Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/15/2004
Publication Date: 4/20/2004
Citation: Veiseth, E., Shackelford, S.D., Wheeler, T.L., Koohmaraie, M. 2004. Indicators of tenderization are detectable by 12 h postmortem in ovine longissimus. Journal of Animal Science. 82:1428-1436. Interpretive Summary: Variation in meat tenderness continues to be an issue for the meat industry. Since meat tenderness is important for the consumers¿ acceptance of the products, the unpredictable variation in tenderness has economic consequences for the meat industry. It is well known that most meat, if subject to proper cooler storage, will tenderize with aging, however, some meat will never become tender. For this reason, a priority for the U.S. beef industry is to develop an objective, non-invasive system that can predict ultimate tenderness of meat. Due to the structure of the U.S. beef industry, such a system will have to be used on-line with ribbed carcasses between 24 and 72 h postmortem. It is difficult to predict aging potential, so to increase the accuracy of the system we must try to accelerate the tenderization process. It has been confirmed by previous studies in this laboratory that u-calpain is responsible for the meat tenderization process. This experiment was conducted to characterize early postmortem changes in longissimus from lambs and to identify the earliest time points at which tenderization could be detected. The encouraging results from this experiment showed that indicators of tenderization were detected as early as 12 h postmortem. Nevertheless, it is still desirable to accelerate the tenderization process. Having characterized early postmortem changes in multiple traits of ovine longissimus, this information can be used as a baseline for more detailed analysis of the calpain proteolytic system, and assist in experiments aiming to accelerate and enhance the tenderization process.
Technical Abstract: Postmortem changes in osmotic pressure, ionic strength, pH, temperature, u- and m-calpain, calpastatin, desmin degradation and myofibril fragmentation index (MFI) were determined in ovine longissimus. Our objectives were to characterize changes in these variables, and to identify postmortem time points where significant proteolysis and tenderization could be detected. Seven crossbred lambs (Dorset × Romanov) were slaughtered and samples of longissimus were removed at 0, 3, 6, 9, 12, 24, 72 and 360 h postmortem. Osmotic pressure increased from 379 to 528 mOs during the postmortem storage period, with two-thirds of the increase occurring within the first 24 h. By measuring conductivity, we showed that ionic strength increased from 8.13 to 9.78 mS/cm during the storage period, which is equivalent to 79 and 97 mM NaCl solutions, respectively. In accordance with pH and temperature, conductivity reached ultimate levels at 24 h postmortem. Within 9 h postmortem u-calpain activity had decreased from at-death values, and continued to decrease until 72 hours at which time it was undetectable. It was still possible to detect the 76-kDa isoforms immunologically, which implies that the loss of activity is not caused by extensive autolysis. In contrast, m-calpain activity remained constant throughout the aging period, while calpastatin activity was stable until 24 h postmortem, after which it gradually declined. Co-elutions of u-calpain and calpastatin revealed that at all times postmortem u-calpain activity was detectable in the presence of calpastatin. Autolysis products of u-calpain were detected at 3 h postmortem, indicating that u-calpain was active at that time. Moreover, the impact of u-calpain activity upon myofibrillar substrates was first seen at 9 h postmortem, when a 23% loss of native desmin was detected. This degradation translated into an increase in MFI at 12 h. Collectively, these data imply that u-calpain is active in postmortem muscle in the presence of calpastatin, and that effects of u-calpain activity, leading to tenderization, are detectable during the first 12 h postmortem.