Differences in the post-mortem kinetics of the calpain system in meat frombulls and steers

Strip loins (longissimus thoracis et lumborum) from bulls with normal ultim ate pH (NOR, pH(u) < 5.7), bulls with unacceptably high pH (HI, pH(u) > 5.7 ), and steers were compared after storage at 15 degrees C. HI samples had h igher shear forces 120 hours post-slaughter than NOR and steer samples (P < 0.05). Calpastatin and mu-calpain activities were higher in the NOR bulls than in steers, but the rates of decline in these activities were more rapi d in NOR samples. The activity of mu-calgain was low at all times and appea red to be involved in the increased toughness of the HI samples. The activi ty of m-calpain and the calpastatin : mu-calpain activity ratio provided a good prediction of shear force 120 hours post-slaughter in the strip loin ( R-2 = 0.70; P < 0.001). This suggests that calpastatin, mu-calpain, and m-c alpain all play a role in tenderisation and that on-farm and pre-slaughter management rather than post-slaughter treatment need to be used to decrease the incidence of high pH meat.