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Cattle size in the United States has been on the rise resulting in heavier beef carcasses. The additional weight on the carcass has presented challenges during carcass chilling that lead to quality-related abnormalities such as meat color defects. The round is a large primal that accounts for roughly 6% of the entire carcass weight. Variations in the location and size of muscle groups within the round have exhibited different chilling behaviors. The deep portion of the top round has been observed to chill slower than the superficial section. It is not uncommon to see top round steaks exhibiting the defect of “two-toning” in retail cases. The superficial section of the steak is often redder while the deep section is visibly lighter in color. It has been estimated that the US beef industry endures an approximate annual loss of $3.7 billion attributed to meat discoloration. It has also been established by prior research that carcass size impacts retail presentation and sensory experience. Alternative management strategies for oversized beef carcasses should be explored to address these considerations. Thus, this study proposes an alternative fabrication method to be performed on the kill floor with the goal of aiding in the chilling process of the top round, especially the deep portion. The primary objective of this study is to assess the impact of an alternative fabrication method on pH and temperature decline during the initial chill time, color, and tenderness of cuts from the top round and the knuckle, focusing on heavy weight beef carcasses.
Bos taurus carcasses with hot carcass weight (HCW, >1,000 lbs, n = 11) were obtained from a commercial beef finishing operation and slaughtered at the University of Idaho Meat Laboratory under USDA inspection. One side of each carcass had the knuckle separated from the top and bottom round at the seams, partially exposing the femur bone while the adjacent side remained intact. Temperature and pH decline at the deep and superficial locations of the top round were measured during chilling (48 h postmortem). Top rounds (NAMI#169) were fabricated and wet-aged in vacuum packaging until 14 days postmortem and cut into steaks. Steaks were separated into deep and superficial sections and assigned to one of three assignments: 1) retail shelf-life analysis (objective and subjective steak color, lipid oxidation, pH); 2) instrumental tenderness (Warner-Bratzler Shear Force); 3) consumer taste panel. A packer survey to collect industry feedback on potential willingness to adopt the proposed alternative fabrication method was distributed. Chilling and pH decline rates were estimated with a non-linear exponential decay model. Analysis of variances used a mixed model with locations and fabrication methods as fixed effects and animal as random effect. All data were analyzed using R Statistical Software (v4.3.1; R Core Team 2023). P < 0.05 was used to determine statistical significance.
Regardless of the locations, consumers rated top round steaks from the alternatively fabricated sides to be more flavorful and more acceptable. Time of retail display significantly impacted the amount of lipid oxidation (P < 0.001) regardless of location and treatment of the top round steaks. Prior research had pointed out that chilling rate impacts the profile of volatile and non-volatile compounds that are responsible for flavor in raw meat (Xiang et al., 2021). Xiang et al., 2021 also concluded that more rapid chilling positively influenced aromatic compounds in raw meat. It has been studied that humans determine flavor using a complex process involving the gustatory sensory cells (taste), olfactory bulb (smell) and trigeminal nerves (feel) and a strong relationship has been identified between flavor and overall acceptability (Kerth & Miller, 2015). Since peeling down the knuckle resulted in an accelerated chilling rate of the top round, consequently alterations in flavor compounds could have occurred. Superficial sections of the top round steaks yielded an average shear force value (kgf) below the threshold for USDA “certified tender” during instrumental tenderness evaluation. Overall location and retail time were more impactful on both subjective and objective color instead of the fabrication method.
Heavy beef carcasses with hot carcass weight over 1000 lbs had shown challenges regarding chilling rate in the deep portion of the top round. The current study proposed an alternative fabrication method performed during slaughter prior to entering the cooler to aid in the top round chilling process. Results suggested that the deep portion of the top round chilled faster by peeling down the knuckle during harvest. The study found that the proposed fabrication method resulted in top round steaks with more favorable ratings for flavor and overall acceptability by consumers. Although the fabrication method did not have a major impact on top round steak retail color, the study offered insights into instrumental tenderness variations at the superficial and deep sections. Results from the current study suggest that the superficial section of top round steaks meets the criteria of “certified tender” by the USDA. Findings regarding tenderness variations due to location and increased consumer satisfaction due to the alternative fabrication method can be used as a gateway to further explorations of alternative marketing strategies to increase industry profit margins.