Acid adaptation of Lactobacillus helveticus during continuous cultures to improve undissociated lactic acid production

This study aims at improving the undissociated lactic acid production by Lactobacillus helveticus using a whey-based fermentation. It first describes the effect of pH on the ability of this bacterium to produce lactic acid, by considering final lactic acid concentration, production rate, volumetric productivity and sugar consumption. As a low performance was achieved at pH 4.3, an adaptive evolution of Lb. helveticus LH-B01 to acidic conditions was performed during continuous cultures of sweet hydrolysed whey. Two mutants have been isolated, which exhibited different characteristics. The mutant Lb. helveticus LH-B01-B4 displayed the higher maximal total lactic acid concentration (37.9 g/L), sugar consumption (82%) and volumetric productivity (0.39 g/L/h), when compared to the parental strain and the mutant Lb. helveticus LH-B01-A4. This performance was explained by the higher critical undissociated lactic acid concentration (10.1 g/L) of Lb. helveticus LH-B01-B4, compared with those of the parental strain (8.7 g/L) and the mutant Lb. helveticus LH-B01-A4 (7.5 g/L). From these results, the mutant strain Lb. helveticus LH-B01-B4 was the most promising option to produce undissociated lactic acid during low pH fermentation, thus making it suitable for industrial use as a descaling agent and biocide in detergents.