Co-production of oligosaccharides and fermentable sugar from wheat straw by hydrothermal pretreatment combined with alkaline ethanol extraction

- Hydrothermal combined with alkaline ethanol extraction was used to treat wheat straw.
- The products and their distribution in the hydrolysate were determined.
- A maximum xylo-oligosaccharides yield of 61.69 g/kg wheat straw was achieved.
- The digestibility of the residue was 3.5 times higher than that of the raw material.

Co-production of high value-added oligosaccharides and fermentable sugar from wheat straw is very attractive. In this study, hydrothermal pretreatment combined with alkaline ethanol extraction was developed to pretreat wheat straw for the production of both oligosaccharides and fermentable sugar. The major products in the hydrolysate and the enzymatic digestibility of the remaining residue were evaluated. Results showed that xylo-oligosaccharides (XOS) and gluco-oligosaccharides (GluOS) were the major products in the hydrolysate, and a maximum XOS yield of 61.69 g/kg wheat straw was achieved as the wheat straw was hydrothermally pretreated at 180 °C for 0.5 h. The HSQC results revealed that the degraded product in the hydrolysate was mainly (1 →  4)-β-d-xylan attached with α-d-arabinose, 4-O-methyl-d-glucuronic acids, and/or acetyl group. Additionally, the enzymatic hydrolysis rate of the cellulose-rich fractions obtained from the combined treatment process was enhanced 1.5 and 3.5 times, respectively, than that of the hydrothermally pretreated and raw wheat straw.