The effect of temperature and time on activity of calpains and lysosomal enzymes and degradation of desmin in porcine longissimus muscle

The experiment was conducted to determine the effect of temperature and time during heat treament on the activity of µ- and m-calpain and cathepsin B + L. In addition the degradation of the structural protein desmin was studied. Porcine longissimus muscle was sampled at 24 hours postmortem and incubated at temperatures of 25, 40, 55 and 70°C for the next 24 hours. At 25°C µ-calpain lost most of its extractable activity within the first 3 hours, whereas m-calpain was more stable. At 40 °C m-calpain activity disappeared within 3 hours. At 55°C µ-and m-calpain was rapidly inactivated, whereas cathepsin B + L was remained active throughout the heat treatment up to 24 hours. At 70°C calpains were inactivated within 10 minutes, cathepsin B + L within 90 minutes and desmin was not degraded. Desmin was degraded more rapidly at 40°C than at 25°C, whereas less degradation occurred at 55 °C. In conclusion, the data suggests that meat proteolysis is accelerated during the initial stages of cooking. Calpains were active for 1 to 3 hours at 40°C. Cathepsin B and L remained active at 55°C, but only around 1 hour at 70°C.