《食品化学》课程教学资源（书籍文献）Principles of Food Chemistry，Third Edition，John M. deMan, PhD

Principles of Food ChemistryThird EditionJohn M. deMan, PhDProfessor EmeritusDepartmentof FoodScienceUniversity of GuelphGuelph, OntarioAChapman&HallFood ScienceBookANASPENPUBLICATION?Aspen Publishers, Inc.Gaithersburg,Maryland1999

Principles of Food Chemistry Third Edition John M. deMan, PhD Professor Emeritus Department of Food Science University of Guelph Guelph, Ontario A Chapman & Hall Food Science Book AN ASPEN PUBLICATION® Aspen Publishers, Inc. Gaithersburg, Maryland 1999

The author has made every effort to ensure the accuracy of the information herein. However, appropriateinformation sources should be consulted, especially for new or unfamiliar procedures, It is the responsi-bilityofeverypractitionerto evaluatethe appropriateness of aparticularopinion in the context ofactualclinical situations and with due considerations to new developments.The author,editors,and the publishercannotbe held responsibleforanytypographical orother errors found in this book.AspenPublishers,Inc.,is notaffiliated with theAmericanSociety of Parenteral and Enteral NutritionLibrary of Congress Cataloging-in-PublicationDatadeMan, John M.Principles offood chemistry/John M, deMan.-3rd ed.p.,cm.Includes bibliographical references and index.ISBN0-8342-1234-X1.Food—Composition.I.Title.TX531.D431999664dc2198-31467CIPCopyright1999byAspenPublishers,Inc.AllrightsreservedAspen Publishers,Inc.,grants permissionforphotocopyingfor limited personalor internal use.This consent doesnotextend to otherkinds ofcopying,such as copyingforgeneral distribution,foradvertisingorpromotional purposes,forcreating new collective works,orfor resale.For information,address Aspen Publishers, Inc.,Permissions Department,200OrchardRidgeDrive,Suite200,Gaithersburg,Maryland20878Orders: (800) 638-8437Customer Service: (800)234-1660About Aspen Publishers·For more than 35 years,Aspen has been a leading professionalpublisher in a variety of disciplines. Aspen's vast information resources are available in both printand electronic formats. We are committed to providing the highest quality information available inthe most appropriate format for our customers, Visit Aspen's Internet site for more informationresources, directories,articles,and a searchable version of Aspen's full catalog,including themostrecentpublications:http://www.aspenpublishers.comAspen Publishers, Inc. · The hallmark of quality in publishingMemberof the worldwideWolters KluwergroupEditorial Services:JaneColillaLibrary of Congress Catalog Card Number: 98-31467ISBN:0-8342-1234-XPrintedin theUnited States of America12345

The author has made every effort to ensure the accuracy of the information herein. However, appropriate information sources should be consulted, especially for new or unfamiliar procedures. It is the responsi￾bility of every practitioner to evaluate the appropriateness of a particular opinion in the context of actual clinical situations and with due considerations to new developments. The author, editors, and the pub￾lisher cannot be held responsible for any typographical or other errors found in this book. Aspen Publishers, Inc., is not affiliated with the American Society of Parenteral and Enteral Nutrition. Library of Congress Cataloging-in-Publication Data deMan, John M. Principles of food chemistry/ John M. deMan.—3rd ed. p. cm. Includes bibliographical references and index. ISBN 0-8342-1234-X 1. Food—Composition. I. Title. TX531.D43 1999 664—dc21 98-31467 CIP Copyright © 1999 by Aspen Publishers, Inc. All rights reserved. Aspen Publishers, Inc., grants permission for photocopying for limited personal or internal use. This consent does not extend to other kinds of copying, such as copying for general distribution, for advertising or promotional purposes, for creating new collective works, or for resale. For information, address Aspen Publishers, Inc., Permissions Department, 200 Orchard Ridge Drive, Suite 200, Gaithersburg, Maryland 20878. Orders: (800) 638-8437 Customer Service: (800) 234-1660 About Aspen Publishers • For more than 35 years, Aspen has been a leading professional publisher in a variety of disciplines. Aspen's vast information resources are available in both print and electronic formats. We are committed to providing the highest quality information available in the most appropriate format for our customers. Visit Aspen's Internet site for more information resources, directories, articles, and a searchable version of Aspen's full catalog, including the most recent publications: http://www.aspenpublishers.coni Aspen Publishers, Inc. • The hallmark of quality in publishing Member of the worldwide Wolters Kluwer group. Editorial Services: Jane Colilla Library of Congress Catalog Card Number: 98-31467 ISBN: 0-8342-1234-X Printed in the United States of America 1234 5

PrefaceThis book was designed to serve as a text forlipids,low caloric fats, and biotechnology havecourses in food chemistry in food science proreceived a good deal of attention.Our under-grams following the Institute of Food Technolo-standing of the functionality of proteins expandsgists minimum standards. The original idea inwith increasing knowledge about their composi-the preparation of this book was to present basiction and structure. Carbohydrates serve manyinformationonthecomposition offoods andthefunctions in foods, and the noncaloric dietarychemical and physical characteristics theyfiber has assumed an important role.Color,flavor,and texture are importantundergo during processing,storage,andhandling. The basic principles of food chemistryattributes of food quality, and in these areas,remain the same, but much additional researchespecially those of flavor and texture, greatcarried out in recent years has extended andadvances have been made in recent years.deepened our knowledge.This required inclu-Enzymes are playing an ever increasingpart insion of new material in all chapters. The lastthe production and transformation of foodschapter in the second edition,Food AdditivesModern methods of biotechnology have pro-has been replaced bythe chapter Additives andduced a gamut of enzymes with new andContaminants,andan additional chapter,Regu-improvedproperties.In the literature, information is found usinglatory Control of Food Composition,Quality,and Safety, has been included.This last chapterdifferent systems of units: metric, SI, and theis an attempt to give students some understand-English system.Quotations from the literatureing of the scientific basis of the formulation ofare presented in their original form. It would belawsandregulationsonfoodandontheincreasdifficult to change all these units in the book toing trend toward international harmonization ofone system. To assist the reader in convertingtheselaws.Anumberofimportantfoodsafetythese units, an appendix is provided with conver-issues have arisen recently,and these havesion factors for all units found in the text.emphasized the need for comprehensive andIt is hoped that this new edition will continue toeffectivelegalcontrols.fulfill the need for a concise and relevant text forIn the area of water as a food component, thethe teaching of food chemistry.Iexpress gratitudeissue of the glass transition has received muchto those who have provided comments and sug-attention.This demonstrates the important rolegestionsfor improvement,and especiallyto myof water in food properties.Lipids have receivedwife, Leny,who has provided a great deal of sup.much attention latelymainlybecause of public-port and encouragement during the preparation ofity related to nutritional problems. Sutructuredthe third edition.vii

Preface This book was designed to serve as a text for courses in food chemistry in food science pro￾grams following the Institute of Food Technolo￾gists minimum standards. The original idea in the preparation of this book was to present basic information on the composition of foods and the chemical and physical characteristics they undergo during processing, storage, and han￾dling. The basic principles of food chemistry remain the same, but much additional research carried out in recent years has extended and deepened our knowledge. This required inclu￾sion of new material in all chapters. The last chapter in the second edition, Food Additives, has been replaced by the chapter Additives and Contaminants, and an additional chapter, Regu￾latory Control of Food Composition, Quality, and Safety, has been included. This last chapter is an attempt to give students some understand￾ing of the scientific basis of the formulation of laws and regulations on food and on the increas￾ing trend toward international harmonization of these laws. A number of important food safety issues have arisen recently, and these have emphasized the need for comprehensive and effective legal controls. In the area of water as a food component, the issue of the glass transition has received much attention. This demonstrates the important role of water in food properties. Lipids have received much attention lately mainly because of public￾ity related to nutritional problems. Sutructured lipids, low caloric fats, and biotechnology have received a good deal of attention. Our under￾standing of the functionality of proteins expands with increasing knowledge about their composi￾tion and structure. Carbohydrates serve many functions in foods, and the noncaloric dietary fiber has assumed an important role. Color, flavor, and texture are important attributes of food quality, and in these areas, especially those of flavor and texture, great advances have been made in recent years. Enzymes are playing an ever increasing part in the production and transformation of foods. Modern methods of biotechnology have pro￾duced a gamut of enzymes with new and improved properties. In the literature, information is found using different systems of units: metric, SI, and the English system. Quotations from the literature are presented in their original form. It would be difficult to change all these units in the book to one system. To assist the reader in converting these units, an appendix is provided with conver￾sion factors for all units found in the text. It is hoped that this new edition will continue to fulfill the need for a concise and relevant text for the teaching of food chemistry. I express gratitude to those who have provided comments and sug￾gestions for improvement, and especially to my wife, Leny, who has provided a great deal of sup￾port and encouragement during the preparation of the third edition

ContentsviiPreface11.Water1PhysicalPropertiesofWaterandIce2StructureoftheWaterMolecule4SorptionPhenomena11TypesofWater14FreezingandIceStructure23WaterActivityandFoodSpoilage26WaterActivityand Packaging28Water Bindingof Meat30WaterActivityandFoodProcessing332.Lipids33Introduction35ShorthandDescriptionofFattyAcidsandGlycerides36ComponentFattyAcids45ComponentGlycerides50Phospholipids51Unsaponifiables54Autoxidation63Photooxidation65Heated Fats-Frying70FlavorReversion71Hydrogenation77Interesterification81Physical Properties94FractionationiiThis page hasbeen reformatted byKnovel toprovideeasier navigation

This page has been reformatted by Knovel to provide easier navigation. iii Contents Preface . vii 1. Water . 1 Physical Properties of Water and Ice . 1 Structure of the Water Molecule . 2 Sorption Phenomena . 4 Types of Water . 11 Freezing and Ice Structure . 14 Water Activity and Food Spoilage . 23 Water Activity and Packaging . 26 Water Binding of Meat . 28 Water Activity and Food Processing . 30 2. Lipids . 33 Introduction . 33 Shorthand Description of Fatty Acids and Glycerides . 35 Component Fatty Acids . 36 Component Glycerides . 45 Phospholipids . 50 Unsaponifiables . 51 Autoxidation . 54 Photooxidation . 63 Heated Fats – Frying . 65 Flavor Reversion . 70 Hydrogenation . 71 Interesterification . 77 Physical Properties . 81 Fractionation . 94

ivContents95CocoaButterandConfectioneryFats101EmulsionsandEmulsifiers106Novel OilsandFats107FatReplacers1113.Proteins111Introduction111AminoAcidComposition113ProteinClassification115ProteinStructure118Denaturation120Nonenzymic Browning131ChemicalChanges134Functional Properties138AnimalProteins152PlantProteins1634.Carbohydrates163Introduction163Monosaccharides167RelatedCompounds169Oligosaccharides183Polysaccharides203DietaryFiber2095.Minerals209Introduction209MajorMinerals217TraceElements223MetalUptakeinCannedFoods2296.Color229Introduction229CIESystem236MunsellSystem237HunterSystemThispagehasbeenreformattedbyKnoveltoprovideeasiernavigation

iv Contents This page has been reformatted by Knovel to provide easier navigation. Cocoa Butter and Confectionery Fats . 95 Emulsions and Emulsifiers . 101 Novel Oils and Fats . 106 Fat Replacers . 107 3. Proteins . 111 Introduction . 111 Amino Acid Composition . 111 Protein Classification . 113 Protein Structure . 115 Denaturation . 118 Nonenzymic Browning . 120 Chemical Changes . 131 Functional Properties . 134 Animal Proteins . 138 Plant Proteins . 152 4. Carbohydrates . 163 Introduction . 163 Monosaccharides . 163 Related Compounds . 167 Oligosaccharides . 169 Polysaccharides . 183 Dietary Fiber . 203 5. Minerals . 209 Introduction . 209 Major Minerals . 209 Trace Elements . 217 Metal Uptake in Canned Foods . 223 6. Color . 229 Introduction . 229 CIE System . 229 Munsell System . 236 Hunter System . 237

ContentsV238LovibondSystem239Gloss239Food Colorants2637.Flavor263Introduction263TasteOdor282291DescriptionofFoodFlavors294Astringency296FlavorandOff-Flavor297FlavorofSomeFoods3118.Texture311Introduction313TextureProfile316ObjectiveMeasurementofTexture320DifferentTypesofBodies328ApplicationtoFoods334TexturalPropertiesofSomeFoods341Microstructure347WaterActivityandTexture9.355Vitamins355Introduction355Fat-SolubleVitamins366Water-SolubleVitamins385VitaminsasFoodIngredients.38910.Enzymes389Introduction389NatureandFunction395Hydrolases413Oxidoreductases423ImmobilizedEnzymesThis page hasbeen reformatted byKnovel toprovideeasier navigation

Contents v This page has been reformatted by Knovel to provide easier navigation. Lovibond System . 238 Gloss . 239 Food Colorants . 239 7. Flavor . 263 Introduction . 263 Taste . 263 Odor . 282 Description of Food Flavors . 291 Astringency . 294 Flavor and Off-Flavor . 296 Flavor of Some Foods . 297 8. Texture . 311 Introduction . 311 Texture Profile . 313 Objective Measurement of Texture . 316 Different Types of Bodies . 320 Application to Foods . 328 Textural Properties of Some Foods . 334 Microstructure . 341 Water Activity and Texture . 347 9. Vitamins . 355 Introduction . 355 Fat-Soluble Vitamins . 355 Water-Soluble Vitamins . 366 Vitamins as Food Ingredients . 385 10. Enzymes . 389 Introduction . 389 Nature and Function . 389 Hydrolases . 395 Oxidoreductases . 413 Immobilized Enzymes . 423

viContents42911.AdditivesandContaminants429Introduction431IntentionalAdditives449IncidentalAdditivesorContaminants12.RegulatoryControlofFoodComposition,Quality,and475Safety475HistoricalOverview477SafetyU.S.FoodLaws479481CanadianFoodLaws482EuropeanUnion(EU)FoodLaws484InternationalFoodLaw:CodexAlimentarius488Harmonization491Appendices491AppendixA.UnitsandConversionFactors495AppendixB.GreekAlphabetIndex497ThispagehasbeenreformattedbyKnoveltoprovideeasiernavigation

vi Contents This page has been reformatted by Knovel to provide easier navigation. 11. Additives and Contaminants . 429 Introduction . 429 Intentional Additives . 431 Incidental Additives or Contaminants . 449 12. Regulatory Control of Food Composition, Quality, and Safety . 475 Historical Overview . 475 Safety . 477 U.S. Food Laws . 479 Canadian Food Laws . 481 European Union (EU) Food Laws . 482 International Food Law: Codex Alimentarius . 484 Harmonization . 488 Appendices . 491 Appendix A. Units and Conversion Factors . 491 Appendix B. Greek Alphabet . 495 Index . 497

1CHAPTERWaterTable1-1TvpicalWaterContentsofSomeWater is an essential constituent of manySelectedFoodsfoods.It may occur as an intracellular orextracellular component in vegetable andProductWater(%)animal products, as a dispersing medium or95solvent in a variety of products, as the dis-Tomato95persed phase in some emulsified productsLettuce92such as butter and margarine, and as a minorCabbage90constituent in other foods. Table 1-1 indi-BeerOrange87cates the wide range of water content in87foods.Apple juiceMilk87Because of the importance of water asaPotato78food constituent, an understanding of itsBanana75properties and behavior is necessary.The70Chickenpresence of water influences the chemical67and microbiological deterioration of foods.Salmon,cannedMeat65Also,removal (drying)or freezing of waterCheese37is essential to some methods of food preser-35vation. Fundamental changes in the productBread, white28Jammay take place in both instances.Honey2016ButterandmargarinePHYSICALPROPERTIESOFWATER12Wheat fiourANDICERice125Some of the physical properties of waterCoffeebeans,roasted4and ice are exceptional, and a list of these isMilkpowder0presentedin Table1-2.Muchof this infor-ShorteningmationwasobtainedfromPerry(1963)andLandolt-Boernstein (1923).The exception-ally high values of the caloric properties ofoperations such as freezing and drying.Thewater are of importance for food processingconsiderable difference in density of water1

Water is an essential constituent of many foods. It may occur as an intracellular or extracellular component in vegetable and animal products, as a dispersing medium or solvent in a variety of products, as the dis￾persed phase in some emulsified products such as butter and margarine, and as a minor constituent in other foods. Table 1-1 indi￾cates the wide range of water content in foods. Because of the importance of water as a food constituent, an understanding of its properties and behavior is necessary. The presence of water influences the chemical and microbiological deterioration of foods. Also, removal (drying) or freezing of water is essential to some methods of food preser￾vation. Fundamental changes in the product may take place in both instances. PHYSICAL PROPERTIES OF WATER AND ICE Some of the physical properties of water and ice are exceptional, and a list of these is presented in Table 1-2. Much of this infor￾mation was obtained from Perry (1963) and Landolt-Boernstein (1923). The exception￾ally high values of the caloric properties of water are of importance for food processing Table 1-1 Typical Water Contents of Some Selected Foods Product Water (%) Tomato 95 Lettuce 95 Cabbage 92 Beer 90 Orange 87 Apple juice 87 Milk 87 Potato 78 Banana 75 Chicken 70 Salmon, canned 67 Meat 65 Cheese 37 Bread, white 35 Jam 28 Honey 20 Butter and margarine 16 Wheat flour 12 Rice 12 Coffee beans, roasted 5 Milk powder 4 Shortening O operations such as freezing and drying. The considerable difference in density of water Water CHAPTER 1

2PRINCIPLES OFFOODCHEMISTRYTable1-2SomePhysicalPropertiesofWaterandIceTemperature (℃)040602080Water1004.5817.53Vaporpressure (mmHg)55.32149.4355.2760.0Density (g/cm°)0.99980.99820.99220.98320.97180.95831.00740.99880.99800.99941.00231.0070Specificheat (cal/gC)Heat of vaporization597.2586.0574.7563.3551.3538.9(cal/g)0.4860.5150.5400.5610.5760.585Thermal conductivity(kcal/m2h℃)Surface tension75.6272.7569.5566.1762.6058.84(dynes/cm)1.7921.0020.6530.4660.3550.282Viscosity (centipoises)Refractive index1.33381.33301.33061.32721.32301.318088.080.473.366.760.855.3Dielectric constant2.073.875.386.57Coefficient of thermalexpansion×10-4Temperature (C)0-5-15-2025Ice-10-303.011.951.240.77Vaporpressure (mmHg)4.580.470.2879.8Heatoffusion (cal/g)-666.7Heatof sublimation (cal/g)677.8672.3662.30.91680.91710.9178Density(g/cm3）0.91750.91820.91850.91880.48730.47700.4647Specificheat (cal/gC)0.45049.27.15.54.43.93.63.5Coefficientofthermalexpansion×10-52.06Heatcapacity (joule/g)1.94STRUCTUREOFTHEWATERandicemayresult instructuraldamagetofoods when they are frozen. The density ofMOLECULEice changes with changes in temperature,The reason for the unusual behavior ofresulting in stresses in frozen foods. Sincesolidsaremuchless elasticthan semisolids.water lies in the structure of the water mole-structural damage may result from fluctuat-cule (Figure 1-1) and in the molecule's abil-ing temperatures,even if the fluctuationsityto formhydrogen bonds.In the waterremain belowthefreezingpoint.molecule the atoms are arranged at an angle

and ice may result in structural damage to foods when they are frozen. The density of ice changes with changes in temperature, resulting in stresses in frozen foods. Since solids are much less elastic than semisolids, structural damage may result from fluctuat￾ing temperatures, even if the fluctuations remain below the freezing point. STRUCTURE OF THE WATER MOLECULE The reason for the unusual behavior of water lies in the structure of the water mole￾cule (Figure 1-1) and in the molecule's abil￾ity to form hydrogen bonds. In the water molecule the atoms are arranged at an angle Table 1-2 Some Physical Properties of Water and Ice Temperature (0C) Water Vapor pressure (mm Hg) Density (g/cm3 ) Specific heat (cal/g°C) Heat of vaporization (cal/g) Thermal conductivity (kcal/m2 h°C) Surface tension (dynes/cm) Viscosity (centipoises) Refractive index Dielectric constant Coefficient of thermal expansion x 1 (T4 O 4.58 0.9998 1.0074 597.2 0.486 75.62 1.792 1 .3338 88.0 20 17.53 0.9982 0.9988 586.0 0.515 72.75 1.002 1 .3330 80.4 2.07 40 55.32 0.9922 0.9980 574.7 0.540 69.55 0.653 1.3306 73.3 3.87 60 149.4 0.9832 0.9994 563.3 0.561 66.17 0.466 1.3272 66.7 5.38 80 355.2 0.9718 1.0023 551.3 0.576 62.60 0.355 1 .3230 60.8 6.57 100 760.0 0.9583 1 .0070 538.9 0.585 58.84 0.282 1.3180 55.3 Temperature (0C) Ice Vapor pressure (mm Hg) Heat of fusion (cal/g) Heat of sublimation (cal/g) Density (g/cm3 ) Specific heat (cal/g 0C) Coefficient of thermal expansion x 1 0~5 Heat capacity (joule/g) O 4.58 79.8 677.8 0.9168 0.4873 9.2 2.06 -5 3.01 0.9171 7.1 -10 1.95 672.3 0.9175 0.4770 5.5 -15 1.24 0.9178 4.4 -20 0.77 666.7 0.9182 0.4647 3.9 1.94 -25 0.47 0.9185 3.6 -30 0.28 662.3 0.9188 0.4504 3.5

Water3that water has unusually high values for cer-tain physical constants, such as meltingpoint, boiling point, heat capacity, latent heatof fusion, latent heat of vaporization, surfacetension, and dielectric constant. Some ofthese values are listed in Table 1-3.Watermayinfluence the conformation ofmacromolecules if it has an effect on anyofthe noncovalent bonds that stabilize the con-Figure 1-1 Structure of the Water Moleculeformation of the large molecule (Klotz1965).Thesenoncovalentbonds maybeoneof three kinds: hydrogen bonds,ionic bonds.of 105 degrees, and the distance between theor apolar bonds.In proteins,competitionnucleiof hydrogen and oxygen is 0.0957nm.exists between interamide hydrogen bondsThe water molecule can be considered aand water-amidehydrogen bonds.Accordingspherical quadrupole with a diameter ofto Klotz (1965), the binding energy of such0.276nm,wheretheoxygennucleus formsbonds can be measured by changesin thethe center of the quadrupole. The two nega-near-infraredspectraofsolutionsinN-methtive and two positive charges form the anglesylacetamide.The greater the hydrogen bond-of a regular tetrahedron.Because of the sepa-ing ability of the solvent, the weaker theC=O...H-N bond. In aqueous solvents theration of charges in a water molecule, theheat of formation or disruption of this bondattraction between neighboring molecules isis zero.This means that a C-O...H-N hydro-higherthan isnormal with van der Waalsforces.gen bond cannot provide stabilization inaqueous solutions.The competitive hydro-gen bonding by H,O lessens the thermody-namic tendency toward the formation ofinteramidehydrogenbondsThe water molecules around an apolar solHutebecomemore ordered,leading to a lossIn ice, everyH,O molecule is bound by fourin entropy. As a result, separated apolarsuch bridges to each neighbor. The bindinggroups in an aqueous environment tend toenergy of the hydrogen bond in ice amountsto 5 kcal per mole (Pauling 1960).SimilarTable1-3PhysicalPropertiesofSomestrong interactions occur between OH andHydridesNH and between small, strongly electronega-MeltingBoilingMolarHeatoftive atoms such as O and N. This is the rea-Sub-PointPointVaporizationson for the strong association in alcohols,(℃)(℃)stance(cal/mole)fatty acids, and amines and their great affin-CH4-1841612,200ity to water. A comparison of the propertiesNH378335,550of water with those of the hydrides of ele-HFments near oxygen in the Periodic Table- 92+197,220H,00(CH4,NH3,HF, DH3,H,S,HCl)indicates+1009,750

Figure 1-1 Structure of the Water Molecule of 105 degrees, and the distance between the nuclei of hydrogen and oxygen is 0.0957 nm. The water molecule can be considered a spherical quadrupole with a diameter of 0.276 nm, where the oxygen nucleus forms the center of the quadrupole. The two nega￾tive and two positive charges form the angles of a regular tetrahedron. Because of the sepa￾ration of charges in a water molecule, the attraction between neighboring molecules is higher than is normal with van der Waals' forces. that water has unusually high values for cer￾tain physical constants, such as melting point, boiling point, heat capacity, latent heat of fusion, latent heat of vaporization, surface tension, and dielectric constant. Some of these values are listed in Table 1-3. Water may influence the conformation of macromolecules if it has an effect on any of the noncovalent bonds that stabilize the con￾formation of the large molecule (Klotz 1965). These noncovalent bonds may be one of three kinds: hydrogen bonds, ionic bonds, or apolar bonds. In proteins, competition exists between interamide hydrogen bonds and water-amide hydrogen bonds. According to Klotz (1965), the binding energy of such bonds can be measured by changes in the near-infrared spectra of solutions in TV-meth￾ylacetamide. The greater the hydrogen bond￾ing ability of the solvent, the weaker the C=O-H-N bond. In aqueous solvents the heat of formation or disruption of this bond is zero. This means that a C=O-H-N hydro￾gen bond cannot provide stabilization in aqueous solutions. The competitive hydro￾gen bonding by H2O lessens the thermody￾namic tendency toward the formation of interamide hydrogen bonds. The water molecules around an apolar sol￾ute become more ordered, leading to a loss in entropy. As a result, separated apolar groups in an aqueous environment tend to Table 1-3 Physical Properties of Some Hydrides In ice, every H2O molecule is bound by four such bridges to each neighbor. The binding energy of the hydrogen bond in ice amounts to 5 kcal per mole (Pauling 1960). Similar strong interactions occur between OH and NH and between small, strongly electronega￾tive atoms such as O and N. This is the rea￾son for the strong association in alcohols, fatty acids, and amines and their great affin￾ity to water. A comparison of the properties of water with those of the hydrides of ele￾ments near oxygen in the Periodic Table (CH4, NH3, HF, DH3, H2S, HCl) indicates Sub￾stance CH4 NH3 HF H2O Melting Point ( 0C) -184 -78 -92 O Boiling Point ( 0C) -161 -33 + 19 +100 Molar Heat of Vaporization (cal/mole) 2,200 5,550 7,220 9,750