Enzymatic degradation of lignin for valorization: A sustainable bridge towards advanced lignin-based biorefineries

Lignin, the second most abundant natural polymer after cellulose, is typically discarded or incinerated, contributing to environmental issues. Enzymatic lignin degradation offers a sustainable pathway for biomass valorization by enabling selective depolymerization under mild conditions. Establishing an appropriate enzyme-assisted methodology for lignin depolymerization is crucial for enzymatic valorization of lignocellulosic biomass. Detailed descriptions of primary components and lignin structures in different plant biomass sources facilitate in selecting appropriate lignocellulosic biomass for enzymatic lignin valorization. In-depth evaluations of lignin modifying enzymes and lignin degrading auxiliary enzymes provide valuable insights that accelerate the development of effective strategies in enzymatic lignin degradation, emphasizing their role as eco-friendly biocatalysts. The current applications of lignin degradation enzymes are outlined, investigating their potential in food, paper industry, nanobiotechnology, pharmaceutical intermediates synthesis, pollutants biodegradation, etc. Discussions of existing challenges in enzymatic lignin degradation and their possible solutions aim to promote further research and industrial implementation in this field. This review seeks to provide a comprehensive overview of current literature on lignin degradation enzymes to establish a cost-effective and high-performance system for enzymatic lignin bioconversion, highlighting the advantages of integrating enzymatic-assisted strategies into lignocellulosic biorefineries. • Enzymatic utilization of lignin holds promising potential for advancing lignin-based biorefineries. • A comprehensive overview of primary components and lignin structures across various plant biomass sources is provided. • The features of lignin degradation enzymes and lignin-degrading auxiliary enzymes are summarized. • Recent advancements in enzymatic lignin valorization are highlighted. • Proposed solutions for the challenges associated with enzymatic lignin degradation are presented.