Saccharification for distiller’s grains based on combined hydrolysis with acid and enzyme

China is a big country of white spirit production and consumption. When brewing white spirit, large amounts of distiller’s grains (DG) are left over, which are as the byproduct in white spirit production. In virtue of high content of cellulose and hemicellulose, DG is a kind of lignocellulosic biomass. In order to make full use of a distiller´s grains (DG), the feasibility of using DG in making fermentable sugars by the two-step hydrolysis method of mixed acid and cellulase was explored. The key parameters of temperature, mixed acid concentrations, solid-liquid ratio and hydrolysis time were studied with the index of the concentrations of reducing sugar and xylose. In addition, the structural characteristics of DG in different hydrolysis stages were examined by means of scanning electronic microscopy (SEM), infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The results indicated that there was 59.32 g/L reducing sugar and 6.49 g/L xylose in the conditions of temperature 100℃, solid-liquid ratio 1:12 g×mL-1, acid concentrations 2.0% and time 120 min, with the conversions of 77.38% and 62.50% for hemicellulose and cellulose, respectively. There were 13.27 g/L reducing sugars in the enzymatic hydrolysis conditions of cellulase dosage 4000 U/g, temperature 45℃, pH value 4.8 and time 2.5 h. The conversion rate and enzymatic hydrolyzation of the cellulose were 66.67% and 90.73%, respectively. The studies of structural characteristics showed that the changes in morphology caused by acid and enzymatic hydrolysis successively were significant in comparison to those of feedstock, resulting in increasing surface exposure and porosity. The disorganized morphological structure of AHR allows for greater accessibility to cellulase, which facilitates enzymatic hydrolysis. The spectrograms of FTIR and XRD suggested that the characteristic strength peaks for the corresponding typical functional groups of each component were changed and the crystallinity index of the solid residues were increased, compared with DG. In short, the saccharification process based on the combined hydrolysis of acid and enzyme to produce fermentable sugars was feasible and efficient.