Mycelial distribution in rice Koji

Abstract Mycelial distribution of Aspergillus oryzae in rice koji was measured to elucidate the steric growth mode in the solid-state culture. Mycelial density showed a exponential distribution against the distance from the surface of rice koji . On the basis of this phenomenon, mycelial distribution was expressed by a mathematical model and total mycelia were shown by the following equation: Y t = ac ∫e b ( R − r ) r 2 d r + Y s where Y t is the total mycelia in koji , the first term in right side is the mycelia in the inner part of rice grain and Y s is the surface mycelia. The variable r is the distance from the center of the koji , R is the radius of the koji , and a , b , and c are parameters. The values of each parameter were obtained by the least squares method using the experimental data and the distribution of mycelia both in the surface and in the matrix of rice grain was shown quantitatively. The steric growth mode of fungi in rice grain was shown using these techniques. The mycelial distribution and enzyme composition in rice koji made in sake factories were examined and the results were analyzed by a principal component analysis. The results suggested that when the degree of mycelial penetration is low the activities of acid protease and acid carboxypeptidase are high.