Pilot Study On The Transformation Of Selenium With Yeast

Selenium is a kind of necessary trace element which is correlated to many illnesses. Currently over2/3of area in the world has no sufficient selenium in soil and in food, so many researches reported about how to supply selenium. So far, the safe and the efficient way is transforming the inorganic selenium to organic one through yeast and supplying selenium-rich yeast for replenishers. In our work, we already screened a high-efficiency yeast and for the further research, we optimized the fermentation conditions on a large scale.Starting with the yeast screened by our lab and considering its nutritional characteristics, we chose seven kinds of normal agricultural products which were wheat bran, corn bran, sugar cane molasses, potatoes, sweet potatoes, rice bran, soybean meal as the yeast fermentation materials. Taking their characteristics into account, our team optimized these seven fermentation materials to make them suitable for the yeast growth and reproduction. Soybean meal hydrolyzate is rich in nitrogen source but it lacks carbon source. Wheat bran, corn bran, potato, sweet potato and rice bran hydrolyzate can be used as complete media of yeast and while cane molasses is a good carbon source but short in nitrogen, salts and growth factors.From our data, the yeast we used had different selenium transformation activity in different media and especially in sugar cane molasses diluted liquid, it had highest biomass and selenium content. Through the single factor and orthogonal experiments, the best medium components for our yeast were10%sugar cane molasses diluted liquid,0.25%potassium dihydrogen phosphate,4.0%peptone,0.3%yeast extract and0.02%magnesium sulfate.Our team optimized the culture conditions in sugar cane molasses diluted liquid medium at the scale of shake flask,5L,50L and500L fermentation system. Finally, we had the optimum conditions of the500L pilot fermentation as follows:inoculation quantity10%, rotation speed200rpm, aeration rate600L/h, fermentation time50h, pH6, atmospheric pressure. Under these conditions, we can obtain9.291g/L of the biomass and13543.86ug/L of total selenium content from each fermentation.