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Food CompositionFood contains chemical moleculesChemical composition may be determined in laboratoryTables of food composition availableUSDA National Nutrient Databasehttp://www.ars.usda.gov/main/site_main.htm?modecode=12354500

Food CompositionChemical substances found in the largest amounts in food:Water found inside cells in plants and animalsCarbohydratesFatsProtein

WaterAll foods contain at least some waterFree waterHeld inside cells Maintains properties of free waterMay be removed by pressureBound waterIs part of molecule structureReduced mobilityDoes not retain properties of free water

Water ActivityMore bound water, then less water activity Water activityRatio of the vapor pressure of water in a food at a specified temperature to the vapor pressure of pure water at same temperature

Water ActivityFoods more perishable if higher water activityMicroorganisms need water!To reduce water activityDryFreezeAdd sugar or salt

Uses of Water in Food PrepUniversal solventHeat transferFreezingCleansing agentPromotion of chemical changesIonization of saltBaking powderWater and pHHydrolysis reactions

Nature of WaterH2OTwo hydrogen atoms bonded with covalent bonds to one oxygen atomIs dipolarNegative on oxygen sidePositive on hydrogen sidesHydrogen bondsH +

Oxygen H +

Figure 9-3 Water molecules cluster together because the positive charge on the hydrogen side of the molecule is attracted to the negative charge on the oxygen side of the molecule, forming a weak bond.

Figure 9-4 A hydrogen bond forms as water molecules are attracted to each other.

Water HardnessTypes of hard waterTemporaryPermanentHard water and food preparationRehydration and softening of dried beans slowedAlkalinity may affect color of vegetablesPromote cloudiness in teaWater may be softened

CarbohydratesSimple sugars Complex starch and fiber

CarbohydratesMade of Carbon (C)Hydrogen (H)Oxygen (O)One molecule of H2O for each atom of carbon

Chemical ClassificationClassified by number of basic sugar units linked togetherMonosaccharide One unitDisaccharides Two unitsOligosaccharides 10 or fewer unitsPolysaccharides Up to 1000 units

Figure 9-6 Chemical structures are shown for monosaccharides and disaccharides of importance in food preparation.

MonosaccharidesGlucoseFructoseGalactose

DisaccharidesSucroseGlucose + FructoseLactoseGlucose + GalactoseMaltoseGlucose + Glucose

OligosaccharidesRaffinose and StachyoseNot broken down by digestive tractFound in dried beans

PolysaccharidesStarch AmyloseAmylopectinDextrinsProduced when starch molecules are partially broken down by enzymes, acid, or heat.Less thickening power than starch

PolysaccharidesGlycogenPlant Fiber Components

Figure 9-7 Portions of starch molecules, of which there are two types: (a) amylose, a long-chain-like molecule, also called the linear fraction, contributes gelling characteristics to cooking and cooled starch mixtures, and (b) amylopectin, the branched fraction, contributes thickening properties to cooked starch mixtures. Each small unit represents one molecule of glucose.

Plant Fiber ComponentsCalled dietary fiber / roughage / bulkCelluloseHemicelluloseBeta-glucansFound in oats and barleyAssociated with reduced risk of heart disease

Plant Fiber ComponentsCalled dietary fiber / roughage / bulkPectic substancesPectin forms gels in jams, jellies, and preservesVegetable gums

Browning of FoodsCarmelizationHeating of sugars above melting pointMaillard ReactionInvolves carbohydrateCarbonyl group of sugar combines with amino group of a protein with removal of water. After additional reactions brown pigments are formedi.e. browning of bread during baking

Lipids or FatsInsoluble in waterFeel greasyThree major groupsTriglyceridesPhospholipidsSterols

TriglyceridesAccount for 90-95 percent of fatty substances in food.Composed of3 fatty acids linked atoms of carbon with organic acid groupOne molecule glycerol 3 carbon atoms and three hydroxyl groups

Figure 9-8 Glycerol and three fatty acids are joined by an ester linkage to produce triglyceride as shown. Take note how the circled (with a dotted line) H + HO result in the production of H2O as shown next to the depiction of triglyceride.

Fatty AcidsMost fatty acids in foods are combined in triglycerides.Fatty acids differNumber of hydrogen atoms attachedLength of carbon chainCarbon chainsUsually even numbered

Types of Fatty AcidsSaturated fatsNo double bonds between carbon atoms, so no more hydrogen can be addedUnsaturatedDouble bonds between some of the carbon atoms that can be broken to add hydrogen

Types of Fatty AcidsMonounsaturatedOne double bond

Figure 9-9 The structure of three saturated fatty acids (butyric, stearic, and palmitic) are shown. Saturatedfatty acids have either a carbon (C) or a hydrogen (H) atom attached to each of the four possible carbonbonds. Thus, these fatty acids are saturated with hydrogen, leaving no room for the bonding of additionalhydrogen.

Omega 3 fatty acidsPolyunsaturated fatty acids with double bond between 3rd and 4th carbon from the left on the structure.Found in fatty fishProtective for heart disease

Figure 9-10 Oleic and linoleic unsaturated fatty acids are shown in this figure. Oleic is a monounsaturated fatty acid containing only one double bond between carbons (C). Linoleic acid is a polyunsaturated fatty acid with two double bonds between carbons (C). If the double bonds were broken by adding hydrogen, these fatty acids would become more saturated.

Linoleic AcidAn essential fatty acidCannot be made by the body must be consumed in food

Cis Trans ConfigurationCisHydrogen atom on both sides of bondTransHydrogen atoms on opposite sides of bond

Figure 9-11 The cis and trans configurations of triglycerides are depicted here. Cis hydrogen atoms are on the same side of the double bond between the carbons (C). Trans hydrogen atoms are on the opposite sides of the double bond between the carbons (C).

PhospholipidsFound in food in relatively small amountsFunction as emulsifiersOne side of molecule attracts fat One side attracts water i.e. lecithin

Figure 9-12 The structure of a phospholipid is shown here. Phospholipids differ from triglycerides by the joining of a phosphoric acid and nitrogen base to the glycerol instead of a third fatty acid as found in triglycerides. Compare this figure with Figure 9-8 to see the similarities.

SterolsCholesterolWidely known sterolFound ONLY in animal foodsIs associated with coronary heart diseaseOur bodies also make cholesterolPlant sterolsPhytosterolsInterfere with absorption of cholesterol

Fat in Food PreparationTenderizing in baked foodsContribute to leavening Creaming of fat and sugarPromote moistnessMajor components of salad dressings

Fat in Food PreparationMay be heated to high temperaturesFrying of foodsContribute flavorButter

ProteinsEssential nutrientIn food preparation several important rolesBinding waterForming gelsThickeningProducing foamsAiding browning

ProteinContainCarbonHydrogenOxygenNitrogenPotentially also sulfur, phosphorus, ironLarge molecules Hundreds or thousands of amino acids joined with peptide linkage

Protein StructurePrimaryLong chainsSecondarySpringlike coiling - Alpha helixTertiaryFolding of coils forming globular shapeQuaternary Combining of globular proteins

Protein QualityAmino acids used as building blocks for proteinsNine amino acids are essential for adult human nutritionComplete proteins include essential amino acids

Isoleucine LeucineLysineMethioninePhenylalanineThreonineTryptophanValineHistidine

Food SourcesMeats, Fish, and PoultryEggs and DairyNutsDry legumesCereal grains in lesser amounts

Properties and ReactionsBufferingDenaturation and CoagulationEnzymes

Figure 9-14 Denaturation of a protein involves unfolding of the molecule. The denatured molecules may bond together again to form a coagulated mass.

Solutions and DispersionsGas dispersed in liquidAir in whipped egg whiteLiquid dispersed in liquidOil dispersed in vinegarSolid dispersed in liquidA protein such as casein dispersed in milk

Figure 9-15 A dispersion system.

Solutions and DispersionsSolutionsColloidal solutionsSolGelFoamsEmulsionsSuspensions

Figure 9-16 A representation of gel formation. This is sometimes called sol-gel transformation and is typical of colloidal dispersions.