The Effect Of Dissociation Of Acomyosin On Chicken Tenderness

Meat tenderness is considered as one of the most important traits, and its post-mortem changes and underlying mechanisms have been received lots of attention from meat scientists. In the present study, the contribution of changes in actin/myosin interaction and proteolysis on meat tenderization during post-mortem storage were investigated, and the effects of AMP, IMP and pH on the dissotiation of actomyosin were followed, at last the effects of Ca2+、EGTA、E-64on the dissotiation of actomyosin and protein proteolysis were studied.1. The roles of actin/myosin interaction and proteolysis in tenderization during aging of chicken muscleThe objective of this study was to investigate the contribution of changes in actin/myosin interaction and proteolysis on meat tenderization during post-mortem storage. Following slaughter, chicken breast muscles were removed and stored at4℃. Changes in actin/myosin interaction during48hours of aging were determined by monitoring the Mg2+and Ca2+-ATPase activities. Shear force values, pH, protein degradation, calpain activities and myofibrillar ultrastructures were also investigated. Results showed that the initial weak actin/myosin interaction strengthened at12hours post-mortem but then followed by a gradual weakening, which was supported by decrease in Mg2+-ATPase activities and a lengthening of sarcomeres. According to SDS-PAGE and Western blotting analysis, the30kDa troponin-T fragment could not be readily detected until12h whereas, at the same time, desmin had been rapidly degraded. However, there was a gradual decline in μ-calpain activity commencing after about6h. Meanwhile, the largest decline in shear force was observed between12and24h post-mortem. These findings suggest that weakening of strong actin/myosin interaction, formed at rigor, may play a large role in meat tenderization during the early period of storage. It is proposed that weakening of actin/myosin interaction results in lengthening of sarcomere, and activated calpains are then more able to reach their targeted sites, enabling proteolysis. These two factors may be involved in the conversion of muscle to tender meat during post-mortem storage.2. The effect of ATP/AMP/IMP and pH on the dissociation of actomyosinIn this study actomoysin extracted from chicken breast muscle was dissolved in different solutions with ATP/AMP/IMP or different pH, then incubated at4℃for16h, and the effect of these treatments on the dissociation of actomyosin was investigated. Results showed that actomyosin incubated with ATP/AMP/IMP had a lower Mg2+-ATPase activity in contrast with the control, especially sample incubated with ATP had the lowest activity. It was also found that actin was released from actomyosin after incubated with ATP, while the release of actin in the AMP/IMP treatment sample occurred only after the acomyosin was heated at60℃for some time. As to the pH treatment, following the pH decline the interaction between actin and myosin inclined to decrease. At pH6.5or5.5, actin was dissociated from myosin, as a result Mg2+-ATPase activity decrease obviously. In addition, the SDS-PAGE results showed that MLC1was released to the supernatant when the release of actin happened. All the results suggest that actomyosin was dissociated by ATP while AMP/IMP weakened the interaction in actomyosin and the weakening actomyosin was dissociated after heated at low temperature. Meanwhile, acid environment could also lead to the dissociation of actomyosin. It is also suggested that MLC1may be involved in the weakening the interaction in actomyosin and the release of actin.3. The effect of Ca2+、EGTA and E-64on the dissociation of actomyosin and proteolysis in chicken breast muscle post-mortemThe objective of this study was to investigated the effect of Ca2+、EGTA and E-64on the dissociation of actomysoin and degradation of myofibrillar proteins. In this study, chicken breast muscle was incubated in different solutions containing Ca2+, or EGTA or E-64, at different times myofibrillar Mg2+/Ca2+-ATPase activity, degradation of sarcomplasmic and myofibrillar proteins and μ/m-calpain activity were determined. It was showed that the Mg2+-ATPase of myofibril from all the treatment samples inclined to decrease. However, myofibril extracted from muscle treated with Ca2+had the high level Mg2+-ATPase activity while myofibril extracted from samples treated with EGTA or E-64had the low level activity. In contrast, myofibrillar Ca2+-ATPase activity in all the treatment showed the opposite changes. Meanwhile, μ/m-calpain activity of samples treated with EGTA decrease slightly during48h post-mortem storage, however we can not detect any calpain activity in the samples treated with Ca2+. It was observed that troponin T and desimin degraded faster in muscle treated with Ca+. Though EGTA and E-64inhibited obviously the degradation of these proteins, there are about67.1%or31.5%of total desmin which are degraded after48h, respectively. These results suggest that the interaction between actin and myosin was weakened during post-mortem storage in all the treatments; other proteinases besides μ/m-calpain are likely to be involved in the degradation of myofibrillar proteins pos-mortem.