Using objective measures of muscle color to predict beef longissimus tenderness.

This research was conducted to determine whether objective measures of muscle color could be used to classify beef carcasses with respect to tenderness. Bos taurus (161 steers) and Bos indicus cross (101 steers, 55 heifers) cattle were fed a high-concentrate diet and slaughtered in seven groups when ultrasound scans indicated approximately 1.1 cm fat thickness. Following low-voltage electrical stimulation and a 24-h chill, all routine carcass data, USDA grade data, and colorimeter readings (luminance, L*; redness, a*; yellowness, b*) of the exposed longissimus muscle were obtained. The longissimus lumborum was sampled for ultimate pH (pHU) measurement, shear force at 1, 4, 7, 14, 21, and 35 d postmortem, and taste panel assessment at 14 d postmortem. The pHU was correlated (P < .05) with L*, a*, and b* values (r = -.48, -.52, and -.60, respectively). Correlations of color measurements with tenderness measurements were higher than correlations of marbling score with tenderness measurements. Of the three color measurements, b* value showed the highest correlation with shear force value (r = -.38) and taste panel tenderness rating (r = .37). A classification system (lowest 25%, middle 50%, highest 25%) based on marbling score resulted in classes of beef that were 9, 3, and 4% tough, respectively. A classification system (darkest/bluest 25%, middle 50%, lightest/yellowest 25%) based on colorimeter readings resulted in classes of beef that were 15, 3, and 0% tough, respectively. Bos taurus cattle had lower shear force values, higher panel tenderness ratings, higher L* values, and lower a* values (P < .05) than Bos indicus cross cattle.