Screening of an Alcohol Tolerant and High-yield L-lactic Acid Strain and Optimization of Culture Medium

In order to increase the yield of L-lactic acid and reduce the production cost of L-lactic acid, a strain of Lactobacillus rhamnosus AK-0779 with alcohol tolerance and high yield of L-lactic acid was screened and domesticated. Corn distiller's grains were used as the nitrogen source for the fermentation medium of strain AK-0779 instead of part of yeast powder. On the basis of single factor experiments, three factors and three levels response surface optimization experiments were carried out on the addition of glucose, yeast powder and corn distiller's grains. The results showed that the optimal fermentation medium was glucose 9.80%, corn distiller's grains 0.98%, yeast powder 1.72%, L-lactic acid yield 78.91 g/L and sugar acid conversion rate 80.52%. There was no significant difference in the yield of L-lactic acid compared with yeast powder, which was 82.36 g/L, indicating that corn distiller's grains could effectively replace part of yeast powder as the nitrogen source of fermentation medium and reduce the production cost of L-lactic acid.