Abstract
Lignin is a key structural constituent of lignocellulosic biomasses that have substantial untapped potential to substitute environmentally unfriendly and non-renewable fossil-based resources. Unfortunately, multifaceted composition, heterogeneity, and structural recalcitrance of the lignin are the biggest technical challenges for its effective deconstruction and bioconversions to an array of bio-based products, e.g., specialty chemicals and biomaterials. Physicochemical methods for lignin depolymerization require strict reaction conditions, high energy to execute processes, and environmental apprehensions. In contrast, biological platforms harnessing the catalytic potentiality of microorganisms and their robust enzymatic armory are thought to be efficient means for lignin decomposition. Enzymes, derived from natural origin, are highly proficient and eco-friendly biocatalysts that manifest high selectivity, require milder reaction conditions, and reduce resource requirements. The utilization of enzymes for lignin conversion and pre-treatment of biomass for detergent, textile, pulp and papers, and food sector applications has been investigated for decades. Herein, we reviewed lignin bioconversion by biological means, focusing on ligninolytic enzyme-assisted pretreatment approaches. In the first half, we outlined the lignin as a multipurpose raw feedstock, fixation of CO2 to lignin biosynthesis and tailored lignin approach, and sources and types of lignin. The bio-based pre-treatment approaches for lignin depolymerization, including white-rot fungi, brown-rot fungi, bacteria, and ligninolytic enzymes, i.e., manganese peroxidase (MnP) lignin peroxidase (LiP), Laccase (Lac), versatile peroxidase (VP), and dye-decolorizing peroxidases (DyP) are thoroughly vetted in the second half.
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•Lignin valorization is discussed to meet sustainable and cleaner production.•Biomass transformation potential of ligninolytic armory has become new frontiers.•Sources and potential applications of valorized lignin in various industries are given.