Changes of Trachurus japonicus Muscle Quality and Protein Physicochemical Properties during Frozen Storage and Correlation Analysis

In order to explore the changes of Trachurus japonicus freshness quality during frozen storage, the color, conductivity, ice crystal size and morphology, texture, K value, TBA value, Raman spectrum, secondary structure of total protein, total sulfhydryl content, active sulfhydryl content and Ca²⁺-ATPase activity of myofibrillar protein were investigated during the frozen storage of −18 ℃ for 90 days with vacuum and air packaging. The results showed that the K value, L^* value, whiteness value and TBA value of samples both in VP and AP groups increased gradually with the extend of storage time, among which the K value increased by 65.83% and 66.44% after frozen storage for 90 days, respectively. At the same time, the porosity of ice crystal in fish muscle increased gradually, while a^* value, b^* value, hardness, chewiness and resilience decreased gradually, however the cohesiveness and conductivity increased firstly and then decreased. The α-helix percentage of muscle protein decreased from 63.28% to 43.70% and 41.91%, respectively, while β-folding, β-turning and random curling percentage increased gradually. The total sulfhydryl content and active sulfhydryl content of myofibrillar protein decreased gradually, Ca²⁺-ATPase activity decreased by 63.58% and 72.52%, respectively. The packaging had little different effect on muscle quality during frozen storage, but had a certain effect on protein biochemical characteristics in which vacuum packaging effect was slightly better than that of air packaging. Correlation analysis showed that K value, whiteness value, TBA value, sulfhydryl content, Ca²⁺-ATPase activity, total protein secondary structure content of the samples of the two groups were significantly correlated (P<0.05) or highly significantly correlated (P<0.01) with the frozen storage time and each other, indicating that those indexes could be used as effective indexes to evaluate the quality change of T. japonicus during frozen storage. This study provided a theoretical reference for the further studying of the quality change mechanism and the shelf life prediction of T. japonicus.