Optimization of Fermentation Conditions for Xylosidase Production by Aspergillus niger
TANG Yong, DING Honghao, CAI Jun
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In order to fully utilize corn cob powder as an agricultural by-product, the submerged fermentation of Aspergillus niger using corn cob powder as a substrate was optimized for enhanced xylosidase activity. Firstly, one-factor-at-a-time method was used to investigate the effects of fermentation period, temperature, inoculum size, initial fermentation pH, medium volume and shaker speed on xylosidase activity. The results showed that a fermentation period of 144 h, a temperature of 34 ℃, an inoculum size of 7%, an initial fermentation pH of 3.0, a shaking speed of 180 r/min, and a medium volume of 110 mL in 300-mL shake flasks were found to be the best conditions. Further, using the Plackett-Burman design, lowest addition experiments, the steepest ascent method, and response surface methodology with central composite design, the optimal levels for medium components were determined as follows: corn kernel powder 31.55 g/L, yeast powder 8.00 g/L, peptone 5.48 g/L, magnesium sulfate 0.70 g/L, sodium chloride 1.00 g/L, and calcium chloride 1.50 g/L. A quadratic polynomial model was developed with a determination coefficient R2 of 0.991 0, and an adjustment coefficient R2 of 0.982 9. The analysis of variance (ANOVA) showed that the model was significant with a P value greater than 0.05 for lack-of-fit, supporting its use for the theoretical prediction of enzyme production. Under the optimized conditions, an 8.89-fold increase was observed in xylosidase activity of Aspergillus niger.