Relationship between pre-rigor temperature of pork longissimus muscle, myofibril-bound calpain activity and protein degradation

The effect of pre-rigor temperature incubation on the activity and distribution in sarcoplasmic and myofibrillar fractions of calpains, and meat quality attributes was investigated. Porcine longissimus thoracis muscles were incubated pre-rigor at 14, 22, 30 and 38 degrees C to 6 h postmortem, followed by another 2 h incubation at 14 degrees C. Thereafter, muscles were stored at 2 degrees C for 1 or 4 days. With higher pre-rigor temperature, sarcoplasmic Ca2+ concentration, purge loss and myofibril-bound calpain-1 content increased, while shear force declined. Water-holding capacity of isolated myofibrils was lower after pre-rigor incubation at 38 degrees C. Desmin and troponin T degradation, and myofibril fragmentation was greater upon incubation of isolated myofibrils with added Ca2+ in the order 800 mu M Ca2+ > 40 mu M Ca2+ > no Ca2+, suggesting that calpain-1 and calpain-2 were associated to myofibrils and proteolytically active with sufficient Ca2+. Activity of myofibril-bound calpain-1 in muscle incubated pre-rigor at 22 and 30 degrees C were higher than when incubated at 14 and 38 degrees C. These results indicate that calpains translocate from the sarcoplasm onto myofibrils with higher pre-rigor temperature to 30 degrees C and the proteolytic potential of myofibril-associated calpains is thereby increased.