Background: There has been an increasing demand for optically pure D-lactic and Llactic acid for the production of stereocomplex-type polylactic acid. The D-lactic acid production from lignocellulosic biomass is important owing to its great abundance in nature. Corn steep liquor (CSL) is a cheap nitrogen source used for industrial fermentation, though it contains a significant amount of L-lactic acid, which decreases the optical purity of D-lactic acid produced. Method and results:To remove L-lactic acid derived from the CSL-based medium, Llactate oxidase (LoxL) from Enterococcus sp. NBRC 3427 was expressed in an engineered Lactiplantibacillus plantarum (formally called Lactobacillus plantarum) strain KOLP7, which exclusively produces D-lactic acid from both hexose and pentose sugars.When the resulting strain was applied for D-lactic acid fermentation from the mixed sugars consisting of the major constituent sugars of lignocellulose (35 g L -1 glucose, 10 g L -1 xylose, and 5 g L -1 arabinose) using the medium containing 10 g L -1 CSL, it completely removed L-lactic acid derived from CSL (0.52 g L -1 ) and produced 41.7 g L -1 of Dlactic acid. The L-lactic acid concentration was below the detection limit, and improvement in the optical purity of D-lactic acid was observed (from 98.2% to > 99.99%) by the overexpression of LoxL. Conclusion and implications:The LoxL-mediated consumption of L-lactic acid would enable the production of optically pure D-lactic acid in any medium contaminated by L-lactic acid.