Abstract:

In this study, the tenderness indexes (muscle fiber diameter (MFI) and myofibril ultrastructure) and calpain
activity of the meat of yaks of different ages during postmortem were measured. The results showed that MFI of yak meat
at different ages significantly changed (P < 0.05), myofibril ultrastructure was completely disrupted, Z line was ruptured,
and calpain activity was significantly decreased (P < 0.05) during aging. In addition, calpain activity of male yak meat was
higher than that of female yak meat during aging. The aging time showed a significant correlation with tenderness indexes
and calpain activity (P < 0.01). After seven days, the distinction of yak meat at different ages was decreased; meanwhile, the
tenderness of meat was improved. The aging time of male yak meat was longer than that of female yak meat.

Key words: yak, age, calpain, tenderness