Microbial production of stereospecific lactic acid from sugarcane trash hydrolysate with no pre-detoxification step

Abstract

Sugarcane trash (SCT) is a promising underused lignocellulosic material for the production of chemicals in biorefineries. In this work, we studied the use of SCT to produce lactic acid (LA), an important commodity chemical used in food and bioplastic industries. SCT was pretreated with a hydrothermal liquid hot water step followed by saccharification with Cellic® CTec2, which resulted in the SCT hydrolysate containing 30.42±0.08 g/L total sugar, equivalent to 88.10% and 42.92% glucose and xylose recoveries, respectively. Screening of stereospecific LA production exhibited Lactococcus lactis BCC 68868 and Leuconostoc lactis BCC 62792 efficiently utilized SCT hydrolysate converted to entirely L-LA and D-LA, respectively. A detoxification step was unnecessary for hydrolysate fermentation to LA, and the addition of CaCO3 for pH control enabled complete hydrolysate utilization. La. lactis BCC 68868 converted SCT hydrolysate into optically pure L-LA at 19.34 g/L, equivalent to a conversion yield of 0.95 g LA/g sugar. While Le. lactis BCC 62792 produced D-LA at 10.39 g/L, equivalent to a conversion yield of 0.45 g LA/g sugar with ethanol and acetic acid as the by-products, suggesting their homofermentative and heterofermentative characteristic, respectively. This work demonstrates a promising strategy to produce enantiomerically defined LA from this underutilized agricultural waste.