Subcellular dissolution of xylan and lignin for enhancing enzymatic hydrolysis of microwave assisted deep eutectic solvent pretreated Pinus bungeana Zucc.

The mechanism for enhancing enzymatic hydrolysis during microwave-assisted deep eutectic solvent (Mw-DES) pretreatment in deconstruction of plant cell wall was proposed by combining wet chemical analysis and microscopic measurements. Mw-DES pretreatment achieved significantly higher enzymatic conversion of 81.90% with lower lignin and comparable xylan removal (42.81% and 74.73%, respectively). While DES pretreated sample with higher lignin and xylan removal (66.59% and 74.93%, respectively) obtained limited sugar yield (45.67%). There were no significant differences with respect to chemical structures of lignin fraction between DES and Mw-DES pretreatment but primary discrepancies of topochemical and morphological changes were observed. Non- or low-substituted xylan was directly removed from secondary walls (SW) exposed more cellulose for enzyme attacking after Mw-DES pretreatment. Meanwhile, high-substituted xylan and lignin were synergistically dissolved from cell corner middle lamella (CCML). These topochemical changes of components resulted in cracked and porous cell wall structure, thus facilitating the accessibility of cellulose.