Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/18/2006
Publication Date: 6/21/2006
Citation: King, D.A., Wheeler, T.L., Shackelford, S.D., Koohmaraie, M. 2006. Contribution of postmortem proteolysis and sarcomere length to variation in beef gluteus medius and triceps brachii tenderness. Meeting Abstract. Proc. 59th Reciprocal Meat Conference, June 18-21, 2006, Champaign-Urbana, IL. Available: http://www.meatscience.org/pubs/rmcarchv/2006/presentations/RMC06_Abstracts.pdf
Technical Abstract: The objective of this experiment was to determine 1) the effects of quality grade and postmortem aging time on tenderness of gluteus medius and triceps brachii steaks, and 2) the contribution of postmortem proteolysis and sarcomere length to variation in tenderness of gluteus medius and triceps brachii steaks. Top sirloin butts (n = 100) and shoulder clods (n = 100) were obtained from US Choice and Select carcasses in a commercial processing facility and aged for either 14 or 42 d. Subprimals were assigned to treatments in a completely randomized 2 (quality grade) × 2 (aging time) arrangement. After aging, steaks (2.54 cm) were cut from each subprimal and cooked to an internal temperature of 70°C before slice shear force values were determined. The two halves of the sheared slices were frozen and later sampled for sarcomere length measurements and Western blotting of desmin, which were conducted on a sub-sample (n = 60) of each muscle. Select gluteus medius steaks had lower (P < 0.05) slice shear force values than Choice gluteus medius steaks (17.6 and 18.3 kg, respectively). Gluteus medius steaks aged for 42 d had lower (P < 0.05) slice shear force values than those aged for 14 d (16.59 and 19.29 kg, respectively). At 14 d postmortem, desmin degradation in gluteus medius steaks was similar (P > 0.05) between quality grades (37.9 and 43.5% for US Select and Choice, respectively), but increased (P < 0.05) with postmortem storage and was greater (P < 0.05) in US Select gluteus medius steaks (71.6%) than in US Choice (58.4%) steaks after 42 d. Sarcomere length of gluteus medius steaks was not affected (P > 0.05) by USDA quality grade or postmortem aging. The Pearson correlation coefficient between slice shear force and desmin degradation in gluteus medius steaks was -0.31 (P = 0.02). A stronger, negative correlation (r = 0.61; P = < 0.001) was observed between slice shear force and sarcomere length in the gluteus medius. Slice shear force was not affected (P > 0.05) by quality grade in the triceps brachii (13.3 and 13.4 kg for Choice and Select, respectively). Postmortem aging reduced (P < 0.05) slice shear force values in the triceps brachii (14.2 and 12.5 at 14 and 42 d, respectively). At 14 d postmortem, US Select triceps brachii steaks had less (P < 0.05) desmin degraded than did steaks from Choice carcasses (22.1 versus 39.4%). However, after 42 d of postmortem aging, desmin degradation had increased in cuts from both quality grades and was similar (P > 0.05) between US Choice and Select triceps brachii steaks (67.8 and 72.0%, respectively). Sarcomere length was not affected by quality grade or postmortem aging in triceps brachii steaks. Desmin degradation in triceps brachii steaks was moderately negatively correlated (r = -0.36; P = < 0.01) to slice shear force, while a lower, negative correlation (r = 0.22; P = 0.09) was detected between sarcomere length and slice shear force. These data indicate that proteolysis contributes to variation in tenderness of gluteus medius and triceps brachii steaks, while sarcomere length contributes to variation in tenderness of gluteus medius steaks.