Optimization for rice koji preparation using aspergillus oryzae CJCM-4 isolated from a korean traditional meju

To obtain a useful mold strain in rice-doenjang production, enzyme activities were investigated in rice and wheat koji prepared with 13 different strains isolated from traditional Korean meju. The CJCM-4 strain, which had been selected as a superior strain for the production of protease, was identified as Aspergillus oryzae by the gene sequence of the ITS-5. 8S rDNA region as well as aflatoxin production capacity. The enzyme activities of koji prepared with CJCM-4 according to the polishing degree of rice bran were examined. The enzyme activities of koji prepared with 70% milling degree of rice bran were higher than those of other kojis. Protease activity showed its highest level on day 3 at 30°C. Glucoamylase activity showed its highest level on day 2 at 30°C. The optimum enzyme production of koji was determined at different conditions such as incubation time, temperature, moisture, and inorganic salt content. The optimum ratio of water added to the rice for the production of enzymes was 35% on the dry basis of the rice, and the optimum temperature was 25°C. When inorganic salts were added to increase enzyme activity, the combined addition of 0. 15% CaCO₃ and 0. 05% NaH₂PO₄ resulted in the highest enzyme activities.