Statistical optimization of xylanase production by Aspergillus niger AN-13 under submerged fermentation using response surface methodology

Response surface methodology (RSM) was performed to evaluate the effects of cultivation time, pH and substrate concentration on production of xylanase by Aspergillus niger AN-13. Agricultural residue wheat bran was used as main substrate under submerged fermentation. Xylanase production was optimized by Box-Behnken design (BBD). Statistical analysis of results showed that, the linear and quadric terms of these three variables had significant effects, and evident interactions existing between pH and substrate concentration were found to contribute to the response at a significant level. Furthermore, Box-Behnken design (BBD) used for the analysis of treatment combinations gave a second- order polynomial regression model, which was in good agreement with experimental results, with R-2=0.9959 (P<0.05). By response surface methodology and canonical analysis, the optimal fermentation parameters for enhanced xylanase production were obtained. Under these conditions, namely cultivation time of 53.3 h, pH of 7.92 and wheat bran concentration of 54.2 g.L-1, the model predicted a xylanase activity of 125.14 U U.mL(-1). Verification of the optimization showed that xylanase production of 127.12 U.mL(-1) was observed under the optimal condition, which had a marked increase compared with a xylanase activity of 4.80 U.mL(-1) in experiments according to Box-Behnken design.