Studies On Screening Of Fine Strains And Fermentation Condition For Chromium-rich Yeast

GTF (Glucose Tolerance Factor) is an active substance, which can maintain Glucose level of the body, and therapy or prevent diabetes. Chromium-rich yeast is the main source of GTF.We can find the better Chromium-rich yeast strains by using screening and mutation, then optimized it's fermentation conditions.In this way, We can obtained high-yield and high activity GTF. So we mutated and screened the Chromium-rich yeast, researched its shake flask and high cell density culture conditions, which provide academic foundation for GTF mass production.This study includes four parts. Screening Chromium-rich yeast by using chromium tolerance test, mutagenesis and screening mutants, the dynamic rule of Chromium-rich yeast fermentation and the high cell density culture rules of Chromium-rich yeast. Ten the highest chromium-resistant strains that growth well in 5.125 g/L Cr3+ YEPD flats were screened from 11 original tested strains. Finally, after duplication screening, we chose YS-3 which fermentation property was stable and have high biomass and high organic Chromium content as the original strains for mutagenesis.We confirmed the optimum N+ ion dose was 4×2.6×1013 ion/cm2 at 50 KeV after analyzing the dosage-effect curve. The mutagenesis was conducted by 50 KeV N+ ion implantation with the dose of 4×2.6×1013 ion/cm2 to YS-3,obtained a strain YSI-3.7 which Chromium content increased by 17.59 %,and Its fermentation property was stable after 5 generation transfer inoculation. We mutated YSI-3.7 use the same method, and obtained a strain YS2I-3.2 which fermentation property was stable. Its biomass is 0.84g dry cells /100mL, and Its organic Chromium content increased by 51.28%, achieved 2266.50±2.77μg/g.By studying on dynamic rule of YSI-3.7 through the single factor experiments , L9(34) orthogonal design and economic analysis, the results indicated the optimum parameter for producing GTF were: temperature 28℃, inoculation contents 10%,shaker speed 200 r/min, and time 30h. Cr3+ remarkably restrained the growth of Chromium-rich yeast. Addition Cr3+into seed culture increased organic Chromium content (GTF yield), and decreased biomass; in the beginning of fermentation addition Cr3+can obtain high organic Chromium content and high biomass; Addition 1.55 g/L Cr3+also increased organic Chromium content, and decreased biomass at fermentation 24h, but the organic Chromium content increased degree more than biomass decreased degree, so this fermentation method can be used to product GTF. Supplied culture at the time that Glucose level obviously decreased made biomass and organic Chromium content were got down.At 24h of high cell density fermentation supplied 1.55 g/L Cr3+ obtained biomass 0.96g dry cells /100mL, organic Chromium content 3118.27μg/g; supplied culture at 14h can obtain high biomass, but the organic Chromium content get down.