Hydrolysis:TransesterificationTransFattyAcids.Process to rearrange acyl groups on triglycerides福Transfatsreferstotriglyceridescontaining Hydrolyze to remove fatty acidsunsaturated fattyacids inthetrans conformationFree fatty acidsReattach fatty acids by esterification- Found in partially hydrogenated fats or oils Help to solidify food (melting point higher than cis)P00OhydrolysisO0P:FDAadoptednewfood labelingPH,O-0-labels give weight of trans fatOHOHrestrict low fat definitions by trans fat content18:1OHOH16:0+OHOHSome margarines are sold as"trans free"-H,O.No hydrogenationModify nutritionalo?Mixed sat d and unsat' d fats0and physical.Tend to be soft spreadsOPesterificationpropertiesApplicationsof lnteresterificationInteresterificationwith1,3-SpecificLipases-Lard:interesterificationreduces16:0atsn-2positionTopreparevalue-addedproducts:confectionaryfatsfrom64%to24%andcrystallizesindesirableβ'form:Stearic16:018:016:0improvedplasticityandbaking qualitiesacid18:118:118:1+-Margarine:interesterificationofmixtures of18:018:016:0-18:0vegetableoilswithhydrogenatedoilgivesPOSPOPsosdesirable crystallineβ'form-Zero-transMargarines:interesterificationofPalm mid-fraction, rich in POp,reacts at 1-and 3-positionsmixturesofpalmstearinwithvegetableoilsorPOP 58%9%vegetableoil stearinwithpalmoilPOS13%32%Fatsenriched inn-3PUFA:interesterificationof13%SOS2%hardfatwithfishoil.Product:cocoa buttersubstitute
6 Trans Fatty Acids • Trans fats refers to triglycerides containing unsaturated fatty acids in the trans conformation – Found in partially hydrogenated fats or oils – Help to solidify food (melting point higher than cis) • FDA adopted new food labeling • labels give weight of trans fat • restrict low fat definitions by trans fat content – Some margarines are sold as ”trans free” • No hydrogenation • Mixed sat’d and unsat’d fats • Tend to be soft spreads Hydrolysis: Transesterification • Process to rearrange acyl groups on triglycerides – Hydrolyze to remove fatty acids – Reattach fatty acids by esterification P O esterification H2O P O + O O P P Modify nutritional and physical properties 16:0 18:1 P P O O + O O P O P P OH OH OH OH OH OH + hydrolysis H2O Free fatty acids + Interesterification with 1,3-Specific Lipases 16:0 16:0 18:1 POP To prepare value-added products: confectionary fats Palm mid-fraction, rich in POP, reacts at 1- and 3-positions POP 58% POS 13% SOS 2% 9% 32% 13% Product: cocoa butter substitute 16:0 18:0 18:1 18:0 18:0 + 18:1 POS SOS Stearic acid 18:0 Applications of Interesterification • Lard: interesterification reduces 16:0 at sn-2 position from 64% to 24% and crystallizes in desirable β' form: improved plasticity and baking qualities • Margarine: interesterification of mixtures of vegetable oils with hydrogenated oil gives desirable crystalline β' form • Zero-trans Margarines: interesterification of mixtures of palm stearin with vegetable oils or vegetable oil stearin with palm oil • Fats enriched in n-3 PUFA: interesterification of hard fat with fish oil
PhasesofOxidationReactionLipid Oxidation: Lipid oxidation occurs by a ffee radical chain reaction.Threephases of reaction:-Initiationcontains an unpaired electronSlowRHR- + H-HHChain rea-Propagationrapid:R+OROO-self-perpetuatingROO.+RHROOH+ R--TerminationNeeds high levels of freeROO-+RO0 stable productsradicals or low O,RH: lipidRHR-+H-RepresentasROO-:peroxy free radicalsROOH:hydroperoxideFormationofLipidRadicalKINETICSOFAUTOXIDATIONbyfreeradicalmechanism.Hydrogensoncarbonsnexttodoublebondsondiosayuenaomosteasilyremoved (a-carbon)EnergyforHremoval+Radical(kcal/mole)PromoterH-CH,-CH,-CH,100(Catalysts)+RadicalStopperH-CH=CH,103(Antioxidants)H-CH,-CH=CH,85B0TimeCH,=CH-CH-CH=CH,65AutocatalyticInductionTerminationH→H on carbon niexttodoublebond easierto remove
7 Lipid Oxidation • Lipid oxidation occurs by a free radical chain reaction C O - O - C H H + H• C O - O - C H • Represent as RH R• + H• contains an unpaired electron Phases of Oxidation Reaction • Three phases of reaction: – Initiation RH R• + H• – Propagation R• + O2 ROO• ROO• + RH ROOH + R• – Termination ROO• + ROO• stable products Chain reaction-very rapid; self-perpetuating Slow Needs high levels of free radicals or low O2 RH: lipid ROOH: hydroperoxide ROO•: peroxy free radicals KINETICS OF AUTOXIDATION Formation of Lipid Radical by free radical mechanism • Hydrogens on carbons next to double bonds most easily removed (α-carbon) H - CH2 - CH2 - CH3 H - CH = CH2 H - CH2 - CH = CH2 CH2 = CH - CH - CH = CH2 H Energy for H removal (kcal/mole) 100 103 85 65 → H on carbon next to double bond easier to remove