Hind-limb protein metabolism and calpain system activity influence post-mortem change in meat quality in lamb

This study is concerned with the rate of protein turnover in the hind limb muscle bed of intact lambs, the activity of calpain proteolytic system in t he M. biceps femoris, and subsequent rates of myofibre breakdown and tender isation in the M. longissimus dorsi. Feed restriction increased protein deg radation in hind-limb muscle of lambs (p < 0.1), with a concominant decreas e in the extractable activity of calpastatin (p < 0.01), the endogenous inh ibitor of calpain. IGF-1 analog treatment decreased both protein degradatio n and assayed mu-calpain activity (p < 0.05) with no effect on the activity of calpastatin. beta-Agonist treatment increased hind-limb protein synthes is (p < 0.01), calpastatin activity (p < 0.1) and decreased (p < 0.01) mu-c alpain activity, but did not effect protein degradation. Significant correl ations were observed between Myofibril Fragmentation Index (MFI) values dur ing postmortem storage and initial post-slaughter calpastatin activity at d ays 3 (r = -0.34, p < 0.1), 5 (r = -0.58, p < 0.01) and 9 (r = -0.58, p < 0 .1), and mu-calpain activity at days 5 (r = 0.35, p < 0.1) and 9 (r = 0.41, p < 0.05). However, stronger correlations were observed between the ratio of mu-calpain to calpastatin, an estimate of potential mu-calpain proteolyt ic activity, and the rate of myofibril fragmentation (r = 0.75, p < 0.001) and tenderisation (r = -0.64, p < 0.01) during aging. These results are con sistent with the calpain system being the major proteolytic system involved in myofibril fragmentation and hence aging-related tenderisation of meat. (C) 1999 Elsevier Science Ltd. All rights reserved.