Exploring lignin depolymerization by a bi-enzyme system containing aryl alcohol oxidase and lignin peroxidase in aqueous biocompatible ionic liquids.

Enzymatic depolymerization of lignin to produce low molecular weight products requires mild reaction conditions and exhibits higher selectivity compared to thermochemical lignin depolymerization. However, it remains challenging to depolymerize lignin enzymatically, partially due to the low solubility of lignin in aqueous phase. This study aimed to develop a novel approach to combine aqueous lignin extraction with enzymatic lignin depolymerization in biocompatible ionic liquids. A bi-enzyme system containing aryl alcohol oxidase (AAO) and lignin peroxidase (LiP) was developed to depolymerize lignin. Temperature and pH profiles for LiP and AAO were determined. Biocompatibilities of LiP and AAO in different deep eutectic solvents and ionic liquids were investigated. Aqueous cholinium glycinate was found to be an efficient and suitable solvent to solubilize lignin and serve as a biocompatible medium for enzymes to work. LiP and AAO together reduced lignin molecular weight in both solid and liquid phase after enzymatic lignin depolymerization.