Selenium Speciation in Selenium-Enriched Plant Foods

Organic selenium in plant foods is an efficient and safe source of Se supplements that support human nutrition and health. An effective method for the speciation of five stable Se species involving compound enzymatic hydrolysis with a high Se extraction rate was demonstrated in this study, and a reversed-phase ion-pair chromatography technique combined with triple quadrupole inductively coupled plasma mass spectrometry (RPIC/ICP-MS) was established and optimized. The sample extraction method involved mixing 0.1-g aliquots of the sample with 5% (enzyme-to-sample mass ratio) alcalase, trypsin, and protease K in 15 mL of Tris–HCl buffer (pH = 8.5), followed by magnetic stirring for 4 h. In terms of the chromatography conditions, the mobile phase containing 30 mM (NH4)2HPO4, 0.5 mM TBAH, and 2.0% (v/v) MeOH (pH 6.0) was isocratically eluted at 1.0 mL min−1 at 30 °C. All five Se species (Se (IV), Se (VI), MeSeCys, SeMet, and SeCys2) were separated in 8.5 min. The limits of detection (LODs) and limits of quantification (LOQs) of the five Se species were in the ranges of 0.08–0.15 μg L−1 and 0.27–0.51 μg L−1, respectively. The recoveries of the five Se species varied between 83.0 and 106% (RSDs ≤ 6.4%). The Se extraction rates of various Se-enriched plant foods ranged from 69.7 to 97.9%. Se speciation was achieved by the developed extraction method and RPIC/ICP-MS, which also revealed the existence of various Se species in different plant foods.