Center for Integrated Animal Genomics

1. Figure 1 – Desmin Western blot Intact desmin Tenderness Values Degraded desmin SM 1 d SM 7 d SM 14 d Ref. Figure 5 was adapted from Anderson et al., 2007. • Research Experience in Molecular Biotechnology & Genomics • Summer 2008 Center for Integrated Animal Genomics J. M. Binning, M. J. Anderson, S. M. Lonergan, E. Huff-Lonergan Postmortem degradation of desmin in specific muscles from the beef round Results and Discussion Abstract The objective of this study was to determine the differences in amount desmin degradation and rate of desmin degradation in specific muscles of the beef round. Ten market weight beef cattle were slaughtered, and muscles were removed from both sides of the carcasses at 24 hours after slaughter. Muscles removed included the longissimus dorsi (LD; control muscle) and the following muscles from the round: gracillus (GR), adductor (AD), semimembranosus (SM), sartorius (SAR), vastus lateralis (VL), vastus intermedius (VI). Steaks were aged at 4°C for a total of 24 h, 7 d or 14 d postmortem. Degradation of the protein desmin was determined using western blot analysis. Differences existed in the amount and rate of desmin degradation between beef round muscles. VL had the greatest amount of desmin degradation at 24 h postmortem. The SM had significantly (P < 0.05) more degradation that all other muscles at 7d. The SM had significantly (P < 0.05) more desmin degradation that the VI at 14 d. In the VL, no significant (P > 0.05) desmin degradation occurred over time. The VI, SM, and GR differences in degradation were observed between 1 d and both 7 d and 14 d. The AD and SAR only differed in degradation between 1d and 14d. The rate and amount of desmin degradation affects the length of storage time necessary for aging. Introduction The beef industry has struggled with the inconsistency in meat tenderness. This problem significantly affects the quality, marketability, and profitability of their products. The lack of consistent tenderness negatively impacted the beef industry, and conservative estimates have shown that is has cost them 216,000,000 annually (Morgan, 1995). The muscles of the round have typically been generalized as being less tender than some of the higher quality cuts. Recent muscle profiling data supported by NCBA has documented the characteristics of many of these muscles, and the data indicate that several muscles have potential to be marketed as individual value cuts (NCBA, 2000). The muscles from the round also exhibit significantly different biochemical characteristics, which in turn could relate to the tenderness of these muscles. These muscles have the potential to reveal possible indicators for tenderness. It is understood that the degradation of muscle proteins in postmortem muscle plays a role in meat tenderization process. One area that greatly affects tenderness is the degradation of muscle proteins in postmortem muscle. One particular protein of interest is desmin, which ties the myofibril to the cell membrane. Desmin is a substrate of calpain and could be used as an indicator of overall degradation by the calpain system and potentially the rate of tenderization (Huff-Lonergan et al., 1996). Desmin also influences water-holding capacity, another desirable meat quality trait. Because of desmin, contraction of myofibrils results in the shrinkage of the cell. Increasing the amount of degraded desmin potentially increases the cells water-holding capacity by allowing myofibrils to contract, without shrinking the entire cell (Melody, 2004). The objective of this study was to determine the differences in amount desmin degradation and rate of desmin degradation in specific muscles of the beef round. This may reveal insight into the tenderization process of the beef round muscle and the underlying biochemical attributes that govern these processes. • At 24h postmortem, VL had the greatest amount of desmin degradation product, however this muscle also did not have a significant (P > 0.05) change in desmin degradation product over time (Figure 2). • At 7d, the SM had significantly (P < 0.05) more degradation that all other muscles (Figure 3). • At 14d, the SM had significantly (P < 0.05) more desmin degradation than the VI (Figure 4). • GR, SAR, SM, and VI had significant desmin degradation between day 1 and 7 postmortem, but no significant desmin degradation between days 7 and 14 postmortem (Figure 5). • Previous research in our lab showed the SM had a greater quantity of degraded desmin, but had no significant (P > 0.1) change in tenderness values. This indicates that other features (perhaps composition of connective tissue) of this cut contribute to tenderness. • Previous research in our lab showed the LD, AD, GR, VI, and VL had significant (P < 0.1) increase in tenderness between 1d and 14d. • Previous research in our lab showed the VL was significantly (P < 0.05) less tender than LD at 14d postmortem. This could be explained by the little desmin degradation that occurred over time. Objective The objective of this study was to determine the differences in amount desmin degradation and rate of desmin degradation in specific muscles of the beef round. Conclusion • Seven muscles (6 round, 1 reference) were removed from 10 beef cattle at 24 h postmortem. • -Longissimus dorsi (LD; reference) -Semimembranosus (SM) • -Vastus Intermedius (VI) -Gracillus (GR) • -Vastus Lateralis (VL) -Adductor (AD) • -Sartorius (SAR) • Muscles were aged 1, 7 and 14 days • Whole muscle protein samples were prepared for SDS-PAGE and Western blotting according to (Huff-Lonergan, E., Mitsuhashi, T., Parrish, F.C. & Robson, R.M., 1996) • Western blotting was for desmin. • 1- polyclonal desmin diluted 1:20,000 • 2- goat-anti-rabbit diluted to 1:20,000 • Labeled antibodies were detected using Chemilumenescence (ECL PLUS, GE Healthcare, Piscataway, NJ) and a CCD Camera (Alpha Innotech Chemilmager) • A reference sample that exhibited the desmin degradation • product was loaded onto each gel. • Analysis of the detected desmin degradation product band • was done by densotometry using Alpha Innotech software. • Intensity of the desmin degradation product was compared • to the intensity of the degradation product of the reference • sample on each western. The intensity was reported as a • ratio of the sample band to the reference band. (Figure 1) • Means were separated by muscle and by day • using the GLM procedure in SAS. Methods and Materials Differences in the amount and rate of formation of postmortem desmin degradation product existed between beef round muscles. The rate of degradation will affect the length of storage time necessary for aging. The VL needs very little aging (looking at the degradation and tenderness data). The VI, SM, GR only need about 7 days before differences were observed in those muscles. The AD and SAR kept changing over the entire 14 d period. It is evident that the rate of desmin degradation in the first few days postmortem is linked to sensory panel tenderness, except for the SM. The SM has a large amount of connective tissue which likely explains its lower tenderness values. This demonstrates that there any various factors that govern the tenderization process, and that further studies on characterizing beef round muscles may lead to a greater ability to identify higher quality cuts and reveal greater insight into the tenderization process. Literature Cited Anderson, M.J., K. Mou, E. Steadham, C. Fedler, K. Prusa, S.M. Lonergan, and E. Huff-Lonergan. 2007. Round Muscle Profiling: Influence of aging on palatability of specific wholesale round cuts. Proceedings, 60th Reciprocal Meat Conference, June 17-20 South Dakota State University, Brookings, SD. Huff-Lonergan, E., T. Mitsuhashi, D. D. Beekman, F. C., Parriah, Jr, D. G. Olson, and R. M. Robson. 1996. Proteolysis of specific muscle structural proteins by mu-calpain at low pH and temperature is similar to degradation in postmortem bovine muscle. J Anim Sci 74: 993-1008 Melody, J. L., S. M. Lonergan, L. J. Rowe, T. W. Huiatt, M. S. Mayes, and E. Huff-Lonergan. 2004. Early postmortem biochemical factors influence tenderness and water-holding capacity of three porcine muscles. J Anim Sci 82: 1195-1295 Morgan, J. B. 1995. Enhance taste-palatability, National Cattlemens Beef Association, Centennial, CO. NCBA. 2000. Muscle profiling, National Cattlemen’s Beef Association, Denver, CO. Program supported by the National Science Foundation Research Experience for Undergraduates DBI-0552371