Tenderisation of pork as affected by degree of cold-induced shortening

Porcine M. longissimus dorsi from 12 carcasses were used to study the effect of ante mortem exercise treatment, time of boning and different ageing periods on tenderness and tenderisation in pork. The pigs were randomly allocated into three groups, of which the pigs (in two of them) were exposed to work on a treadmill: (1) 30 min rest after work, then slaughtered; (2) slaughtered without rest after work; and (3) controls, which were not exposed to work before slaughter. At 1 and 6 h post-stunning, samples from right side of each carcass were excised and immediately chilled in icewater until 24 h post-stunning. The left side loins were used as controls and were chilled on the carcasses at 12-14°C for 90 min and then at 2°C before boning at 24 h post-stunning. The effect of ageing, 0 or 7 days at 2°C, was studied. No parameter in this study was significantly affected by ante mortem treatment. WB shear force decreased significantly with increasing boning time and was correlated to the degree of muscle shortening in unaged excised samples. Muscle shortening for the 1 h excised cuts showed an average value of 27·4%, while an average value of only 6·1% was obtained for 6 h excised cuts. Ageing for 7 days resulted in only minor (7·3%) tenderness improvement for the 1 h excised cuts as compared to the 24·5% decrease in WB shear force obtained from the 6 h excised, less cold-shortened cuts. These differences in ageing rate, however, did not result in detectable changes in the degradation profile of myofibrillar proteins as analysed by SDS-PAGE.