Effect of Degree of Dark-Cutting on Tenderness and Flavor Attributes of Beef

The objective of this study was to determine the effect of degree of dark-cutting (DC) on the tenderness, juiciness and flavor descriptive attributes of beef. During carcass grading at a large U.S. commercial beef harvesting facility, DC carcasses and matching normal cohort (NC) carcasses (n=160) were selected. Longissimus lumborum (LL) pH was determined online and DC carcasses were classified as severe (SEDC; mean pH=6.9, n=40), moderate (MODC; mean pH=6.6, n=40), mild (MIDC; mean pH=6.4, n=40) or shady (SHDC; mean pH=6.1, n=40). Vacuum-packaged strip loins (LL) were obtained from the left side of each carcass and aged for 14 d postmortem at 2?C. One steak (2.54 cm) was collected for fresh slice shear force (SSF). A 6 cm section was frozen and used for trained descriptive analysis of tenderness, juiciness and flavor. Cooked SSF pieces were frozen and utilized for western blotting of desmin to determine extent of postmortem proteolysis. Thaw and cook loss decreased as intensity of DC increased with SEDC having the lowest loss (1.83% and 10.1%, respectively) compared to NC (3.37% and 14.9%, respectively). Slice shear force was higher (P<0.05) for SHDC (25.6 kg) and MIDC (22.9 kg) compared to SEDC (16.8 kg), MODC (19.4 kg) and NC (17.8 kg). Sarcomere length was shorter (P<0.05) between DC class and NC (1.66, 1.67, 1.71 and 1.73 ?m for SEDC, MODC, MIDC and SHDC) and NC (1.86 ?m). Postmortem proteolysis of desmin was greater (P<0.05) for NC compared to all DC classes (59.83% vs. 49.20%, 40.31%, 42.07% and 43.30% for SEDC, MODC, MIDC and SHDC, respectively). Trained sensory panel ratings for tenderness differed (P<0.05) among DC class with SEDC (6.51) the most tender, followed by MODC (6.04), then MIDC (5.19) while SHDC (4.66) and NC (4.93) were the toughest. Juiciness ratings differed (P<0.05) among each DC class (5.9, 5.7, 5.4 and 5.2 for SEDC, MODC, MIDC and SHDC, respectively), with no difference between MIDC or SHDC compared to NC (5.23). Fat-like, rancid, heated oil, chemical and musty/earthy/hummus flavors increased (P<0.05) while metallic, sour and salty flavors decreased as severity of DC increased. This study showed DC and NC differed in LL tenderness, juiciness and flavor. The direction and/or magnitude of those differences were greatly dependent of severity of DC. Steaks from intermediate pH (SHDC) are most likely to be tough, yet are regularly included in U.S. Select and U.S. Choice product lines.