Predicting beef-longissimus tenderness from various biochemical and histological muscle traits.

Our objective was to determine the predictive value of various biochemical and histological traits for tenderness of the longissimus muscle. Data collected from 27 crossbred cattle included longissimus pH, temperature, sarcomere length, total and percentage of soluble collagen, muscle-fiber type and area, cathepsin B and B + L activities, calcium-dependent protease (CDP)-I, -II and inhibitor activities, myofibril fragmentation indices (MFI), Warner-Bratzler shear (WBS) force, sensory-panel tenderness (SPT) ratings and carcass traits. Stepwise regression analyses were performed among breeds or pooled within breeds with WBS and SPT as dependent variables. When MFI were included in the analysis, MFI at d 7 explained 50% of the variation in WBS and SPT at d 14. An additional 19% of SPT was accounted for by the addition of CDP inhibitor d 1 activity and percentage-area of alpha R fibers to the model. However, because variation in MFI was not significant within breed subclasses and MFI could be classified more as a dependent variable, it was removed from the model. This resulted in CDP inhibitor d 1 activity explaining 44% of the variation in WBS and SPT at d 14. Also, percentage-area of beta R fibers, 6 h pH and cathepsin B + L d 14 activity appeared in the model. In addition, CDP inhibitor activity was the only variable to be significant within breed groups. These data suggest that d 7 MFI could be used as a single predictor of d 14 longissimus muscle tenderness; however, CDP inhibitor d 1 activity (a biological event) also may be useful in predicting tenderness.