TENDERNESS VARIATIONS AMONG BEEF STEAKS FROM CARCASSES OF THE SAME USDA QUALITY GRADE

Beef loin steaks (80) were selected on the basis of tenderness differences from a population of 1005 steaks from carcasses of known USDA [USA Department of Agriculture] grade (US Choice A maturity, 20; US Choice B maturity, 10; US Good A maturity, 20; US Good B maturity, 10; US Commercial C maturity, 20). Among steaks from USA Choice A maturity carcasses, the most tender steaks had (P 0.05) more intramuscular fat, less intramuscular moisture, higher water holding capacity and a lower fragmentation index. Among steaks from US Good A maturity carcasses, the most tender steaks had a lower (P < 0.05) fragmentation index. Among steaks from US Commercial C maturity carcasses, those that were most tender had (P < 0.05) more intramuscular fat, less intramuscular moisture, higher water holding capacity, longer sarcomeres, higher collagen solubility and a lower fragmentation index. Among steaks from the 5 grade-maturity groups characterized, multiple regression equations containing 17 chemical, physical and histological measurements as independent variables accounted for 62.8-96.4% of the variation in shear force values. The independent variables that contributed most in accounting for the observed variability in tenderness were fragmentation index, sarcomere length, intramuscular moisture percentage and soluble collagen percentage. Samples of muscle from 2 tenderness levels were not different (P > 0.05) in any of 14 myofibrillar protein fractions.