CASPASE AND CALPAIN ACTIVITY IN BEEF TENDERIZATION IN TWO BOVINE SKELETAL MUSCLES

The tenderness of beef is one of the most important factors that can influence consumer choices. Among the factors that affect tenderness, post mortem proteolysis has a key role. Calpains and capsases are two families of cytosolic proteases essential for a proper skeletal muscle function and are consider having a key role in the post mortem tenderization process. The goal of this work was to evaluate the activities of μ-calpain and caspase-3 in two different muscle types, Longissimus Dorsi (LD) and Infraspinatus muscle (IS), of Simmental young bulls at slaughter and during ageing, and their relationship with the beef tenderness. Samples of Longissimus dorsi and Infraspinatus muscles were collected within 20 minutes (T0), 48h (T48h) and 7 days (T7) from slaughtering of 17 Italian Simmental young bulls, and stored at -80 °C until the analysis. By SDS-PAGE, alpha II spectrin, PARP-1 and their degradation products, and fast and slow myosin heavy chain (MHC) were separated and then quantified in relative terms. In particular, the activity of μ-calpain and caspase-3 was assessed by the quantification of alpha II spectrin cleavage products of 145 kDa (SBDP145) and of 120 kDa (SBDP120) respectively. Moreover the activity of caspase-3 was assessed also by the quantification of poly (ADP-ribose) polymerase-1 (PARP-1) cleavage products of 89 kDa. Warner-Bratzler Share Force (WBSF) analysis was carried out after 7 days of ageing. The analysis of MHC isoforms revealed that LD was mainly composed by fast-MHC (67%) and consequently can be considered a white muscle, while IS was mainly composed by slow-MHC (84%) and can be considered a red muscle. IS showed higher WBSF than LD (P<0.01). At slaughter, the alpha II spectrin full length 250 kDa (SBDP250) level was higher in IS than LD (P<0.01), it means that, at slaughter, alpha II spectrin was less degraded in IS than LD, also a positive correlation between SBDP250 and WBSF was found (r=0.810; P<0.01), indicating that a different early proteolysis between muscles may contribute to explain their different tenderness. LD showed higher level of SBDP145 than IS (P<0.01), while SBDP120 was similar between muscles (P>0.05). Also the 89 kDa from PARP-1 degradation was found. At T48h SBDP250 and PARP-1 cleavage product were not detected and no differences were found between muscles in the level of SBDP145 and SBDP120. However the level of SBDP145 was higher than those of SBDP120 in both muscles. After 7 days of ageing neither alpha II spectrin nor PARP-1 cleavage products were found. Taking into account the results of this study, the different tenderness observed between LD and IS muscles was greater infl uenced by μ-calpain than caspase-3 activity. Indeed the activity of μ-calpain was higher than those of caspase-3 in both muscles and detectable at 48h of ageing. Conversely caspase-3 was similar between muscles and seems active only in the early post mortem.