This laboratory scale pretreatment was carried out in an electrically heated oil bath. A total of 3 g of biomass sample and 18 mL pretreated solution was placed in a 30 mL sealed stainless steel tank at a solid/liquid ratio of 1:6 (w/v) for pretreatment. In pretreatment process, magnesium bisulfite dose, pretreatment temperature and pretreatment time have been optimized respectively for investigating their effects. After pretreatment, the reactor was immediately cooled down in a water bath. The pretreated substrate was collected by filtration, washed with warm water for at least three times and stored at 4 °C. Solid loss was determined from the measure wet weight and moisture content of the solid. The spent liquor was stored in −20 °C for further analysis. All the experiments were carried out in two replicates.