Metal Salt-Based Deep Eutectic Solvent Pretreatment of Moso Bamboo to Improve Enzymatic Hydrolysis

Abstract

Research on metal salt-based deep eutectic solvent (DES) pretreatment is still in its infancy, and the effect of hydroxyl groups on Cl− in choline chloride (ChCl) is not resolved. In this study, a type IV DES composed of metal salt and glycerol (Gly) was prepared for pretreatment of moso bamboo to improve its enzymatic hydrolysis. The correlation between enzymatic hydrolysis and the contents of hemicelluloses and lignin was evaluated using the Box–Behnken design. The results showed that FeCl3-based DES was optimal among various DES. The solid recovery was reduced to 55.54% following FeCl3/Gly pretreatment, which was effective in the removal of hemicelluloses and lignin compared with ternary DES pretreatment (with ChCl) under mild conditions (100 °C, 3 h). With the increase of pretreatment temperature (120 °C, 2 h), a significant proportion of hemicelluloses (76.07%) and lignin (62.77%) was removed. The structure of FeCl3/Gly pretreatment residue was seriously damaged, and the glucose yield increased to 91.13% following enzymatic hydrolysis. This correlation indicated that the hemicelluloses’ content had a significant influence on enzymatic hydrolysis of the residue following FeCl3/Gly pretreatment. This study elucidates the pretreatment effect of metal salt-based DES, which will be helpful in the value-added conversion of moso bamboo under mild conditions.