Production of prebiotic xylo-oligosaccharides from rice straw via combined dilute-acid hydrolysis

Rice straw is an abundant agricultural residue that can serve as a renewable feedstock for the production of value-added prebiotic ingredients. This study investigated the production of xylo-oligosaccharides (XOS) from rice straw using single- and combined-acid hydrolysis and evaluated the biological functionality of the resulting products. Rice straw was hydrolyzed using hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and phosphoric acid (H₃PO₄) under thermal treatment at 121 °C for 15–60 min. Among the single-acid treatments, 1% H₃PO₄ for 30 min produced the highest XOS yield (31.60%). Structural analyses revealed that phosphoric acid selectively disrupted hemicellulose while preserving cellulose structure, thereby favoring oligomer formation. To further improve XOS production, a combined-acid system was evaluated. The optimum condition, consisting of 1% H₃PO₄ and 0.5% HCl for 30 min, increased the XOS yield to 60.03% with a total XOS concentration of 18.27 g/L. The purified rice straw-derived XOS exhibited low cytotoxicity toward THLE-2 human hepatocytes at concentrations up to 0.1 mg/mL. In vitro fermentation demonstrated that the produced XOS effectively supported the growth of Lactobacillus fermentum TISTR 055 and generated organic acid profiles comparable to those obtained with commercial XOS and fructo-oligosaccharides under the investigated fermentation conditions. These findings suggest that combined H₃PO₄–HCl hydrolysis is an effective strategy for enhancing XOS production from rice straw, while the resulting XOS exhibited promising functional properties with potential applications in food and nutraceutical products.