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This study's objective was to understand the relationships between biochemical tenderness components and subject/objective tenderness of eight muscles from beef carcasses. Longissimus thoracis (LT), pectoralis profundus (PP), supraspinatus (SS), triceps brachii (TB), gluteus medius (GM), rectus abdominus (RA), rectus femoris (RF), and semitendinosus (ST) were collected from 10 USDA upper 2/3 Choice beef carcasses and assigned to a two- or 21-day aging period (n=160). Troponin-T (TNT) degradation, desmin degradation, sarcomere length, collagen content, mature collagen crosslink density, intramuscular lipid content, pH, Warner-Bratzler Shear Force (WBSF) and trained sensory panel analyses were measured. A Pearson correlation analysis was conducted to determine the relationship between each tenderness contributor measured in this study with WBSF or the overall tenderness evaluated by the trained panelist for each of the eight muscles. In addition, multivariate regression models were constructed to confirm this relationship. The results showed that muscle anatomical locations and physiological functions driven by muscle fiber types may explain some of the biochemical/tenderness differences found in this study. The correlation analysis showed that each muscle had a specific tenderness factor(s) that contributed to the overall tenderness. For instance, tenderness for LT, TB, GM, RA, and ST may be influenced more by proteolytic degradation, while the collagen characteristics may primarily influence tenderness for PP. Also, lipid content has a significant influence on GM tenderness. Finally, the multivariate regression model showed that almost all of the biochemical measurements conducted in this study played a minor but important role as an overall tenderness predictor on a whole carcass basis. Increasing the knowledge base on the various tenderness components' level of contribution will allow end-users to develop specific tenderness management strategies to ensure consistent tenderness in beef products.

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The objective of this study was to identify the relative contribution of tenderness factors for 3 beef muscles with similar tenderness ratings. Longissimus lumborum (loin), tensor fascia latae (tri-tip) and gastrocnemius (heel) were collected from 10 USDA choice beef carcasses, fabricated into steaks and assigned to a 5 or 21 d aging period (n=60). Heel had the greatest relative troponin-T degradation %, followed by tri-tip and loin (68.10, 53.42 and 35.01 % respectively; P< 0.01). Tri-tip had the longest sarcomere, followed by heel and loin (3.01, 2.59 and 1.71 µm, respectively; P < 0.01), and heel increased in sarcomere length from 5 to 21 d of postmortem storage (2.49 vs 2.70 µm; P< 0.05). As expected, heel had the greatest collagen content, followed by tri-tip and loin (6.06, 3.98 and 2.76 mg/g of muscle tissue, respectively; P< 0.01), and collagen content decreased for all cuts from 5 to 21 d of postmortem storage (4.64 vs 3.90 mg/g muscle tissue; P< 0.05). Out of the 3 cuts, heel had the highest collagen crosslink density (0.20 mol/mol collagen; P< 0.05), while loin and tri-tip did not differ (0.13 and 0.15 mol/mol collagen, respectively; P >0.05). Collagen crosslink density increased for all cuts from 5 to 21 d of postmortem storage (0.14 vs 0.20; P< 0.01). Heel had lower lipid content than the others (2.68 %; P< 0.01), while tri-tip and loin did not differ in lipid content (8.24 vs. 6.99 %; P >0.05). Loin was ranked by the trained panel to have the highest overall tenderness, while tri-tip and heel did not differ in overall tenderness (P >0.05). The overall tenderness value for heel was positively correlated with troponin-T degradation (P< 0.01). On the other hand, overall tenderness value for loin was negatively correlated with lipid content (P< 0.05), and overall tenderness value for tri-tip was negatively correlated with collagen content (P< 0.05). These results indicated that each beef cut had a unique profile of tenderness contributors.