Breeding Of L-lactic Acid Bioproduction Strain And The Primary Research On Its Fermentation Conditions

This paper focused on the screening and identify of the L-lactic acid producing bacteria, then studying the fermentation and cultivation condition of the strain. The detailed contents were as followed:1. In this study, the strain of producing L-lactic acid was screened from a variety of soil samples and 42 acidogenic strains were isolated and preserved, through fermentation test, the L-lactic acid production of strain ES-23 was significantly higher than other strains, and was selected for further study. The physiological characterization of the strain was studied, based on the 16S rDNA sequence and the physiological and biochemical test, the strain was finally identified as Bacillus coagulans.2. It was determined that the optimum cell growth temperature of the strain was 40℃, the biomass was increased when adding 10 g/L of CaCO3 into the seed medium, and the best culture duration was 18 h. The fermentation culture and condition of the strain were investigated. It was determined that the best carbon source was corn syrup; nitrogen source was yeast extract and cotton-seed protein. Besides, the metal ions Mn2+, Fe2+ and Mg2+ can also improve the L-lactic acid production. The optimal fermentation condition was:10% of inoculating volume, 150 r/min of shaking, 45℃. Furthermore, response surface methodology were applied to optimize the fermentation culture, and it was found that L-lactic acid yield reached 96.68 g/L, when concentraton of corn steep liquor, yeast extract, cottonseed protein, CaCO3 and trace element solution were 120 g/L, 14 g/L, 14 g/L, 90 g/L and 11.25 ml/L, respectively.3. A lab-scale fermentation conditions were studied with a 7 L fermentor.Three different fermentation neutralizer was compared, it seemed that CaCO3 can not neutrailize acid imediately; Ca(OH) 2 was easy to plug the pipe because of its low solubility; when using ammonia as the neutralizer, it indicated that which can better control the pH, and L-lactic acid production was increased as compared with calcium carbonate.4. A subsection dissolved oxygen controlling strategy was proposed to enhance both biomass and L-lactic acid production. Using dissolved oxygen controlling strategy, that is, ventilation was used during the first 16 hours with the aerationspeed as 0.2 vvm, then was closed till the end, significantly, L-lactic acid production reached 109.70 g/L, which was increased by 20.06% as compared with anaerobic fermentation.