Trans Fatty Acids Hydrolysis:Transesterification .Trans fats refers to triglycerides containing Process to rearrange acyl groups on triglycerides -Hydrolyze to remove fatty acids -Found in partially hydrogenated fats or oils -Reattach fatty acids by esterification Free fatty acids -Help to solidify food (melting point higher than cis) 0 OO P FDA adopted new food labeling 一P+ hydrolysis -0 P O P -P -0 160 181 OHOH 二oH+二oH HO OH OH Mixed sat'd and unsat'd fats ·Tend to be soft spreads E Modify nutritional esterification and physical properties Interesterification with 1,3-Specific Lipases Applications of Interesterification To prepare value-added products:confectionary fats Lard:interesterification reduces 16:0 at sn-2 position from 64%to 24%and crystallizes in desirable B'form acid→ 18:1 improved plasticity and baking qualities Margarine:interesterification of mixtures of POp POS vegetable oils with hydrogenated oil gives desirable crystalline B'form Zero-trans Margarines:interesterification of Palm mid-fraction,rich in POP,reacts at 1-and 3-positions mixtures of palm stearin with vegetable oils or P0P58% 9% vegetable oil stearin with palm oil P0S13% 32% Fats enriched in n-3 PUFA:interesterification of S0S2% 13% hard fat with fish oil. Product:cocoa butter substitute
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
Lipid Oxidation Phases of Oxidation Reaction Lipid oxidation occurs by a free radical chain reaction Three phases of reaction: contains an unpaired electron 一+ Slow H分2 -Propagation 0. C、入入入 R+02一R00 ROO+RH ROOH +R- 0 -Termination ROO+ROO. ·stable products RH:lipid Represent as RH R+H ROOH:hydroperoxide ROO:peroxy free radicals Formation of Lipid Radical KINETICS OF AUTOXIDATION by free radical mechanism Hydrogens on carbons next to double bonds +Radical - Promoter (kcallmole) H-CH2-CH2-CH3 (Catalysts) 100 Radical Stopper H-CH=CH2 103 Antioxidants) CH,-CH-CH, 85 Time Induction Autocatalytic Termination 4m年-c-am 6 -.H on carbon next to double bond easier to 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