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![2 Proteins in Food Processing
milk, and eggs as well as food products such as bread and cheese. Interactions of pro-
teins with other components are exemplified in protein-starch interactions observed
during dough processing and baking, protein-hydrocolloid interactions in dairy prod-
ucts, protein-fat interactions in comminuted meat emulsions, mayonnaise and cheese,
protein-water as well as protein-protein matrix interactions in fish surimi gels, yogurt,
and cheese (Lluch et al., 2001).
With this complexity in mind, this chapter first describes the basic chemical and
physical properties of proteins and their amino acid building blocks. It then provides
an overview of the factors that can influence the properties of proteins in food systems
and highlights the current trends in food protein research.
Table 1.1 Total protein content of some foods and beveragesa
Food productb
Protein (g/100g)
Almonds [12061] 21.15
Almond milk, sweetened, vanilla flavor [14016] 0.42
Apples, raw, with skin [09003] 0.26
Bananas, raw [09040] 1.09
Beef, grass-fed, strip steaks, lean only, raw [13000] 23.07
Bread, white [18069] 8.85
Broccoli, raw [11090] 2.82
Cheese, cheddar [01009] 22.87
Cheese, feta [01019] 14.21
Chicken, breast, skinless, boneless, meat only, raw [05062] 22.50
Chocolate, dark, 70%–85% cacao solids [19904] 7.79
Corn flakes, cereals, ready-to-eat [08020] 7.50
Egg, whole, raw [01123] 12.56
Ice creams, vanilla [19095] 3.50
Lentils, raw [16069] 24.63
Milk, whole, 3.25% milkfat, with added vitamin D [01077] 3.15
Oranges, raw, navels [09202] 0.91
Pasta, whole-wheat, dry [20124] 13.87
Potatoes, russet, flesh and skin, raw [11353] 2.14
Quinoa, uncooked [20035] 14.12
Rice, white, glutinous, unenriched, uncooked [20054] 6.81
Salmon, Atlantic, wild, raw [15076] 19.84
Soymilk, original and vanilla, with added calcium, vitamins A and D
[16139]
2.60
Tofu, raw, firm, prepared with calcium sulfate [16426] 17.27
Tuna, light, canned in water, drained solids [15121] 19.44
Yogurt, plain, low fat [01117] 5.25
Yogurt, Greek, plain, nonfat [01256] 10.19
a
The information in this table was obtained from the US Department of Agriculture, Agricultural Research Service,
Nutrient Data Laboratory. USDA National Nutrient Database for Standard Reference (Release 28. Released September
2015, slightly revised May 2016). Available from: https://ndb.nal.usda.gov/ndb/ (24 January 2017).
b
Numbers in square brackets are the NDB numbers (the 5-digit Nutrient Databank number that identifies each
food item).](https://image.slidesharecdn.com/73260-250723153317-4dd3fd49/75/Proteins-in-Food-Processing-2nd-Edition-Rickey-Y-Yada-24-2048.jpg)
Proteins in Food Processing 2nd Edition Rickey Y. Yada
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- 9. Woodhead Publishing Seriesin Food Science, Technology and Nutrition Proteins in Food Processing Second Edition Edited by Rickey Y. Yada An imprint of Elsevier
- 10. Woodhead Publishing isan imprint of Elsevier The Officers’ Mess Business Centre, Royston Road, Duxford, CB22 4QH, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, OX5 1GB, United Kingdom © 2018 Elsevier Ltd. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-08-100722-8 (print) ISBN: 978-0-08-100729-7 (online) For information on all Woodhead publications visit our website at https://www.elsevier.com/books-and-journals Publisher: Andre Gerhard Wolff Acquisition Editor: Nina Rosa Bandeira Editorial Project Manager: Karen Miller Production Project Manager: Omer Mukthar Cover Designer: Miles Hitchen Typeset by SPi Global, India
- 11. Contents List of contributorsxi Preface xv 1 Properties of proteins in food systems: An introduction 1 E.C.Y. Li-Chan, I.M.E. Lacroix 1.1 Introduction 1 1.2 Structural properties of proteins 3 1.3 Factors affecting properties of proteins in food systems 12 1.4 Future trends 18 1.5 Sources of useful information 20 References 20 2 Impact of processing on the chemistry and functionality of food proteins 27 A.N.A. Aryee, D. Agyei, C.C. Udenigwe 2.1 Introduction 27 2.2 Structure and chemistry of food proteins 28 2.3 Functionality of food protein 30 2.4 Effect of processing on food protein functionality 34 2.5 Effect of process-induced protein modifications on chemosensory properties of food 40 2.6 Conclusion 42 References 42 Further reading 45 Part One Sources of proteins 47 3 The caseins: Structure, stability, and functionality 49 T. Huppertz, P.F. Fox, A.L. Kelly 3.1 Introduction 49 3.2 Chemistry of caseins 50 3.3 Casein interactions 62 3.4 Casein-mineral interactions 64 3.5 Casein micelles 65 3.6 Stability of casein micelles 69 3.7 Casein-based ingredients 74
- 12. viContents 3.8 Conclusions andfuture perspectives 79 References 79 4 Whey proteins 93 A. Kilara, M.N. Vaghela 4.1 Introduction: What are whey proteins? Sources of whey (acid, sweet) 93 4.2 Analytical methods for determining protein content 94 4.3 Structure of whey proteins 98 4.4 Functional properties of whey proteins 102 4.5 Improving functionality of whey proteins in foods: Physical processes and enzymatic modification 109 4.6 Future trends 117 References 118 Further reading 126 5 Muscle proteins 127 Y.L. Xiong 5.1 Introduction 127 5.2 Structure of muscle proteins 127 5.3 Endogenous proteases 130 5.4 Muscle protein functionality 132 5.5 Prepared muscle proteins as functional ingredients 139 5.6 Future trends 143 5.7 Sources of further information 143 References 144 6 Soy as a food ingredient 149 K. Nishinari, Y. Fang, T. Nagano, S. Guo, R. Wang 6.1 Introduction 149 6.2 Structure of soybean proteins 151 6.3 Gels and gelling of soy proteins 156 6.4 Emulsification of soy proteins 163 6.5 How to improve the functionality and processability 169 6.6 Applications 171 6.7 Conclusion 177 References 177 Further reading 184 7 Proteins from oil-producing plants 187 S.D. Arntfield 7.1 Introduction 187 7.2 Characteristics of oilseed proteins 187 7.3 Factors limiting protein utilization 191 7.4 Extraction and isolation of proteins 196 7.5 Preparation and use of oilseed protein hydrolysates for health benefits 202
- 13. Contentsvii 7.6 Technofunctional propertiesof proteins 204 7.7 Techniques to improve functional properties 207 7.8 Utilization of oilseed proteins 209 7.9 Future of these proteins 210 References 211 8 Cereals proteins 223 N. Guerrieri, M. Cavaletto 8.1 Introduction 223 8.2 Protein function in the seeds 225 8.3 Protein classifications 229 8.4 Gluten properties 232 8.5 Cereals and pseudocereals proteins in food processing 235 8.6 Future trends 238 Acknowledgements 240 References 240 Further reading 244 9 Seaweed proteins 245 J. Fleurence, M. Morançais, J. Dumay 9.1 Introduction: Seaweed and protein content of seaweed 245 9.2 Composition of seaweed proteins 248 9.3 Algal protein digestibility 250 9.4 Uses of algal proteins in food 255 9.5 Future trends 255 9.6 Sources of further information and advice 258 References 259 10 Insects as an Alternative Protein Source 263 Y. Akhtar, M.B. Isman 10.1 Introduction 263 10.2 History of entomophagy 266 10.3 Nutritional value of insects for human consumption 266 10.4 Amino acids 268 10.5 Dietary energy and fat content 274 10.6 Impact on the environment 277 10.7 Challenges 280 10.8 Conclusion 283 Acknowledgments 283 References 283 Further reading 287 11 Proteins in cultured beef 289 M.J. Post 11.1 Introduction—Why cultured beef? 289 11.2 Technology 290
- 14. viiiContents 11.3 Optimizing theproduct 292 11.4 Whole cuts of meat 294 11.5 Road to product development 295 11.6 Summary 296 References 297 Part Two Analyzing and modifying protein 299 12 Food proteins for health and nutrition 301 N. Shang, S. Chaplot, J. Wu 12.1 Introduction 301 12.2 Growing demand for protein and sustainability 302 12.3 Protein intake 303 12.4 Protein quality and its measurement 304 12.5 Bioactivities of proteins 305 12.6 Applications 321 12.7 Safety and legal aspects of protein 323 12.8 Summary 325 References 325 Further reading 336 13 Factors affecting enzyme activity in food processing 337 M.G. Scanlon, A.W. Henrich, J.R. Whitaker 13.1 Introduction 337 13.2 Enzyme types 338 13.3 Parameters affecting enzymatic activity 340 13.4 Endogenous enzymes 349 13.5 Exogenous enzymes 350 13.6 Future trends 360 Acknowledgments 361 References 362 14 Detection and deactivation of allergens in food 367 C.L. Okolie, A.N.A. Aryee, C.C. Udenigwe 14.1 Introduction 367 14.2 Mechanism of food-induced allergic reaction 368 14.3 Detection of food allergens 369 14.4 Food processing and allergenicity 372 14.5 Conclusion 381 References 382 15 Food protein-derived peptides: Production, isolation, and purification 389 R.E. Aluko 15.1 Introduction 389 15.2 Protein sources 389 15.3 Enzymatic hydrolysis of proteins: Basic concepts 396 15.4 Peptide separation and isolation methods 400
- 15. Contentsix 15.5 Purification protocols403 15.6 Structural identification and amino acid sequencing 404 15.7 Current uses 404 15.8 Future trends 405 References 406 Further reading 412 16 Modifying seeds to produce proteins 413 S.T. Häkkinen, A.M. Nuutila, A. Ritala 16.1 Introduction 413 16.2 Methods used for seed modification 415 16.3 Applications in seed modification 421 16.4 Future trends 430 16.5 Sources of further information and advice 431 References 431 Part Three Applications 443 17 Seafood proteins 445 M.A. Mazorra-Manzano, J.C. Ramírez-Suárez, J.M. Moreno-Hernández, R. Pacheco-Aguilar 17.1 Introduction 445 17.2 Nutritional aspects of seafood proteins 446 17.3 Technological and functional aspects of seafood proteins 447 17.4 Seafood processing and its impact on protein quality 450 17.5 Seafood proteins as food ingredients 458 17.6 Recovery of high-value proteins from seafood and its by-products 461 17.7 Proteins used as markers of quality and authenticity in seafood 464 17.8 Future trends 466 References 467 18 Edible films and coatings from proteins 477 A. Chiralt, C. González-Martínez, M. Vargas, L. Atarés 18.1 Introduction 477 18.2 Proteins as film-forming agents 478 18.3 Physical and chemical methods to improve properties of protein films 478 18.4 Active protein films 489 18.5 Final remarks 493 Acknowledgment 493 References 494 Further reading 500 19 Protein gels 501 C.D. Munialo, S.R. Euston, H.H.J. de Jongh 19.1 Introduction 501 19.2 Protein sources 502
- 16. xContents 19.3 Gel formationby proteins 504 19.4 Proteins as gelling agent 505 19.5 Mechanical properties of protein gels 506 19.6 Gel properties 508 19.7 Relation between gel morphology and macroscopic responses 514 19.8 Comparison between plant and animal protein gels 515 19.9 Future trends 516 19.9.1 Conclusion 516 References 517 20 Health-related functional value of dairy proteins and peptides 523 B. Miralles, B. Hernández-Ledesma, S. Fernández-Tomé, L. Amigo, I. Recio 20.1 Introduction 523 20.2 Health benefits of dairy proteins and peptides on metabolic syndrome 524 20.3 Effects of dairy proteins and peptides on intestinal epithelium 536 20.4 Other effects of dairy proteins and peptides 546 20.5 Conclusions and future challenges 550 References 552 21 The use of immobilized enzymes to improve functionality 569 N.S. Hettiarachchy, D.J. Feliz, J.S. Edwards, R. Horax 21.1 General overview about enzymes and immobilized enzymes 569 21.2 Enzyme immobilization methods: Descriptions, benefits, and drawbacks 577 21.3 Usage of immobilized enzymes in food production, medicine, and other fields 581 21.4 The use of immobilized enzymes either in producing proteins, carbohydrates, or lipids; or utilizing proteins, carbohydrates, or lipids as the matrix, support, or carrier 586 21.5 Other important applications of immobilized enzymes 588 21.6 The practice of cell immobilization 589 21.7 Potential and developing applications of immobilized enzymes 590 References 590 Further reading 597 22 Impact of proteins on food color 599 P.L. Dawson, J.C. Acton 22.1 Introduction 599 22.2 Role of proteins in color 606 22.3 Improving protein functionality in color control 620 22.4 Applications to maintain color quality 622 22.5 Future trends 632 References 632 Further reading 638 Index 639
- 17. List of contributors J.C.Acton Clemson University, Clemson, SC, United States D. Agyei University of Otago, Dunedin, New Zealand Y. Akhtar University of British Columbia; DE Labs Inc., Vancouver, BC, Canada R.E. Aluko University of Manitoba, Winnipeg, MB, Canada L. Amigo Institute of Food Science Research, CIAL (CSIC-UAM), Madrid, Spain S.D. Arntfield University of Manitoba, Winnipeg, MB, Canada A.N.A. Aryee Delaware State University, Dover, DE, United States L. Atarés Universitat Politècnica de València, Valencia, Spain M. Cavaletto University of Piemonte Orientale, Vercelli, Italy S. Chaplot University of Alberta, Edmonton, AB, Canada A. Chiralt Universitat Politècnica de València, Valencia, Spain P.L. Dawson Clemson University, Clemson, SC, United States H.H.J. de Jongh ProtIn Consultancy, Zeist, The Netherlands J. Dumay University of Nantes, Nantes, France J.S. Edwards University of Arkansas, Fayetteville, AR, United States S.R. Euston Heriot-Watt University, Edinburgh, United Kingdom Y. Fang Hubei University of Technology, Wuhan, China D.J. Feliz Independent Food Scientist Consultant, Baltimore, MD, United States S. Fernández-Tomé Institute of Food Science Research, CIAL (CSIC-UAM), Madrid, Spain
- 18. xii List ofcontributors J. Fleurence University of Nantes, Nantes, France P.F. Fox University College, Cork, Ireland C. González-Martínez Universitat Politècnica de València, Valencia, Spain N. Guerrieri Institute of Ecosystem Study, CNR-ISE, Verbania, Italy S. Guo China Agricultural University, Beijing, China S.T. Häkkinen VTT Technical Research Centre of Finland Ltd, Espoo, Finland A.W. Henrich CSM Bakery Solutions, Bingen am Rhein Germany B. Hernández-Ledesma Institute of Food Science Research, CIAL (CSIC-UAM), Madrid, Spain N.S. Hettiarachchy University of Arkansas, Fayetteville, AR, United States R. Horax University of Arkansas, Fayetteville, AR, United States T. Huppertz NIZO, Ede, The Netherlands M.B. Isman University of British Columbia, Vancouver, BC, Canada A.L. Kelly University College, Cork, Ireland A. Kilaraa Arun Kilara Worldwide, Chapel Hill, NC, United States I.M.E. Lacroix The University of British Columbia, Vancouver, BC, Canada E.C.Y. Li-Chan The University of British Columbia, Vancouver, BC, Canada M.A. Mazorra-Manzano Research Center for Food and Development (CIAD), Hermosillo Sonora, Mexico B. Miralles Institute of Food Science Research, CIAL (CSIC-UAM), Madrid, Spain M. Morançais University of Nantes, Nantes, France J.M. Moreno-Hernández National Institute in Forestry, Agriculture and Livestock (INIFAP), Culiacan Sinaloa, Mexico a Deceased.
- 19. List of contributorsxiii C.D. Munialo Heriot-Watt University, Edinburgh, United Kingdom T. Nagano Kawasaki University of Medical Welfare, Okayama, Japan K. Nishinari Hubei University of Technology, Wuhan, China A.M. Nuutila VTT Technical Research Centre of Finland Ltd, Espoo, Finland C.L. Okolie Dalhousie University, Truro, NS, Canada R. Pacheco-Aguilar Research Center for Food and Development (CIAD), Hermosillo Sonora, Mexico M.J. Post Maastricht University; MosaMeat B.V., Maastricht, The Netherlands J.C.Ramírez-SuárezResearchCenterforFoodandDevelopment(CIAD),Hermosillo Sonora, Mexico I. Recio Institute of Food Science Research, CIAL (CSIC-UAM), Madrid, Spain A. Ritala VTT Technical Research Centre of Finland Ltd, Espoo, Finland M.G. Scanlon University of Manitoba, Winnipeg, MB, Canada N. Shang University of Alberta, Edmonton, AB, Canada C.C. Udenigwe University of Ottawa, Ottawa, ON, Canada M.N. Vaghela Nestle Development Center, Solon, OH, United States M. Vargas Universitat Politècnica de València, Valencia, Spain R. Wang China Agricultural University, Beijing, China J.R. Whitaker Deceased J. Wu University of Alberta, Edmonton, AB, Canada Y.L. Xiong University of Kentucky, Lexington, KY, United States
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- 21. Preface As one ofthe major components of food, proteins not only play a vital role in their nutritional quality but also to the physicochemical, sensory, health aspects, and utili- zation. Proteins in food processing, 2nd edition is an update of the 1st edition and re- views the mounting body of research on understanding protein structure, and existing and emerging sources as multifunctional ingredients for the food industry. The book is comprised of two introductory chapters followed by three parts. The two introductory chapters outline the basic properties of proteins in food systems and the impact of processing on their chemistry and functionality. Part 1 discusses both ex- isting and emerging sources of proteins, for example, insect and cultured beef. Part 2 illustrates the analysis and modification of proteins, and included chapters on pro- teins for health and nutrition, factors affecting enzyme activity, allergens in food, food protein-derived peptides, and the modification of seeds to produce proteins. The book concludes with Part 3 devoted to the application of proteins as well as those examining their modification, health impact, and contribution to color. Rickey Y. Yada University of British Columbia, Vancouver, BC, Canada
- 22. This page intentionallyleft blank
- 23. Proteins in FoodProcessing. https://doi.org/10.1016/B978-0-08-100722-8.00002-4 © 2018 Elsevier Ltd. All rights reserved. 1 Properties of proteins in food systems: An introduction E.C.Y. Li-Chan, I.M.E. Lacroix The University of British Columbia,Vancouver, BC, Canada 1.1 Introduction The word “protein” is defined as any of a group of complex organic compounds, consisting essentially of combinations of amino acids in peptide linkages, that contain carbon, hydrogen, oxygen, nitrogen, and usually, sulfur. Widely distributed in plants and animals, proteins are the princi- pal constituent of the protoplasm of all cells and are essential to life. (Going back to a Greek word meaning 'first' or 'primary;' because of the fundamental role of proteins in sustaining life.) (Morris, 1992) Proteins play a fundamental role not only in sustaining life, but also in foods de- rived from plants and animals. Foods vary in their protein content (Table 1.1), and even more so in the properties of those proteins. In addition to their contribution to the nutritional properties of foods through the provision of amino acids that are essential to human growth and maintenance, proteins impart the structural basis for various functional properties of foods. The objective of this chapter is to provide an introduction to the chemical and phys- ical properties of food proteins that form the basis for their structural and functional properties. However, food scientists wishing to study proteins in food systems must be cognizant of the complexity of such systems in terms of composition and spatial organization. Food systems are usually heterogeneous with respect to (a) protein com- position (foods usually do not contain a single protein entity, but multiple proteins); (b) other constituents (most foods contain not only water and proteins, but also lipids, carbohydrates as major components, and various other minor components such as salt, sugars, micronutrients, minerals, phenolic compounds, flavor compounds, etc.); and (c) structural or spatial organization (proteins exist in foods as tissue systems, gels, coagula, films, emulsions, foams, etc., and not usually as the dilute solutions or crystalline forms that are typically investigated in model systems). Furthermore, sig- nificant changes in the properties of the proteins are induced by environmental factors and processing conditions that are typical of food systems. Lluch et al. (2001) and Coultate (2009) have written excellent chapters describing the complexity of food pro- tein structures. The diversity of the structural role of proteins is illustrated by compar- ing protein structures in various raw food materials such as muscle and plant tissues,
- 24. 2 Proteins inFood Processing milk, and eggs as well as food products such as bread and cheese. Interactions of pro- teins with other components are exemplified in protein-starch interactions observed during dough processing and baking, protein-hydrocolloid interactions in dairy prod- ucts, protein-fat interactions in comminuted meat emulsions, mayonnaise and cheese, protein-water as well as protein-protein matrix interactions in fish surimi gels, yogurt, and cheese (Lluch et al., 2001). With this complexity in mind, this chapter first describes the basic chemical and physical properties of proteins and their amino acid building blocks. It then provides an overview of the factors that can influence the properties of proteins in food systems and highlights the current trends in food protein research. Table 1.1 Total protein content of some foods and beveragesa Food productb Protein (g/100g) Almonds [12061] 21.15 Almond milk, sweetened, vanilla flavor [14016] 0.42 Apples, raw, with skin [09003] 0.26 Bananas, raw [09040] 1.09 Beef, grass-fed, strip steaks, lean only, raw [13000] 23.07 Bread, white [18069] 8.85 Broccoli, raw [11090] 2.82 Cheese, cheddar [01009] 22.87 Cheese, feta [01019] 14.21 Chicken, breast, skinless, boneless, meat only, raw [05062] 22.50 Chocolate, dark, 70%–85% cacao solids [19904] 7.79 Corn flakes, cereals, ready-to-eat [08020] 7.50 Egg, whole, raw [01123] 12.56 Ice creams, vanilla [19095] 3.50 Lentils, raw [16069] 24.63 Milk, whole, 3.25% milkfat, with added vitamin D [01077] 3.15 Oranges, raw, navels [09202] 0.91 Pasta, whole-wheat, dry [20124] 13.87 Potatoes, russet, flesh and skin, raw [11353] 2.14 Quinoa, uncooked [20035] 14.12 Rice, white, glutinous, unenriched, uncooked [20054] 6.81 Salmon, Atlantic, wild, raw [15076] 19.84 Soymilk, original and vanilla, with added calcium, vitamins A and D [16139] 2.60 Tofu, raw, firm, prepared with calcium sulfate [16426] 17.27 Tuna, light, canned in water, drained solids [15121] 19.44 Yogurt, plain, low fat [01117] 5.25 Yogurt, Greek, plain, nonfat [01256] 10.19 a The information in this table was obtained from the US Department of Agriculture, Agricultural Research Service, Nutrient Data Laboratory. USDA National Nutrient Database for Standard Reference (Release 28. Released September 2015, slightly revised May 2016). Available from: https://ndb.nal.usda.gov/ndb/ (24 January 2017). b Numbers in square brackets are the NDB numbers (the 5-digit Nutrient Databank number that identifies each food item).
- 25. Properties of proteinsin food systems: An introduction3 1.2 Structural properties of proteins 1.2.1 Amino acids commonly found in proteins It is commonly recognized that 20 amino acids form the building blocks of most pro teins, being linked by peptide (amide) bonds formed between α-amino and α-carboxylic acid groups of neighboring amino acids in the polypeptide sequence. As shown in Fig. 1.1, 19 of these 20 amino acids have the general structure of H2NCαH(R)CO2H, differing only in R, which is referred to as the side chain, while the 20th amino acid is in fact an “imino” acid, in which the side chain is bonded to the nitrogen atom. With the exception of the amino acid glycine, in which the side chain is a hydrogen atom, the α-carbon atom exhibits chirality. Typically, only the L-form of the amino acids is found in proteins, being incorporated through the transcription and trans lation machinery of the cell. The D-enantiomers of amino acids are present in a few peptides, including some found in the cell walls of bacteria (Nelson and Cox, 2005). Readers interested in learning about the discovery of these amino acids are referred to Belitz et al. (2009). Table 1.2 shows the three-letter abbreviations and single-letter symbols as well as some key properties of the 20 amino acids commonly found in food proteins. These amino acids can be grouped in five main classes based on their side chain type: aro- matic (Phe, Trp, Tyr), nonpolar, aliphatic (Ala, Gly, Ile, Leu, Met, Pro, Val), polar, un- charged (Asn, Cys, Gln, Ser, Thr), positively charged (Arg, His, Lys), and negatively charged (Asp, Glu) (Table 1.2). This classification, however, should not be considered absolute since some amino acids, particularly Gly, His, and Cys, do not fit perfectly into a specific group. Moreover, as noted above, two of the amino acids are unique in being achiral (Gly) or an imino rather than amino acid (Pro). The two amino acid residues occurring at greatest frequency in proteins possess aliphatic side chains (10.3% and 8.1% for Leu and Ala, respectively), while Gly is the third most frequently occurring amino acid at 7.2% (Jordan et al., 2005). With the exception of His, more than 80%–90% of the positively and negatively charged amino acid residues in proteins usually locate such that they are primarily exposed to the solvent (Bordo and Argos, 1991; Leibniz Institute on Aging—Fritz Lipmann Institute, 2016a). Similarly, amino acid residues with polar side chains (Ser, Thr, Asn, Gln) as well as Pro are also primarily accessible to the solvent. Conversely, with the exception of Tyr, which contains an aromatic phenolic group, less than 50% of the aliphatic and aromatic groups have solvent-exposed areas greater than 30Å. Nevertheless, only 40%–50% of aliphatic and aromatic residues would be considered to be “buried,” with solvent-exposed areas of less than 10Å. These observations indicate that while charged residues are almost always located near the surface or solvent-accessible re- gions of protein molecules, the converse cannot be assumed for nonpolar aliphatic or aromatic residues, probably due to insufficient capacity in the interior of the molecule. Thus, both charged and hydrophobic groups reside at the surface or solvent-accessible regions of protein molecules, whereas charged groups are found much less frequently in the buried interior of protein molecules. In fact, it has been reported that approx- imately 58% of the average solvent-accessible surface or “exterior” of monomeric
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- 27. 304 The Elementsof Perspective Join A E. Then, by the second Corollary of Problem II., a e is a horizontal line. Draw t v parallel to a E, cutting the sight-line in v. .'.v is the vanishing-point of a e. Corolla? thC constructions of Problem II. and its second Then by Problem II. a b is the line A B drawn in perspective ; and by its Corollary a e is the line A E drawn in perspective. From v erect perpendicular v p, and produce a b to cut it in P. Join T P, and from e draw / parallel to A E, and cutting A T in f. S Now in triangles EBl and AET,as^ is parallel to E B and c /to A E ; — e b : ef : : E B : A E. But T v is also parallel to A E and P v to e b. Therefore also in the triangles apv and a V T, e b : e f : : p v : v T. Therefore PV:vt::eb:ae. And, by construction, angle T v p= angle A E B. Therefore the triangles T v p, a e b, are similar; and T P is parallel to A B.
- 28. Appendix 305 Nowthe construction in this problem is entirely general for any inclined line A B, and a horizontal line A E in the same vertical plane with it. So that if we find the vanishing-point of A E in v, and from v erect a vertical V P, and from T draw T P parallel to A B, cutting v P in P, P will be the vanishing-point of A B, and (by the same proof as that given at page 226.) of all lines parallel to it. Next, to find the dividing-point of the inclined line. Fig. 77. I remove some unnecessary lines from the last figure and repeat it here, Fig. 77., adding the measuring-line a M, that the student may observe its position with respect to the other lines before I remove any more of them. Now if the line A B in this diagram represented the length of the line A B in reality (as A B does in Figs. 10. and 1 1.), we should only have to proceed to modify Corollary III. of Problem 1 1, to this new construction. We shall see presently that A B does not represent the actual length of the inclined line A B in nature, nevertheless we shall first proceed as if it did, and modify our result afterwards.
- 30. 306 The Elementsof Perspective In Fig. 77. draw a d parallel to A B, cutting B T in d. Therefore a d is the sight-magnitude of A B, as a R is of A B in Fig. 11. Remove again from the figure all lines except P v, v T, P T, a b, a d, and the measuring-line. Set off on the measuring-line a ?n equal to a d. Draw P Q parallel to a m, and through bdraw m Q, cutting P Q in Q. Then, by the proof already given in pages 230. and 303., P Q = P T. Therefore if P is the vanishing-point of an inclined line A B, and Q P is a horizontal line drawn through it, make P Q equal to p T, and a m on the measuring- line equal to the sightmagnitude of the line A B in the diagram, and the line joining m Q will cut a P in b. We have now, therefore, to consider what relation the length of the line A B in this diagram, Fig. 77., has to the length of the line A B in reality. Now the line A E in Fig. 77. represents the length of a e in reality. But the angle A E B, Fig. 77., and the corresponding angle
- 32. Appendix 307 inall the constructions of the earlier problems, is in reality a right angle, though in the diagram necessarily represented as obtuse. Therefore, if from E we draw E C, as in Fig. 79., at right angles to A E, make E C = E B, and join A c, A c will be the real length of the line A B. Now, therefore, if instead of a m in Fig. 78., we take the real length of A B, that real length will be to a m as A C to A B in Fig. 79. And then, if the line drawn to the measuring-line P Q is still to cut a P in 6, it is evident that the line P Q must be shortened in the same ratio that a m was shortened ; and the true G- ?9dividing-point will be Q' in Fig. 80., fixed so that Q' p shall be to Q P as a in is to a m ; a m representing the real length of A B. But a m is therefore to a m as A C is to A B in Fig. 79. Therefore P Q' must be to P Q as A C is to A B. But P Q equals P T (Fig. 78.) ; and P v is to v T (in Fig. 78.) as B E is to A E (Fig. 79.). Hence we have only to substitute P v for E C, and v T for A E, in Fig. 79 . and the resulting diagonal A C will be the required length of P Q'. It will be seen that the construction given in the text
- 34. 308 The Elementsof Perspective (Fig. 46.) is the simplest means of obtaining this magnitude, for v D in Fig. 46. (or v M in Fig. I5.) = v T by construction in Problem IV. It should, however, be observed, that the distance P D or P x, in Fig. 46., may be laid on the sight-line of the inclined plane itself, if the measuring-line be drawn parallel to that sight-line. And thus any form may be drawn on an inclined plane as conveniently as on a horizontal one, with the single exception of the radiation of the verticals, which have a vanishing-point, as shown in Problem XX.
- 35. The text onthis page is estimated to be only 26.80% accurate INDEX TO ELEMENTS OF DRAWING Aerial Perspective, 139 Art, coarse, its inferiority, 14 ; not perfect if depending on visible lines, 81 ; excellence of, dependent on expression of the individuality of natural objects, 99 ; of painting, in what it consists, 4 (note) Artists, list of those whose works are to be studied, 195-201 Background, to be drawn exactly as seen, 45 Banks, their beauty, 89 Bewick, 199 Black, rightly to be made conspicuous, '33. 134 Blake, 199 Body-colour drawing, 1 17-120 Boldness, not to be aimed at by the beginner, 29, 141 Books, what to read, 202-204 Boughs, ramification of, 73 ; individuality of, 169 ; limitation of, 169 Branches, structure of, 164 Bridge, ideal construction of, 153, 154 Caraco, conventionalism of, 102 Chiaroscuro, the masters of, 57 ; its importance in water painting, 106 Clouds, best introduction to drawing of, 38 ; 109, 1 10 ; mistakes of ordinary artists in drawing, no; their sculptured form, no, in ; how to sketch the lighter wreaths of, in ; as drawn by Turner, Titian and Tiutoret, 112 Colour, cause of, 4 (note) ; smooth, how to produce, 5-7 ; depth of, represented by depth of shade, 19 , relation of, to shade, 24, 25 ; scales of, how to prepare, 24, 25 ; cast back by objects in reflected light, 33 ; of water, 107, 108 ; relativeness of, 113; importance of, in comparison with form, 115 ; relative merits of transparent and opaque n 7-120; gradations in, 126-128 ; how obtained, 120 ff.; in nature, 123, 133, 136 ; colour power a sign of mental health, 136 ; its relation to form, 137 ; how expressive of distances, 137-139 ; how best to obtain harmony of, 186 Composition, 141 ff ; law of principality, 144-147 ; of repetition, 147-150 ; of continuity, 150-155; of curvature, 155-161 ; of radiation, 161-173 ; of contrast, 173-179 ; of interchange, 170- 180 ; of consistency, 180-183 ; of harmony, 183-193 Confusion. See Nature Consistency, law of, 180-183 Continuity, law of, 150-155 Contrast, law of, 173-179 Coreggio, 117, 176 Cracks or fissures, how expressible, 3L 32, 35 Cruikshank, his etchings, 58, 187, see Appendix Curvature, law of, 155-161 Curves, of shore, necessity of right drawing of, 105 ; necessary of, to good composition, 157
- 36. Detail, cannot beexpressed in drawing as it is in reality, 44 Distance, how expressed by colour, 137-139 Drapery, difficulty of drawing, 37 Drawing, good, an abstract of natural facts, 183 Durer, his perfection of chiaroscuro, 57, 59. 64, 66 Economy of execution, as shown in the work of great masters, 61 Engraving, more difficult than common drawing, 56 Execution, how to distinguish that of the great masters, 61 ; habit of, opposed to true drawing of detail, 99 Eye, innocence of, 3 (note) ; how to obtain accuracy of, 8, 9 Flatness, nowhere found in the natural world, 27 ; tendency towards in fine drawing and painting, 44 Foliage, important element in effect of, 52 ; in the works of Harding, 92, 93 ; radiation and enclosure of, 93 ; as drawn by Turner, 101 ; by Titian, 102 Foreground, bad in all engravings, 56 Form, perception of, 3 (note) ; expression of, on what it depends, 10 ; refinement of, difficulty of obtaining, 29; how expresseJ by Nature, 31 ; 309
- 37. 3io Index moregained by drawing of, than labouring at texture, 36 ; expressed by colour, 36 ; how expressed by great artists, 43 ; vital facts of, 70 ff. ; absoluteness of, 113; disguised by colour, 137 Freedom, error of aiming at, 9 French art, 184 (note) Gainsborough, his foliage, 96 Gradation of colour, difficulty of obtaining evenness of, 29 ; roundness and projection expressed by, 36 ; how to obtain, 40-42, 120 ff. ; in Nature, 126 ; beauty of, 127 ; universality of law of, 133 Ground-surface, linear expression of, 109 Hand, lightness of, required for shading, 8 Harding, J. D., foliage by, 92 ; its excellences and shortcomings, 90 Harmony, law of, 183-193 ; how best obtained, 186 Hunt, Holman, 116 Hunt, William, 42, 132 I.vitation, to be aimed at as far as possible, 60 India-.ubber, use of, 8 (note), 12 Individuality of natural objects as opposed to general law, 95, 96, 97 ; excellence of art dependent on expression of, 99 ; of boughs, 169 Inimitableness of natural objects, 52, 69 Interchange, law of, 179-1S0 Landscape drawing, three main laws to be considered in regard to, 95, 96 Leaves, how to draw, 45 ff. ; foreshortening of, 46 ; lustre of, 51 ; causes of form of, being altered and hidden, 52 ; structure of, 92, 93 ; individual caprice of, as opposed to general law, 94 ; radiation of, 162 Leech, woodcuts of, in Punch, 58 Lewis, John, n6, see Appendix Light, reflected, 33 ; receives colour from objects from which cast, 33 ; neutrality of, 33 Lines, difficulty of drawing them well slowly, 9 ; straight, great draughtsmen unable to draw, 15, 16 (note) ; rules for direction of, 59, 60 ; Straight, used for shading, 61 ; leading or governing, importance of, 70 ; two kinds of harmonies of, 161 Lustre, of leaves, 51 ; a defect in painting, 118 Memoranda, usefulness of, 85, 86 Mulready, 116 Mystery of foliage, 66 ; of other natural objects, 96, 100 ; as shown by Turner, 101 Natural objects, inimitableness of, 52 ; mystery concealing, 96 Nature, character of confusion of, 47, 48 ; how to express, 49 ff., 66-68 ; mystery of 96 ; colours in, 123, 133, 136 ; gradation of colours in, 126 ; symmetry in, 149 Neutrality of reflected light, 33 Outline, more or less interrupted in good work, 62 ; false and true, 62, 63 ; for what purposes to be used, 64 ; to what objects to be confined, 65 Painting, technical powers of, 3 (note) ;
- 38. art of, inwhat it consists, 4 (note) Paper, colour and quality to be used, 110 Patterns, drawing of, good exercise for gaining perception of tint, etc., 37. 38 . Perspective, aerial, 139 Perugino, Madonna of, 150 Pigments to be used in water-colour drawing, 116 ff. Power, only gained by care, 29 Preciousness of colour, how obtained, 135 . Precision, less danger for amateurs in, than in vagueness, 58 Principality, law of, 144-147 Projection, expressed by gradation, 36 ; impossible to show, 44 ; deceptively produced by partial exaggeration of shadow, 44 Prout. his St. Nicholas, 172; his principles of composition, 180, see Appendix Radiation, of foliage, 93 ; lawof, 161173 ; beauty of groups of form dependent on, 170 Raphael, his hesd of Angel ; 63, his ' St. Catherine, 82 ; his Disputa, 146 Reflection, law of, 106 ; colour of, 107, 108 Rembrandt, his precision of line, 57 ; his perfection in chiaroscuro, 57 Repetition, law of, 147-150 Rethel, 58, see Appendix Retsch, 62, 200 Richter, 58 ; illustrations by, 187, see Appendix
- 39. The text onthis page is estimated to be only 25.40% accurate Index 3ii Rivers, general character of, 152 Rossetti, 116, see Appendix Roundness, drawing dependent on power of representing, 27 ; expressed by gradation, 36 Salvator Rosa, his foliage, 96 Scales of colour, how to prepare, 24, 25 ; principle underlying 26 Shade, gradation of, with pen, 10-T2 ; with pencil, 12- 14 depth of.colour represented by depth of, 19 ; good work more or less touched with, 62 Shadow, generally darker than dark side of object, 34-35 ; impossibility of getting all the gradations of, seen in Nature, 43 ; value lent to objects by their, 86 ; colouring of, 134^ Shore, curves of, 105 ; perspective of, 107 Sight, keenness of, required for shading, 8 Sketching from Nature, what to choose, and what to avoid for subject, 87-91 Sky, difficulty of drawing, as compared to earth subject, 109, no; inimitable brilliancy of, 123 Solids, illuminated, how generally seen, 32, 33 ; colour of, 34 Stone, how to draw a, 26, 29, 32 ; colours of, ro7 Subjects, most suitable for drawing, 87 ff. Surface, lustrous, expression of, 38 ; how expressed by Rethel and Richter, 58 ; softness of, of trees, 103 Symmetry in Nature, 149 Texture, chief points to study in the drawing of, 38 ; how expressed by Leech, 58 Tinting, 8r ; unity of, with line, 82 Tintoret, 9 (note) ; drawing of clouds by, ri2 ; 118. 172 Titian, 47 ; drawing of foliage by, 102 ; ofrloudsby, 112; 146, 172 Translucency, beauty of, ri8 (note) Transparent colour drawing, 117 ; relative merits of, as compared with body colour drawing, 1 17 ff. Trees, boughs of, dark against the sky, 17 ; how to learn to draw, 17-T9 ; further study of, 45 ; structure of, 71-73 ; their softness of surface, 103 ; good and bad drawing of, '59 I perfect type of structure, 162, 163 ; four great laws of structure, r68, 160 Turner, drawings by, 53, 54, 74, 77, 78, ioi, 146, 147, 148, rsr, 156, 172, 177, 189, 190 ; foliage, clouds, moonlight by, 55 ; his use of shadow, 85 : mystery of nature expressed by, 101 ; drawing of clouds by, 112 ; his colours, 116 ; his gradation of colour, r28 Unity, organic, of natural objects, 95 Vagueness, to be avoided by amateurs. 58 Vegetable form, radiation of, 162 ; expression of four great laws by,
- 40. 168 Velasquez, 134Veronese, 9 (note), 118, 125, 126, 146, 172 Water, reflections in, 104 ; necessity of careful drawing of lines of disturbance on surface of, 104, 105 ; colour of, 107, 108 Water- colour drawing, how to mix and lay on a flat tint, 20-23 ! a gradated one, 23-24 ; gradated scales of colour, 24,23; materials to be used for, 116 tt.: processes by which gradation and other characters are to be obtained, 120 ff. White, preciousness of, 133 White objects, how to treat, 44 ; how treated by Veronese and Titian, 44 ; by Turner, 44 (note) Wilson, his drawing of trees, 73
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