Distribution and effects of natural selenium in soybean proteins and its protective role in soybean β-conglycinin (7S globulins) under AAPH-induced oxidative stress.

The effects of selenium (Se) on the protein content, amino acid profile, secondary structure and subunit composition of soy proteins and its distribution were evaluated, as was the effect of peroxyl radicals produced by thermal decomposition of AAPH on the conformational changes of Se-enriched β-conglycinin (S-7S). The Se biofortification ability of soy was very strong, 7S had strongest ability to incorporate Se, and lower amounts of inorganic Se existed in Se-enriched beans. Se could promote protein synthesis and thus improve the protein content, increase the total amino acid content with a decrease in cysteine, combine into low-molecular-weight proteins, and influence the secondary structure of soybean proteins. Se was involved in the relevant protein changes in surface hydrophobicity, intrinsic fluorescence, infrared absorption and solubility and played an antioxidant role as an effectual "protector" to reduce the influence of peroxyl radical oxidation on S-7S, thereby maintaining the structural rearrangement between aggregation and protein unfolding.