Abstract: The carcass undergoes a series of complicated physiological and biochemical processes driving the muscle to meat conversion after slaughter. Studying rigor development and postmortem aging is expected to provide theoretical supports for meat quality improvement and processing. Six crossbred rams (Small-tailed Han sheep × Beijing native sheep breed) were slaughtered, and both longissimus dorsi muscles (n = 12) from each carcass were excised and stored at 4 ℃ for 0.5, 2.0, 6.0, 12.0, 24.0, 48.0, 72.0, 120.0 and 168.0 h to determine pH, ATP content, sarcomere length, shear force, myofibril fragmentation index (MFI), protein degradation and μ-calpain activity. During the conversion of muscle to meat, pH initially decreased and then remained not changed significantly at 24 h postmortem (P > 0.05). Shear force first increased until reaching a maximum value at 24 h after slaughter and then decreased. Sarcomere length was first shortened until reaching a minimum value at 48 h and then extended gradually. ATP content was initially increased, then decreased and finally tended to be stable. The 80 kD subunit of μ-calpain degraded almost completely disappeared at 24 h, and a 78 kD subunit was formed firstly and then degraded completely at 48 h after slaughter. Desmin and troponin T as the substrates of μ-calpain were degraded during ageing and intact proteins were scarcely be observed at 168 h. In conclusion, the development of rigor mortis in longissimus dorsi started at 2 h postmortem and reached a peak at 24 h, and it began to disappear at 48 h. The meat tenderness was improved greatly after the complete disappearance of rigor mortis.

Key words: lamb longissimus dorsi muscle, rigor, tenderness, aging