Sustainable removal of phenolic impurities from lignocellulosic-biomass-derived sugars using immobilized laccase and membrane filtration

Efficient removal of phenolic compounds is essential for improving the quality and downstream applicability of lignocellulosic hydrolysates. However, their purification is rendered challenging by their structural diversity, difficulty of separation from sugars, high toxicity even in low concentrations, and limited scalability of existing separation techniques. In this study, we developed an eco-friendly purification strategy that integrates enzymatic radical polymerization with membrane separation to selectively remove phenolic compounds from enzymatically hydrolyzed, glucose- and xylose-rich sugar solutions derived from sweet sorghum bagasse. The crude hydrolysates contained high levels of phenolics (520.2 mg/L in glucose, 3593.1 mg/L in xylose), which are recognized as potent fermentation inhibitors in biorefinery processes. Laccase treatment prior to membrane filtration enhanced phenolic removal efficiency in glucose solutions while minimizing sugar loss. Ultraviolet–visible spectra confirmed selective polymerization of phenolic compounds, as indicated by high absorbance at 280 nm, enabling their effective removal via ultrafiltration or nanofiltration. Although activated carbon treatment achieved comparable phenolic removal, it resulted in significant sugar loss (up to 50 % in xylose) and required large quantities of non-reusable adsorbent, raising environmental and economic concerns. To improve enzyme recyclability, laccase was covalently immobilized on poly(lactic acid)/poly(ε-caprolactone)-based microfibers. The immobilized laccase retained 48–58 % of its initial removal efficiency after 12 reuse cycles (glucose: 28/58; xylose: 29/50), demonstrating operational stability under the optimized conditions. These findings highlight the potential of integrating immobilized laccase with membrane-based purification as a selective, sustainable, and scalable approach for removing phenolic impurities from biomass-derived sugar streams, thereby enhancing the efficiency of lignocellulosic biorefinery operations. This study presents a practical platform that effectively removes microbial inhibitors during biosugar production, supporting the sustainable transition to biofuels and biochemicals. • Eco-friendly method to recover sugar from sweet sorghum bagasse hydrolysate. • Integrated enzymatic and membrane purification incurs minimal sugar loss. • Uses immobilized laccase for enzymatic radical polymerization of phenolic compounds. • Biopolymer-based microfiber supports facilitate enzyme reuse.