Study on the Change of Muscle Proteins During the Half-Dried Salt-Cured Silver Carp (Hypophthalmichthys molitrix) Processing

Changes in the muscle protein during processing of half-dried salt-cured silver carp (Hypophthalmichthys molitrix) was studied. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) assay indicated that hydrolysis of the muscle proteins took place during processing, particularly at the drying stage. Further in vitro assay on the activities of Cathepsins B and L, which are related to the degradation of the myofibrillar proteins, indicated that Cathepsins B and L still had high activity at the last stage. Total soluble nitrogen (TSN) and nonprotein nitrogen (NPN) showed significant decrease (p < 0.05) and then increased during the drying stage (p < 0.05), which may be caused by the degradation of the myofibrillar proteins and other insoluble proteins. Furthermore, the retained enzymatic activity of Cathepsins B and L may contribute to the proteolysis. Our research indicates that heat pump drying is a novel drying method that can produce the traditional flavor of dried aquatic products, and the formation of high-quality flavor may be due to the degradation of the myofibrillar proteins and water-soluble proteins.