An evaluation of current and alternative systems for quality grading carcasses of mature slaughter cows.

Strip loins from 354 female bovine carcasses, selected to represent 30 skeletal maturity (A, B, C, D, and E) x marbling score (SA/MA/AB, MD, MT, SM, SL, and TR/PD) subclasses, were used to evaluate current and alternative systems for classifying cow carcasses into expected-palatability groups. Strip loins were vacuum-packaged, stored for 14 d postmortem at 2 degrees C, and frozen (-27 degrees C). Five steaks from each strip loin, each cooked to a different internal temperature (60, 66, 71, 77, or 82 degrees C), were used for shear force determinations. Two steaks from each strip loin, one cooked to 66 degrees C and the other to 77 degrees C, were used for sensory evaluation. Increased carcass maturity was associated with decreased tenderness and juiciness, increased flavor intensity, and a higher incidence of flavors described as "painty," "fishy," and "grassy." Position of a carcass within a maturity group had a negligible effect on palatability. Increased marbling was associated with greater tenderness and juiciness, a lower incidence of steaks with a "grassy" flavor, and a higher incidence of steaks with a flavor described as "fatty." Relationships between marbling and beef palatability traits were consistent across all maturity groups. Carcasses of maturities A through E were most effectively stratified according to differences in palatability when marbling scores were grouped as follows: 1) MD and higher; 2) SL, SM, MT; and 3) TR/PD. Among mature (C, D, and E maturity) carcasses, yellow-colored fat was associated with greater beef toughness and higher detection rates for "grassy" and "fishy" flavors. Higher end-point temperatures were associated with higher shear force values and lower ratings for muscle fiber tenderness, connective tissue amount, overall tenderness, and juiciness. Two alternative grading approaches (one involving current quality grading factors and the other involving the use of fat color as an additional grade factor) were developed for possible use in classification of cow carcasses into expected-palatability groups. Both alternative systems provided a more effective stratification of cow carcasses according to palatability differences than did the current USDA quality grading system.