There has been tremendous growth in the production of optically pure L-lactic acid from lignocellulose-derived
sugars. In this study, Enterococcus mundtii QU 25 was used to ferment a glucose/xylose mixture to L-lactic acid. Maintenance
of the xylose concentration at greater than 10 g/L achieved homo-lactic acid fermentation and reduced the
formation of byproducts. Furthermore, carbon catabolite repression (CCR) was avoided by maintaining the glucose
concentration below 25 g/L; therefore, initial concentrations of 25 g/L glucose and 50 g/L xylose were selected. Supplementation
with 5 g/L yeast extract enhanced the maximum xylose consumption rate and consequently increased
lactic acid production and productivity. Finally, a 129 g/L lactic acid without byproducts was obtained with a maximum
lactic acid productivity of 5.60 g/(L$h) in fed-batch fermentation with feeding a glucose/xylose mixture using ammonium
hydroxide as the neutralizing agent. These results indicate a potential for lactic acid production from glucose and
xylose as the main components of lignocellulosic biomasses.