Shigeomi Ushijima

Improvement of Industrial Aspergillus Fungi

The koji molds play important roles as producers of various hydrolyzing enzymes in the production of various fermented foods, i.e., soy sauce, sake, miso, and shochu (a Japanese spirit). For example, the protease of koji molds contributes to the solubilization of the nitrogen constituents, and the glutaminase causes the liberation of glutamate, one of the most important flavor components in soy sauce. The breeding of koji molds has long been investigated in attempts to increase their enzyme productivities, using mainly two kinds of methods. One kind involves mutation (Sekine et at., 1969) with several mutagenic agents such as X rays, ultraviolet (UV) light, N-methyl-N’-nitro-N-nitrosoguanadine (MNNG), and so on, and the other involves crossing (Oda and Iguchi, 1963). The latter method was developed after the finding that koji molds, Aspergillus oryzae and Aspergillus sojae, have a so-called “parasexual” life cycle (Pontecorvo et at., 1953).