Alaa El-Din A. Bekhit

The relationship between meat tenderization, myofibril fragmentation and autolysis of calpain 3 during post-mortem aging.

The objective was to study the potential role of calpain 3 in postmortem myofibril breakdown and meat tenderization. We determined the temporal changes in calpain 3 protein in the ovine m. longissimus thoracis et lumborum (LTL, n=4) during post-mortem storage. Concurrently, we also determined the kinetics of tenderization level, changes in MFI, degradation of nebulin and desmin, and autolysis of calpain 1. The autolysis of calpains 1 and 3 were strongly correlated with the kinetics of tenderization and changes in MFI. The best correlation was between the appearance of the autolyzed calpains 1 and 3 and nebulin degradation. Taken together, the results indicated that calpains 1 and/ or 3 might be playing a key role in post-mortem tenderization of LTL via the proteolysis of specific muscle structural proteins such as nebulin. This is the first report that relates calpain 3 to myofibrillar protein degradation in post-mortem skeletal muscle.

Up- and down-regulation of Longissimus tenderness parallels changes in the myofibril-bound calpain 3 protein

The objective of this study was to utilize Ca(2+) and Zn(2+) treatments of meat to critically explore the possible role of calpain 3 in meat tenderisation. Calpains 1 and 2 were also examined for comparative purpose. Control animals plus animals infused with CaCl(2), ZnCl(2) or H(2)O were used (six lambs per treatment) to determine the temporal changes in muscle calpain 3 protein in the Longissimus thoracis et lumborum (LTL) during post-mortem storage. Concurrently, the temporal changes of; (1) shear force, (2) sarcomere length, (3) proteolysis of titin and nebulin and (4) calpains 1 and 2 proteins were also determined. Infusing LTL with Ca(2+) or Zn(2+) caused significant up- and down-regulation of LTL tenderisation, respectively, compared to water infusion and the control animals. Furthermore, the rate of breakdown of calpain 3, the rate of proteolysis of titin and nebulin and the rate of meat tenderisation during post-mortem storage of LTL in the various treatments were highly correlated. These studies suggest that calpain 3, like calpain 1, may be involved in the tenderisation of meat through limited proteolysis of specific muscle structural proteins such as titin and nebulin.

Does the newly discovered calpain 10 play a role in meat tenderization during post-mortem storage?

The objective was to study calpain 10 during meat tenderization. Western assays were developed and changes in calpain 10, tenderization level and desmin were determined in Longissimui (LTL) during post-mortem storage. A comparison between some characteristics of calpains 1, 2 and 10 indicated differences in the pI and sub-cellular distribution. Tenderness improved gradually during post-mortem storage and was accompanied by a decline in intact desmin level. Western analysis indicated that calpain 10 is present in sheep LTL probably as two proteins (MW 73.6 and 70.7 kDa). Post-mortem storage caused a decline in the level of the 73.6 and 70.7 kDa proteins in the sarcoplasmic fraction and a concomitant increase in these proteins in the myofibrillar fraction. Changes in the myofibrillar calpain 10 proteins were strongly correlated with the rate of tenderization. To conclude, calpain 10 proteins are present in sheep LTL and the sub-cellular distribution is dynamic during post-mortem storage.