recorded intrinsic viscosities were 8.76 and 4.41 dL g−1 , and molecular weights were 134 and 42.4 kDa, respectively. These differences were in very good agreement with their rheological properties, and it was pointed out that IFPG is probably depolymerized by acryl amide esterification, as a result of which the solubility increased. A molecular weight of 99 kDa for PG, which increased to 333 kDa upon irradiation at 4 kGy, was also recently reported [52]. The reported intrinsic viscosity (7.14 dL g−1 ) for SFPG [51] is in good agreement with what were reported earlier: 7.08 and 8.76 dL g−1 , respectively [39, 48]. Comparing the reported molecular weights [35, 40, 41, 51] with other gums reveals that the molecular weight of SFPG is at least 30-fold higher than those reported, for instance, for P. persica (1.3644 × 105 Da) [53] with similar botanical origin (see Section 11.1). Moreover, the reported Mw of gum arabic (1.56 × 106 Da) [35, 51] is also five times larger than what was already reported (3.2828 × 105 Da) [54]. It should be noted that in these studies [35, 40, 51], NaCl (0.1 and 0.2 M) was utilized (for preparation of solutions and as an eluent for GPC) without considering the possible detrimental interaction of PG and SFPG with monovalent ions and their precipitations. It had been already confirmed [33] that PG may precipitate in the presence of NaCl, and its concentration in these studies was very high. Therefore, the molecular weights determined may be more associated with the non-indigenous (i.e., aggregated) SFPG than with the native SFPG. On the other hand, the reported numbers [48, 52] are several fold smaller but in good agreement with the aforementioned hydrocolloid. Despite these efforts, there is still ambiguity and uncertainty regarding the molecular weight of PG and its fractions, which therefore needs to be extensively clarified in the future.

11.6 Rheological Properties Polysaccharides, due to their high molecular weights, chain entanglement, and polymer–solvent interactions, are usually used to control the rheology (flow, deformation, and texture) of solutions, dispersions, and emulsions [43–46, 55, 56]. Thus, understanding the rheological characteristics of PG dispersions and their soluble fraction (SFPG solutions) is of great importance and needs to be extensively investigated. Due to the complexity of the existing reports, for the sake of the readers, in the following paragraphs, first the effects of concentration (PG or SFPG), temperature, pH, and ionic strength (type, concentration, and valence of salts) on the steady and dynamic shear rheological properties will be discussed. Later, the influences of irradiation or chemical modifications on the rheological properties will be described. It needs to be emphasized that the interaction of PG and SFPG with proteins and other hydrocolloids as well as their applications in emulsions and their subsequent effects on rheological characteristics is another interesting subject that has drawn the attention of researchers. However, they will be discussed in the following subsection. In regard to the influence of gum concentration (up to 5% w/w) on the apparent viscosity of PG dispersion, a direct but nonlinear correlation is reported [33, 37, 51]. From the rheological point of view, these results cannot be fully relied on as two thirds (∼70% w/w) of PG is insoluble, which potentially could cause serious problems during measurement. Considering this, there are other studies which have reported on the

11.6 Rheological Properties

effect of SFPG concentration (up to 3% w/w) on apparent viscosity, in which they have also shown direct relationship: the higher the SFPG content, the higher the viscosity [33, 39, 42, 47, 48]. It is obvious that the apparent viscosity of SFPG solution, at any distinct concentration, was almost half that of PG dispersion. It is worth emphasizing that the viscosity of PG was also reasonably smaller than that of gum tragacanth, xanthan, and karaya, but more than gum arabic and ghatti at comparable (e.g., 1% w/w) concentrations. In terms of temperature (up to 90 ∘ C), similar to many hydrocolloids, it has shown an adverse effect on the apparent viscosity of PG dispersions as well as of SFPG solutions over a wide range of concentrations [33, 37, 42, 51]. It is noteworthy that the temperature dependency of viscosity is reversible, and upon cooling, the viscosity regains its initial value. Moreover, a strange behavior has been reported [33] at 60 and 90 ∘ C, where the viscosity of PG dispersions increased but their color diminished (from brownish to colorless). In regard to SFPG, at 60 ∘ C, its viscosity increased, but at 90 ∘ C it was reduced. These observations have not been confirmed by later reports. The natural pHs of PG and SFPG are reported as acidic (∼4.60), and they are classified as anionic polysaccharides [29]. In this regard, researchers have also investigated their stability under various pHs (highly acidic, neutral, and basic) as well as their influences on the apparent viscosity. In spite of its natural pH, the highest viscosity of PG dispersions and SFPG solutions occurred in an almost neutral range (∼7.0), but decreasing (down to 2.0) or increasing (up to 12.0) the pH diminished the viscosity [33, 37, 42, 47, 48]. Owing to their acidic and anionic nature, PG dispersions and, more importantly, SFPG solutions should have been very sensitive to ionic strength. From this point of view, the effects of monovalent (KCl and NaCl), divalent (MgCl2 , CaCl2 , and FeCl2 ) and trivalent (FeCl3 and AlCl3 ) salts over a wide range of concentrations (up to 500 mM) have been evaluated [33, 37, 42]. It can be generally concluded that the valence, type, and concentration of salts strongly affected the apparent viscosity and flow behavior of PG and SFPG: the higher the valence and concentration of the ions, the lower the apparent viscosity. However, Khalesi et al. [37] noticed an increase in viscosity (above 100 mM) in the presence of CaCl2 . Nevertheless, over certain concentrations (>100 mM), Dabestani [33] also observed precipitation and gritty (sandy) texture, particularly in IFPG, during storage (after few days). Therefore, it seems that the PG dispersions and SFPG solutions cannot withstand high ionic strengths and precipitate. The rheological behavior of PG dispersion and SFPG solution is non-Newtonian, shear thinning, thixotropic, and the best-fitting model to describe their timeindependent behavior is the power law [29, 31–33, 35, 39, 42, 47, 48, 52, 57]. However, under certain circumstances, some other mathematical models have shown better fitting [32, 35, 47, 48]. For instance, the effect of pH (2–7) on the flow behavior of SFPG (0.6% w/w) revealed some clear differences. Over the mild pH range (4–6), the rheology followed the power law and Herschel–Bulkley models, but at lower pH (2–3) the rheology followed the Bingham model. It was argued that this was due to the protonation of carboxyl groups at low pH; the electrostatic repulsion decreased, the flexibility of the SFPG backbone increased, and as a consequence, the apparent viscosity reduced too [32]. Anyhow, Hosseini et al. [42] have extensively discussed how the concentration, temperature, pH, and salts could affect the power-law parameters. They have also noticed thixotropic behavior as a result of a hysteresis loop between the upward and downward curves of the shear stress versus the shear rate.

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Dabestani [33] also examined whether sonication could improve the solubility and consequently the rheology of PG dispersion. It was found that high-power sonication profoundly increased the solubilization and eased the phase separation, though the viscosity decreased. However, the influence of the duration of sonication was much more pronounced than the intensity. The effect of irradiation doses (up to 30 kGy) on the apparent viscosity of PG dispersion (0.5% w/w) has been investigated [52]. On the basis of this report, by irradiation at 4 kGy, the apparent viscosity and consistency coefficient increased (33.5 mPa s and 0.7 mPa sn ), but when treated at higher doses (up to 30 kGy) it significantly diminished. These findings revealed the detrimental effects of irradiation on the structure and the rheological properties by altering the shear-thinning behavior of the un-irradiated samples to Newtonian behavior in the case of irradiated (irradiated at 30 kGy) ones. It was argued that irradiation (4–8 kGy) likely disrupted the side branches, cross-links, and somehow hydrogen bonds which contribute to the apparent and intrinsic viscosities. Chemical modification and esterification are other processes that showed significant effects on the rheology of PG, SFPG, and IFPG. As an example, the flow behaviors of PG, OSA-PG, SFPG, and OSA-SFPG dispersions (1% w/w) were shear thinning. Nevertheless, the apparent viscosity of PG was lower than that of OSA-PG, in contrast to the higher apparent viscosity of SFPG compared to its esterified counterpart (OSA-SFPG). The partial solubilization of IFPG, depolymerization of large molecules, and their consequent esterification with OSA were highlighted as the main reasons for these rheological differences [47]. Similar to the ordinary SFPG, the SFPG which was separated from the chemically modified IFPG (esterified by acryl amide) showed shear-thinning flow behavior at 1.8% w/w [48]. However, the apparent viscosity of the latter was reasonably lower than the former one, probably due to partial depolymerization under alkali pH. The majority of the discussed rheological data were achieved on the basis of steady shear measurements. Nonetheless, there is another approach to investigate the viscoelastic and structural properties, which is called the oscillatory (dynamic) method. Using the latter method [35], PG dispersion showed a predominantly viscous behavior (i.e., the loss modulus was larger than the storage modulus); however, it showed elastic behavior at moderate time scales as its complex viscosity was high and loss tangent was small. The frequency sweep curves were also very similar to those of dilute solutions of unlinked polymers. In addition, the differences in cross-over frequencies were attributed to their Mw : the higher the Mw , the smaller the cross-over frequency.

11.7 Interaction with Other Macromolecules From the practical point of view, the compatibility and interactivity of PG and SFPG with other macromolecules (proteins and polysaccharides) is very critical and needs to be clarified. Hence, the following subsections will discuss their interactions with these two major macromolecules. 11.7.1

Polysaccharides

The application of PG:maltodextrin (5:35–1:39, 40% w/w) for emulsification of d-limonene has shown that they are most likely compatible, particularly at high ratios of PG, since the resulting emulsions were completely stabilized [58, 59].

11.7 Interaction with Other Macromolecules

The compatibility of SFPG with the soluble fraction of gum tragacanth (SFGT) at various ratios (20:80, 50:50, 80:20), concentrations (0.5, 0.75, 1% w/w), pH (3, 5, 7), and salts (NaCl, CaCl2 , AlCl3 ) at different concentrations (0.002–0.10 M) has also been extensively studied [33]. It was shown that these two polysaccharides were very compatible regardless of their mixing ratios, concentrations, and pH. Moreover, due to the significantly higher viscosity of SFGT, compared to SFPG at the same concentration, it was noticed that by mixing a small portion of SFGT with SFPG, the viscosity of the mixture can be greatly increased, which could be very beneficial for industrial applications, bearing in mind the large differences in their prices (GT is currently 50–100 times expensive than PG). The effects of salts, pH, and heating were generally similar to those of SFPG and SFGT individually. Surprisingly, in the presence of AlCl3 (1–5 mM), the mixtures gelled. The higher the SFGT ratio, the stronger the gel, according to oscillatory measurements. It is noteworthy that for the first time the gelling effect of AlCl3 (1–5 mM) on GT, SFGT, and IFGT were noticed; nevertheless, GT and SFGT gels were absolutely reversible, but IFGT gel was fragile. This could be very interesting for industrial applications. 11.7.2

Proteins

Generally speaking, proteins and polysaccharides usually play important roles (as emulsifiers, foaming agents, carriers, stabilizers, thickeners, and gelling agents) in food formulations. However, their functionalities strongly depend on the quality of the solution (concentration, pH, ionic strength, and temperature), their intrinsic properties (molar mass, molecular structure, polydispersity, and charge density), and their interactions with solvents and co-solutes (e.g., sugars) via intra- and inter-molecular interactions. As a result, under certain conditions (typically, near the isoelectric point, at high ionic strength, or at high temperature), functionality can be totally or partially lost, particularly for proteins. To overcome such issues and in order to produce novel emulsifiers, the covalent and electrostatic complexation of different proteins with various polysaccharides had been already addressed [56, 60–62]. In line with this idea, the interaction of PG and SFPG with four different proteins, namely, gelatin, whey protein isolate (WPI), casein (CN), and β-lactoglobulin (β-L) has also been studied and will be reviewed in the following subsections. 11.7.2.1

Gelatin

A study on the compatibility of PG and its fractions with gelatin, from the standpoint of partial replacement in the formulation of jellies and gummy candies, has shown that despite the gelation capability of IFPG, PG and SFPG cannot gel in the presence of even high sugar content (35% w/w). Nonetheless, they showed compatibility with gelatin at various mixing ratios (10:90–90:10). However, only at an IFGT:gelatin ratio of 40:60 (10% w/w) were the mechanical properties similar to those prepared with gelatin alone (10% w/w) [30]. 11.7.2.2

Whey Protein Isolate

In a recent report [32], it was attempted to find appropriate ratios of WPI:SFPG and WPI:SFGT to avoid precipitation over a wide range of pH (2–7). According to the optical density, zeta potential, and rheological measurements, the desired ratios were 0.4:2

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and 0.4:1 (%w/w), and the responsible mechanisms for the stability were electrostatic and steric repulsion as well as high bulk viscosity. Despite the anionic nature of the polysaccharides, SFGT was more efficient than SFPG, probably due to the higher steric repulsion caused by overlapped side chains as well as inter- and intramolecular interactions of the SFGT chains. Finally, it was pointed out that these complexes can be used as surface-active agents in the formulation of emulsions. The interaction of WPI (up to 8% w/w) with SFPG (up to 1% w/w) at neutral pH (7) has also been studied [36]. On the basis of methylene blue spectrophotometry, surface tension measurement, and zeta potentiometry, the occurrence of weak electrostatic interactions, even when both biopolymers were net negatively charged, was confirmed. The WPI:SFPG ratio showed its importance, and the most significant effect was observed at 1:1 ratio. In the next report [38], by examining the effects of various pH (3–7) and mixing ratios (1:3, 1:1, 3:1, 6:1, and 9:1% w/w WPI/PG), it was revealed that pHc and pH𝜙1 moved toward higher pH values when the WPI:PG ratio was increased. In addition, solubility was increased at pHc > pH > pH𝜙1 for all mixtures, and lowering the pH toward pH𝜙1 decreased the size of complexes, while any further decrease led to larger particles. Heating also had no significant effect on pHc and pH𝜙1 at neutral pH, although the turbidity of heated mixtures was higher than that of unheated ones due to the formation of larger aggregates. It was concluded that these findings could be potentially useful for designing novel microstructure for special functionalities in food systems. The effects of the mixing ratio (0.1:1, 0.2:1, 0.5:1, 1:1, 2:1, 5:1, 10:1, total biopolymer concentration 0.5% w/w) and pH (2–7) on the complexation of WPI:PG was also investigated [40]. Upon decreasing the pH and increasing the mixing ratio, the net neutrality shifted to the higher pH values, and neutralization occurred at pHopt (the formation of neutralized complexes). The maximum precipitation yield occurred at pH 3.4 for the 1:1 ratio. However, again this work was conducted on PG that had not been fractionated. 11.7.2.3

Casein

The phase behavior of sodium caseinate (3%–8.5% w/w) with SFPG (1%–3.5% w/w) at neutral pH and in the presence of NaCl (0.05 M) was investigated [63]. The plotted phase diagram clearly demonstrated the prevailing effect of SFPG on the incompatibility of biopolymers as the mixture of the two at different locations retained various microstructures. The flow behavior of mixtures was strongly dependent on the composition of the equilibrium phases and the corresponding microstructure of the system. The composition of equilibrium phases also showed a minor contribution of sodium caseinate to the thermodynamic incompatibility. The interaction of SFPG and SFGT with sodium caseinate (Na-CN) over a wide range of pHs (2–7) in order to provide soluble complexes was investigated [32]. According to the optical density, zeta potential, and rheological measurements, the desired ratio for both was 0.4:0.6 (% w/w). It was argued that at these concentrations, the anionic polysaccharide content was not only adequate to neutralize the positive charge of protein at acidic pH, but also was sufficient to hinder the approach of protein particles via electrostatic repulsion, due to the prevalence of negative charges in the system. The efficiency and mechanism of PG, SFPG, IFPG, and SFPG:SFGT mixtures on the stabilization of milk–orange juice mixture (pH = 4.2) were also studied [29]. On the basis of visual observations, the zeta potential, and rheological measurements, the mixtures were effectively stabilized by PG, SFPG, and SFPG:SFGT (80:20) at 2.20, 1.00, and

11.7 Interaction with Other Macromolecules

0.37% w/w, respectively. Therefore, it was concluded that SFPG, as an anionic-adsorbing hydrocolloid, adsorbed onto the caseins at the interface, giving rise to enhanced electrostatic and steric repulsion. It is interesting to note that the ratio of SFPG:casein in this study (1:1.5) was similar to that mentioned in a recent report [32]. SFPG and SFGT also proved to be highly compatible adsorbing hydrocolloids, where the presence of the latter improved the effectiveness of the former one. Similar results on the stabilization of milk–sour cherry juice mixture have been reported [57], while in another study [52], it was noticed that, due to some structural changes by irradiation (at 4 kGy), the PG requirement for stabilization of milk–sour cherry juice mixture decreased (from 2.2 down to 1.5% w/w). 11.7.2.4

𝛃-Lactoglobulin

The influence of the PG: β-L ratio (1:2, 1:1, 2:1, at 0.15% w/w) and pH (2–7) on the formation of electrostatic complexes was also investigated [49]. According to the optical density analysis, particle size measurement, and microscopic observations, seven pH-delimited zones were detected, and the maximum solubility was observed at pHc > pH > pH𝜑1 , though this pH was dependent on the biopolymer mixing ratios. pHc, pH𝜑1, and pHopt denoted the formation of soluble complexes, interpolymeric complexes, and neutralized complexes, respectively. The smallest particle (d = 27 μm) was recorded for a 1:2 ratio of PG: β-L at pHopt . The emulsifying properties of the complexes (0.75% w/w) with soybean oil (20% w/w) showed that only the emulsions made with soluble complexes (pH after mixing > pH > pHc and pHc > pH > pH 𝜑1 ) in all ratios were stable (no changes in droplet size over 48 h). It should be noted that PG containing 70% w/w IFPG was used, and for this reason, it was impossible to obtain fully soluble complexes. This is why droplet size distributions were bimodal in some reports [58, 59]. In other studies [50, 64], β-L–PG conjugation at various ratios (1:2, 1:1, 2:1) was studied using the wet Maillard reaction method as a function of time (1–14 days). The covalent linkage of β-L–PG was confirmed by SDS-PAGE. Moreover, the emulsifying activity of β-L:PG (1:1) conjugates as a function of Maillard reaction time showed no significant effect on the emulsion activity index; however, the stability index significantly increased. The emulsification performance of all conjugates (1:1, 1:2, and 2:1) was also much better than that of PG and gum arabic alone at the same emulsifier/oil ratio (1.5% w/w total biopolymer/40% v/v oil). However, the usage of PG without fractionation could be problematic, as already argued in some existing studies [49, 58, 59]. In an extensive study [65], the effects of pH, β-L:SFPG ratios (8:1–1:4), total biopolymer concentration (0.1%–0.6% w/w), salts (NaCl and CaCl2 ), ionic strength (0–100 mM), and temperature (25, 40, and 55 ∘ C) on the electrostatic interaction of β-L:SFPG were elucidated. Similar to the previous reports [32, 36], soluble complexes were formed above the isoelectric point (pI) of β-L; however, pH𝜑1 and pHopt were significantly affected by the mixing ratios and concentration. They shifted toward lower pH values as a result of decreasing the mixing ratio (at a constant concentration) or concentration (at a constant mixing ratio), though pHc (formation of soluble complexes) remained constant. The inhibitory effect of CaCl2 was much more pronounced than that of NaCl, and the higher the ionic strength, the lower the interaction. The roles of electrostatic interaction, hydrogen bonding, and hydrophobic interactions in the complexation process were investigated using isothermal titration calorimetric (ITC) analysis.

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11.8 Surface Activity and Emulsifying Properties Surface activity, or the ability to reduce the interfacial tension, is a special characteristic which can be seen usually in proteins and surfactants but not in polysaccharides. However, it is reported that polysaccharides may also show surface activity if they contain either hydrophilic auxiliary (e.g., methyl and acetyl) groups or are linked to the glycolipids and/or proteinaceous fractions, as in gum arabic [55, 59, 66]. In this regard, it has been shown [28, 39] that PG can diminish the surface tension of distilled water (from 72.5 to 63 mN m−1 ) at low concentrations (0.1% w/w). At higher concentrations (0.9% w/w), the surface tension can drop even lower (56 mN m−1 ). Referring to PG’s chemical composition, one could speculate that its protein and lipid content (∼0.20% w/w each) is almost negligible, which therefore does not explain its surface activity. Fadavi et al. [51] also examined the effect of various concentrations (up to 3% w/w) and color groups (white, yellow, and red) of PG dispersions and observed similar trends; however the behavior of red color was irregular. There is also one report [67] on foaming properties (capacity and stability), which showed that even at 3% w/w, it was unable to create foam, and at high concentrations (>4% w/w), the foam immediately collapsed. The emulsifying property of hydrocolloids is an interesting topic which has been examined by many researchers. With regard to PG, these studies can be classified into two distinct groups: those on PG and those on SFPG. With reference to the latter one (SFPG = 0.5% w/w), it was shown [39] that it is capable of emulsifying up to 5% w/w oil (average droplet size 1.13 μm), although within a day during storage (4, 25, 50 ∘ C), they easily phase separated. When the SFPG concentration increased (2% w/w) but the oil content decreased (1% w/w), the resulting emulsions were quite stable (at 4, 25, and 50 ∘ C) too. The optimum emulsification capacity was 2:1 (the SFPG:oil ratio), when emulsions were stable against thermal processing at 80 ∘ C for 30 min (average droplet size 0.80 μm). However, apart from the possible contribution of the inherent protein and lipids, the emulsifying activity and capability were mostly attributed to the viscosity increase and the possibility of weak surface activity due to methyl and acetyl groups on the sugar residues. The emulsification activity, capacity, and heat stability of SFPG was significantly better than those of gum arabic. Regarding the emulsifying property of SFPG, it is also noticed [48] that the emulsification properties of SFPG which was separated from chemically modified IFPG (esterified by acryl amide) were not as good as those of ordinary SFPG, since its emulsions were partly phase separated in a matter of a few hours. The lower emulsifying activity of SFPG was attributed to its lower molecular weight and viscosity as well as to possible structural alterations. In another study, the effect of SFPG (0.25%–1%) and oil (5%–20%), pH (3.5–8), and storage time (up to 20 days) on the stability, rheological properties, particle size distribution, as well as microstructure was investigated [68]. Accordingly, the emulsions, particularly at higher SFPG concentrations (0.75 and 1% w/w), were stabilized via the bulk viscosity increase. In addition, in mildly alkaline conditions (pH = 8), the stability increased (20% w/w oil, 1% w/w SFPG, was fully stable after heating at 80 ∘ C for 30 min), whereas at pH 3.5, phase separation occurred. The droplet size distributions were unimodal, and average droplet sizes were A. rahensis. Surprisingly, the authors observed that the apparent viscosity of the species increased after the homogenization process. This increas was more pronounced for A. gossypinus compared to other species. This effect is in opposition to other polysaccharides such as alginate, xanthan, k-carrageenan, flaxseed gum, pectin, and methyl cellulose [49–52]. This difference has been attributed to the greater opportunity for GT molecules to contact each other due to the unfolding of their structure and the breaking of the large aggregated particles after homogenization [48]. A. gossypinus with the highest insoluble fraction exhibits the maximum improvement after the homogenization process. 12.4.1.1.7

Effect of Gamma Irradiation

The effect of gamma irradiation on the rheological behavior of two species of GT (Astragalus fluccocus and A. gossypinus) was investigated in a recent study [53]. The

12.4 Functional Properties

authors reported that when the gamma irradiation increased up to 3 kGy, the apparent viscosity of A. gossypinus increased in the range of the tested shear rate. For A. fluccosus, a decrease in the apparent viscosity was observed with increasing irradiation dose from 3 to 10 kGy. The authors observed a rapid decrease in the apparent viscosity of the gum solutions up to a dose of 15 kGy. Teimouri et al. [54] investigated the effect of gamma irradiation on the rheological behavior of Astragalus campactus. From their results, gamma irradiation under different doses increased the consistency coefficient and flow behavior index. 12.4.1.1.8

Synergistic Effect of GT with Other Biopolymers

The steady shear behavior of GT/guar gum mixture as a function of the polymer ratio and the temperature was studied by Silva et al. [55]. They observed that under the tested conditions, guar and GT aqueous systems and their mixture exhibited shear-thinning behavior, and when the temperature increased, the apparent viscosity of the samples decreased. The rheological properties of the mixed system were mainly dependent on the polymer ratio. The GT/guar gum mixture indicated an interesting synergic influence at the polymer ratio of 1:1. The strength of polysaccharide/protein interaction has a detrimental effect on the textural and structural characteristics of mixed gels. The effect of three species of GT (A. gossypinus, A. rahensis, and A. fluccosus) as a function of concentration (0.05–0.2% w/w) on a mixed milk protein system during acid gelation was investigated by Nejatian et al. [56]. The results of the rheological study showed that GT addition to milk protein dispersion resulted in a weaker network structure in comparison to the control sample. This weakening impact was eliminated when the A. gossypinus concentration increased up to 0.3%. As reported above, A. gossypinus exhibited higher content of uronic acid and fucose and a greater insoluble/soluble fraction ratio (presence of more hydrophobic groups), which induced a stronger protein–protein interaction which improved the structural strength of the mixed gel. 12.4.1.2

Dynamic Rheological Properties

In a recent study, the dynamic viscoelastic behavior of six species of GT (A. parrowianus, A. fluccosus, A. rahensis, A. gossypinus, A. microcephalus, and A. compactus) in the presence and absence of NaCl were evaluated (1.5% at 25 ∘ C) [23]. The results of this study showed that A. parrowianus solution is at the borderline of liquid and gel-like states, but the solutions of A. gossypinus, A. rahensis, A. microcephalus, and A. compactus show a weak gel-like behavior (frequency = 1 Hz) in both the absence and presence of Na+ ion. For A. fluccosus, in the presence of NaCl, gum solution exhibits viscous behavior, but with the addition of NaCl, its solution exhibits gel-like behavior. A. compactus, A. fluccosus, and A. parrowianus have higher values of limiting strain and thus have higher stability against the strain amplitude. As mentioned before, GT consists of two fractions (bassorin and tragacanthin) which differ in various species. On the basis of the Spearman correlation coefficient, the gums with a higher soluble/insoluble ratio have a more limiting strain [23]. According to frequency sweep experiments, the values of tan δ for the gums with a higher bassorin fraction of 50% (A. microcephalus, A. compactus, and A. gossypinus) are less than one, demonstrating the more solid-like behavior of these species compared to other species. It has been attributed to the greater swelling power and higher

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Sauter diameter of bassorin compared to tragacanthin, which contributes to the gel-like character of the gums [23]. Similar values of tan δ for A. microcephalus solution in the presence and absence of NaCl have been reported, showing solid-like behavior in both conditions. The value of tan δ for A. gossypinus solution in the absence of NaCl is higher than 0.1 and less than one, showing that its solution is not a true gel. Conversely, in the presence of NaCl, A. gossypinus indicates a crossover point at high frequency; this is indicative of a flexible gel. The effect of NaCl addition on the dynamic viscoelastic behavior of A. gossypinus is more pronounced than on A. microcephalus and A. parrowianus, which is due to the higher amount of uronic acid in A. gossypinus composition [23]. On the other hand, tan δ values for A. rahensis dispersion are higher than one, showing a liquid-like behavior for its dispersion over the frequency range 0.01–100 Hz, and this behavior remains constant at the shortest time scale of the test. The effect of homogenization on the dynamic viscoelastic properties of three species of GT (A. gossypinus, A. compactus, and A. rahensis) was studied by Farzi et al. [48]. The frequency dependence of G′ and G′′ for GT solutions was described. The results showed that homogenization led to the dominance of gel-like behavior for all tested species. The authors also indicated that the change in the dynamic viscoelastic properties of GT species was highly species dependent. 12.4.2

Surface Activity

Surface tension shows how strongly the surface molecules in a solution are attracted by the neighbor’s molecules [57]. According to previous studies [18, 22], GT has an excellent surface activity, and at low concentration (0.50 mg ml−1 .

12.7 Effect of Pre-treatment on GT: Physicochemical Properties

The effect of aqueous solutions of GT is dependent on the bacterial species. A clear microbial inhibition was observed for the aqueous solution of A. parrowianus against four bacteria, especially Listeria monocytogenes. The antimicrobial activity of GT has been attributed to the presence of phenolic compounds in GT’s composition. As stated above, the aqueous solution of A. parrowianus has the highest phenolic compounds (235 mg GAE g−1 gum), produced the highest antibacterial activity. The antimicrobial activity of the phenolic compounds is associated with the interaction between these compounds and bacterial cell membranes. This interaction changes the cell membrane’s permeability, resulting in leakage of intercellular components followed by the death of the cell [78]. Furthermore, these compounds can also penetrate into bacterial cells and coagulate the cell contents [79].

12.7 Effect of Pre-treatment on GT: Physicochemical Properties 12.7.1

Irradiation

Food irradiation is widely applied as the ultimate processing technology. Irradiation up to 10 kGy has been approved by Food and Agriculture Organization (FAO), World Health Organization (WHO), and International Atomic Energy Agency (IAEA). Additionally, a higher dose of irradiation has also been approved for some products [80]. The effect of gamma irradiation on the chemical structure, particle size characteristics, color attributes, and microstructural properties of two species of GT (A. fluccosus and A. gossypinus) were investigated. In this study, the authors demonstrated that irradiation could not change the chemical structure of GT. On the other hand, the particle size characteristics of both types of GT were affected by the irradiation treatment. The authors also showed that the radiation process increased the blueness and yellowness of GT samples. Scanning electron microscopy (SEM) analysis showed that the irradiated samples had a smoother surface [53]. In a study by Teimouri et al. [54], the influence of different levels of gamma irradiation (0, 4, 8, 16, and 30 kGy) on some physicochemical characteristics of GT (A. campactus) was evaluated. Fourier transform infrared spectrometer (FT-IR) analysis showed that gamma irradiation did not have a considerable effect on the functional groups of this gum, which was consistent with previous research [53]. On the other hand, this treatment had a significant effect on water absorption capacity, solubility, and color. In recent research [81], the effect of gamma irradiation on the functional properties of A. gossypinus was evaluated and then used to stabilize an oil-in-water emulsion system. The results of their study showed that applying 1.5 kGy gamma irradiation was more effective for obtaining the maximum stability of the emulsion. GT considerably decreased the interfacial tension of the oil-in-water system. Therefore, it can be stated that GT has a positive impact on the oil-in-water emulsion stability. Due to the mucoadhesive and gel-forming ability of polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA), the inherent wound healing ability of GT, and PVP, Singh et al. [82] attempted to prepare an antibiotic drug “gentamicin” and analgesic drug “lidocaine” incorporated into TG-PVA-PVP hydrogel by the radiation method. Various analyses like 13 C NMR, thermogravimetric analysis (TGA), cryo-SEM, AFM, FTIR, X-ray

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diffraction (XRD), differential scanning calorimetry (DSC), and swelling studies were used to characterize these polymers. Network parameters and some properties such as water vapor permeability, microbial penetration, haemolysis, mucoadhesion, oxygen permeability, and antioxidant activities were also evaluated. The authors found that the films of these polymers were permeable to water vapor and O2 , blood compatible, and impermeable to the microorganism. Further, it was found that the synergic influences of the antimicrobial, mucoadhesive, and antioxidant nature of hydrogel dressings make them appropriate for wound management. Mohammadifar and Abdolmaleki [83] used irradiated A. gossypinus at different doses (0, 1.5, 3, and 5 kGy) to stabilize an oil-in-water emulsion. Rheological and particle size characteristics were measured to monitor the mechanism of stabilization. According to their results, irradiation had a considerable effect on the emulsion stability, particle size distribution, and rheological behavior of an oil-in-water emulsion. The sample irradiated at 1.5 kGy had the most stability. 12.7.2

Heat Treatment

Hatami et al. [84] performed a study on the effects of heat treatment on milk protein–GT mixed gel. Small deformation rheological evaluation demonstrated that the mixed gel network strength increased as follows: heated Na caseinate and heated whey protein with GT alone > heated milk protein dispersion and GT separately > co-heated GT and whey protein > co-heated all three biopolymers. Microstructural analysis of the mixed gel showed that the network of heated Na caseinate and heated whey protein with GT alone was much more homogenous, dense, and coarse than when all three biopolymers were co-heated, while the network of other mixed gels was of intermediate density. The authors suggested that the heat treatment of the biopolymer mixture containing GT is an opportunity to control the rheological and microstructural properties of mixed gels. 12.7.3

High Shear Rate

The light scattering technique is commonly used to observe the reduction in particle size. As mentioned above, GT is composed of bassorin and tragacanthin. The hydrodynamic diameter of bassorin is 200 μm and that of tragacanthin is 0.12 μm [48], indicating GT is a polydisperse system. The effect of high-shear-rate homogenization (0–20 min) on the particle size of different species of GT was evaluated by Farzi et al. [48]. Before homogenization of GT solutions, all the solutions showed a wide distribution of various particle size depending on the GT species. The homogenization of GT solutions made the size distribution sharper, and as the time of treatment increased, the particle size shifted to smaller regions. The authors reported that more pronounced changes were observed for A. compactus and A. rahensis than for A. gossypinus after treatment.

12.8 Food Applications 12.8.1

Ice Cream

Kurt et al. [85] investigated the effect of various concentrations (0%–0.5% w/w) of GT on the internal structure and rheological characteristics (dynamic rheology, thixotropy,

12.8 Food Applications

and creep/recovery behavior) of Salep-based ice cream. According to this study, incorporation of GT into the ice cream formulation increases both the viscous and elastic behavior of ice cream. Additionally, an increase in GT concentration improves the network resistance against stress. The authors suggested that GT can be introduced as a valuable additive to enhance the structural properties of ice cream. In another study, the effectiveness and applicability of using guar gum–gum tragacanth (GG–GT) as a stabilizer and polyglycerol poliricinoleate (PGPR)-lecithin blend as an emulsifier and their effects were evaluated. When GG–GT was used in the ice cream formulation, about 6% improvement in overrun values and 20% increase in overall acceptability and 13% decrease in the melting rate were observed in comparison to the sample prepared with GG. Overall, the authors reported that it is possible to produce an ice cream with 2.8% fat using the double emulsion technique without affecting the quality of the product adversely [86]. 12.8.2

Doogh

The major problem during storage of Doogh, a traditional yogurt drink, is phase separation, which occurs because of aggregation of caseins at low pHs. Therefore, several studies focused on the stabilization of this product. In an attempt to promote the stability of non-fat Doogh, Gorji et al. [87] used GT. On the basis of this study, GT can be used as a suitable additive to enhance the qualitative properties of Doogh. Additionally, GT addition to Doogh leads to prevention of serum separation. The Doogh prepared with GT has a higher complex viscosity, apparent viscosity, and storage modulus, but has a smaller particle size, which has been attributed to the interaction between GT and casein. In another study, Azarikia and Abbasi [62] showed that GT (0.2%) and the soluble tragacanth fraction (0.1%) could prevent phase separation of Doogh. Additionally, they found that with the addition of soluble tragacanth and GT to Doogh, zeta potential values changed from positive to negative. This effect is due to adsorption of soluble tragacanth onto casein and induced stabilization through steric and electrostatic repulsions. 12.8.3

Yogurt

Application of GT (0.25, 0.5, 0.75, and 1 g l−1 ) as fat replacer has no significant effect on total solids, acidity, total protein, and ash content of non-fat yogurt. With increasing GT concentration up to 0.5%, the firmness and syneresis of yogurt remain constant, but when the GT concentration increases above 0.5 g l−1 , a softer gel is produced, and its degree of syneresis increases. Furthermore, incorporation of GT in yogurt formulations produces a more open and coarser structure than the control sample. Overall, the addition of GT does not enhance the syneresis and textural properties of non-fat yogurt [88]. 12.8.4

Cheese

It has been indicated that with increasing GT concentration in cheese formulations, the hardness of this product decreases, but the level of whiteness increases. However,

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it has also been reported that interaction of ripening time with gum concentration during 60 weeks of ripening causes deterioration of cheese properties. In conclusion, GT improves the rheological characteristics of cheese, which has been associated with its water-binding ability [89]. Aminifar et al. [90] investigated the effect of 0.02% GT, milk protein concentrate or sodium caseinate on textural, microstructural, and physicochemical characteristics of Lighvan cheese. The results revealed that incorporation of GT into bovine milk had a considerable effect on the Lighvan cheese properties. The authors proposed that effect of GT on the properties of Lighvan cheese could be related to its heterogeneous, branched, and hydrophilic structure. SEM analysis of GT showed that the addition of cheese samples led to the production of inconsistent black particles containing large white patches, which have been attributed to the water-binding capacity of this gum. Incorporation of GT into cheese formulation decreased the hardness of the final product, which may be due to a decrease in the moisture content of the samples. 12.8.5

Kashk

The influence of various concentrations of GT (A. gossypinus) on the syneresis, particle size distribution, rheological properties, and turbidity of low-fat dried yogurt paste (Kashk) were investigated by Shiroodi et al. [91]. The result of their research indicates that an increase in GT concentration improves the shape retention ability and structural strength of Kashk. Furthermore, it was found that the products containing 0.5% GT have the lowest syneresis. The authors suggested that this effect is probably due to the increase in the viscosity of the continuous phase, which leads to trapping of the aggregated casein. On the other hand, the samples containing 0.1% GT have maximum syneresis and polydispersity. 12.8.6

Flavored Milk Drink

Other findings demonstrated that GT has a desirable effect on the physical and rheological properties of flavored milk drinks manufactured with date syrup. According to these results, it can be concluded that the application of an appropriate concentration and type of GT results in an improvement in the mouthfeel and textural properties of milk drink made with date syrup. Due to this desirable attribute of the product, it is suggested that GT can play a major role in altering trends in the consumption of artificially flavored milk beverages [92]. 12.8.7

Pasta

In a recent study, Chauhan et al. [93] used whole amaranth flour and various gums such as guar gum, acacia gum, and GT to produce pasta without gluten. Their results indicated that the quality of gluten-free pasta improved when the abovementioned gums were added at various concentrations. It also was found that the textural properties (gumminess, hardness, and chewiness) and cooking quality of pasta improved when higher levels of the gums were used. Comparatively, the authors reported that guar gum best enhanced the physicochemical properties of gluten-free pasta.

12.8 Food Applications

12.8.8

Ketchup

Nayebzadeh and Mohammadifar [94] investigated the influence of different concentrations of GT, guar gum, and xanthan gum on the sensory and rheological properties as well as the stability of tomato ketchup. When the gum concentration increased, the syneresis values decreased and spreadability, yield stress, and viscosity increased. Surprisingly, ketchup samples containing guar gum or xanthan gum showed thixotropic behavior, but GT created rheopectic behavior. Comparatively, the overall texture acceptability, stability, spreadability, and yield stress of the samples incorporating xanthan were better than those obtained for the samples containing GT or guar gums. More recently, Komeilyfard et al. [95] studied the influence of Angum gum (AnG) alone and in combination with GT (AnG-GT) on the rheological, sensory, and textural properties of tomato ketchup. The tomato ketchup formulations were control (without gum), GT (0.5%–1.5%), AnG (0.5%–1.5%), and AnG-GT (0.5%–1.5%). The result showed that incorporation of the hydrocolloids into tomato ketchup formulations led to a significant decrease in the Bostwick consistency value and serum separation. With hydrocolloid addition, the particle size of the samples significantly increased. Shear-thinning behavior was observed for all tomato ketchup formulations, and the incorporation of hydrocolloids increased the apparent viscosity. The sensory analysis of the samples indicated that hydrocolloid addition had no significant influence on the color properties (lightness, redness, blueness, hue angle, chroma, and total color differences) of tomato ketchup. The overall acceptability of the samples containing 1.5% AnG, 0.5% TG, and 1% and 1.5% AnG-GT was considerably higher than that of other samples. 12.8.9

Use of GT as Coating Material

Natural gums are broadly used in food systems; however, the use of these biopolymers as an edible coating to extend the shelf life of fruits and vegetable has been explored recently. To date, the effect of GT as coating materials on the physicochemical properties of some fruits such as banana and mushroom has been investigated. The coated mushrooms have a greater shelf life comparing with uncoated samples. Additionally, GT has a protective influence on the hardness of coated mushrooms. Due to the reduction in the weight loss and preservation of the quality of coated mushroom, the application of GT as a coating agent for maintaining the quality of this fruit during storage is recommended. In another research, the effect of a GT coating on the properties of the banana slice has been evaluated by Farahmandfar et al. [96]. According to this paper, the shrinkage of the banana coated with GT is less than that of the uncoated sample. Additionally, coated banana samples have better textural properties as well as greater weight loss, lightness, and rehydration capacity than uncoated samples. These studies showed that use of GT as a banana coating leads to better preservation of its qualitative properties and saving of energy, expense, and time. Anther finding showed that application of Aloe Vera, GT, and a combination of both as edible coatings can change the physical and textural properties, color attributes, weight loss, and carbohydrate percentage of button mushroom [97]. According to this research, the mushrooms coated with Aloe Vera gel, GT, and a combination of both showed less weight loss, color changes, and softening. The authors suggested that the combination of Aloe Vera and GT is more effective in extending the shelf life of button mushroom. More recently, Nasiri et al. [98] used GT impregnated

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with Satureja khuzistania essential oil as a coating material to improve the shelf life and postharvest quality of button mushroom. It was found that button mushroom samples had better textural properties and lower microbial count than untreated ones. Furthermore, coating with GT+ S. khuzistania essential oil can reduce decomposition rate of ascorbic acid and phenolic compounds. In conclusion, GT can be introduced as an appropriate coating material for prolonging the shelf life of fruits and vegetables. 12.8.10 12.8.10.1

Use of GT as Delivery Carrier Complexation and Coacervation

As mentioned before, TG, a biodegradable anionic polysaccharide with the ability to interact with positively charged polymers, can be used as a wall material in encapsulations of various compounds. Gorji et al. [99] evaluated complexation of sodium caseinate with various species of GT as a function of pH. They indicated that the sodium caseinate/GT complex has the following structural transitions: 1) 2) 3) 4) 5)

pH 7.00 to 5.40: no interaction occurred pH 5.40 to 4.80: initiation of the complexes formation pH 4.80 to 4.30: formation of inter-polymer complexes pH 4.30 to 4.02: optimum coacervation pH 4.02 to 2.50: suppression of coacervation

As observed above, the physicochemical characteristics of GT are species dependent, and thus it is expected that the complexation of sodium caseinate and GT is also species dependent. Gorji et al. [99] investigated the effect of different pHs on structural transitions during complexation of sodium caseinate and various species of GT (A. rahensis and A. gossypinus). Their study demonstrated that the system containing different species of GT had various particle sizes and critical pH values, which has been attributed to varying uronic acid content and soluble/insoluble fraction ratios of various species. In another study, the formation of electrostatic complexes between A. gossypinus and sodium caseinate as a function of pH (7.00–2.50), biopolymer concentration, and the ratio of biopolymer mixing was studied [100]. GT addition decreased the pH values of sodium caseinate at which sodium caseinate precipitated, indicating that GT can act as a stabilizing agent for sodium caseinate below the isoelectric pH of casein. The authors also showed that the particle size of GT–sodium caseinate was profoundly affected by the presence of GT, particularly at pH = 4.00. At this pH and in the absence of sodium caseinate, the particle size of GT was large, but in the presence of sodium caseinate, the complexation between these biopolymers led to the formation of nanoparticles which were smaller than the particles of blank GT and sodium caseinate. Firooz et al. [101] monitored the complexation between GT and β-lactoglobulin at different pH values. The primary soluble GT–β-lactoglobulin were formed at pH = 5.3, and the aggregation of the interpolymeric complex was initiated at pH = 4.8. They found that at pH = 4.5, phase separation occurred. The particle size of the assembled structure decreased upon complexation, especially after a pH of 4.5. 12.8.10.2

Encapsulation of Phytochemicals using Coacervation Technique

Astragalus compactus, an Iranian species of TG, in combination with maltodextrin, can be used as an appropriate wall material for encapsulation of 2-methyl butyl acetate

12.9 Conclusions and Future Trends

(flavoring agent of strawberry). Addition of A. compactus (0.5% w/w) to maltodextrin solutions (14.55% w/w) can increase the viscosity and glass transition temperature to an optimal level. Additionally, A. compactus can decrease the physical defects of microcapsules and prevent sickness. With the incorporation of this species of GT into maltodextrin solution, as cell material, the release rate of 2-methyl butyl acetate decreases [102]. TG can form polyelectrolyte complexes and hydrogel, and therefore it can be used as an excipient for protein/peptide delivery. TG particles have a submicron particle size, which contributes to drug delivery. Comparatively, TG has higher mucoadhesion in comparison to chitosan, alginate, and PVP [103]. Nur et al. [103] stated that, on the basis of the particle size, rheological properties, zeta potential value, and loading efficiency of nanoparticles-based TG, it could be used as a suitable carrier for the encapsulation of insulin, as a loaded peptide. The results of their study demonstrated that both insulin and TG have a gelling point at around pH 4.1. The authors reported that the values of particle size and zeta potential for the insulin–TG complex at pH 3.7 were, on average, 566 nm and −14, respectively. Hosseini et al. [104] prepared a pH-responsive nanohydrogel based on TG and various chemical cross-linkers (glyceroldiglycidylether, 3-aminopropyltriethoxysilane, glutaraldehyde, and PVA) and then investigated its drug delivery and swelling properties. The authors indicated that in vitro release behavior of indomethacin, as a model drug, can be controlled by pH. With increasing pH, the rate of indomethacin release significantly increased, which has been attributed to THE ionization of hydroxyl functional groups at higher pH values. In another study, a pH-responsive TG–poly (methyl methacrylate-co-maleic anhydride)-g-poly (caprolactone) microgel was developed for in vitro release of quercetin. It was found that the developed microgels are dependent on pH, gel content, time of immersion, and temperature. Other findings indicated that TG-based pH-responsive microgel protects antibiotics against acidic pH of the stomach and therefore can be utilized as a site-specific drug delivery to release antibiotic to the colon. Application of TG, as a wall material for encapsulation of Aloe Vera extract, is a safe and biocompatible technique for the controlled release of this healing compound. A relative inhibition effect has been reported for Aloe Vera extract–GT particles against E. coli, Candida albicans, and Staphylococcus aureus. Additionally, a functional wound healing activity and also a cell viability of around 98% has been observed for this novel prepared wound healing product [105]. In a recent study, TG has been used for the in situ synthesis of ZnO nanoparticles on cotton fabric [106]. According to this paper, ultrasonic irradiation results in easy and clean production of ZnO nanoparticles at low temperature. The cotton fabric produced by TG exhibits a clear inhibition zone against E. coil, S. aureus, and C. albicans. Furthermore, it has a good photocatalytic activity on methylene blue degradation.

12.9 Conclusions and Future Trends The present chapter presented the chemical composition, molecular structure, rheological behavior, functional properties, and potential application of GT in food and pharmaceutical systems. As reviewed above, the physicochemical and rheological characteristics of GT are considerably species dependent, with different species have

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various functional properties. Furthermore, it was also concluded that any study performed on GT without taking the plant species into consideration will result in misleading results. The future challenge is to elucidate the effect of purification, drying, and further processing conditions on the microstructure, molecular conformation, chemical composition, and functional properties of different species of GT.

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13 Cashew Tree (Anarcadium occidentale L.) Exudate Gum Esther Gyedu-Akoto 1 , Frank M. Amoah 1 , and Ibok Oduro 2 1

New Product Development Unit, Cocoa Research Institute of Ghana, P.O. Box 8, Akim-Tafo, Eastern Region, Ghana Department of Food Science and Technology, Kwame Nkrumah University of Science and Technology, Private Mail Bag, Kumasi, Ashanti Region, Ghana 2

13.1 Introduction The cashew tree is a fast-growing evergreen tropical tree. Although it can withstand high temperatures, a monthly mean of 25 ∘ C is considered optimal. Annual rainfall of 1000 mm is sufficient for production, but 1500–2000 mm can be regarded as optimal [1]. The tree has a well-developed root system and can tolerate drought conditions. It is a strong plant that grows in sandy soils that are generally unsuitable for other fruit trees. Cashew, Anacardium occidentale L., is a member of the Anacardiaceae family, allied with mango, pistachio, poison ivy, and poison oak. The family contains about 73 genera and about 600 species. Anacardium contains eight species native to tropical America, of which cashew is the most important economically. Trees within the Anacardiaceae family are known for having resinous bark and caustic oils in leaves, bark, and fruits which cause some form of dermatitis in humans. The cashew industry, in particular, had to overcome severe limitations imposed by caustic oils in the nutshell. Today, the caustic substance that made the domestication of the plant difficult is a valued by-product of cashew nut production [2]. Cashew is native to North-Eastern Brazil, in the area between the Atlantic and the Amazon rainforests [3]. The area is a predominantly savannah woodland or thorn scrub and includes the almost desert-like Caatinga. Although cashew will grow in tropical wet forests, they rarely produce any nuts, and production is far greater in areas with a distinct wet and dry season, such as its native range in Brazil, India, and East Africa. It was planted in India initially to check erosion, and uses for the nut and pseudo-fruit (cashew apple) were developed much later. Native South Americans discovered many medicinal uses for the apple juice, bark, and caustic seed oil, and these were later exploited by Europeans [4]. India led the world in cashew production for many years until Vietnam surged about threefold in a few years. Currently, the Ivory Coast is the leading producer of cashew. In its native Brazil, cashew nut production ranks in the top five of the world, and virtually all cashew apples and juice products come from this country. Preliminary data indicate that cashew nut production surpassed almond in 2003, and thus cashew is now ranked the first nut crop in the world [5]. Emerging Natural Hydrocolloids: Rheology and Functions, First Edition. Edited by Seyed M.A. Razavi. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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13 Cashew Tree (Anarcadium occidentale L.) Exudate Gum

Apart from the nuts, apples, and the caustic seed oil, another product from the cashew tree gaining popularity in the cashew industry is the cashew tree gum. In this chapter, the production, physicochemical, and rheological properties of cashew gum and its role in food and pharmaceutical formulations and product development have been reviewed to indicate the increasing use of the gum as an important additive in the food and pharmaceutical industries.

13.2 Cashew Tree Gum The gum, which is produced in appreciable amounts by the cashew tree, represents nonconventional alternatives for the farmers [6]. The art of cashew gum use began in China centuries ago, reaching its climax of development during the period of 1368–1644 CE. Due to its insecticidal and good adhesive properties, cashew gum is used primarily in industrial applications for binding books, as adhesives for envelopes, labels, stamps, and posters. Research already exists on its utilization in the making of inks and varnishes. Cashew gum is similar to gum arabic and can, therefore, be used in the pharmaceutical and cosmetic industries as an agglutinant for capsules and pills and in the food industry as a stabilizer, suspension agent, as well as a flavor encapsulating agent [7, 8]. Thus, it has great potential for industrialization, making its extraction another source of revenue for the producer, in addition to the nut. 13.2.1

Production of Cashew Gum

Cashew gum can be obtained by natural exudation or by means of incisions on the trunk and branches of the cashew tree. In Ghana, the gum exudes spontaneously from the trunk and principal branches of the trees around the middle of November, after the rainy season [9]. The dry winds, which prevail after the rainy season, cause the bark to crack, and the gum flows out, and this continues up to March when the dry season ends. The exuded gum thickens and hardens within some few days of exposure to the air, usually in the form of round or oval tears or in straight or curled cylindrical pieces of various sizes. The masses of gum are collected, either while adhering to the bark or after they fall to the ground. Generally, most cashew trees produce white gums, while a few produce amber-colored gums. There is virtually no production of gum during the rainy season, that is, from May to August, when the trees are not under stress. In Ghana, cashew production is concentrated in the Guinea savannah zone and in the transitional belt between the forest and the savannah zones. A study conducted on the production and yield trends of cashew gum in these two areas showed that the location of the trees had no significant effect on the production of the gum [9]. The minimum age of cashew trees for the production of the gum was 4 years, with mature trees (trees more than 10 years old) producing more gum than young trees (young trees 10 years and below). The average yield/tree for the young trees varied from 13.7 to 276.0 g and that for mature trees was from 30.1 to 1237.1 g. However, there was no significant difference between yields from mature trees and those from young trees. During the study, a very old tree which according to local farmers was 45 years in the Guinea savannah zone (Figure 13.1a), produced 7664.1, 3270.1, and 497.7 g of gum for January, May, and August, respectively, confirming that the older tree, the more gum it produces. Higher

13.2 Cashew Tree Gum

(a)

(c)

(b)

(d)

Figure 13.1 (a) A 45-year-old tree with cashew gum oozing from its bark, (b) mixtures of grades 1 and 2 cashew gum, (c) grade 3 cashew gum, (d) cashew gum powder.

gum yields were obtained during the dry season from January to March when there was drought and the trees were under stress. In Brazil, the average production of cashew gum per tree per year is 700 g with a potential annual production of 38 000 MT [10]. Several techniques are now being used to produce gum artificially to guarantee viability and improvement of the quality of the commercial product. These techniques involve systematically controlled tapping and collection procedures. One such technique is the use of chemical stimulants in the extraction of gum from cashew tree [11]. Application of stimulants such as sulfuric acid combined with 2-chloroethyl phosphonic acid and 5% dimethyl sulfoxide also increased gum exudation from the trees in all months following stimulant applications. 13.2.2

Chemical Structure

Cashew gum is a complex polysaccharide of high molecular mass comprising 61% galactose, 14% arabinose, 7% rhamnose, 8% glucose, 5% glucuronic acid, and 2% other sugar residues [8]. Different chemical reactions have been used to determine the structure of the gum. These include complete acid hydrolysis of cashew gum, which shows that

329

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13 Cashew Tree (Anarcadium occidentale L.) Exudate Gum

the gum is made up of D-galactose, L-arabinose, D-galacturonic acid, and L-rhamnose [12]. Characterization of the gum showed that it contains 72%–73% galactose, 11%–14% glucose, 4.6%–5% arabinose, 3.2%–4% rhamnose, and 4.7%–6.3% glucuronic acid [10]. It is mainly composed of three types of galactan units within the core, linked by C-1 and C-3, C-1 and C-6 and C-1, C-3 and C-6. The glucose is present as a side chain up to five units long. Cross-reactions of cashew gum with different anti-sera also confirm the presence of non-reducing galactose units reinforced with L-rhamnose residues. Auto-hydrolysis of cashew gum generates a degraded gum with a molecular weight of 23 250 gmol−1 , which upon graded hydrolysis produces an aldobiouronic acid with an established structure of 6-0- (β- D- galactopyranosyl uronic acid) -D-galactose [13]. Recently, the structures of degraded and natural cashew gums have been established through methylation and Smith degradation experiments. Degraded cashew gum is a branched chain polysaccharide with a repeating unit which has a 1 → 3 linked galactan main chain [13]. This chain has galactose residues attached to it as side chains by 6 → 1 linkages. Every alternate galactose residue carries aldobiouronic acid moieties also joined by 6 → 1 linkages. The natural cashew gum differs from the degraded gum with respect to the size of the main galactan chain and in the number of auxiliary chains. 13.2.3

Organoleptic Properties of Cashew Gum

Cashew gum, just like other gums, is odorless and tasteless, and it can be sorted on the basis of color and brightness. Sorting of cashew gum yielded three different grades [9], with the physical properties of grade 1 gum being glassy and transparent in form, while grades 2 and 3 were translucent. Grades 1 and 2 were whitish yellow in color, with grade 2 being more yellowish than grade 1 (Figure 13.1b). Grade 3 cashew gum was amber or brown in color (Figure 13.1c). The lower grades were generally more strongly colored than the higher grades. The color differences depend on the presence of impurities and the age of the tree that produced the gum. Milled cashew gum was also white or pale brown in color (Figure 13.1d) depending on the color of the gum nodule that was milled. Some studies have also shown cashew gum to be cream to white [14], golden brown to glassy white [15, 16], or pale yellow to reddish in color [13]. They also found it to be tasteless, odorless, translucent, glassy in form, and gritty in texture. However, cashew gum, when purified by dissolving crude gum in water and precipitating it with 96% ethanol, was glassy white, tasteless, odorless, and smooth in texture [15, 16], but when precipitated with acetone, the purified gum was off-white in color and turned brown on exposure to air [17]. 13.2.4

Physicochemical Properties of Cashew Gum

Physicochemical properties of natural gums vary in terms of differences in tree species [18]. Gums from the same tree species but of different ages and from different soil types also differ in physicochemical properties. Some concerns have been raised on the production, processing, and use of natural gums, and these include the accurate identification of the sources of gums and their quality assurance. The use of gums in numerous industries including the food, pharmaceutical, and cosmetic industries has increased widely in these last decades [19], and this is due to the numerous interesting characteristics such as the gelling, stabilizing, and thickening functions of these polymers. These

13.2 Cashew Tree Gum

functions and the physicochemical properties of the gums are used to determine their quality and how they will perform during processing. In view of this, some works have been done on the elementary analysis of cashew gum. Proximate analysis of cashew gum has revealed that it is mostly made up of carbohydrates with some moisture and very low amounts of protein, fat, and fiber. Lima et al. [8] reported that the gum has 7.4% moisture, 0.5% protein, 0.06% fat, 0.95% fiber, 0.95% ash, and 98.0% carbohydrate. Purification of crude cashew gum using 96% ethanol has been found to reduce chemical components of the gum [15, 20]. However, purification increases the pH of the crude gum, making its purified form less acidic (Tables 13.1 and 13.2). Chemical components such as fat, protein, fiber, and tannins were not detected in the purified gum (Table 13.1). The absence of tannins may explain why purified cashew gum is always white in color. Tannins undergo oxidative reactions which result in the development of brown color in the crude gum. Cashew gum purified with acetone has also been reported to have reduced mineral and moisture content compared to its crude form [17]. Table 13.1 Chemical composition of crude and purified cashew gum. Parameter

Crude gum

pH Moisture content (%)

4.69

5.31

11.93

8.31

Ash (%) Total sugars (%)

Purified gum

0.89

0.71

63.44

90.37

Fat (g 100 g−1 )

0.59

—

Protein (g 100 g−1 )

0.57

—

Fiber (g 100 g−1 )

3.92

—

25.08

—

−1

Tannins (mg 100 g )

Source: Adapted from Toure et al. [20].

Table 13.2 Mineral composition of crude and purified cashew gum. Parameter

Crude gum

Moisture content (%)

11.19

Purified gum

10.44

Insoluble matter (%)

0.350

pH

4.90

5.22

883.50

662.40

Potassium (mg kg−1 )

0.08

0.03

Sodium (mg kg−1 )

0.07

0.05

Calcium (mg kg−1 )

0.280

Iron (mg kg−1 )

16.71

2.00

Zinc (mg kg−1 )

8.34

4.14

54.44

50.69

Magnesium (mg kg−1 ) Source: Adapted from Asantewaa [15].

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13 Cashew Tree (Anarcadium occidentale L.) Exudate Gum

Table 13.3 Chemical composition of cashew gum from young and mature trees. Parameter

Young trees

Mature trees

Phenols (%)

0.21–0.35

0.50–2.26

Moisture content (%)

9.80–11.80

11.30–13.20

Insoluble matter (%)

2.40–2.80

1.90–4.80

Ash (%)

1.00

0.50–1.20

Protein (%)

1.40–1.80

1.27–1.41

Sugars (mg g−1 )

0.96–2.10

0.85–1.37

pH

4.00–4.20

3.80–3.90

Calcium (mg kg−1 )

1012–1405

1358–1755

Potassium (mg kg−1 )

139–908

386–1397

Sodium (mg kg−1 )

114–225

152–301

−1

Iron (mg kg )

258–294

313–398

Zinc (mg kg−1 )

6.30–19.80

7.80–35.50

Source: Adapted from Gyedu-Akoto et al. [21].

Studies on the effect of tree maturity on cashew gum have shown that gum from the mature tree was more acidic than that from young trees [21]. The pH of cashew gum ranged from 3.80 to 4.20 (Table 13.3). The phenol content of mature tree gum was higher than that in young tree gum. However, gum from young trees had higher protein and sugar content than those from mature trees (Table 13.3). This may due to the fact that the young trees, which are actively growing, synthesize more nutrients than the mature ones [22]. Proteins are important for the emulsifying properties of gums [18]. The moisture content of cashew gum was found to be between 9.8% and 13.2%, with mature tree gum having higher moisture content, and this may be due to the fact that they produced more gum and would need a longer time to dry. The mature trees also have well-developed root systems which have the ability to take up more water from the soil for their metabolic processes. The mineral content of plant materials is thought to be a function of the composition of the soil on which the plants grow [23]. Cashew gum was found to have very high levels of calcium, sodium, and potassium, with calcium being predominant (Tables 13.2 and 13.3). Gum from mature trees had higher mineral content than that from young trees, and this may be due to the fact their root systems take much of the soil nutrients and store them in other parts of the plants [22]. Sodium and potassium content of the gums tend to increase from the transitional belt to the Guinea savannah zone, and this is an indication of high levels of potassium and sodium in the soils of the Guinea savannah zone. The high levels of minerals which are normally found in their ionic state may account for the acidity of cashew gum [24]. 13.2.5

Rheological Properties of Cashew Gum

There are two rheological properties of particular importance to hydrocolloids: their gel and flow properties. Hydrocolloids are used to thicken and/or gel aqueous solutions in order to modify and/or control the flow properties of liquid products and the

13.2 Cashew Tree Gum

deformation properties of semisolid products [19]. They are generally used in food products at concentrations of 0.25%–0.50%, which indicates their great ability to produce viscosity and to form gels [25]. Many hydrocolloids, which include natural gums, are capable of forming gels of various strengths depending on their structure and concentration as well as on environmental factors such as ionic strength, pH, and temperature. Cashew and acacia gums have been found to have similar rheological properties [14]. Solutions of both gums showed an increase in viscosity with concentration, but the viscosity increase was more gradual with gum arabic, indicating that cashew gum has better thickening capability. Changes in pH, temperature, and storage time affected the viscosity of both gums. However, their effects on viscosity were not significant. Dissolving xanthan gum in cashew juice produced a higher viscosity than dissolving cashew gum in cashew juice, indicating that cashew gum has less thickening capability than xanthan gum [26]. However, when the two gums were blended in cashew juice, it produced juice with a viscosity similar to that with xanthan gum. This is due to the synergistic interactions between the two gums in solution. Addition of zinc oxide (ZnO) at concentrations of 3%, 5%, 7%, and 10% to aqueous cashew gum solution raised its pH from 4.74 to the range 6.3–6.7 and its viscosity from 4.82 to the range 5.07–8.01 mPa s [27]. This shows that zinc oxide essentially controls the acidity of the gum, thereby acting as a stabilizer and a filter agent in the gum. However, the addition of starch to the raw gum solution at the same concentrations as those used in ZnO slightly reduced the pH of the gum to the range 4.5–4.7, while the viscosity increased to the range 4.67–9.56 mPa s. The starch, therefore, acted as a binding agent. Addition of glycerine to the gum at concentrations of 3%, 5%, 7%, and 10% also decreased its pH to the range 4.2–4.5 but increased the viscosity to its highest range, 5.26–10.21 mPa s. In the presence of glycerine, the gum became more slippery, suggesting that glycerine aids the easy spread of the gum. Combinations of the additives, that is, zinc oxide and glycerine, produced pHs between 4.20 and 5.30 and viscosities between 5.20–6.78 mPa s. This indicates that combining cashew gum with additives such as zinc oxide, starch, and glycerin can improve the rheological properties of the gum. Studies have also shown that increasing the cashew gum concentration increases the viscosity and facilitates gelation of the gum [15, 16, 28]. The flow behavior of cashew gum showed that the gum was liquid at concentrations of 4%–12%, viscous at 16%–40%, and gel at 80% and higher, but the gel produced rapidly dissolved when heated at a temperature of 80 ∘ C [28]. The gelation may be accounted for by enhanced interactions among the binding forces of the gum molecules [25]. The viscosity also decreased with an increase in temperature (Figure 13.2a), confirming reports that the major effect of temperature on hydrocolloids is a decrease in viscosity [19]. The change in viscosity with temperature also indicates the possible thermal decomposition of hydrocolloids during heating. However, the mechanism of thermal decomposition of gums is unknown [10]. Therefore, the use of high operating temperatures is not encouraged in processes that involve hydrocolloids such as cashew gum [19]. The average viscosity of 1% cashew gum solution at 25 ∘ C was 10.03 mPa s, and the viscosity of gum arabic as reported by TIC Gums [29] is less than 5 mPa s at 1% solution. This, therefore, makes cashew gum a better thickening or stabilizing agent. Viscosities of cashew gums produced by mature trees were generally lower than those produced by young trees [28]. However, gums coming from different locations and environments were not significant. There were also differences in the viscosities of cashew

333

13 Cashew Tree (Anarcadium occidentale L.) Exudate Gum

25

Viscosity (cPs)

20 Savannah 25 °C

15

Savannah 70 °C 10 Transitional 25 °C 5

Transitional 70 °C

0 2.5 5 Concentration (%)

1

10

(a) 25

20 Viscosity (cPs)

334

Savannah rainy

15

Savannah dry 10

Transitional rainy Transitional dry

5

0 1

2

3

4

5

6

7

8

9

10

Concentration (%) (b)

Figure 13.2 (a) Effect of concentration and temperature on cashew gum viscosity and (b) effect of time of production on cashew gum viscosity.

gum produced at different times of the year. Those produced during the rainy season had lower viscosities than those produced during the dry season (Figure 13.2b). However, the differences were not significant. Storage of the gums for six months and above slightly reduced their viscosities. 13.2.6

Toxicity and Microbial Determination of Cashew Gum

Safety continues to be a matter of great concern to the consumer. Issues of safety include hazards and risks. A hazard is a source of danger such as microbial poisoning and allergic reactions, whereas a risk is a measure of the probability and severity of harm to human

13.2 Cashew Tree Gum

health. Safety is therefore the judgment of the acceptability of risk. A substance can therefore be considered safe if its risks are judged to be acceptable. The risk of exposure to a substance can be determined by identifying a hazard and determining the dose or amount of the substance at which there is the likelihood of the hazard occurring and finally determining the quantity of the substance to which humans are or could be exposed. All substances must be safe for use before marketing and thus must undergo the risk of exposure or toxicity assessment. Acute toxicity is a short-term study where test organisms are exposed to a substance for a short period of time to measure the concentration that will have a significant effect on them. Data from these tests can be used to screen or rank toxicity and to assess the potential for effects in the environment. Examination of rats fed with 5–30 g kg−1 body weight (b.w.) cashew gum for 30 days showed that the gum had no allergic or adverse effect on the rats. The test rats did not show any changes in movement, appetite, water intake, salivation, and urination [9]. They also did not show any symptom of diarrhea. The median lethal dose (LD50 ) for the gum was found to be more than 30 g kg−1 b.w. This indicates that the gum is not acutely toxic according to World Health Organization (WHO) Acute Hazard Rankings (Table 13.4) and also confirms that cashew gum presents no hazard for short-period exposure. Okoye et al. [31] also determined the lethal dose (LD50 ) of cashew gum to be more than 5000 mg kg−1 in rats. Acute toxicity studies on groups of rats fed with gum arabic in their diet for six days showed normal weight gain and food efficiency for the rats [32]. A similar observation was made in another study of cashew gum. The LD50 of gum arabic was in the range 8–18 g kg−1 b.w. as a bolus dose [33]. These observations suggest that although natural polysaccharides such as cashew gum are non-toxic, they are susceptible to microbial growth. Cashew gum has been found to have a very low microbial load. Work by Okoye et al. [31] showed that coliforms and other enteric gram-negative bacteria were absent in the gum. However, gram-positive bacteria, Bacillus spp., were present at a level of 66 cfu g−1 , which was below the accepted limits of 1000 cfu g−1 . This may be due to the presence of anacardic acid, which has been clinically proved to have anti-microbial properties against several microorganisms, including Escherichia coli and Helicobacter pylori [34], in the gum. Other studies showed that E. coli, Pseudomonas aeruginosa, and Staphylococcus aureus were not present in both crude and purified gums. However, Salmonella spp. was found in the crude gum but not in the purified gum. Both crude and purified gums were infected with fungi, but their growth was scanty on the purified gum plate Table 13.4 WHO Acute Hazard Rankings.

WHO toxicity classification

Rat LD50 (mg of chemical per kg b.w.)

Class

Description

Solids (oral)

Liquids (oral)

Ia

Extremely hazardous

2000

IV

Not acutely toxic

>2000

>3000

Source: Adapted from WHO [30].

335

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13 Cashew Tree (Anarcadium occidentale L.) Exudate Gum

compared to the crude gum plate, and this could be attributed to the purification process [15]. Kumar et al. [35] also reported that cashew gum was safe to use. Microbial determination of cashew gum by Gyedu-Akoto et al. [21] showed that the gum contained an average of 3.2 × 103 cfu ml−2 of total microorganisms and 465 cfu ml−1 of yeasts and molds, which can easily be destroyed by heating. Cashew gum was also found to be free from coliforms, which is an indicator of the presence of disease-causing bacteria, such as those that cause typhoid, dysentery, hepatitis A, and cholera. This indicates that cashew gum has no potential of being a health hazard to humans or animals in terms of its microbial status. Statistical analysis of data from the microbial determination of the gum showed no significant difference between gum from mature cashew tree and that from a young tree. This confirms the Walker [33] report, which says that from the toxicological point of view, differences between gums from different tree species are not significant. 13.2.7

Modification of Cashew Gum

Natural gums are commonly used in many industries due to their availability, sustainability, biodegradability, and biosafety [36]. Although they have very good functional properties, there are challenges associated with their applications, and these include uncontrolled rates of hydration, pH-dependent solubility, reduction in viscosity on heating and storage, and possible contamination with microorganisms. These challenges can be addressed by chemical and physical modifications of natural gums. Gums can also be modified for specific purposes. Chemical modification of gums includes acetylation, carboxymethylation, grafting, and cross-linking with other chemicals. Carboxymethylation of cashew gum using monochloroacetic acid as the etherifying agent increased its hydrophilic capacity and solution clarity, and made it more soluble in aqueous systems [17, 37]. Cross-linking of cashew gum using epichlorohydrin also reduced its swelling capacity [17, 38]. On the other hand, Abdulsamad et al. [39] reported that cross-linking cashew gum with a mixture of citric acid and glycerol improved the swelling, water absorption, and retention capacities. Oxidation of the gum increased its solubility, water-holding capacity, and uronic acid from 3.7% to 38% [8]. In another study, oxidation of cashew gum also increased its uronic acid from 7.2% to 36%, viscosity by 0.1 mPa s and reduced its thermal stability from 209 to 191 ∘ C [10]. Acetylation of cashew gum with acetic anhydride increased its viscosity and swelling capacity from 20.20 to 53.4 mPa and 10.9%–45.9%, respectively [40]. Grafting of gums modifies their swelling and film-forming properties. Cashew gum grafted with polyacrylamide using potassium persulfate as the chemical initiator and ultrasound energy produced a flocculant (CG-g-PAM) which had flocculation of 96% compared with the commercial flocculant Flonex-9045 [41]. Chemically modified gums known as semisynthetic gums have been found to be stronger emulsifiers and are less likely to undergo microbial growth.

13.3 Application of Cashew Gum in Foods Plant exudates are gums from various plant species obtained as a result of tree bark injury. They are normally collected as air-dried droplets [42]. They have been found

13.3 Application of Cashew Gum in Foods

to have many lucrative possibilities for industrialization. They have both food and non-food applications. Their non-food applications include pharmaceutical, cosmetic, lithographic, and offset preparations [5]. They are used extensively as adhesives and as sizing and finishing materials in the textile industry. In the food industry, they are used in confectionery, dairy products, snack foods, and bakery products. However, unlike other hydrocolloids, cashew gum has not been used extensively in the food industry, but some studies have been conducted on its utilization in food products to help promote its consumption. 13.3.1

Cashew Gum as an Encapsulating Agent

Encapsulation is a technique used to protect active food components from harmful environmental factors such as water, light, and oxygen. It also facilitates the delivery of active food components, such as converting liquid foods into dry particulates, and making food handling processes easy. Encapsulation of materials rich in volatile compounds by spray drying presents the challenge of removing water by vaporization without loss of odor and/or flavor components. Recent investigations into the use of cashew gum as a material for microencapsulation have been conducted by a few scientists within the food industry. Cryoconcentrated coffee extracts rich in odor components were used as a substrate core to evaluate microencapsulation with cashew gum. Biochemical, structural, and sensory evaluation of the microcapsules of the coffee extracts produced compared to those produced with gum arabic showed that both products have similar aroma protection, external morphology, and size distribution, suggesting that cashew gum is a suitable alternative to gum arabic for odor microencapsulation [43]. Evaluation of cashew gum for encapsulation of fish oil compared to conventional hydrocolloids was conducted based on the properties and oxidative stability of the spray-dried fish oil. The viscosity of emulsions produced with cashew gum was lower than that produced with gum arabic. The particle size of the microparticles produced with cashew gum was larger (29.9 μm) than those produced with the other materials. The cashew gum encapsulation efficiency reached 76%, and this was similar to that of modified starch but higher than the 60% value for gum arabic. Microparticles produced using gum arabic and cashew gums showed greater water adsorption when exposed to higher relative humidity. However, those produced using cashew gum were more hygroscopic, their encapsulation efficiency was higher, and surface oil oxidation was less pronounced [44]. A study involving an attempt to completely or partially replace a conventional hydrocolloid, maltodextrin DE10 (MD10), with cashew tree gum as a drying aid agent in spray drying of cashew apple juice was conducted by De Oliveira et al. [45]. The impact of the drying aid/cashew apple juice dry weight ratio and degree of replacement of MD10 with cashew gum on the ascorbic acid retention (AAR), hygroscopicity, flowability, and water solubility of spray-dried cashew apple juice powder was assessed, and cashew gum was shown to be a promising maltodextrin replacer and a more effective way of reducing the juice powder hygroscopicity. The adequate drying condition resulted in more than 90% of AAR and produced a powder with good flowing properties and water solubility. 13.3.2

Cashew Gum as a Coating Agent (Film-Former)

Attempts to replace gum arabic with cashew as a coating agent in the production of chocolate pebbles, a confection, were made by Gyedu-Akoto et al. [28], and they

337

338

13 Cashew Tree (Anarcadium occidentale L.) Exudate Gum

concluded that the optimum concentration of cashew gum solution for this purpose was 66.7% (w/v). Comparing this to the 100% (w/v) concentration of gum arabic solution normally used for pebbles production confirmed that cashew gum is a better thickening agent than gum arabic. Physicochemical analysis of pebbles with cashew gum showed that their moisture and sugar content (2.33–2.38 and 26.05–29.66, respectively) fell within the acceptable levels for chocolate pebbles [46], which are 1%–3% and 20%–30% for moisture and sugar content, respectively. Their microbial status also conformed to the internal specification of Cocoa Processing Company (a chocolate manufacturer in Ghana) for chocolate products. Their total microbial load and yeasts/molds were 3.0 × 102 and 0 cfu ml−1 , respectively. The total microorganisms were relatively lower for cashew-gum-based pebbles compared to gum-Arabic-based pebbles. However, they both contain no coliforms. Sensory analysis of the two products showed no significant difference. 13.3.3

Cashew Gum as a Gelling Agent

Studies on the use of cashew gum as a gelling agent in pineapple jam production and as a stabilizer in pasteurized cashew juice showed that it was possible to gel pineapple jam with cashew gum at 5%–10% concentration [47]. However, the optimum level of the gum for pineapple jam gelation was predicted to be 5% by using the response surface methodology. Visual observation of cashew juice after heat treatment showed that cashew gum had a clarifying effect on the juice instead of retaining sediments formed in suspension. The addition of cashew gum was found to cause more sedimentation in the juice, and these sediments settled after allowing the juice to stand overnight. The increase in the sedimentation may be due to the galacturonic acid component in its structure, since reports by Baker [48] state that the addition of base-solubilized polygalacturonic acid to fruit juices yields immediate and relatively complete clarification. 13.3.4

Cashew Gum as a Clarifying Agent

Clarification of cashew juice with cashew gum at a concentration of 4.762 g l−1 resulted in 78.0% clarity and reduced the total soluble solids and vitamin C contents of the juice by 6.7% and 25.8%, respectively, but did not have any effect on the total sugar content [20]. However, clarifying with gelatin at 2.349% concentration yielded 54.7% clarity and reduced the total sugar content, total soluble solids, and vitamin C content of the juice by 4.0%, 11.7%, and 26.2%, respectively, making cashew gum a better clarifier than gelatin. A study done by Gyedu-Akoto et al. [47] showed that the addition of different levels of cashew gum (0.00, 0.05, 0.10, 0.15, and 0.20) to cashew juice on the basis of the central composite design clarified the juice at all levels. Sensory analysis of the clarified juices showed that the addition of cashew gum caused more sedimentation than juice without the gum and also reduced the astringency of cashew juice. 13.3.5

Cashew Gum as a Fat-Replacing Agent

Dietary fat is a nutrient needed for a healthy lifestyle. However, high fat intake is associated with increased risk for obesity, cancer, high blood cholesterol, and coronary heart diseases [49]. To help consumers moderate their dietary fat intake, advances in food

13.4 Application of Cashew Gum in the Pharmaceutical Industry

science have allowed for the development of a wide variety of reduced-fat food products. Fat replacers are also developed to duplicate the taste and texture of fats in food [50]. In an attempt to maximize the use of cashew gum, its utilization as a fat replacer in baked doughnuts was studied by Gyedu-Akoto [51], and the results suggested that fat may be replaced by cashew gum in baked doughnuts up to 40%.

13.4 Application of Cashew Gum in the Pharmaceutical Industry Pharmaceutical excipients are substances formulated alongside the active ingredients of drugs. They are included in drugs for several purposes such as stabilization, bulking, enhancing solubility, and reducing viscosity. The selection of excipients depends on the route of administration of the drugs and dosage form, as well as the active ingredients. They are supposed to be pharmacologically inactive, non-toxic, and should not react with the active ingredients or other excipients in the drug. However, they form an essential part of the formulation of drugs. Natural excipients and their derivatives occur mostly in plant and animal materials. Although synthetic excipients have enjoyed a long history of use, their natural counterparts are non-toxic, stable, easily available, and cheap, and they also come with less regulatory issues compared to their synthetic counterparts [52]. One advantage of synthetic excipients over natural ones is that they can be produced to a certain specification because there is more control over the manufacturing process, but most natural-based polymers are not chemically identical because of the variability that exists in nature. For instance, changes in weather from one year to the next may cause slight variations in the structure and properties of natural materials. Such variability in natural excipients can be problematic for drug manufacturers because once their formulation has been approved by the Food and Drug Agency, it becomes difficult to change the formulation components or component levels that were used in the clinical trials [53]. However, this challenge can be overcome through the modification of these natural materials. 13.4.1

Cashew Gum as an Excipient

One of the emerging natural excipients in the pharmaceutical industry is the cashew tree gum. Several attempts have been made to incorporate this gum into the formulation of pharmaceutical products. Investigations by Kumar et al. [35] have shown that the functionality of cashew gum in cotrimoxazole granule and tablet formulation produced the best micrometric properties compared to those formulated with three standard binders, polyvinylpyrrolidone (PVP), gelatin, and corn starch . Development of unidirectional, bilayered, buccoadhesive tablets of curcumin has shown that cashew gum can be used as a polymer in the tablets [54]. The optimum formulation per batch was found to have 20% polymer concentration, 0.1% penetration enhancer, and 40 mg backing layer (ethyl cellulose). This was compressed at 2 tons cm−2 for 10 s. The formulated tablets were stable with respect to their physicochemical and in vitro drug release behavior over a period of 60 days at different temperatures and relative humidity. The kinetics of drug release was also found to be non-Fickian or anomalous diffusion [54]. Studies on the binding efficacy of cashew gum in tablet formulation in comparison with standard binders, acacia gum,

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and polyvinylpyrrolidone (PVP K-30) revealed that cashew gum at a concentration of 2.5% produced a paracetamol tablet of better mechanical strength and dissolution profile of a particular drug substance [55]. In this study, paracetamol granules were prepared with different concentrations of the gum as a binder by the wet granulation method. Evaluation of tablets prepared from the granules showed that formulations containing a minimum concentration of 2.5% cashew gum as binding agent showed short disintegration and fast dissolution with good physicomechanical properties. Crude cashew gum and its modified forms were used in the formulation of a sustained release delivery system with theophylline as a model drug [17]. The modified gums used were cross-linked cashew gum, carboxymethylated cashew gum, and carboxymethylated cross-linked cashew gum with gum-to-drug ratios of 1:1 and 3:1. The optimum formulations were identified using response surface methodology. The best and most stable formulation was found to contain cross-linked cashew gum with an epichlorohydrin-to-gum ratio of E/Gb = 0.15. The kinetic analysis of dissolution data showed a good fit in the Peppas equation, which confirmed an anomalous non-Fickian release mechanism for cross-linked cashew gum with theophylline. The mechanical and coating properties of cashew-gum-based films, using paracetamol as a model drug, was also investigated by Ofori-Kwakye et al. [56]. Free films used were cashew gum, cashew gum/hydroxypropyl methylcellulose (HPMC), and cashew gum–carboxymethyl cellulose (CMC), prepared by solvent casting and glycerol as a plasticizer. The cashew gum films were smooth, uniform, and transparent, while cashew gum/HPMC and cashew gum/CMC films lacked uniformity and surface smoothness, respectively. A film coating of 7.5% (w/v) cashew gum formulation to paracetamol tablet cores enhanced the mechanical strength of the tablets. However, film-coating the tablet cores did not significantly affect the disintegration and drug release properties of the tablets compared to the uncoated tablets. Cashew gum, when applied at 7.5% (w/v), could therefore be useful as non-functional film coatings for conventional solid dosage forms. Sustained release matrix tablets of diclofenac sodium formulated with xanthan gum and cashew gum together with the semisynthetic release modifier HPMC were studied by Obese in 2012 [57]. At different ratios of 100:0, 80:20, 60:40, 20:80, and 0:100 of xanthan:HPMC, xanthan:cashew, and xanthan:cashew:HPMC, the granules produced had good flow properties. All the physical characteristics of the formulated tablets using the granules fell within acceptable limits. The swelling index of the tablets containing only xanthan gum exhibited the highest swelling index followed by tablets containing xanthan and cashew gums in the ratio of 80:20. Overall drug release was found to be a complex mixture of diffusion, swelling, and erosion. The drug release profile of some of the tablets was similar to the reference drug (Voltaren Retard), with the others being slightly different from the reference drug. The results obtained showed that the gums and HPMC used individually could not sufficiently produce sustained release but when combined with various ratios produced effective sustained release [57]. 13.4.2

Pharmacological Studies on Cashew Gum

Pharmacology is the study of the effect of drugs on the body. In this case, cashew gum is used as a drug in the control of diseases and not as an excipient. Cashew gum has been exploited by locals since ancient times for multiple applications, including the treatment

13.4 Application of Cashew Gum in the Pharmaceutical Industry

of diarrheal diseases. Studies have shown that cashew gum administered orally to rats with castor-oil-induced diarrhea at 30, 60, and 90 mg kg−1 body weight (b.w.) had a significant antidiarrheal effect on the rats at all levels of dosage [58]. It also inhibited the total amount of stool and diarrheal stools. The 60 mg kg−1 dose of cashew gum exhibited excellent antidiarrheal activity, reduced the severity of diarrhea in rats, and decreased the volume of castor-oil- and PGE2-induced intestinal fluid secretion (enteropooling) significantly. In addition, similar to loperamide, a standard drug with a dose of 5 mg kg−1 b.w., cashew gum treatment reduced the distance traveled by a charcoal meal in the 30-minutes gastrointestinal (GI) transit model by interacting with opioid receptors. In cholera toxin-induced secretory diarrhea, the 60 mg kg−1 dose of cashew gum significantly inhibited the intestinal fluid secretion and decreased chloride ion loss using cholera toxin-treated isolated loops model of live mice. This was done by competitively binding to cholera toxin-GM1 receptors in the mice. The antidiarrheal activity might be explained by the capacity of cashew gum to inhibit gastrointestinal motility, thereby reducing the accumulation of intestinal fluid and the secretion of water and chloride ions in the lumen of the intestine. The use of cashew gum in the reduction of blood pressure in spontaneously hypertensive rats was studied by Mothe et al. [59]. The blood pressure of rats fed with cashew gum was reduced by 20%. There was also a 4% decrease in the ratio of the left ventricular mass and heart mass of the rats treated with the gum. This indicates that cashew gum could help retard hypertrophy in the rats. Tannins, anacardic acid, and Cardol, which are known to be the active ingredients in the cashew fruit for its medicinal properties, may also be present in the gum [36]. The long-term use of non-steroidal anti-inflammatory drugs is associated with gastrointestinal (GI) lesion formation. A study on the protective activity of cashew gum on naproxen (NAP)-induced GI damage was therefore conducted by Carvalho et al. [60] using male Wistar rats. Results showed that pretreatment with cashew gum reduced the macroscopic and microscopic damage induced by the NAP. Cashew gum significantly attenuated NAP-induced alterations in myeloperoxidase, glutathione, and malondialdehyde levels. Furthermore, cashew gum returned adherent gastric mucus levels to normal values. These results suggest that cashew gum has a protective effect against GI damage via mechanisms that involve the inhibition of inflammation and increasing the amount of adherent mucus in the mucosa. Cashew gum combined with water-soluble β-galactose and other oligosaccharides as well as proteins exhibited a high inhibitory activity of 88% against an implanted sarcoma 180, a solid tumor in mice [61]. In other words, cashew gum can be used for the prevention of cancer, and/or as an adjuvant with cancer chemotherapy drugs, after the removal of a malignant tumor. More investigation should be done with cashew gum as there is a great need for clinical study in neoplasia treatments for humans. Other uses of cashew gum such as the construction of a kind of chromatographic matrix (hydrogel) have become a useful tool for modern biotechnology in underdeveloped countries [8]. It has been found to be an efficient method for the detection and elucidation of galactose-specific lectins. Sarubbo et al. [62] have also studied the partitioning of two proteins, bovine serum albumin (BSA) and trypsin, in an aqueous polyethylene glycol (PEG)–cashew gum system and found the system to be very effective.

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13.5 Conclusion Although it is a known fact that the cashew tree produces appreciable amounts of gum, studies have shown that much of it is produced during the dry season when the tree is under stress. Trees as young as four years can produce the gum. However, the age of the tree and its location do not affect gum production. Chemical stimulants have also been used to induce cashew gum production. Cashew gum conforms to the general organoleptic characteristics of gums by being tasteless, and whitish, yellowish, or brown in color. It also has a glassy, transparent, or translucent appearance. It has good physicochemical and rheological properties, contains an appreciable amount of proteins, and is a rich source of calcium, potassium, sodium, iron, and zinc, making it nutritious. Therefore, it can be used to promote good health through its industrial applications. Cashew gum has high viscosity compared to gum arabic and gels at a very high concentration. However, the viscosity reduces when the gum is heated and stored for a long time. Due to the limited supply and consequent sharp increase in the cost of traditional hydrocolloids, cheaper alternatives such as naturally occurring gums like the cashew tree gum have become very important. It has been shown from this review that cashew gum and its modified derivatives can be used as a film-former or coating agent, clarifier, thickener, drying aid, and gelling agent in the food industry. It can also be used as a fat replacer in baked goods, as an encapsulation material, as well as an emulsifier. Studies reported in this chapter also indicate the potential pharmaceutical uses of cashew gum. The wide range of potential applications of cashew gum may be an important factor for the economic and social growth of developing countries that produce cashew, and it may provide an alternative to the synthetic or semisynthetic polymers currently used in the pharmaceutical industry. Purification and chemical modifications of cashew gum increase its solubility as well as its physicochemical and rheological properties, thus making purified and modified cashew gum important in its applications.

13.6 Future Trends There is no doubt that cashew gum has a wide range of applications. However, new applications of the gum in the pharmaceutical industry as a thickener and suspension agent as well as applications as a functional food due to its significant amounts of protein, mineral, trace elements, and dietary fiber require multidisciplinary research efforts to improve our knowledge of the products that can be developed from the gum. Improvement in production technologies and studies on the impact of agronomic practices on cashew gum production as well as other rheological properties such as non-Newtonian flow behavior, thixotropy, and the viscoelasticity of cashew gum are also required. In the personal care industry, many manufacturers are trying to replace synthetic hydrocolloids with natural ones in order to satisfy consumer demand. This is due to the current trend of moving away from the more chemical-sounding products to food ingredients that are more familiar to the consumer. Therefore, studies on the application of cashew gum in the personal care industry are required as well as the establishment of a network program to help disseminate the information gathered on cashew gum utilization and also to facilitate the concerted action of researchers, government, and industry.

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14 Brea Tree (Cercidium praecox) Exudate Gum María A. Bertuzzi and Aníbal M. Slavutsky Instituto de Investigaciones para la Industria Química, Facultad de Ingeniería, Universidad Nacional de Salta, CP: A4408FVY Salta, Argentina

14.1 Introduction Brea gum is an exudate gum from the brea tree, also known as “palo verde” or “chañar brea.” The accepted name of this species is Parkinsonia praecox (Ruiz & Pav.) Hawkins or Cercidium praecox (Ruiz & Pav.) Harm, as a synonym. This species belongs to the Fabaceae family and grows from northern Patagonia to the southern United States of America, mainly in tropical and subtropical arid habitats. The scientific name Cercidium, from the Greek “kerkidion,” refers to the similarity between the fruit and a weaving shuttle, and praecox means “precocious” [1]. The small trees or large shrubs reach up to 8 m tall (Figure 14.1). The leaves develop after the first rains and shed shortly afterward. Thus, the tree depends on the photosynthetic activity of the light green bark of the stem and twigs. Generally, at each knot, there are solitary thorns up to 2 cm in length. The leaves are small, composed, and characterized by sprouting after the beginning of flowering. The flowers appear in spring and summer, and the tree fructifies in late summer and early autumn [2, 3]. This species has a deep and strong root system that allows it to grow on rocky slopes. Brea is a colonizing species of degraded environments, constituting the native vegetation of the arid and semi-arid zones of America. Intensive grazing and unsustainable forest use in some subtropical arid and semi-arid regions of South America have led to the degradation of soils, favoring the establishment of this species [4]. The desertification of soils also generates an important social impact affecting the economy of the region. Brea wood decomposes fast, so it has no use as wood or coal. Nevertheless, the plant exudes a water-soluble gummy exudate, naturally or through wounds in its trunk or main branches (Figure 14.1). This exudate has similar characteristics to gum arabic, produced by species of the genus Acacia in African countries, which has applications as a thickener in food and pharmaceutical products, and adhesives, among other uses. Therefore, brea gum, as non-wood forest product, is a sustainable productive alternative for the inhabitants of these regions, allows diversification of production, and a sustainable use of the environment by vulnerable rural communities.

Emerging Natural Hydrocolloids: Rheology and Functions, First Edition. Edited by Seyed M.A. Razavi. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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Figure 14.1 Brea tree and branch with exudate.

Coirini et al. [5] studied the conditions of gum extraction and concluded that the best yield was obtained from trees with trunks between 13 and 18 cm in diameter. The authors recommend that to favor the extraction of the gum, helical cuts should be made on the stem with a saw. A direct relationship between productivity and wound size was found, and a 25–30 cm2 incision area was suggested. However, the adopted criterion is that the wound size should not excessively weaken the tree. The gum begins to flow within one to three days after making the incision. After 12 or 15 days, the secretion decreases but does not stop for two months, allowing the collections of 15 to 30 days to be separated. An adult tree can produce between 100 and 300 g of brea gum per year [6]. The production and composition of the brea gum are complex and varies to some extent depending on the geographical origin, climatic conditions, and age of the trees. From an anatomical point of view, the gum comes from the cells of the parenchyma surrounding the vessels of the secondary xylem and causes total or partial occlusion of its lumen, all produced by some traumatism [7]. The recently secreted gum is pale golden yellow, with semi-liquid consistency, and weakly sweetened. As the gum solidifies in contact with air, it takes on different colorations until it reaches a reddish yellow at the point of higher consistency. After solidification, tears are harvested from the trees. The tree produces gum throughout the year, although with significant differences depending on the season. Productivity variation throughout the year is related to the vegetative activity of the tree. The lowest harvests were found during the winter months and the highest during the hot and dry season. Heavy rains wash away virtually all production [6]. The gum is manually collected and pre-cleaned to remove the bark, sand, and other impurities. Some simple treatments such us manual cleaning, sieving, and grinding are common before the sale. The gum is easily soluble in water, forms a homogeneous solution, viscous and clear, and is insoluble in organic solvents [8]. Rural people have traditionally used brea gum as a “woodland candy” since pre-Columbian times without harmful consequences. Von Müller et al. [9] reported a toxicological evaluation of brea gum in mice. Their results suggest that feeding mice at levels up to 5% of brea gum does not produce any toxicological effects, supporting its potential use as a food additive for human consumption. Thus, in August 2013, brea

14.2 Physicochemical Characteristics

gum was authorized as a food additive in Argentina, with its incorporation into the Argentinian Food Code [10]. Currently, the world market for vegetable gums used as food additives is led by gum arabic, a non-wood forest product obtained from Acacia Senegal (L.) Willd., also known as “hashab.” Sudan produces around 90 000 tonnes per year, which is mainly exported to Europe and the United States of America [11, 12]. Small-scale farmers are the main producers of gum arabic in the traditional rain-fed farming areas, both from natural forests, and small plantations. It represents an income diversification strategy to mitigate crop failure. For these populations, which are among the poorest and most vulnerable in Sudan, gum arabic contributes up to 50% of their total cash earnings. Over the past five years, demand for gum arabic has increased by an estimated 2.5% annually and is expected to continue growing at a similar rate. Major drivers of this growth include new product development and the substitution of synthetic thickeners, because consumers are looking for natural ingredients with clean labeling. The countries with the largest food and drink industries are also the largest markets for gum arabic. These markets are strongly dependent on a politically unstable country, such as Sudan. In 2015, Europe, mainly France, imported approximately 50 000 tonnes of gum arabic from Sudan and then re-exported it. Sudan dictates the global prices for gum arabic, and in the past decade, political unrest in Sudan has caused strong price fluctuations. The prices for cleaned and spray-dried gum arabic from Acacia senegal varies between 2700 and 8000 dollars per ton. Currently, prices amounted to 3200 dollars per ton [11]. All this is a very favorable scenario for the introduction in the market of brea gum, as a replacement of gum arabic. Von Müller et al. [13] estimated a price of 1500 dollars per ton for brea gum (without refining) produced in the arid Chaco from Córdoba, Argentina, while Alesso et al. [6] reported a price between 1000 and 2500 dollars per ton for raw brea gum, recollected in arid Chaco from Santiago del Estero, Argentina. These prices demonstrate the competitive advantage of brea gum over gum arabic, showing its potential as a non-wood forest product of secondary forests. Brea tree belongs to the Fabaceae or Leguminosae family. Therefore, in addition to the exploitation of the exudate from the trunk, its seeds can be used for oil extraction. Ortega-Nieblas et al. [14] studied the oxidation process of raw and refined oils extracted from seeds of Cercidium praecox during 122 days storage at room temperature. Corn and soybean oils were used as controls. Crude oil of brea seeds showed similar oxidation indexes to those for the corn raw oil and lower than those of soybean raw oil. Refined oils exhibited a similar performance. The rancid odor was detected after 5 days storage in soybean oil, while brea oil exhibited this odor after 62 days. These results indicate that legume seed of brea tree could be a good alternative as a source of oil.

14.2 Physicochemical Characteristics 14.2.1

Compositions

Gum is harvested from the tree as nodules. The crude exudate of brea gum is purified by dissolution in water. After removing the insoluble material (bark, sand, and other

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Table 14.1 Compositions of brea gum reported by different authors (g kg−1 ). Composition

Anderson et al. [17]

Bertuzzi et al. [16]

Castel et al. [18]

De Pinto et al. [8]

Moisture

127

135 (±5)

48.3 (±1.3)

130.8 (±27.9)

Protein

106

62 (±2)

75.2 (±0.9)

44 (±12.3)

48

38 (±3)

42.3 (±0.9)

Ash Fat

—

—

1.1 (±0.1)

42.5(±9.5) —

Table 14.2 Monosaccharide composition of brea gum (% dry weight). Monosaccharide

Anderson et al. [17]

Cerezo et al. (1969)

D-Xylose

32

58

59

5

16

16

D-Glucuronic acid

—

18

4-O-methyl-Glucuronic acid

—

8

Galactose

29

—

—

Galacturonic acid

34

—

—

L-Arabinose

De Pinto et al. [19]

25

contaminants) by decantation, centrifugation, or filtration, the solution is subjected to drying in order to separate the gum from the solvent. Depending on the drying method, a subsequent grinding and sieving may be required. The composition of brea gum exhibits variability depending on botanical and agronomical features. The precise chemical and molecular structure of the gum differs according to the botanical origin, soil, and climate characteristics, among others, and these differences are reflected in some of the analytical properties of the gum. Some authors have studied the composition of brea gum collected from brea trees in different places in America such as Argentina, Venezuela, and México [8, 15–17]. They found an acidic heteropolysaccharide formed by L-arabinose, D-xylose, D-glucuronic, and 4-O-methyl-D-glucuronic acid, which also contains between 4% and 10% of proteins and around 4% of ash (Table 14.1). According to Anderson et al. [17] and Bertuzzi et al. [16], brea gum has a comparatively high amount of calcium and magnesium and low sodium, in relation to other similar gums. Cerezo et al. [15], de Pinto et al. [8, 19], and Anderson et al. [17] analyzed the carbohydrate fraction of brea gum. Their studies showed a main chain that is a β-(1,4)-linked d-xylan backbone with short branches, possibly (1,2)-linkages, containing residues of D-xylose, L-arabinose, and D-glucuronic acid. Anderson et al. [17] found galactose and galacturonic acid, instead of glucuronic acid and its methyl ether (Table 14.2). The aqueous solution of brea gum is levorotatory. Polysaccharides of brea gum are divided into two fractions. The first fraction (84%) is a polysaccharide of 2.79 kDa molecular mass, and the second fraction (16%) forms a polysaccharide–protein complex with a molecular mass of 1.92 × 102 kDa. In addition, there is a set of proteins with molecular masses ranging from 6.5 to 66 kDa [20].

14.2 Physicochemical Characteristics

The amino acid composition of proteins present in brea gum contains alanine, aspartic acid, hydroxyproline, leucine, threonine, serine, glutamic acid, valine, lysine, glycine, histidine, phenylalanine, isoleucine, and methionine, in descending order of quantity [17]. In native conditions, protein forms aggregates through disulfide bridges [20]. Proteins and carbohydrate–protein complexes are responsible for some of the most relevant gum functionalities, such as interfacial stabilization through hydrophobic protein groups acting as cleavage points to form viscoelastic films at interfaces [20]. Brea gum exhibits a particularly high amount of protein compared to other gums, which are almost solely made up of polysaccharides. This hydrocolloid has three times more protein than gum arabic, which contains between 1.5% and 2.6% of proteins [20, 21]. Some authors suggested that a higher protein content favorably affects the interfacial properties, producing better emulsifying properties [22, 23]. Brea gum is amber color, has semi-liquid consistency, and a faintly sweet flavor. It is highly soluble in water. Solutions are homogeneous and exhibit an acidic character. The natural pH of brea gum is around 4 (3.9–4.3), resulting from the glucuronic acid residues. Considering that brea gum has been proposed as a replacement for gum arabic, it is relevant to describe its main characteristics of the latter. Gum arabic is a complex slightly acidic polysaccharide, obtained from the stems and branches of Acacia senegal. The highly branched backbone of 1,3-linked galactopyranosyl residues are substituted by arabinose, galactose, rhamnose, glucuronic acid, and its methyl ether. This hydrocolloid also contains around 2% of proteins, forming an arabinogalactan–protein complex, and cations like calcium, magnesium, and potassium [21, 24]. The gum is highly soluble in water and insoluble in ethanol. It forms solutions over a wide range of concentrations without becoming highly viscous. The combination of high solubility in water and low viscosity confers on gum arabic its highly valued emulsifying, stabilizing, thickening, and suspending properties. Its main areas of application are food, pharmaceutical, and technical (adhesive) uses [21, 25]. 14.2.2

Color

Color attributes are of prime importance because they directly influence consumer acceptability. The vision sensations sent to the brain create the three dimensions of color judgment response that is known as the three-dimensional color space. In the CIE Lab system, these dimensions are expressed as L*, related to lightness varying from black (zero) to white (100), and the other two related to chromaticity, a* from green (−a*) to red (+a*), and b* from blue (−b*) to yellow (+b*). The color of gum solution is often difficult to predict from the color of tears or powder. The size and conditions of the lumps and powder affect judgment considerably. An appropriate color comparison can then be made in solutions of defined concentrations. The color of brea gum solutions at different concentrations between 1% to 28% w/v was studied. Small changes in a* values (+7 to +17) were observed, whereas b* values (+8 to +77) increased significantly with the increase in the brea gum content (1% to 28%). The decrease in L* values (60 to 34) showed a decrease in the solution luminosity of the solution with increasing concentration [16]. These findings suggest a net increase in amber color and a decrease in the brightness of the solution with increasing brea gum concentration. These results are in agreement with data reported by Rao et al. [26],

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14 Brea Tree (Cercidium praecox) Exudate Gum

where chitosan films were prepared with different proportions of guar gum. They found a net increase in yellow-brown color because of incorporation of guar gum. They also reported that the increase in the concentration of guar gum in the film resulted in a significant decrease in L*. Despite this, the influence of the color of gum powder or solution could be insignificant when it is incorporated into different products. López et al. [27] studied the effect of incorporation of brea gum in fresh bread and observed that the addition of 1% of brea gum to a basic bread formulation does not produce significant differences in the color of the final product. 14.2.3

Density

The solution density can be determined by using pycnometers or buoyancy-type densitometers at a constant temperature. Temperature and brea gum concentration affect the solution density. Increasing temperature decreases the solution density within the temperature range (25–50 ∘ C) and concentration range (0.0–1.5%) studied. Other hydrocolloids show a similar trend. The decrease in solution density with temperature is due to the increase in specific volume caused by the rupture of the hydrogen bonds of the associated polymer molecules in the presence of water molecules [28]. Besides, the solution density increases linearly with gum concentration until saturation values (Figure 14.2). This linear relationship between density and brea gum concentration was maintained even at high concentrations. Brea gum solutions exhibited density values similar to that exhibited by other common hydrocolloids in the temperature range studied. At 1% polymer concentration and 25 ∘ C, the density of guar gum is 1.0014 g mL−1 , sodium alginate is 1.0029 g mL−1 , and hydroxypropyl methylcellulose (HPMC) is 1.0002 g mL−1 [28].

14.3 Functional Properties Gums are used as a thickening, gelling, emulsifying, and stabilizing agents because of their ability to alter the rheological properties of the solvent in which they are dissolved, 1.09

1.07 Density (g mL–1)

352

1.05

1.03

1.01

0.99 0

10 20 Brea gum concentration (%)

30

Figure 14.2 Solution density as a function of brea gum concentration at 25 ∘ C.

14.3 Functional Properties

usually water. Changes in viscosity occur because of the hydrodynamic volume of these high-molecular-weight polymers and the interactions between polymer chains when gums are dissolved or dispersed [29, 30]. These properties have been exploited for their functionality in food systems, including textural attributes and mouthfeel [21]. 14.3.1

Solubility

Solubility is the capacity of a material (solute) to dissolve in a solvent. Gum solubility is an important factor that determines the applications of the gum. Brea gum is highly soluble in water, and its solubility increase with increasing temperature. The rate of gum solubilization depends on particle size and temperature. The high surface tension of very small particles hinders dissolution, as do low temperatures. In aqueous solutions, saturation occurs at 12.8% of brea gum at 5 ∘ C, 28.8% at 25 ∘ C, and 33.0% at 45 ∘ C [16]. Similar behavior was exhibited by other gums like guar gum, alginate, and gum arabic. Generally, other gums cannot exceed 5% concentration in water because of the high viscosity developed (e.g., carboxymethyl cellulose, and κ-carrageen). This characteristic property of brea gum makes it useful for applications where a high solid content is required. However, brea gum powder is insoluble in alcohols like glycerol and ethanol, vegetal oils, and organic solvents such as hexane, acetone, and petroleum ether [16]. Mantell [31] reported that gum arabic was also insoluble in organic solvents. 14.3.2

Surface Properties

The interfacial properties of polymers solutions can be studied through surface tension analysis. The formation and stabilization of foams and emulsions depend on this property. The surface tension of water was significantly reduced by brea gum addition. The surface tension decreased from 72 mN m−1 (pure water) to 51.75 mN m−1 , when hydrocolloid concentration in water solution reaches 5% (Figure 14.3). For higher 75

Surface tension (mN m–1)

70

65

60

55

50

45 0

2

4 6 Concentration (%)

8

10

Figure 14.3 Surface tension as a function of the concentration of brea gum solutions at 25 ∘ C.

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14 Brea Tree (Cercidium praecox) Exudate Gum

concentrations, the surface tension remained practically unaltered, showing that the critical micelle concentration was reached at 5% of brea gum [16]. Klein et al. [32] reported that the surface tension of aqueous solution of gum arabic at 5% concentration was 51.7 mN m−1 , while 5% whey protein isolate reduced the surface tension to 47.8 mN m−1 . They also observed that greater concentration did not show any further reduction in the surface tension of water. 14.3.3

Rheological Properties

Brea gum, as well as gum arabic, exhibits exceptional behavior between vegetal gums because of the high solubility and low viscosity of their solutions. This ability to form highly concentrated solutions contributes to the emulsifying and stabilizing properties of these gums. These unusual characteristics, when compared to those exhibited by other similar-molecular-weight polysaccharides, are related to the branched and more compact molecular structure of brea gum. The rheological properties of brea gum solution are affected by system state variables such as temperature and polymer concentration. The Ostwald viscometer was used to study the effect of temperature (25–50 ∘ C) and brea gum concentration (0%–1.5%) on kinematic viscosity. It was found that the kinematic viscosity of brea gum solution increases with concentration and decreases with temperature. Besides, a more marked effect of temperature on solution viscosity as the concentration increases was detected. Brea gum solution displays a kinematic viscosity between 0.72 and 1.63 cm2 s−1 for gum concentrations between 0.2% and 1.5% at 25 ∘ C. At a brea gum content of 1%, the kinematic viscosity falls from 1.44 to 0.94 cm2 s−1 when the temperature rises from 25 to 50 ∘ C [16]. The Mark–Houwink parameters show that the hydrocolloid acquires a spherical form in water solution. The intrinsic viscosity of brea gum solutions at 25 ∘ C is 52.7 mL g−1 and, the average molecular weight is 6.28 kDa [33]. The viscosity of brea gum solutions of higher concentrations was measured using a rotational rheometer. It was observed that brea gum concentrations lower than 10% and shear rates up to 100 s−1 produce Newtonian behavior, and viscosity values do not depend on the shear rate [16]. William et al. [34] reported low viscosity even at high concentrations of gum arabic solutions, but at a concentration above 30%, the viscosity of gum arabic solutions increases exponentially. Figure 14.4 represents the viscosity of different hydrocolloids, measured at 100 s−1 , as a function of polymer concentration. Our data are compared with those reported by Glicksman [35] for starch and gum arabic, at the same temperature. Brea gum exhibits similar viscosity values than gum arabic in the concentration range studied. The viscosities of gum arabic and brea gum are notoriously lower than those of gelatinized starch solutions and much lower than those of other vegetal gums like gum tragacanth or gum ghatti. Owing to the compact and branched structure, and therefore, small hydrodynamic volume, brea gum solutions are characterized by a low viscosity, allowing the use of high gum concentration. It could be of interest in some applications. The effect of pH on the viscosity of brea gum was studied at 20% concentration and 25 ∘ C. The natural pH of brea gum was between 3.90 and 4.30, resulting from the glucuronic acid residues. The pH of polysaccharide solution affects its viscosity behavior. Acid polysaccharides exist in aqueous solutions in the form of macro-ions, and

14.3 Functional Properties

Viscosity (mPa.s)

100

10 Starch Gum arabic Brea gum

1 0

2

4 6 Concentration (%)

8

10

Figure 14.4 Apparent viscosity as a function of hydrocolloid concentration measured at 100 s−1 and 25 ∘ C.

their charge depends on the pH. The coil dimension of these polyelectrolytes may be expanded by electrostatic repulsions or contracted by electrostatic attraction between chain segments. The addition of acid or alkali modifies the solution viscosity because of the changes in the electrostatic charges on the macromolecule. At the natural pH (around 4), the viscosity of brea gum solution reaches a maximum. At lower pH values, the reduced ionization of acid residues (mainly glucuronic acid) results in a more compact polymer volume, a decrease in the hydrodynamic volume, and thus a decrease in solution viscosity. Above pH 4, additional alkali raises the ionic strength of the solution, which in turn masks the repulsive electrostatic charges and regenerates a compact conformation similar to an acidic condition, lowering the viscosity. William et al. [34] reported the same behavior for 20% gum arabic solution, which exhibited a maximum viscosity at around pH 5.0–5.5. 14.3.4

Foaming Properties

A foam is a coarse dispersion of gas in a liquid, most of the phase volume being gas, with the liquid in thin sheets called lamellae between the gas bubbles [36]. The foaming properties can be described in terms of foam expansion (FE) and foam capacity (FC). FE is the percentage in the volume of foam formed, related to the initial liquid, and FC is the percentage in the volume of liquid incorporated into the foam. Foam formation involves three stages. First, the soluble hydrocolloid (proteins or carbohydrate–proteins complexes of brea gum) diffuses to the air–water interface, becomes concentrated, and reduces the surface tension. Second, macromolecules located at the interface orientate polar moieties toward the water and nonpolar groups toward the air. Third, hydrocolloid molecules interact, forming and stabilizing the film around the bubbles. Polypeptides can interact to form a film with possible partial

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denaturation and coagulation [37]. Thus, foaming ability strongly depends on brea gum concentration. It was observed that FC and FE increase up to 5% of brea gum concentration and then drop sharply. FE increases from 49% to 99% when the brea gum concentration rises from 1% to 5%. After that, FE falls to 51%, when the hydrocolloid concentration reaches 10%. Similarly, FC increases from 650% to 1075% when brea gum content rises up to 5%, and then drops to 475% when the gum concentration reaches 10%. These results evinced that a 5% brea gum content is the critical micelle concentration [16]. Initially, when foams are formed, the air cells are spherical and the lamella is thick with the large amount of solution contained in them. As time passes, the liquid drains from the foam, the lamella thins, and the air cells pack closer and assume polyhedral shapes. Drainage of fluid from the lamella is the main destabilizing force as it allows disproportionation, and large cells grow at the expense of small ones. As the brea gum concentration increases up to 5%, the foam density also rises, and the size of the air cells decreases. The liquid content of the freshly prepared foam increases with brea gum concentration, resulting in thicker lamellas as higher brea gum concentrations are used [16]. Ostwald ripening contributes to foam instability during aging. This involves smaller bubbles shrinking and disappearing at the expense of the growth of bigger bubbles. The thermodynamic driving force for this process is the difference in chemical potentials of molecules in the smaller and larger bubbles [38]. After 24 h, the solution volume retained in the foam is approximately 35% of the volume retained initially when 5% of brea gum is used. For higher concentrations, the drainage of the fluid increases progressively. In foams formed with 10% brea gum solution, after aging, the foam contains 26% of the liquid volume retained into the freshly prepared foam. Foams prepared with 20% brea gum solution contain only 10% of the solution incorporated into the fresh foam, after 24 h of drainage. The Ostwald ripening phenomenon is observed more clearly in high-concentration solutions. These results are consistent with the reduction in FE and FC for concentrations above 5% [16]. The surface properties of brea gum solutions are affected by nanoclay addition because nanoparticles also absorb at the interphase and interact with the hydrocolloid. The effect of the incorporation of montmorillonite (MMT) as nanoclay on the surface tension and FC of 10% brea gum solutions was studied by adding MMT in concentrations ranging between 0% and 5% w/w of the polymer [39]. The results indicate a reduction in FC of brea gum/MMT solutions as the MMT concentration increases. This could be explained by the increase in surface tension of gum solutions (from 51.75 to 62.15 mN m−1 ) caused by the increasing MMT content. Brea gum has around 7% proteins in its composition that are considered surface-active colloids in foam stabilization. Thus, there may be interactions between brea gum and MMT or competitive adsorption on the foam surface, leading to an antagonistic effect on foam stability. Moreover, when brea gum–MMT solution was shaken and aged, the formation of a stable gel was observed. This gel consists of a three-dimensional structure capable of capturing water in its interior. These results provide evidence about the capacity of MMT to interact with the polymeric matrix, and they prove that a structure with greater resistance and stability was formed [39]. Zhang et al. [40] found a synergistic effect with a nonionic surfactant and Laponite, and an antagonistic effect using silica in concentrations lower than 8%.

14.3 Functional Properties

14.3.5

Emulsifying Properties

The emulsions are widely used in the formulation of food, pharmaceutical, and cosmetic products. Moreover, in microencapsulation technology, emulsification is one of the important steps. The emulsion stability and droplet size are highly relevant in the retention of flavors and volatile compounds in microencapsulation by a spray dryer. Most hydrocolloids can act as stabilizers of oil-in-water emulsions, but only a few can act as emulsifiers. The latter functionality requires substantial surface activity at the oil–water interface, and hence the ability to facilitate the formation and stabilization of fine droplets during and after emulsification [38]. gum arabic and brea gum form a polysaccharide–protein complex that has been shown to be responsible for the interface activity and the emulsifying properties of these gums. The proteinaceous components of these complexes would embed in the oil phase, while the carbohydrates would extend out of the surface into the aqueous phase [41, 42]. When the proteinaceous part is removed, the gum tends to lose its surface activity and emulsification capability [43]. In the case of gum arabic, only a small part of the gum mixture is responsible for its activity, and therefore large amounts of gum are required to obtain stability. Brea gum has three times more protein than gum arabic, and so should exhibit a similar increase in emulsifying capacity. The protein diffuses, adsorbs on the surface, reduces the interfacial tension, and provides an interfacial barrier that offers protection against coalescence. The adsorption process is rapid under stirred conditions or at high protein concentration. Protein must unfold to a certain degree and reorient at the interphase, with polar groups directed toward water and the nonpolar groups directed toward oil. A continuous film is formed because of polypeptides’ protein–protein interactions, and associations through electrostatic, hydrophobic interactions, and hydrogen bonds between protein and polysaccharide components. It appears that the spheroidal shape of these gums together with the proteinaceous portion attached to the polysaccharides facilitate alignment and close packing of the gum at the oil–water interface. Spatial separation of the relatively hydrophobic portions of the gum molecule (i.e., methyl groups) from the hydrophilic hydroxyl and ionic regions appears to have a significant effect on its surface activity [44]. In the same sense, Castel et al. [20] indicated that the polysaccharide–protein complex present in the brea gum molecular structure is responsible for their high interfacial activity and good emulsifying properties. Besides, the low pH of brea gum solution and high ionic strength is beneficial for protein emulsification properties, because it favors its unfolding in the interface. Oil-in-water emulsions in the ratio 1:4 were formulated with brea gum solutions of different concentrations in the range 1%–20% w/w. The emulsion was prepared using a homogenizer at 5000 rpm for 5 min [16]. Emulsions show a decrease in droplet diameter and an increase in droplet number with increasing brea gum concentration up to a limit of 5%. However, at higher gum concentrations, the number of droplets decreases, and the droplet size increased sharply. 5% of brea gum was the emulsifier concentration required to produce the minimum mean droplet size (maximum surface area per oil volume unit). Castel et al. [22] reported that an oil-in-water emulsion prepared with brea gum in the ratio 1:9 showed a droplet size distribution similar to that of the emulsion stabilized with gum arabic at the same concentration. But, according to these authors, the brea-gum-based emulsion was more stable than the gum arabic emulsion, possibly due

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14 Brea Tree (Cercidium praecox) Exudate Gum

to the higher viscosity of the brea gum emulsion. Nevertheless, considering that there are no major differences between the viscosities reached by both gums at that concentration, but there are important differences in the protein content in both, it is therefore more likely that the greater emulsion stability of brea gum is caused by its higher protein content. For his part, Dickinson [38] indicated that a 10% of gum arabic is necessary to reach the minimum droplet diameter in an emulsion of oil-in-water of 1:6 and pH = 3. This concentration of gum arabic is twice that required to reach the minimum droplet size for a 1:4 O/W emulsion with brea gum. Wareing [29] reported that at least 12% of gum arabic is necessary to obtain 1:4 O/W emulsion, confirming that the greater protein content of brea gum is responsible for its emulsifying properties. Moreover, the rheological characterization of brea gum solution indicates that the solution viscosity increases with increasing brea gum concentration. Thus, a high concentration of brea gum can improve emulsion stability by retarding the destabilization, due to the increase in the viscosity of the aqueous phase [16, 22]. This is favored by the high solubility of brea gum in water. During aging, emulsion stability increase with brea gum concentration (up to 5% brea gum content). In this range, no observable changes are detected after 24 h storage at 25 ∘ C. Creaming is only observed after five days, and the volume of the top phase increases with brea gum concentration. At concentrations above 5% brea gum, despite the protective effect of the higher viscosity of the water phase, the higher size of oil droplets causes enhanced emulsion separation. A clear aqueous phase separation from the rest of the emulsion is observed after five days of storage. Castel et al. [22] studied the rheological behavior of an O/W emulsion of brea gum and gum arabic. They found that all emulsion flow curves exhibited shear-thinning behavior at low shear rates and a Newtonian plateau at high shear rates. They also reported that mechanical spectra show droplets tending to arrange themselves as a network in the emulsions, which was related to the high stability. Brea gum emulsion exhibited higher viscosity and stability than gum arabic emulsion at the same concentration.

14.4 Applications 14.4.1

Edible Film

An edible film or coating is defined as a thin and continuous layer of edible material formed on the food (coating) or separately and then applied to the food (film). Edible films and coatings generate a modified atmosphere by creating a semi-permeable barrier against O2 , CO2 , moisture, volatile compounds, and solute movement, thus reducing respiration, water and aroma loss, and oxidation reaction rates [45]. Many polysaccharides were used as film-forming materials, including exudate gums, such as gum arabic [46], and mesquite gum [47]. Some authors studied the formulation of edible films based on brea gum and their formation with the casting method [39, 48–50]. Generally, brea gum films exhibit good visual aspect, transparency, and amber color. Microscopic observation shows a dense and homogeneous structure without pores (Figure 14.5). In all cases, glycerol was used as a plasticizer of the film structure, in concentrations that ranged from 0% to 50% w/w based on polymer content. Brea gum films exhibit high solubility in water (80% at 25 ∘ C), and this parameter increases with temperature until full solubilization. Film wettability of brea gum studied through measurements of

14.4 Applications

Figure 14.5 Scanning electron microscopy (SEM) microphotography of brea-gum-based film.

contact angle indicates a variation from 71∘ to 67∘ as the glycerol content increases. This reduction in the contact angle manifests as an increase in wettability or the hydrophilic character of the film produced by the plasticizer, which has a hydrophilic nature [48]. Water sorption isotherms of films, measured at 25 ∘ C, show that at high-water-activity values (above 0.50), the film matrix swells, altering its structure and properties. This is shown by isotherm curves that exhibit a slight slope at low values of water activity, but take an exponential course at water activities higher than 0.5 (Type III of the Brunauer, Emmett, and Teller (BET) classification). Moreover, due to the high solubility of brea gum, film moisture content data above 0.75 of water activity cannot be obtained. At constant water activity, the moisture content of films increases with glycerol content. This increment is more pronounced above 15% of glycerol content [48]. Water vapor permeability remains practically constant up to 20% of glycerol content at a value of 8 × 10−10 gm−1 s−1 Pa−1 and then increases linearly, with a value of 25 × 10−10 gm−1 s−1 Pa−1 at 30% plasticizer content. Glycerol produces the plasticization on brea gum films by increasing chain mobility within the network, producing a decrease of tensile strength and an increase in elongation. Brea gum films are brittle due to the extensive intermolecular forces between the polymeric chains and require plasticization to improve their mechanical properties. Films without plasticization cannot be tested. Tensile strength decreases linearly with glycerol content varying from 12.4 MPa at 10% of glycerol to 2.3 MPa at 55% of a plasticizer. Film elongation is maintained almost constant at around 11% at glycerol concentrations ranging between 20% and 40%. Above 40%, the elongation increases up to 22% when the glycerol content reaches 55% [48]. Formulation of the antimicrobial edible film could be a convenient alternative to the addition of antimicrobials to foods, such as ham, hard, and semi-hard cheeses, with the advantage of concentrating the additive in the zone where the majority of the contamination takes place. In this direction, anti-Listeria active films were prepared using brea gum, as well as other biopolymers like gelatin and wheat gluten, as film matrix, and the enterocin produced by E. faecium CRL1385 at a concentration of ca. 500 UA cm−2 . Results showed that the gelatin and wheat gluten films with enterocin addition can control Listeria contamination. However, brea gum and the enterocin were found to be incompatible since antimicrobial activity was lost in this films [51].

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Various strategies of film formulation have been used to improve the properties of brea gum films, such as nanocomposite films and emulsion-based films. Spotti et al. [50] studied the formulation of emulsion-based brea gum films with the addition of beeswax (20% and 40% w/w of brea gum) and plasticized with glycerol at 0%, 20%, and 40%. This beeswax addition was devoted to improving water barrier properties, considering that the water vapor permeability of edible films plays an important role in food deterioration reactions. Emulsion-based films are homogeneous, without phase separation. Their transparency decreases with increasing beeswax concentration. Moreover, beeswax decreases the water solubility of films considerably because of its hydrophobic nature. Film solubility is reduced from 100% to 87% by the addition of 40% beeswax. Water vapor permeability decreases by almost half when 20% of beeswax is added and by even a little more when 40% of wax is used. Beeswax incorporation results in improvement of water vapor permeability, but at the expense of the mechanical properties of brea gum films. Tensile strength and elongation decrease from 7.6 to 1.5 MPa and from 8% to 3.5%, respectively, when beeswax is added [50]. These values make the film very difficult to manipulate. The functional properties of brea-gum-based films can also be improved by nanocomposite film formulation. MMT is a layered smectite clay mineral with a platelet structure. MMT consists of 1-nm-thick aluminosilicate layers surface-substituted with metal cations and stacked in 10-mm-sized multilayer stacks. Naturally occurring MMT is hydrophilic [52]. MMT can strongly interact with brea gum and reinforce the film structure. The clay content and dispersion feature of the MMT layers influence the properties of the nanocomposite films. Depending on the technique used for MMT incorporation, an exfoliated structure can be obtained in the film matrix. However, microscopic observation cannot detect any change in the dense film matrix when the exfoliated structure is formed. Electrostatic interaction between MMT and the hydrocolloid allows the formation of a network that strengthens the film matrix and reduces film solubility and water sorption capacity. Sorption isotherms of nanocomposite films are adequately fitted by the BET model. MMT decreases film water adsorption in all the water activity ranges. Then, the water content of the monolayer, calculated with the BET equation, reduces with MMT content at all temperatures, indicating a lower affinity to water. The entropy change and net isosteric heat of adsorption show a well-defined peak at monolayer water content, and in both cases indicate a more stable and ordered structure when MMT was added. Negative values of Gibb’s energy changes show the process spontaneity and indicate that the final structure of brea gum–MMT film has less affinity for water than brea gum films. The permeability depends on the diffusivity (the tortuosity of the pathway formed by the MMT nanoparticles) and solubility of the water molecules. The decrease in water vapor permeability with MMT content confirms the adequate dispersion of the nanoclay particles, causing the water molecules to move through a tortuous path as they diffuse through the polymer matrix. The incorporation of 5% MMT decreases the water vapor permeability from 8−10 to 3.7−10 gm−1 s−1 Pa−1 . Thus, MMT incorporation reduces the hydrophilic character of brea-gum-based films, and as a consequence their water vapor permeability [49]. MMT incorporation increases film opacity and affects the mechanical properties of brea gum–MMT films. The increase in Young’s modulus indicates that the film becomes more rigid, resistant to lengthening or stretching with increasing MMT content. The

14.4 Applications

tensile strength also increases from 7.45 to 20 MPa, accompanied by a loss in elongation from 19% to 9%. Gas permeability measurements indicate that MMT addition reduces not only film permeability to O2 , N2 , and CO2 , but also the permselectivity (CO2 /O2 ) of brea gum film from 0.93 to 0.58 [39]. Nanotechnology provides an alternative technique for the improvement of both the barrier and mechanical properties of brea-gum-based films. The brea gum–MMT nanocomposite films, with improved water vapor and gas barrier and mechanical properties, could be used as environmentally friendly food packaging materials for extending food shelf life. 14.4.2

Encapsulation

Encapsulation may be defined as the process of entrapping one substance (active agent) within another substance (wall material). In the food industry, an encapsulation process can be applied as a useful tool to improve delivery of bioactive molecules (e.g., antioxidants, minerals, vitamins, phytosterols, fatty acids), and living cells (e.g., probiotics) into foods. Capsules usually have diameters of a few nanometers to a few millimeters. Since encapsulating compounds are often in liquid form, different technologies based on drying like spray drying, fluid-bed coating, spray-chilling, spray-cooling, or melt injection are used [53]. Other techniques such as complex coacervation are also applied. Biomolecules are mostly used as the material for encapsulation in the food sector. Materials have to provide maximum protection of the active compound, to hold actives within the capsule’s structure during processing and storage, not react with the fill, and have good rheological characteristics at high concentration to facilitate the drying process [53]. The widest biopolymers used for encapsulation in food applications are polysaccharides, such as starch and its derivatives and plant exudates. The capability of brea gum and gum arabic to achieve high concentration and low viscosity make them highly suitable as an external phase for encapsulation. Gum Arabic showed better efficiency as the encapsulating material of fish oil than hemicellulose by spray drying [54]. Butstraen and Salaün [55] prepared microcapsules by complex coacervation of gum arabic and chitosan containing a commercially available blend of triglycerides as the core. They found an optimum formation of the complex at pH 3.6 and a weight ratio of chitosan to gum arabic mixtures of 1:4. Brea gum and gelatin were used for microencapsulation of peppermint essence by complex coacervation. Brea gum and gelatin were cross-linked with glutaraldehyde during formation of the capsules. The capsules were applied onto paper and cloth using polyvinyl alcohol (PVA) adhesive. The capsules based on brea gum and gelatin were compared with those obtained with gum arabic and gelatin. The results indicated that microcapsules obtained with both gums are similar and present high encapsulation efficiency of peppermint essence. However, when capsules were prepared with brea gum, it was necessary only the 60% of the amount of gum arabic required for the same quantity of gelatin [56]. Castel et al. [18] analyzed the capability of brea gum to encapsulate corn oil by spray drying. They studied the effect of inulin incorporation into the emulsion on the resulting capsules. The powders were almost spherical particles, with contractions, but without cracks or apparent porosity, providing good protection and retention of the encapsulated material. Inulin addition increased the encapsulation efficiency by more than

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100%. Their results showed that the combination of brea gum and inulin is a good alternative for the external phase that microencapsulates hydrophobic compounds. 14.4.3

Hydrogels

Polyelectrolytes are macromolecules that possess a relatively large number of functional groups that either are charged or under suitable conditions can become charged. Polyelectrolyte complexes are formed by mixing solutions of oppositely charged polyelectrolytes without any chemical covalent cross-linker. These complexes not only include electrostatic and dipole–dipole association, but also hydrogen and hydrophobic bonds [57]. Polyelectrolyte complexes are studied for drug delivery, pH indicator, temperature indicator prototype, and hydrogels [58–62]. Hydrogels are a group of polymeric materials of hydrophilic structure, which make them capable of holding large amounts of water in their three-dimensional networks. These products are extensively employed in a wide number of industrial and environmental applications. A gel is commonly defined as a cross-linked network of polymers, which can absorb solvent, but which is insoluble therein. The interactions responsible for this solvent absorption correspond to capillarity forces, osmosis, and polymer–solvent molecular interactions, among others [63]. Some gels have the property of undergoing phase transitions when immersed in certain solvents and under certain conditions. These phase transitions change the gel matrix volume by reversible extension or contraction. Volume changes can reach very large values, such as 1000 times the volume of the dry gel, because of changes in external variables, such as temperature, ionic strength, pH or selected solvent. Brea gum presents positive charge below pH 3.7, related to its protein fraction. The isoelectric point is observed in a range of pH between 3.6 and 4.0, and above these values, the polymer is negatively charged due to the presence of uronic acids in the polysaccharide [64]. The positive zeta potential of brea gum is explained by the ionization of the protein fraction of brea gum below its isoelectric point. Jayme et al. [65] studied gum arabic as a stabilizer of O/W emulsion and reported an isoelectric point around pH 2 that was independent of the salt concentration of the gum arabic solution. Hydrogels can be formulated by a combination of pectin and brea gum to form a polyelectrolyte complex. Considering that brea gum presents positive charge below pH 3.7, the formation of a polyelectrolyte complex depends on the pH of the solution mixture. The natural pH of brea gum and pectin solutions is around pH 4. Thus, the pH of brea gum solution must be reduced to 2 in order to ensure the electrostatic interaction and the hydrogel formation. Above a final pH of 3.5, complex formation is not observed, since above this value the zeta potential of the brea gum is negative. Under these conditions, a colloidal solution stabilized by electrostatic repulsions is obtained, considering that pectin is a negative charged colloid. Thus, only when the final solution exhibits a pH below 3.7, the hydrogel is separated from the solution [64]. The addition of nanoparticles of MMT to the hydrogel of brea gum and pectin modifies its properties. The hardness of the hydrogel based on brea gum and gelatin varies from 5.97 to 13 kPa. However, when MMT is incorporated in hydrogel formulation, the hardness values are between 8 and 20 kPa, increasing the effort required to compress the gel structure. Thus, MMT acts as a nano-reinforcer by interacting with both hydrocolloids in the gel structure, the result being a more stable matrix. This is also reflected by

14.4 Applications

an increase in cohesiveness and a decrease in adhesiveness when MMT is incorporated into the hydrogels [66]. Klein et al. [32] studied the interaction between whey protein isolate and gum arabic. They found that electrostatic interactions occur when the protein charge is partially positive. In this pH range, the protein consists of some positive domains that interact with the negatively charged gum arabic to form weak complexes that do not form precipitating coacervates but rather soluble or colloidal adducts that behave like a large molecular entity with amphiphilic and interfacial characteristics. The charge interactions are sufficient to cause a molecular adduct migration of the two biopolymers together to the air–water or oil–water interface, to improve its adsorption into the interface, enhancing the foam or emulsion stability. 14.4.4

Bread Additive

Bread is a widely consumed product, particularly wheat bread. A decrease in bread quality occurs due to aging, which begins just when loaves are removed from the oven [67]. Hydrocolloids are widely used as additives in the food industry because they are used to modify the rheology and texture of aqueous systems [68]. In addition, the hydrophilicity of the hydrocolloids gives them a high water retention capacity [69]. López and Jiménez [70] studied the effect of different proportions of brea gum on the functional characteristics of wheat flour and its impact on the physical quality of bread. The higher levels of brea gum (1% and 2%) decreased the peak viscosity and increased the stability and setback of the flour. The hydrocolloid competes with starch for water molecules, lowering gelatinization of the starch granules. These changes in the functional characteristics of wheat flour affect bread quality. The loaves added with 1% and 2% brea gum exhibited smaller alveoli, developing more compact, harder, and less aerated crumbs. Nevertheless, the humidity of the samples with 1% and 2% brea gum was higher than the moisture of control bread. On the other hand, the incorporation of brea gum at 0.5% did not affect the pasting parameters and bread quality but increased the moisture of the crumb, so this concentration would be most recommended for baking, since higher humidity could favor the shelf life of the product. Moreover, the effect of the addition of brea gum on the aging of wheat bread was also analyzed. Brea gum reduced the hardening of the crumb in white bread, particularly at 48 h storage. This improvement may be due to the higher moisture content of the crumbs containing brea gum. The higher moisture content would also explain the differences found in the microstructure at 72 h storage. The same effect is observed regardless of the amount of brea gum added. However, the presence of the hydrocolloid seems to favor the retrogradation of amylopectin. The bread firming during storage cannot be explained only by the starch retrogradation or by the moisture content. The organization of polymers within the amorphous region or the repartition of water between the amorphous and crystalline regions may play an important role [27]. López and Goldner [71] analyzed the influence of storage time on the acceptability of bread formulated with lupine protein isolate and brea gum. They formulated different bread samples based on wheat flour with the addition of 10% lupine protein and 0.5% brea gum. The crumbs made with flour mixture (wheat and lupine) exhibited higher moisture content at all storage times, and the addition of brea gum further increased these values. After 24, 48, and 72 h storage, the bread crumbs with lupine protein isolate

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(with and without brea gum) were less hard. In general, the addition of brea gum made bread more cohesive, gummy, springy, and chewy. At 48 h storage, brea gum improved in acceptability, and this was accentuated at 72 h storage, where 80% of consumers reacted positively because of the “good crumb flavor.” The addition of this hydrocolloid increased the sensory shelf life of the product. 14.4.5

Medium for Fungal Culture

Mesa et al. [72] studied the behavior of the Aspergillus niger strain ATCC 11414, in a culture media based on the exudate of Cercidium praecox. They evaluated the growth of the colonies and the biomass. The macroscopic and microscopic characteristics of the fungus in this medium were similar to those exhibited in Sabouraud Dextrose Agar. This behavior suggests that A. niger produces the enzymes necessary to hydrolyze the acid hetero-polysaccharides of the gum. The preparation process of the culture medium induced some autohydrolysis in the polymer, releasing arabinose and xylose, substrates used as a carbon source and energy by this microorganism.

14.5 Conclusions Brea tree (Cercidium praecox) is a constitutive species of the native vegetation of arid and semi-arid zones of America that cannot be used as wood. The ecological importance of this species lies in its ability to rapidly colonize degraded lands by overgrazing or deforestation. The brea tree grows from northern Patagonia Argentina to the south of the United States of America in arid and hot regions, and it can be utilized as an economic resource by poor and vulnerable populations. However, this requires the greater organization of producers and intensive tree planting on a large scale. This species produces a water-soluble exudate through wounds on its trunk or main branches, the brea gum, which can be used instead of gum arabic for a large number of applications in food, pharmacy, and other industrial applications such as glues, pigments, and so on. This would allow the replacement of gum importations in the countries where it grows. In addition, the harvest of brea gum would generate an alternative of genuine income in vast areas of territories with significant signs of biological, physical, and social degradation. The chemical, physical, and functional characteristics of brea gum make it an excellent substitute for gum arabic. Its protein content, three times greater than that of gum arabic, results in greater surface activity, which produces greater foaming and stabilizing power. Its high solubility and rheological properties allow the formation of solutions with high soluble solids content and low viscosity, which are very important characteristics for the stabilization of aqueous suspensions. The structure of the polymer enables it to form films with high solubility in water. In addition, as the hydrocolloid has an anionic character, it can interact with cationic polymers to form more complex structures. As the brea tree is a legume, oil can be obtained from its seeds, which in turn can be used be used in the production of biofuels, thus making it an alternative to edible legumes such as soybean.

Acknowledgments

14.6 Future Trends The brea tree is a natural and sustainable resource that plays an important role in the recovery of degraded arid or semi-arid zones, where climatic and ecological conditions are not favorable for agriculture. In Argentina, around 80 000 km2 has potential for the production of the brea tree. In addition to the environmental benefits of the brea tree, brea gum can be obtained from the brea tree in sufficient quantities in these territories to not only replace the national consumption of gum arabic but also to export the surplus. Considering that these regions are inhabited by very poor people and that gum collection requires intensive labor, the production of brea gum could generate a significant source of income for its inhabitants. Nevertheless, new state policies have to be formulated so as to promote investments to support and finance the intensive plantations, the gum collection, the post-harvest processing, and the market structure. Overall, the demand for gum arabic is steadily increasing (2.5% annually). Major drivers of this growth include new product development and substitution of synthetic thickeners. Main suppliers of gum arabic are politically unstable countries like Sudan or Kenya. Thus, the main buyers of gum arabic are attracted by those providers who can guarantee stable supplies of high-quality gums. This large potential market constitutes an important opportunity to introduce brea gum as an alternative to gum arabic. Finally, in order to introduce brea gum as an alternative to gum arabic, it is necessary to widely disseminate information regarding its characteristics and functional properties among potential users. The physical and chemical properties of this polysaccharide allow its application in different fields. In the food industry, brea gum could be used as a stabilizer in the formulation of beverages and to retard the growth of sugar or ice crystals because of its high solubility and low viscosity. Besides, the brea gum solutions are excellent forming and stabilizing agents for emulsions and foams, given their surface properties. In the pharmaceutical industry, brea gum could be utilized as a binder or stabilizer of suspensions. Brea gum is also a useful material to encapsulate active principles due to its gas and solute barrier properties, or as a sacrificial material to delay dehydration, due to its high water retention capacity. In addition, its ability to form complexes with polyanions such as pectin or alginate allows its use in encapsulation or laminates. The particular properties of this gum open a wide field for other potential applications that must be studied and developed.

Acknowledgments The authors thank Ing. Agr. Tania Bertuzzi for technical advice and photographs of the brea tree and the financial support of Consejo de Investigaciones de la Universidad Nacional de Salta (CIUNSa), Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT), and Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET).

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preparation, properties, and uses of a new class of materials. Materials Science and Engineering: R: Reports 28 (1–2): 1–63. Nedovic, V., Kalusevic, A., Manojlovic, V. et al. (2011). An overview of encapsulation technologies for food applications. Procedia Food Science 1: 1806–1815. Tatar, F., Tunç, M.T., Dervisoglu, M. et al. (2014). Evaluation of hemicellulose as a coating material with gum Arabic for food microencapsulation. Food Research International 57: 168–175. Butstraen, C. and Salaün, F. (2014). Preparation of microcapsules by complex coacervation of gum Arabic and chitosan. Carbohydrate Polymers 9: 608–616. Defain Tesoriero, M. V., Murano, M. & Hermida, L. (2014) Utilización de goma brea para la microencapsulación de fragancias por coacervación compleja. 5∘ Jornadas de Desarrollo e Inonvación. Luo, Y. and Wang, Q. (2014). Recent development of chitosan-based polyelectrolyte complexes with natural polysaccharides for drug delivery. International Journal of Biological Macromolecules 64: 353–367. Bigucci, F., Luppi, B., Cerchiara, T. et al. (2008). Chitosan/pectin polyelectrolyte complexes: selection of suitable preparative conditions for colon-specific delivery of vancomycin. European Journal of Pharmaceutical Sciences 35 (5): 435–441. Coimbra, P., Ferreira, P., de Sousa, H.C. et al. (2011). Preparation and chemical and biological characterization of a pectin/chitosan polyelectrolyte complex scaffold for possible bone tissue engineering applications. International Journal of Biological Macromolecules 48 (1): 112–118. Maciel, V.B.V., Yoshida, C.M.P., and Franco, T.T. (2014). Development of temperature indicator prototype: card paper coated with chitosan intelligent films. Journal of Agricultural Chemistry and Environment 3 (01): 5–10. Maciel, V.B.V., Yoshida, C.M.P., and Franco, T.T. (2015). Chitosan/pectin polyelectrolyte complex as a pH indicator. Carbohydrate Polymers 132: 537–545. Costa, M.P.M., Da Ferreira, I.L.d.M., and Cruz, M.T.d.M. (2016). New polyelectrolyte complex from pectin/chitosan and montmorillonite clay. Carbohydrate Polymers 146: 123–130. Ahmed, E.M. (2015). Hydrogel: preparation, characterization, and applications: a review. Journal of Advanced Research 6 (2): 105–121. Slavutsky, A.M., Bravo, J.M., and Bertuzzi, M.A. (2016). Argentina. Obtención de complejos de polielectrólitos a base de pectina y goma brea. In: VI Congreso Internacional de Ciencia y Tecnología de los Alimentos (ed. A.E. León, V. Rosati and C.W. Robledo), 441. Ministerio de Ciencia y Tecnología de la provincia de Córdoba. Jayme, M., Dunstan, D., and Gee, M. (1999). Zeta potentials of gum Arabic stabilised oil in water emulsions. Food Hydrocolloids 13 (6): 459–465. Slavutsky, A.M. and Bertuzzi, M.A. (2016). Obtención De Hidrogeles A Partir De Pectina, Goma Brea Y Montmorillonita. The Journal of the Argentine Chemical Society 103 (1–2), Buenos Aires-Argentina. Bárcenas, M.E. and Rosell, C.M. (2005). Different approach for improving the quality and extending the shelf-life of the partially baked bread: low temperatures and hydrocolloid addition. Food Chemistry 100: 1594–1601. Dziezak, J.D.A. (1991). Focus on gums. Food Technology 45 (3): 115–132.

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69 Lee, M.H., Baek, M.H., Cha, D.S. et al. (2002). Freeze-thaw stabilization of sweet

potato starch gel by polysaccharide gums. Food Hydrocolloids 16 (4): 345–352. 70 López, E.P. and Jiménez, P.L. (2016). Effect of different proportions of brea gum in

the functional characteristics of wheat flour starch: impact on the physical quality of bread. Food Science and Technology 36 (1): 1–7. 71 López, E.P. and Goldner, M.C. (2015). Influence of storage time for the acceptability of bread formulated with lupine protein isolate and added brea gum. LWT-Food Science and Technology 64 (2): 1171–1178. 72 Mesa, C.L.M., Rodríguez, V.S., Beltrán, F.O. et al. (1997). Behavior of Aspergillus Niger in the gum exudates of cercium praecox and cedrela odorata. Boletín micológico 12 (1/2): 35–39.

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15 Chubak (Acanthophyllum glandulosum) Root Gum Hojjat Karazhiyan Department of Food Science & Technology, Torbat-e Heydarieh Branch, Islamic Azad University, Torbat-e Heydarieh, Iran

15.1 Introduction Chubak is a plant belonging to the family Caryophyllaceae and the genus Acanthophyllum (Figure 15.1a). Chubak has wooden pillow-shaped shrubs with biting spurs (their leaves deform to spurs). Some shrubs and some with thick root and mostly grown in Iran are Acanthophyllum, and a number of others, which are annual and perennial but herbaceous, are of the Saponaria genus, which is mostly grown in Europe, but a few are also seen in Iran. A total of 61 species of this genus are found worldwide, and of these, 33 species are capable of growing in Iran, and 23 species are native to this region [1]. On the basis of available sources, most of these species have been identified in the eastern parts of Iran (Khorasan Province) and its adjacent regions (Afghanistan and Turkmenistan) [2]. The root of Chubak (Figure 15.1b) is a valuable source of saponin, which is one of the most important active compounds in it, and many previous works have focused on identifying its structure, physicochemical properties, and biological activity [3–6]. In addition to saponin, polysaccharides and water-soluble gum (hydrocolloids) are also other important compounds whose presence in the roots of the various species of the plant has been reported [7, 8]. The lower parts of the plant are completely wooden, the flowers are white, the length of the plant is 20–25 cm, the length of the leaf is 1–2 cm, it has five petals, the tip is wide and white, and the bottom is red [9]. In general, they are called Saponaria in French and soapwort in English [10]. A species of this genus, called Acanthophyllum squarrosum, has long been known as “Chubak” or “bayk” for people, who have been using the thick root for washing and cleaning clothes due to its saponin substance, which is similar to soap, and for making a sweet dessert (known as Halvah in Iran). The Acanthophyllum genus of the Acanthophyllum mucronatum species was named for the first time in 1831 by Mayer. Since then, 14 species have been introduced in five classes by the Bowsia in the eastern flora. The oldest list of Acanthophyllum species in Iran has been presented by Professor Rahmat Parsa [1, 11]. It has been demonstrated that the purified Chubak extract contains 84.3% carbohydrate, and that this amount of sugar is higher than that of guar gum and a little less than that of xanthan gum and gum arabic. Analysis of monosaccharides by HPLC also showed that the water-soluble polysaccharides extracted from this extract are a type of glucoarabinogalactan polysaccharide [7, 8]. In this chapter, the characteristics of Chubak root hydrocolloidal extract Emerging Natural Hydrocolloids: Rheology and Functions, First Edition. Edited by Seyed M.A. Razavi. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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15 Chubak (Acanthophyllum glandulosum) Root Gum

(a)

(b)

Figure 15.1 (a) Acanthophyllum glandulosum (Chubak) plant and (b) Chubak root.

and its application in different food products based on its functional properties such as emulsifying, aerating, and stabilizing agents are reviewed.

15.2 Chubak Root Extract (CRE) The extraction process is an important primary step in the purification of active compounds in different plant organs. Conventional extraction methods such as Soxhlet extraction method, which has been used for many decades, are very time consuming. In addition, these methods require the use of high levels of solvents [12]. That is why there is a lot of demand for new extraction methods with shorter time, less solvent consumption, greater efficiency, and environmentally safe [13]. The production of the CRE with high saponin content in a shorter time and using less solvent for its use in food formulations was evaluated by Keyhani et al. [14]. The extraction process was performed with the Soxhlet method as well as the ultrasound technique, and the extraction efficiency was evaluated by determining the emulsification index (E24 ) and foaming ability (Fh ) [15, 16]. In order to optimize the extraction conditions, the effects of sonication time, temperature, ultrasonic wave intensity, particle size, solvent-to-sample ratio, and solvent concentration on the extraction yield were determined. It was shown that the saponins extracted by the ultrasonic method has a higher emulsifying and foaming ability (P < 0.05) compared to those extracted by the conventional (Soxhlet) method. The maximum amounts of E24 and Fh were achieved by the conventional method after 480 min of extraction, which was close to the E24 and Fh values after 40 min of extraction with ultrasound, as there was no significant difference between them (P > 0.05). On the basis of this, it can be stated that the extraction time with

15.2 Chubak Root Extract (CRE)

ultrasonic waves decreases by about a factor of 12 compared with the conventional method of producing Chubak extract with high saponin content, but with the same emulsification and foaming characteristics. The capability of the ultrasonic technique to increase the speed of extraction of saponins from the roots of Chubak plant and as a consequence, shortening the extraction process time, is also evident in the results of other researchers [17–22]. Increasing the sonication time from 10 to 40 min increased the E24 and Fh values significantly (P < 0.05); however, in the range of 40–60 min, this increase was much slower and not significant (P < 0.05). In addition, it can be concluded that during extraction of CRE with ultrasonic waves, the major part of saponin compounds are extracted from the Chubak root in the first 40 min of sonication. As a result, it will be possible to achieve extra efficiency in the early stages of extraction. With the continuation of the extraction process and as the phenomenon of diffusion to the more inward parts of the plant tissue continues, the diffusion rate decreases with prolongation and hardening of the diffusion pathway, because of the lower diffusion level and also the decreased concentration gradient in the perimeter of the specimen. Finally, there is no apparent change in the amount of extraction [19, 22]. With increasing temperature, the E24 and Fh values exhibit a significant upward trend (P < 0.05), so that it can be concluded that the extraction efficiency of saponins increased with increasing temperature in a constant time range. Increasing the temperature can also cause the cell walls to open, which makes target compounds available. Moreover, at high temperature, the viscosity of the solvent decreases and the diffusion rate increases; therefore, the extraction efficiency increases [23]. The E24 and Fh values significantly (P < 0.05) increased as the intensity of ultrasound waves was increased by 80%, but by increasing this factor from 80% to 100%, not only was this increase was not observed but a small decrease was observed instead. Then, in the extraction with ultrasonic waves, the amount of energy transferred from the sonicator to the environment is directly related to the sound intensity of the device. Therefore, by increasing the intensity, more energy is introduced into the environment, which increases the extraction efficiency. However, if this output power is too high, it will result in an excessive increase in the number of bubbles in the outer solvent during cavitation, which can reduce the amount of energy generated by the sonication applied, and thus the extraction efficiency will not increase [24]. With a decrease in the particle size of the sample to 0.1–0.4 mm, the values of E24 and Fh increased significantly (P < 0.05), but with a further reduction to 0.05), which was in agreement with Sepúlveda et al. [30] on the extraction of mucilage from Opuntia. On the other hand, temperature significantly affected the yield of yanang leaves [28] and E. sativa mucilage [16]. According to the above results, the optimum conditions for maximum yield (12.14%) of MFG are a temperature of 55 ∘ C, pH of 7, and W/P ratio of 40:1. Comparing the extraction yield of MFG with that of other gums indicates a higher yield value for MFG than those from Durio zibethinus [31], flaxseed [32], E. sativa seed [16], cress seed [15], and yanang leaves [28]. 16.2.3

Effect of Extraction Conditions on Consistency Coefficient

The consistency coefficient (k) of MFG was obtained by fitting the power-law model to the shear stress versus shear rate data. The results indicated that the predicted model was significant (p < 0.01) (Table 16.1). The linear effect of pH and temperature and the quadratic effect of the W/P ratio were significant (p < 0.01) (Table 16.2), although there

399

Table 16.1 Sequential model and sum of squares analyzed for each response (Yield, k, L*, FSI, and ESI). Yield

k

FSI

L

Source

Mean DF Square

Mean Mean Value F Prob. F Square Value F Prob. F Square

Mean

1

1354

—

—

349.2

—

—

Linear

3

6.6

0.74

0.542

37.83

4.11

0.0244 102.5

2FI

3

2.02

0.19

0.8994 1.49

0.14

0.9372 7.15

Mean Value F Prob. F Square

1.437 × 105 —

ESI

Mean Value F Prob. F Square

Value F Prob. F

—

1.331 × 105 —

—

1.366 × 105 —

19.19

0.1

82.36

0.43

0.7355 19.88

0.77

1.45

0.2735 514.05

4.38

0.0241 34.94

1.48

0.5262 0.2662

Quadratic 3

38.68

19.36

0.0002 34.87

9.13

0.0033 12.44

4.66

0.0276 330.33

6.19

0.012

18.1

0.0002

Cubic

4

3.56

1.72

0.2625 9.98

5.43

0.034

1.39

0.28

0.882

67.32

0.91

0.5145 7.5

1.34

0.3564

Residual

6

3.1

—

—

2.76

—

—

7.51

—

—

110.58

—

—

8.41

—

—

Total

20 1407.96 —

—

436.12 —

—

1.438 × 105 —

1.342 × 105 —

—

1.368 × 105 —

—

k, consistency coefficient; L*, color component parameter; FSI, foaming stability index; ESI, emulsion stability index.

86.43

—

16.2 Extraction Optimization using RSM

Table 16.2 ANOVA and regression coefficients of models for the response variables. Response

Source

Sum of square

Extraction yield

Models

Consistency coefficient (k)

DF

Mean square

Value F

Prob. F

43.22

4

10.80

15.09

G′′ , tan δ < 1). The SUPER-BSG emulsion showed the lowest storage modulus (G′ LVE ), loss modulus (G′′ LVE ), yield stress (τy ), flow point stress (τf ), and corresponding modulus (Gf ) and the highest loss-tangent value (tan δLVE ), but there was no significant difference among the other samples for G′ , tan δLVE , τy, and Gf . The results of frequency sweep measurements confirmed the solid-like behavior of BSG and its fractions emulsions, and non-Newtonian shear-thinning behavior was observed as the complex viscosity (η*) decreased linearly with an increase in frequency. The SUPER-BSG emulsion exhibited the lowest G′ , G′′ , η*, and slope of log η*, and the highest tan δ values. BSG showed the highest G′ , G′′ , and η*, which was related to the presence of both fractions together, and the contribution to the elastic storage modulus by PER-BSG and to a low droplet size by SUPER-BSG. CSG and its fractions (F1, F2, and F3) exhibited excellent emulsifying capability (>97%) and stability (>96%). The emulsion capacity increased slightly from F1 to F2 to F3, because of the increasing molecular weight, protein content, and apparent viscosity along the same series. All the emulsions were stable after heating at 80 ∘ C for 30 min, and a slight decrease in the emulsion stability was observed for all the samples; the percentage decrease in emulsion stability increased along the series F1, F2, and F3. The uronic acid content decreased from F1 to F2 to F3, whereas the protein content and viscosity increased, indicating that the uronic acid content had a stronger effect than the protein content and viscosity on the emulsion stability of the samples. Also, a general decrease in viscosity with increasing temperature and a possible negative effect of temperature (80 ∘ C for 30 min) on protein structure could diminish or weaken the effect of these factors on the emulsion stability after heating [20]. 19.3.6.3

Foaming Properties

Naji-Tabasi and Razavi studied the effect of BSG and its fractions (PER-BSG and SUPER-BSG), and also PF-BSG, at different concentrations on the foaming capacity and stability of albumin solution. As shown in Figure 19.3a, SUPER-BSG improved foaming capability significantly at all concentrations, because it had the highest protein content, surface activity, and flexibility. PF-BSG exhibited the weakest foaming capacity because of more hydrophilic and fewer hydrophobic bonds, which could not adsorb at the air–liquid interface. The foaming capacity of all the samples exhibited a decreasing trend when the concentration of gum increased, because the greatly increased viscosity of the aqueous phase did not allow air to enter the system. BSG and its fractions significantly improved the foam stability of albumin solution, and foaming stability increased with increasing gum concentration (Figure 19.3b). The highest foaming stability was observed for BSG at 0.3%, which is attributed to modification of the viscosity of the aqueous phase and the creation of a network, which prevented the air droplets from coalescing. As discussed earlier, the viscosity of the samples followed the order SUPER-BSG < PER-BSG < BSG. SUPER-BSG had the lowest viscosity but demonstrated the strongest stability at 0.1% and 0.2% in comparison with BSG and PER-BSG due to the existence of more hydrophobic chains, flexible structure, high surface activity, and low molecular weight. Therefore, at high viscosity, the foam stability

19.3 Fractionation of New Natural Hydrocolloids

35 Aa

Foaming Capacity (%)

30

AB a

25

AB a AB b

Aa AB

Ab

Ba

AB b

B

A

Ba 20

0.1% Bc

15

Bc

0.2%

Bb

0.3%

10 5 0

BSG

Foaming Stability (%)

100 80

PER-BSG Aa

Bb Bb

Aa Bb Cb

SUPER-BSG (a) A aA a Ba

PF-BSG

Albumin

Ba B ab Cb

60

D C C

0.1% 0.2%

40

0.3%

20 0 BSG

PER-BSG SUPER-BSG (b)

PF-BSG

Albumin

Figure 19.3 Effect of BSG and its fractions on (a) foaming capacity and (b) stability of 0.3% albumin solutions. Different letters of each bar indicate significant differences between fractions (capital letter) and different gum concentrations (small letter) at p < 0.05. Source: Adapted from Naji-Tabasi and Razavi [24] with permission from Elsevier.

was controlled by increasing the bulk-phase viscosity, but at lower gum concentrations, surface tension groups played a major role in preventing drainage because the viscosity could not prevent bubble coalescence [24]. Razmkhah et al. indicated that CSG had a higher foaming capacity and stability compared to its fractions (F1, F2, and F3). CSG could react with ovalbumin (mainly non-covalent bonds) because of its specific molecular structure with high molecular weight. Also, CSG exhibited better surface activity than F1 and F2, which was another reason for its better foaming properties. F3 showed the lowest foaming capacity and stability due to its more compact structure compared to the other fractions and CSG; therefore, it was not able to react with ovalbumin as a foam-forming component. As discussed previously, the chemical composition and molecular weight of the fractions varied significantly, indicating that the fractions had different molecular structures, which is an important factor for foaming properties [20].

493

494

19 Purification and Fractionation of Novel Natural Hydrocolloids

19.4 Conclusions and Future Trends Fractionation and the effect of purification methods on the physicochemical, rheological, and functional properties of some new gums were reviewed in this chapter. Lower yield, protein, fiber, and ash content were reported for purified chia seed gum compared to the crude gum, which was related to the removal of the majority of non-carbohydrate components during the purification. Partial purification of crude BSG by alcoholic precipitation had a significant effect on the quantity and quality of the extracted gum. Protein-free BSG (phenol + ethanol treated)-stabilized emulsions exhibited the highest complex viscosity and the strongest viscoelastic network. The purification processes changed the functionality of BSG in terms of hydrophobicity and conformational structure, altering its adsorption properties and producing bigger emulsions droplets and/or a higher degree of droplet aggregation/coalescence. Four different purification methods (A [isopropanol and ethanol], B [isopropanol and acetone], C [saturated barium hydroxide], and D [Fehling solution]) reduced hydrophobic impurities, thereby decreasing the OHC. The purified samples C and D had the highest and the lowest OHCs among the purified gums, respectively, which is related to the effectiveness of the purification methods A, B, and D in reducing the hydrophobic fractions. The solubility and WHC of durian seed gum increased significantly after purification; Sample A had the lowest WHC among the purified gums due to the presence of higher content of impurities. All the purification methods significantly influenced both the G′ and G′′ of the crude gum, which could be explained by the significant effects of the purification processes on the chemical composition of the crude gum; purification using saturated barium hydroxide produced the highest values for G′ and G′′ . The purified gums A and D showed the highest and least viscosities, respectively, due to the different molecular weights. The chemical composition of crude CSG varied significantly after purification with three different precipitation methods (ethanol [sample E], isopropanol [sample I], and ethanol–isopropanol [sample EI]). The purified samples had a stronger and more elastic network structure than the crude gum due to the elimination of impurities, especially the protein component, after purification. With the elimination of protein to lower levels and increasing molecular weight from I to EI to E, the apparent viscosity and intrinsic viscosity increased along the same series, and the gel network became stronger. All the purification methods increased the thermal stability of CSG, because of elimination of impurities and the formation of more stable and ordered polysaccharide structures; sample EI showed the lowest activation energy (less sensitive to the temperature). The purified gums exhibited stronger thixotropic properties due to their more structured systems. Sample E had the lowest hysteresis loop area among the purified gums, which was consistent with its higher viscoelastic property. The purification methods improved the surface activity of CSG; sample I showed the lowest surface tension among the purified gums because it had the highest protein and uronic acid contents and the lowest molecular weight. All the purification methods improved the emulsifying and foaming properties of CSG, and the emulsifying properties did not differ significantly among the purified gums. Sample I exhibited the highest foaming capacity, and sample E exhibited the highest foaming stability, which can be attributed to the stronger foam network related to its interactions with ovalbumin.

19.4 Conclusions and Future Trends

Controlled depolymerization of CSP yielded various molecular fractions. The intrinsic viscosity decreased with increasing degradation time (0–8 h) due to the reduced molecular weight. The fractions of BSG (fractionated using gradual ethanol precipitation; precipitate [PER-BSG] and supernatant [SUPER-BSG]) exhibited different monosaccharide building units. PER-BSG, in accordance with its higher molecular weight, exhibited a higher viscosity and stronger shear-thinning behavior than the SUPER-BSG fraction. BSG and PER-BSG exhibited the highest and the lowest intrinsic viscosities; the lower intrinsic viscosity and higher molecular weight of PER-BSG were attributed to its more compact conformation. SUPER-BSG had the highest surface activity because it had the lowest molecular weight (a strong tendency to adsorb at the air–water interface), the highest chain flexibility, and the highest content of uronic acid and protein. SUPER-BSG and PF-BSG exhibited the highest and the lowest emulsion stability, respectively. SUPER-BSG formed an emulsion with the lowest mean diameter and size distribution because it had the highest protein content, surface activity, and flexibility. SUPER-BSG improved the foaming capability significantly at all concentrations, because it had the highest protein content, surface activity, and flexibility. Treatment of BSG with protease enzyme (PF-BSG) increased the storage modulus, whereas there was no significant difference between BSG and PF-BSG for the other frequency sweep parameters. PF-BSG showed lower surface activity, foaming capacity, and a low tendency to absorb on interfacial surfaces of oil and water compared to BSG, which was attributed to the elimination of protein. Fractionation of CSG (fractionated using stepwise extraction with water: F1 [first extractant], F2 [second extractant], and F3 [third extractant]) produced different hydrocolloids with different chemical (ash, moisture, protein, and monosaccharide composition), rheological, and functional characteristics in each step. The intrinsic viscosity of the fractions increased along the series F1, F2, and F3 due to the increase in molecular weight and chain flexibility. The dynamic rheological properties indicated that the gum generated from the inner parts of the cress seeds had a stronger and more elastic network structure. The microstructure of F2 was more sensitive to the temperature (highest value of activation energy), and the hysteresis loop area increased significantly along the series F1, F2, and F3 because of their greater shear-thinning behavior; the increase in structural recovery along the same series was related to their more elastic networks. Surface activity increased from F1 to F2 to F3 at low concentrations due to an increase in protein content and chain flexibility along the series F1, F2, and F3. The emulsion capacity increased slightly from F1 to F2 to F3, because of the increasing molecular weight, protein content, and apparent viscosity along the same series. F3 showed the lowest foaming capacity and stability due to its more compact structure compared to the other fractions and CSG; therefore, it was not able to react with ovalbumin as a foam-forming component. It can be concluded that the physicochemical, rheological, and functional properties of crude gums improve after purification, and various purification methods have different effects. Also, fractionation of polymers produces gums with different characteristics which can be applied to various areas. With respect to the increase in demand for natural hydrocolloids with low cost and proper functionality, fractionation and purification of new gums will expand their availability considerably, and they can be used in a variety of applications depending on their characteristics.

495

496

19 Purification and Fractionation of Novel Natural Hydrocolloids

References 1 Bouzouita, N., Khaldi, A., Zgoulli, S. et al. (2007). The analysis of crude and purified

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locust bean gum: a comparison of samples from different carob tree populations in Tunisia. Food Chemistry 101: 1508–1515. Cui, S.W. (2005). Food Carbohydrates: Chemistry, Physical Properties, and Applications. Boca Raton, FL: CRC Press, Taylor & Francis Group. Cunha, P.L.R., Paula, R.C.M., and Feitosa, J.P.A. (2007). Purification of guar gum for biological applications. International Journal of Biological Macromolecules 41: 324–331. da Silva, J.A.L. and Gonçalves, M.P. (1990). Studies on a purification method for locust bean gum by precipitation with isopropanol. Food Hydrocolloids 4: 277–287. Naji-Tabasi, S., Razavi, S.M.A., Mohebbat Mohebbi, M., and Malaekeh-Nikouei, B. (2016). New studies on basil (Ocimum bacilicum L.) seed gum: part I–fractionation, physicochemical and surface activity characterization. Food Hydrocolloids 52: 350–358. Razavi, S.M.A., Mortazavi, S.A., Matia-Merino, L. et al. (2009). Optimization study of gum extraction from basil seeds (Ocimum basilicum L.) using response surface methodology. International Journal of Food Science and Technology 44: 1755–1762. Osano, J.P., Hosseini-Parvar, S.H., Matia-Merino, L., and Golding, M. (2014). Emulsifying properties of a novel polysaccharide extracted from basil seed (Ocimum bacilicum L.): effect of polysaccharide and protein content. Food Hydrocolloids 37: 40–48. Amid, B.T. and Mirhosseini, H. (2012). Effect of different purification techniques on the characteristics of Heteropolysaccharide-protein biopolymer from durian (Durio zibethinus) seed. Molecules 17: 10875–10892. Timilsena, Y.P., Adhikari, R., Kasapis, S., and Adhikari, B. (2016). Molecular and functional characteristics of purified gum from Australian chia seeds. Carbohydrate Polymers 136: 128–136. Razmkhah, S., Mohammadifar, M.A., Razavi, S.M.A., and Ale, M.T. (2016). Purification of cress seed (Lepidium sativum) gum: physicochemical characterization and functional properties. Carbohydrate Polymers 141: 166–174. Kök, M.S. (2007). A comparative study on the compositions of crude and refined locust bean gum: in relation to rheological properties. Carbohydrate Polymers 70: 68–76. Razavi, S.M.A., Cui, S.W., Guo, Q., and Ding, H. (2014). Some physicochemical properties of sage (Salvia macrosiphon) seed gum. Food Hydrocolloids 35: 453–462. Qian, H.F., Cui, S.W., Wang, Q. et al. (2011). Fractionation and physicochemical characterization of peach gum polysaccharides. Food Hydrocolloids 25: 1285–1290. Pamies, R., Hernandez Cifre, J.G., Martinez, M.C.L., and Torr, J.G. (2008). Determination of intrinsic viscosities of macromolecules and nanoparticles. Comparison of single-point and dilution procedures. Colloid Polymer Science 286: 1223–1231. Razmkhah, S., Razavi, S.M.A., and Mohammadifar, M.A. (2016). Purification of cress seed (Lepidium sativum) gum: a comprehensive rheological study. Food Hydrocolloids 61: 358–368.

References

16 Amid, B.T. and Mirhosseini, H. (2012). Influence of different purification and drying

17 18

19

20

21

22

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24

25 26

methods on rheological properties and viscoelastic behaviour of durian seed gum. Carbohydrate Polymers 90: 452–461. Osano, J., Matia-Merino, L., Hosseini-Parvar, S. et al. (2010). Adsorption properties of basil (Ocimum basilicum L.) seed gum. USM R & D 18: 113–117. Koocheki, A., Razavi, S.M.A., and Hesarinejad, M.A. (2012). Effect of extraction procedures on functional properties of Eruca sativa seed mucilage. Food Biophysics 7: 84–92. Jahanbin, K., Moini, S., Gohari, A.R. et al. (2012). Isolation, purification and characterization of a new gum from Acanthophyllum bracteatum roots. Food Hydrocolloids 27: 14–21. Razmkhah, S., Razavi, S.M.A., Mohammadifar, M.A. et al. (2016). Stepwise extraction of Lepidium sativum seed gum: physicochemical characterization and functional properties. International Journal of Biological Macromolecules 88: 553–564. Timilsena, Y.P., Adhikari, R., Kasapis, S., and Adhikari, B. (2015). Rheological and microstructural properties of the chia seed polysaccharide. International Journal of Biological Macromolecules 81: 991–999. Razmkhah, S., Razavi, S.M.A., and Mohammadifar, M.A. (2017). Dilute solution, flow behavior, thixotropy and viscoelastic characterization of cress seed (Lepidium sativum) gum fractions. Food Hydrocolloids 63: 404–413. Naji-Tabasi, S. and Razavi, S.M.A. (2017). New studies on basil (Ocimum bacilicum L.) seed gum: part III–steady and dynamic shear rheology. Food Hydrocolloids 67: 243–250. Naji-Tabasi, S. and Razavi, S.M.A. (2016). New studies on basil (Ocimum bacilicum L.) seed gum: part II–emulsifying and foaming characterization. Carbohydrate Polymers 149: 140–150. Barnes, H.A. (1994). Rheology of emulsions – a review. Colloids and Surfaces A: Physicochemical and Engineering Aspects 91: 89–95. Pal, R. (1996). Effect of droplet size on the rheology of emulsions. AIChE Journal 42: 3181–3190.

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20 Improving Texture of Foods using Emerging Hydrocolloids Ali Rafe Department of Food Processing, Research Institute of Food Science and Technology (RIFST), PO Box 91851-76933, Mashhad, Iran

20.1 Introduction Foods would never be foods if humans did not feel happy and satisfied while eating. From this perspective, palatability is the most important attribute of foods, which is not the case with medicines. Food palatability is determined by organoleptic attributes, including flavor, texture, appearance, sound, and temperature, with flavor and texture being the two major factors that determine food palatability. Flavor, which includes taste and aroma, is associated with relatively small-molecular-weight components, and is perceived through the chemical pathway. On the other hand, texture is associated with relatively high-molecular-weight components, and is perceived through the physical pathway. Texture is the integration of physical, mechanical, and thermal properties perceived in both the oral and pharyngeal phases of the feeding process. Texture is determined by the dispersal, aggregation, and alignment of food constituents, including molecules, particles, cells, and organizations. It has been found that texture governs more than 30% of food palatability, and when limited to staple foods that require a large quantity in every meal, including rice, noodles, bread, and meat, the percentage is higher [1]. Texture has profound effects on customer acceptance of food products because people obtain great enjoyment from eating and perceive changes in texture, which also affects the release profile of flavor through the retronasal pathway. Since food texture can be manipulated by the addition of hydrocolloids in processed food products, the effect of some emerging hydrocolloids on food structure, texture, tribology, and psychology of eating are presented here. Furthermore, fractal dimensions of some hydrocolloids such as basil seed gum (BSG) and carrageenan are provided and ultimately, their functionality and applications, especially texture, are discussed in greater detail.

20.2 Influence of Hydrocolloids on Food Structure Hydrocolloids are a heterogeneous group of long-chain biopolymers characterized by their property of forming viscous dispersions and/or gels when dispersed in water. The Emerging Natural Hydrocolloids: Rheology and Functions, First Edition. Edited by Seyed M.A. Razavi. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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presence of a large number of hydroxyl (-OH) groups markedly increases their affinity for binding water molecules, making them hydrophilic compounds. Further, they produce a dispersion, which is intermediate between a true solution and a suspension and exhibits the properties of a colloid. Considering these two properties, they are aptly termed “hydrophilic colloids” or “hydrocolloids.” The primary reason behind the ample use of hydrocolloids in foods is their ability to modify the rheology of the food system. This includes two basic properties of food system, namely, flow behavior (viscosity) and mechanical solid property (texture). The modification of texture and/or viscosity of food systems help modify its sensory properties, and hence hydrocolloids are used as important food additives to achieve specific objectives. Several hydrocolloids belong to the category of a permitted food additive in many countries throughout the world. Various food formulations like soups, gravies, salad dressings, sauces, and toppings use hydrocolloids as additives to achieve the desired viscosity and mouthfeel. They are also used in many food products like ice creams, jams, jellies, gelled desserts, cakes, and candies to create the desired texture. Considering their role in modifying the viscosity and texture of food formulations, several studies have been conducted in various food systems employing different hydrocolloids, either singly or in combination. Basil (Ocimum basilicum L.) is one of the endemic plants in Iran and is mainly used as a pharmaceutical plant [2]. This plant is grown in many parts of the world especially in warm regions of Asia, Africa, and Central and South America [3]. Besides its use as a traditional medicine, basil seeds are commonly incorporated into food products, such as desserts and beverages, and are used as a source of dietary fiber in Iran and some regions of Asia. These seeds, when soaked in water, swell into a gelatinous mass which has a reasonable amount of gum. It has been reported that the polysaccharides extracted from basil seed comprise two major fractions: (1) glucomannan (43%) and (1 → 4)-linked xylan (24.29%) and (2) a minor fraction, glucan (2.31%). The presence of a highly branched arabinogalactan, in addition to glucomannan and (1 → 4)-linked xylan, has also been shown [4]. BSG has good functional properties comparable to some commercial food hydrocolloids [4–6]. In a study on the steady shear flow behavior of BSG, it was concluded that the existence of yield stress, high viscosity at low shear rates, strong shear-thinning behavior, and the heat-resistant nature of BSG make it a good stabilizer in some food formulations such as mayonnaise, salad dressing, and dairy desserts. BSG, by its effects on the apparent viscosity of ice cream mix, draw temperature, meltdown behavior, and total acceptance, has just shown promising results in stabilizing typical fresh ice cream [6]. In addition, its impact on ice crystallization and recrystallization and on the fat structure in ice cream has been investigated [7]. BSG was used at two concentrations (0.1% and 0.2%) to stabilize ice cream, and its impact on selected physical and structural properties, especially ice crystal size, was compared to that of a commercial blend of carboxymethylcellulose (CMC) and guar gums and to an unstabilized control. Samples were temperature-cycled at subzero temperatures, and ice crystal size was measured before and after cycling. There was no significant difference in ice crystal size after hardening, but the presence of BSG reduced ice recrystallization compared to commercial gums and no stabilizer. The addition of BSG reduced the rate of ice crystal growth by 30%–40% compared to the commercially stabilized ice creams. BSG also decreased the meltdown rate and increased the particle size, thus suggesting that BSG produced a different structure compared to the controls, possibly by lowering the air and fat interfacial tensions. More

20.2 Influence of Hydrocolloids on Food Structure

Table 20.1 Rheological properties of ice cream mix containing different types and concentrations of stabilizers. Formulation

𝜼a (at 50 s−1 , Pa.s)

0.046 ± 0.002c

No stabilizer

0.80 ± 0.03a

a

0.1% BSG

K (Pa.sn )

n (−)

0.180 ± 0.007

0.098 ± 0.005d

bc

0.750 ± 0.038ab

ab

0.63 ± 0.00

0.1% CMC/Guar

0.094 ± 0.004

0.73 ± 0.05

0.270 ± 0.043c

0.2% BSG

0.180 ± 0.010a

0.59 ± 0.01c

0.900 ± 0.031a

0.2% CMC/Guar

b

a

bc

0.170 ± 0.011

0.610 ± 0.020b

0.67 ± 0.03

𝜂 a , Apparent viscosity; n, Flow behavior index; K, Consistency coefficient; BSG, Basil seed gum; CMC, Carboxymethylcellulose. Different letters in a column represent significant differences (P < 0.05, n = 3) BSG basil seed gum, CMC carboxymethylcellulose. Source: Adapted from Bahram Parvar & Goff [7] with permission from Wiley.

studies are needed to understand the mechanisms of action of BSG in cryoprotection and its role as a stabilizer and as an emulsifier in ice cream. The addition of selected stabilizers significantly increased the apparent viscosity and consistency coefficient values of ice cream mixes. BSG created higher viscosity at either 0.1% or 0.2% compared to the combination of CMC and guar at equivalent concentrations (Table 20.1). The viscosity of an ice cream mix is considered a key attribute as it affects the body and texture of the finished product [8, 9]. In some studies, the function of hydrocolloids in enhancing viscosity and decreasing molecular mobility has been correlated to control of ice crystal growth [10]. Therefore, BSG, by producing high viscosity and low flow behavior index values, provided sufficient rheological properties for ice cream. The microstructure of ice creams without stabilizer or containing two levels of stabilizers before and after temperature cycling as seen by cryo-scanning electron microscopy (SEM) is shown in Figures 20.1 and 20.2. Besides the ice structures, BSG incorporation also induced changes in the colloidal structure of the ice cream, specifically the fat and air structures. Large aggregates were shown by particle size analysis, which may

F1

F2

F3

Figure 20.1 Microstructure of air bubbles with fat globules at their interfaces in ice creams subjected to temperature cycling: F1 no stabilizer, F2 containing 0.1% BSG, F3 containing 0.1% CMC/guar. Source: Adapted from Bahram Parvar & Goff [7] with permission from Wiley.

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F1

F2

F3

F4

F5

Figure 20.2 Microstructure of ice cream samples without stabilizer (F1 ) and containing 0.1% BSG (F2 ), 0.1% CMC/guar (F3 ), 0.2% BSG (F4 ), or 0.2% CMC/guar (F5 ) after hardening. Source: Adapted from Bahram Parvar & Goff [7] with permission from Wiley.

be related to the network structure formation of BSG through its emulsifying capacity. Cryo-SEM images demonstrated smaller air cells in the presence of BSG. Further investigations, such as rheological behavior during thawing (viscoelastic properties as a function of temperature), fat and protein analysis in drip and remaining portions during meltdown test, and air bubble size in ice cream, are required for better understanding of the structural changes that occurred with the incorporation of BSG.

20.3 Textural Attributes Food texture can be manipulated by the addition of hydrocolloids in processed food products. The importance of texture is emphasized in our aging society, where the number of patients with mastication and swallowing difficulties is increasing. Studies on food hydrocolloids have been carried out for the texture design of nursing-care foods in terms of the safety of eating [1] as well as physiological functions as a dietary fiber. Food texture should be optimized from the rheological, colloidal, and tribological aspects so that foods can be masticated and swallowed easily even by patients with deficient oral strategy. For example, dysphagia is commonly managed using texture-controlled foods, including thickened liquids and puddings designed to moderate the flow speed of bolus through the pharyngeal phase [11]. For instance, Shahsavani and Rafe [12] have investigated the rheological behavior of binary composite gels of wheat flour and high amylose corn starch, and stated that this composite gel structure can be exploited for dysphagia therapy due to the special textural properties. It has been elucidated that hydrocolloids modify not only food texture but also flavor release from the food matrix. Food products should be formulated using various ingredients to optimize texture, which increases the overall food palatability [13].

20.3 Textural Attributes

60

a

20 Hardness (g)

Hardness (g)

50 40 30 20

a

25

b bc

bc

10

c

b

b

UT

T1 Treatment (b)

15 10 5

0

0 UT

T1

T2 Treatment (a)

T3

T4

T2

Figure 20.3 Effect of thermal treatments on the hardness of BSG. (a) Heating (UT: 25, T1:50, T2:75, T3:100, and T4: 100 ∘ C for 20 min); (b) freezing/thawing (T1:−18 and T2:−25 ∘ C for 24 h). Source: Adapted from Zameni et al. [14] with permission from Springer.

According to the soft texture of BSG gel, the penetration test has been recommended to evaluate its texture [14, 15]. BSG has this ability to form a gel at 3% (w/w), which imparts 13.5 g hardness. As shown in Figure 20.3, BSG gel shows stable hardness after heating treatments at 50, 75, and 100 ∘ C for 20 min; but heating at a higher temperature (121 ∘ C) not only has a destructive effect on BSG but also produces a gel network with relatively high strength and hardness. It may be hypothesized that higher temperature during gel formation may have more effectively opened and exposed the BSG molecules, thus favoring their interaction, formation of junction zones, and producing a stiffer network. Freezing of BSG gel also improves gel hardness, and this alteration is more pronounced after freezing at −25 ∘ C for 24 h (Figure 20.3) [14]. Adhesiveness is the ability of gel sample to become sticky. This parameter is important, because it may influence the overall quality, appearance, and shelf life of food. BSG gel has 16.79 g.s adhesiveness, which increases significantly after heat treatment (Figure 20.4). BSG gel adhesiveness also increases after freezing–thawing, but this increment is not significant (−18 and 25 ∘ C for 24 h), as seen in Figure 20.4. The high levels of adhesiveness of BSG make it desirable for use in salad dressing formulations. The consistency of BSG gel is ∼50 (g.s), which on heating at 121 ∘ C causes a dramatic increment 30

25 20

c

b

ab

ab

a

15 10 5 0 UT

T1

T2 Treatment (a)

T3

T4

Adhesiveness (g.s)

Adhesiveness (g.s)

30

a

25 20

a

a

UT

T1 Treatment (b)

15 10 5 0

T2

Figure 20.4 Effect of thermal treatments on the adhesiveness of BSG. (a) Heating (UT: 25, T1:50, T2:75, T3:100, and T4: 100 ∘ C for 20 min); (b) freezing/thawing (T1:−18 and T2:−25 ∘ C for 24 h). Source: Adapted from Zameni et al. [14] with permission from Springer.

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20 Improving Texture of Foods using Emerging Hydrocolloids

in the consistency of BSG gel. The results suggest an increase in junction zones of the gel during heating because of the existence of a large amount of unsubstituted mannan regions. The prevalence of higher molecules in BSG is likely responsible for the greater consistency of BSG gels under thermal treatments. BSG gel consistency increases negligibly after freezing treatment [14]. It was also understood that BSG can be utilized for coating and biodegradable films. The produced films were transparent with good mechanical properties and excellent barrier properties. Glycerol had an essential role in making homogeneous flexible films and also affected the physical and mechanical properties of BSG films. Overall, the best properties of BSG-based films were observed in glycerol-plasticized films [16]. The effect of freezing treatments (−18 ∘ C for 24 h and − 30 ∘ C for 15 h) on the rheological, emulsifying, foaming, and textural characteristics of cress seed gum (CSG) in comparison with xanthan gum have been investigated [17]. The large-deformation test was showed an increase in the hardness, consistency, and adhesiveness of CSG gel (7% w/w) after freezing treatments, which are more pronounced at -30 ∘ C for 15 h. The adhesiveness property of CSG makes it interesting for coating, binding, and agglomerating powders. The cohesiveness remains constant after freezing at −18 ∘ C for 24 h, but there is an increase in the springiness after the freezing treatments. In contrast, freezing at −30 ∘ C causes a dramatic increase in the gumminess property from 44.19 to 61.73 g. CSG has an excellent ability to control ice crystal growth, because the texture shows minimal change after freezing–thawing. CSG has also good emulsifying capability (490%) that is maintained after freezing. The o/w emulsion containing CSG is stable after heating at 80 ∘ C for 30 min, but a slight decrease in its stability occurs after freezing treatments. Freezing causes both the foaming capacity and foaming stability of CSG solutions to increases slightly. The foam stability of xanthan improves after freezing treatment, but its foam-forming capability decreases. In comparison, CSG has better foaming properties than xanthan after freezing treatments as shown in Figure 20.5. It was suggested Foaming capacity

30 A

Foaming stability A

A

25

% Foaming

504

B

20 15

b

a

bc bc

C

C

c

c

10 5 0 CSG

XG

Control (25°C)

CSG

XG

CSG

XG

Freezing 1(–18°C–24h) Freezing 2(–30°C–15h)

Samples

Figure 20.5 Effect of freeze–thaw treatments on the foaming properties of cress seed gum and xanthan gum. Source: Adapted from Naji et al. [17] with permission from Springer.

20.3 Textural Attributes

that CSG may minimize freezing damage by reducing free water availability, controlling moisture migration, and preventing the growth of ice crystal in frozen foods, on account of the strong cross-linking of the CSG polymer. On the other hand, conversion of water to ice increases molecular association and improves textural characteristics. Therefore, CSG like xanthan gum has potential use in the food industry and can ensure that quality is maintained throughout freezing conditions during processing, transportation, and storage [17]. In another study, Naji and Razavi [18] studied the influences of low temperature (4 ∘ C, 96 h and 10 ∘ C, 40 h) on the functional properties (flow behavior, time dependency, emulsifying, and foaming behavior) and textural attributes of CSG and xanthan gum. CSG gel showed elastic, adhesiveness, and cohesiveness properties, which could maintain product integrity during refrigeration operations and reduce moisture loss throughout the product shelf life; maximum flavor, texture, and color were maintained. CSG gel was also subjected to different thermal treatments (60 ∘ C, 30 min; 80 ∘ C, 23 min; 100 ∘ C, 18 min; and 121 ∘ C, 15 min) to investigate the stability of its textural characteristics using penetration and texture profile analysis (TPA) tests [19]. The results demonstrated that cress seed gel is heat stable with respect to most of the textural attributes (hardness, consistency, adhesiveness, apparent modulus of elasticity, cohesiveness, and springiness), and in some cases, the heat had an improving effect on the gel. Therefore, CSG is employed as a texture modifier in the formulation of foods subjected to high-temperature processes. These properties are especially useful and make it easy to modulate CSG gel in specialty food as a gelling agent, for example, re-structured foods, cold prepared instant bakery, and especially for foods subjected to high temperature that require further processing steps like blanching, pasteurization, and sterilization in food and cosmetic industries. The effect of BSG, CSG, and quince seed gum (QSG) at concentrations of 0.1% and 0.3% on the physical, textural, and rheological properties of low-fat whipped cream with 30% fat content was investigated and compared with a high-fat (HF) whipped cream sample (55%) as a control. Flow curves were analyzed using the Herschel–Bulkley and Carreau models. The rheological results confirmed that all samples were shear-thinning fluid, exhibiting yield stress and thixotropy properties. The frequency sweep test showed that at the same gum concentration, mixtures containing BSG have higher storage, loss moduli, and complex viscosity than those of mixes with QSG and CSG, and all mixes containing gum displayed weak gel-like behavior. Analysis showed that increasing gum content led to increased viscosity, hardness, and overrun, leading to better quality in the final products. Moreover, textural properties showed that the effect of BSG on hardness and adhesiveness was significantly greater than that of QSG and CSG at the same concentration. On the basis of the obtained result, 0.3% concentration of added BSG had a much greater effect on the whipped cream properties than those of mixes with QSG and CSG [20]. Overall, the textural characteristics of whipped cream indicated a positive correlation between gum level and hardness or adhesiveness. QSG samples showed less overrun but 0.3% CSG and BSG with HF whipped cream had the same overrun. Also, QSG mixes showed the least value of drainage volume. Data analysis showed that the hysteresis loop values of whipped cream mixes containing BSG 0.1, CSG 0.1, CSG 0.3, and HF whipped cream were equal. The concentration of added BSG had a much greater effect on the whipped cream properties. All results suggested the appropriate potential application of BSG and QSG in the formulation of whipped cream as fat replacers [20].

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20 Improving Texture of Foods using Emerging Hydrocolloids

20.4 Tribology (Body–Texture Interaction) Food texture is perceived during oral processing, in which a series of oral operations occur in the right sequence with a variety of organs and muscles working in a coordinated manner from the first bite to swallowing [21]. Food oral processing is well described by the in-mouth process model (Figure 20.6) [22]. The x-axis represents time, which increases as the oral processing proceeds, and the y-axis represents the degree of lubrication, which increases as the mixing of food bolus with saliva proceeds. The z-axis represents the degree of structure, decreasing as the mastication proceeds. According to this model, solid foods should be masticated to lower the degree of structure (lower than the plane ABCD) and also should be mixed with saliva to increase the degree of lubrication (to pass the right side of the plane EFGH) prior to swallowing. Solid foods like steak and cake should be masticated and lubricated to break down the structure and to form a coherent bolus, while liquids and raw oyster are swallowed immediately as a bolus is formed without great effort. When the behavior of oral processing is compared between solid foods and liquid foods, solid foods take more time to enter the “swallowing box” along with larger changes in the structure until a ready-to-swallow bolus is formed. The reasons why texture is more important in solid foods than in liquid foods include [23, 24] the following: 1) The mechanical, geometrical, and surface properties of solid foods can be changed to a greater degree than those of liquid foods during oral processing. 2) Residual time in the mouth for solid foods is longer than that for liquid foods. 3) Humans are more sensitive to changes in elasticity than in viscosity [25]. These points emphasize the importance of the optimization of food texture, particularly in developing solid- and gel-type food products. Food oral processing is an essential daily dynamic activity that includes all muscle activities, jaw movements, and tongue movements that contribute to preparing food for swallowing [26]. A number of processes occur in the mouth, including a mechanical E 1 Tender juicy steak 2 Tough dry meat 3 Dry sponge cake 4 Oyster 5 Liquids

F 2 1 Degree of structure

Swallowing box

B 3

4

5

C

H

A

G Time

D

Destructured enough to swallow Lubricated enough to swallow

Degree of lubrication

Figure 20.6 In-mouth process model from mastication to swallowing. Source: Adapted from Hutchings and Lillford [22] with permission from Wiley.

20.4 Tribology (Body–Texture Interaction)

breakdown of solid pieces into smaller fragments, enzymatic reduction of starches into sugars, molecular interaction with microorganisms, and mixing with saliva. It is the first step in the food intake and metabolism process that delivers energy and essential nutrients to our body [27]. The intensity of the muscular, jaw, and tongue movements during oral processing is dependent on the type of food in the oral cavity. Four categories of food products can be defined on the basis of their rheological and sensory properties: liquids, semisolids, soft solids, and hard solids [28] that are defined by Stieger and van de Velde [27] as follows. Liquids flow and do not require chewing before swallowing, although liquids are orally processed (e.g., milk, beverages, yogurt drinks). Semisolids are predominantly squeezed between the tongue and palate during oral processing using the molars (e.g., pudding, custard). Soft solids require (initial) chewing between the molars, but do not elicit “crispy” sensations (e.g., cheese, processed meat). Hard solids are crispy, require chewing between the molars, and generally produce sounds during oral processing (e.g., crackers, raw vegetables, apples). The perception of food texture is vital in determining its acceptance and preference by consumers. Traditionally, texture is measured with a sensory panel; however, this method is subjective and time consuming. Hence, interest is growing in an instrumental method that can provide an objective measure of texture. Once in the mouth, the food is manipulated by the tongue, teeth, inside of the cheeks, and lips with different speeds and pressures [29]. Through the various stages of mastication, food is continuously chewed, mixed up with the saliva, and gradually converted into a bolus ready to be swallowed [30]. Various sensory textural attributes that human senses perceive during different stages of the mastication process include hardness, softness, adhesiveness, springiness, thickness, brittleness, crispiness, sponginess, smoothness, roughness, lumpiness, pastiness, creaminess, slipperiness, and many others [30]. Foster et al. [31] have rightly described sensory perception during oral processing as a dynamic process. Over the past few decades, extensive studies in food texture studies have attempted to qualify and quantify the physical properties of foods using techniques such as a texture analyzer [32], posthumous funnel [33], viscometer [34], and rheometer [35–37]. Many textural features, such as hardness, springiness, adhesiveness, fracturability, and thickness perceived during oral processing, have been well explained by some specific physical parameters measured using these techniques [21]. However, these approaches are essentially based on bulk destruction and shear deformation. Therefore, these methods are feasible only for those texture properties which are linked directly to bulk phase deformation but are not applicable to some of the sensations that are detected by rubbing and squeezing actions (upward/downward movement along with horizontal movements) of the tongue against the palate, such as creaminess, slipperiness, and smoothness. Such actions create both a normal and a shearing force in the mouth and generate a friction/lubrication sensation between the palate and the tongue with the food product (or food–saliva mixture) acting as the lubricant. These oral actions are no longer associated with bulk phase deformation but have more to do with thin layer rheology or tribology. In view of the limitation of the rheometer, posthumous funnel, viscometer, and texture analyzer, which tend to utilize either the normal force or the shear force to describe some of the oral sensations, tribology, the study of thin film and lubrication, has attracted growing interest in the past decade in food texture studies. It has been hypothesized that food tribology could explain the physical fundamentals for food texture studies where rheology and texture analysis have failed. One of the

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20 Improving Texture of Foods using Emerging Hydrocolloids

most obvious implications of food tribology is the study of smoothness sensation, an essential texture feature linked to oil/fat presence and creaminess perception. The food industry is under a growing pressure to develop tasty fat-reduced food to combat the increased number of fat-related diseases worldwide and an instrument that can mimic fat-related sensory attributes such as creaminess and fattiness [38]. Tribology, a sub-category of rheology, is the study of friction between two interacting surfaces, and is related to wearing and lubrication. Tribology promotes a fundamental understanding of food structure–texture relationships [38]. During oral processing, food structure is continually broken down, and the food is mixed with saliva, resulting in the formation of a thin film on the oral surfaces, particularly just prior to, during, and after swallowing. At this stage, the tribology of the tongue–palate contact rather than the bulk rheological properties of the food dominate textural sensations. Liquid and semi-solid foods have short oral retention times ( 93%). The M/G ratio of the SSG polysaccharide is the range 1.78–1.93, which is fairly similar to that of guar gum (1.43–2.0) It has been found that mannose (61.50%) and galactose (33.15%) are the major carbohydrate fractions, but glucose (2.78%), arabinose (1.41%), and rhamnose (1.17%) are minor ones [42]. At certain concentrations, it is able to thicken aqueous dispersions, form gels, and reduce the surface tension of water [43, 44]. 21.2.11

Salep Glucomannan

Salep, a member of the family Orchidaceae, is obtained from the dried tubers of orchids growing in different parts of Iran and Turkey. It is rich in polysaccharides (11%–44%), which gives it an important stabilizing capacity since it swells when used with water and milk. Salep is known to be a valuable source for glucomannan, and its mannose-to-glucose ratio is in the range 2.0–3.0. The thickening, gelling, and stabilizing abilities of Salep in food systems such as emulsions, ice creams, milk desserts, and

529

530

21 New Hydrocolloids in Ice Cream

drinks were discovered by earlier researchers [45]. It is commonly used for imparting hardness and elasticity to Turkish ice cream (Kahramanmaras-type). In addition, Salep is traditionally applied as one of the essential ingredients of Iranian ice cream [46–48]. There are two forms of Salep, having either (1) palmate (branched) tubers or (2) rounded (unbranched) ones. It has been reported that at similar concentrations, palmate-tuber Salep exhibited a higher consistency of gum solutions in comparison to the rounded-tuber type [49]. 21.2.12

Gum Tragacanth

Gum tragacanth is a natural exudate obtained by slitting the stems and branches of the Astragalus species (family Leguminosae). Astragalus plants grow in sections of Asia Minor and in the semi-desert and mountainous regions of Iran, Syria, and Turkey as well as Australia. The name “tragacanth” is derived from the Greek tragos (goat) and akantha (horn), referring to the white curled ribbons [50]. This hydrocolloid is a very complex heterogeneous anionic polysaccharide composed of two main fractions: a water-insoluble component called bassorin which has a chain of galacturonic acid units, and a water-soluble arabinogalactan component known as tragacanthin. Because of the easy separability of bassorin and tragacanthin, it has been suggested that the two fractions are in a physical mixture and not chemically bonded [51]. Gum tragacanth has been widely used in food technology applications on the basis of its gelling and thickening ability, good suspending action, unusually high stability to heat and acidity, emulsifying characteristics, creamy mouthfeel, good flavor-release properties, and very long shelf life [52].

21.3 Functions of New Hydrocolloids in Ice Cream 21.3.1

Stabilizing

21.3.1.1

Rheological Properties

It has been reported that the flow behavior index of ice cream mixes is less than unity (n < 1) [6]. The decrease in shear stress with an increase in the shear rate may be owing to the increased alignment of the constituent molecules, complex entanglement of partially broken-down micellar casein at the droplet surface and aggregation of fat globules in ice cream mix [53–56]. However, the dilatant behavior has been reported by others for mixes containing Salep and Isfarzeh mucilage [47, 57]. There are many different models to determine the rheological properties of non-Newtonian fluids. In this regard, the power-law model (Eq. (21.1)) is generally used to describe the rheology of ice cream mixes [48]: 𝜏 = k 𝛾̇ n

(21.1)

where 𝜏 (Pa) is the shear stress, k (Pa.s ) is the consistency coefficient, 𝛾̇ (s ) is the shear rate, and n (dimensionless) is the flow behavior index. Table 21.1 shows the values of the flow behavior index and consistency coefficient of some ice cream mixes including new hydrocolloids as stabilizer. Previous studies have revealed that the shear-thinning behavior become more prominent as the concentration of stabilizer increases, which is n

−1

21.3 Functions of New Hydrocolloids in Ice Cream

Table 21.1 Parameters of the power-law model determined for regular mixes containing new hydrocolloid stabilizers. Stabilizers

k (Pa.sn )

n (−)

Reference

Isfarzeh seed mucilage, basil seed gum, Salep

1.25–2.43

0.30–1.40

[57]

Qodume Shahri seed gum, cress seed gum

3.61–11.52a)

0.41–0.55b)

[54]

Basil seed gum, carboxymethylcellulose, guar gum

0.27–0.90c)

0.63–0.73d)

[58]

Balangu seed gum, carboxymethylcellulose, palmate-tuber Salep

0.05–6.82

0.45–1.15

[47]

Basil seed gum, guar gum, κ-carrageenan

19.51–20.41

0.40–0.42

[59]

Cress seed gum

0.89–7.14e)

0.53–0.74f )

[60]

Okra cell wall and polysaccharide, guar gum

—

0.52–0.71g)

[61]

k, consistency coefficient; n, flow behavior index a) k value for ice cream mix without stabilizer was 1.29. b) n value for ice cream mix without stabilizer was 0.63. c) k value for ice cream mix without stabilizer was 0.1. d) n value for ice cream mix without stabilizer was 0.8. e) k value for ice cream mix without stabilizer was 0.712. f ) n value for ice cream mix without stabilizer was 0.776. g) n value for ice cream mix without stabilizer was 0.72.

shown by a decrease in values of the flow behavior index [12, 54, 58, 60–62]. This finding has been related to the increase in serum concentration resulting from the formation of compact polysaccharides entanglements which are very sensitive to the shear rate. The shear-thinning behavior is an important factor for desirable texture and mouthfeel and for choosing the size of the pump for mix handling. Additionally, viscosity, the resistance of a liquid to flow, is the most important aspect of fluid rheology [2, 12]. In general, the magnitudes of the consistency coefficient and viscosity are also enhanced by increasing the concentration of novel stabilizers [12, 54, 57–60, 62, 63]. Hydrocolloids contribute to the mix viscosity and stabilize the protein in the mix due to the capability of interacting with water, proteins, and lipids [6, 57]. The results reported by El-Aziz et al. [62] showed that the mix viscosity was very dependent on the type and concentration of cress seed mucilage, flaxseed mucilage, and guar gum. This observation is related to the effect of sugar, proteins, and salts on the functional properties of the used stabilizers. In another study, ice cream mixes containing Qodume Shahri gum had higher viscosity and consistency coefficients of the power-law and Herschel–Bulkley models than those of mixes with cress seed gum at equivalent concentrations. Azari-Anpar et al. [54] concluded that magnitude of this rheological property was affected by the chemical structure, size, molecular weight, and water-holding capacity of the selected gums. It was also reported that increasing the proportion of basil seed gum in stabilizer mixtures containing commercial gums

531

532

21 New Hydrocolloids in Ice Cream

enhanced the viscosity of the ice cream mix [59, 63, 64]. Similar results have been found by BahramParvar and Goff [58]. On the other hand, Yuennan et al. [61] and Raftani and Ahmadi [65] reported that tragacanth gum and okra polysaccharide produced lower viscosity values, respectively, in comparison with CMC and guar gum at equal amounts. Furthermore, the effects of different proportions of gum tragacanth and Salep glucomannan on some rheological properties of ice cream mix have been investigated [66]. The authors found that an increase in the tragacanth-to-Salep ratio decreased the values of Burger’s model and Maxwell unit parameters. In fact, the addition of gum tragacanth created a stronger network with a greater resistance to deformation. 21.3.1.2

Textural Attributes

The mechanical properties such as hardness and Young’s modulus indicate that how foods respond when they are deformed [1]. There are many important factors that influence ice cream texture. The stabilizer is one such ingredient imparting specific functions to the finished product. This ingredient prevents the formation of large ice crystals and lactose crystals in ice cream mixes during processing and storage by binding water. Therefore, stabilizer is necessary to produce smoothness in body and texture [54, 66]. Numerous studies have evaluated the textural attributes of ice cream. In this regard, El-Aziz et al. [62], in investigating the physical properties of ice cream containing cress seed and flaxseed gums, found that the magnitude of hardness decreased by either adding hydrocolloids or increasing their concentration due to increased viscosity, decreased movement of water molecules, and consequently limited ice crystal growth. On the other hand, Azari-Anpar et al. [54] reported that Qodume Shahri and cress seed gums enhanced the hardness of ice cream, attributing it to low air content and high viscosity. Similar in hardness, both native Iranian gums increased adhesiveness, gumminess, and chewiness. In another study, a novel stabilizer blend composed of 96.94% basil seed gum and 3.06% guar gum was introduced [67]. They assessed the effects of these primary stabilizers in combination with k-carrageenan on the textural properties of ice cream and found that the hardness and consistency of ice cream decreased by the addition of κ-carrageenan, because of the cryoprotective function of this hydrocolloid, but these parameters increased during storage time, which was attributed to recrystallization of ice. Kurt et al. [66] observed that Young’s modulus and stickiness, as indicative properties of Kahramanmaras-type ice creams, increased as a result of adding gum tragacanth. In addition, this gum was used as a substitute for CMC. The results showed that hardness was the lowest for ice creams containing 0.3% CMC and 0.1% tragacanth, and the highest for samples with 0.4% tragacanth. From a textural point of view, the ability of chia seed mucilage to be replaced with the emulsifiers and stabilizers in ice cream was also demonstrated [68]. 21.3.1.3

Overrun

The air content of ice cream is in the form of microscopic bubbles or cells and is determined by the overrun percentage [1]. Overrun is directly tied to quality, yield, and commercial benefits, and therefore tight control over this property is essential [2]. Stabilizers are able to increase the viscosity of the mix, maintain air bubbles, and consequently improve ice cream volume [6]. However, a number of researchers have determined the negative impact of high viscosity on the overrun [6, 47, 58, 59, 61, 62, 65], which was connected to hydrocolloid concentration, so that an increase in the level of

21.3 Functions of New Hydrocolloids in Ice Cream

Table 21.2 Overrun values of regular ice creams containing new hydrocolloid stabilizers. Stabilizers

Overrun (%)

Reference

Basil seed gum, carboxymethylcellulose, guar gum

42.7–62.3a)

[58]

Balangu seed gum, carboxymethylcellulose, palmate-tuber Salep

18.8–28.6

[47]

Basil seed gum, guar gum, κ-carrageenan

55.5–60.9

[59]

Basil seed gum, carboxymethylcellulose, guar gum

30.6–65.2

[64]

Gundelia tournefortii L., guar gum, carrageenan, Salep

43.0–71.0

[29]

Chia mucilage, commercial stabilizer

60.0–96.0

[68]

Gum tragacanth, Salep

32.4–32.8

[66]

Gum tragacanth, carboxymethylcellulose

53.3–57.0

[65]

Okra cell wall and polysaccharide, guar gum

70.0–85.0

[61]

a) Overrun (%) for ice cream without stabilizer was reported as 45.8%.

hydrocolloid decreased the overrun. Therefore, an appropriate amount of viscosity is needed to entrap air and stabilize air bubbles. Other researchers observed no significant changes in the overrun between different concentrations of gum tragacanth and Salep glucomannan [66]. Compared to some well-known commercial stabilizers, chia seed gum and G. tournefortii L. produced superior air incorporation [29, 68]. It is concluded that the overrun of ice cream is mostly affected by the nature and concentration of the stabilizer, and consequently on the machine used to make ice cream. As shown in Table 21.2, the low values of overrun can be due to the incapability of the batch freezer to incorporate air and obtain the desired volume. 21.3.1.4

Melting Resistance

Meltdown is one of the main techniques to characterize the thermal properties of ice cream. It is determined by the meltdown test, which measures the ability of ice cream to resist melting when placed on a wire mesh and exposed to a constant temperature, for example, 25 ∘ C, for a period of time [1]. Numerous factors influence melting resistance, such as the number and surface area of ice crystals, the viscosity of the serum phase, fat globule/cluster size, and the air content [2]. BahramParvar et al. [63] found that the melting rate of ice cream decreased as the level of fat destabilization increased. This observation may be related to the fact that partially coalesced fat is responsible for stabilizing the air cells [2]. Additionally, the greater the overrun, the lower the thermal conductivity of ice cream [1, 57, 62]. BahramParvar et al. [67] also reported that melting resistance of ice cream decreased with storage, due to ice recrystallization. Research findings have shown that hydrocolloids delay the separation of the clear serum from ice cream during the meltdown, which is attributable to their water-holding capacity and microviscosity enhancement ability. In the other words, as the ice crystals melt, the water must diffuse into the serum phase. The increase in hydrocolloid content increases the resistance to flow. Therefore, more time is needed for the water to drip through the

533

534

21 New Hydrocolloids in Ice Cream

screen on which it rests [29, 47, 57, 58, 61–63]. Kurt et al. [66] adjusted gum tragacanth and Salep glucomannan ratios to obtain a constant concentration (1%). They observed that increasing ratio of gum tragacanth in the mixture enhanced the melting resistance. Similarly, the melting rate decreased upon increasing the ratio of basil seed gum in the stabilizer mixture, while the addition of CMC and guar gum increased the melting rate values [6, 63]. In another investigation, ice creams containing palmate-tuber Salep exhibited lower melting resistance than that of samples produced using CMC or Balangu seed gum [47]. 21.3.1.5

Sensory Characteristics

The sensory characteristics of foods can be detected by the sense of sight, smell, taste, touch, and hearing. Most people tend to eat ice cream because of its sensory properties, including a smooth, creamy, and viscoelastic texture, a rich sweet flavor, and cold sensation. The ingredients and processing conditions used in the production of ice cream influence the sensory properties [1, 2]. One function of stabilizers in ice cream is to decrease the icy sensation, as reported in several published works [62, 69]. It can be assumed that the desirable effects of hydrocolloids on the sensory perception of ice cream result from their ability to change the surface properties of ice crystals or to change the perception of ice crystals in the mouth [6]. In other words, hydrocolloids, due to their functional properties, have significant effects on recrystallization, as described in detail in Section 21.3.3. Regarding the results pertaining to the overall acceptability of ice creams containing new hydrocolloids, the samples with basil seed gum, Qodume Shahri seed gum, and SSG showed higher scores than those including Isfarzeh mucilage, cress seed gum, and Salep, respectively [54, 57, 69]. Cakmakci and Dagdemir [29] found that adding G. tournefortii L. leaves significantly decreased the overall acceptability of ice cream compared to the sample with commercial stabilizers. Contrary to this result, there were no statistical differences between CMC and Balangu seed gum in terms of total acceptance [47]. BahramParvar et al. [70], BahramParvar et al. [59], and BahramParvar et al. [64] observed that the combination of basil seed gum and guar gum at the optimum level created acceptable sensory properties, because the hedonic sensory scores of appearance, flavor, body and texture, color, and total acceptance of ice creams were about 7. The instrumental textural properties of ice cream had moderate to high correlations with some sensory properties, including iciness, coarseness, creaminess, smoothness, and greasiness, in a scoop [67]. It has also been reported that some sensory characteristics of ice cream are related to their rheological properties [6]. 21.3.2 21.3.2.1

Fat Replacement Rheological Properties

The evaluation of the time-dependent rheological properties of ice cream mixes is important to assess the relationship between structure and flow during processing [66, 71]. The second-order structural kinetic model was applied to investigate the influence of fat content (2.5% and 10%), fat replacers (guar gum, basil seed gum, and their mixture [50:50]), and the fat replacer level (0.35%, 0.45%, 0.5%, and 0.55%) on

21.3 Functions of New Hydrocolloids in Ice Cream

Table 21.3 Some characteristics of full-fat, low-fat, and light ice creams containing basil seed gum (BSG), guar gum (GG), and their mixture (50:50).

Bb)

Overrun (%)

Melting rate (g min−1 )

Creaminess

Reference

1.25

1.13

29.0

0.83

4.8

[3, 72]

BSG

1.80

4.76

13.9

0.41

5.3

GG: BSG

1.35

3.17

29.2

0.77

4.9

Ice cream

Stabilizer/ fat replacer

𝜼0 /𝜼∞ a)

Full fat (10%)

GG

Light (5%)

Low fat (2.5%)

Extent of thixotropy

GG

—

0.64–3.03

32.1–40.1

0.89–1.00

4.2–7.5

BSG

—

2.96–7.58

23.2–31.1

0.06–0.55

3.5–8.2

GG: BSG

—

0.88–4.97

29.3–44.5

0.79–1.10

3.7–7.0

GG

1.20–1.51

—

23.4–31.5

0.81–0.89

2.8–5.3

BSG

1.60–2.33

—

11.6–21.1

0.25–0.71

3.3–7.1

GG: BSG

1.09–1.39

—

23.4–34.7

0.75–0.91

2.5–6.2

[72]

[3]

a) Extent of thixotropy of full-fat ice cream mixes in comparison with low-fat samples. b) Extent of thixotropy of full-fat ice cream mixes in comparison with light samples.

the time-dependent rheological properties of ice cream mixes [3]. They observed that all formulations were thixotropic, and a decreasing trend of the thixotropy rate constant (k) and extent of thixotropy (𝜂 0 /𝜂 ∞ ) was seen as the fat content decreased, while these parameters were enhanced by either adding fat replacers or increasing their concentration. At the same fat and gum levels, ice cream mixes with basil seed gum exhibited a greater shear-sensitive thixotropic nature than mixes containing guar gum and its blend with basil seed gum (Table 21.3). The authors declared that this observation could be related to the complex nature of basil seed gum. In addition, insignificant differences were observed in the 𝜂 0 /𝜂 ∞ of mixes with 0.35% and 0.45% basil seed gum and gum blend. Other models have recently been applied to characterize the thixotropic behavior of full-fat and light ice cream mixes containing guar gum, basil seed gum, and their mixture (50:50) as a fat replacer. In this regard, Javidi and Razavi [72] stated that fat reduction from 10% to 5% decreased the extent of thixotropy (B), but no specific trend was seen in the values of the breakdown rate constant (k). It was also found that full-fat and light samples with basil seed gum and its blend with guar gum had higher B values than those of mixes containing guar gum at the same concentration. The power-law, Casson, and Herschel–Bulkley models were used to describe the steady-state rheological data of light (5%) and low-fat (2.5%) ice cream mixes, respectively [3, 72]. From the data obtained, values of the flow behavior index (n) of low-fat and light mixes were observed to be less than 1 (0.42–0.74), indicating their pseudoplastic nature. It was found that fat reduction had no significant effect on the n values, whereas the addition of fat replacers and an increase in their concentration were accompanied by an enhancement of the pseudoplasticity of the mixes. The formation of compact polysaccharides entanglements sensitive to the shear rate could explain this observation. The consistency coefficient (k) can be considered to indicate the viscous nature of fluid foods [6]. Research findings by Javidi et al. [3] and Javidi and Razavi

535

536

21 New Hydrocolloids in Ice Cream

[72] showed that k values were reduced as the fat content decreased and increased as fat replacers were added, with samples including guar gum ranked first followed by mixes containing basil seed gum, although the consistency coefficient of basil seed gum samples increased more with concentration than that of ice cream mixes containing guar gum. This could be owing to the molecular chain expansion of basil seed gum resulting from stronger anionic nature of this novel gum in comparison to guar gum. A similar trend was also observed in the Casson plastic viscosity of light mixes as a result of fat reduction and gum addition. The yield stress is defined as the stress at which a material begins to undergo permanent deformation. At the same amount of gum (0.35%), a lower yield stress was found in low-fat (2.5%) and light (5%) samples compared to regular ice cream (10%). On the other hand, higher yield stress values in mixes with higher gum concentrations were connected to the increased intermolecular associations [3, 72]. This parameter, as a quality control tool, is correlated well with the texture, body, and scoopability of the ice cream [73]. 21.3.2.2

Textural Attributes

It is obvious that the type and amount of ingredients such as fat and fat replacers used in ice cream formulations can mainly impact textural properties. The findings by several works indicated that the hardness of light (5%) and low-fat (2.5%) ice creams decreased upon reducing the fat content [3]. The reason for this observation can be attributed to the ice crystal size and ice phase volume. These authors stated that higher hardness values were obtained by increasing the fat replacer concentrations (0.35%, 0.45%, 0.5%, and 0.55%), leading to an increase in the viscosity of the samples. In this regard, the effect of the guar gum–basil seed gum blend (50:50) on hardness was greater than that of the other two systems (guar gum or basil seed gum) at the same concentration, except for 0.55% guar gum. In the other words, low-fat and light ice creams with 0.55% guar gum had the maximum value of hardness in comparison to the corresponding samples containing basil seed gum and its blend with guar gum. Moreover, no significant differences were observed between the hardness of samples including the same amount of individual gums at 0.35%, 0.45%, and 0.55%. The effect of fat and fat replacers on the adhesiveness of ice creams was found parallel to the results of the hardness. However, guar gum and the mixture of guar gum and basil seed gum (50 : 50) generally caused the lowest adhesiveness of light and low-fat ice creams, respectively [3, 72]. 21.3.2.3

Overrun

Fat, hydrocolloids, and proteins are important key factors for the incorporation of air into an ice cream mix and also for controlling the thermodynamically unstable air cells [2]. A certain viscosity is needed to entrap air during the freezing process. In the other words, the vigorous agitation of too viscous ice cream mix causes difficulties and then air incorporation decreases, while in low-viscosity liquid, the film on the surface of the air cells drains [1, 59]. According to previous studies, fat reduction increased the overrun values of low-fat (2.5%) and light (5%) ice creams, but this parameter was decreased by raising the concentration of fat replacers (guar gum, basil seed gum, and their mixture [50:50]), owing to the capability of hydrocolloids to absorb water and consequently increase the viscosity [3, 72, 74]. The observed effect of basil seed gum on the overrun was greater than that of guar gum at the same concentration (Table 21.3). On the other hand, samples including the mixture of guar gum and basil seed gum had a

21.3 Functions of New Hydrocolloids in Ice Cream

Rate of break down (s–1)

0.020 y = –0.019x + 0.022 R2 = 0.856

0.016 0.012 0.008 0.004 0.000 0.00

0.20

0.40 0.60 Melting rate (s–1)

0.80

1.00

Figure 21.2 Correlation between the melting rate data and breakdown rate parameters determined for low-fat ice creams. Source: Adapted from Javidi et al. [3] with permission from Elsevier.

higher overrun than ice creams with guar gum at concentrations of 0.35% and 0.45%. In addition, there were no significant differences between the overrun percentages of the latter two-gum systems at higher concentrations. These results indicate a synergistic interaction between guar gum and basil seed gum. 21.3.2.4

Melting Resistance

The meltdown of ice cream is influenced by heat and mass transfer phenomena in which water has a higher thermal conductivity than fat. So, the fat content and the network of fat globules can mainly affect the melting properties. Compared to full-fat (10%) ice cream, a lower first dripping time and a faster melting rate of light (5%) samples with 0.35% gum were obtained by Javidi and Razavi [72]. Their results also indicated that the addition of a fat replacer (basil seed gum, guar gum, and their mixture [50:50]) increased the first dripping time and reinforced the melting resistance, and basil seed gum was more effective than other gum systems (Table 21.3). Similar results have recently been reported by others [3, 74]. In addition, Javidi et al. [3] investigated the M0 /M150 value (extent of melting) to better describe the melting behavior of low-fat (2.5%) ice creams including basil seed gum, guar gum, and their 50:50 blend as fat replacers. They found that this parameter was considerably influenced by three main factors: (1) fat reduction, (2) fat replacer addition, and (3) fat replacer concentration. As a matter of fact, the addition of basil seed gum to the low-fat ice cream was more effective in reducing the M0 /M150 value, compared to guar gum and their mixture in the ratio 50:50. As shown in Figure 21.2, a significant (p < 0.05) linear negative correlation was also observed between the melting rate data and breakdown rate parameters for low-fat ice creams. The reason for this is probably the structural arrangement of ice creams, encompassing factors such as the extent of partial coalescence of fat [1, 75]. 21.3.2.5

Sensory Characteristics

It is generally acknowledged that fat content affects the sensory quality of ice cream, such as enhancement of creaminess, an increase of mouth-coating, and flavor perception [76]. Vanilla as a primary flavor used in ice cream is a lipophilic component, so

537

538

21 New Hydrocolloids in Ice Cream

dissolution and release of this flavor are strongly influenced by milk fat, which is in agreement with the findings reported by Javidi et al. [3]. They also found that low-fat (2.5%) ice creams had less creaminess and more coldness, coarseness, and hardness than the full-fat (10%) sample. The involvement of fat in the structural characteristics of ice cream such as its lower heat conductivity can describe these results. Also, adding basil seed gum, guar gum, and their blends (50:50) reduced the coldness and coarseness due to the high water-binding capacity of the selected hydrocolloids, which was more prominent in basil seed gum than in the other gum systems. The hardness of low-fat samples with fat replacers was found to be higher than that of corresponding controls. The reason for such an effect could be attributed to the viscosity enhancement ability of the hydrocolloids. As presented in Table 21.3, fat replacers are able to mimic the creaminess of full-fat ice cream, above all in samples containing basil seed gum followed by formulations with a mixture of basil seed gum and guar gum (50:50). In this regard, the authors concluded that the creaminess of ice creams was related to the extent of thixotropy of the mixes. These sensory findings are in accordance with the results reported by Javidi and Razavi [72], who obtained the Pearson correlation coefficients for instrumental and sensory properties. In this case, a positive correlation between the values of creaminess and hardness, adhesiveness, consistency coefficient, Casson yield stress, initial shear stress, the extent of thixotropy, equilibrium shear stress, and sensory hardness was observed, but coldness and coarseness had a negative correlation with creaminess (Table 21.4). Furthermore, principal component analysis (PCA) was used to describe the relationships between samples and their rheological, physical, and sensory attributes. PCA scores were divided into three groups: (1) full-fat (10%) ice creams, (2) light (5%) samples containing basil seed gum and its blend with guar gum at concentrations of 0.35% and 0.45%, and (3) light (5%) ice creams with 0.5% and 0.55% basil seed gum and its blend with guar gum. According to PCA results, the sensory properties of the ice creams exhibited interdependence. 21.3.3

Cryoprotection

Ice recrystallization (coarsening) is a process in which small ice crystals melt, combine, and form larger ones so that there is an increase in the mean crystal size without changing the total amount of ice. The average ice crystal size should be in the range 20–40 μm because ice crystals larger than 50 μm contribute to a coarse and icy texture and affect the quality of ice cream [77]. Thus, to ensure that recrystallization is minimized, useful techniques should be used, such as the addition of ice recrystallization inhibition agents to the mix. In this regard, the recrystallization phenomenon in ice cream can be effectively controlled by the addition of hydrocolloids, and is attributed to the reduction in the kinetics of the ice recrystallization phenomena during storage [2], although these ingredients have little or no effect on the initial ice crystal size distribution at the time of draw from the scraped surface freezer, nor on the initial ice growth during hardening [78]. Their ability to hold water and enhance microviscosity is the first mechanism controlling the rate of ice crystal growth. This functionality of hydrocolloids probably results in hyper-entanglements and solution structure formation in the unfrozen phase of ice cream, affecting the rate of water diffusion to the surface of growing ice crystals or the rate of diffusion of solutes and macromolecules away from the surface of growing crystals during temperature fluctuation [6]. However,

Table 21.4 Correlation coefficients between some properties of full-fat and light ice creams containing basil seed gum and guar gum as fat replacers.

Variables

Hardness

Adhesiveness

Consistency coefficient

Casson yield stress

Initial shear stress

Extent of thixotropy

Equilibrium shear stress

Coldness

Sensory hardness

Coarseness

Creaminess

Hardness

1

0.900

0.524

0.604

0.656

0.546

0.371

−0.404

0.866

−0.566

0.731

1

0.274

0.358

0.781

0.784

0.187

−0.438

0.872

−0.617

0.744

1

0.961

0.378

−0.086

0.845

−0.441

0.375

−0.393

0.678

1

0.416

−0.068

0.893

−0.396

0.398

−0.443

0.677

1

0.810

0.465

−0.768

0.668

−0.834

0.798

1

−0.120

−0.556

0.698

−0.640

0.549

1

−0.513

0.156

−0.504

0.589

Adhesiveness Consistency coefficient Casson yield stress Initial shear stress Extent of thixotropy Equilibrium shear stress Coldness Sensory hardness Coarseness Creaminess

Values in bold are different from 0 with a significance level alpha = 0.05. Source: Adapted from Javidi and Razavi [72] with permission from Springer.

1

−0.424

0.723

−0.757

1

−0.654

0.709

1

−0.719 1

540

21 New Hydrocolloids in Ice Cream

some researchers declared that the mix viscosity did not correlate well with the cryoprotective effect of hydrocolloids under their test conditions [79, 80]. According to the second mechanism of hydrocolloid action, the diffusion characteristics of water and solutes are restricted within their network, and free water is held as the water of hydration around the polysaccharide structure. The reason underlying this mechanism is the ability of hydrocolloids to form cryogel as a result of heat shock. It has been found that a certain firmness and flexibility of the gel is needed to exert a strong opposing force for ice front propagation. On the other hand, some non-gelling stabilizers (xanthan, CMC, and alginate) were more effective in retarding recrystallization than gelling stabilizers (gelatin, carrageenan, and LBG) [78]. It was suggested that the cryoprotective functionality of hydrocolloids may originate from some mechanisms other than steric blocking of the interface or inhibition of solute transport to and from the ice interface caused by their gelation. The incompatibility of hydrocolloids and proteins is considered as the third mechanism, which provokes phase separation and may contribute to retarding recrystallization. Such inhibitory effects of hydrocolloids on ice crystal growth may be enhanced as their concentration increases. Ice creams with different stabilizer systems (basil seed gum and CMC–guar gum blend) were subjected to heat shock by BahramParvar and Goff [58]. They used the values of the ice crystal equivalent diameter at 50% of the cumulative distribution (X50 ) and slope at these X50 values to determine the ice crystal size distributions. There was no significant difference between the ice crystal size of the samples with and without stabilizer after hardening, while temperature cycling significantly increased the ice crystal size. The lowest values of ice crystal size and the highest values of slope at X50 after heat shock were found in ice creams with basil seed gum, which indicates that this novel hydrocolloid is able to reduce the rate of ice crystal growth after temperature cycling (Table 21.5), although a contrary result was observed in samples containing Table 21.5 Ice crystal growth (%) of ice creams containing new hydrocolloid stabilizers.

Stabilizers

Ice crystal growth (%)

—

167.7

0.1% Basil seed gum

127.4

0.1% Carboxymethylcellulose/guar gum

176.3

0.2% Basil seed gum

102.3

0.2% Carboxymethylcellulose/guar gum

185.5

—

132.3

0.15% Guar gum

84

0.15% Okra cell wall

107.9

0.30% Okra cell wall

86.1

0.45% Okra cell wall

66.4

0.15% Okra polysaccharide

87.6

0.30% Okra polysaccharide

59.8

0.45% Okra polysaccharide

32.0

Reference

[58]

[61]

21.4 Conclusions

F1

F2

F3

F4

F5

Figure 21.3 Microstructure of ice cream samples without stabilizer (F1) and containing 0.1% basil seed gum (F2), 0.1% carboxymethylcellulose/guar (F3), 0.2% BSG (F4), or 0.2% carboxymethylcellulose/guar (F5) after hardening. Source: Adapted from BahramParvar and Goff [58] with permission from Springer.

CMC–guar gum blend. The authors also explained that ice crystal growth diminished from 127.4% to 102.3% as the concentration of basil seed gum increased from 0.1% to 0.2% [58]. These findings were confirmed by cryo-scanning electron microscopy (SEM) observations (Figures 21.3 and 21.4), which show the microstructure of ice creams without or with (0.1% and 0.2%) stabilizer before and after temperature cycling, respectively. Similar results were also obtained by Yuennan et al. [61], who evaluated the effects of okra cell wall and polysaccharide on ice recrystallization and stated that the ice crystal growth of samples decreased significantly (from 132.3% to 32.0%) upon either adding stabilizers or increasing their concentration (Table 21.5). In addition, the cryoprotectant effect of okra polysaccharide, a new hydrocolloid, was comparable with that of guar gum, a commercial hydrocolloid, at a concentration of 0.15%.

21.4 Conclusions Ice cream is a structurally complex system that is mostly affected by the nature and concentration of mix ingredients such as a stabilizer and milk fat. A study of the literature shows that hydrocolloid stabilizers are able to bind a high amount of water and enhance the viscosity of the unfrozen phase of ice cream, contribute to acceptable meltdown, and improve the body, texture, mouthfeel, and heat-shock resistance resulting from their hydrophilicity, high molecular weight, and highly branched structure. In this chapter, potential applications of novel hydrocolloids in ice cream have been discussed. It is deduced that the choice of hydrocolloids should be based on their functions. In this regard, some new sources of hydrocolloids can act as a thickener, stabilizer, fat

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F1

F2

F3

F4

F5

Figure 21.4 Microstructure of ice cream samples without stabilizer (F1) and containing 0.1% basil seed gum (F2), 0.1% carboxymethylcellulose/guar (F3), 0.2% BSG (F4), or 0.2% carboxymethylcellulose/guar (F5) after temperature cycling. Source: Adapted from BahramParvar and Goff [58] with permission from Springer.

replacer, and/or cryoprotectant in ice cream, with results that are comparable with those of commercial gums. Furthermore, basil seed gum can mimic flow properties and some physical and sensory attributes, especially creaminess, in a similar manner as milk fat. From the effects of studied novel hydrocolloids on ice cream characteristics that have been established, it can be concluded that these sources are potential ingredients for ice cream development.

21.5 Future Trends As discussed in this chapter, the functional properties of emerging natural hydrocolloids in regular, light, and low-fat ice cream formulations have been identified in recent years. However, it is important to understand the structure–function relationship in these functional agents. Therefore, we believe that the evaluation of new hydrocolloids individually, together, or in combination with commercial hydrocolloids in model systems of ice cream and frozen desserts, under different processing and storage conditions, should be a major topic for future studies. When the mechanisms behind the functions become known, it will be possible to propose scientifically based recommendations for choosing the amount and type of suitable hydrocolloids, which have received little attention up to now. In addition, more work is necessary to show whether the positive results obtained on a laboratory scale can be transferred to pilot-plant and industrial scales. However, there must be a market driver to provide a financial incentive for producers to use new sources of hydrocolloids in ice cream and frozen desserts.

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22 Novel Hydrocolloids for Future Progress in Nanotechnology Sara Naji-Tabasi Department of Food Nanotechnology, Research Institute of Food Science and Technology (RIFST) PO Box, 91895-157.356, Mashhad, Iran

22.1 Introduction The food industry is the largest manufacturing sector in the world [1]. The major challenge in this industry is the preservation of the activity and bioavailability of bioactive compounds during food processing, storage, passage through the gastrointestinal tract, and efficient absorption through cells for the development of functional food [2–4]. Nanotechnology is one of the world’s fastest-growing industries, which controls material dimensions on the scale of approximately 1–100 nm [3, 5]. Nanosystems can provide a polymeric barrier for core materials against the destructive conditions in the food industry and gastrointestinal tract, improving the stability and direct uptake [6]. Food-grade biopolymers such as proteins or polysaccharides can be used to produce nanometer-sized particles. Hydrocolloids are a heterogeneous group of long-chain polymers (polysaccharides or proteins) and are used in technical and regulated applications to thicken and/or stabilize formulations [7]. Polysaccharide-based hydrocolloids are composed of monosaccharides joined by glycosidic bonds, which are suitable carriers for the targeted and controlled release of drugs or nutraceuticals along the human gastrointestinal tract, due to their structural versatility and site-specific digestion properties [8]. The use of polysaccharides as building blocks in the development of nano-sized functional food delivery systems is rapidly growing due to their unique multi-functional groups in addition to their physicochemical properties, including biocompatible, low toxicity, low cost, and stable structure [9]. Natural polysaccharides can be obtained from several resources, including plant (e.g., pectin, cellulose, and starch), animal (chitosan, chitin, and glycosaminoglycan), microbial (e.g., dextran, pullulan, xanthan gum, and gellan gum), and algal origin (e.g., agar, alginate, and carrageenan) [7]. Polysaccharides can be easily modified chemically and biochemically, and new features can be obtained to improve the bioavailability of bioactive compounds included in delivery systems [10, 11]. Furthermore, the presence of hydrophilic groups in their structure is a useful strategy to improve the bioavailability of bioactive compounds [11]. Therefore, finding a new source of biodegradable polymers, especially plant-derived polymers with appropriate properties, is an active area of investigation. Recently, various non-commercial Emerging Natural Hydrocolloids: Rheology and Functions, First Edition. Edited by Seyed M.A. Razavi. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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sources of hydrocolloids have been identified, whose variety of physicochemical properties enables the preparation of a wide array of nanoparticles like Qodume Shirazi (Alyssum homolocarpum) [12], cress (Lepidium sativum) seed gum [13, 14], basil (Ocimum bacilicum L.) seed gum [15, 16], sage (Salvia macrosiphon) seed gum [17], Balangu (Lallemantia royleana) seed gum [18], and Qodume Shahri (Lepidium perfoliatum) seed gum [19]. Various studies have been conducted to evaluate the potential of the new source of hydrocolloids in nanotechnology. Therefore, in this chapter, various types of novel hydrocolloids used as nanostructural systems in food and pharmacy industry and appropriate techniques for their fabrication have been discussed.

22.2 Importance of Finding New Material Sources in Nanotechnology Scientists are beginning to construct all sorts of different types of structures with varying functionalities using nanomaterials as their building blocks. Nanotechnology can be applied in the food industry as new tools for the delivery of bioactive compounds to target sites and for the improvement of safety and the nutritional value of food products [20, 21]. Also, nanotechnology can be used to build new types of food packages; food quality detection tools; sensors which can detect trace contaminants, gasses, or microbes in food; and other measurement tools [22]. The future of functional food is related to the development of novel nanocarriers for oral delivery systems. Various delivery systems are currently under development to minimize bioactive compound degradation and loss, to prevent harmful side effects, and to increase bioavailability. The choice of a polysaccharide as wall material depends on several factors such as their self-assembly capability, cost of the raw materials, ease of fabrication of the delivery system, regulatory status, and full attention must be paid to safety and toxicological issues [11]. As a result, polymers derived from plant origin have evoked tremendous interest because they comply more easily with the requisites of biocompatibility, biodegradability, and the absence of toxicity [10]. Researchers are trying to develop better and more efficient nanocarriers with increased bioavailability without compromising the appearance and taste of the food products in which novel carriers are incorporated. Therefore, access to a new source of hydrocolloid with different physicochemical properties can provide nanoparticles with unique properties. On the other hand, the novel delivery system is a new approach to delivering nutraceutical compounds that addresses the limitations of the common delivery systems. The demand for these substances is increasing, and new sources are being developed [23].

22.3 Nanomaterials Different types of functional nanostructures can be used as building blocks to create novel structures and introduce new functionalities into foods [5]. Nanostructure materials are broadly classified into three: (1) nanofilm, (2) nanofiber, and nanoparticles. Researchers have explored the use of novel sources of hydrocolloids in nanosystems, specifically nanofibers, and nanoparticles, as delivery systems, which are discussed here.

22.3 Nanomaterials

22.3.1

Nanofiber

Nanofibers are defined as fibers with a diameter of less than 100 nm. They can be prepared by interfacial polymerization, electrospinning, and phase separation techniques [24]. Nanofibers possess various advantages such as high porosity with very small pore size, large surface area-to-volume ratio, high gas permeability, and superior mechanical properties, for example, stiffness and tensile strength [25, 26]. Nanofibers can be employed for various applications such as delivery systems, membrane technology, protective clothing, tissue engineering scaffolds, and wound healing [27, 28]. But in the food industry, they are mostly used for food texturizing, enzyme immobilization, filtration, enhancement of film properties [26, 29], as edible carriers for encapsulation of food additives such as encapsulation of vitamins [30], as phenolic compounds [31], and in bioactive packaging technologies [32]. Electrospinning (ES) is one of the best and simplest techniques for fabrication of ultrathin fibers. There is a wide range of polysaccharides that can be electrospun into fine nanofibers, such as chitosan-hyaluronic acid [33], cellulose [34], methylcellulose [35], hydroxypropylmethylcellulose [35], chitosan [36], and so on. As advances continue in the area of nanofiber production from food-grade materials, the use new of natural sources such as basil seed gum (BSG) [37], almond gum [38], cress seed gum (CSG), Alyssum lepidium gum [39], and Ficus-indica mucilage [40] will likely increase. 22.3.1.1

Basil (Ocimum bacilicum L.) Seed Gum

The outer epidermis of basil seeds (Ocimum bacilicum L.), when soaked in water, swells into a gelatinous mass which consists of considerable amounts of unesterified galacturonic acid [41]. BSG is an anionic gum with a high molecular weight (2320 kDa) and two major fractions [42] composed of glucose, rhamnose, galacturonic acid, arabinose, mannose, glucuronic acid, and galactose [43, 44]. It has a random coil conformation in the dilute regime, which can form an ordered conformation under favored conditions such as a high enough concentration, the presence of binding agents, or changes in temperatures and pHs [45]. BSG exhibits shear-thinning properties and high consistency coefficient and yield stress, which is dependent on concentration and temperature [46, 47]. BSG can be used as a natural polymer for the preparation of nanofiber, but it cannot be spun alone and needs to be used with an electrospinning aid agent. Polyvinyl alcohol (PVA) is a good choice as an aid agent due to the presence of a hydroxyl group in its structure [37]. Kurd et al. [37] investigated the electrospinning of different blending ratios of BSG/PVA solution (80:20, 60:40, 40:60, and 20:80) at high-voltage power (18 and 23 kV) and 25 ∘ C. The optimum condition for preparation of BSG nanofiber is a volume ratio of 60:40 under a voltage of 18 kV, and the distance between needle tip and collector should be kept constant at 14 cm (Figure 22.1) [37]. The BSG fiber diameter (179–390 nm) increases with increasing voltage from 18 to 28 mV. Higher voltage, and consequently a higher electrical field, leads to higher solution feeding rates, causing larger fiber diameters. By increasing the BSG proportion in BSG/PVA blend solution, thinner nanofibers are obtained, which can be attributed to the higher solution viscosity and electrical conductivity of BSG, which reflected a higher charge density over the ejected jet and thus higher elongation. On the other hand, increasing the PVA volume ratio results in uniform BSG nanofibers without bead defects, which is related to the

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Figure 22.1 SEM image of nanofibers produced under voltages 18 kV and BSG to PVA volume ratios = 20:80, nozzle-collector distance = 14 cm. Source: Adapted from Kurd et al. [37] with permission from Elsevier.

reduction in repulsive forces within the charged polymeric solution. Also, the thermal properties of nanofiber improve with PVA addition. 22.3.1.2

Almond (Amygdalus communis L.) Tree Exudate Gum

Almond gum/PVA nanofibers were fabricated by electrospinning as a vanillin carrier. Almond gum is a high-molecular-weight (1180 kDa) natural polymer, which exudates from branches, trunks, and fruits of almond gum trees (Amygdalus communis L., a species of genus Prunus belonging to the Rosacea family). The exudation usually starts as a result of a disease (gummosis) or a mechanical injury followed by a microbial attack [38]. The gum exudates are composed, on a dry weight basis, by 2.45% of proteins, 0.85% of fats, and 92.36% of carbohydrates. The latter consist of arabinose, xylitol, galactose, and uronic acid (46.8:10.9:35.5:6.0 mass ratio) with traces of rhamnose, mannose, and glucose [48]. The glycosyl linkage positions were analyzed using gas chromatography–mass spectrometry and showed a main chain composed of galactose units [→3)-Gal-(1→] branched mainly with arabinose residues [Ara-(1→] [49]. Moreover, gum exudates are rich in minerals such as sodium, potassium, magnesium, calcium, and iron [48]. The best conditions for electrospinning of almond gum are as follows: proportion of almond gum to PVA = 80:20 (w/w) and total concentration of 7% (w/w), voltage = 18 kV, needle to collector distance = 15 cm, and flow rate = 0.125 ml h−1 . Electrospinning of almond gum–PVA solution (80:20) at 7% (w/w) concentration produces beaded fibers. But adding vanillin (3% (w/w)) to almond gum–PVA solution (in the proportion of 80:20 and 7% (w/w) concentration) increases the viscosity and conductivity of the solution and reduces its surface tension, which therefore resulted in successful electrospinning of uniform and bead-free nanofibers with a diameter of 77 ± 18 nm. The release kinetics of vanillin from almond nanofiber in different media (distilled water, 10% ethanol, 50% ethanol, and simulated saliva) follows a pseudo-Fickian diffusion mechanism: the burst release of vanillin within the first 5 min, followed by sustained

22.3 Nanomaterials

release for 180 min. Increasing the vanillin concentration from 1% to 3% (w/w) increases the loading efficiency from 68% to 75%. But loading more vanillin (4%, w/w) increases the bead in fibers. BSG nanofibers have relatively good stability under the dry ambient condition and maintained around 58% of the incorporated vanillin for 90 days [38]. 22.3.1.3

Cress (Lepidium sativum) Seed Gum

Cress (Lepidium sativum) seeds are a source of natural gum, which can be used for nanofiber production by electrospinning [50]. Cress seed has been found to contain a high amount of protein and iron, and a significant amount of calcium. As its bran is a source of pentosans (11.0%) with a swelling index of 18–19 ml, it has the potential to be used as a dietary fiber. Cress seed mucilage is an anionic gum with low molecular weight (540 kDa) [13] and intrinsic viscosity (3.92 gr dl−1 ) [51], which has excellent potential in the fabrication of the nanostructure [52]. CSG has the potential to confer stability to the products undergoing high temperatures, refrigeration, or freezing treatments and has high resistance to pH tolerance, salts, and the synergic effect of sugar. Consequently, the ranges of application of CSG will expand because of its desirable stability in different conditions [14, 51]. CSG–PVA nanofiber, produced via electrospinning, has an amorphous structure. The main factors affecting the amorphous structure of CSG–PVA nanofibers are the fast solvent evaporation and the presence of CSG. The morphology and size of CSG fiber are related to the solution viscosity. Under low viscosity, beads are formed rather than uniform fibers due to the domination of surface tension. The better uniformity and smoothness of CSG nanofiber are achieved by increasing the PVA volume ratio, while larger fiber diameters are produced. Also, increasing the CSG–PVA volume ratio increases the electrical conductivity, which is related to the higher electrical conductivity of CSG solution (1175 μS cm−1 ) due to its weak ionic nature compared to PVA (467 μS cm−1 ). In the electrospinning process, the ejected jet carries the charges of the CSG solution, and as the charges increase, elongation of the jet occurs by the electrical field, and therefore a reduction in the diameter of the electrospun nanofiber takes place. The increasing electrical conductivity of solutions causes a significant decrease in the nanofiber diameters [50]. Fahami and Fathi [50] have reported that the optimum electrospun CSG/PVA nanofibers (CSG-to-PVA ratio 60:40; tip-to-collector distance 17 cm, and feed rate 0.2 ml h−1 ) have an average diameter size range of 95–278 nm with a smooth and uniform surface. But Golkar et al. [39] have found that an aqueous solution of CSG–PVA = 80:20, voltage = 18 kV, polymer concentration = 50%, tip-to-collector distance = 10 cm, and feed rate = 0.125 ml h−1 can be successfully used to obtain uniform nanofibers with diameters as low as 139.9 nm. The presence of the CSG in nanofiber has been proved by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The electrospun nanofibers have higher thermal stability in comparison with CSG [50]. 22.3.1.4

Ficus-indica Mucilage

Thomas et al. [40] has investigated Ficus-indica (Ofi) cactus mucilage, as a novel polymer for nanofiber preparation, and used it in membrane filtration for water systems. Ofi mucilage is a clear colorless substance comprised of proteins and polysaccharides. It is composed of varying sugars and is considered a linear chain containing galacturonic

553

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22 Novel Hydrocolloids for Future Progress in Nanotechnology

acid, rhamnose, and galactose, with xylose and arabinose residues attached as side chains. It also contains organic species, which give it the capacity to interact with metals, cations, and biological substances. Like the other high-molecular-weight biopolymers, electrospinning nanofibers of Ofi mucilage alone is difficult because of the long polysaccharide chains. PVA and polystyrene are needed to form long polymer chains for electrospinning. The Ficus-indica mucilage has been electrospun with different volume ratios of mucilage:PVA, mucilage:polystyrene-d-limonene, and mucilage:polystyrene–toluene from 30:70 to 70:30. d-limonene should be used to break down the polystyrene into a solution form. The Ofi cactus mucilage nanofiber membranes have been used as filtration devices for 50 ppb arsenic solutions. PVA:mucilage nanofiber membranes dissolve upon repeated cycling of water solutions, which is attributed to the hydrophilic nature of the PVA and mucilage. On the other hand, 70:30 polystyrene:mucilage nanofiber membranes can remove 9.72% of arsenic from the water. The 50:50 polystyrene:mucilage nanofiber membrane has the ability to remove 18.93% arsenic, which is comparable to a traditional sand columnar filtration (18.33%). The mucilage nanofiber membranes have the potential to serve as the basis for the next generation of economically sustainable filtration devices that make use of a natural non-toxic material for sustainable water systems. Also, the cactus mucilage nanofiber can be used in tissue scaffolding, enzyme carrier, tissue engineering, air filtration, cell culturing, gas filtration, drug delivery, textiles, sensors, and for many other uses [40]. 22.3.2

Nanoparticles

Nanoparticles (NPs) are solid colloidal particles ranging in size from 1 to 100 nm, which are made up of macromolecular materials [11]. But particles >200 nm are not heavily pursued, and nanomedicine often refers to particles sorbitol > PEG 200 > PEG 400 [17]. Interestingly, at low content of PEGs, the WVP of the plasticized films was higher than that of neat gum Cordia films [17]. Although lipid materials possess a hydrophobic nature, fabrication of stand-alone films has not been yet attempted because their monomeric structure gives rise to very brittle films. Nevertheless, lipids have been extensively employed in some film formulations aiming at WVP improvement. Besides, some lipids exhibit a good plasticizing effect and have been categorized as a plasticizer. Note that water molecules permeate through the hydrophilic part of the film matrix, and thus the percentage WVP decrease by lipids is proportional to the hydrophilic-to-hydrophobic ratio of the film composition [21]. The water vapor barrier of some gum-based films have been modified by various lipids as follows: the WVP of BSG and Lepidium perfoliatum seed gum (LPSG) films incorporated with long-chain fatty acids decreased up to 98% and 25%, respectively, and the WVP of brea gum and gum Cordia films containing beeswax reduced up to 57% and 85%, respectively [4, 14, 16, 21]. Edible films and coatings have great carrying capacity for functional components due to both natural origin and direct contact with food. Essential oils might be incorporated

23.3 Film Characteristics

into edible films as antimicrobial and antioxidant agents in order to extend the storage life of food. Additionally, the existing variety of hydrophobic components in essential oils can sometimes promote the water vapor barrier of films. Hashemi et al. [10] observed that the WVP values of BSG coatings were reduced by oregano essential oil due to the interference of distributed oil globules in the transmission of water molecules through the coating matrix. One of the most effective strategies to solve the drawbacks of synthetic and natural packaging films is to incorporate nanoscale materials into the matrix of the film. Compared to lipids, nanomaterials can modify the moisture, aroma, and gas barriers by different mechanisms without a noticeable increase in the edible/biodegradable film’s opacity. A novel nanocomposite film was developed by loading montmorillonite nanoparticles to brea gum film solution [13, 27]. Depending on the montmorillonite content, the WVP of the films decreased from 24% to 47% by two mechanisms: (1) establishment of extensive interactions between brea gum and nanoclay prevents the diffusion of water molecules through the film matrix and (2) generation of a tortuous pathway by nanoclay lengthens the path of water vapor diffusion [13, 27]. It is concluded that incorporation of lipids and nanomaterials can be considered as effective methods for achieving the desired WVP for films based on natural hydrocolloids. In spite of this, as with most polysaccharide-based films, films fabricated from natural hydrocolloids exhibit restricted moisture barrier ability because of their hydrophilic nature, and WVP values are still higher than those measured for synthetic plastic films (Table 23.1). Data collected for the WVP of the best gum-based film (gum Cordia) show values that are about 40-fold higher than those of the best synthetic film (polyvinylidene chloride) and about ninefold lower than the worst synthetic film (cellophane), and BSG film is found to be the most susceptible to water vapor transmission versus cellophane. 23.3.2.2

Oxygen Permeability (OP)

The permeability of packaging materials to oxygen is measured to evaluate the ability to preserve different foods against harmful reactions (oxidation, enzymatic browning, etc.) and microbial growth. On the other hand, some foods, for example, meat, fruit, and vegetables, need a controlled level of oxygen in order to inhibit respiration, blooming, and growth of putrefying bacteria. However, the oxygen transmission rate has to be minimized in most foods to extend storage life. Due to the nature of synthetic and biopolymer-based films, different gases can always pass through the films, and a gas-impermeable film is almost impossible to create. The OP of packaging films is influenced by many factors, especially the RH and temperature. Moreover, polymer polarity, concentration, and type of modifying agent (plasticizers, lipids, nanostructures, antimicrobials, etc.), crystallization degree, and orientation process affect the permeability of films to gases. The effect of plasticizer on the OP of gum-based films has been investigated [7, 17]. Mohammadi Nafchi et al. [7] reported that the OP of Alyssum homolocarpum seed gum (AHSG) films increased with enhancing glycerol content. This is because hydrogen and covalent polymeric bonds among adjacent polymer chains are disrupted by plasticizers, thereby increasing polymer mobility [31]. A similar result was found for gum Cordia films plasticized by various plasticizers [17]. The authors also deduced that glycerol and PEG 400 were the worst and the best, respectively, for the oxygen barrier, and sorbitol and PEG 200 were in between.

577

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23 Edible/Biodegradable Films and Coatings from Natural Hydrocolloids

Different natural or synthetic additives may be loaded into the edible films and coatings to produce active packaging materials. This can be accompanied by changes in the permeability of edible films or coatings. Khazaei et al. [11] found that the OP of BSG film decreased as a result of thymol addition. In contrast, gum Cordia films containing butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and α-tocopherol antioxidants demonstrated a reduced OP compared with the control film [29]. As mentioned earlier, WVP improvement in biopolymers could have been achieved by lipids. On the other hand, OP increase is the next result of lipid incorporation into films. For instance, the OP of gum Cordia film was greatly affected by beeswax and ranged from 0.39 × 10−15 to 23.1 × 10−15 g (m s Pa)−1 [16]. Diffusion and solution are the two essential conditions for gas and vapor permeation through the film. The polarity of gas determines the solubility value, and film structure affects diffusivity [4]. Hydrocolloid-based bioplastics possess more polar structure compared with many synthetic plastics, leading to a higher barrier for nonpolar gases such as O2 , CO2, and N2 . According to the observations of Abdul Haq et al. [16], the addition of a hydrophobic substance to gum Cordia film increased the OP in two ways: (1) decreasing the film polarity and (2) facilitating O2 diffusion within the reconstructed emulsified film. The OP values of gum-based films and conventional synthetic plastic films are tabulated in Table 23.2. It is necessary to measure the OP of all films under the same test conditions for proper comparison; if not, the conditions under which the measurements were obtained must be considered. As can be seen, the measurements have been mostly carried out at 23–25 ∘ C, but at different RHs. At higher RHs, hydrophilic polymers easily absorb environmental moisture, thus enhancing gas permeability [1]. Considering the RH, the OPs of all the tabulated gum-based films are lower than those of low-density polyethylene (LDPE) and methylcellulose and are close to those of polyamide 6 and polyethylene terephthalate (PET), which are potent oxygen barriers. The OP of the ethylene vinyl alcohol (EVOH) film was lower than that of the films developed from BSG and gum Cordia, probably because of greater polarity. Overall, the oxygen barrier characteristics of gum-based edible films are in the range of the values reported for other bio-based and synthetic packaging films. 23.3.3

Density

Density is an additional structural feature, sometimes measured in the edible films, giving more information about film compactness. Density is mainly governed by molecular weight, structure, conformation and packing arrangement, and also film composition. Permeability to water vapor, gases, and aromatic compounds are the attributes that may be affected by density; the higher the compactness of a film’s structure, the harder the diffusion of permeants through the film. Density measurements in the gum-based films (Table 23.3) show that using hydrophilic plasticizers (glycerol and sorbitol) decreased the density [4, 6, 7, 9, 19–21]. The authors hypothesized that moisture absorption by plasticizers may account for the film thickening and compactness reduction [6, 23]. In other work, the small molecular size of polyvinyl alcohol (PVA) in comparison with AHSG polysaccharides and water absorption by hydrophilic PVA were primarily responsible for expanding the tight molecular packing of AHSG film [8]. It was expected to reduce the emulsified film’s density due to the low density of lipids compared with the film’s other components, whereas the opposite effect was seen in LPSG film [21].

Table 23.2 Oxygen permeability (OP) values of gum-based films and some synthetic plastic films.

Gum/polymer

Plasticizer (% w/w)

Additive

Film thickness (mm)

Test conditions (∘ C, %RH)

OP (×10−15 g/m Pa s)

Reference

AHSG

Glycerol (0–45)

—

0.092–0.134

25, 50

0.010–0.016

[7]

Glycerol (50)

PVA (0–100% w/w)

BSG

Glycerol (35)

Thymol (0–10% w/w)

0.066–0.079

23, 50

0.756–0.868

[11]

GC

AHSG

PEG 400 (20)

GMS (0–0.02% w/w) + Beeswax (0–20% w/w)

0.073–0.074

25, 58

0.39–23.1

[16] [17]

GC

0.09–0.12

25, 50

0.00046–0.7065

[8]

Glycerol (10–30)

—

—

25, 58

0.26–5.31

Sorbitol (10–30)

—

—

25, 58

0.27–2.20

PEG 200 (10–30)

—

—

25, 58

0.28–2.42

[17]

PEG 400 (10–30)

—

—

25, 58

0.16–0.84

[17]

Glycerol (20)

—

—

25, 58

0.38

[29]

Glycerol (20)

BHA

—

25, 58

0.51

[29]

Glycerol (20)

BHT

—

25, 58

0.45

[29]

Glycerol (20)

α-tocopherol

—

25, 58

0.43

[29]

MC

30, 0

16.704

[1]

Chitosan

25, 0

0.0182

Wheat gluten

25, 0

0.0396

MC/B

25, 0

15.968

Cellophane

23, 0

0.0428

LDPE

23, 0

32.096

HDPE

23, 100

7.168

Rigid PVC

23, 0

0.512

EVOH

23, 0

0.0064

EVOH

23, 95

0.192

PA6

23, 0

0.380

PET

23, 0

0.380

GC

[17]

AHSG: Alyssum homolocarpum seed gum, BSG: basil seed gum, GC: Gum Cordia, MC: Methylcellulose, MC: Methylcellulose/beeswax, LDPE: Low-density polyethylene, HDPE: High-density polyethylene, PVC: Polyvinyl chloride, EVOH: Ethylene vinyl alcohol, PVA: Polyvinyl alcohol, PA6: Polyamide 6, PET: Polyethylene terephthalate, GMS: Glycerol monostearate.

Table 23.3 Water-related (moisture content, water solubility, and moisture uptake) and density values of gum-based films.

Gum/mucilage

Plasticizer (% w/w)

Additive

Moisture content (%)

Water solubility (%)

Moisture uptake (%)

Density (g/cm3 )

Reference

AHSG

Glycerol (0–45)

—

14.2–19.1

38.1–53.2

6.9–8.43a)

1.18–1.29

[7]

AHSG

Glycerol (50)

PVA (0–100% w/w)

23.1–54.1

13–75

—

BSG

Glycerol (100)

Palmitic acid (0–25% w/w)

38.3–48.7

37.6–55.4

107.4–146.0

1.33–1.34

[4]

Glycerol (100)

Stearic acid (0–25% w/w)

35.8–48.7

31.4–55.4

106.1–146.0

1.33–1.34

[4]

Glycerol (100)

Oleic acid (0–25% w/w)

42.4–48.7

27.2–55.4

91.1–146.0

1.33–1.34

[4]

Glycerol (40–100)

—

26.8–48.7

39–50

107.6–143.1

1.34–1.37

[4]

Sorbitol (40–100)

—

10.1–11.5

35–46

69.5–85.5

1.38–1.43

[4]

BSG

Glycerol

ZMEO (1–3% v/v)

—

23.8–29.3

—

—

[26]

BSG

Glycerol (0–50)

—

16.2–18.5

47.3–53.7

—

—

[9]

BSG

Glycerol (30)

OVES (0–6% w/w)

17.5–17.9

—

—

—

[10]

BSG

Glycerol (30)

OVES (0–5% w/w)

17.8–17.8

—

—

—

CF

Glycerol (16)

Maize starch (0–200% w/w)

7.2–12.2

23.4–55.5

—

—

[25]

CSM

Glycerol (25–75)

—

18.1–41.8

52.7–84.5

—

—

[15]

CSG

Glycerol (35)

ZMEO (0–4% w/w)

14.0–16.8

35.2–42.5

—

—

[18]

1.12–1.47

[8]

[32]

CSG

Glycerol (25–50)

—

15.4–18.7

48.3–54.1

—

1.22–1.30

[19]

LPSG

Glycerol (40–70)

—

23.2–7.66

38.9–58.0

127.4–155.1

0.88–0.93

[20]

LPSG

Glycerol (60)

GPP (20–80% w/w)

22.1–25.1

27.4–58.1

56.1–104.9

1.33–1.42

[6]

Glycerol (70)

GPP (20–80% w/w)

24.9–30.4

30.5–62.4

59.6–108.5

1.28–1.40

[6]

Glycerol (80)

GPP (20–80% w/w)

29.1–37.1

38.8–67.1

64.2–115.5

1.19–1.27

[6]

Glycerol (60)

Palmitic acid (0–30% w/w)

26.6–32.7

40.0–56.8

57.3–152.6

0.91–1.05

LPSG

[21]

Glycerol (60)

Stearic acid (0–30% w/w)

24.3–32.7

35.5–56.8

56.9–152.6

0.91–1.05

[21]

PSG

Glycerol (15–35)

—

13.5–16.7

47.7–52.9

—

—

[22]

SSG

Glycerol (40–100)

—

26.6–48.8

79–83

110.8–139.1

1.32–1.40

[23]

Sorbitol (40–100)

—

13.4–14.1

65–84

68.6–91.9

1.27–1.41

[23]

—

LBG (0–100% w/w)

12.0–16.2

—

43.8–95.8

0.91–1.04

[24]

GT

AHSG: Alyssum homolocarpum seed gum, BSG: Basil seed gum, CF: Chia flour, CSM: Chia seed mucilage, CSG: Cress seed gum, LPSG: Lepidium perfoliatum seed gum, PSG: Psyllium seed gum, SSG: Sage seed gum, GT: Gum tragacanth, PVA: Polyvinyl alcohol, ZMEO: Zataria multiflora essential oils, OVES: Origanum vulgare (oregano) essential oil, GPP: Grass pea protein, LBG: Locust bean gum. a) g/g dried film.

23.3 Film Characteristics

It seems that fatty acid molecules fill the gaps and voids of the biopolymer matrix, and produce a more compact morphology compared to the neat LPSG film. Nonetheless, the density of BSG film was not significantly changed by the addition of fatty acids [4]. 23.3.4 23.3.4.1

Water-Related Properties Moisture Content

The presence of moisture in the structure of most edible films and coatings is unavoidable because water is used as a solvent. One of the best functions of water is the plasticizing effect on biopolymer-based films. On the other hand, the moisture content of the edible films may negatively influence water vapor and gas permeability, and films with high moisture are not appropriate for sensitive foods [8]. Hydrocolloid-based films and coatings are expected to capture more water owing to their hydrophilic nature. Gum-based films are not an exception to this rule, and their moisture content ranged from 10% to 54% (Table 23.3). In addition to their biopolymer nature, other components of the film (plasticizer, essential oil, lipid, nanoparticle, etc.) may influence the moisture content. It has been proved by the findings of different studies that the moisture content of all gum-based films substantially increased in response to glycerol increase, but there was no significant change upon sorbitol increase [4, 6, 7, 9, 15, 19, 20, 22, 23]. This increase was attributed to the hygroscopic character of glycerol, which gives it an excellent capacity for water binding [4, 9, 20]. Because of this, sorbitol may be the preferred plasticizer for gum-based films when high moisture content is harmful. Lipid derivatives may decrease the film’s moisture by promoting matrix hydrophobicity [4, 21]. This is observed in the researches of Mohammad Amini et al. [4] and Seyedi et al. [21] for BSG and LPSG films, respectively. Also, incorporation of functional additives might affect the film’s water content, as reported in the following studies. Oregano essential oil had no effect on the moisture content of BSG films [10], whereas this parameter was reduced by addition of ZMEO into cress seed gum (CSG) films [18]. Interactions among the hydroxyl groups of CSG film and the essential oil components, as well as a decrease in the film’s hydrophilicity, may account for the limited water holding capacity, and the subsequent moisture content reduction [18, 33]. 23.3.4.2

Water Solubility

Unlike synthetic polymers, which are mostly characterized as hydrophobic materials, biopolymers are hydrophilic. Hence, the water solubility of edible/biodegradable films and coatings is of interest for pharmaceutical and food applications. Generally, higher water solubility would imply lower water resistance and greater hydrophilicity of the film components. Films with high water solubility cannot serve as appropriate packaging for foods with high moisture content or for foods stored at high RH. However, greater water solubility may be beneficial in some cases. For example, film solubility is advantageous in situations when the films will be consumed with a product that is heated prior to consumption such as dry soup mixes, and or controlled release of drugs. Furthermore, it was proved that the water solubility of films facilitates their disintegration and biodegradability [34, 35]. Similar to other members of the polysaccharide family, gum-based films usually possess intermediate or high water solubility (Table 23.3). Combining gums with various polymers may result in films whose behavior varies in the water solubility test. Some

581

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23 Edible/Biodegradable Films and Coatings from Natural Hydrocolloids

protein-based films such as native proteins of milk also exhibit high solubility. Heating is a common treatment during film fabrication which mainly leads to protein unfolding, exposing the hydrophobic parts of the protein, and the formation of new covalent SS bonding during drying, thereby reducing film water solubility. The result of a study showed that addition of grass pea protein isolate (GPPI) to LPSG films containing 60% glycerol decreased water solubility from 58% to 27% due to the influence of heat-denatured proteins [6]. In another study, blending PVA, a synthetic polymer rich in hydroxyl groups, with AHSG in the ratio 0%–80% increased the water solubility of the composite films by more than four orders of magnitude [8]. Edible films and coatings are more susceptible to disintegration in water in the presence of hydrophilic plasticizers. There are many reports of an increase in the water solubility of gum-based films with increasing plasticizer concentration [6, 7, 9, 15, 17, 19, 20, 22, 23]. The authors hypothesized that the plasticizers can easily penetrate into the interface of biopolymer chains due to their small molecular size, restricting intermolecular linkages between them and consequently facilitating solubility in water [36]. A research into the effect of plasticizer type (glycerol, sorbitol, PEG 200, and PEG 400) on the water solubility of films made from gum Cordia revealed no relationship between plasticizer type and solubility changes [17]. This result was confirmed by the findings of other researchers for SSG and BSG films plasticized by both glycerol and sorbitol [4, 23]. A negative effect of different additives on the water solubility of gum-based films was reported by different workers. Lipid derivatives such as beeswax and long-chain fatty acids could improve the resistance of gum-based films to disintegration in water due to the hydrophobicity enhancement of BSG, LPSG, brea gum, and gum Cordia [4, 14, 21, 29, 37]. However, the solubility of gum Cordia films was not influenced by oil-soluble antioxidants, probably owing to their small amounts [29]. Moreover, essential oils and nanoclay can contribute to reducing the solubility in water of gum-based films [12, 13, 18, 26]. Establishment of hydrogen bonds between the exfoliated structure of nanoclay particles and the polysaccharide chains was described by Slavutsky et al. [13] as a reason for the decreased solubility of brea gum nanocomposites. In conclusion, film-making treatment, the quantity of free -OH in the film matrix, plasticizer content, additives, solubilizing conditions (water temperature, agitation, and time), and crystallinity, polarity, and cross-linking of the biopolymer are the main factors influencing the solubility of hydrocolloid-based films and coatings [8, 15, 22]. And, depending on the application, the water solubility of the films can be modified by considering these factors. 23.3.4.3

Water Contact Angle

Contact angle measurement provides information regarding surface energy and surface tension [38]. The water droplet contact angle characteristic can be used as the hydrophilicity index of edible/biodegradable films and coating surfaces, too [34]. A contact angle smaller than 90∘ implies that water will spread over a large area on the surface (high wettability); contact angles greater than 90∘ indicate that water will minimize its contact with the surface (low wettability), and the corresponding material is defined as hydrophobic (Figure 23.1) [39, 40]. Synthetic packaging films commonly exhibit fairly high contact angles, and therefore their surfaces have to be modified prior

23.3 Film Characteristics

θ < 90°

θ = 90° γ1v

θ

θ > 90°

γsv

γs1

Figure 23.1 Illustration of contact angles formed by sessile liquid drops on a smooth homogeneous solid surface. Source: Adapted from Yuan and Lee [39] with permission from Springer.

to their printing [38]. However, a high value for water contact angle is of interest in packaging films used for food preservation. The water contact angles of some polymeric and biopolymeric films are shown in Table 23.4. It can be seen that the values are in the range 51∘ –105.4∘ for synthetic films and 27∘ –130.4∘ for hydrocolloid-based edible films. Among the synthetic films, the ones with more polar groups such as PVA, polyvinyl acetate, and nylon 6 show a lower contact angle, and upon decreasing the polarity of these films, the contact angle tends to reduce. The water contact angle may decrease when the surface is highly hydrophilic, that is, in hydrocolloid-based films. In fact, the neat films, or the films made from pristine or native hydrocolloids, usually exhibit a high affinity for moisture, which justifies the need for surface hydrophobization by means of chemical modification [40]. Nevertheless, some hydrocolloids produce films with adequate contact angles (gliadin films = 85–105∘ and agar film = 92.6∘ ), which obviate the surface modification requirements [42, 43]. A number of studies have been conducted to modify starch, hemicellulose, chitosan, and chitin polysaccharides, with the aim of imparting higher hydrophobicity to the surface of the film [40]. As a result, for example, the water contact angle was shifted from 43∘ for the native starch to 123∘ with the modified starch (Table 23.4). Various studies have shown that the type and concentration of plasticizer and hydrophobic substances can deeply influence this characteristic, besides the nature of the biopolymer as the most effective factor. The contact angle of many gum-based films was in the range 30∘ –80∘ . It is expected that with increasing hydrophilic plasticizer content, the surface of the film would be easily wetted, as observed in different studies [4, 7, 9, 19, 20, 22]. However, findings for brea gum, LPSG, and SSG films, plasticized with sorbitol and glycerol, were inconsistent. No logical reason was presented for this phenomenon [3, 6, 23]. Generally, organic components increase the surface hydrophobicity, obviating the need for chemical modification (hydrophobization). Incorporation of long-chain fatty acids (C16–C18) into gum-based films changed the contact angle from 70.2∘ to 130.4∘ in LPSG films [21]. This value is close to that of the superhydrophobic surfaces, with the water contact angle being greater than 150∘ , indicating hardly any contact between the deposited liquid droplet and the surface [39]. On the other hand, the hydrophilicity of some films such as cellophane is so large that water droplets are immediately absorbed, and the contact angle cannot be measured [43]. Increasing film hydrophobicity is not always the reason for contact angle increase. For example, Hashemi et al. [32] suggested that covering hydrophilic groups of BSG active film with oregano essential oil increased the contact angle by more than 30∘ . The values displayed in Table 23.4 are mostly the initial water contact angles, and it is expected to

583

Table 23.4 Water contact angle values of gum-based films and some synthetic plastic films. Gum/ mucilage

Plasticizer (% w/w)

Additive

Water contact angle (∘ )

Reference

Plastic

Water contact angle (∘ )

Reference

AHSG

Glycerol (0–45)

—

48.8–75.6

[7]

PVA

51

[41]

62.6

AHSG

Glycerol (50)

PVA (0–100% w/w)

30.9–74.6

[8]

Nylon 6

BSG

Glycerol (100)

Palmitic acid (0–25% w/w)

52.7–81.5

[4]

PMMA

70.9

Glycerol (100)

Stearic acid (0–25% w/w)

52.7–97.33

[4]

Nylon 12

72.4

Glycerol (100)

Oleic acid (0–25% w/w)

52.7–93.6

[4]

PET

72.5

Glycerol (40–100)

—

51.3–74.3

[4]

PVDC (Saran)

80

Sorbitol (40–100)

—

41.8–63.0

[4]

PC

82

BSG

Glycerol (0–50)

—

39.1–83.4

[9]

PVC

85.6

BSG

Glycerol (30)

OVES (0–5% w/w)

48.5–82.0

[32]

PS

87.4

BG

Glycerol (0–30)

—

67.3–71.2

[3]

Nylon 10,10

94

CSG

Glycerol (25–50)

—

43.7–79.8

[19]

PE

96

LPSG

Glycerol (40–70)

—

68.3–72.9

[20]

PP

102.1

LPSG

Glycerol (60)

GPP (20–80% w/w)

60.5–75.9

[6]

LDPE

105.4

LPSG

Glycerol (60)

Palmitic acid (0–30% w/w)

70.2–122.9

[21]

LDPE

100.7

[43]

LPSG

Glycerol (60)

Stearic acid (0–30% w/w)

70.2–130.4

[21]

Chitin

50–84

[40]

[42]

PSG

Glycerol (15–35)

—

41.0–84.4

[22]

Chitosan

27–82

[40]

SSG

Glycerol (40–100)

—

32.2–55.9

[23]

Starch

43–123

[40]

SSG

Sorbitol (40–100)

—

41.5–103.1

[23]

Hemicellulose

70–123

[40]

Agar

Glycerol (15)

15

92.6

[42]

Zein

62.3

[44] [44]

CS

Glycerol (15)

15

50.4

[42]

Zein plasticized with glucose

52.3

AX

Glycerol (15)

15

65.5

[42]

Zein plasticized with galactose

56.2

[44]

Zein plasticized with fructose

50.1

[44]

Glycerol (15)

68.6

[43]

Glycerol (15)

Palmitic acid (30% w/w)

64

[43]

Glycerol (15)

Stearic acid (30% w/w)

68.6

[43]

Glycerol (15)

Triolein (30% w/w)

39

[43]

AHSG: Alyssum homolocarpum seed gum, BSG: basil seed gum, BG: Brea gum, CSG: Cress seed gum, LPSG: Lepidium perfoliatum seed gum, GPP: Grass pea protein, PSG: Psyllium seed gum, SSG: Sage seed gum, CS: Cassava starch, AX: Arabinoxylan, OVES: Origanum vulgare (oregano) essential oil, PVA: Polyvinyl alcohol, LDPE: Low-density poly ethylene, EVOH: Ethylene vinyl alcohol, PET: Polyethylene terephthalate, PMMA: Polymethyl methacrylate, PVDC: Polyvinylidene chloride, PC: Polycarbonate, PS: Polystyrene, PE: Polyethylene, PP: Polypropylene.

23.3 Film Characteristics

decrease the angles with lapse of time for hydrophilic surfaces due to rapid changes in the surface properties [34]. 23.3.4.4

Moisture Uptake and Moisture Sorption Isotherm

Moisture uptake characteristics could be a good indicator of the edible/biodegradable film’s water sensitivity. At high RH, water uptake can soften the film structure through plasticization, making it easier for diffusing molecules to pass through the film. Accordingly, it is essential to minimize the tendency of the film to absorb moisture in order to increase the shelf life of foods. The uptake of moisture by films depends on both the chemical structure (interactions, number of accessible sites for absorption, film components such as plasticizers, different additives and modifying agents) and film morphology [8, 24, 34]. Also, due to the hydrophilic nature of hydrocolloid-based edible films, all their properties are commonly governed by the RH of the surrounding environment. For this reason, determination of water uptake has been performed under two RH conditions: constant and variable. At constant RH, a saturated salt solution with a relatively high RH such as potassium sulfate or sodium chloride is used for testing the moisture uptake of films pieces. In the second method, moisture sorption isotherms can be generated over a wide range of water activities (aw ) by using different saturated salt solutions. The determination of the moisture sorption isotherms can be useful for predicting the durability of edible films and also of wrapped foods during preservation at stores with various RH values [6]. For instance, the result of one study indicated that brea gum films disintegrated at RH values higher than 75% owing to great hygroscopicity [3]. In general, moisture absorption of hydrophilic films increases as a function of water activity, but the moisture absorption rate may be different within a wide range of aw [6]. Similar to foodstuffs, the sorption behavior of edible films and coatings has been extensively elucidated by using two well-known isotherm equations of Guggenheim, Anderson, and de Boer (GAB) and Brunauer, Emmett, and Teller (BET) [45]. Despite the fact that a much broader range of aw values (0.05–0.8) is covered by GAB compared with BET, both of them have been employed for fitting experimental sorption isotherm data of edible films. Monjazeb et al. [8] investigated the sorption isotherms of composite films made from AHSG and PVA in the aw range 0.11–0.90. The obtained data for absorptions were fitted with the GAB equation, and a sigmoidal shape was produced for all films (Figure 23.2). They observed a slow rate of moisture absorption at low and intermediate aw values, and then a steep rise in the films’ moisture content at aw > 0.53. In another study, sorption isotherms of films made from brea gum, fitted well with the BET model, showed a small tendency to water absorption at aw < 0.50, and exponentially increased with RH increase [3]. But, in the case of gum Cordia films, there was a linear rise in moisture content until RH 70% was reached, implying lower hydrophilicity of these films compared with brea gum and AHSG films [17]. As with most foods, the hydrophilic character of gum-based films often produces a sigmoidal shape for their sorption isotherms [8, 17]. The use of hygroscopic plasticizers can easily enhance susceptibility to moisture absorption and swelling of hydrocolloid-based films, which was confirmed by many studies. In these studies, moisture uptake of films fabricated from gum or mucilage of AHSG, BSG, LPSG, SSG, brea gum, and gum Cordia gum was increased by different concentrations of glycerol, sorbitol, PEG 200, and PEG 400 plasticizers

585

23 Edible/Biodegradable Films and Coatings from Natural Hydrocolloids

200 Moisture Content, g water/100 g dry basis

586

100:0

180

80:20

160

60:40

140

50:50

120

40:60

100

20:80

80

0:100

60 40 20 0

0

0.2

0.4

0.6

0.8

1

aw

Figure 23.2 Moisture absorption isotherms of PVA–AHSG blend films at 25 ∘ C. Source: Adapted from Monjazeb Marvdashti et al. [8] with permission from Elsevier.

[3, 4, 6, 7, 16, 20, 21, 23]. This was because of the hydrophilic character of the abovementioned plasticizers originating from their hydroxyl groups, which show high affinity for binding with the water molecules of the surrounding atmosphere. Although the type and content of the plasticizer were unimportant factors to influence the sorption isotherms, they dramatically influenced the moisture uptake, and with an increase in plasticizer concentration, water absorption of gum-based films increased [3, 4, 7, 20, 23]. According to the findings, glycerol acted as a potent hygroscopic material compared with sorbitol in BSG and SSG films, and the water absorption value of BSG film was 1.5–1.7 orders of magnitude larger than that of SSG film [4, 23]. This claim was confirmed by the research of Abdul Haq et al. [46]. They observed that the moisture susceptibility of gum Cordia films including various plasticizers at different RH values was in the order of glycerol > sorbitol > PEG 200 > PEG 400 [46]. This can be explained by the molecular size of the plasticizers, which determines how a given plasticizer may contribute in the film structure [46, 47]. Furthermore, at the same concentration of plasticizers, the number of hydroxyl groups per unit mass is an influential factor in moisture uptake, and this ratio of glycerol is higher than that of others [46]. Film properties are usually influenced by the addition of modifying substances. These materials can modify the sorption behavior of edible films. Lipids and nanomaterials are the common additives which reduce the water absorption of hydrophilic films by two different mechanisms. The sorption behavior of some gum-based emulsified or nanocomposite films was examined. In one study, incorporation of 10% w/w palmitic or stearic fatty acids into LPSG film led to a water uptake drop by about 60% [20]. In another study, the same lipids at the level of 25% decreased the absorption value of BSG up to 27% [4]. The authors hypothesized that fatty acids partially cover the hydrophilic sites of the biopolymer, and as a result, the accessibility of water molecules was restricted

23.3 Film Characteristics

[4, 20]. However, montmorillonite, a common nanomaterial and rich in hydroxyl groups, directly binds to hydrophilic groups of the biopolymer and reduces the chances of water molecule absorption. Plots of the sorption isotherms of brea gum nanocomposite films by Slavutsky and Bertuzzi [13, 27] supported the highlighted role of nanoclay in diminishing water uptake. In conclusion, taking into consideration the high water uptake of gum-based films, especially at RH > 50%, it is suggested that these films be used for wrapping foods in regions with a dry and semi-dry climate. In contrast, synthetic films are resistant or less susceptible to water absorption and are thus preferred to package foods subject to intermediate and high RHs. 23.3.5

Mechanical Properties

Food packaging is responsible for protecting food against a variety of external stresses until it is consumed. Hence, proper selection of packaging material with adequate mechanical characteristics is of great importance in order to maintain food quality [34]. An edible film or coating may provide some mechanical protection for a food, reducing bruising and breakage and thus improving food integrity [1]. The mechanical properties of edible/biodegradable films are evaluated by measuring the three usual parameters: tensile strength (TS), elongation at break (EB), and elastic or Young’s modulus (EM or YM) as an index of stiffness. Some other tests like the puncture test may be sometimes performed in certain films, too. The mechanical properties of films are mainly associated with the distribution and density of the intermolecular and intramolecular interactions allowed by the primary and spatial structures [1]. These interactions appear to be very important in protein films compared with polysaccharide ones due to the individual characteristics of proteins, such as four levels of structure, heat sensitivity, enzyme-induced bonds, and so on. The presence of protein and protein derivatives as impurities in the commercial and natural gums might interfere with intermolecular interactions during film preparation, and thereby stabilize the films’ network. Films usually become dry, weak, and brittle without the contribution of plasticizers in the film fabrication process. For this reason, different types and concentrations of plasticizers have been tested to modify brittleness and flexibility, and to achieve films with adequate mechanical properties. Besides mechanical attributes, other attributes of the film will often be changed upon plasticizer interference. Plasticization with polyols usually decreases the stiffness and increases the extensibility of films. The results of mechanical measurements showed that with increasing levels of glycerol, sorbitol, PEG 200, and PEG 400 in the natural hydrocolloids films, EB always increased at the expense of the TS and EM [3, 4, 7, 9, 15, 17, 19, 20, 22, 23]. Plasticizer type may be an important factor that influences film structure, as reported for gum-based films. The films made from SSG, BSG, and gum Cordia containing glycerol showed higher EB and lower TS compared with those plasticized with sorbitol owing to the greater number of hydroxyl groups at the same concentration [4, 17, 23]. Indeed, the greater amount of water absorbed by hydrophilic glycerol enhances the spatial distance between biopolymer chains, thereby reducing the TS [17]. Moreover, gum Cordia films became stiffer upon increasing the plasticizers’ molecular weight, and the magnitude of mechanical variations, as a function of plasticizer content, was lower in comparison to

587

588

23 Edible/Biodegradable Films and Coatings from Natural Hydrocolloids

low-molecular-weight plasticizers [17]. In contrast to polyol plasticizers, the mechanical behavior of edible films does not commonly follow a predictable trend in response to materials with inherited plasticizing capability, for example, fatty acids, essential oils, and other lipid derivatives. This unexpected behavior was observed in gum-based films, too. Incorporation of Zataria multiflora and thyme essential oils into CSG and BSG films, respectively, decreased the TS [12, 18], while ZMEO, in other work, increased the TS of BSG film [26]. In these studies, the flexibility of all films was improved by the aforementioned essential oils [12, 18, 26]. Long-chain fatty acids and beeswax can often degrade the mechanical characteristics of edible emulsified films. This phenomenon was also reported for the films prepared from LPSG, brea gum, and gum Cordia [14, 16, 21]. Lipids generally produce very brittle and weak films because of their monomeric structure; the protein or polysaccharide-based films casted from emulsified solutions possess a non-continuous matrix due to weak interactions between the biopolymer – a polar molecule – and lipid – a nonpolar molecule – resulting in decreased TS and EB [2]. However, Mohammad Amini et al. [4] found that the incorporation of palmitic, stearic, or oleic acids in emulsified BSG films is accompanied by enhanced TS and reduced EB. One of the common methods of film fabrication is blending two different polymers, with the aim of producing a new film (copolymer) with modified properties. Novel biocomposite films were made by blending some natural hydrocolloids with other hydrocolloids such as whey protein concentrate (WPC), locust bean gum (LBG), maize starch, and grass pea protein as well as PVA [6, 8, 24, 25, 48]. Mechanical investigation of the novel films showed that increasing mucilage or gum ratio in Salvia hispanica/WPC [48] and LPSG–grass pea protein [6] blended films achieves the desired mechanical properties, while it decreased cohesion and mechanical resistance in gum tragacanth–LBG [24] and chia flour–maize starch [25] blend films. In the films from AHSG–PVA, increasing the gum concentration reinforced the film network and reduced extensibility [8]. The mechanical properties of films developed from natural hydrocolloids as well as some commercial synthetic films are presented in Table 23.5. Two main advantages of synthetic films compared with the biopolymeric ones are the WVP and mechanical characteristics. In spite of the many attempts that have been made to improve the structure of the bio-based film and make it comparable to that of the synthetic films, the synthetic ones are still under the better conditions. Similar to most biopolymers, gum-based films are relatively weak from the mechanical standpoint. Brea gum and gum Cordia films displayed the lowest (1.3 MPa) and highest (55 MPa) resistance in the tensile test, respectively. Therefore, the value of the strongest gum-based film was very far from that of the strongest synthetic films (polystyrene = 175 MPa). On the other hand, the TS values of LDPE (9–17 MPa), the weakest synthetic film, were between those of the gum-based films. The lowest extensibility belonged to gum tragacanth–LBG blend films (0.7%–1.1%), which was close to the EB of polystyrene film (1%). From the other point of view, the EB value of LDPE film (500%) was more than seven orders of magnitude greater than the most flexible gum-based film, that is, CSG (EB ≈ 70%). 23.3.6

Visual Characteristics

The visual characteristics (glossiness, color, transparency, etc.) of edible/biodegradable films and coatings are important factors in consumer acceptability and even food quality due to interactions with light. The color of films or coatings is important from the

Table 23.5 Mechanical properties values of gum-based films and some synthetic plastic films.a)

Gum/ polymer

Plasticizer (% w/w)

Additive

Tensile strength (MPa)

Young’s modulus (MPa)

Elongation at break (%)

Reference

AHSG

Glycerol (0–45)

—

11.8–19.4

279–438

25–43

[7]

AHSG

Glycerol (50)

PVA (0–100% w/w)

26.0–37.2

50–3526

1.4–370

[8]

BSG

Glycerol (100)

Palmitic acid (0–25% w/w)

5.7–8.4

—

29.9–37.1

[4]

Glycerol (100)

Stearic acid (0–25% w/w)

5.7–9.9

—

25.8–37.1

[4]

Glycerol (100)

Oleic acid (0–25% w/w)

5.7–5.8

—

33–37.1

[4]

Glycerol (40–100)

—

5.5–15.4

—

10.3–22.5

[4]

Sorbitol (40–100)

—

5.5–35.4

—

3.5–11

[4]

BSG

Glycerol

ZMEO (1–3% v/v)

19.7–34.6

—

21.5–39.5

[26]

BSG

Glycerol (0–50)

—

18.1–31.7

—

18.5–39.4

[9]

BSG

Glycerol (30)

Thymol (0–3% w/w)

2.3–9.1

—

10.1–12.2

[12]

BG

Glycerol (0–30)

—

3–13

—

24–2

[3]

BG

Glycerol (25)

Montmorillonite (0–5% w/w)

7.4–20.9

392–738

9.3–19.9

[13]

BG

Glycerol (0–40)

Beeswax (0–40% w/w)

1.3–7.5

—

3.5–8

[14]

CSM (Salvia hispanica)

Glycerol (50)

WPC (75% w/w)

3.8–4.7

—

16.3–17.3

[48]

CSM (Salvia hispanica)

Glycerol (50)

WPC (80% w/w)

2.7–3.9

—

15.1–15.2

[48]

CSM

Glycerol (25–75)

—

9.4–17.7

105–778

1.9–15.9

[15]

GC

PEG 400 (20)

GMS (0–0.02% w/w) + Beeswax (0–20% w/w)

3–15

190–900

5–28

[16]

GC

Glycerol (10–30)

—

3–55

5–1900

0–62

[17]

Sorbitol (10–30)

—

12–55

5–1900

0–50

[17]

PEG 200 (10–30)

—

17–55

600–1900

0–40

[17]

PEG 400 (10–30)

—

24–55

950–1900

0–23

[17] (Continued)

Table 23.5 (Continued)

Gum/ polymer

Plasticizer (% w/w)

Additive

Tensile strength (MPa)

Young’s modulus (MPa)

Elongation at break (%)

CSG

Glycerol (35)

ZMEO (0–4% w/w)

6.7–9.8

20–33.1

28.8–69.6

[18]

CSG

Glycerol (25–50)

—

7.8–12.8

17–65

19–40

[19]

LPSG

Glycerol (40–70)

—

3.4–3.9

49–110

1.2–4.3

[20]

LPSG

Glycerol (60)

Palmitic acid (0–30% w/w)

11.5–11.9

—

3.2–3.7

[21]

LPSG

Glycerol (60)

Stearic acid (0–30% w/w)

11.3–11.9

—

3.2–3.7

[21]

PSG

Glycerol (15–35)

—

7.8–14.3

14–29

24.5–34.7

[22]

SSG

Glycerol (40–100)

—

4.4–16.5

—

9–38

[23]

SSG

Sorbitol (40–100)

—

18.6–26.2

—

4–14

[23]

GT

—

LBG (0–100% w/w)

11.6–24.3

—

0.7–1.7

[24]

LDPE

9–17

—

500

[1]

HDPE

17–35

—

300

PP

40

—

300

OPP

165

—

50–75

Polyester

175

—

70–100

HPMC

69

—

10

PS

35–55

—

1

MC

62

Amylose

70

—

23

Cellophane

55–124

—

16–60

Reference

10

AHSG: Alyssum homolocarpum seed gum, BSG: Basil seed gum, BG: Brea gum, CSM: Chia seed mucilage, GC: Gum Cordia, CSG: Cress seed gum, LPSG: Lepidium perfoliatum seed gum, PSG: Psyllium seed gum, SSG: Sage seed gum, GT: Gum tragacanth, LDPE: Low-density poly ethylene, HDPE: High-density poly ethylene, PP: Polypropylene, OPP: Oriented polypropylene, HPMC: Hydroxypropyl methylcellulose, PS: Polystyrene, MC: Methylcellulose, PVA: Polyvinyl alcohol, GMS: Glycerol monostearate, WPC: Whey protein concentrate, LBG: Locust bean gum, ZMEO: Zataria multiflora essential oils. a) Test conditions: 25 ∘ C, RH = 50%.

23.3 Film Characteristics

psychological point of view, too. Color carries meaning and can influence consumers’ thoughts, feelings, and behaviors [49]. Synthetic packaging films might sometimes be colored by colorants for different purposes. Coloration may be also done for edible films and coatings because they have the carrier potential for various nutraceutical and functional additives such as color. The marketability and light protection of wrapped foods could be positively influenced by adding the permitted and food-grade coloring agents to films. The filmogenic solutions from natural hydrocolloids leave colorful or colorless, see-through films after drying, which increases consumer confidence (Figure 23.3). The color of the final edible films and coatings is strongly dependent on the nature and purity of the biopolymer. For instance, the films developed from CMC are colorless and transparent, while the gum-based films exhibit a variety of colors depending on the gum or mucilage impurities. The color developed by the extracted mucilage probably originates from the tegument pigments or tannic substances [50]. The extraction process is occasionally followed by partial purification of gum or mucilage, often by alcoholic precipitation, thereby producing a fairly pure product. But the gum powder still retains some impurities like protein and pigments. There are such impurities even within commercial gums, which, for example, induce a pale yellow color for gum arabic and guar gum. Also, according to the literature, the protein content of commercial guar, locust bean, and Tara gums is 10%, 8%, and 3.13%, respectively [50]. The remaining pigments (directly) and proteins (indirectly) – Millard reactions during heating of film-forming solution – may affect the film’s color. Besides the impurities, hydrocolloid extraction conditions, the plasticizer content, the ratio of major components (in the composite or blended films), and the film-making technique have been shown to influence color [51]. The L*, a*, and b* CIE Lab color values, total color difference (ΔE), and whiteness and yellowness indexes are used to describe film color and its changes. L* refers to the lightness component, which ranges from 0 to 100, and parameters a* (green to red or redness) and b* (blue to yellow or yellowness) are two chromatic components which Figure 23.3 Psyllium seed gum film plasticized with glycerol. Source: Adapted from Ahmadi et al. [22] with permission from Elsevier.

591

592

23 Edible/Biodegradable Films and Coatings from Natural Hydrocolloids

range from −120 to +120 [52]. The result of color measurements showed that the L*, a*, and b* values of gum-based films ranged from 57 to 83, −18.26 to 14.9, and −6.4 to 50, respectively [3, 4, 7, 9, 12–15, 19–23, 46]. The relatively high L* value of these films suggests that their lightness is acceptable. The film lightness may vary slightly or significantly depending on the plasticizer concentration; unusually, for chia seed mucilage (CSM) [15] and LPG [20] films, the L* value exhibited an upward trend as the level of plasticizer increased [3, 4, 7, 9, 14, 19, 22, 23, 46]. On the other hand, nanoclay, essential oils, and lipid derivatives, as film additives, negatively influenced the lightness of some gum-based films [12–14, 21]. The gum-based films’ color became yellowish (greater value for b*) in the presence of higher plasticizer levels, except for the films from brea gum and gum Cordia [3, 46]. Variations of a* in the films did not follow the specific pattern. The deepest variations for color occurred for brea gum films containing 25% glycerol, in which the a* and b* values changed by three and four orders of magnitude, respectively [3], and for BSG films containing 50% glycerol, in which L* increased from 64 to 79 [9]. It seems that glycerol is probably and interestingly the most effective agent for color changes in gum-based films. Besides color, light transmittance from films has been received more attention and is described by the terms transparency and opacity (cloudiness and turbidity). Although the product content could be viewed behind the transparent films, destructive UV light also pass through them and adversely affect food by generating free radicals in products by a wide variety of organic photochemical reactions [35]. On the other hand, opaque films can protect food well against UV light at the expense of film attractiveness. Some treatments for improving the permeability and mechanical properties of films might be associated with unwanted changes in opacity. Nanosized materials (nanoclay, metal oxides, etc.) and lipids with a high melting point such as waxes and saturated long-chain fatty acids can usually cause cloudy films (Figure 23.4). For instance, incorporation of stearic and palmitic acids into LPSG and BSG films increased turbidity, while the contribution of oleic acid in BSG film turbidity was small [4, 23]. Researchers have deduced that the function of lipid molecules in the light transmission and, consequently, film opacity, originates from their dispersion in the film matrix and light scattering. This phenomenon was observed for brea gum films in the presence of montmorillonite [13]. The light transmittance behavior of films when loaded with transparent liquid plasticizers and essential oils is unpredictable, and transparency may increase or decrease. This was evidenced by measurement of transparency in gum-based films by different workers [3, 12, 15, 20, 32, 46]. (a)

(b)

(c)

Figure 23.4 Brea gum films (plasticized by glycerol) incorporated with (a) 0, (b) 20, and (c) 40 g/100 g Beeswax. Source: Adapted from Spotti et al. [14] with permission from Elsevier.

23.4 Applications

62.94 um

27 KV

500 X

100 um

KYKY-EM3200

SN:0661

27 KV

500 X

100 um

KYKY-EM3200

SN:0661

Figure 23.5 Scanning electron micrograph of cross section of cress seed gum films: (Left) 0% ZMEO, (right) 4% ZMEO. Source: Adapted from Kazerani et al. [18] with permission from the publisher.

23.3.7

Scanning Electron Microscopy (SEM)

SEM has been used to visualize the surface morphology and microstructure of edible films and coatings. The captured micrographs from the surface or cross section are useful for elucidating film characteristics such as the WVP, mechanical properties, opacity, and density. Generally, there are some bubbles in the structure of natural hydrocolloids films, especially at a higher concentration of materials, or because of ineffective degassing during film preparation, which would negatively influence the characteristics of the film. SEM micrographs of gum-based films indicated a smooth surface and homogenous structure for many unplasticized films, with a small number of cracks [3, 7, 8, 14, 15, 18, 20, 21, 46]. In some cases, the incorporation of plasticizers or lipid derivatives induced a coarse surface, and no crack was revealed due to their plasticizing effect [3, 7, 9, 14, 20, 21]. Cross-sectional studies of emulsified films can provide important information about biopolymer and lipid interactions. Abdul Haq et al. [16] observed a laminar structure in the cross-sectional image of the gum Cordia–beeswax emulsified films because of the coalescence of lipid globules during film drying. They declared that these lipid layers profoundly affected the WVP of the emulsified films [16]. A structural discontinuity induced by stearic and palmitic fatty acids was also found in the cross-sectional images of LPSG films, which explains the poor mechanical properties of these emulsified films [21]. Additionally, coalescence of fatty acids in the emulsified LPSG films exposed to drying (or even keeping) occurred and led to surface roughness and structural reorganization [21]. The volatility of most essential oils is problematic for the film matrix, and SEM micrographs verified that the BSG and CSG films loaded with thyme and ZMEOs, respectively, have a loose texture with a sponge-like structure due to evaporation of essential oils during film drying (Figure 23.5); hence, the authors concluded that one of the reasons for the reduction in the water vapor barrier of these films as a function of the increase in essential oils was the formation of pores and holes in the microstructure of the films [12, 18].

23.4 Applications Unlike biodegradable films, edible films and coatings are not meant to fully replace with conventional non-edible films and coatings. They are used as primary packaging which

593

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23 Edible/Biodegradable Films and Coatings from Natural Hydrocolloids

is in contact with the product but not as secondary or tertiary levels of packaging. Edible films and coatings are an excellent carrier for various functional and nutraceutical components such as antioxidants, antimicrobial, and vitamins, and thus using them in direct contact with fruits, vegetables, and ready-to-eat foods will provide high value-added foods with extended shelf life. Moisture and oil migration, volatility of aromatic compounds, and oxygen permeation are customary mass transfer problems, and nearly all foods are exposed to at least one of them [1]. Coatings not only act as integrity maintainers and appearance enhancers but also decrease mass transfer, especially leaching of liquefied food components during the heating process. A number of studies have been conducted on the development and use of edible coatings from natural hydrocolloids in order to introduce novel coatings for food preservation. BSG edible coating containing oregano essential oil was used for fresh-cut apricots. The release of essential oil during storage reduced the microbial population of the fruit due to antimicrobial performance, and effectively retarded the spoilage. The coated apricots exhibited higher soluble phenolics, antioxidant activity, aroma, and overall acceptability compared with uncoated ones [10]. BSG coating loaded with thymol was applied to decrease oil uptake and oxidation in shrimp during deep-fat frying. The coating considerably lowered both oil uptake and moisture loss; the oxidation indexes (peroxide value and thiobarbituric acid), toughness, and stiffness of the coated shrimps were lower than those of the uncoated ones [53]. In another work, the microbial count of shrimp during cold storage was lessened by thymol-incorporated BSG coating, without harmful effects on organoleptic properties [11]. Abdul Haq et al. [54] prepared an edible coating by addition of methanolic extract of the fruit of Cordia myxa into gum Cordia coating solution; using this coating increased the shelf life of pine nuts (a rich source of unsaturated fatty acids) by postponing oil oxidation. Applying LPSG edible coating on chiffon cake improved cohesiveness and softness, and retained most of its moisture content [55]. Plantago major seed mucilage coating incorporated with Anethum graveolens (dill) essential oil was employed for increasing the shelf life of beef in refrigerated storage; the coating prevented microbial growth and lipid oxidation owing to the antioxidant and antimicrobial potentials of the essential oil, thereby enhancing the quality and storage life of beef. Also, the color and overall acceptability of coated beef were much better than those of the uncoated samples after 18 days of refrigerated storage [56]. An emulsified coating was fabricated from a combination of Psyllium seed gum and sunflower oil; application of the coating on the fresh-cut papaya could slow water loss and prolonged shelf life up to two weeks [57]. In order to limit the oil uptake and enhance the quality of deep-fat fried French-fries, potato sticks were treated by two hydrocolloid-based (methylcellulose and tragacanth) coating solutions before frying; these coatings successfully reduced water loss and oil uptake and enhanced product appearance and crispiness [58].

23.5 Conclusions and Future Trends This chapter focused on the preparation and measurement of films and coatings from novel natural hydrocolloids. Gum-based films with appropriate quality and adequate thickness were successfully developed in accordance with customary methods. Due to the hydrophilic nature of gum and mucilage powders, the films and coatings are mostly water sensitive, and the WVP, moisture uptake, water solubility, and water contact angle are strongly influenced by water molecules. The easiest way to reduce the water

References

susceptibility of the films is to incorporate lipid derivatives and nanoclay, one of the most well-known nanomaterials, which improves the abovementioned characteristics at the expense of transparency, OP, and, occasionally, mechanical properties. Also, plasticizer type and especially concentration usually show significant effects on the films’ quality. The WVP is comparable with that of other polysaccharide-based films, but it is more often several orders of magnitude greater than that of synthetic films. The OP of gum-based films is relatively low due to the inherited polarity of polysaccharides, and the values are in the range reported for most polymers and biopolymers. As expected, and similar to other polysaccharide-based films, the water solubility of gum-based films is intermediate, and in some cases it is high, which may be beneficial in some food and pharmaceutical applications, and also after the films are discarded. Measurement of surface hydrophilicity indicates that the water contact angle of natural hydrocolloid films is lower than that of plastic films and is mainly localized in a narrow range. However, hydrophobization by hydrophobic materials made the contact angle of some films equal to that of the most hydrophobic plastics. Investigation of the behavior of films at different RH values revealed relatively high moisture absorption, especially at RH > 50%, which restricts their application. Although gum-based films are mechanically inferior to synthetic films, the mechanical properties of some of these films are promising. Also, resistance against tensile force is further improved through nanoparticle inclusion. The impurities in gum and mucilage powders impart a light color to films and coatings, thereby increasing attractiveness without detrimental effects on the product. In conclusion, the characteristics of the films from natural hydrocolloids are very close to those of most commercial polysaccharide-based films and can be used as primary packaging for protecting and extending food shelf life. More recently, many studies have been published on the development of edible/biodegradable films from new resources, especially natural hydrocolloids. They show considerable potential for film and coating making. Blended, nanocomposite, and emulsified films are derivatives of films made from gums or mucilages that aim for performance improvement. However, more studies are needed to overcome gum-based films’ deficiencies and make them more and more similar to synthetic plastic films. Growing concerns about environmental problems, and also the limitations of oil resources are good motivators for further research on the use of renewable resources for providing packaging materials and will help ensure a promising future for gum-based films.

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emulsified films based on pistachio globulin protein and fatty acids. Journal of Food Engineering 100 (1): 102–108. 3 Bertuzzi, M.A. and Slavutsky, A.M. (2013). Formulation and characterization of film based on gum exudates from brea tree (Cercidium praecox). Journal of Food Science and Engineering 3 (3): 113–122. 4 Mohammad Amini, A., Razavi, S.M.A., and Zahedi, Y. (2015). The influence of different plasticisers and fatty acids on functional properties of basil seed gum edible film. International Journal of Food Science & Technology 50 (5): 1137–1143.

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seed gum: a new source of carbohydrate to make a biodegradable film. Carbohydrate Polymers 101: 349–358. Seyedi, S., Koocheki, A., Mohebbi, M., and Zahedi, Y. (2015). Improving the physical and moisture barrier properties of Lepidium perfoliatum seed gum biodegradable film with stearic and palmitic acids. International Journal of Biological Macromolecules 77: 151–158. Ahmadi, R., Kalbasi Ashtari, A., Oromiehie, A. et al. (2012). Development and characterization of a novel biodegradable edible film obtained from psyllium seed (Plantago ovata Forsk). Journal of Food Engineering 109 (4): 745–751. Razavi, S.M.A., Mohammad Amini, A., and Zahedi, Y. (2015). Characterisation of a new biodegradable edible film based on sage seed gum: influence of plasticiser type and concentration. Food Hydrocolloids 43: 290–298. Mostafavi, F.S., Kadkhodaee, R., Emadzadeh, B., and Koocheki, A. (2016). Preparation and characterization of tragacanth-locust bean gum edible blend films. Carbohydrate Polymers 139: 20–27. Dick, M., Henrique Pagno, C., Haas Costa, T.M. et al. (2016). Edible films based on chia flour: development and characterization. Journal of Applied Polymer Science 133 (2): 42455–42464. Hashemi Gahruie, H., Ziaee, E., Eskandari, M.H., and Hosseini, S.M.H. (2017). Characterization of basil seed gum-based edible films incorporated with Zataria multiflora essential oil nanoemulsion. Carbohydrate Polymers 166: 93–103. Slavutsky, A.M. and Bertuzzi, M.A. (2015). Thermodynamic study of water sorption and water barrier properties of nanocomposite films based on brea gum. Applied Clay Science 108: 144–148. McHugh, T.H., Avena-Bustillos, R., and Krochta, J. (1993). Hydrophilic edible films: modified procedure for water vapor permeability and explanation of thickness effects. Journal of Food Science 58 (4): 899–903. Abdul Haq, M. (2013). Development and Application of Edible Films and Coatings from Gum Cordia (Cordia Myxa)k. University of Karachi. Rossi Marquez, G., Han, J.H., Garcia-Almendarez, B. et al. (2009). Effect of temperature, pH and film thickness on nisin release from antimicrobial whey protein isolate edible films. Journal of the Science of Food and Agriculture 89 (14): 2492–2497. Kester, J.J. and Fennema, O.R. (1986). Edible films and coatings: a review. Food Technology 40: 47–59. Hashemi, S.M.B. and Mousavi Khaneghah, A. (2017). Characterization of novel basil-seed gum active edible films and coatings containing oregano essential oil. Progress in Organic Coatings 110: 35–41. Jouki, M., Tabatabaei Yazdi, F., Mortazavi, S.A., and Koocheki, A. (2014). Quince seed mucilage films incorporated with oregano essential oil: physical, thermal, barrier, antioxidant and antibacterial properties. Food Hydrocolloids 36: 9–19. Oleyaei, S.A., Zahedi, Y., Ghanbarzadeh, B., and Moayedi, A.A. (2016). Modification of physicochemical and thermal properties of starch films by incorporation of TiO2 nanoparticles. International Journal of Biological Macromolecules 89: 256–264. Zahedi, Y., Fathi Achachlouei, B., and Yousefi, A.R. (2018). Physical and mechanical properties of hybrid montmorillonite/zinc oxide reinforced carboxymethyl cellulose nanocomposites. International Journal of Biological Macromolecules 108: 863–873.

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rier, and thermal properties of polyol-plasticized biodegradable edible film made from kefiran. Carbohydrate Polymers 84 (1): 477–483. Cecchini, J.P., Spotti, M.J., Piagentini, A.M. et al. (2017). Development of edible films obtained from submicron emulsions based on whey protein concentrate, oil/beeswax and brea gum. Food Science and Technology International 23 (4): 371–381. Silvestre, C. and Cimmino, S. (2013). Ecosustainable Polymer Nanomaterials for Food Packaging: Innovative Solutions, Characterization Needs, Safety and Environmental Issues. CRC Press. Yuan, Y. and Lee, T.R. (2013). Contact angle and wetting properties. In: Surface Science Techniques, 3–34. Springer. Cunha, A.G. and Gandini, A. (2010). Turning polysaccharides into hydrophobic materials: a critical review. Part 2. Hemicelluloses, chitin/chitosan, starch, pectin and alginates. Cellulose 17 (6): 1045–1065. Critical Surface Tension and Contact Angle with Water for Various Polymers, https://www.accudynetest.com/polytable_03.html?sortby=contact_angle (Accessed 29 November 2017). The, D.P., Debeaufort, F., Voilley, A., and Luu, D. (2009). Biopolymer interactions affect the functional properties of edible films based on agar, cassava starch and arabinoxylan blends. Journal of Food Engineering 90 (4): 548–558. Peroval, C., Debeaufort, F., Despre, D., and Voilley, A. (2002). Edible arabinoxylan-based films. 1. Effects of lipid type on water vapor permeability, film structure, and other physical characteristics. Journal of Agricultural and Food Chemistry 50 (14): 3977–3983. Ghanbarzadeh, B., Musavi, M., Oromiehie, A. et al. (2007). Effect of plasticizing sugars on water vapor permeability, surface energy and microstructure properties of zein films. LWT-Food Science and Technology 40 (7): 1191–1197. Timmermann, E., Chirife, J., and Iglesias, H. (2001). Water sorption isotherms of foods and foodstuffs: BET or GAB parameters? Journal of Food Engineering 48 (1): 19–31. Abdul Haq, M., Jafri, F.A., and Hasnain, A. (2016). Effects of plasticizers on sorption and optical properties of gum cordia based edible film. Journal of Food Science and Technology 53 (6): 2606–2613. Donhowe, I.G. and Fennema, O. (1993). The effects of plasticizers on crystallinity, permeability, and mechanical properties of methylcellulose films. Journal of Food Processing and Preservation 17 (4): 247–257. Munoz, L., Aguilera, J., Rodriguez-Turienzo, L. et al. (2012). Characterization and microstructure of films made from mucilage of Salvia hispanica and whey protein concentrate. Journal of Food Engineering 111 (3): 511–518. Labrecque, L.I., Patrick, V.M., and Milne, G.R. (2013). The marketers prismatic palette: a review of color research and future directions. Psychology & Marketing 30 (2): 187–202. Koocheki, A., Taherian, A.R., Razavi, S.M., and Bostan, A. (2009). Response surface methodology for optimization of extraction yield, viscosity, hue and emulsion stability of mucilage extracted from Lepidium perfoliatum seeds. Food Hydrocolloids 23 (8): 2369–2379.

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24 Health Aspects of Novel Hydrocolloids Jafar M. Milani and Abdolkhalegh Golkar Department of Food Science & Technology, Sari Agricultural Sciences and Natural Resources University (SANRU), Sari, Iran

24.1 Introduction The term hydrocolloids includes all the polysaccharides and proteins that are widely used in industrial sectors. Hydrocolloids are important parts of our daily diet in food systems such as yogurt, mayonnaise and salad dressing, ice cream, dessert, bakery products, and so on [1, 2]. The increasing occurrence of different diseases in the world has given rise to a demand for healthy foods containing natural compounds such as hydrocolloids (e.g., dietary fiber) and phytochemical compounds (e.g., antioxidants, and so on) with a high level of compounds with health benefits [3]. For many years, hydrocolloids have been used in food systems as functional ingredients for the control of microstructure, texture, flavor, and shelf life. In fact, these are a diverse group of high-molecular-weight polymers and may be named thickeners, gelling agents, stabilizers, bulking agents, and emulsifiers on the basis of their functionality [1, 4]. Beside functional attributes, hydrocolloids are presently being reported to have many increasing applications in healthy foods. The alteration of people’s lifestyle has been caused by a growing awareness of the relationship between diet and health and new processing technologies. These changes have led to the production of novelty food with a high level of fiber and low-fat content. Consequently, this has increased the demand for hydrocolloids in the food industry [5]. The term dietary fiber was first used in 1953 by Eben Hipsley in his observation publication noting that populations with diets high in fiber-rich foods tended to also have lower rates of pregnancy toxemia [6]. Previously, the analytical term crude fiber had been used for the portion of plant foods that escaped solvent, acid, and alkali extractions [7]. The WHO (World Health Organization) and FAO (Food and Agriculture Organization) agree with the AACC (American Association of Cereal Chemists) definition but with a slight variation. They state that dietary fiber is a polysaccharide with 10 or more monomeric units which is not hydrolyzed by endogenous hormones in the small intestine [8]. Epidemiological evidence suggests that a high intake of dietary fiber is associated with numerous health benefits. The fiber hypothesis proposed by Burkitt and Trowel suggested some three decades ago that there was a link between the consumption of a diet rich in fiber and the level of protection against many of the “First World diseases” [7, 9]. In previous research papers, the dietary fiber properties of various food Emerging Natural Hydrocolloids: Rheology and Functions, First Edition. Edited by Seyed M.A. Razavi. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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24 Health Aspects of Novel Hydrocolloids

hydrocolloids have been discussed. Intakes of food containing dietary fiber reduced the risk for developing different diseases such as coronary heart disease, diabetes, obesity, and so on [4, 10–13]. In addition, it has been suggested that public awareness of these important ingredients will be required. Although several review papers have been published reporting on the health benefits of commercial food hydrocolloids [2, 4, 14, 15], none of them has addressed novel hydrocolloids in particular. So, the important points of this chapter are the investigation of the health aspects of novel hydrocolloids on the basis of recent publications.

24.2 Health Benefits of Hydrocolloids With the spread of different disease in the world and the increasing demand for functional and healthy food products, scientists have conducted research to solve these problems. Hydrocolloids as food ingredients related to unique functional properties have been used for many years. These ingredients can be used as fibers with specific health benefits. The literature has examples of novel food hydrocolloids that exhibit important roles in foods as new dietary fiber sources in addition to their traditional applications as thickening, coating, gelling, and emulsifying agents. Dietary fiber and whole grains are an abundant source of nutrients including vitamins, minerals, and slowly digestible carbohydrates. Also, they contain phytochemicals that are not classified as essential nutrients but may play important roles in human health [16]. First, researchers found that a diet with guar gum prolongs mouth to cecum transit time, delays gastric emptying, slows down the increase in postprandial glycemia, and aids colonic function [17–19]. In the following sections, the proposed health benefits of well-known and novel food hydrocolloids as dietary fiber will be introduced. The health aspects of commercial hydrocolloids have been deeply studied, and some of them are summarized in Table 24.1. Numerous papers are annually published on the characterization of new hydrocolloids with health claims, and a wide range of novel hydrocolloids are reported to have health benefits in line with good functional properties in food systems. In Table 24.2, some recent studies on the possible health effects of novel hydrocolloids are presented. 24.2.1

Anti-diabetic Effects

Diabetes mellitus is a chronic metabolic disorder characterized by a high blood glucose level (hyperglycemia) due to insulin deficiency and/or insulin resistance [66]. Diabetes is spreading worldwide, affects approximately 4% of the population, and is expected to increase by 5.4% in 2025. Diabetes is a multifactorial disease which is characterized by hyperglycemia, defects in reactive oxygen species scavenging enzymes, and high-oxidative-stress-induced damage to pancreatic beta cells [67]. Generally, diabetes mellitus is a group of metabolic diseases characterized by hyperglycemia resulting from defects in insulin secretion, insulin action, or both. Diabetes mellitus is classified into two groups: type-1 diabetes is characterized by the destruction of pancreatic β-cells. Type-2 diabetes is the major form of diabetes mellitus and is caused by insulin resistance and impaired insulin production, secretion, and function [49]. For diabetes mellitus

24.2 Health Benefits of Hydrocolloids

Table 24.1 Health benefits of most well-known hydrocolloids. Hydrocolloid

Health aspect

Reference

Pectin and Guar gum

Cholesterol-lowering effect

[20]

Psyllium

Blood glucose and insulin lowering effect

[21]

Alginate

Enhancing satiety and controlled energy intake

[22]

Hydroxypropylmethylcellulose (HPMC)

Anti-diabetic effect

[23]

Oat β-glucan

Hypoglycemic effect, satiety effect

[24, 25]

Gum arabic

Reduction of blood pressure, anti-obesity effect

[26, 27]

Chitosan

Antioxidant effect

[28]

Cellulose

Anti-obesity effect, blood-glucose-lowering effect, Cholesterol-lowering effect

[28–30]

Resistant starch

Blood glucose and insulin control

[31]

Barley β-glucan

Satiety effect

[32]

Inulin

Prebiotic effect

[33]

Arabinoxylan

Anti-diabetic effect

[34]

Carrageenan

Antitumoral activity

[35]

Alginate

Active compounds carrier

[36]

therapy, a series of agents, including sulfonylureas, thiazolidinedione, α-glucosidase inhibitors, and Biguanide, which are commercial products, have been used for decades. But these drugs have adverse effects depending on the amount consumed (weight gain, liver damage, bone loss, diarrhea, vomiting, and so on). As the treatment of this disease usually involves very long periods, in some cases, serious problems may occur. Although new drugs such as DPP-4 inhibitors and GLP-1 analogs have been introduced to the market, but their high price as well as the absence of clear safety characteristics have led to a large demand for natural drugs to treat diabetes mellitus. The new trend is for patients to use functional foods and complementary or alternative medicine. Researchers report that a variety of active compounds from natural products such as polysaccharides and dietary fibers have a high potential for application in diabetes mellitus treatment [68]. Viscous forms of dietary fiber have been shown to improve blood glucose control by trapping ingested carbohydrates inside the viscous gel formed after digestion. As a result, sugars are absorbed into the bloodstream more slowly, limiting the rise in blood glucose seen after a meal. High-viscosity fibers usually reduce the palatability of products, and this property is a major problem for practical application, although they are necessary for maximizing the beneficial effect on blood glucose [69]. In addition, some suggest that insoluble fiber increases the passage rate of foodstuff through the gastrointestinal tract, decreasing the absorption of nutrients (such as simple carbohydrates). Insoluble fiber can cause reduced appetite and food intake, and short-chain fatty acids (via fermentation) have been shown to reduce the postprandial glucose response [8]. Recently, an improvement in glycemic control was observed with psyllium in patients with type-2 diabetes mellitus [70].

603

Table 24.2 Possible health benefits of novel hydrocolloids (extracted from the published works during the years 2010–2017). Hydrocolloid

Health aspect

Cyanobacteria Nostoc commune polysaccharides

Antioxidant activity

Highlight

• 92.71% hydroxyl radical scavenging activity at the concentration of 10 mg ml−1 • 0.445 reducing capacity at the concentration of 10 mg ml−1

[37]

Reference

Almond gum polysaccharides (Prunus amygdalus)

Antioxidant activity Antimicrobial activity

• Higher antioxidant activity beyond 3 mg ml−1 than BHA • IC50 for almond gum polysaccharides and BHA were 6.6 ± 0.7 and 0.4 ± 0.02 mg ml−1 , respectively • Antimicrobial activity against five pathogenic strains (E. coli, S. aureus, E. faecalis, P. aeruginosa, and S. typhimurium) beyond 60 mg ml−1 • Inhibition of lipid oxidation and microbial growth in ground beef meat containing almond gum hydrolysis was significantly (p < 0.05) reported

[38, 39]

Sulfated polysaccharide from Ulva pertusa (Chlorophyta)

Antihyperlipidemic activity

• High sulfate content ulvan decreased 28.1% and 28.4% of triglyceride and low-density lipoprotein cholesterol (LDL-C), respectively. • Antihyperlipidemic activity influenced by sulfate content of ulvan

[40]

Levan and its derivative from Bacillus subtilis NRC1aza

Antitumor activity Antioxidant activity Hypolipidemic effect

• High selective cytotoxicity against hepatocellular carcinoma HepG2 cells • DNA damaging and fragmentation via the mitochondrial pathway • Reducing the extent of atherosclerosis by oxidative stress and serum total cholesterol, triglycerides, LDL cholesterol and raising HDL cholesterol

[41, 42]

Levan polysaccharide

Anti-diabetic activity

• Decreasing glucose level in plasma by 52% • Decreasing thiobarbituric acid reactive substances and increasing superoxide dismutase enzyme in the organs of diabetic rats

[43]

Artemis sphaerocephala Krasch. Gum

Antioxidant activity Anti-diabetic activity

• Polysaccharide had dose-dependent on superoxide dismutase, malondialdehyde, and hydroxyl in liver and serum of rats • Similar protective effect reported between 2.7% gum and metformin

[44]

Extracted polysaccharides from Bryopsis plumosa

Antioxidant activity

• Inhibitory effects of superoxide radical and DPPH with IC50 values were 9.2 μg ml−1 and 1.7 mg ml−1

[45]

Polysaccharides from Sargassum thunbergii

Antitumor activity

• Biological activity influence by harvesting time and polysaccharides concentration

[46]

Acidic polysaccharide from Tuber sinoaestivum

Immunomodulator effect

• Exhibiting dose-dependent complement fixation activity

[47]

Polysaccharides from Diaphragma juglandis fructus

Antioxidant activity Antibacterial activity

Peach-gum-derived polysaccharides

IC50 for DPPH scavenging activity was 1.068 mg ml−1 IC50 for the ABTS radical scavenging activity was 0.649 mg ml−1 4 mg ml−1 concentration had 90.91% OH radical scavenging activity Antibacterial activity increased with increasing concentration (0.2–1.2 mg ml−1 ) in the following order: S. aureus > P. aeruginosa > E. coli > L. monocytogenes

[48]

Anti-diabetic effect

• Dose-dependent behavior on lowering blood glucose level • Hypoglycemic effect (more than 1.86%) on blood glucose compared with metformin hydrochloride at the same concentration

[49]

Lycium barbarum L. Polysaccharides

Anticancer effect Antioxidant activity Hypoglycemic effect Neuroprotective effect

• Significant (P < 0.01) inhibition of the SW480 cells growth at the higher concentration of 400 mg l−1 • Significant (P < 0.01) inhibition of the Caco-2 cells growth at the higher concentration of 200 mg l−1 • Showing long-term anti-proliferative effect by crystal violet assay • Antioxidant activity is a dose-response with polysaccharide concentration • Protective effect against skin oxidative injury • Nontoxic at the high dosage of polysaccharide for hypoglycemic activity • Promoting pancreatic β cell proliferation

[50–53]

Zizyphus jujuba Mill Polysaccharide

Antioxidant activity Hyperlipidemic effect Immunomodulatory activity

• In vitro antioxidant and hyperlipidemic activity were a dose-dependent manner. • This polysaccharide improved the phagocytosis activity of THP-l cells and had an effect on the expression of pro-inflammatory cytokines (TNF-α, lL-1β, lL-6)

[54–57]

• • • •

(Continued)

Table 24.2 (Continued) Hydrocolloid

Health aspect

Plantago spp. Polysaccharide

Immunomodulatory effect Antioxidant activity

Highlight

• Assessment of splenocyte proliferation index and production of NO and TNF-α from macrophages in the 5–125 μg ml−1 concentration • This property may be related to the arabinose and mannose units, (1 → 3)-linked mannopyranosyl in the backbone and 1,5-linked Araf (41.4%) • In vitro phenolic content of P. algarbiensis, P. almogravensis, and P. lagopus were 480.06 ± 3.11, 215.11 ± 3.47, and 146.08 ± 2.62 μmolGAE g−1 • In vitro DPPH IC50 of P. algarbiensis, P. almogravensis, and P. lagopus were 19.90 ± 0.75, 46.76 ± 1.66, 88.99 ± 2.31 μg ml−1 • The ethanol-based extracts stimulated wound healing in the porcine skin at 1.0 mg ml−1 concentration (on the dry weight basis)

[58–60]

Reference

Morus spp. Polysaccharide

Antioxidant activity Anti-obesity activity

• Dose-dependent behavior of DPPH, hydroxyl, superoxide, ABTS radical scavenging activities • Inhibiting the proliferation of 3T3-L1 pre-adipocyte cells through induction of cell apoptosis • Mediated through regulation of MAPKs (ERK and p38) signaling pathway, induction of mitochondrial dysfunction and DNA fragmentation

[61, 62]

Rehmannia glutinosa polysaccharide

Anticancer activity

• Inducing the proliferation of natural killer cells in mice in vivo • Enhancing cytotoxic activities • - Inhibiting CT26 tumor growth in the mice’s lung

[63]

Malva aegyptiaca polysaccharides

Antioxidant activity Antimicrobial

• IC50 for DPPH scavenging activity was 1.94 mg ml−1 • β-carotene bleaching inhibition capacity was IC50 = 1.56 mg ml−1 • 10 mg ml−1 polysaccharide concentration had 84.2–90.3% inhibition rate against gram-positive bacteria

[64]

Cress (Lepidium sativum) seed gum

Hypoglycemic activity Hypolipidemic activity Antimicrobial activity

• Decreasing blood glucose level in streptozotocin-induced diabetic rat at 20 mg kg−1 • Decreasing serum cholesterol, LDL cholesterol, serum creatinine, urea, liver cholesterol and total lipid levels • - Application against P. aeruginosa in combination with penicillin G and erythromycin

[65]

24.2 Health Benefits of Hydrocolloids

Jia et al. [71] investigated the hypoglycemic and hypolipidemic activities of Laminaria japonica polysaccharides (LJPs) by alloxan injection and found that LJP administration prevented body weight loss, decreased fasting blood glucose levels, and increased serum insulin levels in diabetic mice. Furthermore, it decreased total cholesterol, total triglyceride, and LDL-C levels, and increased HDL-C levels in these mice [71]. The same results were also seen in the studies of Li et al. [72]. Huang et al. [73] isolated a fucose-containing exopolysaccharide from a culture broth of Enterobacter cloacae Z0206 with molecular weight 1.1 × 106 Da and composed of fucose, glucose, galactose, glucuronic acid, and pyruvic acid in the approximate molar ratio 2:1:3:1:1, and found that exopolysaccharide exhibited hypoglycemic and hypolipidemic effects, possibly through regulating AMP-activated protein kinase and SirT1-mediated effects on carbohydrate and lipid metabolism. Selenium-ECZ-EPS (exopolysaccharide) is a water-soluble selenium-enriched exopolysaccharide which is isolated from the submerged culture broth of E. cloacae Z0206. Se-ECZ-EPS significantly reduces fasting blood glucose, glycated serum proteins (GSPs), total cholesterol, and total triglyceride contents in the liver [73]. Cunha et al. [66] found that galactomannan from Caesalpinia ferrea seeds lowered hyperglycemia in diabetic rats and significantly decreased serum TAG (mediated effects on carbohydrate and lipid metabolism). The anti-diabetic benefits of these hydrocolloids are associated with smooth glucose uptake and slow starch digestion [74]. As seaweed contains a large number of soluble polysaccharides, they therefore have potential functions as dietary fiber. Thus, they might be considered to have beneficial effects on cardiovascular diseases risk factors [75]. 24.2.2

Antioxidant Activity and Cancer Prevention

There has been increasing interest in researching natural antioxidants since they can protect the human body from free radicals and retard the progress of many chronic diseases and cancer [76]. Accordingly, there is a growing interest in applying new natural antioxidant compounds to prevent metabolic disorders of oxidative stress origin [64]. A number of natural polysaccharides and their derivatives have been demonstrated to possess potent antioxidant activities and potential applications as antioxidants [41]. In the last decade, it has been reported that some seaweed sulfated polysaccharides (such as carrageenan and fucoidan) showed antioxidant activities [77–79]. The antioxidant capacity of commercial carrageenan from Gigartina skottsbergii and Schizymenia binderi, and fucoidan from Lessonia vadosa was also evaluated by the oxygen radical absorbance capacity method [80]. In addition, peach-gum-derived oligosaccharides showed high hydroxyl radical scavenging activity (86.12%) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity (91.70%) at a concentration of 100 μg ml−1 as well as high reducing capacity at a concentration of 50 μg ml−1 [81]. Bouaziz et al. [38] reported that almond gum oligosaccharide (by enzymatic hydrolysis) had significant antioxidant and antimicrobial activity. This oligosaccharide has been tested in beef meat preservation, and microbial growth and lipid oxidation were monitored for nine days at 4 ∘ C. They found significant inhibitions (p < 0.05) of lipid oxidation and microbial growth in ground beef meat containing almond gum oligosaccharide [38].

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Cancer treatment strategies are actually focused on improving three main strategies: (1) prevention, based on promoting lifestyles associated with low tumorigenesis risks; (2) surgery, consisting often in the ablation of the tumor, ideally before the epithelial-mesenchymal transition, which leads to metastasis; and (3) by inducing tumoral cell death via targeted radio- or chemotherapy [75]. Epidemiological studies have suggested a reverse association between intake of dietary fiber, the ingested parts of plant materials, and risk of colon cancer. Dietary fibers influence colon carcinogenesis by increased fecal bulk, reduced colonic transit time, and diluted fecal toxin contents, which consequently reduce the exposure of colonic mucosa to the luminal carcinogens. In addition, the interaction between dietary fiber and colonic microbiota and bile acids, and the production of short-chain fatty acids resulting from fermentation are believed to protect against colon cancer development [82]. Dahech et al. [43] investigated the antitumor and anti-cytotoxic effect of Levan polysaccharide produced by Bacillus licheniformis. In the in vitro antitumor activity test of Levan against some tumor cell lines, relatively significantly high activity was observed against hepatocellular carcinoma, human (HepG2 ). The strongest inhibiting activity appeared at the highest dosage of Levan (12.5 mg ml−1 ) [43]. 24.2.3

Immunostimulant Activity

Immunomodulation is considered an important biological function of natural polysaccharides, which act as immunomodulators or biological response modifiers. Various reports have suggested that polysaccharides and proteoglycans with high arabinose and galactose content exhibit immunomodulatory activities, including complement fixing activities and/or modulation of macrophage function. The results from in vitro tests of cashew nut tree gum exudate using murine peritoneal macrophages showed that this gum can be used as an anti-inflammatory [83]. Also, a recent study suggested that water-soluble polysaccharide from Erythronium sibiricum bulb is a potential immunostimulator. An in vitro assay showed that this polysaccharide significantly promoted the proliferation and neutral red phagocytosis of RAW 264.7 macrophage cells. Moreover, it stimulated the production of secretory molecules (nitric oxide, TNF-α, and IL-1β) of RAW 264.7 macrophage cell in a dose-dependent manner [84]. Ji et al. [85] found that Ziziphus jujuba polysaccharide fractions (RQP1d and RQP2d) induced significant increases in nitric oxide formation in RAW 264.7 cells, and both extracts stimulate the innate immune response. However, RQP1d and RQP2d are dissimilar in their chemical compositions and molecular weights. Low concentrations of RQP2d had a synergistic effect with lipopolysaccharide on splenocyte proliferation. The immunomodulatory actions of polysaccharides are associated with their molecular weights, chemical compositions, glycosidic linkages, and so on [85]. 24.2.4

Antimicrobial Activity

Various researchers have attempted to find new antimicrobials to inhibit food spoilage and food poisoning, which are important problems in the food industry [64]. Nowadays, it is possible to control pathogenic microorganisms in foods by synthetic antimicrobials. But the increase of bacterial resistance to conventional antimicrobial agents and consumer awareness of the side effects of these compounds has motivated the search for

24.2 Health Benefits of Hydrocolloids

novel substrates of natural origin. According to Kubo et al. and Campos et al., cashew tree gum has antimicrobial activity against several microorganisms, which is attributed to the presence of anacardic acid [86, 87]. Peach-gum-derived oligosaccharides demonstrated antimicrobial activity against Bacillus subtilis, Staphylococcus aureus, and Escherichia coli at a concentration of 100 μg ml−1 [81]. On the basis of recent researches, almond gum polysaccharides (Prunus amygdalus) have potent antimicrobial activities against the pathogenic strains S. aureus, Pseudomonas aeruginosa, Salmonella typhimurium, Enterococcus faecalis, and E. coli [38, 39]. Alginate, fucoidans, and laminaran extracts were tested for their antimicrobial activity against bacteria (E. coli, Staphylococcus, Salmonella, and Listeria). Sodium alginate has been established as a strong antibacterial agent [88]. In addition, alginates can be used as bioactive coatings against Listeria monocytogenes for fish products during refrigerated storage such as cold-smoked salmon slices and fillets [89]. 24.2.5

Anti-obesity

Obesity has become a worldwide epidemic affecting people on every continent. More than just obesity itself, the major drawback of being obese is the high incidence of the associated health risks, like metabolic syndrome, type-2 diabetes, and cardiovascular problems. It is generally accepted that a disruption in the balance between energy intake and energy expenditure is an extremely important factor in the incidence of obesity [90]. Its rate is increasing dramatically, and it has been estimated that 58% of the world population will become obese by 2030 [91]. So, one of the interesting approaches of the food industry for the prevention of weight gain is to provide products with high satiating capacities and low-energy densities. Dietary fibers seem to be ideal candidates for the achievement of this function [74]. Increasing dietary fiber consumption may decrease energy absorption by diluting a diet’s energy availability while maintaining other important nutrients [8]. Calame et al. found that blends of gum arabic (EmulGold and PreVitae ) are able to satiety enhancement and decrease the caloric intake significantly after consumption [90]. Several studies have been performed that suggest a link between seafood consumption and obesity-related disorders [92, 93]. Several actions have been proposed for the mechanism linking seaweed’s polysaccharides and obesity disorders. One of them is the action of fiber in the seaweed’s biomass, and another is attributed to antioxidants, minerals, and omega 3 fatty acids that interfere in obesity prevention [75]. Generally, the capability of dietary fiber to decrease body weight could be related to the following:

®

®

(A) Fermentation of soluble fiber resulting in the production of GLP-1 (glucagon-like peptide) and peptide YY (PYY), which play a satiety role. (B) Dietary fiber also may significantly decrease energy intake. (C) Dietary fiber may decrease the dietary metabolizable energy, which is the gross energy minus the energy lost in the feces, urine, and combustible gases [8]. In Figure 24.1, the effect of hydrocolloids on the passage rate and enzyme digestion processes of foods during small intestine transfer is shown. Hydrocolloids can play a key role in modulating small intestinal behavior [94]. As seen in Figure 24.1, enzymes and

609

610

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Bile

Enzymes

Duodenum

Water, salts

Bile

Glucose, amino acids, fatty acids, micronutrients

Jejunum

Ileum

Figure 24.1 Schematic illustration of particulate food remnants and non-digested hydrocolloids (red symbols) in the small intestine. Source: Adapted from Gidley [12] with permission from Elsevier.

bile are secreted into the first section (duodenum), digestion/absorption and water/salt uptake occur in parallel throughout the rest of the small intestine, and bile is re-absorbed at the end of the jejunum and in the ileum. The concentration of non-digested hydrocolloids increases along the small intestine due to the uptake of both water and nutrients [12]. The presence of hydrocolloids in either viscous soluble form or as an encapsulating matrix is likely to have a major effect on the rate of small intestinal enzymatic digestion of starch, proteins, and lipids. This could be due to one or more of (1) slow transport or restricted access of enzyme to its substrate, (2) direct inhibition of enzyme activity through site-specific binding, and (3) slow or restricted transport of products from the enzyme to the site of absorption. Recent modeling and experimental data suggest that factor (3) may be important in viscous solutions [95]. 24.2.6 Blood Pressure and Cholesterol-Lowering Effects (Cardiovascular Health) Despite significant development in its prevention, cardiovascular disease remains the leading cause of death in the United States and most Western countries. Saturated fat, cholesterol intake, and increasing cis-saturated fat intake are the major parameters in the risk of cardiovascular diseases [20]. High consumption of whole grains is associated with a significant reduction in cardiovascular diseases. Psyllium gum and oat β-glucan are the most widely used sources of soluble fiber and have been approved for health benefits related to protection from cardiovascular diseases by the FDA. The mechanisms for an association between fiber linkage and cardiovascular disease are unclear, but it is suggested that fiber can reduce blood cholesterol levels by altering cholesterol and bile acid absorption and by its effects on hepatic lipoprotein production and cholesterol synthesis [10, 74]. The relationship between water-soluble fibers and decreasing serum LDL cholesterol concentrations are summarized in Figure 24.2. The viscous water-soluble fibers form a thick unstirred water layer in the intestinal lumen, thereby decreasing the (re)absorption of cholesterol and bile acids. This leads to an

24.2 Health Benefits of Hydrocolloids

C

BA + C Bile duct

Diet

Liver

BA

7-α-Hydroxylase

C HMG CoA reductase

Intestine

C

C BA Uptake

C

AcCoA

LDL-R

C Enterohepatic circulation

C

BA

(re)absorption

BA + C

Circulation Downregulation/ decrease

BA C

Upregulation/ increase

AcCoA Acetyl Coenzyme A BA

Bile acids

C

Cholesterol

LDL-R Cholesterol receptor

Excretion

Figure 24.2 Postulated hypocholesterolemic mechanism of water-soluble fibers. Source: Adapted from Theuwissen and Mensink [20] with permission from Elsevier.

increased fecal output of these two components. As a result, hepatic conversion of cholesterol into bile acids increases, hepatic pools of free cholesterol decrease, and – to reach a new steady state – endogenous cholesterol synthesis will increase. This leads to increased activities of 7-α-hydroxylase and HMG-CoA reductase to compensate for the losses of bile acids and cholesterol from the liver stores. In addition, hepatic LDL cholesterol receptors are upregulated to re-establish hepatic free cholesterol stores. These processes will ultimately lead to decreased serum LDL cholesterol concentrations [20]. Panlasigui et al. found that carrageenan-enriched diets are beneficial for lipid balance in regard to lowering the risk of the cardiovascular disease [96]. In addition, Paxman et al. proposed that alginate has indirect cardiovascular beneficial effects by modulating glucose and cholesterol uptake from the small intestine [97]. Researchers reported that Acacia (sen) SUPERGUMTM is suitable for diabetes mellitus patients and could assist in the control of the systolic blood pressure to reduce the risk of renal impairment [98]. Oat β-glucan influences the blood cholesterol levels, and LDL cholesterol-lowering effects depend on viscosity, which is controlled by the molecular weight and amount of oat β-glucan solubilized in the intestine [99]. 24.2.7

Mineral Absorption Effect

Previous animal and human studies have reported increased rates of calcium absorption and associated improvements in bone mineral density with ingestion of prebiotics [100]. In addition to encapsulation within hydrocolloid gels, plant tissues, or other food structures, it is possible that nutrients bind directly to food structures. This phenomenon is

611

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24 Health Aspects of Novel Hydrocolloids

now recognized as being important for a range of phytonutrients, particularly phenolic compounds, which appear to be bound sufficiently strongly to plant cell walls that they escape solubilization and uptake in the stomach and small intestine [12]. The dietary fiber fermentation in the large intestine can influence the intestinal absorption of elements. Short-chain fatty acids are fermentation products that are responsible for lowering the pH of cecal content, which in turn increases mineral solubility, leading to improved mineral absorption. Animal studies have revealed enhanced absorption of calcium, magnesium, and iron with gluco-oligofructose, fructo-oligofructose, and inulin in the colon, and five out of eight studies in humans also show a benefit, most importantly in adolescents [101]. In addition, inulin influences the intestinal absorption of calcium and magnesium in rats [102]. 24.2.8

Prebiotic Effects

A prebiotic is a food ingredient that is not hydrolyzed by human digestive enzymes in the upper gastrointestinal tract and beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria (Bifidobacteria or Lactobacilli) in the colon that can improve host health [74]. Dietary ingredients such as indigestible carbohydrates modify the gut microflora in favor of probiotics and hence potentially reduce the risk of colorectal diseases [103]. Typical of prebiotics are inulin and oligofructose, both naturally present in a number of fruits and vegetables, and another resistant oligosaccharide such as inline-type fructans [10]. Although all prebiotic is fiber, not all fiber is prebiotic. Classification of a food ingredient as a prebiotic requires a scientific demonstration that the ingredient [104]: • Resists gastric acidity, hydrolysis by mammalian enzymes, and absorption in the upper gastrointestinal tract • Is fermented by the intestinal microflora • Selectively stimulates the growth and/or activity of intestinal bacteria potentially associated with health and well-being The ability to favorably alter the intestinal microflora has been demonstrated by a number of other fiber and plant food sources. A specific role for resistant starch in stimulation of bacteria able to produce butyric acid has been reported [105]. Acacia gum was shown to produce a greater increase in bifidobacteria and lactobacilli than an equal dose of inulin and resulted in fewer gastrointestinal side effects, such as gas and bloating [90]. Polydextrose consumption resulted in a dose-dependent decrease in Bacteroides, as well as an increase in lactobacilli and bifidobacteria [106]. Wheat dextrin has also been shown to increase lactobacilli and reduce Clostridium perfringens and increase bifidobacteria [107]. Psyllium was found to have a prebiotic effect in healthy women [108]. Some reports exist about the role of prebiotics in cancer prevention [101], benefits in atopic disease [109], and reduction of blood cholesterol and triglycerides [101]. 24.2.9

Biomedical Applications

Other applications of hydrocolloids are tissue engineering (including biological signaling, cell adhesion, cell proliferation, cell differentiation, cell responsive degradation, and

24.2 Health Benefits of Hydrocolloids

remodeling), wound dressing/healing, and drug delivery systems; the above three major topics are grouped under biomedical applications. Hydrocolloids have some advantages over synthetic polymers in that they are nontoxic, biodegradable, biocompatible, and less expensive [14]. Alginate, chitin, chitosan, hyaluronic acid, cellulose, chondroitin sulfate, starch, and their derivatives have been studied as biomaterials for tissue engineering applications [110]. Moreover, chitin and chitosan as scaffolds for tissue engineering [111], composites of chitosan with hydroxyapatite, and grafted chitosan with carbon nanotubes have been developed for artificial bone and bone regeneration [112]. Application of other polysaccharides for bone, cartilage, and/or skin tissue engineering applications have also been explored [113]. Hydrocolloids have been widely used to prepare wound healing materials. Collagen sponge dressing was used to treat skin wounds in the rat [114]. Hooper et al. studied the antimicrobial activity of a RESTORE silver alginate dressing with a silver-free control dressing using a combination of in vitro culture and imaging techniques. The data highlighted the rapid speed of kill and antimicrobial suitability of this RESTORE silver alginate dressing on wound isolates and its overwhelming ability to manage a microbial wound bioburden in the management of infected wounds [115]. Moreover, sodium alginate films containing natural essential oils have been reported that may be applied as disposable wound dressings [116]. Various hydrocolloid-based drug delivery systems have been developed for specific targeted delivery or controlled release. The release of entrapped drugs or certain molecules can be triggered by the changes of conditions such as pH, ions, temperature, certain molecules, and so on [117]. Several hydrocolloids such as pectin, chitin, chitosan, guar gum, xanthan gum, gellan gum, dextran, and chondroitin have also been developed for drug delivery or controlled drug release [118, 119]. 24.2.10

Other Benefits

Some hydrocolloids can be applied to prevent the human enamel from erosion (dissolution and softening). For examples, Beyer et al. [120] reported that pectin, alginate, and gum arabic have potential to reduce citric acid erosion in soft drinks. The suggested interactions of such biopolymers with the enamel surface and between biopolymers are graphically shown in Figure 24.3. In the case of enamel erosion, two interactions are proposed: (1) interaction between negatively charged carboxyl groups of polymers and Ca2+ -ions of the enamel surface and (2) interaction between negatively charged carboxyl groups of different polymer molecules in the presence of positively charged Ca2+ -ions by forming a chelate complex [120]. In addition, some fiber-containing foods may need to be avoided in certain allergies. In fact, dietary fiber is fermented in the colon by anaerobic bacteria into short-chain fatty acids, mainly acetate, butyrate, and propionate. These short-chain fatty acids bind metabolite-sensing G-protein-coupled receptors. These receptors are expressed on epithelial cells as well as on immune cells [121]. Moreover, seaweeds contain a variety of polysaccharides and fibers that can be used in the prevention and treatment of various diseases in humans [75]. For examples, fucoidans are fucose-containing sulfated heteropolysaccharides [122]; fucoxanthin is a metabolite [123]; carrageenans [35] are extracted from red seaweeds, where this

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–OOC

COO– Ca2+

–OOC

Ca2+

Enamel Interaction 1: Polymers binding with Ca2+-ions of enamel.

Enamel

Ca2+ COO–

Enamel Interaction 2: Chelatbuilding between polymer molecules.

Polymer covered enamel in-vitro.

Figure 24.3 Two models of erosion inhibiting polymers in citric acid solutions. Source: Adapted from Beyer et al. [120] with permission from Elsevier.

substance plays a structural function; and laminarin is an active component from the brown seaweeds [124]. They have been documented in various biological activities including antiviral, anti-inflammatory, anticoagulant, antiangiogenic, immunomodulatory, and anti-adhesive activity. Moreover, the anti-constipation effect of some hydrocolloids such as psyllium, gellan gum, karaya gum, and xanthan have been reported [2].

24.3 Conclusions and Recommendations There has been an extremely alarming growth in chronic diseases such as cardiovascular disease, diabetes mellitus, and cancer, which has been connected to the overconsumption of high-fat as well as high-calorie foods. Also, the immoderate consumption of food carbohydrates has been a source of concern, and a joint FAO/WHO report has required people to decrease the consumption of sugars and to correspondingly increase dietary fiber consumption [125]. Hydrocolloids are the most important groups of food components that, in addition to functionality, have beneficial characteristics in the digestive tract and subsequent nutritional and health outcomes. Food industries are changing the production approach in response to people’s awareness and increasing demand for healthy food products. Nowadays, hydrocolloids (particularly dietary fiber) as one of the health components have been considered. As mentioned above and on the basis of published data, it can be suggested that usually, bioactive polysaccharides of natural origin such as algae have several biological effects in both in vitro and in vivo experiments. The information reviewed here may be helpful to design product formulations with novel hydrocolloids in view of their potential for therapeutic use or for use as ingredients in functional foods. In fact, the application of novel hydrocolloids as dietary fibers and functional ingredients is vital for the future studies and development of food industries.

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21 Moreaux, S.J.J., Nichols, J.L., Bowman, J.G. et al. (2011). Psyllium lowers blood glu-

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623

Index a Abelmoschus esculentus 529 Acanthophyllum bracteatum 397, 407, 419, 497 Acanthophyllum glandulosum 16, 20, 51, 371–396 Acid hydrolysis 329, 444, 473, 483, 484 Activation energy 67, 68, 73, 137, 149, 151, 157, 169, 171, 175, 208, 211, 255, 306, 307, 308, 413, 414, 479, 494, 495 Additive bread additive 363 food additive 1, 7, 20, 299, 348, 349, 500, 508, 551 film additive 573, 579, 580, 584, 589, 590 functional additive 442, 581, 591, 592 Adhesive 4, 10 adhesive force 378, 387 adhesiveness 177, 185, 194, 196, 240, 241, 266, 363, 378, 387, 388, 503, 504, 505, 506, 532, 536, 538, 539 Agar 1, 5, 6, 8, 9, 10, 11, 364, 510, 549, 571, 583, 584 Algal 6, 16, 549 Alginate 5, 6, 8. 9, 10, 11, 26, 28, 29, 30, 603, 609, 611, 613 Almond gum/almond tree exudate gum 14, 19, 35, 36, 273, 275, 291, 293–294, 297, 325, 551, 552–553, 566, 604, 607, 609, 617 Aloe vera/Aloe vera barbadensis Miller gum/Aloe vera mucilage 10, 14, 29, 33, 317, 319, 325, 326, 367

Althaea officinalis (A. officinalis) 14, 21, 32, 397–424 Alyssum homolocarpum (A. homolocarpum) i 13, 15, 18, 26, 43, 44, 53, 55, 205–223, 397, 413, 415, 418, 422, 574–575, 577–580, 582, 584–586, 588–590 Amplitude sweep 103, 104, 124, 125, 139, 159, 164, 166 Amygdalus A. communis L. 35 552 A. scoparia Spach 14, 19, 273–298, 421 Anacardium occidentale L. 14, 20, 327, 346, 558 Anadenanthera macrocarpa 559, 596 Angelica sinensis 556, 563, 568 Angico gum 556, 559 Antagonistic 152, 153, 357 Anticancer 430, 444, 605, 606, 617, 622 Anti-diabetic 24, 557, 602, 603, 604, 605, 607, 618 Antimicrobial 159, 271, 292, 298, 312–314, 359, 367, 374, 375, 389, 565, 572, 577, 594–597, 604, 606–609, 613, 620 Anti-obesity 603, 606, 609, 618 Antioxidant 14, 15, 21, 24, 30, 31, 35, 44, 51, 183, 200, 205, 213, 221, 274, 275, 292, 294, 312, 314, 324, 374, 375, 389, 390, 391, 398, 410, 417, 419, 421, 427, 428, 430, 431, 443–446, 448, 544, 572, 577–578, 582, 594, 596, 597, 601, 603, 604–607, 609, 617–620

Emerging Natural Hydrocolloids: Rheology and Functions, First Edition. Edited by Seyed M.A. Razavi. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.

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Index

Antitumor activity 31, 346, 603–605, 608, 617 Apparent modulus of elasticity 194, 505 Apparent viscosity 83–85, 89, 90, 92, 94, 95, 97, 122, 123, 137, 138, 161, 171, 174–176, 179, 185, 190, 195–197, 207, 210, 211, 215, 218, 228–230, 233, 235, 252, 254–257, 267, 284–286, 306–309, 315, 317, 355, 376, 379, 382, 411, 413–415, 438, 441, 476–479, 487, 488, 490, 492, 494, 495, 500, 501 Arabinose 18, 162, 186, 199, 207, 253, 279, 280, 301–303, 329–330, 350–351, 364, 408, 417, 433, 434, 436, 437, 474, 483, 527–529, 551, 552, 554, 559, 561, 606, 608 arabinogalactan 5, 187, 280, 300, 301, 351, 434, 500, 530 arabinoxylan 5, 49, 253, 269, 470, 584, 598, 603, 616 Arrhenius 67, 137, 148–151, 169–170, 171, 211, 255, 307, 413, 417, 438, 478, 487 Astragalus gummifer Labil gum 14, 19, 299–326 Avogadro number 58, 69, 115, 152

b Bakery

1, 9, 199, 218, 266, 268, 291, 292, 337, 374, 384, 505, 601 Balangu/Balangu–Shirazi 13, 15, 18, 27, 42, 53–57, 60–74, 183–203, 408, 416, 420, 527, 531, 533–534, 543, 545, 550, 565 Barhang 15, 45 Barrier properties 20, 43, 216, 218, 222, 263–265, 270–271, 360, 365, 368, 442, 504, 596–597 Basil seed gum (BSG) 13, 15, 22, 26, 37, 38, 39, 55, 61, 66, 69, 72, 473, 474, 476, 481–495, 499–523, 527, 531–542, 551, 557, 571, 573–583, 585–590, 592–594 Batter 9, 11–12, 30–31, 218, 266–268, 272, 393–394 Beer 8–10, 12, 21, 28, 77, 380, 381, 389

Berry number 66, 73 β-carotene/beta carotene 52, 431, 555, 567–568, 606 β-glucan/beta glucan 5, 10, 29, 63–64, 77, 249, 376, 391–392, 603, 610–611, 616, 620 β-lactoglobulin (BLG) 37–38, 142, 147, 156–157, 222, 246, 283, 287, 289, 296–298, 318, 326, 368, 513, 517, 521–523 Binary blend/binary mixture/binary biopolymer blend 41, 70, 77, 132, 135–136, 138, 154, 156, 180, 266 Binder 4, 14–17, 19, 32, 44, 133, 135, 262, 339, 340, 345, 365, 397, 544, 557, 568 Binding agent 10, 160, 333, 340, 551 Bingham/Bingham model 92–93, 95, 170, 175, 189, 285, 379 Bioactive compound 18, 215, 442, 444, 549–550, 555, 561–562, 620 Biodegradable 5, 18, 24, 41, 43, 46, 49, 181, 215–216, 222, 243, 266, 270–271, 275, 318, 442, 504, 520, 549, 554, 571–572, 576, 581–582, 585, 587–588, 593, 595, 613 Biopolymer 2, 4, 5, 12, 13, 17, 18, 24, 29, 41, 56, 67, 474, 475, 571, 576–578, 581–583, 586–588, 591, 593, 595 blend 41, 97, 99, 132–133, 154, 156, 180 Brachystegia eurycoma 16, 49 Bread 10, 12, 20, 29, 32, 36, 48, 183, 199, 200, 219, 266–267, 272, 352, 363–364, 367, 370, 384, 393, 499, 527, 543 Breakdown rate constant 89, 97, 172–173, 490, 535 Brea tree (Cercidium praecox) exudate gum 14, 20, 34, 35, 347–349, 571–573, 575–577, 582–585, 587–590, 592 Brittleness 105, 241, 264, 507, 572, 576, 587 Building blocks 23, 281, 549, 550 Bulking agent 16, 601 Burger model 117–118, 142–143, 169–170

Index

c Caesalpinia C. ferrea 416, 423, 667 C. spinosa 322, 422 Cake 9–10, 12, 21, 27–28, 47, 51, 92, 199, 203, 218, 223, 266–267, 375, 382–386, 389, 391, 393–394, 500, 506, 594, 599 Canary seed 13, 50, 53–54, 61, 63, 65, 67–68, 70–72, 74, 77 Carboxyl/carboxylate/carboxylic 19, 82, 102, 140, 146, 162, 171, 186, 208, 211, 217, 264, 282–283, 285, 304, 311, 415, 417, 435, 438–439, 448, 559, 613 Carboxymethylcellulose/carboxymethyl cellulose (CMC) 4, 9, 27, 28, 69, 97, 99, 132, 140, 194–195, 201–202, 222, 230, 270, 306, 308, 320, 353, 415, 422, 500–501, 510, 525, 531, 533, 540, 541–542, 546, 597, 599 Carrageenan 3, 5, 6, 8–11, 19, 26–31, 38, 48, 64, 67, 69, 78, 132, 134, 139–140, 146–147, 155–156, 210, 238–241, 245, 248, 266, 271, 308, 438–439, 443, 449, 472, 499, 509–512, 514–515, 521, 523, 525, 531–533, 540, 546–547, 549, 571, 603, 607, 611, 613, 616, 619–620 Carreau (model) 189, 441, 505 Carrier 8, 9, 14, 16, 29–30, 49, 243, 287, 318–319, 326, 345, 549–552, 554, 557, 560, 564–565, 567–568, 591, 594, 603 Casein/caseinate 6, 8, 30, 45, 137–138, 140, 242, 246, 248–249, 288, 297, 314, 316, 318, 326, 555, 567, 568 Cashew/cashew gum 7, 14, 20, 35, 327–346, 556, 558, 568 Casson model 92–93, 175, 189, 231, 535, 536, 538, 539 model 95 plastic viscosity 536 yield stress 538, 539 Casting 215, 340, 358, 572–573 Cellulose 4, 6, 25, 56, 76, 185, 253, 280, 419, 428, 479, 549, 551, 566, 603, 613, 616, 619

backbone 82, 102 carboxymethylcellulose/carboxymethyl cellulose (CMC) 4, 9, 27, 28, 69, 97, 99, 132, 140, 194–195, 201–202, 222, 230, 270, 306, 308, 320, 353, 415, 422, 500–501, 510, 525, 531, 533, 540, 541–542, 546, 597, 599 derivatives 4, 76, 438 hemicellulose 36, 51, 56, 220, 361, 369, 419, 428, 583–584, 598 hydroxyetylcellulose 306, 367 hydroxypropylcellulose/hydroxypropyl cellulose (HPC) 9, 62 hydroxypropyl methyl cellulose (HPMC) 4, 9, 10–11, 29, 64, 78, 340, 352, 367, 551, 590, 603, 616 methylcellulose (MC) 4, 9, 11, 30, 279, 308, 323, 510, 551, 578–579, 590, 598–599, 616 microcrystalline cellulose (MCC) 4, 9, 28, 510, 616 nanocrystalline cellulose (NCC) 512, 521 Cercidium praecox 14, 20, 34–35, 347–370, 595–596 Chaenomeles sinensis 15, 44, 617 Chain flexibility 67, 208 Cheese 1, 9, 11, 26, 36, 92, 131, 133, 197, 202, 218, 222, 246, 291, 297, 315–316, 325, 359, 425, 454–455, 460, 507, 544 Chemical composition 4, 12, 20, 21, 23, 36, 45, 48, 161–162, 185–187, 190, 227, 253, 269, 294, 300–302, 312, 319–320, 331–332, 398, 407, 422, 427–429, 432, 436–437, 444–446, 462, 464, 474, 476, 482, 483, 486, 493, 494, 608 modification 5, 7, 24, 35, 38, 73, 284, 286, 296, 336, 342, 345, 583, 619 structure 4, 5, 31, 217, 244, 248, 275, 279, 280–282, 293, 313, 321, 329, 474, 487, 531, 585 Cherry 14, 35–36, 275, 289, 291, 296, 368 Chewiness 194, 241, 266, 316, 532

625

626

Index

Chia/chia seed gum/chia seed mucilage 7, 13, 16, 22, 46, 47, 62, 64–65, 67, 72, 77, 394, 421, 454–455, 458, 460, 470, 473–474, 483, 485, 494, 496–497, 527, 532–533, 544, 547, 556, 561–562, 568–569, 575, 580, 588–590, 592, 596–597 Chichá gum 556, 559 Chitosan 1, 5, 6, 8, 10, 20, 55, 62, 67–69, 75, 79, 154, 164, 208, 220, 222, 271, 303, 306, 319, 352, 361, 367, 369, 549, 551, 554–556, 558–559, 562–563, 566–568, 579, 583–584, 598, 603, 613, 619, 621 Cholesterol 24, 45, 183, 200, 230, 246, 338, 386, 388–389, 390, 395, 425, 603–604, 606–607, 610–612, 615, 617, 620 Chromatography 57, 76, 162, 186, 248, 279, 300–301, 368, 433–434, 437, 473, 529, 552 Chubak/chubak root extract 16, 20, 21, 51, 371–396 Cinnamon 292, 555 Cissus populnea 14, 32 Clarifying agent 8, 10, 338, 344 Clouding agent 10, 12, 29 Coacervation 303, 318, 326, 361, 555–556 Coalescence 18–19, 213, 233–234, 261, 292, 357, 387, 482, 493–494, 537, 593 Coarseness 534, 538–539 Coating 3, 4, 8, 10, 12, 14, 19, 21, 24, 29, 31–33, 36, 45, 92, 222, 262–263, 267, 270, 272, 291–292, 298–299, 317–318, 325–326, 337, 340, 342, 358, 361, 368–369, 427, 441, 444, 449, 469, 504, 529, 565, 571–599, 602, 609, 620 Cochlospermum gossypium 14, 33–34, 421, 462, 469 Cohesiveness 194, 239–241, 266, 363, 504–505, 594 Coil 12, 64, 66–67, 71, 78, 83, 111, 192, 208, 414, 438, 557 dimensions 69, 71, 86, 163, 188, 209, 355 overlap 65–66

radius 69–70, 73, 208–210 volume 69–70, 208–209 Cole-Cole plot 153 Collagen 613, 621 Color parameters 161, 217, 263, 381, 442 Complex modulus 97, 103–104, 115, 126, 129, 144, 148–149, 160, 166–168, 174–175, 196 Complex viscosity 97, 113–114, 122–123, 125–126, 130, 134, 139, 141–142, 145, 153, 160, 165–166, 176–177, 192–193, 212, 232, 258, 286, 315, 441, 476–477, 482, 485–487, 492, 494, 505 Compliance 97, 117–119, 126–127, 138, 142–143, 153, 160, 169–170, 172 Conformation 7, 12–13, 54, 59, 65–67, 70, 73, 75–79, 81–82, 85, 97, 101–102, 108, 114, 118, 125, 128–129, 152, 159, 162–165, 169, 179, 188, 192, 199, 210–211, 220, 236, 238, 247, 256, 300–301, 303, 320, 355, 410, 414, 438, 441, 475, 484, 489, 495, 551, 557, 569, 578 Consistency coefficient 84–85, 88, 91, 94–95, 97, 188–191, 195–197, 207, 210, 211, 214, 253–255, 261, 262, 267, 398, 399, 400, 401, 405, 406, 407, 408, 412, 413, 414, 415, 417, 530–532, 535–536, 538–539 Contact angle 178, 215–217, 263, 265, 359, 582–584, 594–595, 598 Controlled release 8, 30, 215, 319, 549, 564, 565, 581, 613 Cordia abyssinica 14, 32 Cosmetic 17, 20, 135, 160, 179, 236, 275, 293, 299, 328, 330, 337, 443, 505 Cosolute 13, 54, 57, 60–62, 66, 67, 70, 72, 73 Cox–Merz rule 102, 121–123, 127, 130, 159–160, 176–177, 192–193 Creaminess 92, 507–509, 534, 537–539, 542 Creep 41, 98, 102, 117–120, 126, 130, 133–134, 138, 142–143, 155–156, 169–170, 172, 181, 315, 448

Index

creep/recovery 118, 119, 130, 142, 170, 315 Cress seed gum (CSG) 13, 15, 17, 22, 39, 40, 53, 62, 63, 64, 66, 72, 399, 407, 416, 419, 423, 473–495, 504, 505, 518, 527–528, 531–532, 534, 553, 554, 575, 580–581, 584, 588, 590, 593 Crispiness 507, 594 Critical concentration/critical polymer concentration 12, 66, 243, 259, 462 shear rate 83, 97, 138, 307 strain 83, 103, 139, 164, 192, 239, 476, 485, 509, 513 Cross model 437 Crossover frequency 112–113, 126, 130, 164 Cryoprotection 23, 501, 526, 538 Curcumin 30, 50, 339, 345, 555, 567–568 Cyathea medullaris 14, 34 Cydonia C. oblonga Miller 15, 45, 446, 454 C. vulgaris Pers. 15, 44 Crystal growth inhibitor 15, 266 Crystallization inhibitor 10, 12

d Dairy

3, 8–9, 28, 30, 87, 100, 133, 199, 218–219, 231, 245, 266, 291, 337, 500, 510, 543 Deformability 103, 240 Degradation 5, 28, 149, 161, 169, 280–281, 306, 319, 323, 330, 475–478, 483–485, 495, 550, 612 Degree of crosslinking 113, 115, 121, 130 Delivery system 15, 23, 35, 39, 340, 343, 549–551, 554, 556, 564, 565, 568, 613, 621–622 Delonix regia 15, 46, 138, 140, 146 Density 57, 72, 91, 112–115, 122, 126, 130, 150, 159, 171, 183, 198, 215–218, 233, 262, 265, 287–289, 314, 352, 356, 386, 396, 452, 478, 487, 512, 551, 560, 573, 575, 578–581, 584, 587, 590, 593, 604, 611

Descurainia sophia 16, 47, 298, 321, 418, 456, 471 Desolvation 40, 554, 556, 568 Dextran 6, 53, 62–64, 67, 69, 70–71, 209, 297, 438, 549, 555, 568, 613 Diabetes 219, 275, 295, 425–426, 443–444, 602–603, 609, 611, 615–616, 619 Diet 1, 2, 5, 200, 269, 335, 428, 443, 601–602, 611, 616, 617, 620 Dietary fiber 10, 24, 29, 75, 320, 324, 338, 342, 391, 426–427, 445, 500, 502, 547, 553, 601–603, 607–609, 612–615, 619, 620–622 Dilatant 530 Dilute regime 13, 67, 136, 208, 475, 483, 551 solution 13, 38, 40–43, 50, 52, 53–79, 98, 131, 136, 151, 155, 163, 180, 187, 201, 210, 220, 232, 247, 286, 416, 420, 423, 447, 475, 484, 497, 543, 565, 569 Divalent/divalent ions/divalent cations 41, 50, 57, 62–63, 68–70, 74, 163, 180, 238, 256, 278, 285, 423, 434, 438–439, 448 D-limonene 11, 18, 30, 41, 44, 177, 215, 222, 286, 291–292, 554, 556, 560–561, 568 Dough 10, 11, 29, 32, 133, 199, 219, 266, 374, 381–385, 529 Doughnut 20–21, 51, 339, 374–375, 389–391 DPPH 21, 312, 409–410, 417, 605–607 Ductility 103, 126, 240 Durian/durian seed gum 22, 268, 419, 473–474, 476, 479, 481, 494, 496–497 Durio zibethinus 268, 399, 419, 474, 496 Dynamic rheology 21, 41, 49, 117, 121, 132–133, 256, 300, 314, 470 Dynamic shear 39, 41, 43, 99, 112, 130, 132, 150, 165–166, 169, 177, 180, 192, 196, 221, 284, 475, 484, 487, 566 Dynamic viscosity 67, 110, 112, 114, 121–123, 129, 145–146, 192, 307, 441, 486, 511

627

628

Index

e Edible film 18, 20, 24, 30, 31, 198–199, 215, 262, 263, 264, 268, 358–361, 571–573, 576–578, 581–583, 585–588, 591, 593–595 Egg yolk 51, 386–387, 395 Elastic gel 114, 142, 170, 237–238, 476 Elastic modulus 105, 109–110, 126, 129, 139–140, 146–147, 232, 237–238, 256–257, 476, 485 Elasticity 101, 106, 109, 118, 141–142, 151, 170, 172, 194, 239–241, 263, 265, 378, 387, 476, 486, 505–506, 512–513, 530 Electrospinning 33, 470, 551–554, 565–566 Electrospray 44, 215, 222, 556, 560–561, 564, 568 Electrospun 35, 551, 553–554, 565 Electrostatic complex 287, 289, 318, 556, 567 Electrostatic repulsion 54, 86, 211, 230, 243, 256, 285, 288, 312, 315, 355, 362, 438, 491, 562–563 Elongation at break, EB 198, 216, 263–266, 587–590 Emulsifying 7–8, 15–16, 24–25, 27–28, 33–34, 36, 38, 44, 52, 82, 102, 160, 187, 197, 200, 205, 213, 233, 251, 279, 282, 289–292, 296–297, 299–301, 304, 306, 311–312, 324, 332, 351–352, 354, 357–358, 367–368, 372, 386, 388, 393, 395, 435, 439, 448, 481–482, 491–492, 494, 497, 502, 504–505, 517, 526–528, 530, 564, 602 Emulsion capacity 163, 492, 495 multiple emulsion/W/O/W emulsion 39, 567 oil-water-emulsion/oil in water emulsion/O/W emulsion 18, 20, 34, 43, 46, 50, 51, 52, 97, 187, 195, 197, 202, 213, 214, 221, 222, 223, 234, 244, 249, 261, 262, 269, 270, 311, 312, 313, 314, 323, 324, 325,

357, 358, 362, 369, 386, 387, 392, 395, 439, 448, 482, 504, 527, 543 stability 21, 161, 163, 178, 179, 196, 197, 252, 261, 291, 311, 312, 313, 314, 357, 358, 363, 398, 400, 401, 402, 406, 407, 417, 491, 492, 495, 528, 561, 562 water-oil-emulsion (W/O emulsion) 4, 244 Encapsulation 8, 15, 18, 21, 30, 44, 215, 222, 303, 318–319, 326, 337, 342, 361, 365, 369, 427, 442, 551, 558–562, 564, 567–568, 611 encapsulating agent 11–12, 328, 337, 449 Entangled 1, 66, 68, 114, 118, 141, 144, 171, 188, 306 Entanglement 66, 83, 85–86, 88–89, 91, 103, 105, 111–112, 114, 118, 121–122, 136, 165, 171, 179, 210, 255, 284, 306, 376, 386–387, 411, 478, 485–487, 508, 530–531, 535, 538 density 91, 112, 171, 478, 487 Enthalpy 62, 151–152, 157, 161, 264, 409 Equilibrium shear stress 538–539 Eruca sativa 15, 47, 397, 419, 497 Espina corona 15, 18, 45, 225–249 Essential oil 11, 30, 44–45, 159, 179, 290–292, 297, 318, 326, 390, 555–556, 558, 567–568, 572–573, 575–577, 580–584, 588, 590, 592–594, 596–597, 599, 613, 621 Euclidean distance 94–96, 128–129 Excipient 20, 35, 47, 200, 219–220, 238, 268, 319, 339–340, 343, 345, 557, 565, 569 Extent of thixotropy 97, 148, 172–173, 175, 212, 490, 535, 538–539 Exudate gum 6, 8, 20, 35, 275, 277–278, 280, 303, 327–346, 347–370, 546, 552, 559

f FAO (Food and Agriculture Organization) 26, 293, 313, 366, 427–428, 430, 445, 601, 614

Index

Farsi gum 276, 296, 298 Fat replacer 3, 8, 14–16, 19–20, 23, 28, 36–37, 39, 196–197, 202, 222, 266, 291, 297, 315, 325, 339, 342, 505, 526, 534–539, 543 Fat substitute 11, 16, 345 Fenugreek/fenugreek gum/fenugreek seed gum 5–7, 9, 15, 27, 47, 59, 64, 76, 171, 187, 268, 323, 416, 419, 423, 453 Firmness 199, 218, 243, 266, 315, 384, 387, 429–430, 441, 509, 540 Flaxseed 5–7, 253, 308, 322, 399, 405, 411, 416, 420, 422, 448, 455, 470, 528, 531–532, 544, 546 Flixweed 16, 456 Flow behavior index 84, 88, 91, 95, 97, 137–138, 153, 161, 170–173, 188–189, 191, 195–196, 207, 210–211, 214, 228–229, 231, 233, 255, 262, 267, 307–309, 376–377, 382, 384, 386, 388, 411–415, 462, 469, 487, 489, 491, 501, 530–531, 535 curve 87–88, 126, 138, 228, 230, 233, 358, 379, 411, 480, 505 point stress 105, 129, 139, 160, 476–477, 485–486, 492 properties 17, 23, 32, 40–43, 79, 81–82, 87, 97, 100–101, 177, 180, 189, 195, 201–202, 210, 221, 253, 262, 270, 332, 340, 392, 395, 419, 422, 438–439, 526, 542–543 Foaming agent 15, 235, 287, 388 capacity 46, 163, 198, 381, 482, 492–495, 504, 528 stability 163, 400–401, 406, 482, 492–494, 504 Food formulations 7, 20, 53, 81–82, 97, 102, 130, 154, 171, 179, 226, 255, 287, 293, 307, 372, 388–389, 417, 463, 500, 508 Food industry 2, 8, 20, 23, 25, 46, 49, 82, 87, 102, 179, 219, 236, 238, 241, 247, 291, 308, 328, 337, 342, 361, 363, 365, 380, 393, 431, 471, 505, 508,

526, 549–551, 554, 565, 571, 601, 608–609 Forward-backward 189, 196, 411 Fourier transform rheology 106 Fractal 23, 28, 266, 272, 499, 511–514, 518, 521–522 Fractionation 22, 35–36, 38, 277, 280, 289, 293, 321, 367–368, 420, 422–423, 447, 473, 482–496, 544, 566 Fracturability 240, 507 Fracture point 105, 129 strain 103–105, 129, 166 stress 103–105, 127, 129, 166 Fragile 166, 239, 287 Fragility 240 Frequency dependence 18, 112, 114, 140–142, 164–165, 175, 310, 439–441, 513 factor 149, 152, 157, 169, 307 sweep 102, 112, 114, 124–125, 139, 141–142, 144, 146, 150, 164, 166, 169, 175, 192–193, 212, 257, 286, 309, 476–477, 485–487, 492, 495, 505 Friction 159, 183, 254, 421, 507–509, 514, 517–518, 520, 522 FTIR 38, 207–208, 218, 279, 282–283, 313, 474, 483, 558, 567 Functional 1, 3, 4, 7, 8, 12, 13, 18, 19, 20, 21, 22, 205, 211, 218, 219, 251, 253, 255, 256, 265–268, 473–475, 479, 482, 483, 490, 494, 495, 601, 614

g Galactan 5, 207, 330, 560 arabinogalactan 187, 280, 300, 301, 351, 367, 371, 434, 500, 530 rhamnogalactan 18, 434 Galactomannan 5, 12, 16, 18, 27, 44–50, 76, 78, 82, 85, 87, 91, 96, 99, 102, 109, 128–129, 131–132, 134–135, 137–140, 146–147, 154–156, 161–162, 189, 207, 225, 227, 230, 236–239, 242–249, 322, 419, 421–423, 433, 438, 447, 479, 529, 607

629

630

Index

Galactose 18, 21, 82, 91, 102, 137, 140, 161–162, 186, 199, 207, 227, 236–238, 253, 279–28, 301–303, 329–330, 341, 350–351, 397, 408, 417, 433–434, 436–437, 479, 483, 527–529, 551, 554, 558–560, 562, 584, 607–608 Galacturonic acid 82, 102, 186–187, 280, 301–303, 311, 323, 330, 338, 350, 397, 408, 417, 433–434, 436–437, 528–530, 551–562 Gel gel like behavior 114–115, 140, 144–145, 167, 257, 309–310, 439, 441, 476, 486–487, 505 gelling agent 2–4, 8–9, 14–17, 24–26, 28, 49, 53, 73, 135, 199, 205, 235, 246, 251, 287, 338, 342, 344, 367, 397, 452, 470, 505, 521, 528, 564, 601 gelling point temperature 150 gel network 91, 105, 108, 114, 116, 120, 257, 314, 376, 476, 486, 494, 503, 512–513 Gelatin 2–3, 5–6, 9–11, 28–31, 33, 45, 53, 56, 140, 195, 230, 246, 287, 292, 295, 298, 338–339, 359, 361–362, 442, 449, 472, 508–510, 515, 521, 522, 540, 564–565 Gelatinization 78–79, 219, 266, 363 Gelation 26–27, 29, 38, 46, 132–133, 146–147, 150–151, 155, 163, 177, 235, 238–239, 241, 243, 247–249, 268, 270, 279, 287, 309, 323, 333, 338, 422, 439, 472, 490, 511–515, 519, 521–522, 540, 555–557, 567 Gellan 1, 6, 8–11, 26, 29–30, 62, 76–77, 134, 248, 279, 515, 549, 555, 560, 565, 567, 613–614 Gibbs free energy 135, 151–152, 161 Glass transition temperature 47, 167, 198, 216–217, 264–265, 306, 319 Gleditsia amorphoides 15, 18, 45, 225–246, 248 Gleditsia triacanthos 15, 45, 138, 141, 155, 225

Glucan 5, 10, 29, 77–78, 433, 500, 527 Glucomannan 5, 16, 51, 55, 75, 99, 132, 137, 140, 154, 155, 207, 222, 247, 500, 527, 529, 532–534, 619 Glucose 63, 73, 162, 186, 190–191, 207, 209, 253, 301, 302, 308, 329–330, 408, 417, 427, 431, 434, 444, 483, 527–529, 551–552, 558, 562, 584, 602–607, 610–611, 616 Glucuronic acid 82, 102, 146, 186, 236, 329, 330, 350, 351, 354, 355, 397, 408, 417, 434, 528, 551, 558, 559, 562, 607 Glutathione 39, 293, 341, 544, 556–558, 568 Gluten-free 10, 12, 29, 266–267, 316, 325, 527 Glycerol 178, 198, 215–216, 222, 262–264, 266–270, 292, 336, 340, 345, 353, 358–360, 441–442, 470, 504, 572–587, 589–592, 596 Gracilaria grevill 16 Guar/guar gum 1–7, 9–10, 13, 17–18, 27, 34, 37–38, 41, 45, 53, 55, 59, 63–64, 67, 77–78, 82, 84–86, 88–90, 93, 95–99, 102, 104, 109–110, 116, 119, 121, 123–124, 126, 128, 131–132, 134, 138, 153, 155, 159, 180, 189–190, 192, 194–195, 220, 227–228, 245, 247, 249, 253–254, 261, 266, 271, 309, 312, 315–317, 321–323, 325, 352–353, 367, 371, 394, 421–422, 432–433, 435–436, 496, 500–502, 525, 529, 531–543, 546–547, 571, 591, 602–603, 613, 615 Gum Arabic 3–10, 25–27, 29, 35–36, 77, 136, 140, 155, 187, 275, 280, 284–285, 290–292, 296, 298, 301, 304, 306, 320–322, 324, 328, 333, 335, 337–338, 342–345, 347, 349, 351, 353–355, 357–358, 361–369, 395, 435–436, 443, 448, 508–510, 521, 528, 554–555, 560, 567, 591, 603, 613, 616, 620, 622

Index

Cordia 32, 571, 573, 575–579, 582, 585–588, 590, 592–594, 596–599 ghatti 6, 9, 187, 320, 354, 420, 432–433, 447 karaya 6, 7, 9, 285, 321, 560, 562, 614 tragacanth 6, 9, 19, 34, 78, 275, 285, 287, 295, 296, 299–326, 354, 392, 408, 420, 530, 532, 533, 534, 546, 575, 580, 588, 590 Gumminess 194, 241, 266, 316, 504, 532 Gundelia tournefortii 528, 533, 544

h Han curve 153–154 Hardness 159, 177–179, 183, 185, 192, 194–196, 240–241, 266–267, 291, 315–317, 362, 375, 378, 383, 503–505, 507, 530, 532, 536, 538–539 Health aspects 601–622 Healthy food 601–602, 614 Heart disease 23, 338, 526, 602 Heinz (model)/Heinz–Casson (model) 94, 175 Herschel–Bulkley (model) 92, 94, 137, 170–173, 175, 178, 188–189, 191, 231, 285, 377, 386–387, 477–478, 487–489, 491, 505, 531, 535 Heteropolysaccharide 31, 82, 102, 346, 350, 496, 562, 613 Hibiscus sabdariffa 16, 48, 49, 221 Hierarchical/hierarchical algorithm/hierarchical clustering technique (HCA) 17, 87, 94, 97, 98, 102, 125, 129–131 High density polyethylene (HDPE) 198, 575, 579, 590 Higiro (model) 60, 61, 67, 74, 79, 82, 98, 102, 131, 136, 163, 209, 416–417 Hsian-Tsao/Hsian-Tsao leaf gum 13, 14, 31, 32, 53, 61, 63, 64, 66, 69, 72, 73, 74, 139, 156, 247 Huggins constant 60, 64, 65, 163, 188, 208, 475, 483, 484

Huggins (model) 60–62, 76, 136, 163, 209, 416, 417, 475, 484, 485 Hyaluronic acid 77, 444, 551, 613 Hydration parameter 71–73, 188, 208, 209 Hydrodynamic radius 46, 162, 187, 188 volume 12, 54, 59, 77, 188, 353, 354, 416, 438 Hydrogel 26, 30, 41, 50, 51, 55–57, 72, 75, 76, 91, 114, 115, 133, 134, 188, 244, 249, 313, 314, 319, 325, 326, 341, 362–363, 369, 512, 514, 515, 517, 518, 521, 522, 528, 558, 568 Hydroxypropylcellulose/hydroxypropyl cellulose (HPC) 9, 62 Hydroxypropyl methyl cellulose (HPMC) 4, 9, 10–11, 29, 64, 78, 340, 352, 367, 551, 590, 603, 616 Hylocereus undatus 14, 31 Hypoglycemic 427, 430–431, 603, 605–607, 617, 619 Hypolipidemic 430–431, 604, 606–607, 617–619 Hysteresis/hysteresis area/hysteresis loop 13, 82, 87–88, 94–95, 97, 146–148, 167, 172–173, 191–192, 214, 231, 259, 285, 415, 479–480, 488, 494–495, 505

i Ice cream 1, 3–4, 8–10, 12, 18, 23, 27, 29, 37–39, 42, 44, 92, 99, 194–195, 201–202, 235, 266, 271, 314–315, 325, 500–502, 519, 527–547, 601 Iciness 534 Immiscibility 143, 152, 154 Immunomodulatory 605–606, 608, 614, 618 Immunostimulant activity 608 Infinite-shear viscosity 84–86, 95, 189, 478, 487, 489 In-shear structural recovery 13, 82, 87, 90, 95, 97, 153, 173–174, 480 Instantaneous elastic compliance 117, 126, 142, 169 Instantaneous viscosity 108

631

632

Index

Interaction 2, 12–13, 17, 19, 28, 37, 41–42, 45–46, 48, 54, 59, 62, 64–65, 69, 72, 74, 77–79, 81, 83, 87, 89, 97–101, 103, 105, 112, 115, 118, 122, 131–132, 134–156, 163–164, 171, 177, 179–181, 188, 190, 198, 201, 208–211, 213, 216–218, 222, 226, 236–238, 239–242, 244, 247, 249, 253, 255, 259, 262–264, 271, 277, 282–284, 286–289, 295, 297, 301, 303, 306–307, 309, 313, 315–316, 318, 333, 353, 357, 360, 362–363, 367, 377, 393, 405–406, 408, 423, 438–439, 441–443, 448, 474, 476, 478–479, 482–487, 492, 494, 503, 506–507, 509, 512, 518–519, 521, 537, 543, 547, 559, 567, 572–573, 576–577, 581, 585, 587–588, 593, 596, 598, 603, 613–614, 616 Interfacial tension 19, 177–178, 261, 290, 311, 313, 357, 481, 500 Intrinsic viscosity 12–13, 18, 21, 40, 54, 59–64, 67–68, 70, 72, 74, 76–77, 79, 82, 87, 97, 99, 102, 129, 131, 136–137, 163, 179, 187–188, 190, 200, 209–210, 220, 282–284, 300, 322, 354, 398, 416–417, 419, 422–423, 438, 462, 475, 483–485, 494–495, 544, 553, 557, 560, 567 Inulin 5, 10, 296, 361–362, 367, 376, 392, 603, 612, 616, 619–621 Ion gelation 555–556 Ionic strength 47, 52, 56–57, 62–63, 65, 68, 72–74, 79, 188, 230, 236–238, 241, 277, 284–285, 287, 289, 308, 333, 355, 357, 362, 398, 415, 438–439, 441 Isfarzeh mucilage 530, 534 Isolation 21, 31, 44, 46, 48–50, 389, 419, 423, 435, 447, 451–464, 466, 469–470, 472, 617–618, 620

j Juice

10, 12, 20–21, 29, 157, 288–289, 291–292, 295–297, 327, 333, 337–338, 344–345, 375, 388–389,

391, 395–396, 421, 425, 453–454, 456–457, 616 Junction zone 86, 159, 165, 170, 236, 239, 476, 486, 503–504

k Kelvin–Voigt 117–118, 126, 142, 169 Kenger gum 528 Ketchup 9, 21, 27, 51, 292, 298, 317, 325, 379–380, 389, 392 Kondagogu gum 556, 562 Konjac 6, 9, 27, 51, 55, 64, 75, 137, 140, 171, 222, 247, 407, 619 Kraemer/Kraemer constant/Kraemer model 60–62, 76, 136, 163, 209, 416–417, 475, 484

l Lactose 38, 43, 57, 63, 65–67, 69–72, 74, 79, 188, 190–191, 210, 220, 525, 532 Lallemantia royleana 13, 15, 18, 38, 42, 53, 74, 183–202, 420, 527, 543, 545, 550, 565 Large amplitude oscillatory shear (LAOS) 105–106, 109, 111, 129, 132, 508, 521 Large deformation 85, 90, 106, 109, 112, 122–124, 160, 175, 185, 192, 196, 239, 246, 248, 504, 508, 511, 523 Lepidium perfoliatum 15, 19, 43, 163, 197, 251–272, 322, 397, 422, 449, 529, 545–546, 550, 565, 575–576, 580, 584, 590, 596–599 Lepidium sativum 13, 15, 39–40, 53, 74, 79, 82, 98–99, 102, 131, 163, 197, 271, 397, 407, 419, 423, 456, 471, 482, 496–497, 519, 527, 544, 546, 550, 553, 564, 567, 606, 618 Leucaena leucocephala 16, 49, 422 Levan 62, 64, 77, 416, 422–423, 604, 608, 617–618 Light scattering 57–60, 76–78, 87, 186, 248, 279, 284, 314, 368, 563, 592 Linear viscoelastic region (LVE/LVR) 103, 104, 106, 164, 170, 192, 231, 473, 476, 477, 479, 484–487, 492, 509 Linum usitatissimum 269–270, 455, 528 Lippia sidoides essential oil 556, 558, 568

Index

Liquid-like behavior 103, 121, 130, 170, 310, 485 Lissajous curves 106, 111 plot 106–108 Litchi chinensis 16, 50 Locust bean gum (LBG) 1, 4–6, 9, 12, 19, 30, 37, 45, 55, 59, 63, 67, 74, 77, 79, 98–99, 131–132, 139–140, 146–147, 170–171, 181, 189–190, 192, 194, 225, 236, 237, 245, 247, 253–254, 261, 266, 376, 392, 408, 416, 420, 422–423, 432–433, 435, 443, 447, 449, 471, 496, 540, 547, 571, 575, 580, 588, 590, 597 Loss factor 257 modulus 97, 104, 126, 139–141, 144, 150, 153, 160, 164, 192, 212, 215, 257–259, 286, 477, 485–486, 492 tangent 103–105, 111, 126, 129, 139, 144, 153, 160, 164–166, 192, 196–197, 212, 286, 477, 485–486, 492 Low density polyethylene (LDPE) 575, 578–579, 584, 588, 590 Lubricant 15, 507–508, 514, 517

m Malva (nut) gum 399, 407, 419, 421 Malva aegyptiaca 606, 618 Mango (Mangifera indica L.) 16, 50, 324, 327, 396, 428 Marshmallow/marshmallow flower gum (MFG) 14, 21, 32, 397–422 Master curve 66–67, 77, 136, 163, 396 Maximum compliance 118–119, 126, 143, 153 Maxwell (model) 114–115, 117–118, 120, 126, 130, 134, 141–143, 145, 165, 169, 175, 532 Mayonnaise 178, 181, 233, 292, 298, 386–389, 392, 395, 500, 601 Mechanical spectra 112, 139–141, 144, 159, 175, 193, 212, 232, 234, 237, 258, 440 Melting rate 266, 315, 533–535, 537

Mesona chinensis 14, 31 Mesona Blumes 16, 48, 137, 155–156, 269, 411, 422 Mesquite gum 59, 62, 76–77, 271, 322, 358, 368, 399, 416, 419, 421, 554 Methylcellulose (MC) 4, 9, 11, 30, 279, 308, 323, 510, 551, 578–579, 590, 598–599, 616 Microcrystalline cellulose (MCC) 4, 9, 28, 510, 616 Microencapsulation 337, 357, 361 Microstructure 26, 28, 37, 46, 88, 90–91, 105–106, 108, 132, 154, 174, 210, 241, 246, 248–249, 266, 270, 280, 290, 301, 320, 325, 363, 411, 470, 488, 495, 501–502, 509, 515, 518, 520, 522–523, 525–526, 541–542, 593, 598, 601 Moisture sorption isotherm 585 Moisture uptake 178, 216, 580, 585–586, 594 Molding 10 Molecular conformation 65–67, 73, 163, 300, 320, 475 structure 2, 12, 19, 21, 59, 114, 187, 200, 287, 319, 350, 354, 357, 433, 474, 476, 479, 482, 491, 493, 514, 515, 517 weight 1, 12–13, 18, 21–23, 31, 54, 57–59, 68–69, 72, 75–76, 78, 81–83, 86, 96, 101–102, 110, 113–115, 129, 147, 161, 167, 186, 187, 198, 207, 217, 227–229, 232, 242, 244, 261, 263, 277, 279, 280, 282–284, 290, 300, 306, 312, 321–323, 330, 353–354, 395, 419, 427, 431, 434, 439, 446, 473–495, 499, 521, 525, 527–528, 531, 541, 551, 552–554, 560, 562–563, 578, 587–588, 601, 607–608, 611, 616, 619, 622 Monosaccharide composition 186, 280, 350, 408, 433–434, 474, 476, 478, 483, 487, 495 Montmorillonite 34, 356, 368, 369, 574, 577, 587, 589, 592, 596, 597 Moore (model) 82–86, 93, 95, 97, 138, 171, 175, 488

633

634

Index

Mouthfeel 23, 85, 92, 178, 195, 218, 231, 246, 267, 316, 353, 500, 509–510, 521, 525, 526, 530–531, 541 Mucilaginous seed 7, 21–22, 183, 205, 252, 304, 432, 451–472, 527–529 Mucuna flagellipes seed gum 416, 423 Muffin 21, 51, 381–384, 389, 391, 394 Mustard seed (gum) 6–7, 399, 419

n Nanocomposite 34, 360, 361, 369, 569, 571, 577, 582, 586, 587, 595–597 Nanocrystalline cellulose (NCC) 512, 521 Nanoemulsion 9, 27, 290, 292, 449, 555, 556, 567, 568, 597 Nanoencapsulation 30, 555, 558, 562, 565, 567, 568 Nanofiber 35–36, 550–554, 560, 563, 565–567 Nanofilm 550 Nanomaterials 550–563, 577, 586, 587, 595, 598 Nanoparticles 20, 26, 30, 33, 39, 40, 44, 48, 75, 78, 222, 246, 318, 319, 326, 356, 360, 362, 496, 550, 554–564, 567–569, 571, 572, 581, 595, 597, 621 Nanoprecipitation 556 Nanotechnology 23, 26, 361, 549–566, 568 Network parameters degree of crosslinking 113–115, 121, 126, 130 distance between sequential crosslinking points 113–116, 126, 130 elastic active network chain 113, 115, 126 molecular weight between crosslinks 113, 114, 115 number density of crosslinks 113–115, 126, 130 Newtonian behavior 178, 210, 255, 286, 307, 308, 354, 377, 437, 442, 462, 469 fluid 111, 130, 218 plateau 83, 110, 306, 358 Nonlinear viscoelasticity 132, 519

viscoelastic region, n-LVE, NLVE 103, 106, 139, 159, 160, 164, 166 Non-Newtonian non-Newtonian fluid 530 non-Newtonian behavior 210, 255, 308 Nopal 14, 32, 33, 426, 428, 431–434, 438, 444, 446, 447 Nutraceutical 275, 549, 550, 564, 591, 594 Nutrient 332, 338, 430, 435, 507, 602–603, 609–612, 620

o Obesity 23, 338, 443, 526, 602, 609, 616, 620 Ocimum basilicum L. 13 37, 53, 74, 397, 407, 418, 420, 453, 462, 470, 474, 496–497, 500, 519, 527, 544, 546, 564, 566, 568–569, 596 Okra (cell wall, gum, polysaccharide) 529, 531–533, 540–541, 544–546 Optimal 161, 184, 198, 319, 327, 374, 405–407, 429, 453, 458, 462 Optimization 18, 29, 32–33, 37–40, 42–46, 161, 180, 200, 205, 219, 246, 252, 268, 271, 294, 297, 392, 394–395, 397–399, 401–405, 407, 418–420, 470–471, 496, 506, 519, 545–546, 565, 568, 598, 618 Optimum conditions 161, 398–399, 407, 456, 459, 463, 469, 551 Opuntia Ficus indica (O. Ficus indica) 21, 32–33, 141, 269, 322, 405, 407, 414–415, 420, 423, 425–449, 566 Organoleptic 22, 53, 199–200, 330, 342, 391, 499, 509, 594 Oscillation 232, 511, 562 Overrun 194–195, 266, 315, 505, 532–533, 535–537 Oxygen permeability (OP) 18, 199, 215, 217, 314, 577–579, 595

p Packaging 10, 18, 24, 30, 178, 216, 218, 361, 427, 444, 551, 565, 571–573, 577–578, 581–583, 587, 591, 593–595, 598

Index

Particle size 7, 12, 23, 34, 51, 83, 111, 133, 197, 207, 214, 220, 242, 253, 262, 289, 290, 304, 311, 313–319, 322, 337, 353, 372–374, 440, 477, 481, 491, 500, 501, 554, 557–560, 562, 563, 567 Pattern recognition 81, 94, 101 Peach (gum) 14, 36, 275, 296, 416, 420, 423, 429, 496, 605, 607, 609, 619 Pectin 1, 2, 4–6, 9–11, 13, 17, 19, 26, 27, 29–31, 33, 37, 53–55, 59, 62–64, 72, 75–78, 82, 84–86, 88–90, 93, 95–96, 98, 102, 104, 109, 110, 116, 119, 121, 123, 124, 126, 128, 131, 157, 178, 181, 210, 279, 308, 320, 322, 323, 362, 369, 397, 428, 429, 433, 434, 439, 443, 446–449, 510, 511, 525, 549, 555, 567, 571, 598, 603, 613, 615, 622 Penetration (test) 177, 192, 194, 243, 339, 503, 505 Pereskia aculeate Miller 14 Permeability 18, 178, 198, 199, 215–217, 263, 270, 313, 314, 359–361, 442, 551, 573, 574, 576–579, 581, 592, 598 Persian acorn 16, 50 Persian gum (PG) 19, 34, 273–298, 323 pH 206, 207, 211, 219, 252, 256, 398, 399, 401, 402, 403, 404, 405, 406, 407, 414, 415, 416, 417 Phalaris canariensis 16, 50, 77 Pharmaceutical 4, 8, 17, 19, 20, 21, 22, 24, 53, 73, 130, 134, 154, 160, 179, 187, 200, 205, 235, 238, 267, 273, 275, 279, 291, 293, 299, 300, 304, 311, 319, 328, 330, 337, 339, 342, 347, 351, 357, 365, 388, 428, 443, 451, 500, 557, 571, 581, 594 Phytochemical 21, 47, 200, 219, 303, 318, 324, 427, 443–445, 601–602, 615 Pistachio butter 37, 38, 196, 202 Plantago major L. 15, 45, 46, 470, 594, 618 Plantago ovate 528 Plasticizer 32, 178, 198, 215, 216, 222, 262–264, 270, 340, 358, 359, 441, 442, 449, 572–574, 576–593, 595, 596, 598 Plastic viscosity 189, 379, 536 Plum 14, 275, 605

Polydispersity index (PDI) 57, 162, 187, 195, 558–560 Polyelectrolyte 12, 79, 82, 86, 96, 102, 105, 108, 129, 161, 186, 207, 211, 256, 303, 308, 311, 319, 355, 362, 369, 435, 438, 446, 483, 512, 521, 528, 555, 557, 558, 567 Polyethylene glycol (PEG) 178, 341, 346, 442, 574, 576–577, 579, 582, 585–587, 589 Polysaccharide-protein complex 350, 357 Polyvinyl alcohol (PVA) 35, 43, 216–218, 222, 313, 319, 361, 551–554, 566, 574–575, 578–580, 582–590, 596 Polyvinyl chloride (PVC) 515, 575, 579, 584 Polyvinylidene chloride (PVDC) 575, 577, 584 Porosity 159, 183, 199, 266, 361, 381, 383–385, 551, 558 Power-law model 21, 66, 82–84, 86, 87, 91, 94, 97, 112, 115, 125–127, 136, 138, 139, 141, 142, 153, 165, 166, 170, 171, 174, 177, 188, 189, 191, 195, 210, 228, 233, 235, 254, 255, 285, 386, 399, 411–414, 417, 437, 476, 486, 488, 489, 513, 514, 530, 531, 535 Prebiotic 24, 36, 253, 269, 291, 292, 603, 611, 612, 620, 621 Precipitation 8, 207, 226, 227, 284, 285, 287, 288, 295, 311, 454–456, 473, 474, 477, 482, 483, 494–496, 556, 569, 572, 591 Principal component analysis (PCA) 17, 82, 94, 97, 102, 125, 129, 130, 134, 538 Prosopis P. juliflora 140, 156, 416, 423 P. ruscifolia 416, 421, 447 Prunus P. amygdalus 14, 36, 604, 609, 617 P. armeniaca L. 14, 26, 35, 275, 321 P. avium 36 P. cerasus 14, 31, 321, 446 P. cerasoides 14, 35, 448 P. domestica 14, 35 P. dulcis 14, 36, 275, 566

635

636

Index

Prunus (contd.) P. insitia 14 P. virginiana 14, 275 Pseudoplastic/pseudoplasticity 85, 97, 112, 123, 130, 132, 137, 188, 191–192, 195–197, 200, 210, 211, 214, 228, 235, 236, 244, 255, 376, 411, 477, 478, 487, 489, 535 Psyllium (seed gum) (PSG) 49, 132, 253, 470, 528, 544, 575, 580, 584, 590–591, 594, 597, 603, 610, 612, 614, 619, 621 Pullulan 8, 59, 62, 76, 270, 514, 522, 549 Purification 22, 26, 36, 40, 48, 76, 184, 185, 213, 226, 227, 245, 268, 277, 320, 323, 331, 336, 342, 372, 389, 419, 423, 432, 433, 444, 453, 456, 460, 461, 471, 473–482, 494–497, 591, 617, 618 Purity 207, 225, 279, 408, 432, 433, 435, 461, 462, 464, 466, 474, 591

q Qodume Shahri (Lepidium perfoliatum) 13, 15, 19, 197, 251–268, 272, 529, 531–532, 534, 550 Qodume Shirazi (Alyssum homolocarpum) 13, 15, 18, 43, 53, 205–219, 221, 223, 268, 405, 418, 550 Quercus brantii Lindle 16, 50 Quince 15, 44–45, 222, 325, 397, 406–407, 419, 434, 446, 454, 457, 461–462, 470–471, 505, 519, 597, 617

r Radius of gyration 58–59, 162, 187, 300 Random coil 18, 65–67, 73, 78, 85, 99, 114, 125, 133, 164, 192, 210, 220, 438, 440–441, 448, 475, 483–484, 551, 557 Recovery parameter 90, 97, 170, 174–175 rate 90–91, 95, 173–174 reaction order 90, 118, 127, 173–174 Recrystallization 29, 500, 519, 532–534, 538, 540–541

Relaxation modulus 141, 159, 167, 172, 511–512 Relaxation spectrum 115–116 Relaxation time 84, 86, 95, 115–117, 120–122, 126–127, 130, 141, 145, 150, 159, 165, 167, 169, 171, 175, 189, 438, 478, 487 Resilience 239 Response surface methodology, RSM 21, 29, 32, 36, 37, 39, 40, 42, 43, 44, 161, 179, 180, 202, 205, 219, 245, 268, 271, 282, 323, 338, 340, 343, 392, 397–399, 401, 403, 405, 407, 418, 419, 420, 449, 462, 470, 471, 496, 545, 546, 598 Retardation time 117–118, 127, 142–143, 153, 169–170 Rhamnose 18, 21, 82, 102, 186–187, 199, 207, 253, 279–281, 301–303, 329–330, 351, 397, 408, 417, 433–434, 436–437, 483, 527–529, 551–552, 554, 558–559, 562 Rheological properties dynamic shear rheological properties 17, 43, 73, 101–134, 156, 212, 256, 270, 284, 309, 440, 475, 484, 495 steady shear rheological properties 13, 21, 50, 81–100, 191, 196, 210, 227, 306, 411–415, 417, 476, 487 transient shear rheological properties 101–134, 138, 142 Rheometer 83, 99, 103, 228, 354, 392, 507–508 Rheopexy 87, 212 Rigid conformation 97, 108, 114, 129, 165, 179 chain conformation 85 rod conformation 162 Rigidity 89, 103, 118, 125, 130, 136, 240, 252, 264, 414 Rod-like 66, 73, 85, 112 Roselle 16, 49, 221

s Sage seed gum (SSG) 13, 17, 37, 41, 42, 55, 59, 61, 62, 64, 66–74, 82–86,

Index

89–99, 102–126, 128–129, 130, 132, 133, 136–139, 141–145, 148–150, 152–156, 159–181, 208, 405–408, 414, 416, 423, 529, 534, 545, 573, 575, 576, 580, 582–587, 590, 597 Salep 27, 99, 132, 194, 195, 201, 202, 210, 221, 298, 315, 325, 529–534, 545, 547 Salt 13, 17, 18, 34, 35, 39–42, 56, 62, 63, 66, 69, 70, 73, 74, 78, 98, 99, 131, 135, 136, 150, 163, 171, 180, 184, 185, 188, 190, 191, 201, 211, 214, 219, 225, 230, 236–238, 244, 247, 255, 256, 267, 270, 277, 284, 285, 287, 289, 296, 308, 312, 324, 362, 420, 423, 438, 448, 471, 520, 528, 531, 543, 544, 553, 565, 567, 585, 610 Salvia hispanica 15, 46, 47, 394, 415, 421, 454, 470, 527, 544, 556, 561, 568, 569, 588, 589, 598 Salvia macrosiphon 13, 15, 17, 40–42, 53, 76, 82, 98–100, 102, 131, 134, 159–181, 321, 397, 407, 418, 420, 422, 447, 456–459, 462, 466, 469, 471, 496, 529, 545, 547, 550, 565 Saponin 21, 51, 371–375, 381, 382, 385, 388–391, 395 Sauce 8, 9, 18, 28, 178, 291, 292, 379, 386, 389, 500 Scaling (behavior)/scaling (law) 38, 511–515, 520–522 Schizolobium parahybae 16, 50 Segment–segment interaction 89, 112, 118, 177 Semi-dilute (domain, regime, solution) 12, 66, 67, 447 Semi-rigid 66, 82, 85, 102, 114, 118, 188, 192, 199 Sensory 27, 28, 31, 36–39, 42, 44, 45, 48, 87, 98, 99, 131–133, 178, 179, 181, 194, 195, 197, 199, 202, 203, 218, 222, 223, 227, 230, 231, 241, 246, 255, 266, 292, 298, 317, 325, 337, 338, 364, 380, 391–393, 395, 500, 507–509, 520–522, 527, 534, 537–539, 542–547 Shape factor 70, 71, 73, 163 Shape function 70, 71, 164, 188, 208, 209

Shear stress decay 13, 82, 87, 88, 95, 173, 212 Shear thickening 34, 83, 84, 97, 99, 106, 108, 110, 111, 127, 129 Shear thinning 12, 18, 19, 21, 83–85, 92, 105, 106, 108–112, 114, 122, 123, 126, 129, 133, 137, 138, 142, 145, 159, 165, 167, 170, 171, 174, 177, 178, 188–189, 191, 210, 214, 218, 228, 231, 233, 244, 253, 255, 262, 267, 285, 286, 306, 308, 309, 317, 358, 376, 382, 385–388, 411, 417, 437, 438, 441, 448, 466, 476, 477, 486–489, 491, 492, 495, 500, 505, 508, 530, 531, 551 Shelf life 3, 21, 27, 29, 32, 45, 51, 218, 233, 266, 271, 278, 292, 298, 317, 318, 326, 361, 363, 364, 368, 369, 374, 389, 390, 430, 439, 441, 446, 449, 503, 505, 530, 571, 573, 585, 594, 595, 599, 601 Single shear decay 172 Sisko (model) 138, 170, 488, 489 Slipperiness 507, 509 Small amplitude oscillatory shear (SAOS) 103, 142, 174, 176, 177, 508 Smoothness 194, 197, 340, 507–509, 532, 534, 553 Softness 121, 178, 218, 219, 384, 507, 594 Sol-gel transition 156, 511, 512, 515, 521, 522 Solid-like behavior 18, 103, 116, 121, 130, 142, 165, 170, 309, 310, 484, 492 Solubility 7, 8, 20, 54, 59, 65, 76, 178, 186, 198, 215–218, 253, 262, 263–265, 270, 277, 279, 282–284, 286, 288, 289, 293, 300, 310, 313, 336, 337, 339, 342, 351, 353, 354, 358–360, 364, 365, 405, 433, 439, 458, 459, 473, 477, 479, 484, 494, 557, 558, 560, 576, 578, 580–582, 594, 595, 612 Sonication 286, 293, 297, 372, 373, 462, 463, 466, 469 Sophora alopecuroides L. 15, 44 Sophora japonica 16, 45, 48, 140, 146 Sorbitol 26, 51, 178, 222, 270, 442, 573–587, 589–590

637

638

Index

Specific viscosity 60, 136, 137 Specific volume 54, 55, 70, 72, 75, 188, 199, 208, 209, 266, 352, 381–385 Spreadability 92, 105, 106, 129, 130, 179, 317 Springiness 194, 241, 504, 505, 507 Stabilizer 3, 8, 9, 14–17, 20, 23, 33, 38, 42, 53, 135, 171, 178, 179, 194, 195, 202, 214, 218, 223, 233, 235, 251, 258, 266, 268, 271, 275, 287, 292, 296, 311, 315, 324, 328, 333, 338, 357, 362, 365, 368, 397, 417, 449, 463, 500–502, 519, 525, 526, 528, 530–535, 540–543, 546, 547, 601 Stabilizing (agent) 2, 7–10, 15, 18, 19, 22, 24, 28, 44, 73, 160, 187, 188, 194, 195, 205, 213, 233, 244, 245, 251–254, 261, 267, 279, 292, 299, 301, 306, 311, 318, 330, 333, 351, 352, 354–356, 364, 365, 372, 379, 386, 389, 406, 427, 435, 439, 451, 478, 487, 500, 517, 525, 527, 529, 530, 533 Starch modified starch 3, 9, 10, 28, 29, 222, 337, 509, 510, 555, 567, 583 resistant starch 603, 612, 621 starch nanocrystal 9, 27 Steady shear 13, 21, 50, 81–100, 191, 196, 210, 227, 306, 411–415, 417, 476, 478, 487–489, 491 Stepwise extraction 40, 473, 482, 483, 495, 497 Sterculia striata 559 Stickiness 22, 177, 185, 194, 323, 532 Stiffness 68, 69, 73, 79, 114, 116, 118, 141, 151, 159, 162, 165, 194, 263, 265, 301, 378, 551, 587, 594 STMP 513, 514, 517, 518, 522 Strain hardening 105, 108 modulus 108 overshoot 103, 105, 129 softening 106, 108–109, 111, 129 stiffening 106, 108, 129 sweep 102, 103, 124, 129, 142, 143, 164, 192, 193, 256, 476, 477, 484, 485 thinning 105, 129

Stress decay 13, 82, 87, 88, 95, 173, 189, 190, 192, 212 decomposition 106 ramp 92, 93, 95, 175 relaxation 102, 120, 121, 130, 134, 172, 512 sweep 476, 486, 492 Storage modulus 97, 103, 104, 115, 129, 139, 140, 141, 144, 147, 150, 151, 153, 159, 160, 167, 192, 212, 215, 232, 257–260, 286, 315, 439, 440, 476, 477, 485–487, 492, 495 Structural breakdown 87, 89, 172, 231, 255 kinetic model 89, 97, 172, 190, 490, 534 parameter 88, 438, 473 strength 91, 103, 164, 257, 259, 309, 316, 477, 485 Structure development 149, 169 structure-function 81, 97, 101, 130, 132, 179, 220, 246, 301, 398, 508, 542 Sucrose 29, 38, 43, 57, 63, 65–67, 69–72, 74, 77, 79, 98, 99, 131, 188, 190, 191, 196, 210, 211, 220, 308, 620 Sugar beet pectin 9, 448 Surface activity 18, 19, 38, 51, 187, 213, 290, 310, 311, 357, 364, 388, 390, 420, 435, 481, 490–496, 566 Surface properties 275, 353, 356, 365, 390, 506, 534, 585 Surface tension 162, 187, 197, 215, 288, 290, 310, 323, 353–356, 380, 481, 490, 491, 493, 494, 529, 552, 553, 560, 573, 582, 598 Suspending (agent) 9, 10, 12, 187, 205, 238, 251, 306, 351, 527, 529, 530, 557, 562, 569 Swelling 11, 26, 56, 75, 187, 205, 309, 314, 319, 326, 336, 340, 460, 514, 517, 518, 553, 585 Syneresis 11, 195, 199, 231, 239, 245, 315–317, 376, 378, 389, 391, 509 Synergistic 12, 17, 19, 49, 137–140, 146, 147, 151, 152, 154, 155, 231, 236, 238, 247, 266, 309, 333, 356, 537, 608, 615

Index

t Tamarind (Tamarindus indica L.) 7, 15, 16, 47, 50, 416, 422, 455, 459, 471, 544 Tanglertpaibul–Rao (model) 60–62, 77, 82, 102, 136, 163, 209, 416, 417 Tara gum 5, 6, 9, 64, 171, 236, 322, 422, 591 Temperature dependency 41, 97, 98, 156, 160, 181, 255, 285 gradient (sweep) 145, 167, 168 profile (sweep) 146, 148, 149, 167, 168, 457 sweep 146, 148, 149, 152, 167, 168, 196, 258 table (sweep) 145, 167, 168 Tensile strength 11, 47, 178, 198, 216, 263–265, 359–361, 442, 551, 587, 589, 590 Textural properties 42, 133, 156, 177, 180, 192, 201, 267, 315–318, 325, 326, 376, 378, 502, 505, 518, 528, 532, 534, 536 Texture analysis 183, 185, 192, 378, 387, 507 Texture profile analysis (TPA) 192, 194, 196, 239–241, 387, 505 Thermal stability 76, 179, 215, 217, 264, 306, 336, 478, 494, 553, 561 Thermodynamic incompatibility 151, 152, 288 Thermo-irreversible 259 Thermoreversible 166, 236, 515, 521 Thermorheological 150, 169 Thickener 1–3, 8, 9, 14–17, 21, 53, 135, 179, 231, 258, 268, 287, 342, 347, 349, 365, 379, 392, 397, 417, 463, 510, 511, 521, 541, 557, 601 Thickening 1, 2, 7–10, 12, 14, 15, 18, 19, 24–26, 28, 52, 53, 73, 74, 82, 83, 114, 160, 187, 205, 213, 215, 220, 227, 238, 245, 246, 251, 253, 254, 259, 267, 299, 311, 322, 330, 333, 338, 351, 352, 418, 427, 448, 451, 478, 487, 517, 527, 529–530, 564, 573, 602

Thickness 23, 92, 215, 262, 425, 463, 491, 507, 509, 511, 563, 573–574, 576, 579, 594, 597 Thixotropic behavior 13, 87, 88, 91, 174, 189, 192, 196, 197, 212, 285, 317, 415, 416, 479, 490, 535 breakdown 89, 148, 175 Thixotropy 12, 38, 40–43, 50, 73, 87–90, 97–99, 131, 133, 156, 172–174, 181, 201, 202, 212, 221, 231, 314, 342, 415, 419, 422, 488, 490, 497, 505, 538, 543, 547 Time time dependency 13, 43, 82, 89, 91, 121, 148, 172, 173, 212, 221, 415, 422, 505 time-dependent 37, 87–91, 94, 95, 99, 120, 124, 134, 148, 149, 172, 174, 175, 189, 192, 196, 202, 212, 415, 488, 490, 534, 535 time-independent 39, 41, 73, 83–85, 87, 88, 91, 94, 178, 188, 411 Timescale (time scale) 13, 82, 89, 103, 112, 115, 118, 121, 124, 130, 159, 164, 167, 174, 175, 177, 179, 286, 310 Time sweep 102, 146, 150, 196 Time-temperature superposition 150, 156, 169 Tragacanth 6, 7, 9, 14, 19, 27, 34, 69, 78, 275, 279, 285, 287, 295, 296, 298, 299–326, 354, 392, 408, 420, 530, 532, 533, 534, 546, 575, 580, 588, 590, 594, 597, 599 Transforming growth factor-beta 1 (TGF-𝛽1) 556, 563 Transparency 178, 198, 215, 216, 218, 263, 266, 278, 358, 360, 442, 588, 592, 595, 599 Tribology 44, 499, 506–510, 520, 524 Trigonella foenum-graecum 15, 47, 453, 470

u Ultrasonic 213–214, 249, 261, 297, 319, 372–374, 390, 461–463, 466

639

640

Index

Ultrasound 35, 43–44, 51, 221, 261, 271, 326, 336, 345, 372–374, 389–390, 395, 461–464, 466–469, 471–472 Ulva fasciata 16, 52 Uronic acid 18, 20–21, 69, 82, 102, 161, 186, 207, 279–280, 282, 303, 307–312, 318, 330, 336, 362, 407, 410, 421, 433, 435–438, 474, 481, 483, 487, 491–492, 494–495, 527–528, 552, 559–560

v Viscoelastic 17–18, 29, 38, 40–41, 43, 47, 99, 103–106, 108, 117–118, 120–122, 125, 129–130, 132–135, 138–139, 142, 146, 154, 156, 159, 164–166, 170, 175, 181, 192, 196, 212, 221, 231–233, 236, 238, 240, 246–247, 250, 257, 268, 309–310, 351, 395, 439, 444, 476–477, 479, 482, 484–486, 494, 497, 502, 508–509, 512, 515, 519, 522, 534, 545 Viscoelasticity 12, 101, 118, 120–121, 132–133, 146, 231, 342, 419, 512, 521 Viscometer 60, 136, 283, 300, 354, 379, 386, 507 Viscoplastic 175, 188 Viscosity apparent viscosity 83–85, 89, 90, 92, 94, 95, 97, 122, 123, 137, 138, 161, 171, 174–176, 179, 185, 190, 195–197, 207, 210, 211, 215, 218, 228–230, 233, 235, 252, 254–257, 267, 284–286, 306–309, 315, 317, 355, 376, 379, 382, 411, 413–415, 438, 441, 476–479, 487, 488, 490, 492, 494, 495, 500, 501 dynamic viscosity 67, 110, 112, 114, 121–123, 129, 145–146, 192, 307, 441, 486, 511 intrinsic viscosity 12, 13, 18, 21, 40, 54, 59, 60–64, 67–68, 70, 72, 74, 76–77, 82, 96–97, 99, 102, 129, 131, 136–137, 163, 179, 187–188, 190, 200, 209–210, 282–284, 300, 322, 354, 398, 416–417, 419, 422–423,

438, 462, 475, 483–485, 495, 544, 553, 557, 560, 567 relative viscosity 60, 554 Viscous character 17, 101, 150 modulus 126, 139, 232–233, 237–238, 257, 439, 440 Viscosifying 8, 179, 227, 299, 303, 307, 435, 452, 472 Vocadlo (model) 92, 94, 170 Voluminosity 70, 72, 73, 163

w Water absorption 7, 56, 253, 262, 266, 279, 313, 336, 374, 379, 479, 514, 517, 529, 578, 585–587, 616 Water binding capacity/water-binding capacity 210, 231, 255, 316, 379, 538 Water holding capacity/water-holding capacity (WHC) 195, 199, 215, 231, 243, 336, 479, 494, 531, 533, 581 Water sorption isotherm 359, 598 Water uptake 463, 585–587 Water vapor permeability (WVP) 178, 198–199, 215–217, 263–265, 270, 314, 359–360, 442, 573–574, 576–578, 593–595, 597–598 Water vapor transmission/water vapor transmission rate (WVTR) 263, 265, 573, 577 Weltman (model) 148, 174–175, 190, 212 Whipped cream 9, 12, 28, 505, 519 Whipping agent 10, 12 World Health Organization (WHO) 313, 335, 344, 395, 601, 614 Williamson (model) 189, 437

x Xanthan 1–3, 6, 8–10, 12–13, 17, 19, 27–29, 37, 39, 40–41, 45, 48, 50, 53, 55, 63–64, 67–68, 72, 74–75, 77–79, 82, 84–86, 88–90, 93, 95, 96–99, 102, 104, 109–110, 116, 119, 121, 123–124, 126, 128, 131–132, 135, 137–138, 140, 144, 145, 147, 152,

Index

160, 190, 192, 194, 196–197, 208, 210, 230, 236–239, 246–248, 253–254, 261, 267, 271–272, 301, 306, 308, 317, 333, 340, 344, 368, 371, 387, 394, 407, 416, 421, 423, 435–436, 438–440, 448, 504–505, 509–510, 519, 528, 540, 549, 564, 567, 571, 599, 613–614 Xylose 21, 186, 207, 253, 279, 280, 301–303, 350, 364, 408, 417, 433–434, 437, 474, 483, 527–528, 554, 559, 562

y Yield stress 82, 92–93, 95, 99, 153, 175, 188–189, 191–192, 196–197, 253, 255, 257, 261, 262, 267, 398, 399,

400, 401, 402, 407, 476–478, 485–487, 489, 492, 536, 538–539 dynamic yield stress 82, 92–93, 99, 153, 175 static yield stress 92–93, 95, 175 Yogurt 1, 8–11, 18, 21, 30, 45, 49, 178, 195, 202, 218, 223, 230–231, 246, 315–316, 325, 376–379, 389, 391–392, 507, 509, 521, 544, 601

z Zero-shear viscosity 84–87, 94–95, 97, 138, 153, 159, 171, 189, 478, 487 Zeta potential 177, 195, 207, 242, 256, 262, 287–288, 295, 311, 315, 319, 362, 369, 554, 557–560, 562 Zimm plot 58, 59

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