Table of Contents

Cover

Title Page

List of Contributors

Preface

Section I: The Biology of Bitterness Perception

Chapter 1: Biochemistry of Human Bitter Taste Receptors

1.1 Introduction
1.2 Bitter Taste Receptors: T2Rs
1.3 T2R Signal Transduction
1.4 Bitter Taste Perception and T2R Polymorphisms
1.5 Ligand Binding and Activation Mechanisms of T2Rs
1.6 Nutrigenomics of Taste
1.7 Bitter Taste Blockers
1.8 Expression of T2Rs in Extraoral tissues
1.9 Conclusion
Acknowledgement
References

Chapter 2: Physiological Aspects of Bitterness

2.1 Introduction
2.2 Anatomy
2.3 Taste Signal Transduction
2.4 Gustatory Bitter Taste Receptor Gene Expression
2.5 Extragustatory Bitter Taste Receptors
2.6 Outlook
Acknowledgements
References

Chapter 3: Bitterness Perception in Humans: An Evolutionary Perspective

3.1 Bitter Taste Receptors - A Group of G Protein-Coupled Receptor (GPCR) Members
3.2 Tas2R Gene Family - A Highly Diverse Family in Vertebrates
3.3 The Evolution of Tas2R Gene Family in Vertebrates
3.4 Diverse Selective Forces Drove the Evolution of Tas2R Genes in Primates
3.5 Genetical Basis of Tasteblindness – Human PTC Perception as an Example
3.6 PTC Tasteblindness in Humans and Chimpanzees - Shared Phenotype Resulted From Unshared Genotypes
3.7 Closing Remarks
Acknowledgement
References

Section II: The Chemistry of Bitterness

Chapter 4: Fruits and Vegetables

4.1 Introduction
4.2 Fruits
4.3 Vegetables
4.4 Future Progress
References

Chapter 5: Bitterness in Beverages

5.1 Introduction
5.2 Bitterness in Tea
5.3 Bitterness in Coffee
5.4 Bitterness in Cocoa/Hot Chocolate
5.5 Bitterness in Beer
5.6 Bitterness in Wine
5.7 Bitterness in Cider
References

Chapter 6: Structural Characteristics of Food Protein-Derived Bitter Peptides

6.1 Introduction
6.2 Bitter Peptides Preparation and Taste Evaluation
6.3 Role of Amino Acid Composition and Position Arrangement in Determining Peptide Bitterness Intensity
6.4 Peptide Debittering Methods
6.5 Conclusions
Acknowledgement
References

Section III: Analytical Techniques for Separating and Characterizing Bitter Compounds

Chapter 7: Sensory Evaluation Techniques for Detecting and Quantifying Bitterness in Food and Beverages

7.1 Screening Methods
7.2 Test Methods
7.3 Techniques to Maximize Bitterness Perception
7.4 Use of Standards
7.5 Conclusion
References

Chapter 8: Analysis of Bitterness Compounds by Mass Spectrometry

8.1 Introduction
8.2 Overview of LC-MS
8.3 Data Acquisition in LC-MS
8.4 LC-MS Application of Bitterness Compounds
8.5 Challenges and Future Perspectives
8.6 Optimisation of Mass Spectra Parameters
8.7 Recording of MS Profile
8.8 Challenges in the Collection of HRMS Data
8.9 Conclusions
References

Chapter 9: Evaluation of Bitterness by the Electronic Tongue: Correlation between Sensory Tests and Instrumental Methods

9.1 Introduction
9.2 The Electronic Tongue
9.3 The Electronic Tongue and Food Production
9.4 Electronic Tongue and Bitterness
9.5 Evaluating Bitterness in Food Products Using Electronic Tongues
9.6 Conclusion
References

Section IV: Methods for Removing Bitterness in Functional Foods and Nutraceuticals

Chapter 10: Methods for Removing Bitterness in Functional Foods and Nutraceuticals

10.1 Introduction
10.2 Reducing and Removing Bitter Components
10.3 Conclusion
References

Index

End User License Agreement

List of Illustrations

Chapter 1: Biochemistry of Human Bitter Taste Receptors

Figure 1.1 Predicted secondary structure model of the bitter taste receptor T2R4. The coding region is 299 amino acids long, has a short extracellular N-terminus, three extracellular loops, seven transmembrane (TM1-TM7) helices, three intracellular loops and a short C-terminus.
Figure 1.2 Bitter taste signaling pathway (IP₃ pathway) Abbreviations: PLCβ2, phospholipase C β2; PIP₂, phospatidyl-inositol-biphosphate; DAG, diacylglycerol; IP₃, inositol triphosphate; ER, endoplasmic reticulum; Ca²⁺, calcium; Na⁺, sodium.

Chapter 2: Physiological Aspects of Bitterness

Figure 2.1 Signal transduction in bitter taste receptor cells. The bitter taste receptor (here shown as a seven transmembrane domain glycoprotein) transmits its activation via heterotrimeric G proteins (consisting of α-, β-, and γ-subunits). After the dissociation of the G protein complex, the βγ-subunits induce the turnover of phosphatidylinositol-4,5-bisphosphate leading to the generation of diacylglycerol (DAG) and inositol-1,4,5-trisphosphate (IP₃) by the activity of phospholipase Cβ2. The IP₃ triggers the release of calcium ions (Ca²⁺) from intracellular stores via activation of the type III IP₃-receptor (IP₃R). Increasing intracellular calcium ion levels in turn result in the opening of the cation channel TRPM5 leading to depolarization and subsequent release of the neurotransmitter ATP (not shown).
Figure 2.2 Bitter taste receptor expression in human circumvallate papillae. Cross-section through a human circumvallate papillae stained with antibodies specific for the human bitter taste receptor TAS2R38. Note that within each taste bud several cells express TAS2R38 (white). The taste buds are circled for easier visibility.
Figure 2.3 Bitter taste receptor gene expression throughout the human body. Tissues reported to express bitter taste receptor genes in human or other mammals are labeled in red. Note that large parts of the respiratory tract and the alimentary canal express bitter taste receptor genes. Additional sites of expression are brain, heart, urinary bladder and testes.

Chapter 3: Bitterness Perception in Humans: An Evolutionary Perspective

Figure 3.1 The Tas2R gene repertoires in vertebrates. Dietary information and the number of Tas2R genes are shown after each species name. The scale beneath the phylogeny indicates the divergence time and the one below the bars indicates the total number of Tas2R genes (intact, partial and pseudogenes) in each species. (Modified from Li & Zhang, 2013).

Chapter 4: Fruits and Vegetables

Figure 4.1 Delayed bitterness in citrus, formation of Limonin derived from Nomilin via Limoneic acid A-ring lactone
Figure 4.2 Flavanone neohesperidoside Naringin inducing bitterness in grapefruit and other citrus
Figure 4.3 Cyanogenic glycosides amygdalin and prunasin and release of glucose, benzaldehyd and HCN
Figure 4.4 Glucosinolates in Brassica
Figure 4.5 The phenolic bitter compound 3-Methyl-6-methoxy-8-hydoxy-3,4-dihydroisocoumarin named 6-Methoxymellein (6-MM) in carrots
Figure 4.6 Polyacetylenes (Falcarinols) in carrot and other Apiaceae food plants (Czepa and Hofmann, 2003, Christenen and Brandt, 2006).
Figure 4.7 Glycoalkaloids in potato: α-solanine, α-chaconine and β₂-chaconine (Fenwick et al., 1990).
Figure 4.8 Glycoalkaloid Tomatin in tomato (Fenwick et al., 1990).

Chapter 5: Bitterness in Beverages

Figure 5.1 Major catechins of green tea (Narukawa et al., 2011)
Scheme 5.1 Bitter lactones identified in coffee. 5-0-caffeoyl-muco-γ-quinide (2), 3-0-caffeoyl-γ-quinide (3), 4-0-caffeoyl-muco-γ-quinide (4), 5-0-caffeoyl-epi-δ-quinide (5), and 4-0-caffeoyl-γ-quinide (6), as well as the novel 3-0-caffeoyl-epi-γ-quinide (7) formed upon thermal treatment (30 min., 230°C) of 5-0-caffeoylquinic acid (1)
Scheme 5.2 Reaction mechanism leading to the formation of (furan-2-yl) methylated benzene diols and triols 1,3,5,6 from furfuryl alcohol and 5-0-chlorogenic acid upon coffee roasting
Figure 5.2 Scheme showing conversion of α-acids to iso-α-acids and tetra-iso-α-acids (Humulones: R = isobutyl, cohumulones: R = isopropyl, adhumulones: R = sec butyl)
Figure 5.3 Phenolics in cider.

Chapter 6: Structural Characteristics of Food Protein-Derived Bitter Peptides

Figure 6.1 Correlation between bitterness intensity of cheese and β-casein f193-209 concentration in the aqueous extract of cheese at 180 days () and 270 days ().
Figure 6.2 Relative activation rates of T2R1 in response to different peptides calculated based on their EC₅₀ values. All values were normalized to the EC₅₀ value of FFF.

List of Tables

Chapter 4: Fruits and Vegetables

Table 4.1 Bitter phytonutrients in fruits and vegetables

Chapter 6: Structural Characteristics of Food Protein-Derived Bitter Peptides

Table 6.1 Bitterness intensity of peptides (X-X) and equivalent free amino acid mixtures (X+X)
Table 6.2 Structure-taste properties of typical bitter peptides

Chapter 7: Sensory Evaluation Techniques for Detecting and Quantifying Bitterness in Food and Beverages

Table 7.1 Review of sensory panels with bitter products

Chapter 8: Analysis of Bitterness Compounds by Mass Spectrometry

Table 8.1 The list of compounds and the analytical methods employed for their determination in various foods

Chapter 9: Evaluation of Bitterness by the Electronic Tongue: Correlation between Sensory Tests and Instrumental Methods

Table 9.1 Summary of selected studies with application of electronic tongue systems in bitterness analysis in food products

Chapter 10: Methods for Removing Bitterness in Functional Foods and Nutraceuticals

Table 10.1 Reducing, Removing and Masking Bitter Compounds

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Library of Congress Cataloging-in-Publication Data

Names: Aliani, Michel, editor. | Eskin, N. A. M. (Neason Akivah Michael), editor.

Title: Bitterness : perception, chemistry and food processing / edited by Michel Aliani, Manitoba, Canada; Michael N. A. Eskin, Manitoba, Canada.

Other titles: Bitterness (John Wiley & Sons)

Description: First edition. | Hoboken : John Wiley & Sons, Inc., 2017. | Series: Institute of food technologists series | Includes bibliographical references and index.

Identifiers: LCCN 2016049478 (print) | LCCN 2016049871 (ebook) | ISBN 9781118590294 (hardback) | ISBN 9781118590317 (pdf) | ISBN 9781118590232 (epub)

Subjects: LCSH: Bitterness (Taste) | BISAC: TECHNOLOGY & ENGINEERING / Food Science.

Classification: LCC TX546 .B58 2017 (print) | LCC TX546 (ebook) | DDC 664/.07–dc23

LC record available at https://lccn.loc.gov/2016049478

Cover Design: Wiley

Cover Images: Background Image: fcafotodigital/Gettyimages; Inset Images (from top to bottom): luckyraccoon/shutterstock; ansonsaw/Gettyimages; Brent Hofacker/shutterstock

List of Contributors

Dr. Ayyappan Appukutan Aachary
Department of Human Nutritional Sciences, University of Manitoba, Winnipeg, Canada

Dr. Michel Aliani
Department of Human Nutritional Sciences, University of Manitoba, Winnipeg, Manitoba, Canada

Dr. Rotimi Aluko
Department of Human Nutritional Sciences, U of Manitoba, Winnipeg, Canada

Dr. Daniel Baumgartner
Agroscope, Institute for Food science IFS, Schloss, Switzerland

Dr. Malik Behrens
Department of Molecular Genetics, German Institute of Human Nutrition, Potsdam, Rebbruecke, Nuthenal, Germany.

Raj Bhullar
Department of Oral Biology, Faculty of Dentistry, University of Manitoba, Winnipeg, Canada

Dr. Prashen Chelikani
Department of Oral Biology, Faculty of Dentistry, University of Manitoba, Winnipeg, Canada

Dr. Geraldine Dowling
Department of Pharmacology and Therapeutics, School of Medicine, Trinity Centre for Health Sciences, St. James's Hospital, James's Street, Dublin, Ireland

Dr. Michael N. A. Eskin
Department of Human Nutritional Sciences, University of Manitoba, Winnipeg, Canada

Dr. Erin Goldberg
Department of Human Nutritional Sciences, University of Manitoba, Winnipeg, Manitoba, Canada

Jennifer Grant
Department of Human Nutritional Sciences, University of Manitoba, Winnipeg, Canada

Dr. Ernst Hoehn
Swiss Federal Research Station

Dr. Wolfgang Meyerhof
Department of Molecular Genetics, German Institute of Human Nutrition, Potsdam, Rebbruecke, Nuthenal, Germany

Donna Ryland
Department of Human Nutritional Sciences, University of Manitoba, Winnipeg, Manitoba, Canada

Dr. Peng Shi
State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, China.

Nisha Singh
Department of Oral Biology, Faculty of Dentistry, University of Manitoba, Winnipeg, Canada

Jasbir Upadhyaya
Department of Oral Biology, Faculty of Dentistry, University of Manitoba, Winnipeg, Canada

Preface

Bitterness is one of the most interesting and least studied/understood of all the human tastes. It produces aversive reactions because it was originally associated with the plant source being poisonous. In fact, it was considered a defence mechanism for avoiding the ingestion of such harmful substances so that early human survival was based on the knowledge and ability to discriminate between edible plants particularly those with potentially harmful effects. With the advent of modern technology our understanding of bitterness is far more sophisticated and that we now know that not all bitter compounds are poisonous. In fact there are many foods in which bitterness is quite acceptable such as in some cheeses and beverages. In this book we have attempted to provide a comprehensive review of bitterness, from the novel genes in humans responsible for the expression of bitterness to methods used to remove or reduce bitterness in functional foods and nutraceuticals.

The book is organized into four sections. The first section covers the biology of bitterness perception with chapter 1 discussing the biochemistry of the 25 human bitter taste receptors of the TAS2R gene family. Chapter 2 examines the physiological aspects of bitterness while chapter 3 discusses human bitterness from an evolutionary perspective.

Section II covers the chemistry of bitterness with chapter 4 detailing those secondary plant metabolites responsible for the bitterness of selected fruits and vegetables. The compounds responsible for the bitterness of such beverages as tea, coffee, cocoa, wine and cider are reviewed in chapter 5, whereas ‘food protein-derived bitter peptides’ is the subject of chapter 6.

The analysis of bitterness, both sensory and chemical, is detailed in section III. Chapter 7 is a comprehensive review of sensory methods for assessing the bitterness of foods and beverages while chapter 8 is focused on the application of mass spectrometry for identifying bitter compounds. The final chapter in this section, chapter 9, discusses the ability of the electronic tongue to analyze bitterness and its correlation with sensory analysis.

The final section, section IV, covers the physical and chemical methods available for removing or masking bitterness in functional foods and nutraceuticals. The recent development of bitter blockers is also discussed as it provides a healthy alternative to adding sugar or salt for masking bitterness.

We hope this book will provide useful information to food scientists as well as those working in the food and flavor industries. We are grateful to colleagues from around the world for their important contributions to this book and acknowledge the excellent editorial assistance provided by the staff of Wiley.

Michel Aliani and Michael N. A. Eskin

Perception, Chemistry and Food Processing

The Biology of Bitterness Perception