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.