Effects of muscle shortening and proteolysis on Warner-Bratzler shear force in beef longissimus and semitendinosus.

Interactions between muscle shortening and proteolysis and their effects on Warner-Bratzler (WB) shear force were investigated in beef m. longissimus (LD) and m. semitendinosus (ST). Muscles were taken within 30 post-mortem from eight Hanwoo steers, divided into three portions, and incubated at 5, 15, or 36 °C for 24 h, during which time rigor mortis developed. ST at 36 °C had a significantly (P<0.05) lower pH at 3 h than LD incubated at the same temperature. However, pH values became similar after 3 h. Both muscles at 5 and 15 °C had almost similar pH during rigor development, with significantly (P<0.05) lower pH for ST. Sarcomere length and WB-shear force did not differ significantly between muscles incubated at the same temperature. For both muscles at 5, 15, and 36 °C, sarcomere length was 1.52, 1.76 and 1.44 μm, and WB shear force was 93.2, 55.9 and 45.1 N. The rates of μ-calpain autolysis and Troponin-T degradation were in the order of 36 °C>15 °C⩾5 °C, with a tendency for ST to have a slightly faster rate than LD muscle. Thus, the effect of sarcomere length on shear force may depend on the extent of proteolysis and the potential of endogenous proteolysis may supersede toughness caused by short sarcomeres. The toughness of cold shortened meat may depend more on endogenous enzymatic tenderization than shortened sarcomere length per se.