Highly efficient l-lactic acid production from xylose in cell recycle continuous fermentation using Enterococcus mundtii QU 25

Abstract

A few strains of lactic acid bacteria metabolise xylose into optically pure L-lactic acid (LA). This study achieved an effective homofermentative cell recycle continuous fermentation of xylose to L-LA with high concentration, productivity, and yield using Enterococcus mundtii QU 25. In conventional continuous fermentation, the optimal xylose concentration in the feeding solution is 50 g L⁻¹, and the optimal dilution rate is 0.15 h⁻¹. Continuous fermentation with cell recycling using a microfiltration membrane module produced an L-LA concentration of 32.3 g L⁻¹ with a yield of 0.789 g g⁻¹ and a productivity of 5.33 g L⁻¹ h⁻¹. Controlling pH and optimising the feeding medium were important for achieving a high L-LA yield with strain QU 25. Using corn steep liquor-containing medium at pH 6.2, a maximum L-LA concentration, yield and productivity were achieved at 41.0 g L⁻¹, 1.01 g g⁻¹, and 6.15 g L⁻¹ h⁻¹, respectively. This study is the first to report on continuous fermentation with cell recycling for lactic acid production from xylose.