Integrated alkaline deep eutectic solvent pretreatment and high-solids enzymatic hydrolysis for high-titer sugars...

Ramie straw, though chemically suitable for biorefining, remains a highly underutilized resource. This study developed a choline chloride-based deep eutectic solvent (DES) for ramie straw pretreatment, with conditions optimized via response surface methodology (RSM), coupled with high-solid enzymatic hydrolysis for high-titer sugar production. Results showed that pretreatment with [choline chloride][ethanolamine] (1:6 mol ratio) elevated the glucose yield for 3.8-fold compared to the raw material. Under optimal conditions (105 °C, 4.5 h, 5 % w/v solid loading), 64.3 % hemicellulose and 67.1 % lignin were removed, generating a porous residue with exposed fibers to facilitate enzymatic saccharification, thereby achieving a glucose yield and glucose recovery rate of 91.5 ± 0.67 % and 84.4 ± 0.22 %. After three DES reuse cycles, the enzymatic hydrolysis efficiency of pretreated residue remained above 80 %, with cellulase loading reduced using a sophorolipid-assisted enzyme consortium. Fed-batch enzymatic hydrolysis (initial solids: 8 % w/v; supplemented with 7 %, 6 %, 5 %, and 4 % w/v at 6, 12, 18, and 24 h) alleviated mass transfer limitations, yielding glucose and xylose yields of 72.1 ± 0.51 % and 79.1 ± 0.73 %, representing 26.0 % and 30.3 % enhancements over batch mode, respectively. The integrated approach achieved a total sugar titer of 136.1 g/L and a biomass conversion efficiency of 304.4 g/kg, establishing a sustainable ramie straw biorefining pathway.