Production of selenium-enriched yeast using a Plackett-Burman design

Today dietary deficiency of selenium (Se), an important mineral in human nutrition, is common in many regions and communities. Se-enriched yeast, obtainable by growing Saccharomyces cerevisiae in Se-rich media, is considered as a source of organic Se suitable for alleviating its deficiency due to its high bioavailability, stability, digestability, and absorbability. Using a Plackett-Burman design, the effects of various culture medium conditions, including temperature (28 and 30 °C), initial pH (4.5 and 5.8), shaking speed (130 and 160 rpm), fermentation duration (24 and 48 h), size of inoculum (30 and 60 g/l), Se concentration (15 and 25 µg/ml) and time of Se addition (0 and 9 h), on the bioaccumulation of Se in the yeast were investigated.. The Se content in the yeast was determined by graphite-furnace atomic-absorption spectroscopy. The results showed that Se concentration, size of inoculums, temperature, time of Se addition and fermentation duration were, in ascending order, the most significant factors on the yield of total Se accumulation and organic Se formation in the yeast. Manipulating these conditions/variables could markedly affect the magnitudes of incorporation of Se and formation of organic Se in the yeast, the ranges being 107.9 to 287.6 mg/kg and 93.27 to 269.05 mg/kg, respectively. The most suitable culture medium conditions to attain the highest level of total and organic selenium Se biotransformation in yeast are a concentration of 25 µg/ml sodium selenite, an inoculum size of 30 g/l, a temperature of 28 °C, an initial pH of 5.8, a shaking speed of 130 rpm, an incubation time of 48 h, and adding the selenium source to the culture medium 9 hours after the start of fermentation.