Screening The High Production L-Lactic Acid Bacteria And Optimizing Fermentation Condition

In this paper, screening, induction of mutation, fermentation condition were investigated for producing L-lactic acid.The best strain Lactobacillus caseiGL-4 was screening from four strains, Lactobacillus caseiGL-1, Lactobacillus caseiGL-2, Lactobacillus caseiGL-3 and Lactobacillus caseiGL-4.This strain can be cultivated in the media whose the glucose concentration is over 160g/L,pH below 3.5,at 37C.The productivity Lactobacillus caseiGL-4 is 0.238g/L/h after 72h, higher than other strains.A few attempts were made to improve and modify lactic acid production, producing L-lactic acid. Lactobacillus caseiGL-4 -2 was obtained after implanted by Nitrogen ions with energy 20KeV and ion fluent from 10-1500 ions/cm2. The best ions value is 1000 ions/cm2 and the value of survive is 32%. The amount of lactic acid by Lactobacillus caseiGL-4 -2 increases two-fold higher than Lactobacillus caseiGL-4.Lactobacillus caseiGL-4 -2 was treated by U.V. irritation for 120s.After that, Lactobacillus caseiGL-4 -2-3 was obtained. The Lactobacillus caseiGL-4 -2 can survive about 22% after U.V. irritation for 120s.The amount of lactic acid by Lactobacillus caseiGL-4 -2-3 can be enhanced about two-fold higher than by Lactobacillus caseiGL-4 -2.Dimethyl sulphate was used to deal with Lactobacillus caseiGL-4 -2-3. The concentrations of Dimethyl sulphate are 0.2% and 0.1%.The optimum time of mutation are 30 min and 40min respectively and the survival value is 21% and 28% respectively. After that, Lactobacillus caseiGL-4-G was obtained. Twofold in the amount of lactic acid was increased.Different nitrogen sources were added to the media such as corn steep liquor, wheat bran and root of malt. When the corn was hydroiyzed, the peptidase was added .The optimum condition of fermentation was 1% wheat bran, 2%root of malt and 4% corn steep liquor, 120g/Lglucose 37癈. In the optimum condition, after 72h the total amount of lactic acid by Lactobacillus caseiGL-4-G is about five-fold higher than Lactobacillus caseiGL-4.