Food Carbohydrate Chemistry

RONALD E. WROLSTAD, Ph.D. is Distinguished Professor of Food Science & Technology, Emeritus in the Department of Food Science & Technology, Oregon State University, Corvallis, OR. Dr. Wrolstad has authored over 150 professional publications, including 115 papers in refereed journals and 17 books or book chapters. He has served on the editorial boards of numerous scientific journals including Food Chemistry, Journal of Food Processing and Preservation, and Journal of Food Science Education, and has served as chair of the Food Chemistry Division and Fruit & Vegetable Division of the Institute of Food Technologists.

• Contributors xv Acknowledgments xviiIntroduction xix1 Classifying, Identifying, Naming, and Drawing Sugars and Sugar Derivatives 1Structure and Nomenclature of Monosaccharides 2Aldoses and Ketoses 2Configurations of Aldose Sugars 3D- vs. L-Sugars 3Different Ways of Depicting Sugar Structures 5Fischer, Haworth, Mills, and Conformational Structures 5Classifying Sugars by Compound Class—Hemiacetals, Hemiketals, Acetals, and Ketals 7Structure and Nomenclature of Disacchaarides 8Structure and Optical Activity 10A Systematic Procedure for Determining Conformation (C-1 or 1-C), Chiral Family (D or L), and Anomeric Form (or ) of Sugar Pyranoid Ring Structures 13Structure and Nomenclature of Sugar Derivatives with Relevance to Food Chemistry 14Glycols (Alditols) 14Glyconic, Glycuronic, and Glycaric Acids 15Deoxy Sugars 17Amino Sugars and Glycosyl Amines 17Glycosides 18Sugar Ethers and Sugar Esters 19Vocabulary 20References 212 Sugar Composition of Foods 23Introduction 23Sugar Content of Foods 24Composition of Sweeteners 24Cane and Beet Sugar 24Honey 26Starch-Derived Sweeteners 27Inulin Syrup 28Sugar Composition of Fruits and Fruit Juices 28Vocabulary 31References 313 Reactions of Sugars 35Introduction 35Mutarotation 35Oxidation of Sugars 39Glycoside Formation 40Acid Catalyzed Sugar Reactions 42Alkaline-Catalyzed Sugar Reactions 43Summary 45Vocabulary 47References 474 Browning Reactions 49Introduction 50Key Reactions in Maillard Browning 51Introductory Comments 51Sugar-Amino Condensation 51The Amadori and Heyn’s Rearrangements 53Dehydration, Enolization, and Rearrangement Reactions 54The Strecker Degradation 55Final Stages: Condensation and Polymerization 58An Alternate Free-Radical Mechanism for Nonenzymatic Browning 58Measurement of Maillard Browning 59Control of Maillard Browning 60Introductory Comments 60Water Activity 60The Importance of pH 61Nature of Reactants 62Temperature 65Oxygen 68Chemical Inhibitors 68Other Browning Reactions 68Caramelization 68Ascorbic Acid Browning 69Enzymatic Browning 69Assessing Contributing Factors to Nonenzymatic Browning 70Vocabulary 72References 725 Functional Properties of Sugars 77Introduction 77Taste Properties of Sugars 78The Shallenberger–Acree Theory for Sweetness Perception 80Sugar Solubility 83Crystallinity of Sugars 85Hygroscopicity 86Humectancy 87Viscosity 87Freezing Point Depression and Boiling Point Elevation 87Osmotic Effects 88Vocabulary 88References 886 Analytical Methods 91Introduction 91Physical Methods 92Refractometry 92Density 94Polarimetry 95Colorimetric Methods 95Total Sugars by Phenol-Sulfuric Acid 95Reducing Sugar Methods 96Chromatographic Methods 96Paper and Thin-Layer Chromatography 96Gas–Liquid Chromatography 97HPLC 100Enzymic Methods 102Carbon Stable-Isotopic Ratio Analysis (SIRA) 103References 1047 Starch in Foods 107Introduction 108Sources of Starch 108Molecular Structure of Starch 109Starch Granules 112Gelatinization and Pasting: The Cooking of Starch 113Retrogradation and Gelation: The Cooling of Cooked Starch 115Monitoring Starch Transitions 118Microscopy 118Viscometric Methods 118Differential Scanning Calorimetry 119Starch Hydrolytic Enzymes 120-Amylase 121-Amylase 122Modified Starches 122Physical Modifications 123Chemical Modifications 125Resistant Starch 127Concluding Remarks 129Vocabulary 129References 1318 Plant CellWall Polysaccharides 135Introduction: Why Plant Cell Walls are Important 135Cellulose 137Hemicelluloses 139Xyloglucans 139Heteroxylans 140(1→3),(1→4)--D-Glucans 140Mannans 141Pectic Polysaccharides 141Interactions Between Polysaccharides and Cellulose 143The Plant Cell Wall Structure 144Vocabulary 145References 1459 Nutritional Roles of Carbohydrates 147Introduction 147The Digestive Process: From the Bucchal Cavity through the Small Intestine 148Absorption of Sugars 149Sugar Metabolism 152The Large Intestine and the Digestive Process 153The Colon 153Intestinal Microflora 153Fate of Nonabsorbed Monosaccharides, Sugar Derivatives, and Oligosaccharides 155Dietary Fiber 158Carbohydrate Nutrition and Human Health 159Vocabulary 162References 163Appendices 165Unit 1. Laboratory/Homework Exercise—Building Molecular Models of Sugar Molecules 167Unit 2. Homework Exercise—Recognizing Hemiacetal, Hemiketal, Acetal, and Ketal Functional Groups 171Unit 3. Laboratory/Homework Exercise—Specification of Conformation (C-1 or 1-C), Chiral Family (D or L), and Anomeric Form (or ) of Sugar Pyranoid Ring Structures 175Unit 4. Demonstration of the Existence of Plane-Polarized Light and the Ability of Sugar Solutions to Rotate Plane-Polarized Light 181Unit 5. Laboratory Exercise—Sugar Polarimetry 183Unit 6. Laboratory Exercise or Lecture Demonstration—The Fehling’s Test for Reducing Sugars 187Unit 7. Laboratory Exercise—Student-Designed Maillard Browning Experiments 189Unit 8. Laboratory Exercise or Lecture Demonstration—Microscopic Examination of Starch 193Unit 9. Names and Structures of Oligosaccharides 197Index 211

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