High yield production of sugars from deproteinated palm kernel cake under microwave irradiation via dilute sulfuric acid hydrolysis

Recent years, great interest has been devoted to the conversion of biomass-derived carbohydrate into sugars, such as glucose, mannose and fructose. These are important versatile intermediate products that are easily processed into high value-added biofuels. In this work, microwave-assisted dilute sulfuric acid hydrolysis of deproteinated palm kernel cake (DPKC) was systematically studied using Response Surface Methodology. The highest mannose yield (92.11%) was achieved at the optimized condition of 148 °C, 0.75 N H2SO4, 10 min 31 s and substrate to solvent (SS) ratio (w/v) of 1:49.69. Besides that, total fermentable sugars yield (77.11%), was obtained at 170 °C, 0.181 N H2SO4, 6 min 6 s and SS ratio (w/v) of 1:40. Ridge analysis was employed to further verify the optimum conditions. Thus, this work provides fundamental data of the practical use of DPKC as low cost, high yield and environmental-friendly material for the production of mannose and other sugars.