Influence of laccase pre-treatment and matrix composition on hydrothermal extraction of fibers from lignocellulosic agri-food residues

The valorization of agri-food residues increasingly relies on mild, water-based processes capable of recovering intact polysaccharides for food and biorefinery applications. However, the structural diversity of lignocellulosic by-products, and the dominant role of lignin in limiting accessibility, often restricts hemicellulose extraction under gentle conditions. Here, we evaluated a laccase-assisted approach to loosen biomass architecture and improve hydrothermal extraction of lignocellulosic residues, such as nutshells, leafy biomass, and fruit processing wastes, at 150 °C, the standard temperature for hemicellulose solubilization, and at a milder 125 °C, where extraction is usually limited. A comprehensive molecular characterization of insoluble dietary fiber revealed lignin contents ranging from 8 to 72% and hemicellulose proportions from 12 to 58%, which largely dictated extraction behaviour. At 150 °C, laccase pre-treatment had little impact on recalcitrant, lignin-rich matrices (e.g., hazelnut shells: ≤ 4% sugar recovery). In contrast, at 125 °C, where conventional extraction is markedly limited, the enzymatic step significantly increased solubilization only in low-lignin, structurally open residues. The most notable case was orange waste, where extraction rose from 22 to 59% of total dietary fiber. However, the solubilized fractions were not hemicellulose-rich: arabinose- and galacturonic acid–containing polysaccharides represented up to 45–50% of released sugars, indicating a preferential mobilization of pectic domains. Altogether, the study delineates the realistic contribution of laccase in low-severity extraction schemes, highlighting where it can enhance polysaccharide recovery and providing practical guidance for designing targeted valorization strategies.