Effect Of Tea Polyphenol On Quality Change Of Cultured Large Yellow Croaker During Refrigerated Storage

Large yellow croaker is as an important representative of Chinese economic saltwater fish because of its good taste and high nutritional value. However, fish is liable to suffer spoilage due to the high content of the proteins, high activities of proteases, so protein degradation of fish will occur during storage time, eventually leading to the decline of its freshness and reduce the acceptance of the flesh for human consumption. Biochemical changes of proteins are closely associated with the quality of large yellow croaker during storage. Tea polyphenols (TP) is the generic terms of compounds with antioxidation, bacteriostasis and cholesterol-lower. It is used for the research fresh keeping of aquatic product.In view of the above-mentioned facts, the large yellow croaker was studied under controlled ice-temperature condition. For these reasons, first of all, the objective of our study was to evaluate large yellow croaker fillets quality using sensory, microbiological and physicochemical analyses over a period of25days. We aimed to provide important theoretical basis for the TP preservation mechanism. Secondly, the effect of TP on biochemical and functional characteristics of muscle protein from large yellow croaker were studied based on the denaturation and degradation of protein. Finally, the proteomics technologies were applied to study the effect of TP on the integrity of muscle protein All of the evaluated parameters were used to identify those factors that are most sensitive to post-mortem changes to explore the mechanism of TP effect on quality occurring in the fillet that may be related to freshness. The main results were described as following:1. The moisture, crude protein and fat, ash content of cultured large yellow croaker were66.42%,17.91%,13.55%and1.25%respectively. We used the TP solution concentrations of0.1%,0.2%and0.3%to treat large yellow croaker, and quality changes of the fillet of large yellow croaker stored at controlled ice-temperature storage were observed. It was showed that TP could inhibited the increase of TVC, kept at the relative low TBA, K and pH values, enhances hardness and maintains springiness and delayed the other physical and chemical parameters. The higher the concentration of TP was, and the more obvious preservation effects were. The results showed that the TP solution of0.2%and0.3%was the optimal preservation. 2. The changes of biochemical characteristics and tissue microstructure of large yellow croaker were studied by salt solubilities, Ca2+-ATPase activities, sulfhydryl contents, UV characteristic curve, SDS-PAGE analysis and muscle microstructure from large yellow croaker treated with different concentration TP during ice-temperature storage. The results showed that TP could slow down the decrement of the salt solubilities, total contents of sulfhydryl and Ca2+-ATPase activities of myofibrillar protein significantly. The SDS-PAGE analysis indicated that TP can decelerate the rate of myofibrillar protein degradation during ice-temperature storage, too. The results of UV characteristic absorption spectra scanning made further expansion that TP could effectual suppressed the oxidative damage of proteins. At the same time, the pictures of muscle microstructure were showed the fiber area was decrease and the gaping area was increase significantly. So TP could remarkable protected protein of large yellow croaker and the best concentration was about0.2%and0.3%.3. We studied the changes in functional characteristics of myofibrillar protein in large yellow croaker treated with different concentration of TP during ice-temperature storage. The results showed that the concentration more than0.2%of TP could slow down the decrement of emulsion and emulsification stability and the increment of surface hydrophobicity of myofibrillar protein. TP not only could increase the gel strength substantially, but also impact gel form by protein becoming. G’valve was gradually reduced with the extending of storage time, however, escalating along with the increasing of concentration of TP. TP could improve the emulsifying and gel properties of fish protein significantly when the concentration of TP was0.2%and0.3%.4. The changes in the integrity of muscle protein in large yellow croaker treated with TP by the proteomics technologies were studied during ice-temperature storage. The results showed that we observed different expression of twelve protein spots which described as the statistically significant and significance of the analyzing. Based on fingerprint analysis and comparison of the database, we retrieved six proteins. TP may significantly affect the variety of the functional proteins, including G protein-regulated inducer of neurite outgrowth1, vesicle-associated membrane protein, SH3and PX domain-containing protein and Laminin subunit gamma.