Predictors of beef tenderness among carcasses produced under commercial conditions1

Beef carcasses (n = 240), processed using conventional commercial procedures and selected to differ in weight and s.c. fat thickness, were used to evaluate marbling score, s.c. fat thickness, 3-h pH (pH3) of the longissimus muscle (LM), and early-postmortem measurements of LM temperature as predictors of rib steak tenderness. Of the carcass traits evaluated, marbling score was the best single predictor of shear force (WBS) and panel ratings for myofibrillar tenderness (MFT). However, marbling, used alone, accounted for only 9.0 and 5.1% of the variation in WBS and MFT, respectively, and was not associated with panel ratings for connective tissue amount (CTA). Including pH3 in the prediction equation for WBS increased the R2 to .115, and inclusion of s.c. fat thickness in the equation for MFT increased the R2 to .062. Ratings for CTA were most effectively predicted using a regression equation that included 9-h LM temperature, pH3, and s.c. fat thickness (R2 = .063). Marbling score was the most effective factor evaluated for classifying carcasses into tenderness groups. Use of a minimum fat thickness constraint of .5 cm was effective for identifying tenderness differences among Select grade carcasses but was less effective within the Choice grade. Compared with marbling and s.c. fat thickness, pH3 was less effective for use in classifying carcasses into tenderness groups; however, pH3 values below 6.2 were associated with a reduction in tenderness variation. Measurements of early-postmortem LM temperature were not effective for use in identifying differences in tenderness.