Mode of α-amylase production by the shochu koji mold Aspergillus kawachii

Abstract

Aspergillus kawachii produces two kinds of α-amylase, one is an acid-unstable α-amylase and the other is an acid-stable α-amylase. Because the quality of the shochu depends strongly on the activities of the α-amylases, the culture conditions under which these α-amylases are produced were examined. In liquid culture, acid-unstable α-amylase was produced abundantly, but, acid-stable α-amylase was not produced. The acid-unstable α-amylase was produced significantly when glycerol or glucose was used as a carbon source, similarly to the use of inducers such as starch or maltose. In liquid culture, A. kawachii assimilated starch at pH 3.0, but no α-amylase activity was recognized in the medium. Instead, the α-amylase was found to be trapped in the cell wall. The trapped form was identified as acid-unstable α-amylase. Usually, acid-unstable α-amylase is unstable at pH 3.0, so its stability appeared to be due to its immobilization in the cell wall. In solid-state culture, both kinds of α-amylase were produced. The production of acid-stable α-amylase seems to be solid-state culture-specific and was affected by the moisture content in the solid medium.