Production of xylo-oligosaccharides from wheat straw using microwave assisted deep eutectic solvent pretreatment

This study aimed to investigate the effect of microwave assisted deep eutectic solvent (MW-DES) pretreatment on the solubilization of xylan and release of xylo-oligosaccharides (XOS) from wheat straw. The samples were treated with choline chloride: formic acid at different microwave powers (209-594 W) and pretreatment times (10-120 s). The corresponding microwave energy applied to the samples was calculated in the range of 466-1965 J/g. The xylan yield in the solid fraction decreased almost linearly with an increase in microwave energy. The xylose monomer and oligosaccharide yields in the liquid fraction first increased with the microwave energy applied and then declined. The highest xylose monomer and total xylo-oligosaccharide yield (observed at 209 W, 80 s (1309 J/s)) were 20 % and 32 % (13.6 and 72.7 g/kg wheat straw), respectively. HPAEC-PAD analysis revealed that XOS with a degree of polymerization (DP) below 6 comprised 43 % of the total XOS at this condition. Increase in solvent amount (from 1:10 to 1:15 g:mL) improved the xylo-oligosaccharide yields only by 14 %. Approximately 68 % reduction in furfural yield was achieved with 5 % water addition in deep eutectic solvent.