Valorization of Defatted Rice Bran for Xylose-Rich Syrup Production via Enzymatic Hydrolysis using Response Surface Methodology

Defatted rice bran (DRB), a major agro-industrial by-product, contains abundant arabinoxylan that can be enzymatically converted into value-added pentose sugars. Growing demand for alternative sweeteners has intensified interest in sustainable alternatives to conventional glucose syrups. In this context, DRB provides an underutilized substrate for producing a xylose-rich syrup through green bioprocessing. This study aimed to optimize the enzymatic hydrolysis of DRB for the production of a xylose-rich syrup using response surface methodology. A central composite design was employed to evaluate the effects of pH, enzyme concentration, and hydrolysis time on reducing sugar yield (expressed as xylose equivalents). Results showed that pH and enzyme concentration significantly influenced sugar production (p ≤ 0.05). The optimal conditions were determined to be pH 4.0, enzyme concentration 1.50%, and hydrolysis time 23.48 h, yielding 3,580.25 mg/L reducing sugars (as xylose equivalents) with a high model correlation (R² = 0.9197). The syrup exhibited desirable physicochemical properties, including pH 5.54, 65 °Brix total soluble solids, viscosity of 41 cP, and 90.9% reducing sugar content, and remained stable over two months of storage at room temperature. Thin-layer chromatography confirmed xylose as the predominant sugar component. Compared with conventional glucose or fructose syrups, the DRB-derived xylose-rich syrup demonstrated comparable physicochemical characteristics; however, its functional properties require further validation. The valorization of rice bran into xylose-rich syrup provides a sustainable utilization pathway for agricultural by-products and supports circular-bioeconomy strategies within the national Bio–Circular–Green (BCG) framework.