Production of amylase by Aspergillus foetidus on rice flour medium and characterization of the enzyme.

Aspergillus foetidus ATCC 10254 was selected from nine starch-utilizing microorganisms for its high amylolytic activity. This mould produced high levels of extracellular alpha-amylase in rice starch medium and degraded the available starch efficiently. Optimal conditions for enzyme production on 2.0% rice medium included 28 degrees C, initial pH of 6.6, and supplementations with 0.02% NaNO2, 0.08% KH2PO4, and 0.08% corn steep liquor. Eleven-fold purification of the enzyme was obtained after ammonium sulphate and ethanol precipitations from spent medium. The molecular weight was estimated at 41 500. Optimum pH and temperature for enzyme activity were 5.0 and 45 degrees C. Michaelis-Menten constants were 1.14 mg/ml on amylopectin, 2.19 mg/ml on soluble starch and 7.65 mg/ml on amylose. Amylose produced substrate inhibition while glucose or maltose did not inhibit the enzyme. This alpha-amylase may be used as a saccharifying enzyme for rice starch. Aspergillus foetidus ATCC 10254 also presents a potential for treatment of starch-containing waste waters.