Abstract:Lactobacillus panis has been identified as the major lactic acid-producing bacterium in the fermentation of Maotai-flavor liquor. However, the effects of different environmental conditions on lactic acid metabolism and expression level of key genes in the lactic acid pathways of L. panis have not been studied. In this work, different environmental factors relevant to fermentation processes were selected, such as temperature, lactic acid, ethanol, and glucose concentrations. Results showed that under different environmental conditions, the growth and lactic acid yield of L. panis were significantly regulated. Lactic acid and ethanol were identified to be the key factors of lactic acid biosynthesis by L. panis. The maximum amount (12.3 g/L) of lactic acid was achieved when 10 g/L lactic acid was added to the growth medium. In contrast, the addition of 40 g/L ethanol reduced lactic acid production to 7.2 g/L, which was the lowest level among the different environmental conditions. Quantitative real-time PCR analysis of key genes involved in lactic acid metabolism with lactic acid supplementation showed that lactic acid addition significantly facilitated up-regulation of key gene for lactic acid synthesis, including ldhL and ldhD encoding L-lactic acid dehydrogenase and D-lactic acid dehydrogenase, respectively. However, their expression levels were down-regulated if ethanol added, implying a decreased metabolic flux through the lactic acid synthetic pathway. The analysis of key environmental factors determining lactic acid production of L. panis is of great significance for modulation of lactic acid synthesis during fermentation, and would also be useful for controlling the brewing microbial community and quality of the liquor.
