Knowledge about vitamin bioavail-ability from food is essential for the estimation of dietary requirements.Equally important is knowledge of a vitamin’s stability toward post-harvest han
Trang 3Published in 2006 by
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Library of Congress Cataloging-in-Publication Data
Ball, G.F.M.
Vitamins in foods : analysis, bioavailability, and stability / by George F.M Ball.
p cm (Food science and technology ; 156) Includes bibliographical references and index.
ISBN 1-57444-804-8 (alk paper)
1 Food Vitamin content I Title II Food science and technology (Taylor & Francis) ; 156 TX553.V5B358 2005
Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com
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dk4945_Discl.fm Page 1 Wednesday, September 21, 2005 3:48 PM
Trang 4This work is dedicated to my wife and dearest friend, Kazuko (Kako)
Trang 6About the Author
George Ball has accumulated many years of commercial and researchlaboratory experience in pharmaceutical analysis, clinical analysis, bio-chemical analysis, and food analysis He has contributed to originalresearch publications relating to biochemistry (platelet function) andendocrinology (control of ovulation) and is the author of several booksand book chapters on vitamins He received the B.Sc honors degree inagricultural sciences from the University of Nottingham, UK in 1975
Trang 8Optimal vitamin status is a prerequisite for good health, and approved food fortification strategies are deemed necessary to ensureadequate intake of certain vitamins Knowledge about vitamin bioavail-ability from food is essential for the estimation of dietary requirements.Equally important is knowledge of a vitamin’s stability toward post-harvest handling of food, processing, storage, and preparation for con-sumption To acquire this knowledge, one must learn about vitaminchemistry and how the vitamin is absorbed and metabolized Successfulresearch into vitamin bioavailability and stability is entirely dependent
government-on the development and validatigovernment-on of suitable analytical methods.Vitamin bioavailability from food is subject to many variables imposed
by food constituents and the preparation of food Great progress hasbeen made over the past decade, largely attributable to innovativeanalytical methodology, but there are many inconsistencies and the con-tinuation of a multipronged research effort from independent laboratoriesmust be encouraged to achieve solid and vital data
I would like to acknowledge the expertise and diligence of Lynn Saliba
at the British Library
George F M Ball
Trang 10Chapter 1 Nutritional Aspects of Vitamins
1.1 Definition and Classification of Vitamins 3
1.2 Nutritional Vitamin Deficiency 4
1.3 Vitamin Requirements 4
1.4 Vitamin Enhancement of Foods 5
1.5 Stability of Vitamins 6
1.5.1 Water Activity and Lipid Oxidation 6
1.5.2 First-Order Kinetics 7
1.5.3 Effects of Food Processing on Vitamin Retention 9
1.5.3.1 Dehydration 9
1.5.3.2 Blanching 10
1.5.3.3 Canning 11
1.5.3.4 Pasteurization and Ultra-High-Temperature Processing 11
1.5.3.5 Microwave Heating 12
1.5.3.6 Hydrothermal Processes (Flaking, Puffing, and Extrusion) 13
1.5.3.7 Freezing 14
1.5.3.8 Irradiation 14
1.5.3.9 High Hydrostatic Pressure Treatment 15
1.5.3.10 Curing and Smoking 16
1.5.4 Milling 17
1.5.5 Effects of Food Storage on Vitamin Retention 17
1.5.6 Effects of Domestic Cooking on Vitamin Retention 17
References 18
Chapter 2 Intestinal Absorption and Bioavailability of Vitamins: Introduction 2.1 General Principles of Solute Translocation 23
2.2 Intestinal Absorption 24
2.2.1 The Villus 24
2.2.2 The Luminal Environment 25
2.2.3 Adaptive Regulation of Intestinal Nutrient Transport 25
Trang 112.2.3.1 Nonspecific Anatomical Adaptations to
Changing Metabolic Requirements and
Food Deprivation 25
2.2.3.2 Dietary Regulation of Intestinal Nutrient Carriers 26
2.2.4 Digestion, Absorption, and Transport of Dietary Fat 27
2.2.5 Transport of Glucose and Fructose: A Model for the Absorption of Some Water-Soluble Vitamins 28
2.2.6 Effects of Dietary Fiber on Absorption of Nutrients 30
2.3 Bioavailability 32
2.3.1 General Concepts 32
2.3.2 Methods for Estimating Vitamin Bioavailability in Human Subjects 33
2.3.2.1 Plasma Response 33
2.3.2.2 Urinary Excretion 34
2.3.2.3 Oral-Fecal Balance Studies and the Determination of Prececal Digestibility 34
2.3.2.4 Use of Stable Isotopes 35
References 36
Chapter 3 Vitamin A: Retinoids and the Provitamin A Carotenoids 3.1 Background 39
3.2 Chemical Structure, Biopotency, and Physicochemical Properties 40
3.2.1 Structure and Biopotency 40
3.2.1.1 Retinol 40
3.2.1.2 Provitamin A Carotenoids 41
3.2.2 Physicochemical Properties 43
3.2.2.1 Appearance and Solubility 43
3.2.2.2 Stability in Nonaqueous Solution 45
3.2.2.2.1 Retinoids 45
3.2.2.2.2 Carotenoids 45
3.3 Vitamin A in Foods 45
3.3.1 Occurrence 45
3.3.1.1 Vitamin A 46
3.3.1.2 Provitamin A Carotenoids 47
3.3.2 Stability 48
3.3.2.1 Introduction 48
3.3.2.2 Vitamin A in Milk 51
3.3.2.3 Supplemental Vitamin A in Corn Flakes and Rice 56
Trang 123.3.2.4 Provitamin A Carotenoids 57
3.3.3 Vitamin A Equivalency 60
3.3.4 Applicability of Analytical Techniques 61
3.4 Intestinal Absorption, Metabolism, and Transport 61
3.4.1 Absorption 62
3.4.2 Metabolic Events Within the Enterocyte 63
3.4.2.1 Esterification of Retinol 63
3.4.2.2 Conversion of Provitamin Carotenoids to Retinoids 63
3.4.3 Liver Uptake of Chylomicron Remnants and Storage of Vitamin A 66
3.4.4 Plasma Transport of Retinol and Carotenoids 66
3.4.5 Tissue Uptake and Metabolism of Retinol 67
3.5 Bioavailability 67
3.5.1 Introduction 67
3.5.2 In vivo Methods of Assessing b-Carotene Bioavailability 68
3.5.2.1 Use of Radioisotopes in Cannulated Patients 68
3.5.2.2 Animal Models 69
3.5.2.3 Serum, Plasma, or Chylomicron Responses not Involving Isotopic Tracers 69
3.5.2.4 Methods Involving Stable Isotopes 71
3.5.3 In vitro Methods of Assessing b-Carotene Bioaccessibility and Bioavailability 74
3.5.3.1 In vitro Digestion Methods to Assess b-Carotene Bioaccessibility 74
3.5.3.2 In vitro Studies of b-Carotene Absorption Using Caco-2 Cells 76
3.5.4 Host-Related Factors Affecting the Bioavailability of b-Carotene 77
3.5.5 Dietary Factors Affecting the Bioavailability of b-Carotene 77
3.5.5.1 Location of Carotenoids in the Plant Source 77
3.5.5.2 Food Matrix 78
3.5.5.3 Dietary Protein 80
3.5.5.4 Dietary Fat and Energy 81
3.5.5.5 Dietary Fiber 86
3.5.5.6 Plant Sterols 87
3.5.6 Conclusions 88
3.6 b-Carotene Supplementation 88
3.6.1 Effect of Vegetable Consumption on Vitamin A Status in Populations at Risk of Vitamin A Deficiency 88
Trang 133.6.2 Effects of b-Carotene Supplementation on
Breastmilk Carotenoids 90
References 92
Chapter 4 Vitamin D 4.1 Background 107
4.2 Chemical Structure, Biopotency, and Physicochemical Properties 108
4.2.1 Structure and Biopotency 108
4.2.2 Physicochemical Properties 108
4.2.2.1 Appearance and Solubility 108
4.2.2.2 Stability in Nonaqueous Solution 109
4.3 Vitamin D in Foods 110
4.3.1 Occurrence 110
4.3.2 Stability 112
4.3.3 Expression of Dietary Values 113
4.3.4 Applicability of Analytical Techniques 113
4.4 Intestinal Absorption, Transport, and Metabolism 114
4.5 Bioavailability 115
References 116
Chapter 5 Vitamin E 5.1 Background 119
5.2 Chemical Structure, Biopotency, and Physicochemical Properties 120
5.2.1 Structure 120
5.2.2 Biopotency 121
5.2.3 Physicochemical Properties 122
5.2.3.1 Appearance and Solubility 122
5.2.3.2 Stability in Nonaqueous Solution 122
5.2.3.3 In Vitro Antioxidant Activity 122
5.3 Vitamin E in Foods 123
5.3.1 Occurrence 123
5.3.2 Stability 126
5.3.3 Expression of Dietary Values 128
5.3.4 Applicability of Analytical Techniques 128
5.4 Intestinal Absorption and Transport 128
5.4.1 Absorption 129
5.4.2 Plasma Transport and Distribution 129
5.4.3 Preferential Secretion of 2R-a-Tocopherol Stereoisomers by the Liver 129
5.4.4 Storage 130
5.5 Bioavailability 130
5.5.1 Efficiency of Vitamin E Absorption 130
Trang 145.5.2 Effects of Polyunsaturated Fats on Vitamin E
Absorption 131
5.5.3 Effects of Dietary Fiber on Vitamin E Absorption 131
5.5.4 Effect of Plant Sterols on Vitamin E Bioavailability 132
5.6 Vitamin E Requirements 132
References 132
Chapter 6 Vitamin K 6.1 Background 137
6.2 Chemical Structure, Biopotency, and Physicochemical Properties 138
6.2.1 Structure and Biopotency 138
6.2.2 Physicochemical Properties 139
6.2.2.1 Appearance and Solubility 139
6.2.2.2 Stability in Nonaqueous Solution 139
6.3 Vitamin K in Foods 139
6.3.1 Occurrence 139
6.3.2 Stability 141
6.3.2.1 Effects of Hydrogenation 142
6.3.3 Applicability of Analytical Techniques 142
6.4 Intestinal Absorption and Transport 143
6.4.1 Absorption and Transport of Dietary Vitamin K 143
6.4.2 Bacterially Synthesized Menaquinones as a Possible Endogenous Source of Vitamin K 143
6.5 Bioavailability 145
References 146
Chapter 7 Thiamin (Vitamin B1) 7.1 Background 149
7.2 Chemical Structure, Biopotency, and Physicochemical Properties 149
7.2.1 Structure and Potency 149
7.2.2 Physicochemical Properties 150
7.2.2.1 Appearance and Solubility 150
7.2.2.2 Stability in Aqueous Solution 150
7.3 Thiamin in Foods 151
7.3.1 Occurrence 151
7.3.2 Stability 152
7.3.3 Applicability of Analytical Techniques 154
7.4 Intestinal Absorption 154
7.5 Bioavailability 155
7.5.1 Bioavailability of Thiamin in Foods 155
7.5.2 Antithiamin Factors 156
Trang 157.5.2.1 Thiaminases 156
7.5.2.2 Polyphenols 157
7.5.3 Effects of Alcohol 159
7.5.4 Effects of Dietary Fiber 160
References 160
Chapter 8 Flavins: Riboflavin, FMN, and FAD (Vitamin B2) 8.1 Background 165
8.2 Chemical Structure, Biopotency, and Physicochemical Properties 165
8.2.1 Structure and Potency 165
8.2.2 Physicochemical Properties 167
8.2.2.1 Appearance and Solubility 167
8.2.2.2 Stability in Aqueous Solution 167
8.3 Vitamin B2in Foods 168
8.3.1 Occurrence 168
8.3.2 Stability 169
8.3.3 Applicability of Analytical Techniques 171
8.4 Intestinal Absorption 171
8.4.1 Absorption of Dietary Vitamin B2 171
8.4.2 Absorption of Bacterially Synthesized Vitamin B2 in the Large Intestine 172
8.5 Bioavailability 173
References 173
Chapter 9 Niacin 9.1 Background 177
9.2 Chemical Structure, Biopotency, and Physicochemical Properties 178
9.2.1 Structure and Potency 178
9.2.2 Physicochemical Properties 179
9.2.2.1 Appearance, Solubility, and Other Properties 179
9.2.2.2 Stability in Aqueous Solution 179
9.3 Niacin in Foods 179
9.3.1 Occurrence 179
9.3.2 Stability 181
9.3.3 Applicability of Analytical Techniques 182
9.4 Intestinal Absorption 183
9.5 Bioavailability 183
9.5.1 Niacin 183
9.5.2 Tryptophan 187
References 187
Trang 16Chapter 10 Vitamin B6
10.1 Background 189
10.2 Chemical Structure, Biopotency, and Physicochemical Properties 190
10.2.1 Structure and Potency 190
10.2.2 Physicochemical Properties 191
10.2.2.1 Appearance and Solubility 191
10.2.2.2 Stability in Aqueous Solution 192
10.3 Vitamin B6in Foods 193
10.3.1 Occurrence 193
10.3.2 Stability 194
10.3.3 Applicability of Analytical Techniques 197
10.4 Intestinal Absorption 198
10.5 Bioavailability 199
10.5.1 Bioavailability of Vitamin B6in Foods 199
10.5.2 Effects of Alcohol 201
10.5.3 Effects of Dietary Fiber 201
10.5.4 Glycosylated Forms of Vitamin B6 202
References 205
Chapter 11 Pantothenic Acid 11.1 Background 211
11.2 Chemical Structure, Biopotency, and Physicochemical Properties 211
11.2.1 Structure and Potency 211
11.2.2 Physicochemical Properties 212
11.2.2.1 Appearance and Solubility 212
11.2.2.2 Stability in Aqueous Solution 213
11.3 Pantothenic Acid in Foods 213
11.3.1 Occurrence 213
11.3.2 Stability 213
11.3.3 Applicability of Analytical Techniques 216
11.4 Intestinal Absorption 216
11.4.1 Digestion and Absorption of Dietary Pantothenic Acid 216
11.4.2 Absorption of Bacterially Synthesized Pantothenic Acid in the Large Intestine 217
11.5 Bioavailability 217
References 218
Chapter 12 Biotin 12.1 Background 221
12.2 Chemical Structure, Biopotency, and Physicochemical Properties 221
Trang 1712.2.1 Structure and Potency 221
12.2.2 Physicochemical Properties 222
12.2.2.1 Appearance and Solubility 222
12.2.2.2 Stability in Aqueous Solution 223
12.3 Biotin in Foods 223
12.3.1 Occurrence 223
12.3.2 Stability 223
12.3.3 Applicability of Analytical Techniques 225
12.4 Intestinal Absorption 226
12.4.1 Digestion and Absorption of Dietary Biotin 226
12.4.2 Absorption of Bacterially Synthesized Biotin in the Large Intestine 227
12.5 Bioavailability 228
References 229
Chapter 13 Folate 13.1 Background 231
13.2 Chemical Structure, Biopotency, and Physicochemical Properties 232
13.2.1 Structure and Potency 232
13.2.2 Physicochemical Properties 233
13.2.2.1 Appearance, Solubility, and Ionic Characteristics 233
13.2.2.2 Stability in Aqueous Solution 234
13.3 Folate in Foods 236
13.3.1 Occurrence 236
13.3.2 Stability 238
13.3.3 Applicability of Analytical Techniques 244
13.4 Absorption, Transport, and Metabolism 245
13.4.1 Deconjugation of Polyglutamyl Folate 245
13.4.2 Absorption of Dietary Folate 246
13.4.3 Influence of Folate-Binding Protein on the Absorption of Folate from Milk 247
13.4.4 Adaptive Regulation of Folate Absorption 249
13.4.5 Salvage of Dietary 5-Methyl-5,6-DHF 249
13.4.6 Absorption of Bacterially Synthesized Folate in the Large Intestine 250
13.4.7 Plasma Transport and Intracellular Metabolism 251
13.4.8 Folate Homeostasis 251
13.5 Bioavailability 252
13.5.1 Introduction 252
13.5.2 Methods for Assessing Folate Bioavailability 252
13.5.2.1 Plasma Response 252
Trang 1813.5.2.2 Stable-Isotopic Methods 253
13.5.2.3 Use of Ileostomy Subjects 255
13.5.3 Inherent Bioavailability of Monoglutamyl and Polyglutamyl Folates 256
13.5.4 Bioavailability of Naturally Occurring Folate in Fruits and Vegetables 257
13.5.5 Bioavailability of Folate in Milk 258
13.5.6 Effects of Soluble Food Components on Folate Bioavailability 260
13.5.7 Effects of Dietary Fiber on Folate Bioavailability 262
13.5.8 Bioavailability of Folate in Fortified Foods 263
13.5.9 Effects of Alcohol on Folate Status 264
References 264
Chapter 14 Vitamin B12(Cobalamins) 14.1 Background 275
14.2 Chemical Structure, Biopotency, and Physicochemical Properties 276
14.2.1 Structure and Potency 276
14.2.2 Physicochemical Properties 277
14.2.2.1 Appearance and Solubility 277
14.2.2.2 Stability in Aqueous Solution 278
14.3 Vitamin B12in Foods 278
14.3.1 Occurrence 278
14.3.2 Stability 279
14.3.3 Applicability of Analytical Techniques 281
14.4 Absorption and Conservation 281
14.4.1 Digestion and Absorption of Dietary Vitamin B12 282
14.4.2 Conservation of Vitamin B12 283
14.5 Bioavailability 283
14.5.1 Efficiency of Absorption 283
14.5.2 Bioavailability Studies 284
14.5.2.1 Effects of Dietary Fiber 284
14.5.2.2 Effects of Alcohol 284
14.5.2.3 Effects of Smoking 285
References 285
Chapter 15 Vitamin C 15.1 Background 289
15.2 Chemical Structure, Biopotency, and Physicochemical Properties 290
15.2.1 Structure and Potency 290
Trang 1915.2.2 Physicochemical Properties 291
15.2.2.1 Solubility and Other Properties 291
15.2.2.2 Stability in Aqueous Solution 292
15.3 Vitamin C in Foods 292
15.3.1 Occurrence 292
15.3.2 Stability 294
15.3.3 Applicability of Analytical Techniques 299
15.4 Intestinal Absorption 300
15.4.1 General Principles 300
15.4.2 Transport Mechanisms 301
15.4.2.1 Ascorbic Acid 301
15.4.2.2 Dehydroascorbic Acid 302
15.4.3 Efficiency of Ascorbate Absorption in Humans 302
15.5 Bioavailability 303
15.5.1 Bioavailability of Vitamin C in Foods 303
15.5.2 Effects of Dietary Fiber 304
15.5.3 Effects of Alcohol 305
References 305
Part II Analysis of Vitamins Chapter 16 Analytical Considerations 16.1 Bioassays 311
16.2 In Vitro Analytical Techniques 312
16.3 Analytical Approach 312
16.4 Preparation of Sample Extracts for Analysis 313
16.4.1 Extraction 314
16.4.2 Cleanup 314
16.5 Method Evaluation 314
16.5.1 Measurement Value and Uncertainty 314
16.5.2 Quality Assurance 316
16.5.3 Food Reference Materials 316
16.5.4 Method Validation 318
References 320
Chapter 17 Extraction Techniques for the Water-Soluble Vitamins 17.1 Vitamin B1 321
17.2 Vitamin B2 322
17.3 Niacin 323
17.4 Vitamin B6 326
Trang 2017.5 Pantothenic Acid 328
17.6 Biotin 328
17.7 Folate 329
17.8 Vitamin B12 331
17.9 Vitamin C 332
References 333
Chapter 18 Microbiological Methods for the Determination of the B-Group Vitamins 18.1 Introduction 339
18.2 General Principles 339
18.2.1 Turbidimetric Methods 339
18.2.2 Methods Based on the Measurement of Metabolic Carbon Dioxide 341
18.3 Conventional Turbidimetric Method Using Test Tubes 342
18.3.1 Summary 342
18.3.2 Laboratory Facilities and Cleaning of Glassware 343
18.3.3 Media 344
18.3.4 General Assay Procedure 344
18.3.4.1 Maintenance of Stock Cultures 345
18.3.4.2 Preparation of the Inoculum Culture 346
18.3.4.3 Preparation of the Assay (Basal) Medium 347
18.3.4.4 Extraction of the Vitamin from the Test Material 348
18.3.4.5 Setting Up the Assay 348
18.3.4.6 Quantification 349
18.3.5 Partial Automation of the Assay Procedure 350
18.4 Turbidimetric Method Using Microtiter Plates 350
18.5 Assays of Individual B-Group Vitamins 351
18.5.1 Vitamin B1 351
18.5.2 Vitamin B2 352
18.5.3 Niacin 354
18.5.3.1 Determination of Total Niacin 354
18.5.3.2 Determination of Bound Nicotinic Acid 355
18.5.3.3 Determination of Added Nicotinic Acid 356
18.5.4 Vitamin B6 356
18.5.5 Pantothenic Acid 359
18.5.6 Biotin 360
18.5.7 Folate 360
18.5.8 Vitamin B12 361
References 363
Trang 21Chapter 19 Physicochemical Analytical Techniques
(Excluding HPLC)
19.1 AOAC Titrimetric Method for Vitamin C 369
19.2 Direct Spectrophotometric Determination of Vitamin C 372
19.3 Colorimetric Methods for Niacin and Vitamin C 373
19.3.1 Determination of Niacin by the Ko¨nig Reaction (AOAC Method) 373
19.3.2 Colorimetric Methods for Vitamin C 374
19.4 Fluorometric Methods for Thiamin, Riboflavin, Vitamin B6, and Vitamin C 375
19.4.1 Thiamin (AOAC Method) 375
19.4.2 Riboflavin (AOAC Method) 375
19.4.3 Vitamin B6 376
19.4.4 Vitamin C (AOAC Method) 377
19.5 Enzymatic Methods for Nicotinic Acid and Ascorbic Acid 378
19.5.1 Nicotinic Acid 378
19.5.2 Ascorbic Acid 379
19.6 Continuous-Flow Analysis 380
19.6.1 Segmented-Flow Methods 380
19.6.2 Flow-Injection Analysis 380
19.6.3 Applications to Food Analysis 381
19.6.3.1 Fat-Soluble Vitamins 381
19.6.3.2 Thiamin 381
19.6.3.3 Riboflavin 382
19.6.3.4 Thiamin and Riboflavin Simultaneously 382
19.6.3.5 Niacin 382
19.6.3.6 Vitamin C 383
19.7 Gas Chromatography 385
19.7.1 Principle 385
19.7.2 Column Technology 385
19.7.3 Detectors 386
19.7.4 Derivatization Techniques 386
19.7.5 Quantification 387
19.7.6 Applications to Food Analysis 387
19.7.6.1 Vitamin E 387
19.7.6.2 Thiamin 388
19.7.6.3 Niacin 388
19.7.6.4 Vitamin B6 388
19.7.6.5 Pantothenic Acid 389
19.8 Supercritical Fluid Chromatography 390
19.8.1 Principle 390
19.8.2 Instrumentation 391
Trang 2219.8.3 Columns 39319.8.4 Applications to Food Analysis 39419.9 Capillary Electrophoresis 39419.9.1 Principle 39419.9.2 Capillary Zone Electrophoresis 39619.9.3 Micellar Electrokinetic Capillary Chromatography 39619.9.4 Operational Aspects 39719.9.5 Applications to Food Analysis 399
19.9.5.1 Thiamin 39919.9.5.2 Riboflavin, FMN, and FAD 39919.9.5.3 Niacin 40619.9.5.4 Vitamin C 408References 409Chapter 20 Determination of the Fat-Soluble Vitamins by HPLC20.1 Nature of the Sample 41920.2 Extraction Procedures 41920.2.1 Alkaline Hydrolysis (Saponification) 419
20.2.1.1 Vitamin A 42120.2.1.2 Carotenoids 42220.2.1.3 Vitamin D 42220.2.1.4 Vitamin E 42320.2.2 Alcoholysis 42420.2.3 Enzymatic Hydrolysis 42420.2.4 Direct Solvent Extraction 425
20.2.4.1 Vitamin A and Carotene 42620.2.4.2 Carotenoids 42720.2.4.3 Vitamin D 42720.2.4.4 Vitamin E 42820.2.4.5 Vitamin K 42820.2.5 Matrix Solid-Phase Dispersion 42920.2.6 Supercritical Fluid Extraction 430
20.2.6.1 Principle 43020.2.6.2 Instrumentation 43020.2.6.3 Applications 43120.3 Cleanup Procedures 43520.3.1 Precipitation of Sterols 43620.3.2 Open-Column Chromatography 436
20.3.2.1 Magnesia 43620.3.2.2 Alumina 43620.3.2.3 Silica Gel 43720.3.3 Solid-Phase Extraction 437
20.3.3.1 General Considerations 43720.3.3.2 Application in Vitamin D Determinations 438
Trang 2320.4 HPLC Systems 43920.4.1 Principle 43920.4.2 Explanations of Chromatographic Terms 440
20.4.2.1 Retention 44020.4.2.2 Separation 44020.4.2.3 Resolution 44120.4.2.4 Efficiency 44220.4.3 The Column 44220.4.4 Chromatographic Modes 444
20.4.4.1 Normal-Phase Chromatography 444
20.4.4.1.1 Adsorption
Chromatography 44420.4.4.1.2 Polar Bonded-Phase
Chromatography 44720.4.4.2 Reversed-Phase Chromatography 44820.4.4.3 Two-Dimensional HPLC 45220.4.5 Detection Systems 453
20.4.5.1 Introduction 45320.4.5.2 Absorbance Detection 45420.4.5.3 Fluorescence Detection 45520.4.5.4 Electrochemical Detection 45620.4.5.5 Mass Spectrometry 45720.5 Applications of HPLC 45720.5.1 Vitamin A 457
20.5.1.1 Detection 45720.5.1.2 Quantification 46320.5.1.3 Normal-Phase Separations 46520.5.1.4 Reversed-Phase Separations 46620.5.2 Provitamin A Carotenoids 469
20.5.2.1 Sources of Variation in the
Methodology 46920.5.2.2 Detection 46920.5.2.3 Potential Problems with the
Chromatography 47220.5.2.4 Normal-Phase Separations 47420.5.2.5 Reversed-Phase Separations 475
20.5.2.5.1 C18-Bonded Phases 47520.5.2.5.2 C30-Bonded Phases 48620.5.3 Vitamin D 489
20.5.3.1 Detection 48920.5.3.2 Quantification 48920.5.3.3 Cleanup Procedures 49920.5.3.4 Normal-Phase Separations 50020.5.3.5 Reversed-Phase Separations 500
Trang 2420.5.4 Vitamin E 505
20.5.4.1 Detection 50620.5.4.2 Quantification 51020.5.4.3 Normal-Phase Separations 51120.5.4.4 Reversed-Phase Separations 52620.5.5 Vitamin K 527
20.5.5.1 Detection 52820.5.5.2 Normal-Phase Separations 54020.5.5.3 Reversed-Phase Separations 54120.5.6 Simultaneous Determination of Two or
Three Vitamins 54620.5.6.1 Normal-Phase Separations 54920.5.6.2 Reversed-Phase Separations 562References 567
Chapter 21 Determination of the Water-Soluble
Vitamins by HPLC
21.1 HPLC Systems 58521.1.1 The Column 58521.1.2 Chromatographic Modes 585
21.1.2.1 Ion Exchange Chromatography 58521.1.2.2 Ion Exclusion Chromatography 58721.1.2.3 Reversed-Phase Chromatography 58821.1.2.4 Reversed-Phase Ion-Pair
Chromatography 58921.1.3 Derivatization 59121.2 Applications of HPLC 59221.2.1 Thiamin 592
21.2.1.1 Detection 59221.2.1.2 Methodology 59421.2.2 Vitamin B2 598
21.2.2.1 Detection 59821.2.2.2 Methodology 60021.2.3 Niacin 612
21.2.3.1 Detection 61221.2.3.2 Methodology 61221.2.4 Vitamin B6 624
21.2.4.1 General Considerations 62421.2.4.2 Detection 62521.2.4.3 Methodology 62621.2.5 Pantothenic Acid 638
21.2.5.1 Detection 63821.2.5.2 Applications 639
Trang 2521.2.6 Biotin 645
21.2.6.1 Detection 64521.2.6.2 Application 64621.2.7 Folate 646
21.2.7.1 General Considerations 64621.2.7.2 Cleanup Procedures 64821.2.7.3 Detection 65021.2.7.4 Methodology 65321.2.8 Vitamin B12 67621.2.9 Vitamin C 677
21.2.9.1 Detection 67721.2.9.2 Methodology 68221.2.10 Multiple Vitamin Analyses 701
21.2.10.1 Thiamin and Riboflavin 70121.2.10.2 Riboflavin and Pyridoxine 71521.2.10.3 Nicotinamide and Pyridoxine 71521.2.10.4 Three or More Vitamins 716References 720Chapter 22 Biospecific Methods for Some of the
B-Group Vitamins
22.1 Introduction 73522.2 Immunoassays 73522.2.1 The Immunological Reaction 73522.2.2 Radioimmunoassay 737
22.2.2.1 Principle 73722.2.2.2 Determination of Pantothenic Acid 73722.2.3 Enzyme-Linked Immunosorbent Assay 738
22.2.3.1 Principle 73822.2.3.2 Determination of Pantothenic Acid 74022.2.3.3 Determination of Vitamin B6 74122.3 Protein-Binding Assays 74122.3.1 Radiolabeled Protein-Binding Assays 741
22.3.1.1 Principle 74122.3.1.2 Determination of Biotin 74322.3.1.3 Determination of Folate 74322.3.1.4 Determination of Vitamin B12 74522.3.2 Enzyme-Labeled Protein-Binding Assays 747
22.3.2.1 General Procedure 74722.3.2.2 Determination of Biotin 74722.3.2.3 Determination of Folate 74722.3.2.4 Determination of Vitamin B12 74822.4 Biomolecular Interaction Analysis 74922.4.1 Principle 749
Trang 2622.4.2 Biosensor-Based Immunoassay for Supplemental
Biotin and Folate 75022.4.3 Biosensor-Based Protein-Binding Assay for
Supplemental and Endogenous Vitamin B12 751References 752Chapter 23 Summarized Appraisal of Analytical Techniques
23.1 Microbiological Assays 75723.2 High-Performance Liquid Chromatography 75823.2.1 Introduction 75823.2.2 Fat-Soluble Vitamins 759
23.2.2.1 Vitamin A 75923.2.2.2 Carotenoids 75923.2.2.3 Vitamin D 76023.2.2.4 Vitamin E 76023.2.2.5 Vitamin K 76023.2.3 Water-Soluble Vitamins 761
23.2.3.1 Thiamin and Flavins 76123.2.3.2 Niacin 76223.2.3.3 Vitamin B6 76223.2.3.4 Pantothenic Acid 76323.2.3.5 Biotin 76323.2.3.6 Folate 76323.2.3.7 Vitamin C 76323.3 Supercritical Fluid Chromatography 76423.4 Capillary Electrophoresis 76423.5 Flow-Injection Analysis 76523.6 Biospecific Methods 76523.7 Evaluation of Vitamin Bioavailability From Food
Analysis Data 76723.7.1 Fat-Soluble Vitamins 76723.7.2 Water-Soluble Vitamins 767
23.7.2.1 Thiamin 76723.7.2.2 Vitamin B2 76823.7.2.3 Niacin 76823.7.2.4 Vitamin B6 76923.7.2.5 Pantothenic Acid 76923.7.2.6 Biotin 76923.7.2.7 Folate 76923.7.2.8 Vitamin B12 77023.7.2.9 Vitamin C 770References 770Index 777
Trang 28Part I
Properties of Vitamins
Trang 30Nutritional Aspects of Vitamins
1.1 Definition and Classification of Vitamins
Vitamins are a group of organic compounds that are, in very smallamounts, essential for the normal functioning of the human body Theyhave widely varying chemical and physiological functions and arebroadly distributed in natural food sources Thirteen vitamins are recog-nized in human nutrition and these may be conveniently classified intotwo groups according to their solubility The fat-soluble vitamins arerepresented by vitamins A, D, E, and K; also included are the 50 or socarotenoids that possess varying degrees of vitamin A activity Thewater-soluble vitamins comprise vitamin C and the members of thevitamin B group, namely thiamin (vitamin B1), riboflavin (vitamin B2),niacin, vitamin B6, pantothenic acid, folate, and vitamin B12 Thissimple classification reflects to some extent the bioavailability of the vita-mins, as the solubility affects their mode of intestinal absorption and theiruptake by tissues The solubility properties also relate to the distribution
of vitamins in the various food groups, and have a direct bearing on theanalytical methods employed
For many of the vitamins, biological activity is attributed to a number
of structurally related compounds known as vitamers The vitamerspertaining to a particular vitamin display, in most cases, similar quali-tative biological properties to one another, but, because of subtledifferences in their chemical structures, exhibit varying degrees ofpotency Provitamins are vitamin precursors, that is, naturally occurringsubstances which are not vitamins themselves, but which can beconverted into vitamins by normal body metabolism
Most of the vitamins are absolutely essential in the human diet becausethe body tissues cannot synthesize them Two notable exceptions arevitamin D and niacin Cutaneous synthesis of vitamin D depends onadequate exposure of the skin to sunlight, and the synthesis of niacindepends on a sufficient intake of its amino acid precursor, tryptophan,bound within protein Plants have the ability to synthesize vitamins,except for vitamin B12, and serve as primary sources of these dietaryessentials
3
Trang 311.2 Nutritional Vitamin Deficiency
Several B-group vitamins serve as coenzymes for enzymes that function
in the catabolism of foodstuffs to produce energy for the organism Atypical coenzyme consists of a protein (apoenzyme) to which thevitamin is attached The vitamin portion of the coenzyme is usuallyresponsible for the attachment of the enzyme to the substrate If thespecific vitamin is not available to form the coenzyme, the sequence ofchemical changes in the metabolic process cannot proceed and theproduct whose change is blocked accumulates in the tissues: alternatively,metabolism is diverted to another pathway
For some B-group vitamins, clinical deficiency results in a biochemicaldefect, which is manifested as a disease with characteristic symptoms.Other vitamins have less dramatic deficiency symptoms in humans, buttheir deficiency in certain animal species may give rise to distinctive signs.Some human individuals can benefit from vitamin supplements, indicatingthat they may have been subclinically vitamin deficient to begin with.The causes of nutritional vitamin deficiency are any one or combination
of the following: inadequate ingestion, poor absorption, inadequateutilization, increased requirement, increased excretion, and increased cat-abolism The capacity of the body to store vitamins is another factor:humans can store thiamin for only about 2 weeks, whereas vitamin B12
can be stored in the liver for several years
Metabolic processes must respond to the immediate needs of the bodyand therefore vitamin requirements are subject to continuous variationbetween certain limits The Food and Nutrition Board of the Institute ofMedicine in the U.S defines a requirement as the lowest continuingintake level of a nutrient that, for a specific indicator of adequacy, willmaintain a defined level of nutriture in an individual A recommendeddietary allowance (RDA) of a nutrient is the average daily dietaryintake level that is sufficient to meet the requirement of nearly all(97 –98%) apparently healthy individuals in a particular life stage andgender group The RDA is derived from an estimated average require-ment (EAR), which is an estimate of the intake at which the risk of inade-quacy to an individual is 50% RDAs have been published for vitamins A,
D, E, and K, thiamin, riboflavin, niacin, vitamin B6, folate, vitamin B12, andvitamin C In the case of pantothenic acid and biotin, there is insufficientevidence to calculate an EAR, and a reference adequate intake (AI) is
Trang 32provided instead of an RDA The AI is a value based on experimentallyderived intake levels or approximations of observed mean nutrientintakes by a group (or groups) of apparently healthy people [1].
The terms restoration, fortification, enrichment, standardization, andnutrification have been used to describe various ways of enhancing thevitamin content of foods [2]
Restoration involves the replacement, in full or in part, of vitamin lossesincurred during processing The addition of vitamins A and D toskimmed milk powder, and of vitamin D to evaporated milk, areexamples of nonlegislative vitamin restoration in the U.K Other examplesare the replacement of B-group vitamins in flour to compensate for thelosses incurred in the milling of cereals to low extraction rates, and theaddition of vitamin C to instant potato
Fortification refers to the addition of vitamins to foods that are suitablecarriers for a particular vitamin, but which do not necessarily containthat vitamin naturally It is especially carried out to fulfill the role of afood in the diet Thus margarine is fortified with vitamin A in manycountries to replace the vitamin A that is lost from the diet when margar-ine is substituted for butter Vitamin D is added to margarine at higherlevels than found in butter as a public health measure, as the extra isconsidered necessary for the population as a whole In the U.S., fortifica-tion of cereals and grains with folic acid began in 1996 and, since January
1998, all cereal grain products are fortified with 140 mg of folic acid/100 g
In the U.K., fortification of foods with folic acid is still voluntary.Enrichment refers to the addition of vitamins above the initial natural levels
to make a product more marketable Standardization refers to additionsdesigned to compensate for natural fluctuations in vitamin content Forinstance, milk and butter are subject to seasonal variations in their vitamin
A and D contents, and hence these vitamins are added to some dairyproducts to maintain constant levels Nutrification means the addition ofvitamins to formulated or fabricated foods marketed as meal replacers.Vitamins are also added to perform specific processing functions Forinstance, b-carotene (the principal source of dietary vitamin A) is added
to products such as pasta, margarine, cakes, and processed cheeses toimpart color Vitamin E and vitamin C (in the form of ascorbyl palmitate)can be used as antioxidants to stabilize pure oils and fats Ascorbic acid isused for a variety of purposes in food processing, such as a reducing agentinvolved in the formation of the cured meat color in the curing of baconand ham
Vitamins in Foods: Analysis, Bioavailability, and Stability 5
Trang 331.5 Stability of Vitamins
New food product development aims to retain as much of the naturallyoccurring vitamin content as possible, to protect added vitamins, and tominimize the appearance of undesirable breakdown products Factorsthat play a role in the degradation of vitamins during processing andstorage include temperature, air or oxygen, light, moisture content,water activity, pH, degradative enzymes, and metal trace elements,particularly iron and copper Ryley et al [3] discussed the use of kineticdata and mathematical models for predicting vitamin retention in foodprocessing
1.5.1 Water Activity and Lipid Oxidation
The water activity of a food is one of the primary factors determining therate of food deterioration by various biochemical reactions Raw foodswith a high content of active water, such as leafy vegetables and meat,deteriorate in only a few days, whereas dry seeds, containing only struc-tural water, can be stored for years under proper conditions
Water activity measures the availability of the water present in thesystem: it is more closely related to the physical and chemical properties
of food than is total moisture content Within the heterogeneous foodmatrix, the reactivity of each constituent is influenced by its affinity forsurrounding water molecules and the competing influences of neighbor-ing hydrophilic or hydrophobic chemical groups Changes in the environ-ment, such as heat, light, pressure, pH, additives, and modification ofparticle size, may alter the molecular state of water, and thereby influenceconstituent reactivities and functional properties
The total water-binding energies of constituent chemical groups arereflected in the equilibrium water vapor pressure or absolute humidity
of the food material At constant temperature, the vapor pressure may
be expressed as equilibrium relative humidity (ERH) or the related gous water activity Water activity (Aw) can be defined as the ratio of theequilibrium vapor pressure exerted by the food material ( p) to the vaporpressure of pure water ( p0) at the same temperature:
Trang 34means of evaluating water-binding activity The nonlinear, generally moidal relationship between Awand total moisture content, expressed as
sig-a moisture sorption isotherm, is sig-a fundsig-amentsig-al chsig-arsig-acteristic of sig-a foodproduct [4]
A low water activity (Aw,0.6) does not permit microbial or enzymaticactivity It is generally accepted that growth of bacteria and most yeastsvirtually ceases at Aw,0.9, while molds do not grow at Aw,0.7 [5].The presence of water has a profound effect on lipid oxidationhas dis-cussed by Labuza [6] This has relevance to vitamin A and carotenoids,which undergo coupled oxidation in the presence of lipids The kinetics
of lipid oxidation are best studied in model systems using a swellablesolid matrix, since the variables can be controlled At Aw¼ 0 (as in a dehy-drated food), lipid oxidation is rapid, but the rate of oxidation decreases
as the water activity increases up to Aw¼ 0.5, where a leveling-off occurs.The protective effect of water within this range of water activity may bedue to two mechanisms working together First, hydrogen bondingtakes place between water and lipid hydroperoxides produced duringthe propagation stage of lipid peroxidation This bonding prevents themetal-catalyzed decomposition of the hydroperoxides into peroxyl andalkoxyl radicals that intensify propagation of the chain reaction.Second, hydration of metal catalysts makes them less effective throughchanges in their coordination sphere
In the intermediate moisture range of Aw¼ 0.55–0.85, the solvent andmobilization properties of water become dominant, and lipid oxidationincreases with increasing water activity The catalysts present are moreeasily mobilized and swelling of the solid matrix exposes new catalyticsites This detrimental effect of water has been confirmed in actualintermediate moisture foods [7]
As might be expected from the effect of water on lipid oxidation, theloss of all-trans-retinol suspended on microcrystalline cellulose inthe dark, in air, increased with increasing water activity in the range ofintermediate-moisture foods (Aw¼ 0.4–0.75) [8] In contrast, increasingthe water activity from 0 to 0.73 decreased the rate of b-carotene degra-dation in the dark [9] A protective effect of water against oxidation ofcarotenoids in the intermediate-moisture region was also observed byRamakrishnan and Francis [10] This difference in behavior betweenretinol and b-carotene can possibly be attributed to the poorer solubility
of b-carotene in water
1.5.2 First-Order Kinetics
The analytical approach in calculating and predicting food qualitydeterioration involves a kinetic/mathematical model The model mayVitamins in Foods: Analysis, Bioavailability, and Stability 7
Trang 35include equations of mass and energy balance, thermodynamics, port and chemical properties, and coefficients These equations havebeen simplified for specific conditions Saguy and Karel [11] produced astatus report on the modeling of quality deterioration during food proces-sing and storage.
trans-Most reactions involving the deterioration of a nutrient fit a first-ordermathematical expression:
dC
where C is the nutrient concentration at a given reaction time (t), and k
is the degradation reaction rate constant When Equation (1.1) is grated, and log (C/C0) versus t is plotted, the slope of the straight lineobtained defines the rate constant (k), where C0 is the initial concen-tration of nutrient
inte-As an example, consider the effect of microwave processing on soluble vitamins, as carried out by Okmen and Bayindirli [12] Vitaminsolutions were heated at constant temperatures of 60, 70, 80 and 908C inthe microwave oven Aliquots (1 ml) were taken from the heat-treatedsamples after 20, 40, 60 and 80 min intervals and analyzed for vitaminconcentration The first-order reaction rate constants at the four differenttemperatures were calculated from the slopes of the log (C/C0) versus tplots shown in Figure 1.1
water-Other reaction orders besides first are possible A zero-order reactionoccurs if the loss of nutrient is so small in the time period studied thatthe value of C does not change significantly Therefore, the right-handside of Equation (1.2) is a constant [13] Ascorbic acid oxidation inliquid infant formula under limited presence of dissolved oxygen takesplace by a second-order reaction [14]
0 –0.02
Int J Food Prop., 2 (3), 255, 1999 Copyright 1999 With permission.)
Trang 361.5.3 Effects of Food Processing on Vitamin Retention
Commercial food processing preserves food quality and extends shelf life
by destruction of food-spoilage microorganisms and certain endogenousenzymes, which could otherwise promote spoilage and/or reducenutritive value Since all processed foods have to be stored until theyare consumed, proper food packaging is essential to maintain pre-servation Time and temperature during processing and storage areclosely controlled in good manufacturing practice Distribution controls,however, are less stringent, except for very perishable products
The main factors contributing to vitamin losses are oxidation (airexposure), heat (temperature and time), catalytic effect of metals, pH,action of enzymes, moisture, irradiation (light or ionizing radiation),and various combinations of these factors Some vitamins are sensitive
to processing and storage, while others are more or less stable Thewater-soluble vitamins are susceptible to leaching losses during commer-cial washing and blanching, and domestic cooking Vitamin C is verysusceptible to chemical oxidation during processing, storage, andcooking Thiamin is heat-sensitive in neutral and alkaline foods, and isunstable in air Riboflavin is notoriously susceptible to decomposition
by light Niacin and vitamin B6are stable under a variety of processingconditions Vitamins A and E are destroyed under conditions that accel-erate the oxidation of unsaturated fats, such as access of air, heat, light,trace metal ions, and storage time Vitamin K is stable to heat, but extre-mely sensitive to both fluorescent light and sunlight Vitamin D is littleaffected by processing and storage
Some losses of certain vitamins during food processing are inevitable.However, one should consider the relative importance of the loss of aspecific vitamin from a particular commodity For example, vitamin Closs from milk during pasteurization and refrigerated storage is relativelyunimportant, as milk is an insignificant source of this vitamin in thedaily diet compared to other foods, such as citrus fruits and juices.Another point to consider is that natural variations in the vitamincontent of a raw food material may affect the content of that vitamin inthe final product more than the processing itself
Retention studies of vitamins to assess the effects of food processing onthe nutritive value of foods are of great importance to food technologistsand consumers In this section, the broad effects of various processingtechniques on vitamin retention are discussed The effects of processing
on specific vitamins are discussed in the relevant chapters
1.5.3.1 Dehydration
Removal of the biologically active water from foods through dehydrationstops the growth of microorganisms, whilst also reducing the rate ofVitamins in Foods: Analysis, Bioavailability, and Stability 9
Trang 37enzyme activity and chemical reactions Rancidity of the lipid ents of dehydrated foods is reduced if the protective structural water isleft intact Fruits, vegetables, juices, meats, fish, milk, and eggs areamong the foodstuffs commonly subjected to dehydration processes.Appropriate drying techniques are used in the processing of dehy-drated foods The sun-drying of fruit, fish, meat, and grain is still ofimportance in certain parts of the world In the tunnel-drying of fruitsand vegetables, the produce is spread onto trays or a conveyer andpassed into a high-velocity air stream in the temperature range of
constitu-60 –938C Spray-drying is a highly efficient process for drying milk,eggs, and coffee In spray-drying, liquids are dispersed in fine dropletsand sprayed into an upward-flowing stream of hot air Materials thatcan be made into a paste, such as mashed potatoes and tomato puree,can be dried by spreading thinly on steam-heated revolving drums Asthe product is in direct contact with the hot drums, vitamin losseswould be expected to be greater than those resulting from tunneldriers and spray driers In commercial freeze-drying, the frozen food
is placed into a chamber, which is evacuated and then heated Because
of the low pressure, ice does not melt, and the water vapor passesdirectly from a solid to a vapor phase (sublimation) The freeze-dryingprocess is applied mainly to meats and results in the least change inthe physical characteristics of the product The result is a dry, porousproduct, though there will always be some small amount of residualwater Compression of freeze-dried foods gives improved stability instorage by reducing the surface area exposed to oxygen and moisture.Except for sun-drying, the actual process of dehydration does notcause major losses of vitamins Retention of ascorbic acid is better inrapid drying at high temperatures than in slower drying at lowertemperatures Drying methods that expose the food to air result inlosses of vitamin A, b-carotene, and vitamin C due to oxidation Freeze-drying, which is carried out in the absence of oxygen, does not causeloss of vitamin C
1.5.3.2 Blanching
The blanching of vegetables and fruits entails subjecting the fresh produce
to temperatures in the range of 75 –958C for 1– 10 min prior to canning,freezing, or dehydration Blanching serves several purposes: as a cleaningprocess; to reduce the volume of bulky vegetables by wilting; to expel airfrom the plant tissues, thereby reducing the potential for oxidativechanges; and to inactivate endogenous enzymes that would otherwisecause quality deterioration Blanching with hot water is still the mostcommon system, despite the significant loss of water-soluble vitaminsthrough leaching This is because of the relatively low capital and
Trang 38running costs compared with more efficient procedures, such as steam ormicrowave blanching.
The immediate scalding of plant tissues is desirable to minimize theoxidation of ascorbic acid by ascorbic acid oxidase If the inactivatingtemperature of about 858C is not immediately reached, the breakdown
of cell structure will allow contact between active enzyme and substrate.Thus inefficient blanching will incur some loss of vitamin C by oxidation,
as well as by leaching [15] Unlike thiamin, ascorbic acid is essentiallystable to the heating conditions during blanching When peas wereblanched at 82– 888C for 3 min, losses of thiamin, niacin, vitamin B6,and vitamin C were 4, 20, 18, and 17%, respectively [16]
1.5.3.3 Canning
The heat treatment of canned foods will ideally sterilize the food, that is,destroy all viable microorganisms present Some microorganisms andtheir spores are extremely resistant to heat, and very stringent heattreatments would be required to destroy them Unfortunately, such treat-ments would promote unacceptable organoleptic changes and nutrientlosses, therefore the temperatures applied in commercial practice aim toachieve maximum microbial destruction commensurate with acceptableorganoleptic and nutritional value The rate of destruction of heat-resistant bacteria is increased approximately tenfold with a 108C increase
in temperature [17] Canned foods are considered to be “commerciallysterile” because the conditions within the can are such that any remainingmicroorganisms or spores will not grow during storage [18]
Heat sterilization causes destructive losses of the thermolabile mins The extent of the losses depends on the time/temperature con-ditions and the rate of heat transfer into the product In the case of cannedcured pork luncheon meat, the retentions of thiamin and pantothenic acidwere greater after processing at a high retort temperature for a short timethan after processing to the same sterilizing value at lower retort tempera-tures for longer periods [17] Heat transfer is slow in canned solids such asmeat, and excessive heat must be applied to the container to ensure sterility
vita-in the center Canned beans (a semisolid) retavita-in approximately 55% of thethiamin content, while canned tomatoes (a more liquid product) retain alarger percentage [19] Vitamin C losses are increased by the inclusion ofoxygen during canning Low-temperature storage improves retention ofvitamins in canned foods
1.5.3.4 Pasteurization and Ultra-High-Temperature Processing
In the pasteurization process, the foodstuff is subjected to a temperaturehigh enough to destroy all pathogenic microorganisms present UnlikeVitamins in Foods: Analysis, Bioavailability, and Stability 11
Trang 39sterilization procedures, some nonpathogenic microorganisms survivepasteurization It is fundamental that the higher the temperature andthe shorter the processing time, the greater is the nutrient retention Theaccepted methods of milk pasteurization in the U.S include the batch
or holding method of heating the milk for 30 min at 1458F (62.88C) andthe high temperature – short time (HTST) method of heating at 1618F(71.78C) for 15 sec [20] Orange juice is traditionally pasteurized by heattreatment at 958C for 15 sec, or at 908C for 1 min [21] In aseptic packaging,fluid products such as milk and fruit juices are pasteurized by HTST treat-ment, rapidly cooled, then placed into sterile containers and sealed Theheat treatment is applied to a thin layer of the milk or juice in a heatexchanger, or by direct steam injection These packages are likely tohave a higher content of residual and headspace oxygen than “in-container” pasteurized products, which are exhausted at blanch tempera-tures and vacuum-seamed prior to heat treatment [22] The pasteurization
of milk has little or no effect on the water-soluble vitamins, apart from a
20 –25% loss of the vitamin C content [23] The pasteurization of fruitjuices inactivates endogenous enzymes that would otherwise promotethe oxidation of ascorbic acid
Ultra-high-temperature (UHT)-milk generally refers to milk that hasbeen heated to at least 1308C for not less than 1 sec and then asepticallypackaged The process may be described as either UHT-sterilization orUHT-pasteurization, depending on the temperature and holding time
In general, UHT-milk processing involves temperatures of 130– 1508Cand holding times of 2 –8 sec Heating and cooling methods employed
in UHT processing involve direct heating with saturated steam underpressure followed by expansion cooling, or indirect heating and coolingthrough a heat-conducting barrier Equipment for indirect heat processingmay sometimes include vacuum flash vessels to remove gas and vapor[24] UHT-milk can be stored unrefrigerated for several months
1.5.3.5 Microwave Heating
Microwaves are electromagnetic waves of radiant energy, which easilypenetrate materials containing dielectric molecules such as water Therapidly oscillating electromagnetic field forces the molecules to undergorapid reorientation By this process, electromagnetic energy is convertedinto thermal energy In conventional cooking, heat is applied to thesurface of the food and then conducted to the inner parts with unevendistribution Microwaves generate heat throughout the bulk of the food,resulting in a comparatively uniform and rapid temperature rise through-out the product
Microwave processing offers precise control of heating, making it usefulfor several commercial food processing operations [25,26] Some examples
Trang 40are as follows: (i) in the microwave tempering of frozen meat, frozenblocks of meat are brought to a temperature of 24 to 228C The partiallythawed meat can then be used to make hamburger patties or other pro-ducts (ii) In the processing of pasta products, the pasta is first dried byconventional drying with controlled humidity Microwave drying isthen used to redistribute water from the moist inner parts to the surface.
A third conventional drying step achieves the final moisture content.(iii) For the precooking of meat, fish, and chicken products, microwavecooking is often combined with conventional cooking methods Thisresults in less overcooking of surface parts and lower losses of moisture.(iv) Microwave-vacuum-drying is used for production of fruit juice con-centrates (v) Microwave heating within a conveyerized tunnel is usedfor pasteurizing pasta products, bread, and prepared meals
Microwave heating has the potential for a greater retention of heat-labilevitamins compared with other more conventional methods because theheating time is shortened Ascorbic acid content is higher in vegetablescooked by microwave heating than by conventional methods [27] Thecooking of pork and chicken in microwave ovens led to greaterretentions of vitamins B1, B2, and B6than in conventional electric ovens[28,29] Vitamin B1retentions in conventionally roasted and microwavedsamples ranged between 48 –67% and 86 –94%, respectively Comparativeretentions of vitamin B6were 22– 48% and 60– 87% [29]
1.5.3.6 Hydrothermal Processes (Flaking, Puffing, and Extrusion)
Subjecting whole or almost whole cereal grains to the simultaneous effect
of moisture and heat creates a fine and voluminous structure, makingthese products suitable for breakfast cereals and snacks Flaking entailssteam treatment followed by passing through rollers, drying, and toasting.For puffing, the grains are treated with water, then enclosed in a pressurechamber (puffing gun) and heated to 267– 2948C for 3 – 5 sec to increasethe vapor pressure Sudden opening of the gun releases the pressure,and the expansion of water vapor and other gases results in a 5 – 15times increase in volume of the cereals In the extrusion process, foodingredients are conveyed through a screw within a tightly fitting station-ary barrel The food is subjected to a combination of heat sources, includ-ing frictional heat, direct steam injection, and heat transfer from steam
or water in jackets surrounding the extruder barrel At the discharge ofthe extruder, the high-temperature, pressurized, cooked dough mass isforced through a small restrictive opening called a die The suddenchange from high pressure and high temperature to ambient conditions
on emergence through the die leads to product expansion
Barna et al [30] measured the changes in the content of four soluble vitamins (thiamin, riboflavin, niacin, and vitamin B6) duringVitamins in Foods: Analysis, Bioavailability, and Stability 13