CONDITIONS OF SORGHUM STEM FOR MAXIMUM SUGAR RECOVERY USING STATISTICAL APPROACH Article Highlights

• Sorghum stem was used as a cheap raw material for production of fermentable sugars • Alkali pretreatment was effective to increase the enzymatic digestibility of sorghum • Alkali pretreatment conditions of sorghum bicolor stem were optimized using RSM • At the optimum condition, the glucose yield increased by 7.14 fold Bioethanol production from lignocellulosic biomass provides an alternative energy-production system. Sorghum bicolor stem is a cheap agro-waste for bioethanol production. In this study, response surface methodology (RSM) was used to optimize alkali pretreatment conditions for sorghum bicolor stem with respect to substrate concentration, NaOH concentration and pretreatment time based on a central composite rotary design. The main goal was to achieve the highest glucose and xylose yields after enzymatic hydrolysis. Under optimum conditions of pretreatment (time 60.4 min, solid loading 4.2%, and NaOH con-centration 1.7%), yields of 98.94 % g glucose/g cellulose and 65.14 % g xyl-ose/g hemicellulose were obtained. The results of a confirmation experiment under the optimal conditions agreed well with model predictions. Pretreatment of sorghum bicolor stem at the optimum condition increased the glucose and xylose yields by 7.14 and 3.02 fold, respectively. Alkali pretreatment showed to be a great choice for the pretreatment of sorghum bicolor stem