Each factor level was selected based on preliminary studies. Preliminary results from a full factorial design had shown significant curvature (data not shown), hence a central composite design was chosen, in particular, a ‘face

centered’ design as only two types of extruded biomass were available (7% and 80% xylose removal). The ratio of the total amount of glucose produced in the hydrolyzate to the total theoretical amount of glucose in the steam-exploded corncobs (analyzed after acid hydrolysis) was chosen as the response for analysis. The experimental design was developed using the software Design Expert, version 8.0.7.1 (Stat Ease, selleck inhibitor Inc. USA). The resulting 22 experimental conditions, as well as three center point replicates for each type of biomass, were tested in triplicate and data is presented as the average of triplicates ± standard deviation. All experiments were performed fully

randomized, and the data was fitted via linear regression to a second order model: equation(2) y=β0+Σi=1kβixi+Σi=1kβiixi2+Σ1≤i≤jkβijxixj+ϵWhere y is the predicted response, xi represents the independent variables, k is the number of variables, β0 is the interception coefficient, βi represents the linear coefficient of each independent variable, βii represents the coefficients Seliciclib of the quadratic terms, βij represents the coefficients of the interaction effects and ε is the random error. Analysis of the variance (ANOVA) was performed and the significance of each variable, the interaction, and quadratic effects were determined

based on a significance of α = 0.05 using the F -test. The fitted model was evaluated by R2, adjusted R2, adequate precisior and the lack of fit coefficient for determining the adequacy. In addition, the fitted model was validated by performing experiments using the identified conditions of the significant variables [1]. The carbohydrate composition of the investigated corncobs before and after steam explosion and after different extruder treatments was measured after acid hydrolysis [9], [21] and [5]. N-acetylglucosamine-1-phosphate transferase The data are shown in Table 1 (based on total dry matter). The relative glucose content, which was the largest fraction of monosaccharides, increased from 41% to 66% and 58%, respectively, depending on different extrusion process conditions. The hemicelluloses fraction was largely hydrolyzed to xylose under high temperature and pressure during the steam explosion pretreatment. 7% xylose removal from the steam exploded corncobs was achieved through the extrusion process at a barrel temperature of 65 °C and a screw speed of 100 rpm without adding water, while 80% xylose removal was achieved when the barrel temperature increased to 100 °C and water was injected at Barrel 8 at 2.9 kg/h. Arabinose, galactose, and mannose were found in minor fractions (<5.0%). SEM images of untreated and extruded corncobs with different xylose removals at different magnifications are shown in Fig. 2.