A Co-Fermentation Strategy from Corncob Hydrolysate to Enhance Simultaneous Co-Production of Lactic Acid and Ethanol

Efficient co-utilization of mixed sugars from lignocellulosic hydrolysates is often hindered by carbon catabolite repression and pretreatment-derived inhibitors. In this study, a co-fermentation strategy using Saccharomyces cerevisiae (S. cerevisiae) and Enterococcus mundtii (E. mundtii) was developed to simultaneously produce ethanol and lactic acid from non-detoxified corncob hydrolysate. Co-fermentation performed at 39 °C significantly improved substrate utilization compared with monoculture systems, achieving pentose and total sugar utilization percentages of 67.1% and 83.7%, respectively. S. cerevisiae preferentially consumed glucose and effectively detoxified furfural and 5-hydroxymethylfurfural (5-HMF), thereby alleviating inhibitory stress and carbon catabolite repression on E. mundtii. By optimizing the inoculation sequence, a 3 h delayed inoculation of E. mundtii significantly enhanced pentose utilization from 68.6% to 80.2% and increased total sugar utilization to 90.4%. This synergistic co-fermentation strategy provides an effective approach for improving mixed-sugar utilization and multi-product bioconversion efficiency in lignocellulosic biorefineries.