The Effects Of Tea Polyphenol Combined With Chitosan Coating On Muscle Protein Of Refrigerated Large Yellow Croaker(Pseudosciaena Crocea)

Large yellow croaker (Pseudosciaena crocea) is an important economic fish in the coastal of China. It is popular due to its delicious meat, high protein and unsaturated fatty acid value. But like other fish, large yellow croaker is susceptible to spoilage. Therefore, how to evaluate fish freshness objectively and explore appropriate preservatives has been a hot issue to be studied in aquatic area. The traditional evaluation method is through the sensory evaluation, microorganism, physics and small molecules. But it has been well known that protein is one of important ingredients of fish muscle, and it can have a better relationship between aquatic quality deterioration and protein degradation. Currently, the study on protein denaturation and degradation during fish storage is still in its infant stage, and little information is available on protein indicators of freshness based on the proteomics technology. The protein used as aquatic freshness evaluation method has been reported rarely. This paper investigated the effects of tea polyphenol combined with chitosan coating on muscle protein of refrigerated large yellow croaker.(1) This issue researched the changes of myofibril protein and tissue microstructure of large yellow croaker muscle, which provided relative theoretical reference about developing biological preservatives and muscle quality.(2) Explore the effects of tea polyphenol and chitosan on types of muscle protein by SDS-PAGE.(3) The proteomics technology was applied to investigate the changes in muscle protein and research the protein indicators of freshness. The main results were showed as follow.1. The dissolution quantity, Ca2+-ATPase activities, as well as "4℃" and "0℃" groups of SH contents of myofibril protein obviously decreased with the extension of storage time, while "4℃+preservative" and "0℃+preservative" groups of SH contents changed little."4℃"\"0℃" groups of surface hydrophobicity increased sharply in the initials phase of storage, then began to flat, however "4℃+preservative" and "0℃+preservative" groups were opposite. The decline of dissolution quantity and Ca2+-ATPase activities was due to the oxidation of SH. The increase of surface hydrophobicity caused the oxidation of SH on the internal hydrophobic groups. The results also showed that tea polyphenol and chitosan delayed the exposure of hydrophobic groups and the oxidation of SH directly and indirectly, and the higher the temperature was, the faster myofibril protein denaturaed. The microstructure of the muscle was changed quickly in the early stage of storage, including the significant decrease of the fiber area, and the increase of the gaping area. Low temperature, tea polyphenol and chitosan had a certain inhibition effect on denaturation of myofibril protein and deterioration of microstructure.2. The molecular weight of large yellow croaker muscle protein was mainly in the range of6.5-200.0kDa. At the end of storage, the relative optical density of24.1kDa,21.2kDa protein bands in total soluble proteins and40.3kDa、33.4kDa、30.3kDa、25.4kDa protein bands in high-salt soluble proteins had suffered decrease with the different degree. In water soluble proteins, the relative optical density of24.1kDa,21.2kDa protein bands also declined, and "4℃","0℃" groups of77.7kDa,33.5kDa protein bands decreased rapidly in the initial stage, then flattened out. The relative optical density of94.9kDa、41.7kDa、36.6kDa、26.6kDa and19.8kDa protein bands in low-salt soluble proteins decreased significantly during storage. Therefore, these seven bands may be thought to be potential protein indicators of freshness. The content of TCA soluble peptide showed a good linear positive correlation with storage time, which could be considered as quality indices of large yellow croaker, especially at4℃. Generally, low temperature and bio-preservatives were effective in the inhibition of protein degradation.3. Using2-DE technology, nineteen and twenty-one different protein spots were obtained from "4℃+preservative" and "0℃+preservative" groups. Most of these spots declined during storage, which inferred that preservatives could inhibit denaturation and degradation of protein. Two of them were identified by MS. They were desmin (Takifugu rubripes) and zinc finger protein84-like (Danio rerio). These two proteins and other unidentified differential protein could be considered as the protein indicators of freshness.