Meta-fermentation system with a mixed culture for the production of optically pure l-lactic acid can be reconstructed using the minimum isolates with a simplified pH control strategy

Meta-l-lactic acid fermentation from non-treated kitchen refuse was reconstructed using a combination of isolated bacterial strains under several pH control strategies. The meta-fermentation system was successfully reconstructed using a combination of Weizmannia coagulans MN-07, Caldibacillus thermoamylovorans OM55-6, and Caldibacillus hisashii N-11 strains. Additionally, a simplified constant pH control strategy was employed, which decreased fermentation time and increased production. The optimum pH (6.5) for the reconstructed meta-fermentation was favorable for the respective pure cultures of the three selected strains. The l-lactic acid production performance of the reconstructed meta-fermentation system was as follows: concentration, 24.5 g L⁻¹; optical purity, 100%; productivity, 0.341 g L⁻¹ h⁻¹; yield, 1.06 g g⁻¹. These results indicated that constant pH control was effective in the reconstructed meta-fermentation with the best performance of l-lactic acid production at pH optimal for the selected bacterial growth, while the switching from swing pH control would suppress the activities of unfavorable bacterial species in un-isolated meta-fermentation.