Evaluation of factors influencing palatability of beef strip loin steaks from mature cattle of varying finishing diets and marbling scores

The objective of this study was to investigate the changes in subjective and objective beef palatability measurements from mature cattle of varying finishing diets and marbling scores. Beef strip loins (n = 15 per treatment) from two marbling score groups [slight (SL) and traces/practically devoid (TR/PD)] and three carcass types [young fed (YF), mature fed (MF), and mature unfed (MU)] were collected in commercial processing facilities. Mature unfed strip loins were selected from mature cows that were fed a maintenance diet prior to harvest. After aging (21 d), strip loins were cut into 2.5 cm thick steaks and frozen at -20°C until analysis. Proximate analysis was performed on one steak from each subprimal to determine fat, protein, and moisture values. Consumer and trained sensory panels were used to evaluate steaks for tenderness, flavor, and juiciness. Steaks for consumer and trained sensory analysis were cooked on a propane gas grill to a medium degree of doneness (71°C). Panelists evaluated cooked samples on 100 mm line scales verbally anchored at both ends. Additionally, Warner-Bratzler shear force, collagen solubility, sarcomere length, and volatile flavor compounds were assessed and used as objective measures to help explain variation in sensory tenderness and flavor. Consumer ratings were only influenced (P < 0.05) by marbling score. Slight samples were rated more favorably (P < 0.05) than TR/PD samples for tenderness, juiciness, flavor and overall like. Consumer acceptability for all traits was greater (P < 0.05) for SL samples than for TR/PD samples. Carcass type also had an effect on acceptability. Tenderness acceptance was greatest (P < 0.05) in YF steaks and least (P < 0.05) for MU steaks. Juiciness acceptance (P < 0.05) was greatest in MU steaks followed by YF and MF steaks, respectively. Marbling score by carcass type interactions were observed (P < 0.05) for flavor liking and overall liking acceptance. Flavor liking and overall liking acceptance scores were lesser (P < 0.05) for MF and MU carcass types when steaks had TR/PD marbling scores. Trained panelists rated SL steaks greater (P < 0.05) than TR/PD samples for sustained juiciness. Initial and sustained tenderness were influenced by both marbling score and carcass type. Panelists found samples from SL carcasses to be more tender (P < 0.01) than TR/PD samples. Additionally, YF and MU steaks were the most and least tender (P < 0.01), respectively. No differences were recorded in SL samples for beef flavor, beef flavor intensity, or off-flavor intensity. However, within TR/PD treatments, MF and MU carcasses had a more intense presence of off-flavors (P < 0.01). Consumer overall like scores were most strongly correlated (P < 0.05) to flavor (r = 0.89), followed by tenderness (r = 0.72) and juiciness (r = 0.69). Warner-Bratzler shear force values were improved as a result of grain finishing. Cooked steaks from YF and MF carcasses sheared lower (P < 0.01) than steaks from MU carcasses. Shear force values were negatively correlated (P < 0.01) to trained tenderness (r = -0.61), as well as, to consumer tenderness (r = -0.38). Concentrations of heat soluble collagen were least (P < 0.01) in MF and MU carcasses; however, the percent of heat soluble collagen was greater (P < 0.01) for SL-MF than for SL-MU carcasses. Percent of heat soluble collagen was not improved between TR/PD-MF and TR/PD-MU carcasses. Percent heat soluble collagen was moderately correlated (P < 0.01) to trained tenderness (r = 0.30). Within SL treatments, sarcomere length was not affected by carcass type. However, MF and MU carcasses with TR/PD marbling scores had shorter (P < 0.05) sarcomeres than YF carcasses. Additionally, TR/PD-MU had the numerically shortest sarcomeres, which seemed to be the result of a lack of external fat for insulation during carcass chilling. Sarcomere length only showed weak correlations to other measurements of tenderness. The trends seen by the group of pyrazines were the only consistent trends seen in the concentrations of isolated volatile compounds. Methylpyrazine, 2,5-dimethylpyrazine, trimethylpyrazine, and 2-ethyl-3,5-dimethylpyrazine were all extracted in greater (P < 0.01) concentrations from SL samples. All pyrazines were positively correlated (P < 0.05) with percent fat, as well as, all pyrazines were correlated (P < 0.05) to favorable flavor attributes, with the exception of consumer off-flavor intensity. Other trends for volatiles were seemingly inconsistent and only a few weak correlations were made to trained and consumer sensory scores. Overall palatability improvements were seen as a result of grain finishing cull cow beef. Samples with SL marbling scores appeared to benefit the greatest from grain finishing when compared to TR/PD treatments, in terms of both subjective and objective measurements. No differences in consumer ratings or acceptance were found, regardless of maturity or finishing diet, suggesting that an adequate degree of marbling was present to offset negative palatability traits typically associated with mature unfed beef. Additionally, the role of gas grilling and the formation of pyrazines as they relate to beef flavor need to be further investigated in order to better understand their role in masking potential off-flavors.