Assignment of low-molecular-weight selenometabolites in the root section of white cabbage

Quantitative and qualitative selenium speciation analyses of the root of white cabbage reveal the presence of elemental Se, selenate, selenomethionine and deaminated derivatives of selenohomolanthionine. White cabbage (Brassica oleracea convar. capitata var. alba) is one of the most consumed vegetable brassicas of the Brassica oleracea species whose production is compatible with the recent strip-till and no-till type farming policies. White cabbage has been in the focus of selenium research for decades as a possible source of food-derived selenium supplementation; however, the root section of the plant has hardly been targeted, being a by-product that is left in or plowed into the soil to serve as an organic fertilizer. The root of selenium-enriched white cabbage, planted on three different soil types (sand, silty sand, and silt), was analyzed for selenium speciation with the complementary use of liquid chromatography inductively coupled plasma mass spectrometry (LC-ICP-MS) and electrospray ionization high-resolution mass spectrometry (LC-ESI-HR-MS) methods after orthogonal (anion/cation exchange) chromatographic purification. Elemental selenium (Se⁰) was the major selenospecies in all cases, accounting for 28-43% of total selenium content. Water and proteolytic extractions could recover a median of 28% of total selenium through the quantification of selenate and selenomethionine, leaving a series of selenocompounds unassigned. Among these latter species, accounting for up to an additional 6% of total selenium, eight low-molecular-weight selenocompounds were detected; five out of the eight compounds could be tentatively identified as deaminated derivatives of selenohomolanthionine.