Optimization of Medium Composition for the Production of Extrac-Ellular Amylase by Thermobifida fusca Using a Reponse Surface Methodology

Response surface methodology was employed to study the effect of medium composition on the production of extracellular amylase by Thermobifida fusca NTU22 in a 500 mL Hinton flask. The interactions were investigated with four variables, namely, soluble starch, yeast extract, ammonium sulfate, and initial medium pH, using a central composite design. When cultured in the optimum medium suggested by the response surface methodology approach, which consisted of 20 g/L soluble starch, 4.0 g/L yeast extract, 4.0 g/L ammonium sulfate, 0.2g/L MgCl2．6H2O3, 11.0 mg/L CaCl2 and 13.6h/L KH2PO4 (pH9.0) with shaking at 50℃ for 24 h, the maximum extracellular amylase activity was 6.20 ± 0.23 U/mL. This was almost the same as the predicted value (6.25 U/mL) obtained from response surface methodology model. Under optimum fermentation conditions, the maximum extracellular amylase activity was 9.40 U/mL after 60 h of cultivation in a 5-L fermenter.