Factors affecting activity of the calcium-dependent proteases and their participation in the process of meat tenderization

Abstract

The endogenous calpain system plays a major role in regulating proteolysis of muscle proteins under postmortem conditions. Substrates of calpains, such as desmin, synemin, talin and vinculin, form part of the citoskeletal framework of the muscle cell. The calpain system is composed of several isoforms of calcium-dependent cysteine proteases and their specific competitive inhibitor, calpastatin. The two best-characterized isoforms of calpains are -calpain and m-calpain, which both degrade the same specific set of myofibrillar and cytoskeletal proteins as muscle is converted into meat. Alterations in pH and/or ionic strength may cause conformational changes that allow an increase in the hydrophobicity and aggregation of the enzyme. Likewise, pH/ionic strength may alter conformation of the substrate and make them less susceptible to cleavage by -calpain. The pH optimal of the calpainas is 7.0, although, at lower pH, the enzymes show some catalytic activity. Research on this topic is abundant but results are very controversial. Temperatures of refrigeration also play a key rol in the autolysis of the calpains and calpastatin. Recent experimental evidence shows that proteolysis of key cytoskeletal proteins, such as the intermediate filament protein, desmin, may be related also to drip loss or water holding capacity of the carcass.