Factors contributing to proteolysis and disruption of myofibrillar proteins and the impact on tenderisation in beef and sheep meat

This review seeks to examine the current theories of tenderisation with respect to red meat where tenderisation is defined as the reduction in toughness post-rigor. This examination is in the light of recent research on meat biochemistry, and from this, areas of research that may prove fruitful are highlighted. Based on available data, the major candidate to explain tenderisation post-rigor is the calpain protease system. Evidence that change in the binding of actomyosin (the complex of contractile proteins formed at rigor) or cleavage of myofibrillar proteins due to Ca2+ ions contributes to tenderisation is far from compelling. Equally it appears that the cathepsin proteases are unlikely to have a role in early post-mortem cleavage of proteins (proteolysis) and thus tenderisation. The mode of action of the calpains is not yet fully defined and questions remain as to the role of m-calpain given the in vitro requirement for a Ca2+ ion concentration exceeding that observed in post-mortem muscle. The existence of the calpains in living muscle and other tissues suggests a mode of action more subtle than currently thought. Additionally, the observation that the degradation of myofibrillar proteins occurs in the presence of effective synthetic and natural calpain inhibitors suggests that other enzymes may also have a role in tenderisation. Inevitably, the accumulated evidence points to a complex system likely to involve interacting proteases and ions, and only through open minded investigation with reliance on developments in the medical and biochemical fields will a more complete model of tenderisation be developed.