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

29WaterHamm (1959a,1959b)has proposed thatNH2during the first hour after slaughter, bivalentNH3metal ions of muscle are incorporated into0ooc①00c-the muscle proteins at pH 6, causing a con-traction of the fiber network and a dehydra-Otion of the tissue. Further changes in hy-NH3NH2dration during aging for up to seven days canbeexplainedbyanincreaseinthenumberofCOOOcoooavailable carboxyl and basic groups.TheseOresultfromproteolysis.Hamm andDeather-NHage (1960a)found that freeze-drying of beefNH2results in a decrease in water-binding capac-ityintheisoelectricpH rangeof themuscle.The proteins form a tighter network, which isPH 7.0pH 5.5stabilized by the formation of new saltand/orFigure 1-34 Water Binding in Meat as Influ-hydrogen bonds.Heating beef at tempera-enced by pHtures over 40°C leads to strong denaturationandchangesinhydration(HammandDeatherage 1960b).Quickfreezingof beefresults in a significant but small increase inthe water-holding capacity,whereas slowfreezing results in a significant but smallwork of membranes and filaments of thedecrease in water binding. These effectsstructural proteins as well as by cross-link-were thought to result from the mechanicalages and electrostatic attractions betweenaction of ice crystals (Deatherage and Hammpeptide chains. It is assumed that changes in1960).Theinfluence of heatingon waterwater-binding capacity of meat during aging,binding of pork was studied by Shermanstorage, and processing relate to the free(1961b),who also investigated the effect ofwater and not the real water of hydration.the addition of salts on water binding (Sher-The free water is held by a three-dimensionalman 196la).Water binding can be greatlystructure of the tissue, and shrinkage in thisaffectedby addition of certain salts,espe-network leads to a decrease in immobilizedcially phosphates (Hellendoorn 1962). Suchwater; this water is lost even by applicationsalt additions are used to diminish cookingof slight pressure.The reverse is also possi-lossesbyexpulsionof waterincanninghamsble. Cut-up muscle can take up as much asand to obtain a better structure and consis-700 to800gof waterper100gof proteinattency in manufacturing sausages.Recentlycertain pH values and in thepresence of cer-the subject of water binding has been greatlytain ions.Immediately after slaughter there isextended in scope (Katz 1997).Water bind-a drop in hydration and an increase in rigid-ing is related to the use of water as a plasti-ity of muscle with time. The decrease incizer and the interaction of water with thehydration was attributed at about two-thirdscomponentsof mixedfood systems.Retain-to decomposition of ATP and at about one-ing water in mixed food systems throughoutthird to loweringof thepH.their shelf life is becoming an important

pH 5.5 pH 7.0 Figure 1-34 Water Binding in Meat as Influ￾enced by pH work of membranes and filaments of the structural proteins as well as by cross-link￾ages and electrostatic attractions between peptide chains. It is assumed that changes in water-binding capacity of meat during aging, storage, and processing relate to the free water and not the real water of hydration. The free water is held by a three-dimensional structure of the tissue, and shrinkage in this network leads to a decrease in immobilized water; this water is lost even by application of slight pressure. The reverse is also possi￾ble. Cut-up muscle can take up as much as 700 to 800 g of water per 100 g of protein at certain pH values and in the presence of cer￾tain ions. Immediately after slaughter there is a drop in hydration and an increase in rigid￾ity of muscle with time. The decrease in hydration was attributed at about two-thirds to decomposition of ATP and at about one￾third to lowering of the pH. Hamm (1959a, 1959b) has proposed that during the first hour after slaughter, bivalent metal ions of muscle are incorporated into the muscle proteins at pH 6, causing a con￾traction of the fiber network and a dehydra￾tion of the tissue. Further changes in hy￾dration during aging for up to seven days can be explained by an increase in the number of available carboxyl and basic groups. These result from proteolysis. Hamm and Deather￾age (196Oa) found that freeze-drying of beef results in a decrease in water-binding capac￾ity in the isoelectric pH range of the muscle. The proteins form a tighter network, which is stabilized by the formation of new salt and/or hydrogen bonds. Heating beef at tempera￾tures over 4O0C leads to strong denaturation and changes in hydration (Hamm and Deatherage 196Ob). Quick freezing of beef results in a significant but small increase in the water-holding capacity, whereas slow freezing results in a significant but small decrease in water binding. These effects were thought to result from the mechanical action of ice crystals (Deatherage and Hamm 1960). The influence of heating on water binding of pork was studied by Sherman (196Ib), who also investigated the effect of the addition of salts on water binding (Sher￾man 196Ia). Water binding can be greatly affected by addition of certain salts, espe￾cially phosphates (Hellendoorn 1962). Such salt additions are used to diminish cooking losses by expulsion of water in canning hams and to obtain a better structure and consis￾tency in manufacturing sausages. Recently, the subject of water binding has been greatly extended in scope (Katz 1997). Water bind￾ing is related to the use of water as a plasti￾cizer and the interaction of water with the components of mixed food systems. Retain￾ing water in mixed food systems throughout their shelf life is becoming an important

30PRINCIPLES OFFOOD CHEMISTRYrequirement infoods of lowfat content.Suchfoods aregoverned by awandpH; awcon-trolled foods are those with pH greater thanfoods often havefat replaceringredientsbased on proteins orcarbohydrates,and their4.6 andawless than0.85.AtpH less than 4.6interaction with water is of great importance.and aw greater than 0.85, foods fall into thecategory of low-acid foods; when packagedWATERACTIVITYANDFOODin hermeticallysealed containers, thesePROCESSINGfoods mustbeprocessed toachieve commer-Water activity is one of the criteria forcially sterile conditions.establishing good manufacturing practiceIntermediate moisture foods are in the aw(GMP) regulations governing processingrange of 0.90 to 0.60.They can achieve sta-requirements and classification of foodsbility by a combination of awwith other fac-(Johnston and Lin 1987).As indicated intors,such as pH, heat,preservatives,and E,(equilibrium relative humidity)Figure 1-35, the process requirements for1.00Federal Regulations*AcidifiedFoods21CFR1138108.350.958ThermallyProcessedAcidLow-Acid Foods PackagedFoodsin Hermetically0.90Sealed ContainerspH<4.6pH>4.6aw>0.85awaw>0.850.8511021CFFAcid &awControlledaw Controlled FoodsFoods0.80PH >4.6PH<4.6aw<0.85aw<0.850.751-11644.681012pHAcidifiedFoods21CFR114108.25Figure1-35The Importance of pH and awon ProcessingRequirements forFoods.Source:Reprintedwithpermission from M.R.Johnston and R.C.Lin,FDAViews on the ImportanceofawinGood Manufacturing Practice, Water Activity:Theory and Application to Food,L.B.Rockland and L.R.Beuchat,eds.,p.288,1987,by courtesyofMarcel Dekker,Inc

requirement in foods of low fat content. Such foods often have fat replacer ingredients based on proteins or carbohydrates, and their interaction with water is of great importance. WATER ACTIVITY AND FOOD PROCESSING Water activity is one of the criteria for establishing good manufacturing practice (GMP) regulations governing processing requirements and classification of foods (Johnston and Lin 1987). As indicated in Figure 1-35, the process requirements for foods are governed by aw and pH; aw con￾trolled foods are those with pH greater than 4.6 and aw less than 0.85. At pH less than 4.6 and aw greater than 0.85, foods fall into the category of low-acid foods; when packaged in hermetically sealed containers, these foods must be processed to achieve commer￾cially sterile conditions. Intermediate moisture foods are in the aw range of 0.90 to 0.60. They can achieve sta￾bility by a combination of aw with other fac￾tors, such as pH, heat, preservatives, and Eh (equilibrium relative humidity). Federal Regulations 21 CFR 113 & 108.35 Thermally Processed Low-Acid Foods Packaged in Hermetically Sealed Containers pH > 4.6 a w > 0.85 "Acidified Foods & Acid Foods pH<4. 6 a w > 0.85 Acid & a w Controlled Foods pH < 4.6 a w < 0.85 a w Controlled Foods pH >4. 6 a w < 0.85 •Acidified Foods - 21 CFR 114 & 106.25 Figure 1-35 The Importance of pH and aw on Processing Requirements for Foods. Source: Reprinted with permission from M.R. Johnston and R.C. Lin, FDA Views on the Importance of aw in Good Man￾ufacturing Practice, Water Activity: Theory and Application to Food, L.B. Rockland and L.R. Beuchat, eds., p. 288, 1987, by courtesy of Marcel Dekker, Inc. PH a w

31WaterREFERENCESHellendoorn, E.W. 1962.Water binding capacity ofAcker,L.1969.Water activityand enzyme activityFood Technol.23: 1257-1270.meat as affected by phosphates.Food Technol. 16:119-124.Aguilera, J.M., and D.W.Stanley.1990.Microstruc-Honkel, K.G. 1989.The meat aspects of water andtural principles of food processing and engineeringLondon: Elsevier Applied Science.food quality. In Water and food quality, ed. TM.Berlin, E., B.A. Anderson, and M.J. Pallansch. 1968.Hardman.New York: Elsevier Applied Science.Effectof watervapor sorption onporosityof dehyJohnston,M.R,and R.C.Lin.1987.FDAviews on thedrated dairy products.J.DairySci.51:668-672importance ofawingoodmanufacturing practice.InWater activity: Theory and application to food, ed.Bone,D.P.1987.Practical applications of water activL.B.Rockland and L.R.Beuchat.New York: Marcelity and moisture relations in foods. In Water activity:Dekker, Inc.Theory and application to food, ed. L.B. Rocklandand L.R.Beuchat. New York: Marcel Dekker, Inc.Jouppila,K., and Y.H.Roos.1994.The physical stateBourne, M.C.1986.Effect of water activity on textureof amorphouscorn starchand its impactoncrystalli-zation.CarbohydratePolymers.32:95-104.profile parameters of apple flesh. J.Texture Studies17:331-340.Kapsalis, J.G. 1987. Influences of hysteresis and tem-Brunauer, S.,PJ.Emmett, and E.Teller.1938.Absorp-perature on moisture sorption isotherms.In Wateractivity: Theory and application to food, ed. L.B.tion of gasses in multimolecular layers.J.Am.Rockland and L.R. Beuchat. New York: MarcelChem.Soc.60:309-319Dekker, Inc.Bushuk,W.,and C.A.Winkler.1957.Sorption of waterKatz, F. 1997.The changing role of water binding.vapor on wheat flour, starch and gluten. CerealChem.34:73-86.Food Technol.51,no.10:64.Klotz,I.M.1965.Role of water structure in macromol-Busk Jr., G.C. 1984.Polymer-water interactions inecules.FederationProc.24:S24-S33.gelation.Food Technol.38:59-64.Chirife, J., and M.P. Buera. 1996.A critical review ofLabuza,T.P.1968.Sorptionphenomenainfoods.FoodTechnol.22:263-272the effect of some non-equilibrium situations andglass transitions on water activity values of food inLabuza,T.P.1980.The effect of water activity on reac-the microbiological growth range. J.Food Eng.25tionkinetics of food deterioration.Food Technol. 34.531-552.no.4:36-41,59Deatherage,FE.,and R,Hamm.1960.Influence ofLabuza, T.P., S.R.Tannenbaum, and M.Karel. 1970Water content and stability of low-moisture andfreezing and thawing on hydration and charges ofthemuscleproteins.FoodRes.25:623-629intermediate-moisture foods. Food Technol. 24:543-550.Hamm,R.1959a.Thebiochemistry of meataging.I.Landolt-Boernstein.1923.In Physical-chemical tablesHydration and rigidity of beef muscle (In German).Z.Lebensm.Unters.Forsch.109:113-121.(In German), ed. W.A. Roth and K. Sheel. Berlin:Springer Verlag.Hamm,R.1959b.Thebiochemistry of meat aging.II.Protein charge and muscle hydration (In German).Z.Leung,H.K.1987.Influence of water activity onLebensm.Unters.Forsch.109:227-234.chemical reactivity. In Water activity: Theory andHamm,R.1962.The water binding capacity of mam-application to food, ed. L.B. Rockland and L.R.Beuchat.New York: Marcel Dekker, Inc.malian muscle.VIl.Thetheory ofwater binding (InLevine, H.,and L. Slade. 1992. Glass transitions inGerman).Z.Lebensm.Unters.Forsch. 116:120-126foods. In Physical chemistry of foods. New York:Marcel Dekker, Inc.Hamm,R.,and F.E.Deatherage.196Oa.Changes inLoncin, M., J.J. Bimbenet, and J. Lenges. 1968. Influ-hydration and charges of muscle proteins duringheating of meat.Food Res.25:573-586.enceoftheactivityofwateronthespoilageoffood-Hamm,R., and F.E.Deatherage.1960b.Changes instuffs. J. Food Technol. 3: 131-142.hydration, solubility and charges of muscle proteinsLusena, C.V., and W.H.Cook.1953.Ice propagation induring heating of meat.Food Res.25:587-610.systems of biological interest.I.Effect of mem-

REFERENCES Acker, L. 1969. Water activity and enzyme activity. FoodTechnol. 23: 1257-1270. Aguilera, J.M., and D.W. Stanley. 1990. Microstruc￾tural principles of food processing and engineering. London: Elsevier Applied Science. Berlin, E., B.A. Anderson, and MJ. Pallansch. 1968. Effect of water vapor sorption on porosity of dehy￾drated dairy products. J. Dairy ScL 51: 668-672. Bone, D.P. 1987. Practical applications of water activ￾ity and moisture relations in foods. In Water activity: Theory and application to food, ed. L.B. Rockland and L.R. Beuchat. New York: Marcel Dekker, Inc. Bourne, M.C. 1986. Effect of water activity on texture profile parameters of apple flesh. J. Texture Studies 17:331-340. Brunauer, S., PJ. Emmett, and E. Teller. 1938. Absorp￾tion of gasses in multimolecular layers. /. Am. Chem.Soc. 60:309-319. Bushuk, W., and C.A. Winkler. 1957. Sorption of water vapor on wheat flour, starch and gluten. Cereal Chem. 34: 73-86. Busk Jr., G.C. 1984. Polymer-water interactions in gelation. Food Technol. 38: 59-64. Chirife, J., and M.P. Buera. 1996. A critical review of the effect of some non-equilibrium situations and glass transitions on water activity values of food in the microbiological growth range. /. Food Eng. 25: 531-552. Deatherage, EE., and R. Hamm. 1960. Influence of freezing and thawing on hydration and charges of the muscle proteins. Food Res. 25: 623-629. Hamm, R. 1959a. The biochemistry of meat aging. I. Hydration and rigidity of beef muscle (In German). Z. Lebensm. Unters. Forsch. 109: 113-121. Hamm, R. 1959b. The biochemistry of meat aging. II. Protein charge and muscle hydration (In German). Z Lebensm. Unters. Forsch. 109: 227-234. Hamm, R. 1962. The water binding capacity of mam￾malian muscle. VII. The theory of water binding (In German). Z. Lebensm. Unters. Forsch. 116: 120— 126. Hamm, R., and EE. Deatherage. 196Oa. Changes in hydration and charges of muscle proteins during heating of meat. Food Res. 25: 573-586. Hamm, R., and EE. Deatherage. 196Ob. Changes in hydration, solubility and charges of muscle proteins during heating of meat. Food Res. 25: 587-610. Hellendoorn, E.W. 1962. Water binding capacity of meat as affected by phosphates. Food Technol. 16: 119-124. Honkel, K.G. 1989. The meat aspects of water and food quality. In Water and food quality, ed. TM. Hardman. New York: Elsevier Applied Science. Johnston, M.R, and R.C. Lin. 1987. FDA views on the importance of aw in good manufacturing practice. In Water activity: Theory and application to food, ed. L.B. Rockland and L.R. Beuchat. New York: Marcel Dekker, Inc. Jouppila, K., and YH. Roos. 1994. The physical state of amorphous corn starch and its impact on crystalli￾zation. Carbohydrate Polymers. 32: 95-104. Kapsalis, J.G. 1987. Influences of hysteresis and tem￾perature on moisture sorption isotherms. In Water activity: Theory and application to food, ed. L.B. Rockland and L.R. Beuchat. New York: Marcel Dekker, Inc. Katz, F. 1997. The changing role of water binding. Food Technol. 51, no. 10: 64. Klotz, LM. 1965. Role of water structure in macromol￾ecules. Federation Proc. 24: S24-S33. Labuza, TP. 1968. Sorption phenomena in foods. Food Technol. 22: 263-272. Labuza, TP. 1980. The effect of water activity on reac￾tion kinetics of food deterioration. Food Technol. 34, no. 4: 36-41,59. Labuza, TP, S.R. Tannenbaum, and M. Karel. 1970. Water content and stability of low-moisture and intermediate-moisture foods. Food Technol. 24: 543-550. Landolt-Boernstein. 1923. In Physical-chemical tables (In German), ed. W.A. Roth and K. Sheel. Berlin: Springer Verlag. Leung, H.K. 1987. Influence of water activity on chemical reactivity. In Water activity: Theory and application to food, ed. L.B. Rockland and L.R. Beuchat. New York: Marcel Dekker, Inc. Levine, H., and L. Slade. 1992. Glass transitions in foods. In Physical chemistry of foods. New York: Marcel Dekker, Inc. Loncin, M., JJ. Bimbenet, and J. Lenges. 1968. Influ￾ence of the activity of water on the spoilage of food￾stuffs. J. Food Technol. 3: 131-142. Lusena, C.V., and W.H. Cook. 1953. Ice propagation in systems of biological interest. I. Effect of mem-

32PRINCIPLESOFFOODCHEMISTRYbranes and sofutes in a model cell system.Arch.Bio-Roos,Y.H.,and M.Karel.1991a.Amorphous stateanddelayed ice formation in sucrose solutions.Int. J.chem.Biophys.46:232-240.FoodSci.Technol.26:553-566Lusena, C.V., and W.H. Cook. 1954. Ice propagation inRoos,Y.H.,and M.Karel.1991b.Non equilibrium icesystems of biological interest. II.Effect of solutes atformation in carbohydrate solutions. Cryo-Letters.rapid cooling rates. Arch. Biochem. Biophys. 50:12:367376.243-251.Roos, Y.H., and M. Karel. 199lc. Phase transition ofLusena, C.V.,and W.H.Cook.1955.Ice propagation inamorphous sucrose and frozen sucrose solutions.J.systems of biological interest. II. Effect of solutesFoodSci.56:266-267.on nucleationand growth of icecrystals.Arch.BioRoos,Y.,and M.Karel.199ld.Plasticizing effect ofchem.Biophys.57:277-284.water on thermal behaviour and crystallization ofMartinez,F,andT.P.Labuza.1968.Effectofmoistureamorphousfoodmodels.J.FoodSci.56:38-43.content on rate of deterioration of freeze-driedRoos,Y.,and M.Karel.199le.Water and molecularsalmon.J.Food Sci.33: 241-247.weighteffects onglass transitions in amorphous car-Meryman, H.T.1966.Cryobiology.New York: Aca-bohydrates and carbohydrate solutions.J.Food Sci.demic Press.56:1676-1681.Pauling, L.1960.The nature of the chemical bond.Ith-Salwin,H.,andV.Slawson.1959.Moisturetransfer inaca, NY:Cornell University Press.combinations of dehydrated foods. Food Technol.Perry,J.H. 1963.Chemical engineers' handbook.New13:715-718.York: McGraw Hill.Saravacos,G.D.1967.Effectof thedryingmethodonRiedel, L.1959.Calorimetric studies of the freezing ofthe water sorption of dehydrated apple and potato. J.Food Sci. 32: 81-84.white bread and other flour products. Kaltetechn. 11:Sherman,P.1961a. The water binding capacity of fresh4146.pork. I. The influence of sodium chloride, pyrophos-Rockland.L.B.1969.Water activity and storage stabil-phate and polyphosphate on water absorption. Foodity.FoodTechnol.23:1241-1251Technol.15:79-87.Rockland,L.B.,and S.K.Nishi.1980.InfluenceofSherman, P. 1961b. The water binding capacity ofwateractivity on food product qualityand stabilityfresh pork.III.The influenceof cooking temperatureFoodTechnol.34,no.4:42-51.59.on thewaterbinding capacity of lean pork.FoodRoos, Y.H.1993.Water activity and physical stateTechnol.15:90-94.effects on amorphous food stability.J.Food ProcessSpeedy,R.J.1984.Self-replicating structures inwater.Preserv.16:433-447J.Phys.Chem.88:3364-3373Roos, Y.H.1995.Glass transition-related physico-van den Berg,C.,and S.Bruin.1981.Water activitychemical changes in foods. Food Technol. 49, no.and its estimation in food systems:Theoretical10:97-102.aspects. In Water activity--Influences on food qual-Roos,Y.H., and M.J.Himberg.1994.Nonenzymaticity,ed.L.B.Rockland and G.F.Steward.NewYorkbrowning behavior,as related to glass transition ofaAcademic Press.food model at chilling temperatures. J. Agr FoodVandenTempel,M.1958.Rheology of plastic fats.Chem.42:893-898.Rheol. Acta 1: 115-118.Roos,Y.H,K.Jouppila,and B.Zielasko.1996.Nonen-Wierbicki,E.,and F.E,Deatherage.1958.Determinazymatic browning-induced water plasticization.Jtion of water-holding capacity of fresh meats.J.AgrThermal.Anal.47:1437-1450FoodChem.6:387_392

branes and solutes in a model cell system. Arch. Bio￾chem. Biophys. 46: 232-240. Lusena, C.V., and W.H. Cook. 1954. Ice propagation in systems of biological interest. II. Effect of solutes at rapid cooling rates. Arch. Biochem. Biophys. 50: 243-251. Lusena, C.V., and W.H. Cook. 1955. Ice propagation in systems of biological interest. III. Effect of solutes on nucleation and growth of ice crystals. Arch. Bio￾chem. Biophys. 57: 277-284. Martinez, R, and T.R Labuza. 1968. Effect of moisture content on rate of deterioration of freeze-dried salmon. J. Food Sd. 33: 241-247. Meryman, H.T. 1966. Cryobiology. New York: Aca￾demic Press. Pauling, L. 1960. The nature of the chemical bond. Ith￾aca, NY: Cornell University Press. Perry, J.H. 1963. Chemical engineers' handbook. New York: McGraw Hill. Riedel, L. 1959. Calorimetric studies of the freezing of white bread and other flour products. Kdltetechn. 11 : 41-46. Rockland, L.B. 1969. Water activity and storage stabil￾ity. FoodTechnol. 23: 1241-1251. Rockland, L.B., and S.K. Nishi. 1980. Influence of water activity on food product quality and stability. Food Technol 34, no. 4: 42-51, 59. Roos, YH. 1993. Water activity and physical state effects on amorphous food stability. J. Food Process Preserv. 16:433-447 Roos, YH. 1995. Glass transition-related physico￾chemical changes in foods. Food Technol 49, no. 10: 97-102. Roos, YH., and MJ. Himberg. 1994. Nonenzymatic browning behavior, as related to glass transition of a food model at chilling temperatures. /. Agr. Food Chem. 42: 893-898. Roos, YH, K. Jouppila, and B. Zielasko. 1996. Nonen￾zymatic browning-induced water plasticization. J. Thermal. Anal. 47: 1437-1450. Roos, YH., and M. Karel. 199 Ia. Amorphous state and delayed ice formation in sucrose solutions. Int. J. Food Sd. Technol. 26: 553-566. Roos, Y.H., and M. Karel. 199Ib. Non equilibrium ice formation in carbohydrate solutions. Cryo-Letters. 12: 367-376. Roos, YH., and M. Karel. 199Ic. Phase transition of amorphous sucrose and frozen sucrose solutions. /. Food Sd. 56:266-267. Roos, Y, and M. Karel. 199Id. Plasticizing effect of water on thermal behaviour and crystallization of amorphous food models. J. Food ScL 56: 38-43. Roos, Y, and M. Karel. 199Ie. Water and molecular weight effects on glass transitions in amorphous car￾bohydrates and carbohydrate solutions. J. Food Sd. 56: 1676-1681. Salwin, H., and V. Slawson. 1959. Moisture transfer in combinations of dehydrated foods. Food Technol. 13:715-718. Saravacos, G.D. 1967. Effect of the drying method on the water sorption of dehydrated apple and potato. J. Food Sd. 32: 81-84. Sherman, P. 196 Ia. The water binding capacity of fresh pork. I. The influence of sodium chloride, pyrophos￾phate and polyphosphate on water absorption. Food Technol. 15: 79-87. Sherman, P. 196 Ib. The water binding capacity of fresh pork. III. The influence of cooking temperature on the water binding capacity of lean pork. Food Technol. 15: 90-94. Speedy, RJ. 1984. Self-replicating structures in water. /. Phys. Chem. 88: 3364-3373. van den Berg, C., and S. Bruin. 1981. Water activity and its estimation in food systems: Theoretical aspects. In Water activity—Influences on food qual￾ity, ed. L.B. Rockland and G.F. Steward. New York: Academic Press. VandenTempel, M. 1958. Rheology of plastic fats. Rheol.Actal: 115-118. Wierbicki, E., and EE. Deatherage. 1958. Determina￾tion of water-holding capacity of fresh meats. /. Agr. Food Chem. 6: 387-392

2CHAPTERLipidsINTRODUCTIONmaterial consist of such esters,known as fatsand oils. Fats are solid at room temperature,It has been difficult to provide a definitionand oilsare liquid.for the class of substances called lipids.EarlyThe fat content of foods can range fromdefinitions were mainly based on whether thevery low to very high in both vegetable andsubstance is soluble in organic solvents likeanimal products,as indicated in Table 2-1.Inether,benzene,or chloroform and is not solu-nonmodifiedfoods, such as meat,milk,cere-ble in water. In addition, definitions usuallyals, and fish, the lipids are mixtures of manyemphasize the central character of the fattyof the compounds listed inFigure 2-1, withacids--that is, whether lipids are actual ortriglycerides making up the major portion.potential derivatives of fatty acids.Every def-The fats and oils used for making fabricatedinition proposed so far has some limitations.foods,such as margarineand shortening,areFor example, monoglycerides of the short-almost pure triglyceride mixtures. Fats arechain fatty acids are undoubtedly lipids, butsometimes divided into visible and invisiblethey would not fit the definition on the basisfats.In the United States,about 60percent ofof solubility because they are more soluble intotal fat and oil consumed consists of invisi-water than in organic solvents. Instead of try-ble fats-that is,those contained in dairying to find a definition that would include allproducts (excluding butter),eggs, meat,poul-lipids,it is better to provide a schemetry, fish, fruits, vegetables, and grain prod-describing the lipids and their components,asucts. The visible fats, including lard, butter,Figure2-1 shows.Thebasic components ofmargarine,shortening,and cookingoilslipids (also called derived lipids)are listed inaccountfor 40 percent of total fat intake.Thethe central column with the fatty acids occu-interrelationship of most of the lipids is repre-Pying the prominent position. The left col-sented in Figure 2-1.A number of minorcomponents, such as hydrocarbons, fat-solu-umnliststhelipidsknownasphospholipidsble vitamins, and pigments are not includedThe right column of the diagram includes thein this scheme.compounds most important from a quantita-tive standpoint in foods. These are mostlyFats and oils may differ considerably inesters of fatty acids and glycerol. Up to 99composition, depending on their origin.Bothpercent of the lipids in plant and animalfatty acid and glyceride composition may33

INTRODUCTION It has been difficult to provide a definition for the class of substances called lipids. Early definitions were mainly based on whether the substance is soluble in organic solvents like ether, benzene, or chloroform and is not solu￾ble in water. In addition, definitions usually emphasize the central character of the fatty acids—that is, whether lipids are actual or potential derivatives of fatty acids. Every def￾inition proposed so far has some limitations. For example, monoglycerides of the short￾chain fatty acids are undoubtedly lipids, but they would not fit the definition on the basis of solubility because they are more soluble in water than in organic solvents. Instead of try￾ing to find a definition that would include all lipids, it is better to provide a scheme describing the lipids and their components, as Figure 2-1 shows. The basic components of lipids (also called derived lipids) are listed in the central column with the fatty acids occu￾pying the prominent position. The left col￾umn lists the lipids known as phospholipids. The right column of the diagram includes the compounds most important from a quantita￾tive standpoint in foods. These are mostly esters of fatty acids and glycerol. Up to 99 percent of the lipids in plant and animal material consist of such esters, known as fats and oils. Fats are solid at room temperature, and oils are liquid. The fat content of foods can range from very low to very high in both vegetable and animal products, as indicated in Table 2-1. In nonmodified foods, such as meat, milk, cere￾als, and fish, the lipids are mixtures of many of the compounds listed in Figure 2-1, with triglycerides making up the major portion. The fats and oils used for making fabricated foods, such as margarine and shortening, are almost pure triglyceride mixtures. Fats are sometimes divided into visible and invisible fats. In the United States, about 60 percent of total fat and oil consumed consists of invisi￾ble fats—that is, those contained in dairy products (excluding butter), eggs, meat, poul￾try, fish, fruits, vegetables, and grain prod￾ucts. The visible fats, including lard, butter, margarine, shortening, and cooking oils, account for 40 percent of total fat intake. The interrelationship of most of the lipids is repre￾sented in Figure 2-1. A number of minor components, such as hydrocarbons, fat-solu￾ble vitamins, and pigments are not included in this scheme. Fats and oils may differ considerably in composition, depending on their origin. Both fatty acid and glyceride composition may Lipids CHAPTER 2