Upgrading steam pretreatment by converting water-soluble carbohydrates into lactic acid prior to pretreatment

Abstract

Steam pretreatment is an effective approach to open up the intact lignocellulosic matrix for biofuels and animal feed production. However, crop residues especially corn stover contain certain amounts of water-soluble carbohydrates (WSC), which are easily degraded into toxic 5-hydroxymethylfurfural (HMF) at high temperature and bring negative effects on subsequent utilization of lignocellulose biomass. Few studies have focused on the WSC loss and proposed a corresponding solution to utilize them in steam pretreatment. This study introduced a solid-state fermentation prior to steam pretreatment of corn stover to convert WSC into lactic acid, which could catalyze the hydrolysis of hemicellulose and acetyl groups in pretreatment. Compared to the regular steam pretreatment at the same severity (180 °C for 5 min), the conversion yields of xylan and arabinan in the steam pretreatment were both increased from 9.6% and 37.2% to 28.8% and 69.6%, respectively. Cellulose conversion also increased from 48.1% to 50.7% in the subsequent enzymatic hydrolysis. On the other hand, the generation of the toxic HMF reduced by 42.1% due to the pre-conversion of WSC into the relatively thermal stable lactic acid. This study provided an effective approach to process corn stover with higher hydrolysis yield and lower inhibitor generation.