The supplement of vitamin C facilitates l-lactic acid biosynthesis in Lactobacillus thermophilus A69 from sweet sorghum juice coupled with soybean hydrolysate as feedstocks

Abstract

Regulating oxidative damage is an effective way to enhance cell growth and metabolite accumulation in microbial strains. However, this strategy on lactic acid production has not been systematically reported yet. In present study, the effect of antioxidant vitamin C on cell growth and l-lactic acid production was investigated in Lactobacillus thermophilus A69, and an addition of 75 mM vitamin C resulted in significant improvement in cell growth and l-lactic acid accumulation. The total antioxidant capacity (T-AOC) and key enzyme activities involving in glycolytic pathway (such as hexokinase, phosphofructokinase, pyruvate kinase, and lactate dehydrogenase) were also significantly enhanced by vitamin C addition. Finally, with the addition of optimal concentrations of vitamin C into sweet sorghum juice coupled with cheaper soybean hydrolysate as feedstocks, a final l-lactic acid titer of 118.8 g/L with the productivity of 3.71 g/L/h was achieved by A69 strain. This study provided an efficient and economical approach for enhancement of l-lactic acid fermentation efficiency using sweet sorghum juice as a feedstock.