Direct quantitative speciation of selenium in selenium-enriched yeast and yeast-based products by X-ray absorption spectroscopy confirmed by HPLC-ICP-MS

Inductively coupled plasma/MS, LC/MS, Se, Speciation, Yeast.

Selenium (Se)-enriched yeast has probably been the most widely investigated food supplement and the literature on Se speciation in the Se-enriched yeast is fairly abundant, however, the strategy for Se speciation commonly requires complicated pretreatment procedures such as digestion and stepwise extraction. The present study was carried out to apply X-ray absorption spectroscopy (XAS) for the direct speciation of Se species with minimal pretreatment steps. By comparison of the XAS spectra of Se-enriched yeast samples with that of the standard Se species, organic R-Se-R (represented by selenomethionine) was found to be the main chemical form of Se. Quantitative speciation through principal component analysis (PCA) and least-squares linear combination (LC) fitting the Se-enriched yeast samples found 83%, 85% and 81% of R-Se-R (probably selenomethionine which is known to exist in yeast) for SelenoPrecise^® yeast, SelenoPrecise^® tablets, and Xiweir^® tablets, respectively, which is in agreement with those from HPLC-ICP-MS analysis. More broadly, XAS can also be applied to other Se-enriched products with the merit of minimal pretreatment. However since XAS, specifically XANES, can only identify the chemical type rather than specific molecules, other methods like HPLC-ICP-MS are necessary to give not only the coordination environment of Se but also the identity of the Se species.