Influence of early pH drop rates on calpain activity and protein degradation in pork

Early post-mortem pH development plays an important role in determining the rate and extent of muscle tenderization. The calpain system was demonstrated to be involved in the proteolytic tenderization of muscle, and is known to be influenced by pH. In the present work we studied the influence of pH drops in porcine Longissimus dorsi muscle on the activity of calpain and on myofibril degradation. The activity of calpain was studied with the zymography method. A faster decrease in pH resulted in reduced amount of extractable µ-calpain activity and increased autolysis of the enzyme, and thereby an earlier loss of activity revealing that calpain has a higher activity in muscles with a fast pH drop. The higher calpain activity in the muscles with a fast pH drop also resulted in a higher myofibril fragmentation at 24 h post-mortem, which was no longer evident in the later phase of the tenderization process. In conclusion, the rate of pH decrease early postmortem influenced the rate, but not the extent of myofibril degradation.