Investigation of the relationships between different enzymes and postmortem duck muscle tenderization

Postmortem tenderization is induced by the cooperation of various related enzymes. In this study, CaCl2 and MDL-28170 (Cbz-Val-Phe-H, a calpain inhibitor) were used to regulate the postmortem tenderization process of duck breast muscle. Then the relationship between muscle tenderness change and different enzymes was investigated. At day 0, day 1, and day 4 of the postmortem ageing, the shear force, myofibril fragmentation index (MFI), enzymatic activities of calpains, cathepsin-B, caspase-3, Na+/K+-ATPase, and Ca2+-ATPase were respectively determined. The results showed that duck muscle tenderness could be significantly raised by CaCl2 and reduced by MDL-28170, respectively (P < 0.05). The CaCl2 treatment did not promote the calpains activity as predicted (P > 0.05), but significantly up-regulated the activity of cathepsin-B (P < 0.05). The MDL-28170 significantly inhibited the activity of the calpain system at day 1 (P < 0.05) and raised the activities of the selected 3 apoptosis-related enzymes, including caspase-3, Na+/K+-ATPase, and Ca2+-ATPase, at both day 1 and day 4 (P < 0.05). These data indicated that in duck, the calpain system could be well activated after death, and cathepsin-B might also play an important role in postmortem muscle tenderization. The caspase-3, Na+/K+-ATPase, and Ca2+-ATPase probably have no significant effects on duck muscle tenderness. It might provide useful information for duck production and further research on postmortem muscle tenderization.