The Role Of Calpain In Postmortem Chicken Meat Quality Changes

The role of calpain in the improvement of postmortem livestock meat quality has been proved by a lot of work,however the calpain system in poultry shows distinct differences in the type,the sensitivity of Ca2+ and activity with those in livestock.Therefore studies about the role of calpain in avian meat quality still need further researches.In this thesis,the variation of calpain activity and molecular characteristics were studied,we also analyzed the correlation between calpain activity,meat quality changes and the degradation of myofibril proteins.Besides the role of calpain and caspase in postmortem chicken were compared.This study focused on the special characteristics of calpain in poultry and would contribute to the establishment of calpain role mechanism in postmortem chicken meat quality changes.1.Autolysis of ?/m-calpain during postmortem aging of chicken breast muscleThis study investigated the changes occurring in p/m-calpain in postmortem chicken muscles and to determine the origin of the unknown bands found in calpain casein zymography.Results showed that the unknown bands were corresponding to ?/m-calpain,and dephosphorylation by protein phosphatase did not change their appearance.The products of ?/m-calpain partial autolysis were found to be consistent with the appearance of the unknown bands.Therefore,the appearance of these bands did not result from phosphorylation of ?/m-calpain as previously hypothesized,but from partial autolysis of?/m-calpain.2.The correlation between ?/m-calpain and postmortem meat quality changesThe role of calpain especially poultry specific ?/m-calpain in the proteolysis of chicken breast muscle during storage was analyzed.Casein zymography shows p-calpain underwent early activation and its activity disappeared after 12 h postmortem,while obvious degradation of ?/m-calpain was detected only after 1 day later.Correlation results indicated that ?-calpain was significantly correlated with most of the meat quality indicators like tenderness,WHC and proteolysis during first 12 hours,while such significant correlation of ?/m-calpain was only found after 12 hours' storage.3.The role of ?/m-calpain during the later stage of postmortem chicken storageIn order to do further research on the role of ?/m-calpain in the proteolysis of postmortem chicken breast muscle,we treated the muscle with calpain and caspase inhibitor respectively and measured the differences by detecting the calpain activity,the changes of myofibril ultrastructure and the proteolysis of myofibril proteins.Results showed that the activity of calpain was entirely inhibited after the treatment of calpain inhibitor(MDL-28170),accompanied by the inhibition of myofibril structure breaken,desmin degradation and the accumulation of 28-32 kDa products.The treatment of caspase inhibitor(z-VAD-fmk)inhibited the calpain activity in 1 and 3 d,while the degradation of desmin and the producing of 28-32 kDa products were also inhibited.In 7 d,the activity of calpain was activated,and then the degradation of desmin increased significantly.Besides,the myofibril structure breaken and the producing of 28-32 kDa products of Troponin-T were inhibited in 1-7d.Then we concluded that both the MDL-28170 and z-VAD-fmk treatments inhibited the proteolysis of myofibrillar protein proteolysis,but ?/m-calpain played a major role while caspase also played partial roles by controlling the activity of calpain.