Variability in rates of pH fall and of lactate production in the muscles on cooling beef carcasses.

The rate of pH fall in four major muscles on cooling beef carcasses varied by about twofold. Thus the time taken to reach pH 6·0 from initial pH values of about 7·1 varied between 8 and 16h, and in one extreme case of an LD muscle was as low as 3·5 h. Some of this variability was due to different rates of cooling between muscles in the same animal, but even after correction of the rates to a constant temperature of 38°C the variability was still about twofold in the higher range of pH (7·0-6·7) and slightly lower in the lower range (6·6-5·8). Similar variability was shown in excised TB muscles, kept at a constant temperature of 38°C. Damage to muscles during excision can lead to much higher variability than this (in rabbit LD muscles, to about sixfold). The rate of pH fall is determined by the rate of ATP-turnover, and so the variability in the former rate is likely to be due to varying intracellular free Ca(2+) levels exerting a stimulating effect on the actomyosin ATP-ase. Some of this extra Ca(2+) may arise from calcium release from mitochondria as they become anaerobic after death.