Optimization of Hydrolysis Process to Obtain Fermentable Sugars from Sweet Sorghum Bagasse Using a Box–Behnken Design

Abstract

Sweet sorghum (Sorghum bicolor (L.) Moench) bagasse is a lignocellulosic material consisting mainly of hemicellulose and cellulose, a potential source of fermentable sugars. The present study aimed to optimize the hydrolysis of sweet sorghum bagasse to obtain the highest concentrations of xylose and glucose with the minimum amount of inhibitor compounds. Seven varieties of sweet sorghum bagasse were used for the hydrolysis experiment, carried out in three stages with a 2³ Box–Behnken factorial design; the critical factors selected for both stages were H₂SO₄ and H₂O₂ concentrations, time and liquid–solid ratio (LSR). The alkaline hydrolysis was carried out with a subsequent enzymatic hydrolysis using 0.4 mL cellulose and 0.5 mL beta-glucosidase. The optimum conditions for acid hydrolysis were H₂SO₄ (1.375 % w/v), time (36 min) and LSR (4.9:1 v/w of bagasse) resulting in values of 11.55 g/L glucose and 41.27 g/L xylose, respectively; for alkaline hydrolysis H₂O₂ (4.5 % w/v), time (45 h) and LSR (16:1 v/w of bagasse) were the optimum values. Under these conditions, 65.96 g/L glucose concentration was obtained. Validation of the model indicated no difference between predicted and observed values in the optimization of the hydrolysis process.