CARCASS CHARACTERISTICS, THE CALPAIN PROTEINASE SYSTEM, AND AGED TENDERNESS OF ANGUS AND BRAHMAN CROSSBRED STEERS

We used 69 steers of varying percentage Brahman(B) breeding(0% B, n = 11; 25% B, n = 13; 37% B, n = 10; 50% B, n = 12; 75% B, n = 12; 100% B , n = 11) to study the relationship between carcass traits, the calpai n proteinase system, and aged meat tenderness in intermediate B crosse s. Calpains and calpastatin activities were determined on fresh longis simus muscle samples using anion-exchange chromatography. The USDA yie ld and quality grade data (24 h) were collected for each carcass. Long issimus steaks were removed and aged for 5 or 14 d for determination o f shear force and 5 d for sensory panel evaluation. Even though some y ield grade factors were affected by the percentage of B breeding, USDA yield grades did not differ (P > .15) between breed types. Marbling s core and USDA quality grade decreased linearly (P < .01) with increasi ng percentage of B breeding. Shear force after 5 and 14 d of aging was higher(P < .05) in the 100% B steers than in all other breed types, w hich were not significantly different. Sensory panel tenderness and co nnective tissue scores decreased linearly (P < .05) with increasing B breeding. A quadratic effect was also noted for tenderness and connect ive tissue scores; 37% B steers received the highest scores. A similar response was found in mu-calpain activities; the 37% B steers had the highest activities. Conversely, calpastatin activity increased linear ly (P < .01) with increasing percentage B breeding. These data show st rong linear relationships between calpastatin activity (positive), mar bling score (negative), and percentage B breeding, suggesting a possib le combined effect of these traits on aged tenderness of intermediate Brahman crosses.