Correlation between changes in freshness and biochemical characteristics of Larimichthys crocea muscle protein during cold storage

In order to study the correlation between Larimichthys crocea muscle protein and freshness quality during cold storage, the quality was judged by freshness indicators such as color, TPA, TVB-N and sensory score, water-soluble protein and salt-soluble protein were extracted from L. crocea muscle and biochemical characteristics were analyzed during storage, including protein content, total sulfhydryl content, carbonyl content, protein molecular weight and particle size distribution. The correlation between changes in freshness and biochemical characteristics of L. crocea muscle protein was analyzed. The L^*, a^* and W values of L. crocea fish meat decreased, while the b^* value increased; the chewiness, stickiness and hardness of L. crocea decreased obviously; TVB-N increased from (4.42±0.21) mg/100 g to (38.46±0.87) mg/100 g, and approached the secondary freshness standard on the 8th day, but the sensory evaluation score was not acceptable on the 8th day. During storage, the content of salt-soluble protein, water-soluble protein, total sulfhydryl content, and carbonyl content of L. crocea had similar changes. The content of salt-soluble protein increased slightly in the early stage and decreased in the late stage, from (159.36±6.51) mg/g to (91.99±13.82) mg/g. The quality score decreased by 42.27%. The content of water-soluble protein decreased from (33.68±2.13) mg/g to (17.57±0.70) mg/g, and the quality score decreased by 47.77%. The contents of sulfhydryl group and carbonyl group of salt-soluble protein increased from (3.95±0.04) mol/10⁵ g pro to (1.08±0.13) mol/10⁵g pro and from (1.08±0.04) nmol/mg to (3.94±0.43) nmol/mg, respectively. The sulfhydryl and carbonyl contents of water-soluble protein changed from (4.74±0.17) mol/10⁵ g pro to (2.66±0.15) mol/10⁵ g pro and (0.21±0.14) nmol/mg to (2.67±0.25) nmol/mg, respectively. The particle size of salt-soluble protein increased from (203.32±5.44) nm to (425.40±8.63) nm during 0-8 days of cold storage, and decreased to (317.03±1.20) nm after 2 days. The particle size of water-soluble protein decreased from (190.80±0.30) nm to (144.23±1.32) nm. In the SDS-PAGE electrophoresis, there was a new protein band produced at about 30 ku, and the amount of protein was reduced. The results showed that the biochemical properties of water-soluble protein and salt-soluble protein have a good correlation with freshness, and water-soluble protein has better correlation.