Muscle proteinases and meat aging

The purpose of this manuscript is to review and summarize the results of experiments conducted in our laboratory regarding the mechanism of meat tenderization during post mortem storage of carcasses at refrigerated temperatures. Clearly, the conversion of muscle to meat and the subsequent tenderization process are complex phenomena and much remains to be learned. However, current experimental data suggest that proteolysis of key myofibrillar proteins is the principal reason for improvement in meat tenderness during post mortem storage. Speculatively, the weakening and/or degradation of Z-disks and degradation of desmin (and probably degradation of titin) are responsible for the increased fragility of myofibrils during post mortem storage. There is substantial experimental evidence suggesting that the calpain proteolytic system is resposible for post mortem proteolysis that results in meat tenderization. Calpain is the only proteolytic system that has all of the characteristics that are necessary for bringing about post mortem changes that result in meat tenderization. Undoubtedly, other factors (such as rate pH and temperature decline during rigor development, ionic strength and others) influence the process. However, we believe that the rate and extent of post mortem proteolysis best explain the observed variation in tenderness at a constant age. Therefore, research efforts should be direct toward understanding the regulation of the calpain proteolytic system in post mortem muscle.