Effects of different dry heating temperatures on the spatial structure and amino acid residue side-chain oxidative modification of soybean isolated proteins.

• A temperature-based relationship between protein oxidation and structure is modeled. • The first study of oxidative modifications of SPI heated by proteomics method. • The modifications of amino acids with varied properties are described for the first time. • Possible conversion of cysteine to methionine with SPI heating was found. • The structural state of SPI under electron microscopy after dry heat was studied. Spatial structure and amino acid residue side-chain oxidative modification of soybean isolated protein (SPI) at different dry heating temperatures (70, 100, 130, 160 and 190 °C) were investigated, respectively in this study. The results showed that the dry heating promoted the formation of disulfide bonds and oxidative modification of SPI, such as carboxylation and hydroxylation under the below 160 °C. With increasing temperature, β-sheet and α-helix shifted to random coil and β-turn. The conformation of SPI changed, the solubility decreased and the particle size became smaller resulting from the combination of protein oxidation and chemical bond redistribution, but the structural integrity of SPI was better ensured below 130 °C. SPI was severely hydrolyzed at 190 °C. These results provide a theoretical basis for the study of protein modification by dry heating, which is a guideline for controlling the degree of protein denaturation in the food industry. [ABSTRACT FROM AUTHOR]