Influence of early pH decline on calpain activity in porcine muscle

This study investigated the influence of post-mortem pH decline on calpain activity and myofibrillar degradation. From 80 pigs, 30 Longissimus dorsi (LD) muscles were selected on the basis of pH values at 3h post-mortem and classified into groups of 10 as fast, intermediate and slow pH decline. The rate of pH decline early post-mortem differed between the three groups, but the ultimate pH values were similar at 24h. Calpain activity and autolysis from 1 to 72h post-mortem were determined using casein zymography and studied in relation to myofibrillar fragmentation. Colour and drip loss were measured. A faster decrease in pH resulted in reduced level of mu-calpain activity and increased autolysis of the enzyme, and hence an earlier loss of activity due to activation of mu-calpain in muscles with a fast pH decline. Paralleling the mu-calpain activation in muscles with a fast pH decline a higher myofibril fragmentation at 24h post-mortem was observed, which was no longer evident in the later phase of the tenderization process. In conclusion, the rate of early pH decline influenced mu-calpain activity and the rate but not the extent of myofibrillar degradation, suggesting an early effect of proteolysis on myofibril fragmentation that is reduced during ageing due to an earlier exhaustion of mu-calpain activity.