Lignincarbohydrate

Lignin-carbohydrate complexes (LCCs) are structural features of plant cell walls in which lignin is covalently and/or associatively linked to carbohydrate polymers. In many biomass sources, the main carbohydrate components involved are xylan, arabinoxylan, and galactoglucomannan, though other hemicelluloses and cellulose can also participate. LCCs arise during lignification and cross-linking processes, creating a network that binds lignin to wall polysaccharides and contributes to the overall architecture of the cell wall.

LCCs are characterized by a range of bond types, including covalent ether and ester linkages between lignin units and carbohydrate residues, as well as more complex aryl-glycosidic and other interfacial connections. The precise distribution and chemistry of LCCs vary with plant species, tissue type, and growth conditions, leading to substantial heterogeneity in their structure. Because they physically couple lignin to carbohydrates, LCCs influence the accessibility of polysaccharides to enzymes and other deconstruction chemistries.

The presence of LCCs is a major factor in biomass recalcitrance, impacting pulping, biorefinery processing, and enzymatic hydrolysis for sugar or biofuel production. Pretreatment strategies often aim to disrupt or remove LCC linkages to improve carbohydrate release, using chemical, oxidative, or combined approaches; in some cases, selective enzymatic or chemical cleavage of ester or ether bonds is pursued to reduce cross-linking.

Analytical study of LCCs employs techniques such as NMR spectroscopy (notably 2D HSQC), FTIR, and degradative methods like thioacidolysis and DFRC to identify and quantify lignin–carbohydrate linkages. Despite methodological advances, LCCs remain a complex and active area of biomass research due to their structural diversity and impact on processing.