Vanillin from lignin-chemicals platform: An overview on current chemo- and biocatalytic processes

Lignin is a major aromatic biopolymer in plant cell walls and represents a promising renewable carbon source. Upon depolymerization, lignin can yield a variety of aromatic compounds, forming a versatile chemical platform for producing high-value chemicals, among them vanillin, a widely used flavouring agent across multiple industries. However, due to its structural complexity and inherent recalcitrance, efficient lignin depolymerization and conversion remain significant challenges. This review outlines both chemical and enzymatic lignin depolymerization strategies, focusing on recent advances in valorisation into vanillin. Enzymatic approaches are highlighted for their sustainability and potential to achieve high yields. Moreover, techniques such as protein engineering, whole-cell bioconversions, and enzyme immobilization are discussed to overcome current limitations in enzymatic processes. The review concludes with perspectives on future developments in enzyme design, process optimization, and integrated lignin biorefinery strategies, emphasizing the central role of protein engineering in driving the circular bioeconomy forward.