4. Conclusion
In this study, the effects of the constituent of ChCl-DHBA DES on WT and TG sorghum stover with in planta accumulation of DHBA were investigated. Binary DES and ternary DESs were synthesized with ChCl, DHBA, and the solvent-based third constituents including water and ethylene glycol. TG biomass had similar chemical composition to WT biomass while becoming more susceptible to enzymatic hydrolysis after the DHBA-based DES pretreatments, therefore, releasing higher amounts of fermentable sugars than WT biomass. The third constituent led to dramatically enhanced pretreatment performances. Binary ChCl-DHBA DES removed over 70% of xylan with less than 20% of delignification. EG-incorporated ternary DES doubled the delignification while having 20% less xylan removal compared to the binary DES. ChCl-DHBA-W DES also increased both high xylan removal and delignification. The applied ternary DESs resulted in a significant enhancement in the conversion of glucan and xylan conversion compared to the binary DES, as expected from the changes in chemical composition. However, the enhanced fermentable sugar production after the pretreatments with ChCl-DHBA-EG and ChCl-DHBA-W are not easily concluded with a single dominant factor, either xylan removal or delignification, in this study. Investigation of lignin structure after pretreatment indicates that using water as the third constituent for ternary DES preserved the most β–O–4 linkage, while binary ChCl-DHBA DES mostly only removed lignin from the low molecular weight fraction. Taking fermentable sugar conversion and lignin structure together, both water and ethylene glycol showed great potential as the third constituent in developing a sustainable biorefinery process for total biomass utilization. The results demonstrated that synthesizing ternary DESs could enhance the pretreatment performance of binary DESs.