Degradation and changes in proteins of beef muscle at various heating temperatures

Heating food, particularly meat, provides a physical stimulus that causes chemical reactions by delivering energy into the meat tissue. The energy transferred into meat tissue during cooking results in changes in different colour, texture, taste, and morphological appearance. The aim of this study was to determine changes in the myofibrillar and sarcoplasmic proteins of beef gastrocnemius muscle in response to various temperatures for 60 min. The changes in physicochemical properties, including the pH, meat colour, protein content, and protein solubility (molecular weight alterations), were investigated in fresh and treated samples. As the heating temperature increased, the contents of both myofibrillar and sarcoplasmic proteins gradually decreased. Specifically, the protein solubility in samples heated at 75 degrees C was significantly lower than that of those of samples treated at 5 degrees C (P<0.05). Protein solubility decreased at temperatures beyond 35 degrees C andbecomeschallengingabove55 degrees C, mostly due to protein aggregation and or protein pyrolysis. The pH values of the freshly and heat-treated samples were different. There was a positive but steady correlation between the increase in temperature and pH value. The changes in pH were attributed to the restructuring of amino acid residues on the surface of the protein and a reduction in intramuscular moisture content. All colour changes are likely a result of iron oxidation and the denaturation of myoglobin into hemichrome. SDS-PAGE results revealed that sarcoplasmic proteins start to denature at35 degrees C and that myofibrillar gelation occurred at 40 degrees C. Further, SDS-PAGE data show that the actin protein (42kDa) was heat stable and almost fully soluble, even at 75 degrees C, which agreed with the protein content data. The data suggest that the thermoconversion of muscle proteins into polymers had anobvious effect on protein solubility. Sarcoplasmic proteins lost approximately 67% of their solubility and the myofibrillar proteins lost approximately 86% of their solubility due to protein polymerization and pyrolysisof the muscle fibers. Ultimately, the data suggest that at any heating temperature above 55 degrees C, the globin on the surface or inside the muscles is fully denatured, with starting changes observed at 35 degrees C .