Preparation of selenium yeasts I. Preparation of selenium-enriched Saccharomyces cerevisiae

Selenium (Se) is an essential micronutrient for human and animal organisms. Organic selenium complexes and selenium-containing amino acids are conside red the most bioavailable. Under appropriate conditions yeasts are capable of accumulating large amoun ts of trace elements, such as selenium, and incorporating them into organic compounds. It has been found that introduction of water-soluble selenium s alt as a component of the culture medium for yeasts produced by conventiona l batch processing results in a substantial amount of selenium being absorb ed by the yeast. Using a culture medium supplemented with 30 mu g/mL sodium-selenite added d uring the exponential growth phase results in selenium-accumulation in the range of 1200-1400 mu g/g dried baker's yeast (Saccharomyces cerevisiae) me asured by ICP-AES method. In our previous studies it was shown that higher amounts of sodium-selenite in the culture medium have a strong inhibitory e ffect on the growth of this yeast. As a consequence of Variations in cultiv ation conditions we obtained selenium yeast with different inorganic seleni um content. The most important parameters influencing incorporated forms of selenium are pH Value and dissolved oxygen level in the culture medium, an d depending on these the selenium consumption rate of the yeast. A 0.40-0.5 0 mg/g h-1 specific selenium consumption rate was found to be appropriate t o obtain selenium-enriched bakers' yeast of a high quality. Under suitable conditions the undesirable inorganic selenium content of the yeast could be suppressed to as low as 5-6% at the expense, however, of approximately a 2 0% decrease in the final biomass.