An evaluation of tenderness of the longissimus muscle of Angus by Hereford versus Brahman crossbred heifers.

Postmortem aging of carcasses obtained from Angus-Hereford (n = 8) and 5/8 Brahman crossbred (n = 8) heifers was investigated to determine the cause of variation in meat tenderness. Raw longissimus muscle (LM) myofibril fragmentation index was lower and cooked LM Warner-Bratzler shear force was greater for the 5/8 Brahman crossbreds (P less than .05). The activities of calcium-dependent protease (CDP) -I and -II were not affected (P greater than .05) by breed; however, CDP inhibitor activity was higher (P less than .05) in the 5/8 Brahman carcasses. The activities of cathepsins B and B + L were not affected by breed or postmortem storage time (0, 1, 3, 7 or 14 d). Hereford-Angus carcasses were fatter opposite the 12th rib and had higher USDA yield grades and marbling scores (P less than .05). Hereford-Angus crossbreds had less dark, coarse band formation around the exterior of the LM and lighter, finer-textured lean (P less than .05). Cooking loss (%) and cooking rate (g/min) were not affected by breed or postmortem aging (P greater than .05). The increased toughness in the 5/8 Brahman carcasses may be due to increased CDP inhibitor activity.