Statistical media optimization and production of ITS alpha-amylase from Aspergillus oryzae in a bioreactor

The production of an intermediate temperature-stable (ITS) α-amylase from Aspergillus oryzae was studied by using a central composite design with three independent variables, viz., starch, yeast extract, and K₂HPO₄. The model equation provided a suitable model for the response surface for α-amylase production, and, from the optimal concentrations of the medium components, a model was predicted, which was then used for enzyme production in a 150-L bioreactor. In the bioreactor studies, the enzyme yields (161 U/ml) were similar to that of the shake flask (133 U/ml); however, the time required for maximum α-amylase production in the bioreactor was reduced to 48 h compared with 120 h in shake flask cultures. An increased level of phosphate in the medium and low inoculum size were necessary to control the excessive foaming in the bioreactor; however, control of the pO₂ level and agitation was not mandatory for enzyme production. The peak enzyme production coincided with the increase in pH of the fermentation broth and was maximal when the pH of the system was above 7.5. Thus, in the present study, pH acted as an indicator of the initiation or end of the enzyme synthesis or of the fermentation cycle. Received: 20 November 2001 / Accepted 31 December 2001