[Fermentation optimization by response surface methodology for enhanced production of beta-glucosidase of Aspergillus niger HDF05].

In order to obtain high beta-glucosidase productivity, we optimized the fermentation parameters for beta-glucosidase production by Aspergillus niger HDF05. First, we screened the important parameters by Plackeet-Burman design. Second, we used the path of steepest ascent to approach to the biggest response region of parameters affecting beta-glucosidase production. Then, we obtained the optimal parameters by central composite design and response surface analysis. We developed a quadratic polynomial equation for predicting beta-glucosidase production level. The results showed that the important parameters were temperature, packing volume, concentrations of wheat bran and (NH4)2SO4. The optimal fermentation parameters were as follows: temperature 28 degrees C, packing volume 71.4 mL/250 mL, wheat bran 36 g/L and (NH4)2SO4 5.5 g/L. Under the optimal conditions, we obtained the maximum enzyme activity of 60.06 U/mL, with an increase of 23.9% compared to the original fermentation parameters. During enzymatic hydrolysis of acid-pretreated corncob, addition of beta-glucosidase from Aspergillus niger HDF05 greatly reduced the inhibition caused by cellobiose, and the hydrolysis yield was improved from 66.7% to 80.4%.