Study on the Koji Mold Producing Substrate—Possible Application as a Food Supplement

In the production of soy sauce, the koji making stage during which koji mold is cultivated, is the key process for producing a high quality final product. Koji mold and contaminated bacteria act as antagonists as the koji making stage proceeds. As a result, the usable moisture content was reduced and an antibacterial substance was produced. Both of these effects were observed during our experiments. We confirmed the presence of antibacterial substances in koji. We purified the two main components and identified their chemical structures precisely. Furthermore, we examined the minimum inhibitory concentrations (MIC) of these substrates using selected bacteria, yeasts and molds. Out of these microorganisms, antibacterial substances in koji showed the strongest antibacterial activity toward Legionella erythra.