Accelerated solvent extraction of high-purity lignin from sugarcane bagasse using sodium xylenesulfonate: Structural refinement and antibacterial-antioxidant enhancement.

Conventional hydrotropic extraction often suffers from poor lignin-carbohydrate separation, high solvent use, and lengthy processing. To resolve these issues, this study applied accelerated solvent extraction (ASE) assisted by sodium xylenesulfonate (SXS). Three variables, SXS concentration (10 % w/v and 20 % w/v), extraction temperature (180 °C and 200 °C), and time (1  h and 3  h), were optimized to assess their effects on lignin extraction efficiency, purity, structure, and bioactivity. At 20 % SXS and 200 °C for 1  h, extraction efficiency peaked (66.18 %) but lignin purity was lowered by carbohydrate contamination (16.82 %). In comparison, the condition of 10 % SXS at 200 °C for 3  h provided a better balance, yielding lignin with high purity (97.61 %) despite its lower extraction efficiency (9.58 %), along with a lower weight-average molecular weight (M_w: 2,100  Da) and extensive β-O-4 bond cleavage, with the lowest residual linkage content (8.82 per 100 aromatic units). An elevated syringyl-to-guaiacyl ratio reflected the preferential release of β-O-4-labile syringyl units. This lignin showed high phenolic (3.31 mmol/g) and carboxyl (0.59 mmol/g) contents. With ABTS and DPPH values of 1105.70 and 939.85 mg Trolox equivalent (TE)/g, respectively, the lignin showed strong antioxidant properties and inhibited pathogenic bacteria at MICs of 0.156-2.5 mg/mL. The MIC against probioticLimosilactobacillus reuteriKUB-AC5 was 1.25  mg/mL. Alkaline-extracted lignin had a higher molecular weight (4,100  Da) but showed reduced antioxidant activity (ABTS: 322.66 and DPPH: 274.26  mg TE/g) and higher MICs (1.25-10  mg/mL), indicating weaker antibacterial effects compared to optimized ASE-SXS lignin.These results affirm the functional advantages of lignin obtained via optimized ASE-SXS extraction.