초록
<P>Medium composition and culture conditions for the acid protease production by <I>Aspergillus niger</I> I1 were optimized by response surface methodology (RSM). A significant influence of temperature, KH<SUB>2</SUB>PO<SUB>4</SUB>, 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<SUP>−1</SUP>) closely matched the yield predicted by the statistical model (172.57 U mL<SUP>−1</SUP>) with <I>R</I><SUP>2</SUP> = 0.914. Compared with the initial M1 medium on which protease production was 43.13 U mL<SUP>−1</SUP>, 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; KH<SUB>2</SUB>PO<SUB>4</SUB> 1.0; NaCl 0.3; MgSO<SUB>4</SUB>(7H<SUB>2</SUB>O) 0.5; CaCl<SUB>2</SUB> (7H<SUB>2</SUB>O) 0.4; ZnSO<SUB>4</SUB> 0.1; Na<SUB>2</SUB>HPO<SUB>4</SUB> 1.6; shrimp peptone (SP) 1.0. The pH was adjusted at 5 and the temperature at 30°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. </P>