Antioxidant activities of Se-SPI produced from soybean as accumulation and biotransformation reactor of natural selenium

•The biotransformation process of Se from natural seleniferous soil was investigated.•Se-SPI content increased remarkably with the increase of Se content.•Se level affected amino acids composition of soybean Se-SPI.•Se played a positive role in enhancing the antioxidant activity of Se-SPI. A study to compare the uptake, translocation, and distribution of selenium (Se) in soybean planted in natural seleniferous soil in Fengcheng city of China was conducted to clarify the relationship between the Se content levels of soybean proteins and their radical scavenging activity. The data showed that the total Se content in different parts of soybean plants varied with the growth periods. The selenoprotein (Se-SPI) content increased remarkably with the increase of Se content in seleniferous soils. The Se-SPI content obtained from the region with the highest Se level was almost 18 times higher than that of the control group, while antioxidant activities were about 4-fold compared to the control, suggesting that Se played a positive role in enhancing the antioxidant activity of Se-SPI. The increase in the Se level also led to changes in amino acids composition, but with nearly no effects on the subunit composition of soybean Se-SPI.