Effect of added μ-calpain and post-mortem storage on the mechanical properties of bovine single muscle fibres extended to fracture

The effects of μ-calpain and post-mortem storage on the strength of single muscle fibres were investigated. During the 10 min of incubation at pH 7.5, μ-calpain became evenly distributed throughout the fibre. μ-Calpain-incubation resulted in thinner (P <0.001) Z-lines and reduced (P <0.001) the strength of the fibres compared to controls. These results demonstrate that μ-calpain is capable of mechanically weakening the muscle fibres. Post-mortem storage of meat for 10 days at 2 °C weakened (P <0.001) the muscle fibres compared to 24-h fibres. The presence or absence of Ca2+ affected fibre stiffness. Fibres incubated at pH 7.5 in 100 μM Ca2+ were less stiff than fibres incubated in 200 μM EGTA. Breaking stress and strain were not affected by Ca2+. We hypothesise that Ca2+ causes conformational changes in some of the load-bearing proteins, which alters their initial resistance to extension, but does not affect the breaking strength of the fibres.