2-Naphthol Impregnation Prior to Steam Explosion Promotes LPMO-Assisted Enzymatic Saccharification of Spruce and Yields High-Purity Lignin

The recent discovery that impregnation with a carbocation scavenger may improve the enzymatic saccharification of steam-exploded softwood has brought a softwood-based biorefinery closer to reality. However, the nature of theimpregnation effect remains unresolved, and its impact on processefficiency and product quality in high-dry matter reactions remainsunderexplored. Here, we show that 2-naphthol impregnationenables the complete saccharification of spruce cellulose by lyticpolysaccharide monooxygenase (LPMO)-containing Cellic CTec2,but not by an LPMO-poor cellulase cocktail (Celluclast), in 10%dry matter reactions with an industrially feasible enzyme dose andreaction time. Importantly, we show that this remarkably highsaccharification yield correlates with increased LPMO activity,which is due to the impact of 2-naphthol on the ability of lignin to drive the LPMO reaction. Thesefindings show that impregnationimproves saccharification not only by reducing cellulase adsorption and inactivation but also by boosting oxidative cellulosedepolymerization by LPMOs. Pyrolysis of the lignin-rich saccharification residues revealed that 2-naphthol impregnation had littleeffect on lignin-derived components in the resulting bio-oil, which, due to the efficient saccharification, showed reduced levels ofcarbohydrate-derived components that reduce oil storage stability. These results bring closer the prospect of a spruce-basedbiorefinery that combines biochemical and thermochemical conversion routes

Automated summary

The use of a carbocation scavenger to improve the enzymatic saccharification of steam-exploded softwood brings us closer to a softwood-based biorefinery. The impregnation effect enables complete saccharification of spruce cellulose with lytic polysaccharide monooxygenase (LPMO)-containing Cellic CTec2, but not with an LPMO-poor cellulase cocktail (Celluclast).