PROTEIN EXTRACTABILITY AND THERMAL GEL FORMABILITY OF MYOFIBRILS ISOLATED FROM SKELETAL AND CARDIAC MUSCLES AT DIFFERENT POSTMORTEM PERIODS

The effects of the post-mortem ageing period on the extractability of myofibrillar proteins from pork cardiac and rabbit skeletal muscles under various conditions of pH and ionic strength were studied with particular reference to the changes in the solubility of individual myofibrillar proteins and their denaturation characteristics. The ultimate influence or these changes on the heat-induced gel forming ability of myofibrils isolated from cardiac and skeletal muscles at different post-mortem stages was also investigated. Results showed that pork cardiac myofibrils always exhibited lower solubility than those from rabbit skeletal muscles under identical conditions of pH. ionic strength and temperature. SDS-PAGE profiles indicated several quantitative differences in the relative proportion of individual protein species present in cardiac and skeletal myofibrils. The solubility of various proteins present in myofibrils was also affected differently on heating in 0.1 and 0.6 M NaCl solution at various pH values. Thermal denaturation of cardiac myofibrils occurred at about 10-degrees-C higher than that of skeletal myofibrils as revealed by differential scanning calorimetry. Cardiac myofibrils formed much weaker heat-induced gels than those produced by skeletal myofibrils under identical conditions of temperature, pH, ionic strength and protein content.