Effect Of Lipid And Protein Oxidation On Warm-over Flavor And Texture Characteristic Of Braised Beef

Warm over flavor and texture deterioration is attributed to lipid and protein oxidation of cooked meat productes during chilled storage.The objective of this paper was to investigate the effect of lipid and protein oxidation of braised beef on warm over flavor and texture characteristic during chilled storage and the role of heme iron and nonheme iron as pro-oxidant on the interaction between lipid and protein oxidation in braised beef during storage time.Hexanal and heme iron had been added to beef myofibrillar protein in order to study the effect of lipid oxidation product and pro-oxidant on myofibrillar protein oxidation and gel formation,illuminating the internal reaction of warm over flavor and texture deterioration.Major results of this paper were showed as follows:1.The effect of lipid oxidation on warm over flavor in braised beef during chilled storage.The Aw had no signficant difference and maintained in the extent of 0.987?0.993 over the chilled storage time.The pH values showed ascending and descending in braised beef with chilled storage time.Peroxide value,TBARs value,lipid carbonyl value and diene value were signficantly increased(p<0.05)in braised beef during storage time.The content and species of phospholipid were more than free fatty acid,and the oxidative rate of phospholipid was highest in 0-1 day storage,saturated fatty acids,monounsaturated fatty acids and polyunsaturated fatty acids were decreased by 57.00%,63.83%and 65.45%respectively.Phospolipid had a great contribution to volatile flavor of braised beef during chilled storage time.Aldehyde,alcohols and ketone compounds accounted for 70%,10%and 11%of total volatile compounds respectovely.Compared to 0 day storage,the total volatile compounds of 1,3,5 days increased by 74.62%,162.6%and 113.92%respectively.The representative volatile compounds of braised beef were hexanal,rl-heptnanal,octanal,nonanal,1-pentanol,1-octene-3-ol,2-pentylfuran and 2,3-octanedione.The key volatile compounds were formed in 0?1 day storage and warm over flavor was emerged when the content of these incresed.The content of volatile compounds were slowly decreased during 3?5 day storage.2.The effect of protein oxidation on texture properties and interaction of lipid and protein oxidation in braised beef during chilled storageThe total content of iron within the range of 17.324 to 18.923 mg/kg in braised beef during chilled storage from 0 to 5 days.Meanwhile,the content of heme iron decreased from 13.874 mg/kg to 9.382 mg/kg(p<0.05),while the content of nonheme iron increased from 4.571 mg/kg to 4.571 mg/kg(p<0.05).Lipid oxidation products(such as hexanal and malondialdehyde)and myoglobin oxidation products(heme iron and nonheme iron)participated in protein oxidation,which led to a significantly increased(p<0.05)of protein carbonyl content,free thiol group generated stable disulfide bond structure and weakened water holding capacity,resulting in the value of hardness and shear force signficantly increased(p<0.05).3.The effect of lipid oxidation product and heme iron on myofibrillar protein oxidationThe content of myofibril protein carbonyl and dipolytyrosine significantly increased(P<0.05)when added 10 mM and 20 mM heme iron.Meanwhile,water holding capacity of heat-induced gel increased to 97%while rheological study showed no significant effect(p>0.05)on protein denaturation temperature and viscoelasticity of gel.The content of protein carbonyl significantly increased(p<0.05)while the content of free sulfhydryl significantly decreased(p<0.05)when increasing the concentration of hexanal.The protein denaturation temperature decreased from 55? to 50? and storage modulus and loss modulus of gel decreased compared with control,while water holding capacity and hardness significantly increased when the concentration of hexanal was 20 mM.When hexanal concentration added to 40 mM,the protein denaturation temperature further decreased to 43? and storage modulus and loss modulus of gel increased substantially.Meanwhile,the hardness of heat-reduced gel increased by 97.8%and due to the formation of strong covalent bond of myofibrillar protein,water holding capacity decreased to 51.9%?54.1%.