In general, all 3 beef cuts had higher WBSF, CTSF, and more connective tissue amount detected by the train panelists at 3 days aging than the rest of the aging periods (P < 0.05). However, no aging effect was found for collagen content (P > 0.10). Two distinct sets of unknown collagenase MMPs activity were detected at 72 and 92 kDa in the collagen zymography. The 72 kDa MMP had the greatest activity at 3 days aging, which the activity decreased from 3 to 21 to 42 days (P < 0.0), and no further decrease was found beyond 42 days of postmortem aging. Seventy-two kDa MMP also had the greatest activity in GN muscle compared to the others (P < 0.01). Finally, degradation of aggrecan by MMPs was measured by antibody recognizing MMP-degradation epitopes in aggrecan. All 3 muscles had a decrease in the aggrecan fragment intensity from 3 to 21 to 42 days (P < 0.05).
No detectable native beef MMP-9 activity was found in 48 h, 21 d nor 42 d gels under simulated industry meat storage condition. However, noticeable native beef MMP-9 activity was found in all three muscle extracts in 63 d gels, which gastrocnemius had greater MMP2 activity than gluteus medius (P < 0.05) and tended to have greater MMP-9 activity than longissimus lumborum (P = 0.07). Furthermore, the addition of 20 µM of ZnCl2 in the developing buffer increased the native beef MMP-9 activity by 9 folds, while the addition of 50 and 100 µM of ZnCl2 increased native beef MMP-9 activity by 6 and 4 folds compared to 5 mM CaCl2 only, respectively (P < 0.05).
In general, all 3 beef cuts had higher WBSF, CTSF, and more connective tissue amount detected by the train panelists at 3 days aging than the rest of the aging periods (P < 0.05). However, no aging effect was found for collagen content (P > 0.10). Two distinct sets of unknown collagenase MMPs activity were detected at 72 and 92 kDa in the collagen zymography. The 72 kDa MMP had the greatest activity at 3 days aging, which the activity decreased from 3 to 21 to 42 days (P < 0.0), and no further decrease was found beyond 42 days of postmortem aging. Seventy-two kDa MMP also had the greatest activity in GN muscle compared to the others (P < 0.01). Finally, degradation of aggrecan by MMPs was measured by antibody recognizing MMP-degradation epitopes in aggrecan. All 3 muscles had a decrease in the aggrecan fragment intensity from 3 to 21 to 42 days (P < 0.05). No detectable native beef MMP-9 activity was found in 48 h, 21 d nor 42 d gels under simulated industry meat storage condition. However, noticeable native beef MMP-9 activity was found in all three muscle extracts in 63 d gels, which gastrocnemius had greater MMP2 activity than gluteus medius (P < 0.05) and tended to have greater MMP-9 activity than longissimus lumborum (P = 0.07). Furthermore, the addition of 20 µM of ZnCl2 in the developing buffer increased the native beef MMP-9 activity by 9 folds, while the addition of 50 and 100 µM of ZnCl2 increased native beef MMP-9 activity by 6 and 4 folds compared to 5 mM CaCl2 only, respectively (P < 0.05).
The findings from this study provided proof that native collagenase MMP-9 are active in postmortem beef muscles. Both CTSF and trained panels indicated connective tissue softening during postmortem aging, but no change in collagen content was observed. Therefore, we suspect the collagenase MMPs do not work by removing collagen but by altering the collagen structure. Our aforementioned study confirmed that native beef MMP-9 can contribute to collagen degradation in extended aged beef (42 d +), and a small increase in intracellular zinc concentration may significantly improve this collagenase activity during aging.