Effects of Different Quick-freezing Methods on Protein Properties of Largemouth Bass (Lateolabrax japonicus)

In this paper, largemouth bass was used as raw material to study the effects of different cooling rates (liquid nitrogen quick freezing (1.81 ℃), freezing liquid quick freezing (0.15 ℃), flat plate quick freezing (0.14 ℃)) in freezing storage (0, 1, 2, 4, 12, 24 weeks), the influence of the physical and chemical properties of largemouth bass protein, by measuring the salt-soluble protein, sulfhydryl group, carbonyl group, Ca²⁺-ATPase activity content, surface hydrophobicity, endogenous fluorescence spectrum and protein composition changes in the fish meat, and using double factor variance and correlation analysis study quick-freezing method and storage time to investigate the degeneration of fish protein after freezing. The results showed that with the passage of frozen storage time, the value of salt-soluble protein showed a downward trend: The plate group and liquid nitrogen group had the lowest and the highest at the end of the frozen storage, respectively; the activity values of sulfhydryl and Ca²⁺-ATPase both increased first and then decreased. The endogenous fluorescence intensity of fibrin increased, resulting in a blue shift phenomenon, and the value of myofibrillar protein carbonyl and surface hydrophobicity increased significantly (P<0.05). The results of SDS-PAGE electrophoresis showed that myofibrillar protein was degraded during the freezing period, while the liquid nitrogen group had a faster cooling rate and a slower degree of protein degradation, while the plate group was the opposite. The volume of ice crystals formed by quick freezing of liquid nitrogen was similar to the distribution of water in the raw material, which was conducive to storage. Compared with liquid nitrogen quick freezing, the time for the formation of the maximum ice crystal zone in the quick freezing of liquid nitrogen was longer than that of liquid nitrogen quick freezing and shorter than that of flat quick freezing, and there was not much difference between the two. The correlation analysis between the two-factor variance and the indicators showed that the quick freezing method had a significant effect on the active sulfhydryl group and the maximum fluorescence intensity of myofibril protein (P<0.05). The freezing time was the main factor affecting the protein of the sea bass. The oxidative modification of amino acid side chain groups in myofibrillar protein was the main factor causing the degradation or aggregation of protein.