A solid-state culture system using a cellulose carrier containing defined medium as a useful tool for investigating characteristics of Koji culture

The purpose of this article is to establish a new solid-state culture syste m that uses a defined medium and allows control of the chemical factors in the medium in solid-state cultivation. To achieve this purpose, we produced a solid substrate, in which the defined medium was packed in a cellulose c arrier with agar, and named it "cellulose agar cube (CA-cube)". In order to obtain growth conditions similar to koji culture, we then determined the m oisture content of the CA-cube. Five runs of column reactor operations were carried out at various moisture contents of the CA-cube in the range of 50 -90%. A very similar mycelial morphology to that of koji culture was observ ed on the surface of CA-cube with moisture content lower than 63%. The gluc oamylase production and the production ratio of glucoamylase to alpha-amyla se (G/A ratio) were both increased exponentially with decreasing moisture c ontent and reached 237.5 units per g dry solid and 13.59, respectively, at the moisture content of 50%, which are almost comparable to those of koji c ulture. In addition, the glucoamylase "glaB", which is mainly produced in k oji culture, was observed in the CA-cube culture with low moisture content. These results indicate that growth conditions similar to koji culture coul d be attained by the column reactor culture with the CA-cube.