Selenium speciation and bioaccessibility in Se-fertilised crops of dietary importance in Malawi

The purpose of this research was to explore the speciation and bioaccessibility of native soil-derived selenium (Se) versus Se applied via fertiliser in the edible portions of maize, groundnut and cowpea grown in Malawi. Fertiliser-derived Se, applied as isotopically labelled selenate, contributed 88-97% of the total Se in the edible portions. Both soil and fertiliser-derived Se were transformed into similar species, with more than 90% of the extracted Se in an organic form. The main form of fertiliser-derived Se in grain was selenomethionine with an abundance of 92.0 +/- 7.6% in maize, 63.7 +/- 6.2% in cowpea and 85.2 +/- 1.9% in groundnut. In addition, cowpea contained 32.7 +/- 6.2% of Se-methyl-selenocysteine. The mean bioaccessibility of fertiliser-derived Se was 73.9 +/- 8.5% with no statistically-significant difference across all crops despite some variation in speciation. Understanding the contribution of fertiliser-derived Se to the formation of organic forms of Se in crops is crucial, given that organic Se species are more bioaccessible than inorganic forms.

Automated summary

The study revealed that fertiliser-derived selenium accounted for the majority of selenium in the edible portions of crops, and both fertiliser-derived selenium and soil-derived selenium were transformed into similar organic species, with selenomethionine being the main form of fertiliser-derived selenium. Despite variations in selenium species among different crops, the bioaccessibility of fertiliser-derived selenium showed almost no difference.