Relationship of Proteolysis and Superoxide Dismutase Activity to Tenderness of Prime and Select Grade Beef

Excessive fat deposition in humans induces metabolic stress, increasing production of reactive oxygen species (ROS). Cattle that grade Prime may have more ROS than cattle that grade Select. Perhaps ROS alters the extent of muscle proteolysis and thereby influences tenderness between high and low marbled beef. Superoxide dismutase (SOD), an endogenous enzyme, helps combat ROS by converting superoxide, the most potent ROS, into less toxic forms of oxygen. Proteolysis can be measured by tracking degradation of troponin T, a protein subunit that helps regulate in muscle contraction. The objective was to investigate the relationship between quality grade, tenderness, troponin T degradation and SOD activity. Beef strip loins (n = 36 Prime and n = 36 Select) were cut into 5 pairs of steaks (one 2.54 cm thick and one 1.27cm thick). Randomly, each pair was aged 2, 7, 14, 21, 28 days. The 2.54 cm thick steaks were cooked to 70°C and six 1.27 cm diameter cores were removed for Warner-Bratzler shear force determination. Samples from 1.27 cm steaks, 2 and 28 days aging, were analyzed for troponin T degradation. The remaining 1.27 inch samples were powdered and stored at -80°C for SOD analysis. Prime steaks were significantly more tender (P < 0.0001) than Select steaks. Select graded steaks had a greater response to aging effect (greater change in Warner-Bratzler shear force) than Prime graded steaks (P = .03). Samples aged 28 days showed significantly more troponin T degradation (P < 0.0001) than samples aged 2 days, but there was no significant difference between Select and Prime graded steaks (P = .16). No significant difference was observed between quality grades for SOD activity (P = 0.69). These results suggest that the differences in tenderness between quality grades cannot be explained by the changes in superoxide dismutase.