RELATIONSHIP BETWEEN pH FALL AND INITIATION OF ISOTONIC CONTRACTION IN POSTMORTEM BEEF MUSCLE

Beef muscles were sampled at various times post-mortem both on and off carcass, and the pH, sarcomere length, and isotonic contraction profiles under various loads recorded. The results demonstrate that muscle under light load will begin to contract at pH 6.3 but more heavily loaded muscle will not contract until pH 5.8. Rapid pH fall produced an earlier initiation of contraction than slow pH fall, but the pH required for initiation of contraction under equal loads was the same. The results of isometric tension development followed by unrestrained contraction during the course of rigor development are presented. The authors suggest that both carcass cooling rate and rate of pH fall are implicated in prerigor contraction of postmortem beef muscle.