A systematic approach to selenium speciation in selenized yeast

Abstract

A systematic approach to the characterization of selenized yeast supplements in terms of the speciation of selenium was developed. The optimized fractionation procedures included the sequential leaching of water soluble, cell-wall bound, and membrane-protein selenium followed by a further fractionation of each extract by high-resolution size-exclusion chromatography. The stability of fractions collected as chromatographic peaks was investigated in the presence of a proteolytic enzyme (pronase XIV) and trypsin in order to discriminate between selenium-containing peptides and other selenocompounds. Reversed-phase HPLC of tryptic digests of size-exclusion chromatographic fractions allowed the identification of selenopeptides by MALDI and electrospray MS. The complexity of the speciation of the water-soluble selenium in yeast was confirmed. Surprisingly, selenomethionine in the water insoluble fraction was found to be bound physically to cell wall constituents rather than being incorporated chemically into the protein structure, in contrast to former studies.

Effects of Inclusion of Selenium-Enriched Yeast in the Diet of Laying Hens on Performance, Eggshell Quality, and Selenium Tissue Deposition

“…Selenium yeast from Saccharomyces cerevisiae may assimilate up to 3000 µg of Se/g (Schrauzer, 2003) where the major product is Se-Met. This is incorporated into yeast proteins or is physically associated with cell-wall constituents (Polatajko et al, 2004) with the result that there is more Se deposition than inorganic form into body tissues and eggs (Utterback et al, 2005;Juniper et al, 2011). The differences in tissue deposition among Se dietary sources are relative to the absorbtion mechanisms.…”

Volatile organoselenium monitoring in production and gastric digestion processes of selenized yeast by solid‐phase microextraction‐multicapillary gas chromatography coupled microwave‐induced plasma atomic emission spectrometry

“…A more systematic approach to the characterization of selenized yeast supplements involves a more sophisticated fractionation procedure, including the sequential leaching of water soluble, cell-wall bound, and membrane-protein selenium followed by a further fractionation of each extract by high-resolution SEC. 25 The basic problem in these studies is the unavailability of sufficient appropriate standards. Apart from ongoing species identification, current investigations focus on stability and reactivity 26 of the already known species, which account for ∼65% of the total selenium 27 found in this kind of matrix.…”

Biochemical Comparison of Commercial Selenium Yeast Preparations

“…Typically, the residual sodium selenite used during production is removed by washing the yeast cream prior to drying [32]. It has been proposed that some SeMet in yeast may not be incorporated chemically into Se-containing proteins but physically associated with cell wall constituents [3,23]. As commercial Se yeast preparations consist of dried and inactivated fragments of S. cerevisiae, it is reasonable to assume that some leaching may occur post-production and prior to drying [12].…”

“…In actuality, selenium bioavailability depends on the digestion of Se-containing yeast, the absorption of Se from the intestinal tract and finally the transport and biotransformation of Se into biologically active forms [11]. Therefore, estimation of adequate levels of Se in the diet requires information not only of the total amount of Se but also of the bio-accessible species in the sample [6,23,24]. Seenriched yeast has been extensively studied and fractionated [12,25] with SeMet reported as the major selenoamino acid in water-soluble yeast extracts, replacing Met by simple competition.…”