Postmortem Changes In Muscle Proteins Of Chinese Shrimp (Fenneropenaeus Chinensis) During Storage

Aquatic products are favored by many people because of its abundant nutrition. Unfortunately, sea foods are liable to suffer spoilage due to the high content of proteins and moisture, floppy muscle tissue, high activities of proteases, autolysis and protein degradation, reducing the acceptance of the flesh for human consumption. Biochemical changes are closely associated with the quality of aquatic products during handling and storage. Recently, considerable research efforts have mainly focused on the biochemical characteristics of muscle proteins of fish; however, there is little information about the postmortem changes of Chinese shrimp (fenneropenaeus chinensis).In this paper, the post mortem changes in muscle proteins of Chinese shrimp during storage, and the effects of tea polyphenols, chitosan, trehalose, and sodium lactate on muscle proteins were studied. The results are described as following:1. The post mortem changes in biochemical properties of muscle proteins in Chinese shrimp(fenneropenaeus chinensis) stored at-2℃,0℃and 4℃were studied by analysising protein composition, salt solubilities, sulfhydryl contents, Ca2+-ATPase activities and SDS-PAGE. The results showed that the contents of myofibrillar, sarcoplasmic and stroma protein reduced gradually, while the contents of alkali-soluble protein increased during storage. The salt solubilities, total contents of sulfhydryl and Ca2+-ATPase activities of actomyosin were all decreased with the extending of time. Actin, myosin heavy chain (MHC) and tropomyosin degraded markedly as shown by SDS-PAGE. These results suggested muscle proteins denatured markedly during storage, the lower storage temperature, the slower protein denaturation. The Ca2+-ATPase activity and total content of sulfhydryl displayed strong correlations with time, the former may be considered suitable indicator for evaluating the degradation of muscle proteins stored at-2℃,0℃and 4℃, and the latter may be considered suitable indicator for evaluating the degradation of muscle proteins stored at-2℃.2. The effects of tea polyphenols and chitosan treatment on biochemical properties of shrimp during chilled storage were studied. The results indicated that tea polyphenols and chitosan could slow down the decrement of the salt solubilities, total contents of sulfhydryl and Ca2+-ATPase activities of actomyosin significantly. The SDS-PAGE analysis showed that the two treatments can delay the degradation of proteins from shrimp stored at 0℃. Moreover, Chitosan exhibited greater protective effect on protein denaturation than tea polyphenols.3. The changes of the biochemical characteristics of muscle proteins during frozen storage at-20℃,-30℃,-40℃and -80℃were investigated. The results showed that the contents of myofibrillar, stroma and sarcoplasmic protein gradually reduced with the extending of time, while the content of alkali-soluble protein increased. The salt solubilities, total contents of sulfhydryl and Ca2+-ATPase activities declined as frozen storage progressed. The temperature of frozen storage exhibited significant influence on the denaturation of actomyosin. Meanwhile, the cooking loss and hardness increased over frozen storage time.SDS-PAGE analysis showed that the myofibrillar protein decomposed during frozen storage, and the decomposition of myofibrillar protein was couple with the frozen storage time. On the other hand, the storage temperature has significant effect on the decomposition of the myofibrillar protein. The lower storage temperature could slow down the denaturation of myofibrillar protein.The changes of histology of shrimp muscle stored at different temperatures were investigated. The results indicated that the fine structure of muscle was destroyed. The gap between the muscle fibers became larger, and the fibers contracted apparently. The degree of destruction related to the temperature of frozen storage. The lower temperature could inhibit the frozen destruction of shrimp muscle.4. The cryoprotective effects of chitosan, trehalose and sodium lactate on shrimp muscle were studied in comparison with negative control during storage at-20℃up to 90 days. Salt solubilities, total contents of sulfhydryl and Ca2+-ATPase activities were detected as quality indicators. The results showed chitosan, trehalose and sodium lactate could retard the protein denaturation of frozen shrimp. Among the above three antifreeze agents, trehalose showed the best antifreezing effect, followed by sodium lactate.