Role of pH-regulation in lactic acid fermentation: Second steps in a process improvement

Lactic acid has versatile application in chemical industries and it can be economically produced from biomass resources, for example from sweet sorghum juice, containing easily fermentable sugars in high concentration (150–180 gL−1). To neutralize the produced lactic acid, alkali addition (i.e., titration) or pH buffering was applied to avoid the inhibitory effect of the undissociated lactic acid. However, such a high concentration of ionized lactate also inhibits the growth and further production. Our task was to find an appropriate pH regulation method and to describe pH dependency of the used strain. Five pH regulation agents were tested and among them trimethylamine gave the best productivity result (3.13 gL−1 h−1), but considering technological aspects (such as dilution) ammonium hydroxide is also recommended. Titration by NH4OH and buffering by CaCO3 were compared, and then combined, resulted in very good productivity (3.55 gL−1 h−1). pH dependence of the used strain was also examined and the optimal pH value was between 6.8 and 7.0.