Distribution and speciation of selenium in soybean proteins and its effect on protein structure and functionality

Although the Se concentration and recovery efficiency of soybean seeds treated with selenate were ∼ 1.8 times those of the selenite treatment, the Se was mainly in the organic form of selenomethionine (>90% of total Se) irrespective of the Se source. The Se concentrations of soybean protein isolate (SPI) and glycinin (11S) were 29.1%–38.6% higher than those of soybean protein concentrate (SPC) and β-conglycinin (7S) in Se-enriched soybeans, with selenomethionine accounting for > 80% of the Se in all proteins. The content of sulfur-containing methionine in SPI and 11S markedly decreased in Se-enriched soybeans compared with the control. No significant effect of Se was observed on protein content, subunit composition, secondary structure, micromorphology, or functionality. Foliar spray of selenate provides an economical and efficient way to produce Se-enriched soybeans without affecting protein structure and functionality, where SPI and 11S display a high ability to enrich Se (mainly selenomethionine).