Degradation and Structural Changes in Beef Muscle Proteins at Different Heating Temperatures

Abstract

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 °C was significantly lower than that of those of samples treated at 5 °C (P < 0.05). Protein solubility decreased at temperatures beyond 35 °C and becomes challenging above 55 °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 at 35 °C and that myofibrillar gelation occurred at 40 °C. Further, SDS-PAGE data show that the actin protein (42 kDa) was heat stable and almost fully soluble, even at 75 °C, which agreed with the protein content data. The data suggest that the thermoconversion of muscle proteins into polymers had an obvious effect on protein solubility. Sarcoplasmic proteins lost appro ximately 67% of their solubility and the myofibrillar proteins lost appro ximately 86% of their solubility due to protein polymerization and pyrolysis of the muscle fibers. Ultimately, the data suggest that at any heating tem perature above 55 °C, the globin on the surface or inside the muscles is fully denatured, with starting changes observed at 35 °C .