Synergistic effects of hydrothermal and deep eutectic solvent pretreatment on co-production of xylo-oligosaccharides and enzymatic hydrolysis of poplar

Full utilization of lignocellulose is critical for its biorefinery development. In this study, a sustainable biorefinery process based upon poplar sawdust was established using sequential hydrothermal and deep eutectic solvent treatment (HP-DES). Results showed that single hydrothermal pretreatment (HP) could produce 53.2% xylo-oligosaccharides (XOS) (based on raw xylan), while the enzymatic digestibility was low. Conversely, single DES treatment achieved effective enzymatic digestibility but low XOS yields. As compared to HP, both DES treatment and HP-DES showed high selectivity for lignin removal and high glucose yield. Surprisingly, most of HP-DES residues had obviously lower enzymatic digestibilities than those of single DES residues. This was mainly explained by the differences of the surface lignin contents between DES and HP-DES residues. Moreover, nearly complete enzymatic hydrolysis of HP-DES residues was achieved with the addition of bovine serum albumin. This work demonstrated this HP-DES yielded XOS, fermentable sugar, and pure lignin with high processibility.