THE USEFULNESS OF MUSCLE COLOR AND PH FOR SEGREGATING BEEF CARCASSES INTO TENDERNESS GROUPS

A total of 3435 beef carcasses from animals 11 to 14 months of age (472 bulls, 978 heifers, 1985 steers) were evaluated over a ten year period to determine the usefulness of measurements of muscle color and pH for segregating carcasses into tenderness groups. All carcasses were aged for 6 days at 2-degrees-C. Color and pH measurements were obtained on the longissimus dagger muscle. A loin steak from the eleventh-twelfth thoracic vertebrae interface was microwaved to approximately 70-degrees-C to determine shear force values. Steers had the lowest ultimate pH and shear force values and bulls had the highest (P = 0.0001). Steers also had lighter colored lean (P = 0.0001) the bulls and heifers (i.e. higher mean colorimeter readings). Arbitrary segregation of carcasses into tenderness groups based on shear force values (less-than-or-equal-to 6.0 tender; > 6.0 tough) resulted in the tender group having higher colorimeter readings (17.40 versus 16.76, P = 0.0001) and ultimate pH values (5.70 versus 5.69, P = 0.02) and lower shear force values (4.89 versus 7.65, P < 0.0001). Year and breed effects were observed in all three traits (P = 0.001). However, time trends were not detected and the range in shear force values among breeds was relatively narrow (6.02-6.74). Subjective color scores, colorimeter readings, and ultimate pH values accounted for 48% or less of the variation in shear force values in all sex, year, and breed groups indicating that generally none of these traits were highly related to tenderness in a linear fashion. Arbitrary segregation of carcasses into tenderness groups based upon shear force value resulted in consistently higher shear force values for the tough group (SV > 6.0) and lower values for the tender group (SV less-than-or-equal-to 6.0) (P < 0.05) than the overall mean shear force value in all sex groups. Plotting of colorimeter readings and ultimate pH values against shear force values resulted in peaks within the range of colorimeter readings 8.5-16.5 and pH values 5.8-6.19. Segregation of carcasses with colorimeter readings within the range 8.5-16.5 was effective in segregating the tough steer and heifer carcasses and the tender bull carcasses, while segregation based upon pH values between 5.8 and 6.19 was effective in segregating the tough carcasses in all sex groups. Segregation based on both color and pH appeared to offer little advantage over the use of pH alone. Segregation of beef carcasses with ultimate longissimus pH values between 5.8 and 6.19 appears to be an easy, nondestructive, practical means to effectively remove the majority of tough carcasses (shear value > 6.0) in all three sex groups, regardless of breed.