Subcritical CO2-assisted autohydrolysis for the co-production of oligosaccharides and fermentable sugar from corn straw

Abstract

Subcritical CO2-assisted autohydrolysis pretreatment for oligosaccharides and fermentable sugars production from corn straw was investigated. The result showed that the prehydrolysate was rich in xylose, and among the xylose, about 90.2% existed in the form of xylo-oligosaccharides (XOS), as well as the functional XOS (DP < 5) took up about 40%. Few inhibitors were formed during the pretreatment and there was almost no effect on subsequent fermentation. Additionally, the highest glucose yield was 90.6% (32.8 g/100 g corn straw) in enzyme hydrolysate and 89.4% (21.2 g/100 g corn straw) of lignin was recovered in the enzymatic hydrolysis residue. The proposed pretreatment method was an effective way to improve corn straw enzymatic hydrolysis with little lignin degradation. Furthermore, the characterization data were also obtained through the analysis of optimally pretreated solids (pretreatment conditions: 170 °C, 5 Mpa CO2 and 40 min residence time) by using HSQC, XRD, FTIR, SEM and TG, which revealed that the XOS was mainly (1 → 4)-β-D-xylan and hemicellulose removal affected subsequent enzymatic hydrolysis dramatically. This study provided an environmentally friendly and economical approach for the co-production of oligosaccharides and fermentable sugars from corn straw that can both be further converted into biomass energy.