Optimization of Acid Protease Production byAspergillus nigerI1 on Shrimp Peptone Using Statistical Experimental Design

Medium composition and culture conditions for the acid protease production byAspergillus nigerI1 were optimized by response surface methodology (RSM). A significant influence of temperature, KH₂PO₄, and initial pH on the protease production was evaluated by Plackett-Burman design (PBD). These factors were further optimized using Box-Behnken design and RSM. Under the proposed optimized conditions, the experimental protease production (183.13 U mL−1) closely matched the yield predicted by the statistical model (172.57 U mL−1) withR2=0.914. Compared with the initial M1 medium on which protease production was 43.13 U mL−1, a successful and significant improvement by 4.25 folds was achieved in the optimized medium containing (g/L): hulled grain of wheat (HGW) 5.0; KH₂PO₄1.0; NaCl 0.3; MgSO₄(7H₂O) 0.5; CaCl₂(7H₂O) 0.4; ZnSO₄0.1; Na₂HPO₄1.6; shrimp peptone (SP) 1.0. The pH was adjusted at 5 and the temperature at30°C. More interestingly, the optimization was accomplished using two cheap and local fermentation substrates, HGW and SP, which may result in a significant reduction in the cost of medium constituents.