A lignin-first biorefinery approach for vine shoots: Integrated recovery of structurally preserved lignin, cellulose, and phenolics via oxalic acid-assisted organosolv

Abstract

Agro-industrial residues are an emerging source of high value-added compounds (cellulose, hemicellulose, lignin, and phenolic compounds) and complete utilization of those residues is required to develop a profitable process and reduce the waste generated. Vine shoots are an abundant agro-industrial residue with high lignin and phenolic content, yet their valorization is limited by the recalcitrant nature and the lack of developed lignin extraction procedures for this residue. For this reason, in this work, a lignin-first biorefinery strategy is proposed, combining hydroethanolic extraction of phenolic extractives with a novel ethanol-oxalic acid organosolv fractionation. An initial optimized solid-liquid extraction enabled the recovery of phenolic compounds with high antioxidant capacity (64.25 TEAC gds⁻¹), while enriching the biomass in structural biopolymers. Subsequent optimized organosolv processing led to efficient lignin recovery (114 mg gds⁻¹) and produced a cellulose-rich solid containing 72.1 % cellulose and 5.1 % hemicellulose. The recovered lignin exhibited low molecular weight (Mn 1,460 Da), mainly composed by G and S subunits, moderate polydispersity, and a high abundance of β-O-4 linkages, as determined by GPC and HSQC-NMR, indicating limited condensation during extraction. Enzymatic saccharification of the cellulose-rich fraction reached a glucose yield of 0.62 g g⁻¹ cellulose, representing a six-fold improvement compared to untreated biomass. Overall, this study demonstrates that the combination of a solid-liquid extraction with an oxalic acid-catalyzed organosolv process enables the fractionation of vine shoots into phenolic extractives, structurally preserved lignin, hemicellulose, and a highly digestible cellulose fraction, highlighting its potential as an effective route for lignin-first biorefineries.