Study On Screening & Fermentation Of L-lactic Acid Bacteria On The Basis Of Distillate Of VHG Ethanol Fermentation From Corn

As energy resources crisis increasingly speeding up in recent days and fuel resources fading away, the raw oil price has exceeded 75 US$ per barrel in April, 2006. Fuel alcohol, which has been thinking as a clean energy to replace the fossil fuel, becomes a hotspot to researchers all over the world. To the fuel alcohol production, how to reduce the cost of ethanol fermentation is one of the most important problems to be solved. The thesis, based on this point, was to research very high gravity (VHG) ethanol fermentation and L-lactic acid fermentation, not only to solve the pollutions of distillate of VHG ethanol fermentation, but also to reduce the cost of VHG ethanol fermentation and L-lactic acid fermentation, laying a foundation for amplified production.Through methods of microorganism separations, an L-lactic acid bacteria was screened from varies samples, and through optical purity analysis, the content of L-lactic acid in lactic acid production was 94.8%. With its fermentation of carbon and nitrogen sources, and through phenotype, physiological and biochemistry characteristics and 16S rDNA sequence blast, the bacterium was identified to be Enterococcus hawaiiensis, named as Enterococcus hawaiiensis WXS temporarily. no report has been seen to use it for L-lactic acid fermentation in published literatures.After repeated treatments to E. hawaiiensis WXS with NTG, one bacterium, E. hawaiiensis WXS58, was got for its high production of L-lactic acid. The E. hawaiiensis WXS58's performance in fermentation was checked in medium with glucose as carbon sources, and its optimal fermentation temperature was 34°C, optimal seed age was from 14 to 18 h, the inoculation amount was 3%, and the primary medium pH was 6.0, in the initial stages of fermentation, proper oxygen can promote L-lactic acid production. With the optimization of the fermentation medium, the optimal medium was determined through orthogonal experiment: peptone 1%, yeast extract 1%, Na2HPO4 0.15%, MgSO4 0.02%. After 48 hours cultures in this medium, L-lactic acid production reached to be 56 g/L.Domestication of E. hawaiiensis WXS58 in distillate of VHG ethanol fermentation was carried out, the results showed very good bacteria growth. After research of the VHG ethanol fermentation and L-lactic acid fermentation, the balance point was checked to be good for both fermentation: the ethanol fermentation was ended between 36 and 40 hours, in which the ethanol concentration was around 12%, after solid parts was centrifuged from broth, the total sugars supernatant containing was between 70 and 80 g/L, which was used for L-lactic acid fermentation.