2009_Book_FoodChemistry

Contents
xiii
3.6.2.2 AlkoxyLipids .......................................... 187
3.6.3 Cutin.................................................. 187
3.7 ChangesinAcylLipidsofFood ........................... 187
3.7.1 EnzymaticHydrolysis ................................... 187
3.7.1.1 TriacylglycerolHydrolases(Lipases)....................... 188
3.7.1.2 Polar-LipidHydrolases................................... 190
3.7.1.2.1 Phospholipases ......................................... 190
3.7.1.2.2 GlycolipidHydrolases ................................... 190
3.7.2 PeroxidationofUnsaturatedAcylLipids.................... 191
3.7.2.1 Autoxidation ........................................... 191
3.7.2.1.1 Fundamental Steps of Autoxidation . ....................... 192
3.7.2.1.2 Monohydroperoxides . ................................... 193
3.7.2.1.3 Hydroperoxide-Epidioxides............................... 195
3.7.2.1.4 Initiation of a Radical Chain Reaction . . . ................... 196
3.7.2.1.5 Photooxidation . . ....................................... 196
3.7.2.1.6 HeavyMetalIons ....................................... 198
3.7.2.1.7 Heme(in)Catalysis...................................... 200
3.7.2.1.8 Activated Oxygen ....................................... 201
3.7.2.1.9 Secondary Products . . ................................... 203
3.7.2.2 Lipoxygenase: Occurrence and Properties ................... 207
3.7.2.3 EnzymaticDegradationofHydroperoxides.................. 209
3.7.2.4 Hydroperoxide–ProteinInteractions........................ 211
3.7.2.4.1 Products Formed from Hydroperoxides . . ................... 211
3.7.2.4.2 Lipid–ProteinComplexes................................. 212
3.7.2.4.3 ProteinChanges ........................................ 213
3.7.2.4.4 Decomposition of Amino Acids ........................... 214
3.7.3 Inhibition of Lipid Peroxidation ........................... 214
3.7.3.1 AntioxidantActivity..................................... 215
3.7.3.2 AntioxidantsinFood .................................... 215
3.7.3.2.1 NaturalAntioxidants..................................... 215
3.7.3.2.2 SyntheticAntioxidants................................... 218
3.7.3.2.3 Synergists.............................................. 219
3.7.3.2.4 Prooxidative Effect . . . ................................... 220
3.7.4 FatorOilHeating(DeepFrying) .......................... 220
3.7.4.1 AutoxidationofSaturatedAcylLipids...................... 221
3.7.4.2 Polymerization ......................................... 223
3.7.5 Radiolysis ............................................. 224
3.7.6 Microbial Degradation of Acyl Lipids to Methyl Ketones . . . . . . 225
3.8 Unsaponifiable Constituents . . . ........................... 225
3.8.1 Hydrocarbons . . . ....................................... 227
3.8.2 Steroids ............................................... 227
3.8.2.1 Structure,Nomenclature.................................. 227
3.8.2.2 SteroidsofAnimalFood ................................. 227
3.8.2.2.1 Cholesterol............................................. 227
3.8.2.2.2 VitaminD ............................................. 229
3.8.2.3 PlantSteroids(Phytosterols) .............................. 229
3.8.2.3.1 Desmethylsterols........................................ 229
3.8.2.3.2 Methyl-andDimethylsterols.............................. 231
3.8.2.4 Analysis............................................... 232
3.8.3 Tocopherols and Tocotrienols . . ........................... 233
3.8.3.1 Structure,Importance.................................... 233