A chemical fractionation process using acidified zinc chloride (ZnCl2) was investigated to recover hemicellulose. The process variables of the fractionation process, including reaction temperature, reaction time, and ZnCl2 concentration, were selected as factors of the experimental design by preliminary tests. The optimal reaction conditions of these three factors for maximal xylose and mannose (XM) recovery yield and purity were determined by statistical experimental design and central composite design (CCD). The determined optimal conditions were 67.9 degrees C reaction temperature, 10.5 min reaction time, and 7.3% ZnCl2 concentration. The predicted maximum XM recovery yield and purity from the regression equation of dependent variable Y (XM yield) were 47.6% and 75.0% respectively. The experiment showed a 54.5% XM recovery and 72.7% purity under the optimal reaction condition. Fractionation using ZnCl2 solution not only solubilizes the hemicellulose fraction of barley straw selectively, but also improves the enzymatic digestibility of the treated cellulose. This study confirmed that the improved enzymatic digestibility of the treated solid was also achieved; i.e., the treated solid at 170 degrees C for 20 min resulted to the highest 96-h enzymatic digestibility (69.3% with 15 FPU and 73.8% with 30 FPU). (C) 2013 Elsevier Ltd. All rights reserved.