The role of ultimate pH in proteolysis and calpain/calpastatin activity in bovine muscle

Abstract

Of a total of three Friesian cows, two of which had been treated with adrenalin before slaughter, Mm longissimus (LO), supraspinatus (SS), triceps brachii (TB) and rectus abdominis (RA) were sampled at different times past mortem (pm). pH, calpain/calpastatin activities and degredation of myofibrillar proteins, as evidenced by SDS-PAGE, were assessed. Contraction characteristics were measured by determining myofibrillar ATPase activities. Adrenalin treatment resulted in a high ultimate pH (6.48 ± 0.40) and a faster decline pm of calpain I activity. The effect was similar in all four investigated muscles (72.4 ± 5.4% decline at 24 h pm). The decline in calpain I activity in the control muscles was muscle-dependent and ranged from 22.8–74.3% at 24 h pm. Differences in ultimate pH did not lead to distinct rates of breakdown of proteins with molecular weights lower than that of myosin heavy chain. Calpastatin levels were muscle-dependent and correlated with myofibrillar ATPase activity ( r = −0.99). In a second experiment Mm rectus abdominis (RA) and psoas major (PM) of adrenalin-treated ( n = 6) and control ( n = 6) Friesian-Holstein calves were sampled at 1 and 29 h pm for assessment of calpain activities. At seven days pm the M longissimus (LO) was sampled for tenderness evaluation. pH values were measured at 30 min, 4 h and 29 h pm. Adrenalin treatment resulted in a higher ultimate pH in the three muscles. Higher ultimate pH resulted in lower calpain activities in the RA at 29 h pm ( P ⩽ 0.025). The decline in calpain activity in the RA of adrenalin-treated animals correlated with ultimate pH ( r = 0.84). Although the decrease in total calpain activity in the PM did not correlate with ultimate pH, the rate at which calpain activity declined correlated to some extent with the rate of pH decline (pH at 30 min pm) in this particular muscle ( r = 0.68). High ultimate pH resulted in more extensive breakdown of high molecular weight proteins in the RA. After seven days of storage at 2°C, LO of treated animals was significantly more tender than the counterpart muscle of the control animals ( P ≤ 0.01).