Effect of pre-rigor stretch and various constant temperatures on the rate of post-mortem pH fall, rigor mortis and some quality traits of excised porcine biceps femoris muscle strips.

Porcine biceps femoris strips of 10 cm original length were stretched by 50% and fixed within 1 hr post mortem then subjected to temperatures of 4 °, 15 ° or 36 °C until they attained their ultimate pH. Unrestrained control muscle strips, which were left to shorten freely, were similarly treated. Post-mortem metabolism (pH, R-value) and shortening were recorded; thereafter ultimate meat quality traits (pH, lightness, extraction and swelling of myofibrils) were determined. The rate of pH fall at 36 °C, as well as ATP breakdown at 36 and 4 °C, were significantly reduced by pre-rigor stretch. The relationship between R-value and pH indicated cold shortening at 4 °C. Myofibrils isolated from pre-rigor stretched muscle strips kept at 36 °C showed the most severe reduction of hydration capacity, while paleness remained below extreme values. However, pre-rigor stretched myofibrils - when stored at 4 °C - proved to be superior to shortened ones in their extractability and swelling.