Parker / Elmore / Methven Flavour Development, Analysis and Perception in Food and Beverages

1. Auflage 2014
ISBN: 978-1-78242-111-5
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, Band 273, 448 Seiten

Reihe: Woodhead Publishing Series in Food Science, Technology and Nutrition

Flavour is a critical aspect of food production and processing, requiring careful design, monitoring and testing in order to create an appealing food product. This book looks at flavour generation, flavour analysis and sensory perception of food flavour and how these techniques can be used in the food industry to create new and improve existing products. Part one covers established and emerging methods of characterising and analysing taste and aroma compounds. Part two looks at different factors in the generation of aroma. Finally, part three focuses on sensory analysis of food flavour. - Covers the analysis and characterisation of aromas and taste compounds - Examines how aromas can be created and predicted - Reviews how different flavours are perceived

Autoren/Hrsg.

Parker, J K

Elmore, Stephen

Methven, Lisa

Inhaltsverzeichnis

1;Front Cover;1
2;Flavour Development, Analysis and Perception in Food and Beverages;4
3;Copyright;5
4;Contents;6
5;List of Contributors;12
6;Woodhead Publishing Series in Food Science, Technology and Nutrition;14
7;Introduction;28
8;Part One: Characterisation and analysis of aroma compounds;32
8.1;Chapter 1: Introduction to aroma compounds in foods;34
8.1.1;1.1. Introduction to aroma;34
8.1.2;1.2. Sensomics and some definitions;34
8.1.2.1;1.2.1. Gas chromatography-olfactometry;35
8.1.2.2;1.2.2. Aroma extract dilution analysis;35
8.1.2.3;1.2.3. Flavour dilution factors;35
8.1.2.4;1.2.4. Stable isotope dilution analysis;35
8.1.2.5;1.2.5. Odour thresholds;36
8.1.2.6;1.2.6. Odour-activity values;36
8.1.2.7;1.2.7. Recombinates;36
8.1.2.8;1.2.8. Omission tests;37
8.1.2.9;1.2.9. Character impact compounds;37
8.1.3;1.3. Structure, aroma and occurrence of compounds containing carbon, hydrogen and oxygen;37
8.1.3.1;1.3.1. Aldehydes;37
8.1.3.2;1.3.2. Alcohols;41
8.1.3.3;1.3.3. Ketones;42
8.1.3.4;1.3.4. Esters;42
8.1.3.5;1.3.5. Lactones;42
8.1.3.6;1.3.6. Carboxylic acids;43
8.1.3.7;1.3.7. Terpenes and terpenoids;43
8.1.4;1.4. Structure, aroma and occurrence of oxygen heterocycles and phenols;44
8.1.4.1;1.4.1. Furans and furanoids;44
8.1.4.2;1.4.2. Furanones;45
8.1.4.3;1.4.3. Pyranones;46
8.1.4.4;1.4.4. Phenols;46
8.1.5;1.5. Structure, aroma and occurrence of nitrogen compounds;47
8.1.5.1;1.5.1. Amines;47
8.1.5.2;1.5.2. Pyrroles, pyrrolines and pyridines;48
8.1.5.3;1.5.3. Pyrazines;48
8.1.6;1.6. Structure, aroma and occurrence of sulfur compounds;49
8.1.6.1;1.6.1. Sulfides;49
8.1.6.2;1.6.2. Thiols;51
8.1.6.3;1.6.3. Thiophenes;51
8.1.6.4;1.6.4. Thiazoles and thiazolines;52
8.1.6.5;1.6.5. Thioesters and mercapto esters;52
8.1.6.6;1.6.6. Isothiocyanates;52
8.1.7;1.7. The future of flavour research;53
8.1.8;1.8. Further reading;53
8.1.9;References;54
8.2;Chapter 2: Extraction techniques for analysis of aroma compounds;62
8.2.1;2.1. Introduction;62
8.2.2;2.2. Choosing an appropriate method for aroma extraction;63
8.2.3;2.3. Good practice;64
8.2.4;2.4. Headspace SPME;65
8.2.5;2.5. Solvent-assisted flavour evaporation;68
8.2.6;2.6. Solid-phase extraction;70
8.2.7;2.7. The future of aroma extraction;73
8.2.8;References;74
8.3;Chapter 3: Aroma extract analysis;78
8.3.1;3.1. Introduction;78
8.3.2;3.2. Gas chromatography and mass spectrometry;78
8.3.2.1;3.2.1. Sample injection;79
8.3.2.1.1;3.2.1.1. Liquid extract;79
8.3.2.1.2;3.2.1.2. Desorption from a solid phase;80
8.3.2.2;3.2.2. Component separation;81
8.3.2.3;3.2.3. Detection;83
8.3.2.4;3.2.4. Data analysis;84
8.3.2.4.1;3.2.4.1. Identification from first principles;84
8.3.2.4.2;3.2.4.2. Library searches;85
8.3.2.4.3;3.2.4.3. Deconvolution;86
8.3.2.4.4;3.2.4.4. Linear retention indices;86
8.3.2.4.5;3.2.4.5. Reference compounds;87
8.3.3;3.3. Quantification;87
8.3.3.1;3.3.1. Stable isotope dilution assay;87
8.3.3.2;3.3.2. Standard addition;88
8.3.3.3;3.3.3. Semi-quantification;88
8.3.4;3.4. Gas chromatography-olfactometry;88
8.3.4.1;3.4.1. Aroma extract dilution analysis;89
8.3.5;3.5. Future trends in GC-MS;90
8.3.6;References;90
8.4;Chapter 4: Analysis of taints and off-flavours;94
8.4.1;4.1. Introduction;94
8.4.2;4.2. The origins of taints and off-flavours in food;94
8.4.3;4.3. Consumer perception and sensory evaluation;96
8.4.4;4.4. Methods of analysis;96
8.4.4.1;4.4.1. Sampling;97
8.4.4.2;4.4.2. Sensory analysis;97
8.4.4.3;4.4.3. Chemical analysis;98
8.4.5;4.5. Examples of taints and the methods employed;102
8.4.5.1;4.5.1. Halogenated phenols and anisoles;102
8.4.5.2;4.5.2. Sulfur compounds;105
8.4.5.3;4.5.3. Taints from packaging;106
8.4.5.4;4.5.4. Taints in water;107
8.4.5.5;4.5.5. Taints from microorganisms;108
8.4.5.6;4.5.6. Off-flavours from lipid oxidation/hydrolysis;108
8.4.5.7;4.5.7. Food processing off-flavours;109
8.4.6;4.6. Future trends;109
8.4.6.1;4.6.1. Sensors/on-site screening approaches;110
8.4.7;References;110
8.5;Chapter 5: Chemical sensors;114
8.5.1;5.1. Introduction;114
8.5.1.1;5.1.1. Sensors used in the EN systems;115
8.5.1.2;5.1.2. Sensors used in the ET systems;119
8.5.1.3;5.1.3. Hybrid EN/ET systems;121
8.5.1.4;5.1.4. Pattern recognition techniques for EN/ET analysis;121
8.5.1.5;5.1.5. Application of chemical sensors in food and beverage industries;121
8.5.1.6;5.1.6. Food industry;122
8.5.1.7;5.1.7. Electronic noses in the food industry;122
8.5.1.8;5.1.8. Electronic tongues in the food industry;125
8.5.2;5.2. Beverage industry;127
8.5.2.1;5.2.1. EN systems in the beverage industry;127
8.5.2.2;5.2.2. ET systems in the beverage industry;128
8.5.2.3;5.2.3. Discussion;130
8.5.3;5.3. Perspectives for application of chemical sensors in the food and beverage industries;130
8.5.4;5.4. Summary and conclusions;131
8.5.5;References;131
8.6;Chapter 6: Aroma release;136
8.6.1;6.1. Introduction;136
8.6.1.1;6.1.1. Scope;136
8.6.1.2;6.1.2. Overview;136
8.6.1.3;6.1.3. Background;137
8.6.2;6.2. Physicochemical properties of aroma compounds;137
8.6.2.1;6.2.1. Partition coefficient;138
8.6.2.2;6.2.2. Phase partitioning;139
8.6.3;6.3. Equilibrium partitioning of flavour compounds;141
8.6.4;6.4. Non-equilibrium partitioning of aroma compounds;142
8.6.4.1;6.4.1. Dynamic dilution physics (diffusion/mass transfer coefficient);142
8.6.4.1.1;6.4.1.1. Mass transfer;142
8.6.4.1.2;6.4.1.2. Volatility;143
8.6.4.1.3;6.4.1.3. State changes;143
8.6.5;6.5. Aroma release during oral processing;145
8.6.5.1;6.5.1. Impact of saliva on flavour delivery;145
8.6.5.2;6.5.2. Impact of mastication on aroma delivery;146
8.6.5.3;6.5.3. Impact of viscosity;146
8.6.5.4;6.5.4. Impact of structure;147
8.6.5.5;6.5.5. In-mouth persistence;148
8.6.6;6.6. Future trends;148
8.6.6.1;6.6.1. Advanced analytical tools;148
8.6.6.2;6.6.2. Aligning analytical data with sensory data;149
8.6.6.3;6.6.3. Untargeted chemometrics approaches;149
8.6.6.4;6.6.4. Control mechanisms to modify aroma delivery;150
8.6.7;6.7. Sources of further information;150
8.6.8;References;150
9;Part Two: Generation of aroma;156
9.1;Chapter 7: Biogenesis of aroma compounds: flavour formation in fruits and
vegetables;158
9.1.1;7.1. Introduction;158
9.1.2;7.2. Biosynthesis of aroma compounds - general aspects;159
9.1.2.1;7.2.1. Primary and secondary aroma compounds;159
9.1.2.2;7.2.2. Identification of fruit and vegetable volatiles;159
9.1.2.3;7.2.3. Fruit flavour versus vegetable flavour: similarities and differences;160
9.1.2.4;7.2.4. Glycosidically bound aroma compounds;161
9.1.2.5;7.2.5. Beneficial health aspects of flavour compounds;162
9.1.3;7.3. Maturation and ripening processes;162
9.1.3.1;7.3.1. Climacteric and non-climacteric fruits;162
9.1.3.2;7.3.2. The role of ethylene;163
9.1.3.3;7.3.3. Influencing the storage period of fruits and vegetables;163
9.1.4;7.4. Formation pathways for flavour compounds;165
9.1.4.1;7.4.1. General aspects;165
9.1.4.2;7.4.2. Fatty acid metabolism;167
9.1.4.3;7.4.3. Amino acid pathway;168
9.1.4.4;7.4.4. Carbohydrate pathway;171
9.1.4.4.1;7.4.4.1. The formation and the role of terpenoid flavour compounds;171
9.1.4.4.2;7.4.4.2. The formation of furanones;173
9.1.4.5;7.4.5. Vegetable flavour derived from glucosinolates;174
9.1.5;7.5. Conclusions;174
9.2;Chapter 8: Thermal generation or aroma;182
9.2.1;8.1. Introduction;182
9.2.2;8.2. The Maillard reaction;183
9.2.2.1;8.2.1. Basic chemistry;183
9.2.2.1.1;8.2.1.1. Carbonyl-amine condensation;183
9.2.2.1.2;8.2.1.2. Keto-enol tautomerisation;183
9.2.2.1.3;8.2.1.3. Aldol condensation;185
9.2.2.1.4;8.2.1.4. Cyclisation and dehydration;185
9.2.2.1.5;8.2.1.5. Cleavage reactions;185
9.2.2.2;8.2.2. The early stage of the Maillard reaction;186
9.2.2.2.1;8.2.2.1. The sugar-amine condensation;186
9.2.2.2.2;8.2.2.2. The Amadori rearrangement;186
9.2.2.2.3;8.2.2.3. Influencing the early stage: the role of amino acid;187
9.2.2.2.4;8.2.2.4. Influencing the early stage: the role of sugar;189
9.2.2.3;8.2.3. The intermediate stage of the Maillard reaction;189
9.2.2.3.1;8.2.3.1. Sugar breakdown and dehydration;190
9.2.2.3.1.1;Low pH;190
9.2.2.3.1.2;High pH;190
9.2.2.3.1.3;Disaccharides;192
9.2.2.3.2;8.2.3.2. Strecker degradation;192
9.2.2.4;8.2.4. The final stages;194
9.2.2.4.1;8.2.4.1. Formation of pyrazines;194
9.2.2.4.2;8.2.4.2. Formation of pyrroles and pyridines;196
9.2.2.4.3;8.2.4.3. Formation of sulfur compounds;196
9.2.2.4.4;8.2.4.4. Aldol condensation;196
9.2.2.5;8.2.5. Generation of taste compounds;197
9.2.2.6;8.2.6. Generation of antioxidants;198
9.2.2.7;8.2.7. Generation of potentially harmful compounds;198
9.2.2.7.1;8.2.7.1. Acrylamide;199
9.2.2.7.2;8.2.7.2. Heterocyclic aromatic amines;200
9.2.2.8;8.2.8. Controlling the Maillard reaction;200
9.2.2.8.1;8.2.8.1. Choice of amino acid;200
9.2.2.8.2;8.2.8.2. Choice of sugar;201
9.2.2.8.3;8.2.8.3. Concentration of precursors;201
9.2.2.8.4;8.2.8.4. Changes in pH;202
9.2.2.8.5;8.2.8.5. Processing conditions: time, temperature, water activity and pressure;203
9.2.2.8.6;8.2.8.6. Interactions with other components of the food;203
9.2.2.9;8.2.9. Summary of the Maillard reaction;204
9.2.3;8.3. Lipid oxidation;204
9.2.3.1;8.3.1. Initiation;204
9.2.3.2;8.3.2. Generation of aroma compounds;204
9.2.4;8.4. Other reactions;206
9.2.4.1;8.4.1. Caramelisation;206
9.2.4.2;8.4.2. Ascorbic acid;207
9.2.4.3;8.4.3. Degradation of thiamine;207
9.2.4.4;8.4.4. Ferulic acid;207
9.2.5;8.5. Process flavours;208
9.2.5.1;8.5.1. The application of the Maillard reaction to produce process flavours;208
9.2.5.2;8.5.2. Examples of process flavours;209
9.2.5.3;8.5.3. Legislation;209
9.2.6;8.6. Summary and future work;212
9.2.7;References;212
9.3;Chapter 9: The role of sulfur chemistry in thermal generation of aroma;218
9.3.1;9.1. Introduction;218
9.3.2;9.2. The Maillard reaction;219
9.3.2.1;9.2.1. The Maillard reaction of cysteine;219
9.3.2.2;9.2.2. Interaction of the Maillard reaction and lipid oxidation;227
9.3.2.3;9.2.3. Stability of sulfur compounds;229
9.3.2.4;9.2.4. Cysteine S-conjugates from the Maillard reaction;230
9.3.3;9.3. The Strecker degradation;231
9.3.4;9.4. Thiamine degradation;232
9.3.5;9.5. Allium species;234
9.3.6;9.6. Roasted sesame seeds;236
9.3.7;9.7. Conclusion;237
9.3.8;References;237
9.4;Chapter 10: Predicting aroma formation with kinetic models;242
9.4.1;10.1. Introduction;242
9.4.2;10.2. Maillard reaction;243
9.4.3;10.3. Kinetics and modelling;247
9.4.4;10.4. Multiresponse modelling;248
9.4.4.1;10.4.1. Generation of a chemical mechanism of the reaction under study;249
9.4.4.2;10.4.2. Generation of a system of differential equations from the reactions that comprise the developed mechanism;249
9.4.4.3;10.4.3. Experiments and chemical analysis;249
9.4.4.4;10.4.4. Mathematical and statistical process;250
9.4.4.4.1;10.4.4.1. Regression analysis;250
9.4.4.4.2;10.4.4.2. The Bayesian approach;251
9.4.4.5;10.4.5. Model discrimination;252
9.4.4.6;10.4.6. Goodness of fit;252
9.4.4.7;10.4.7. Evaluation of the results and criticism of the initial mechanism/model;252
9.4.4.8;10.4.8. Straining the model/start a new modelling cycle;253
9.4.5;10.5. Some model studies on the Maillard reaction;254
9.4.6;10.6. Kinetics and modelling of flavour compounds;255
9.4.7;10.7. Future trends;259
9.4.7.1;10.7.1. Further reading;259
9.4.8;References;260
9.5;Chapter 11: Approaches to production of natural flavours;266
9.5.1;11.1. Introduction;266
9.5.1.1;11.1.1. Market for natural flavours;266
9.5.1.2;11.1.2. Regulatory aspects of natural status of flavour molecules in Europe and the United States;266
9.5.1.3;11.1.3. Some history on development of natural flavour substances;267
9.5.1.4;11.1.4. Basic pathways;268
9.5.2;11.2. Classical fermentation from a sugar source;269
9.5.2.1;11.2.1. Production of natural acids;269
9.5.2.2;11.2.2. Production of natural flavour chemicals from fusel oils;270
9.5.2.3;11.2.3. Production of other compounds;270
9.5.3;11.3. Microbial conversion of a natural precursor molecule;271
9.5.3.1;11.3.1. Production of lactones;271
9.5.3.2;11.3.2. Production of vanillin;274
9.5.3.3;11.3.3. Production of other flavour molecules by microbial conversion;274
9.5.4;11.4. Enzymatic conversion of a natural precursor molecule using a plant homogenate;275
9.5.4.1;11.4.1. Leaf aldehydes and alcohols;275
9.5.4.2;11.4.2. Other flavour molecules produced by enzymatic active plant homogenates;277
9.5.5;11.5. Fermentation from a sugar source using GMO;277
9.5.6;11.6. Conclusion;278
9.5.7;References;278
9.6;Chapter 12: Managing flavour changes during storage;280
9.6.1;12.1. Introduction;280
9.6.2;12.2. Lipid oxidation mechanism;280
9.6.2.1;12.2.1. Types of oxidation;280
9.6.2.2;12.2.2. Initiation reaction;281
9.6.2.3;12.2.3. Propagation;282
9.6.2.4;12.2.4. Termination;282
9.6.2.5;12.2.5. Photo-oxidation;283
9.6.2.6;12.2.6. Lipid oxidation kinetics;284
9.6.3;12.3. Impact of lipid oxidation on flavour;285
9.6.3.1;12.3.1. Volatile formation mechanism;285
9.6.3.2;12.3.2. Volatiles and rancidity;285
9.6.3.3;12.3.3. Oxidation volatiles and flavours;286
9.6.4;12.4. Analysis of lipid oxidation;287
9.6.4.1;12.4.1. Oxidation measurements;287
9.6.4.2;12.4.2. Rancidity measurements;288
9.6.4.3;12.4.3. Oxidative stability measurements;289
9.6.5;12.5. Prevention of lipid oxidation;290
9.6.5.1;12.5.1. Sequestrants;291
9.6.5.1.1;12.5.1.1. EDTA;291
9.6.5.1.2;12.5.1.2. Natural sequestrants;291
9.6.5.1.3;12.5.1.3. Miscellaneous sequestrants;291
9.6.5.2;12.5.2. Antioxidants;292
9.6.5.2.1;12.5.2.1. Synthetic antioxidants;292
9.6.5.2.2;12.5.2.2. Natural antioxidants;293
9.6.5.2.3;12.5.2.3. Natural extracts;294
9.6.5.3;12.5.3. Other stabilisation methods;296
9.6.6;12.6. Novel approaches for the prevention of oxidation;296
9.6.7;12.7. Future trends;298
9.6.8;12.8. Further reading;299
9.6.9;References;299
10;Part Three: Perception of flavour;302
10.1;Chapter 13: Interaction of aroma compounds with food matrices;304
10.1.1;13.1. Introduction;304
10.1.2;13.2. Thermodynamic and kinetic properties of aroma compounds;304
10.1.3;13.3. Physico-chemical interactions in simple systems;305
10.1.3.1;13.3.1. Protein-aroma interactions;305
10.1.3.1.1;13.3.1.1. Protein structure in relation to aroma binding;305
10.1.3.1.2;13.3.1.2. Effect of medium on protein-flavour interactions;307
10.1.3.1.3;13.3.1.2. Nature and strength of the interactions;308
10.1.3.2;13.3.2. Carbohydrate-aroma interactions;309
10.1.3.2.1;13.3.2.2. Effect of sugar;309
10.1.3.2.2;13.3.2.2. Starch-aroma interactions;309
10.1.3.2.3;13.3.2.3. Other carbohydrates;310
10.1.3.2.4;13.3.2.3. Mixtures of carbohydrates;310
10.1.3.3;13.3.2. Lipid-aroma interactions;311
10.1.3.3.1;13.3.2.1. Partitioning of aroma compounds between oil and air;311
10.1.3.3.2;13.3.2.2. Partitioning of aroma compounds between lipid and water phases;312
10.1.4;13.4. Physico-chemical interactions in multiphasic systems;313
10.1.4.1;13.4.1. Emulsions;313
10.1.4.2;13.4.2. Gelified systems;314
10.1.4.2.1;13.4.2.1. Aqueous systems;314
10.1.4.2.2;13.4.2.2. Emulsified systems;314
10.1.4.3;13.4.3. Model and real foods (example of dairy products);314
10.1.5;13.5. Incidence of aroma-matrix interactions on aroma release and perception in cheeses;316
10.1.5.1;13.5.1. In vivo aroma release as a function of cheese composition;316
10.1.5.2;13.5.2. Incidence on aroma perception;319
10.1.6;13.6. Conclusion and future trends;319
10.1.7;13.7. Sources of further information;319
10.1.8;References;320
10.2;Chapter 14: Taste receptors;328
10.2.1;14.1. Introduction;328
10.2.2;14.2. Tastants;328
10.2.3;14.3. Taste receptors: G protein-coupled receptors;338
10.2.3.1;14.3.1. Bitter taste receptors;338
10.2.3.2;14.3.2. Sweet taste receptors;341
10.2.3.3;14 3.3. Umami taste receptors;343
10.2.3.4;14.3.4. Transduction of bitter, sweet and umami stimuli;344
10.2.4;14.4. Taste receptors: ion channels;346
10.2.4.1;14.4.1. Salt taste transduction;346
10.2.4.2;14.4.2. Sour taste transduction;347
10.2.5;14.5. Taste modulators;347
10.2.6;14.6. Conclusion and future trends;350
10.2.7;References;351
10.3;Chapter 15: Umami compounds and taste enhancers;362
10.3.1;15.1. The molecular basis of umami taste perception;362
10.3.2;15.2. Umami taste perception at the receptor level;363
10.3.3;15.3. Identification of taste-active and taste-modulating compounds;364
10.3.4;15.4. Molecular features of umami compounds and taste enhancers;367
10.3.4.1;15.4.1. Nucleotides;367
10.3.4.2;15.4.2. Amides;371
10.3.5;15.5. Natural occurrence of umami compounds and taste enhancers;373
10.3.6;15.6. Summary and outlook: recent advances and trends in umami research;375
10.4;Chapter 16: Techniques in sensory analysis of flavour;384
10.4.1;16.1. Introduction to the fundamental types of sensory evaluation;384
10.4.2;16.2. Analytical versus synthetic measurement;384
10.4.3;16.3. Deciding on a sensory protocol;385
10.4.4;16.4. Analytical sensory techniques and their relevance to flavour evaluation;386
10.4.4.1;16.4.1. Discrimination tests;386
10.4.4.1.1;16.4.1.1. Non-directional and directional forced choice tests;387
10.4.4.1.2;16.4.1.2. Signal detection tests;388
10.4.4.1.3;16.4.1.3. Flavour omission tests;388
10.4.4.2;16.4.2. Descriptive sensory profiling methods;391
10.4.4.3;16.4.3. Psychophysical relationships and magnitude scaling;392
10.4.4.4;16.4.4. Time dependency methods;393
10.4.5;16.5. Individual differences in flavour perception;394
10.4.6;16.6. Conclusion;396
10.5;Chapter 17: Consumer perceptions of food and beverage flavour;400
10.5.1;17.1. Introduction;400
10.5.2;17.2. Multisensory integration and flavour perception;401
10.5.3;17.3. Consumer preferences;403
10.5.4;17.4. Individual differences in perception;403
10.5.4.1;17.4.1. Genetic variations in taste sensitivity;404
10.5.4.2;17.4.2. Thermal tasting;405
10.5.5;17.5. Consumer-oriented methods;406
10.5.5.1;17.5.1. Discrimination;406
10.5.5.2;17.5.2. Perceptual mapping methods;407
10.5.5.2.1;17.5.2.1. Free choice profiling;409
10.5.5.2.2;17.5.2.2. Sorting;410
10.5.5.2.3;17.5.2.3. Projective mapping (napping);411
10.5.5.2.4;17.5.2.4. Check-all-that-apply;412
10.5.6;17.6. Conclusion;412
10.5.7;References;413
10.6;Chapter 18: Physiological impacts of odour compounds;418
10.6.1;18.1. Introduction;418
10.6.2;18.2. Immediate processes and effects;418
10.6.2.1;18.2.1. Immediate physiological effects;418
10.6.2.2;18.2.2. Release, generation and transformation of chemosensorially active substances;419
10.6.2.3;18.2.3. Immediate interaction with physiological chemosensory systems;420
10.6.3;18.3. Post-inhalation and post-ingestion processes;422
10.6.3.1;18.3.1. Resorption and transformation in the airways;422
10.6.3.2;18.3.2. Dermal uptake;422
10.6.3.3;18.3.3. Passage through the gastrointestinal tract and resorption;423
10.6.3.4;18.3.4. Further metabolism and biotransformation processes;424
10.6.3.5;18.3.5. Accumulation and distribution in vivo;425
10.6.3.6;18.3.6. Excretion and exhalation;426
10.6.3.7;18.3.7. Post-inhalation and post-oral physiological effects;428
10.6.3.7.1;18.3.7.1. Metabotropic and ionotropic receptor effects;428
10.6.4;18.4. Conclusions;431
11;Index;440

Leseproben

Introduction
Donald S. Mottram, University of Reading, Reading, United Kingdom Humans have appreciated the flavour characteristics of foods for thousands of years, selecting foods based on their flavours or the flavours that could be generated during cooking or other processing. The human use of taste and smell for food selection likely goes back to a time before human settlements appeared, when the hunter-gatherer probably used his senses of taste and smell to select desirable fruits for consumption. Herbs and spices have been important commodities for thousands of years and a source of international trade. An early reference to spice traders can be found in the Bible, which describes how jealous brothers sold the young Joseph to traders: “A company of Ishmaelites came with their camels bearing spicery and balm and myrrh, going to carry it down to Egypt … and Joseph was sold [by his brothers] to the Ishmaelites for twenty pieces of silver” (Genesis 37 v 25–28). Trade in spices continued to be an important industry. The major sources of spices were India and southeast Asia, and it has been suggested that seeking new routes from western Europe to southeast Asia was one of the driving forces for the European naval explorations of the fifteenth and sixteenth centuries. As skills in the preparation and cooking of food developed, an understanding of how to provide desirable flavour characteristics became increasingly important. Herbs and spices are still very important ingredients for delivering flavour characteristics to foods, whether the food is prepared in the home or by food manufacturers. In addition to herbs and spices, the modern flavouring industry provides other natural flavours and nature-identical chemicals for use by the food industry. The annual turnover of the flavouring industry in 2013 was US$ 2.4 billion (source: http://www.leffingwell.com). Flavour can be defined as the sensation produced by a material taken into the mouth, and it is principally perceived by the chemical senses of taste and smell. But the sensation is also influenced by the textural and mouth-feel characteristics of the food. Our taste (gustation) and smell (olfaction) are very sensitive and only need low concentrations of compounds in foods to elicit a response. Some compounds can even produce a taste sensation at concentrations as low as 1 mg/L in water. However, our sense of smell is much more sensitive than our sense of taste, and some compounds can be detected in aqueous solution by the human olfactory organ at concentrations as low as 2 × 10- 8 mg/L. Such an extremely low concentration is somewhat difficult to comprehend, but to visualise it in a different way, this concentration represents approximately 5 µg of a substance dissolved in the water of an Olympic swimming pool. It is generally recognised that there are five basic tastes: salt, sweet, sour, bitter and umami. Sweet is characterised by sugars, such as glucose and sucrose, which have a taste threshold value of approximately 5000 mg/L, although artificial sweeteners, such as saccharin, have threshold values approximately 1000 times lower. Sweetness is the first taste recognised by babies, who detect and have a positive response to lactose in mothers’ milk. The salt taste is predominantly due to sodium chloride, which has a taste threshold value of 1000 mg/L. Compounds providing the sour taste in foods are principally the fruit acids, such as tartaric, citric and malic acids, and they have threshold values in the range 20–100 mg/L. The human response to bitter compounds is much more sensitive, however, with compounds such as quinine and caffeine having threshold values in the low mg/L range. Many alkaloids have strong bitter tastes, and many are toxic, so the human sensitivity to bitter compounds might be a defence mechanism to prevent harm through eating plants that contain toxic compounds. Prior to the discovery of the umami taste by Kikunae Ikeda in Japan in the early part of the twentieth century, it was generally accepted there were just four basic tastes and, indeed, outside Japan and southeast Asia, the widespread acceptance of umami as the fifth basic taste has only occurred in the last 25 years. This is particularly interesting because this taste has now become very important to chefs, as well as food companies, who wish to develop pleasant savoury flavours in their dishes. The taste is characterised by the sodium salt of the amino acid glutamic acid. Other naturally occurring umami compounds are the ribonucleotides found in meat and fish, such as inosine monophosphate and guanosine monophosphate. There is considerable evidence to show that a synergy exists between umami taste compounds so that a mixture of two or more compounds has a more intense taste than that predicted by the sum of their individual taste intensities. This provides opportunities to enhance the savoury flavour of meat through umami, by adding tomato or cheese, which have relatively high levels of monosodium glutamate, to meat dishes. For more information on umami compounds, see Chapter 15. Taste is perceived by the taste receptors located in the taste buds on the tongue and the sides of the mouth. All compounds with taste characteristics are water soluble because water acts as the carrier that transports the compounds in the food or beverage to the receptors. As a consequence, these compounds are nonvolatile. The biochemical mechanism of taste has been the subject of many studies in the past 20 years and a number of G-protein-coupled receptors have now been identified in human taste cells, which bind with taste compounds (this is discussed in Chapter 14). Although there are essentially five basic tastes, many hundreds of different odours can be detected. In addition, the threshold values for aroma compounds perceived by the odour receptor sites in the olfactory epithelium are much lower than the thresholds for taste receptors. Common aroma compounds, such as esters, aldehydes and terpenes, typically have odour threshold values in the range of 10–0.1 µg/L, but some compounds have even lower threshold values. 2-Methoxy-3-isobutylpyrazine, which has the typical aroma of bell (or sweet) peppers, has an odour threshold value of 1 × 10- 3 µg/L, and the value for bis(2-methyl-3-furyl) disulfide, with the characteristic aroma of cooked meat, is 2 × 10- 5 µg/L. It is obvious, therefore, that only very small quantities of aroma compounds are needed in foods to provide aroma to the food. Aroma compounds need to be volatile in order to be carried to the olfactory organ at the back of the nose by the air inhaled or exhaled during eating. Consequently, they are relatively insoluble in water and principally nonpolar, and they tend to have molecular weights of less than 250. A total of over 7000 volatile compounds have been reported in foods and beverages, although many have relatively high odour threshold values and thus do not contribute to the aroma of foods. Nevertheless, any one food may contain several hundred volatile compounds, many of which contribute to aroma. Depending on the profile of volatiles in a food, a particular compound may make different contributions to the aroma of different foods. Thus, both the qualitative and quantitative profiles of aroma compounds are important in determining the flavour of a particular food. The complexity of aroma, as compared to taste, means that the characteristic flavour of a particular food is largely determined by the profile of aroma compounds. This topic is discussed in Chapter 1. There is no general rule for the relationship between chemical structure and aroma. However, certain functional groups can be linked to classes of aromas. For example, esters usually have fruity aromas, and aliphatic aldehydes and alcohols with six carbons have green aromas. A very important class of aroma compounds is terpenes and sesquiterpenes. These are C10 and C15 aliphatic and alicyclic compounds, many of which are oxygenated. Many hundreds have been reported in plant tissue, and specific terpenes or groups of terpenes provide the aroma of herbs and spices, as well as citrus fruits. Sulfur-containing volatile compounds are among the most potent of aroma compounds. The biochemical and chemical pathways to flavour generation are numerous, and some are well established while many are more speculative. Taste compounds, such as sugars, amino acids and ribonucleotides, are important products of cell metabolism. However, only trace amounts of most aroma compounds are required to deliver flavour to foods and beverages, and therefore, they are quantitatively only minor components. In plant-derived foods most aroma compounds, or their precursors, are generated by enzyme-catalysed biochemical reactions. These enzymes may be endogenous or exogenous to the plant cell. For example, many esters, which have fruity aromas, are formed in the cell through a series of steps involving endogenous enzymes with amino acids and/or fatty acids as the initial reactants. On the other hand, the fresh green aroma of vegetables arises from the formation of C6 aldehydes and alcohols by the action of lipoxygenase enzymes, released from damaged cells, acting on fatty acids. More details of this process are given in Chapter 7. Fermentation involving yeasts and other microorganisms is also important for flavour generation in cheese and alcoholic beverages. For many foods, cooking is essential for making them digestible and generating flavour. The reactions leading to flavour in heated foods involve food...