Impacts of Extended Aging on 3 Beef Muscles and 9-10-11 Rib Dissections to Predict Red Meat Yield

Study 1 aimed to characterize biceps femoris, gluteus medius, and semimembranosus muscles over 8 aging durations. Aging duration was considered a fixed effect, while collection date (n = 2) was treated as a random effect in all univariate analyses. Paired top sirloin butt subprimals (n = 160) and one inside round subprimal (n = 80) were obtained from 80 USDA Modest (500-599) beef carcasses. Whole subprimals were aged for periods of 14, 28, 35, 42, 49, 56, 63, and 70 days in a dark cooler set to a stable temperature of ~2.2°C. At each aging interval, subprimals were opened under aseptic conditions for microbial analysis, measuring lactic acid bacteria (LAB) and aerobic bacteria (AC) levels. The subprimals were then processed into their respective muscles and cut into approximately 2.54 cm steaks, which were analyzed for instrumental color. Steaks were also subjected to further analyses including descriptive sensory evaluation, Rapid Evaporative Ionization Mass Spectrometry (REIMS), and pH measurement based on aging duration. The results indicated a relationship (P < 0.01) between aging duration and the growth of spoilage microorganisms in all three muscles. LAB and AC counts increased with longer aging times, reaching their highest counts at 70 days for both biceps femoris and gluteus medius, while the semimembranosus showed peak microbial growth at 70 days for AC and 56 days for LAB (P < 0.05). Interestingly, pH levels remained consistent throughout the aging periods (P > 0.05), suggesting that the intrinsic properties of each muscle did not change despite the microbial proliferation. Sensory assessments revealed that aging duration impacted flavor attributes and the development of off-flavors with greater intensities of off-flavors like liver-like and metallic notes at extended aging periods. Additionally, instrumental color analysis showed variations in a* values in biceps femoris, gluteus medius and semimembranosus muscles across all aging durations (P  0.05). Moreover, b* values across all aging durations in the gluteus medius and semimembranosus expressed differences (P  0.03). L* values generally remained consistent in the biceps femoris and gluteus medius, but exhibited differences in the semimembranosus (P < 0.01). Study 2 demonstrates the 9-10-11 rib dissection method, as outlined by Hankins and Howe (1946), to estimate the red meat yield in mature cow beef carcasses (N = 66). Predictive models, initially developed from previous cutout data and 9-10-11 rib dissections (Norwood, [Unpublished Data]) were applied to these dissected rib sections to accurately assess red meat yield and carcass components. The predictive models for yield and carcass components included: a % carcass bone model (adj. R² = 0.52; MAE1 = 0.34), a % carcass lean model (adj. R² = 0.89; MAE1 = 58.38), and a % carcass fat model (adj. R² = 0.94; MAE1 = 5.49). Additionally, the models estimated subprimal yield (adj. R² = 0.97; MAE1 = 23.85) and an overall red meat yield (adj. R² = 0.95; MAE1 = 52.85). Each rib was carefully analyzed to measure the proportions of muscle, fat, and bone, which are critical for evaluating overall carcass components and red meat yield. However, enhancing the accuracy of these predictive models with the 9-10-11 rib dissection method would require a larger and more diverse dataset, as the limited sample size in the earlier study restricted the ability to capture the biological variation necessary for precise carcass component predictions.