Is m-Calpain active post-mortem in pork?

According to the literature, µ- and m-calpain play an important role in meat tenderization, however, the roles of the two isoforms are still discussed. The activities of these calpains isozymes have a different rate of decrease in post mortem (PM) muscles. While m-calpain activity remains more or less constant, μ-calpain activity decrease as a function of time post mortem. For this reason some authors consider only μ-calpain involved in the tenderization of meat. The aim of our study was to investigate the µ- and m-calpain activities in two different porcine muscles at 72 hours PM. Italian Duroc x (Landrace x Large White) crossbred pigs (N=75; mainly castrated males) with an average carcass weight of 135 kg were pen-fed and finished under standard Parma-ham practice. Samples were taken 72 hours post mortem (PM) from M .longissimus dorsi (LD) (7th rib) and M. semimembranosus (SM). To determine the activity of μ- and m-calpain the zymography method was used. Day three post mortem calpain showed four bands of enzyme activity on zymography gels. The two upper bands corresponded to native and autolyzed µ-calpain, and the two lower bands to native and autolyzed m-calpain. The detection of fourth band suggests that m-calpain is active in pork post mortem. The activity of native μ- and m-calpain was higher (P < 0.001) in porcine M. longissimus dorsi compared to M. semimembranosus.