Meat Tenderization: Possible Causes and Mechanisms. A Review.

Abstract

The postmortem meat tenderizing process is complex and not fully understood. The nature of changes associated with the improvement in tenderness and the exact mechanisms involved are still unknown. Based on relevant evidence, old and new, this review attempts to clarify the statement of our knowledge of these aspects. Of the diflerent biochemical and ultrastructural changes occurring in meat, a key role of myofibril disruption taking place at the N2-line level in meat tenderization has been emphasized. This may be ascribed to the action of lyosomal enzymes, especially cathespin B and L. However, all the changes thus far identijied can be only explained by a synergistic action of lysosomal and calcium-dependent proteinases. Besides or together with proteolytic enzymes, weakening of myofibrils may also be mediated by the high ionic strength achieved in postmortem muscles. Both mechanisms possibly involved in the meat tenderizing process have been tentatively tested in relation with the large muscle variability in aging rate. It appears that some concepts are in conflict with the results presented. For instance, no direct relationship was found between aging rate and proteinase content of muscles. . Reglation of protein degradation in muscle by calcium. Evidence for enhanced nonlysosomal proteolysis associated with elevated cytosolic calcium. J. Biol. Chem. 260, 13619.

Effect of nutritional factors on biochemical, structural and metabolic characteristics of muscles in ruminants, consequences on dietetic value and sensorial qualities of meat

“…Meat ageing rate is positively correlated to ATPase activity, which defines the contraction rate of muscle [86]. Indeed, fasttwitch glycolytic muscles have a faster ageing rate than slow-twitch oxidative red muscles.…”

“…Release of calcium ions in the cytosol, pH fall and increase in osmotic pressure influence the activity of the different proteolytic systems and the susceptibility of the substrates. The importance of proteolysis depends on the duration and temperature of meat storage [86]. Post-mortem proteolysis is also dependent on muscle type which influences the contents and activities of proteases as well as the susceptibility of myofibrillar proteins to hydrolysis.…”

“…A non-reversible actomyosin complex is then formed, inducing meat toughening; this is the so-called "rigor mortis" phase [59]. However, in parallel to pH decrease, osmotic pressure increases and reaches its maximum value after complete onset of rigor mortis [86]. This increase in osmotic pressure contributes to the alteration of myofibrillar integrity and to the dissociation of contractile proteins.…”

Factors affecting beef palatability — farmgate to chilled carcass

“…Geesink et al (1994b) demonstrated that accelerated tenderisation could also be achieved with pre-rigor infusion with NaCl. This effect was not associated with any increase in calpain activity rather it was postulated that the increase in ionic strength increased the susceptibility of the myofibrillar proteins to proteolysis (Ouali 1990).…”

“…Non-enzymatic mechanisms have also been implicated during post mortem tenderisation. The effective doubling in ionic strength during rigor has been shown to cause conformational changes in proteins and, therefore, increased susceptibility to proteolysis (Ouali 1990). The 'calcium theory' of tenderisation, which is based on the translocation and fragmentation of cytoskeletal proteins in the presence of 0.1 mmol/L Ca 2+ , has also been proposed by Takahashi (1999).…”