Effects of lamb age, muscle type, and 24-hour activity of endogenous proteinases on postmortem proteolysis

The objectives of this study were to examine the amount of postmortem proteolysis in three different lamb muscles at different ages and to determine whether a relationship exists between the extent of myofibrillar degradation and certain endogenous proteinase activities. Wether lambs were slaughtered at 8 (n = 6) and 26 (n = 6) wk of age. Samples were taken from the longissimus (LM), gluteus medius (GM), and supraspinatus (SS) muscles for determining myofibrillar fragmentation index (MFI) at 1 and 7 d postmortem, cathepsins B and B + L, cystatin(s), micro- and m-calpain and calpastatin 24-h activities, and muscle fiber type and area. Muscle samples were removed for SDS-PAGE analysis at 0, 1, and 7 d postmortem. The SS muscle consisted of more (P 0.05) oxidative fibers, whereas no age effects (P 0.10) were observed for fiber type. The younger lambs had higher (P 0.01) cathepsins B and B + L, cystatin, and calpastatin 24-h activities but less (P 0.01) m-calpain activity than did the 26-wk-old lambs. Within each age, the SS muscle had the highest (P 0.05) mu-calpain, m-calpain, and calpastatin specific activities. The MFI values and SDS-PAGE results indicate that less proteolysis occurred in the SS muscle. Samples from 26-wk-old lambs tended to have greater MFI values at 1 and 7 d postmortem, especially for the LM and GM muscles. From these results, it seems that less postmortem proteolysis occurs in younger and more oxidative muscles and this may be attributed to the greater calpastatin 24-h activity