Muscle Quality of Sword Prawn (Parapenaeopsis hardwickii) during Cold Storage Based on Changes of Endogenous Enzyme Activity

Objective: To investigate the changes of endogenous enzyme activity and muscle quality characteristics of Sword prawn (Parapenaeopsis hardwickii) under cold storage. Methods: Sword prawn (Parapenaeopsis hardwickii) was taken as the research object. The muscle texture, TCA-soluble peptide, myofibril protein content and myofibril fragmentation index, as well as the activities of endogenous enzymes in the head and muscle of intact and headless shrimp were compared and analyzed at 0°C for 0, 2, 4 and 6 d. Results: With the extension of cold storage time, the content of TCA-soluble peptide and myofibril fragmentation index in muscle of both groups showed an increasing trend. The myofibril protein content gradually decreased, their content in muscle of whole shrimp group and headless shrimp group reduced by 56.65% and 44.63%, respectively, after 6 d of cold storage. While the hardness and elasticity of shrimp in both groups always decreased. During cold storage, the trypsin activity in the head of whole shrimp group decreased gradually, while the activity in the muscle of whole shrimp group increased continuously. The trypsin activity in the muscle of decapitated shrimp group reduced slowly, and the trypsin activity in the head and muscle of whole shrimp group and the muscle of decapitated shrimp group changed by 16.9%, 68.8%, and 15.2%, respectively. In shrimp muscle, the calpain activity decreased with the extension of cold storage time, and the decrease rate was higher in whole shrimp group. The changes of the activities of cathepsin B, D, H and L were different during cold storage. The cathepsin activities in decapitated shrimp were higher than those in whole shrimp. The activities of cathepsins in each muscle subcellular structure of the two groups decreased gradually during cold storage. And the activities in whole shrimp group were higher than those in decapitated shrimp group. Conclusion: The muscle quality characteristics of the headless shrimp group were better than those of the whole shrimp group, and the endogenous enzyme activities in whole shrimp group were relatively higher than those in decapitated shrimp group during cold storage. Therefore, decapitated shrimp storage is more conducive to protect shrimp meat quality.