High-density cultivation of Lactobacillus sp. USTB-08 and production of lactic acid

Based on the successful isolation of a bacterial strain of Lactobacillus sp. USTB-08 for producing lactic acid, the optimal control conditions including carbon source, nitrogen source, mass ratio between carbon and nitrogen source, temperature and pH values were investigated for the growth of Lactobacillus sp. USTB-08 and the production of lactic acid in batch cultivation and fed-batch fermentation. Sucrose as the sole carbon source, yeast extract as the sole nitrogen source, the mass ratio of carbon to nitrogen source of 5:1, 35℃, the inoculum amount of 1.0% and initial pH 6.50 are the optimal parameters for the growth of Lactobacillus sp. USTB-08 in batch cultivation. In fed-batch cultivation by feeding a mixture of 10% sodium hydroxide and 25% sucrose to control the pH value and supply the carbon source in a 50 L automatic fermenter, the maximum biomass of Lactobacillus sp. USTB-08 (OD_680nm 13.2) and the maximum content of lactic acid (28.0g·L^-1) are obtained at pH 6.50 and pH 7.00 in a pH range from 6.00 to 7. Off, respectively. The strategy of feeding sucrose and controlling the pH value simultaneously was firstly used in the fed-batch cultivation of Lactobacillus sp., and both high cell density and high lactic acid content were obtained.