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

•Vitamin C can promote cellular growth and l-lactic acid accumulation.•Vitamin C enhanced cellular antioxidant capacity and key enzyme activities involving in glycolytic pathway.•L-lactic acid titer of 118.8 g/L with the overall productivity of 3.71 g/L/h was achieved using sweet sorghum juice coupled with soybean hydrolysate as feedstocks.