The Studies Of Antioxidation And Mechanism Of Tea Polyphenols On Grass Carp

China is a big country with extremely rich and various freshwater aquatic resource. The freshwater fish, which with low fat content and high protein content, is an important part of the daily diet structure. The article takes the Hunan grass carp as the research object, use food chemistry and instrumental analysis methods, study the antioxidant effect and mechanism of tea polyphenols in the frozen freshwater fish fat, discuss the application prospect of tea polyphenols on freshwater fish preservation, in order to provide a solid theoretical basis for improving the quality of aquatic products in the processing. The research results are as follows:1.22kinds of fatty acids had been separated and determinated from fresh grass carp fat by GC-MS:the tetradecanoic acid, fifteen acid, palmitic acid, linolenic acid, seventeen eicosapentaenoic acid, seventeen acid, linoleic acid, oleic acid, twenty C five acid, twenty-two C six acid, twenty-two C four acid, twenty-two eicosapentaenoic acid etal. Among them, Saturated fatty acids accounted for27.72%, unsaturated fatty acids accounted for71.63%, in addition to containing the common flora and fauna even-numbered fatty acid, also containing odd-numbered fatty acid such as seventeen eicosapentaenoic acid and margaric acid, which worthy of further study. We have also found that grass carp contains many kinds of fatty acids C20and C22, which have positive effects on the human body.2. In freezing conditions (-20℃), analysis the fatty acids in fish fat with different concentration of tea polyphenols by GC-MS. The result shows:Adding tea polyphenol can effectively inhibit fatty acid oxidation, reduce the decomposition rate of C20, C22fatty acid, the effect is obvious on the unsaturated fatty acid, especially the high unsaturated fatty acid.3. Changes of fatty acid oxidation product malondialdehyde were measured by thiobarbituric acid test, the result shows that:In the early frozen storage period, the value of MDA in fish fat changes little, but with the prolonging of the frozen storage time the MDA value increased, the growth rate significantly speed up especially after six months. Through the comparison of the MDA generating speed in four groups of adding tea polyphenol can be found that tea polyphenols can inhibit the oxidation of grass carp fat, effectively reduces the production of fat oxidation product MDA.4. Sulfhydryl content and surface hydrophobicity of the oxidation fat and protein simulation system in frozen storage conditions had been studied by spectrophotometer and fluorescence spectrophotometer, the result shows:In frozen storage conditions, the sulfhydryl content of myofibrillar proteins can descend, the surface hydrophobicity will increase. Adding oxidized fish oil will make the sulfhydryl content of sulfhydryl myofibrillar protein solution reduce faster, the fish oil oxidation degree is higher and the effect is more remarkable, and also oxidized fish oil will increase the surface hydrophobicity of myofibrillar protein sample. Tea polyphenols can effectively inhibit the reduce of thiol content, they has a protective effect on it. To a certain extent, tea polyphenols can prevent the occurrence of crosslinking and aggregation of protein molecules, but the effect is not obvious on protein surface hydrophobicity increased due to oxidation of fish oil.5. Ectrophoretic analyses of myofibrillar protein in groups of grass carp by SDS-PAGE, the result shows:During frozen storage, the MHC and actin bands were obviously decreased, and with the extension of time, the weakened degree is more and more obvious. In the third month, the new strip belt has appeared above the concentrated gum of Ⅱ and Ⅲ groups. This suggests that the samples generated a certain amount of macromolecular protein substances. Considering the change of thiol and surface hydrophobicity, it shows that oxidized fish oil can make fish protein molecular aggregation, thereby electrophoresis banding moving up. But the strip of the control group which have adding tea polyphenols decreased slowly, it shows that tea polyphenols can inhibit that due to fat oxidation caused the occurrence of protein aggregation.6. Determination of the original myofibrillar protein by infrared spectrometer, the result shows:In the two stage structure, β-folding accounted for30.21%, random-coil accounted for0%, α-helix accounted for38.62%, β-angle accounted for31.17%, it showed a stable ordered structure. During frozen storage, in Ⅱ, Ⅲ group, p-folding and α-helix reduced obviously, β-angle increase obviously, and the crimp degree of protein secondary structure was high. In the sixth month, α-helix of Ⅱ, Ⅲ group have disappeared, β-folding was obviously less than I group. Compared with Ⅳ, Ⅴ, Ⅵ group, which have adding tea polyphenol, changes of protein secondary structure was relatively slow in the sample group with tea polyphenols, it shows that tea polyphenols can inhibit the changes of protein secondary structure caused by fat oxidation.