Research Of Strain Screening Of Organic Selenium And Fermentation Conditions

Selenium, a necessary micro-nutrient for an organism with many biological effects, is an indispensable active component of Glutathione peroxidase. Selenium can protect the permeability of cell membrane, thus it can reduce the occurrence of some human common diseases. However, the selenium in the human body is in a state of lack. In most cases, Selenium content in the natural food is generally very low, If you rely solely on natural foods to supplement selenium, this approach is far form being able to meet the body’s normal requirements.Yeast, because of its growth speed is quick, easy to cultivate, high in protein, rich in B vitamins and other minerals beneficial to human body, has become the most widely and safe nutrition microorganisms. Thus gradually entered the people’s attention.For some micronutrients, yeast also has the very strong enrichment, can will more toxic inorganic selenium into organic selenium absorbed by the body, compared with other inorganic selenium, selenium rich yeast exist the following advantages:1. The high efficiency;2. Low toxicity;3. High nutritional value;4. High selenium content;5. High physiological activity. Using yeast to enriched selenium, therefore, is a safe and efficient way, so se-enriched yeast gradually became one of the hotspot of scientific research at present.In this study, we made the Saccharomyces cerevisiae named Y1as the initial strain in this laboratory. After combined mutagenesis, breeding a strain which has a high bacterial biomass and selenium content.1. The suspension of yeast cells were treated by a mixture solution of the1mL0.1mol/L NaNO2and7mL pH4.4HAc-NaAc. After a certain time by UV irradiation, we get a mutant named Y12with higher selenium content and biomass, bacterial biomass from the8.83g/L up to12.10g/L, and selenium content from611μg/g up to832μg/g.2. We screened five times yielding mutant strain Y12subculture, no back mutations, it certify that the composite mutagenesis strains genetically stable.3. Screening the best medium from several different types of media, at the same time, to determine the types of carbon, nitrogen sources and inorganic salts in the medium composition. Ultimately determine the best medium composition is that malt extract1%, sucrose2%, peptone1%, urea1%, KH2PO40.05%, MgSO40.1%. Under this condition, we obtained bacterial biomass17.65g/L, and selenium content up to931μg/g.4. Through single factor, we finally obtained the optimal combination with higher biomass and selenium content as follows:selenium added20ug/mL, incubation time40h, Fermentation temperature28℃, the inoculum size12%, liquid volume60mL/250mL.5. We selected the mutant strains had significant effect on the biomass and selenium content of selenium content, inoculation quantity and liquid quantity carried out three factors and three levels of orthogonal test, and further the optimal fermentation conditions were determined, the biomass is:18.95g/L, under the condition of selenium content is:993ug/g.