Combined acetic acid and enzymatic hydrolysis for xylooligosaccharides and monosaccharides production from poplar

Efficient production of xylooligosaccharides (XOS) from lignocellulosic biomass without preliminary xylan isolation is challenging. Previously, organic acid has been used to produce XOS from lignocelluloses without xylan isolation. However, the knowledge about XOS production from the residual xylan in acid-hydrolyzed lignocelluloses is still unclear. In this study, acetic acid (AC) hydrolysis of poplar was used to produce XOS, then AC-hydrolyzed poplar was delignified by hydrogen peroxide-acetic acid (HPAC) solution. The AC-HPACpretreated poplar was sequentially hydrolyzed by xylanase and cellulase to produce XOS and monosaccharides. The results showed that the XOS yield of poplar after AC hydrolysis was 31.6% (based on the xylan in raw poplar). A high lignin removal (94.8%) of AC-hydrolyzed poplar was obtained by HPAC pretreatment. The highest XOS yield based on residual xylan in AC-HPAC-pretreated poplar by xylanase was 17.5%, and finally a total XOS yield of 36.5% based on xylan in raw poplar was achieved. The highest glucose yield was 88.0% with 20 FPU/g dry mass cellulase and 1.0 mg/mL Tween 80. Finally, 65.1 g of XOS was obtained from 1,000 g of poplar through this combined process including AC and xylanase hydrolysis, increased by 2.2 times compared with that from xylanase hydrolysis without AC hydrolysis. This work greatly improves the XOS production from poplar and provides a novel strategy to efficiently transform poplar carbohydrates into XOS and monosaccharides.