Early postmortem biochemical factors influence tenderness and water-holding capacity of three porcine muscles1

Abstract

The objective of this study was to determine whether differences in pork tenderness and water-holding capacity could be explained by factors influencing calpain activity and proteolysis. Halothane-negative (HAL-1843 normal) Duroc pigs (n = 16) were slaughtered, and temperature and pH of the longissimus dorsi (LD), semimembranosus (SM), and psoas major (PM) were measured at 30 and 45 min and 1, 6, 12, and 24 h postmortem. Calpastatin activity; mu-calpain activity; and autolysis and proteolysis of titin, nebulin, desmin, and troponin-T were determined on muscle samples from the LD, SM, and PM at early times postmortem. Myofibrils from each muscle were purified to assess myofibril-bound (mu-calpain. Percentage drip loss was determined, and Warner-Bratzler shear (WBS) force was analyzed. Myosin heavy-chain (MHC) isoforms were examined using SDS-PAGE. The pH of PM was lower (P < 0.01) than the pH of LD and SM at 30 and 45 min and 1 h postmortem. The PM had a higher (P < 0.01) percentage of the MHC type IIa/IIx isoforms than the LD. The-LD had the greatest proportion of (P < 0.01) MHC IIb isoforms of any of the muscles. The PM had the lowest (P < 0.01) percentage of MHC IIb isoforms and a greater (P < 0.05) percentage of type I MHC isoforms than the LD and SM. The PM had less (P < 0.01) drip loss after 96 h of storage than the SM and LD. The PM had more desmin degradation (P < 0.01) than the LD and SM at 45 min and 6 h postmortem. Degradation of titin occurred earlier in the PM than the LD and SM. At 45 min postmortem, the PM consistently had some autolysis of mu-calpain, whereas the LD and SM did not. At 6 h postmortem, some autolysis of mu-calpain (80-kDa subunit) was observed in all three muscles. The rapid pH decline and increased rate of autolysis in the PM paralleled an earlier appearance of myofibril-bound mu-calpain. The SM had higher calpastatin activity (P < 0.05) at 45 min, 6 h, and 24 h and had higher WBS values at 48 h (P < 0.01) and 120 h (P < 0.05) postmortem than the LD. At 48 and 120 h postmortem, more degradation of desmin, titin, and nebulin were observed in the LD than in the SM. These results show that mu-calpain activity, mu-calpain autolysis, and protein degradation are associated with differences in pork tenderness and water-holding capacity observed in different muscles.

Postmortem protein degradation is a key contributor to fresh pork loin tenderness

“…5). The presence of intact titin in aged samples is a novel result because titin is typically degraded earlier postmortem by calpain-1 (Huff- Lonergan et al, 1995;Taylor et al, 1995;Melody et al, 2004;Rowe et al, 2004b). The rate of titin degradation is known to be slower in beef that exhibits high-shear-force values regardless of animal age or gender (Huff-Lonergan et al, 1995).…”

“…These results are consistent with observations that degradation of these proteins is associated with differences in measured instrumental tenderness values in pork muscles. Chops from LM had more degradation of troponin-T, less intact desmin, and lower Warner-Bratzler shear force values (kg) than tougher semimembranosus muscles (Melody et al, 2004).…”

“…Autolysis lowers the amount of calcium needed for activation of calpain-1 (Suzuki et al, 1981). Calpain-1 in muscle degrades the proteins desmin, troponin-T, and titin during postmortem aging in beef (Huff-Lonergan et al, 1996a) and pork (Lonergan et al, 2001;Melody et al, 2004). The rate of activation and autolysis of calpain-1 could impact the amount of protein degradation by calpain-1.…”

“…Degradation of proteins influences muscle structure and can play a role in meat tenderness (Taylor et al, 1995;Wheeler et al, 2000;Melody et al, 2004). The calpain system, specifically calpain-1, plays a large role in the proteolysis of muscle proteins (Huff-Lonergan et al, 1996a;Lametsch et al, 2004;Geesink et al, 2006).…”

Liver and skeletal muscle mitochondria proteomes are altered in pigs divergently selected for residual feed intake1,2

“…Strips were passively rehydrated overnight and isoelectric focusing and equilibration were performed according to the manufacture's protocol, as describe previously. After equilibration, strips were loaded onto 12.5% SDS-PAGE gels and run overnight at 20 V. Gels were then transferred and traditional western blotting techniques were used as described by Melody et al (2004).…”