Submitted to: Meat Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/26/2004
Publication Date: 12/20/2004
Citation: Veiseth, E., Shackelford, S.D., Wheeler, T.L., Koohmaraie, M. 2004. Factors regulating lamb longissimus tenderness are affected by age at slaughter. Meat Science. 68:635-640. Interpretive Summary: Consumers consider meat tenderness to be the major quality factor that determines their eating satisfaction. For this reason, identification of biological factors that affect meat tenderness has been a major focus of our research projects. Over the years, by using lamb of different ages for various projects, we have noticed that there appears to be a significant age effect on lamb tenderness. We have noticed that at young ages, lambs yield tougher meat as opposed to meat from older lambs. For this reason, the objective of this experiment was to examine the effect of age on the calpain proteolytic system (an enzyme system that regulates meat tenderness by degrading proteins that hold muscle structure), postmortem proteolysis (degradation of muscle proteins), and meat tenderness of ovine longissimus. Rambouillet lambs were harvested at 2, 4, 6, 8, and 10 months of age and samples of longissimus were collected at 0, 2, and 10 days postmortem. Results indicated that indeed meat tenderness was the lowest at 2 months of age and improved with age such that meat was most tender at 8 months of age. Also, there was no difference in tenderness of meat from lambs that were 8 months and meat from lambs that were 10 months of age.
Technical Abstract: The objective of this experiment was to determine age-related changes in collagen concentration, sarcomere length, calpain (u- and m-) and calpastatin activities, postmortem proteolysis and Warner-Bratzler shear force (WBSF) in ovine longissimus. Rambouillet lambs were slaughtered at 2, 4, 6, 8 and 10 months of age and samples of longissimus were collected at 0, 2 and 10 days postmortem. Collagen concentration and sarcomere lengths were determined from the cores used for WBSF measurements and reflected changes in the background toughness. Collagen concentration did not change significantly from 2 to 8 months (4.08 to 4.46 mg/g cooked muscle, respectively), but did increase at 10 months to 4.93 mg/g cooked muscle. Sarcomere lengths also showed age-related changes, increasing from 1.35 um at 6 months to 1.48 and 1.55 um at 8 and 10 months, respectively. The extent of calpain mediated proteolysis determines the improvement in meat tenderness with postmortem storage. The most notable change in the calpain proteolytic system was the decline in calpastatin activity from 4.18 to 1.91 units per gram muscle between 2 and 10 months. The activity of u-calpain showed a 16% increase from 4 to 6 months, before it dropped again at 8 and 10 months. There was a gradual decline in m-calpain activity with age, and by 10 months m-calpain activity had reduced to 80% of 2 months levels. The ratio of u-calpain to calpastatin activities increased from 2 to 6 months (from 0.31 to 0.56) with no further changes at 8 or 10 months. There were no age-related changes in desmin degradation at day 2, however, examination of day 10 samples showed increased degradation from 2 to 6 months. Thus, the changes observed in the ratio of u-calpain to calpastatin activities are reflected in the extent of postmortem proteolysis. Meat tenderness was measured using WBSF at 2 and 10 days postmortem. Because little proteolysis had taken place at 2 days postmortem, the decline in day 2 WBSF from 6 to 8 months could be explained by changes in sarcomere length. However, at 10 days postmortem, where WBSF was shown to decrease from 2 to 8 months, the improvement in tenderness could be explained by the amount of postmortem proteolysis. The data presented in this paper show evidence that sarcomere length is the main determinant of background toughness in ovine longissimus, and that postmortem proteolysis, resulting from u-calpain activity regulated by calpastatin, is the main determinant of ovine longissimus tenderization during aging. Thus, lamb longissimus tenderness after refrigerated storage is determined by postmortem proteolysis and its interaction with sarcomere length.