The effect of postmortem aging and location on tenderness of steaks from beef Semitendinosus and Longissimus lumborum

Abstract

The objective of this study was to determine the effect of extended postmortem aging (DOA), steak location (LOC), and dietary treatment (TRT) on cooked meat tenderness, sarcomere length, and myofibrillar protein degradation of steaks from the Semitendinosus (ST) and Longissimus lumborum (LL). Crossbred feedlot steers (n = 40; initial body weight 638 ± 29 kg) were fed 45 d with the following diets: a control diet, control diet with microalgae meal, microalgae meal and antioxidants fed at the beginning of feeding, and microalgae meal with antioxidants fed during the final 10 d of feeding. The ST and LL were removed from carcasses. The ST was fabricated into 10 steaks, which were paired with an adjacent steak and assigned 5 LOC; LOC 1 was the most proximal and LOC 5 was the most distal. Each LOC was randomly assigned an aging period of 7, 14, 28, 56 or 112 d. The 6 most posterior steaks of the LL were paired with an adjacent steak and assigned 3 locations; LOC 1 being the most anterior and LOC 3 the most posterior. Each LOC of the LL was randomly assigned an aging period of 7, 28, or 112 d. Shear force, sarcomere length, muscle fiber type and size, postmortem proteolysis, and calpain activity were measured across aging periods for each LOC. Improved Warner-Bratzler shear force (WBSF) values were detected throughout the 112 d aging period for both ST and LL steaks (quadratic; P < 0.01). The largest decrease in shear force occurred between d 7 and 28 for LL and ST steaks. Shear force decreased (P < 0.01) from LOC 1 to LOC 5 (proximal to distal) in ST steaks. Steak LOC 5 had the longest sarcomeres over LOC 1, 2, and 3 on d 7, 14, and 28 (P < 0.01) in the ST; LOC 4 and 5 also had a greater percentage of Type I fibers (P < 0.01). Muscle fiber size in ST steaks decreased (P = 0.01) from LOC 1 to LOC 5. As DOA increased, intact calpain-1 decreased (quadratic; P < 0.01), with intact calpain-1 completely disappearing by d 56 and d 28 in the ST and LL, respectively. Intact desmin and troponin-T decreased throughout the 112 d in ST and LL steaks (linear; P ≤ 0.03). Degraded desmin-38 kDa increased (P < 0.01) between d 14 and d 28; however, degraded desmin-38 kDa did not continue to degrade (P = 0.76) from d 56 to d 112 in ST steaks. Degraded desmin-35 kDa content, however, continued to increase through d 112 (P < 0.01). Muscle fiber size and type along with sarcomere length played a substantial role in tenderness differences in steak LOC, whereas calpain and proteolytic activity played a substantial role across DOA.