Optimization of fermentation conditions for producing acid protease using response surface methodology

Response surface methodology was employed to optimize the fermentation conditions of Aspergillus niger for producing acid protease. In the first optimization step, a full factorial design was used to investigate the effect of temperature, initial pH, inoculum and medium volume on the production of acid protease from A. niger. The results showed that temperature and medium volume had significant effect on protease production, the former had positive effect, while the latter had negative effect. The steepest ascent path was used to approach the optimal region of the protease production. The optimal level of temperature and medium volume was determined by a central composite design and response surface analysis. The maximum activity of acid protease was 1543.01 U/ml under the optimized conditions after 3 d.