Effects Of Protein Oxidation On The Gel Properties Of Grass Carp Myofibrillar Protein

The grass carp muscle is the research object in this study,the influence of the hydroxyl radical-generating system(·OH)and the peroxyl radical-generating system(ROO·)on the physicochemical properties,protein structural and gel properties of myofibrillar protein(MP)were detailed studied,and the effect of protein oxidation induced by different adding antioxidants(adding cryoprotectans,adding cryoprotectans and bamboo leaf antioxidants(AOB),adding cryoprotectans and sodium erythorbate,adding cryoprotectans and PG)on the structural and gel properties of MP were also studied,in order to illustrate the mechanism of fish quality deterioration and protein denaturation caused by oxidation.In order to improve the quality of minced fish products from the perspective of protein oxidation.The main results were as follows:1.Two kinds of simulate oxidation system could changed the structure and conformation of myofibrillar protein in grass carp,The main results were as follows:the carbonyl content increased significantly after oxidization,which increased by 111.35%compared to the initial value when the concentration of H2O2 reached 10 mmol/L,while the AAPH concentration reached to 5 mmol/L,which increased 74.67%.With the increasing concentration of oxidants,the total thiol group levels,free thiol group levels,and free amine content decreased significantly,while bityrosine content and surface hydrophobicity increased significantly.Protein oxidation could caused the secondary structure changes of MP.The structure of a-helix in protein was decreased,while the?-sheet was increased during the oxidation progress.SDS-PAGE pattern analysis showed that aggregation and degradation of protein were observed,resulted in molecular weight greater than 200 Ku protein aggregates.2.Effect of free radicals oxidation on thermally aggregation behaviors in grass carp myofibrillar protein,The main results were as follows:with the increasing of temperature,the oxidized and unoxidized protein particles gradually shifed to the high nanometer,when the ranged of 70?80?,the protein particles began to moved to low nanometer.At the same denaturing conditions,the greater the degree of oxidation,the larger the particle size.The Zeta-potential of the grass carp increased first and then decreased with the increaseing of temperature,and the Zeta-potential value of the grass carp after oxidation was higher than that of the non-oxidized protein.The thermal stability of the protein was determined by DSC,and the thermal stability was increased under low concentration,while decreased under high concentration and the oxidation degree was higher and the enthalpy decreased.While ROO·changeed more complex,but lower than·OH oxidation systems.Turbidity increased similarly "S" type.The heating temperature of 40??50?,the protein turbidity increased the fastest,when reached a certain temperature,the maximum turbidity but different degree of oxidation protein turbidity(Eg,when H2O2 was 0.1,1,10 mM,respectively,the temperature was 80?,70?,60?),ROO·oxidation turbidity changed trend similar to the oxidation of·OH.The hydrophobicity of the low concentration of oxidized protein increased first and then decreased,while the surface hydrophobicity of the high concentration of oxidized protein decreased.protein heated aggragation formed uneven grain size of similar spherical shape.3.Effect of free radicals oxidation on gel behaviors of grass carp myofibrillar proteins,the main results were as follows:protein oxidation could decrease solubility.In addition,gelation properties of myofibrillar protein were also influenced by oxidation,the network structure of the gel were damaged,and the portable water in gel inverted to the free water.Those changes of the gel finally induced the obvious decreases in the gel strength,and gel water-holding capacity.4.The myofibrillar protein structure of samples by different adding antioxidants was changed during frozen storage.The carbonyl content and the bityrosine content increased significantly,indicating protein oxidation was occurred during frozen storage.Results showed that adding PG and AOB during frozen storage can inhibit protein oxidation effectively.After frozen for 120 d,carbonyl content of the control group,adding AOB group,adding sodium erythorbate group,adding PG group were increased by 51.37%,38.20%,38.51%and 28.11%,respectively,while the sulfhydryl content decreased by 34.24%,25.88%,22.90%and 20.69%,respectively.And Ca2+-ATPase activity decreased by 52.17%,39.13%,47.83%,and 30.43%respectively.Gel strength decreased by 12.73%,6.78%,8.09%and 7.76%,respectively,and whiteness decreased by 6.67%,4.14%,5.80%and 4.30%respectively.The water holding capacity decreased by 13.34%,8.24%,9.27%and 7.69%respectively.The analyses of surface hydrophobicity,SDS-PAGE,secondary structure and gel microstructure were also proved this conclusion.Because AOB was a natural antioxidant,so it can be used in frozen surimi process safely,in order to improve the quality of surimi.