Acidic deep eutectic solvent pretreatment for enhancing enzymatic hydrolysis of moso bamboo (Phyllostachys pubescens)

Acidic deep eutectic solvent pretreatment holds great promise for the fractionation of lignocellulose. The influences of lignin presence form and surface structure of pretreated residue on enzymatic hydrolysis are rarely studied. In the present work, choline chloride/oxalic acid (ChCl/OA) was developed to pretreat moso bamboo for promoting its enzymatic hydrolysis, and the effects of residue changes on enzymatic hydrolysis were also explored. Results showed that the removal of hemicelluloses (76.24%) and lignin (60.68%) was remarkable after ChCl/OA pretreatment at mild conditions (at 90 degrees C for 3 h). After enzymatic hydrolysis, the glucose yield was improved from 17.78% (raw) to 60.39% (the residue obtained from pretreatment at 90 degrees C for 3 h). However, the excessive removal of lignin (73.43%) did not facilitate the enzymatic hydrolysis of residue obtained from ChCl/OA pretreatment at 100 degrees C for 3 h. The results of surface morphology, surface physiochemistry, and dye adsorption of ChCl/OA pretreatment residues confirmed that the enzymatic hydrolysis was affected by the surface lignin, hydrophobic interaction, and accessibility, among which the hydrophobicity causing the enzyme non-productive adsorption may be the dominant factor leading to the decrease of glucose yield. Finally, the enzyme non-productive adsorption could be effectively overcome by adding bovine serum protein during enzymatic hydrolysis, and its glucose yield could be improved to 2.3-fold for the residue obtained from pretreatment at 110 degrees C for 3 h.

Automated summary

Acidic deep eutectic solvent (DES) pretreatment is a promising method for lignocellulose fractionation. This study developed a DES consisting of choline chloride and oxalic acid (ChCl/OA) to pretreat moso bamboo and investigated the effects of pretreated residue on enzymatic hydrolysis. The results showed that ChCl/OA pretreatment effectively removed hemicelluloses and lignin, leading to improved glucose yield. However, excessive removal of lignin negatively affected enzymatic hydrolysis. The study also revealed that surface lignin, hydrophobic interaction, and accessibility influenced enzymatic hydrolysis.