Optimizing brown rice liquefaction and saccharification using response surface methodology for grain ethanol...

Brown rice, unlike white rice, retains its bran and germ layers, making it rich in dietary fiber and physiologically active compounds. However, these components lower the efficiency of starch hydrolysis, making brown rice less suitable for fermentation. In this study, we aimed to optimize the brown rice liquefaction and saccharification processes using response surface methodology. In a Box-Behnken design, pH, temperature, and time served as independent variables, while soluble solid, reducing sugar, total sugar, maltose, and glucose concentrations as dependent variables. The liquefaction process demonstrated a good fit and reliability, with P < 0.05 and the coefficient of determination (R²) between 0.9290 and 0.9903 for all models. However, for the saccharification process, only the reducing sugar, maltose, and glucose models showed P < 0.05 and R² ≥ 0.9. We then subjected the sugar syrup prepared under the optimized saccharification conditions (pH 3.5, 65 °C, 4.8 h) to yeast fermentation, achieving an ethanol content of 62.77 mg/mL. Our study was successful in improving brown rice fermentation efficiency through enzymatic liquefaction and saccharification processes. The results may serve as crucial foundational data for the fermented beverage industry.