Post-mortem muscle proteolysis and meat tenderness.

Abstract

Connective tissue provides the support at a number of levels via the endomysium, perimysium or epimysium and maintains the integrity of the contractile apparatus made up of myofibrillar proteins such as actin and myosin and important associated proteins such as titin and nebulin. Proteins such as desmin, talin and α-actinin also help to maintain the framework within which the contractile proteins function. Degradation of proteins such as titin, nebulin and desmin will lead to myofibril disruption and contribute to tenderization. The available evidence does not support a role for the cathepsins B and L in early post-mortem proteolysis and points to the calpain system as the major candidate, despite the fact that the mode of action of the calpains is not yet fully defined. This is consistent with protein turnover in living muscle and with studies that have shown that factors leading to a reduction in protein degradation (i.e. β-agonists) also lead to lower calpain activity. The rise in ionic strength as muscle enters rigor must be considered complementary to biochemical processes, which lead to tenderization post-rigor. The development of rigor and the shortening of fibres counter early proteolysis, but post-rigor the cumulative effect of proteolysis (largely driven by the calpains) reverses the rise in toughness and tenderization will occur. This proposed model is far from complete and in part this reflects our incomplete knowledge of the action of endogenous muscle enzymes. There are several issues that remain to be resolved with respect to the calpains: (i) elucidation of the controlling mechanism for activation in the in vivo environment; (ii) the role of m-calpain and whether the activation of this enzyme can be manipulated post mortem; (iii) the contribution of p94 to tenderization; and (iv) the contribution of myofibril-bound µ-calpain to proteolysis and tenderization. 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 tenderization. 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 tenderization be developed.

The effect of recombinant caspase 3 on myofibrillar proteins in porcine skeletal muscle

“…The degradation of desmin is thought to significantly contribute to tenderisation (Hopkins and Taylor, 2004;Geesink et al, 2006). Research by Koohmaraie et al (1995) found that in lambs carrying the callipyge phenotype, which is associated with increased levels of calpastatin and increased meat toughness, there was a reduction in the degradation of a number of myofibrillar proteins including desmin in comparison to normal lambs, suggesting its importance with regard to meat tenderness.…”

Use of electrical stimulation and chilling to enhance meat tenderness of heavy lambs

“…In addition to cold shortening reduction (Chrystall and Devine 1985;Devine et al 2004), the benefits of ES on meat tenderness may be due to aging acceleration caused by faster ATP depletion, hastening rigor onset and allowing for tenderization to begin sooner and at higher temperature (Hwang et al 2003;Simmons et al 2008). It is well recognized that myofibrillar and cytoskeletal proteolysis occurs during aging and enhances meat tenderness (Koohmaraie 1994;Taylor et al 1995;Hopkins and Taylor 2004), even if mechanisms are still under investigation. The calpain/ calpastatin system plays a major role in the process (Dransfield 1993;Koohmaraie 1994;Koohmaraie and Geesink 2006), but other proteases (Ouali et al 2006;Kemp and Parr 2012) or mechanisms (Wu and Smith 1987;Takahashi 1996) could be implicated.…”

Effects of growth rate on carcass and meat quality traits and their association with metabolism‐related gene expression in finishing pigs

“…Postmortem conversion of muscle to meat involves several biochemical modifications and processes that begin with a metabolic shift from an aerobic to an anaerobic state. This is followed by production of lactic acid which decreases pH of the muscle; activation of different proteinase systems which degrade muscle proteins and activity of other enzymatic mechanisms which effect and/or produce specific metabolites (Hopkins & Taylor 2003). Low growth rate pigs exhibited a fatter carcass, associated with markedly higher activity of enzymes involved in lipogenesis, such as fatty acid synthase and malic enzyme (Bee 2007).…”