Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/1996
Publication Date: N/A
Interpretive Summary: Solving the problem of inconsistency in meat tenderness has been identified as a major concern of the meat industry. Results of various studies conducted at this laboratory have indicated that differences in the rate and extent of postmortem tenderization are the principal sources of variation in meat tenderness and, thus, likely the source of inconsistency in meat tenderness at the consumer level. To solve the tenderness problem even greater understanding of the mechanisms regulating meat tenderness and tenderization must be gained. In an experiment designed to determine the inherent level of meat tenderness at the time of slaughter, we demonstrated that meat is tender at slaughter, toughens during the first 24 h postmortem, and then becomes tender again during postmortem storage at 4 deg C. This experiment was conducted to determine the cause of meat toughening during the first 24 h after slaughter. Results indicate that meat toughening is caused by sarcomere shortening, because it did not occu when sarcomere shortening was prevented. This rigor-induced toughening occurs uniformly in all carcasses. The toughening phase is followed by a tenderization process which is caused by degradation of key structural muscle proteins. The tenderization process, however, is not uniform and results in variation in meat tenderness. Future research should focus on ways to prevent the toughening process and to accelerate the tenderization process.
Technical Abstract: The objective of this experiment was to test the hypothesis that meat toughening during the first 24 h postmortem results from sarcomere shortening during rigor mortis development. Eleven market weight lambs were utilized to measure changes in shear force of clamped longissimus during rigor development. Within 15 min of exsanguination, while attached at both ends, each longissimus was separated from the vertebrae body and clamped between three sets of metal plates to prevent muscle shortening. The clamped sections were placed at -1.1 deg C for 0, 3, 6, 12, or 24 h. After 24 h at -1.1 deg C, the 168 h-section was stored at 4 deg C for an additional 144 h. At each of these times, a section was frozen at -30 deg C, then stored at -5 deg C for 8 d. Sections were sampled for pH, sarcomere length, shear force, and Western blot analyses before and after storage at -5 deg C. Shear force values were the same (P > .05) from 0 to 24 h (4.5 kg at 0 h to 4.9 kg at 24 h), then declined (P < .05) to 3.3 kg at 168 h postmortem. As evident by lack of statistical difference in the sarcomere lengths, we were successful in holding the muscle length constant. Western blot analyses of nebulin, vinculin, and troponin-T indicated that minimum degradation occurred through 12 h, was slightly increased by 24 h, and was relatively extensive by 168 h postmortem. Although limited proteolysis occurred during storage at -5 deg C for 8 d, this by itself had no effect on shear force. Results indicate that shear force values do not increase during rigor development when muscle is prevented from shortening; thus, the toughening that occurs during the first 24 h of slaughter is most likely due to sarcomere shortening.