Studies On Bio-Preservation Techniques And Protein Indicators Of Freshness In Large Yellow Croaker (Pseudosciaena Crocea)During Refrigerated Storage

Freshness is an important factor in the aspect of evaluating the quality of aquatic products, which can determine the products value directly. Therefore, how to evaluate fish freshness objectively, rapidly and comprehensively has been a hot issue to be studied in aquatic products research field. It has been well known that protein is one of the most important ingredients of fish muscle, and it can have close association between aquatic quality deterioration and protein degradation. However, the freshness evaluation method based on muscle protein denaturation and degradation has received little attention, and little information is available on protein indicators of freshness based on the proteomics technology.In view of above reasons, this paper investigated the quality indices as well as indicators of freshness based on muscle protein of large yellow croaker(Pseudosciaena Crocea) by the microbiological, physical, chemical and sensory methods, which provided the basis and reference for bio-preservation techniques. This issue researched the effects of biological preservatives on the quality of large yellow croaker during cold storage. Changes in biochemical characteristics as well as tissue microstructure of large yellow croaker muscle were studied from the aspect of the denaturation of protein, which provided relative theoretical basis. The proteomics technologies (2-DE and MS-MS) were applied to investigate the changes in muscle protein and researched the protein indicators. The work aims to give a new idea for the assessment of aquatic products freshness, to discuss the post-mortem change mechanisms of muscle change. The results were taken as follows:1. The comprehensive models for evaluating large yellow croaker freshness and quality were established. The major quality indices that reflecting freshness of large yellow croaker during the storage at4℃,0℃and-2℃were microorganisms (total viable count, shewanella, pseudomonas, enterobacteriaceae, lactic acid bacteria, photobacterium phosphoreum), pH, TVB-N, PV, TBA, ATP, ADP, AMP, IMP, HXR, HX, K, springiness, resilience, sensory score.2. Based on The comprehensive evaluating models, The effects of tea polyphenol (TP), rosemary extract (R), chitosan (Ch) respectively and compound bio-preservatives on the quality of large yellow croaker during refrigerated storage were evaluated. The results showed that the compound bio-preservatives could more effectively maintain the good quality and could extend the shelf life by8-10days compared with the control group.3. The biochemical characteristics a of large yellow croaker muscle occured obvious changes during refrigerated storage. The salt-solubilities, SH contents, as well as Ca2+-ATPase activities of actomyosin obviously decreased with storage time, while surface hydrophobicity increased sharply in the intial phase of storage. The micro structure of the muscle was changed, including the significant decrease of the fiber area, and the increase of gaping and the gaping area. SH contents showed better correlations with storage time, and it may be considered a potential quality index of freshness.4. The study of muscle protein degradation charactrestics on large yellow croaker were shown that the density of16-17KDa protein band in total soluble proteins,22-23KDa protein band in total soluble proteins,35-36KDa protein band in low-salt soluble proteins, MHC, actin, tropomysion,32-33KDa protein band in high-salt soluble proteins happened significantly change with the storage time. Therefore, this seven bands may be thought potential freshness indices poteins. The content of TCA soluble peptide could be considered as quality indices of large yellow croaker. 5. The proteomics and MS-MS technologies were applied to study the changes in muscle protein of large yellow croaker during refrigerated storage at4℃,0℃and-2℃. Eight differently expressed protein spots were obtained in2-DE maps of peptide mass fingerprinting and MS-MS. They were fast/white muscle troponin T embryonic isoform, pyruvate kinase, tyrosine3-monooxygenase/tryptophan5-monooxygenase activation protein, theta polypeptide b, LDB3protein, myosin heavy chain, alpha-enolase-like isoform1, glyceraldehyde3-phosphate dehydrogenase. The eight proteins could be considered as the indicators of freshness.