The effects of gender and muscle type on the mRNA levels of the calpain proteolytic system and beef tenderness during post-mortem aging

The objective of this study was to determine the effects of gender and muscle type on the mRNA levels of the calpain system and the tenderization of beef meat. The Longissimus thoracis (LT) and the Semimembranosus (SM) were sampled from each bull, steer and heifer after routine slaughter (Six animals per group). The mRNA levels of μ-calpain, m-calpain, calpain-3 and calpastatin were quantified using real-time PCR. Concurrently, tenderness was determined following the Warner-Bratzler Shearforce (WBSF) procedure and rate of tenderization during post-mortem storage was calculated from the WBSF values of 7d and 35d aged steaks. The results show that bulls had significantly lower (P<0.01) WBSF values than heifers which were accompanied by higher (P<0.01) levels of μ-calpain and calpain-3 mRNA but similar levels of calpastatin as compared to heifers. There was a significantly higher (P<0.05) calpastatin expression in steers, as compared to heifers. However, μ-calpain expression was lower (P<0.05) in heifers whose meat was significantly tougher (P<0.05) than that of steers. Steer meat was slightly tougher than that of bulls, while steers had had a tendency to express higher levels of calpastatin but similar μ-calpain and calpain-3 mRNA. The LT had lower (P<0.05) WBSF values than the SM but these muscles tenderised at the same rate, and had similar mRNA levels for all investigated genes. M-calpain mRNA levels were not significantly affected by muscle and gender (P>0.05). Moreover, calpain 3 was negatively correlated to 7d WBSF values (P<0.05). Despite the small sample size, these results suggest that variations in beef tenderness could be modulated through the differential expression of the members of the calpain system, specifically, μ-calpain, calpain 3 and calpastatin.