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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. [Copyright &y& Elsevier]

Application of electrical stimulation in the sheep and beef processing industry has been erratic around the world and this may reflect an incomplete knowledge of how to optimise the technology. Although it is well established that stimulation increases the rate of post-mortem glycolysis, other biochemical and biophysical effects have been implicated with the use of this technology. This review seeks to examine the current theories about the effect of stimulation on post-mortem muscle. The classical view that stimulation prevents muscle from shortening excessively during rigor development has been expanded to include the possibility that it also results in physical disruption of muscle structure. The interaction of these effects with the acceleration of the rate of proteolysis through activation of the calpain protease system has not been comprehensively reviewed in the past. Thus there are two mechanisms which could explain the effect of stimulation on tenderisation, reduced ‘cold-induced’ shortening and alteration of protein structure. A secondary effect is the enhancement of the rate of proteolysis stimulated by release of Ca 2+ at a higher temperature. As a result of this review we highlight several areas that may prove fruitful for further research. The challenge for further development of electrical stimulation systems is optimisation of the activation of the enzyme systems in parallel with manipulation of chilling regimes so as to ensure rigor mortis is achieved at temperatures which minimise shortening. These optimal temperatures largely established at a fixed incubation temperature for detached muscle may be different when measured in intact carcasses. The potential of regional stimulation of sections of the carcass to achieve this outcome is worthy of study given the different fibre composition of muscles and temperature gradients. In addition, to ensure that appropriate amounts of energy are applied to individual carcasses, development of self-response stimulation units, which are able to determine carcass resistance and apply appropriate durations or strengths of stimulation is worthy of future research. This would lead to more effective electrical stimulation practices. [Copyright &y& Elsevier]

Abstract: This study developed a new equation to predict the carcass yield of Hanwoo cattle, as well as re-evaluating a previous prediction equation. Experimental animals comprised 79 cows, 79 steers, and 79 bulls. A stepwise model selection was performed to determine the most practical carcass traits for predicting the yield. Cold carcass weight (CW), backfat thickness (BFT), and ribeye area (REA) accounted for 52% variation in yield, and these were determined as the final parameters. When the kidney, pelvic, and heart fat were included in the model, this increased the percentage variation explained (R 2) by 4%. To compare the newly developed equation (Yield=64.65−0.0198×CW−5.2264×BFT+0.1339×REA) and the previously used one, carcass yields of 377,048 industrial animals (145,695 cows, 225,926 bulls, and 5427 steers) were assessed. For the newly developed equation, the mean difference between experimental animals industrial animals differed only by 1.99–2.68% for all sex groups. In the case of the previous prediction equation, the mean difference ranged from 6.06% for bulls to 11.05% for steers. The results demonstrated that the prediction equation should use a mixture of sex and market weight groups. The results also support our decision to use the newly developed model in predicting the yield of Hanwoo. [Copyright &y& Elsevier]