Study On Selenium-enriched Fermentation Of Candida Utilis

The article was designed to explore the production of selenium-enriched yeast byCandida utilis. At the very beginning, we used the test yeast strains supplied by the lab toscreen, and got the selenium-resistant and selenium-enriched strains, which as theoriginal strain, we carried shake flasks and fermentator experiments, whereas discussedthe properties of the selenium-rich strain and its fermentation optimization.1. Screen of selenium-enriched yeastPlate method was employed to do the test yeast strain selenium-resistantexperiments. Inoculated yeasts on the plate with selenium concentrations 30,40,50,60,70,80,90,100μg/mL respectively, observed their morphologies, at the end onlyCandida utilis Y-5,Y-6 could survived in the medium with selenium concentrationsabove 90μg/mL, it was implied that these two strains had strong selenium-resistantability; Inoculated the test yeast strains in shake flasks with different seleniumconcentrations to select selenium-enriched ability strain, and the selenium concentrationswas 0,5,10,15,20,25μg/mL respectively, the result was that Y-5 strain was thebest one with high biomass, selenium productivity, total selenium content. We chose thisstrain as our start strain for research.2. Shake flask selenium-enriched fermentation of Candida utilis Y-5.Selenium-enriched medium and fermentation conditions were optimized. Accordingto mono-factor test, optimal fermentation condition was made. Medium ingredient: wort,10~0Brix, urea 1 g/L, selenium 15μg/mL, original pH 5.5. fermentation condition:Inoculum 5%, T 28℃, volume 50 mL/250 mL, fermentation time 48h. Under thoseconditions got selenium-enriched yeast with biomass 5.12 g/L, selenium content2268.34μg/g, total selenium content 11613.90μg/L. Based on the mono-factor test,range-test was implemented, the result was that selenium was the major factor whichaffected the yeast selenium-enriched index (biomass, selenium content, total seleniumcontent). on one hand, high selenium concentration inhibited yeast growth and its abilityto enrich selenium, on the other hand, lower selenium content reduce yeast seleniumaccumulation effectiveness. 15μg/mL selenium concentration was the proper one in ourexperiments. 3. Selenium-enriched fermentation test in fermentatorWe mastered the selenium- enriched property of this Candida utilis Y-5 strain byshake flask experiments and got high selenium yeast under those conditions(2000μg/gabove). In order to discuss the probability in industrial scale, 7 L fermentator experimentswere carded out based on the former ones. By our fermentation process researches, theselenium-rich fermentation got the shake flask level result.Shake flask and fermentator experiments shown that Candida utilis Y-5 strain hasstrong selenium accumulation ability, and industrial potentials.