Post‐Mortem Changes in Muscle. I. Chemical Changes in Beef

SUMMARY Chemical changes in the longissimus dorsi muscle of 5 beef carcasses were followed from less than 10 min after death through 20 days post‐mortem. The average initial pH value of 6.99 declined to 5.46 at 48 hr and was 5.57 at 480 hr. Initial values for creatine phosphate, total acid‐soluble phosphate, ortho‐phosphate, lactic acid, total reducing sugars, and glycogen were respectively 9.i, 54.9, 22.1, 13.1, 7.9 and 56.7 μM/g of tissue. Creatine phosphate declined rapidly to only 16% of the initial value by 12 hr post‐mortem, and was not detectable by 24 hr. Ortho‐phosphate, lactic acid and total reducing sugars increased approximately 1.5; 6.5, and 2.25 times from their initial levels during 480 hr post‐mortem. Glycogen appeared to be stoichiometrically degraded to lactic acid and reducing sugars, since the sum of these constituents was approximately constant at all times post‐mortem, if expressed in terms of glucose equivalents. Results suggest that the onset of rigor occurred at 12–15 hr post‐mortem. Development of rigor mortis was virtually complete 24 hr after death. The pattern of chemical changes observed with intact beef carcasses subjected to commercial cooling practices is in essential agreement with earlier results with isolated beef muscle strips. An enzymic method for determining ATP levels was compared with the more commonly used method of acid hydrolysis. ATP values at 24 hr post‐mortem were negligible when determined by the enzymic method, but amounted to about 27% of the original level when determined by acid hydrolysis. Reasons for the discrepancy in the two methods are discussed.