麹菌の米粒上での増殖特性に関する研究

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Rice koji, a solid-state culture of Aspergillus oryzae on steamed rice grains, is used as an enzyme source and raw material for sake fermentation, and the quality of koji is regarded as the most important factor determining the quality of sake. However, the control of solid-state culture is very difficult compared with submerged culture. In Japanese breweries, the control of koji making is traditionally done by observing features such as mycelial distribution and odor. In order to develop an automatic control system for koji making, we first studied the mycelial growth mode in rice grains from the respiratory activity, using a gas analyzer. The relationships between the properties of rice grains and the growth mode was studied, and it was recognized that the growth mode was affected not only by nutritional conditions and moisture, but also by physical properties like hardness and the shape of rice grains. We also studied the features and odor of koji in order to apply the traditional method of controlling koji making to a novel automatic control system by means of an expert system, or fuzzy control system. Mycelial distribution in rice koji was measured to elucidate the steric growth mode in the solid-state culture. The mycelial density showed an 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 shown quantitatively. The mycelial distribution and enzyme composition in rice koji made in sake factories were examined and the relationships between the mycelial distribution and the quality of koji were studied. The results suggested that when the degree of mycelial penetration is low, the activities of acid protease and acid carboxypeptidase are high. The volatile compounds produced by growing A. oryzae on steamed rice during koji making were collected with a Tenax column and analyzed by GC and GC-MS. Eight kinds of alcohols, three kinds of aldehydes, five kinds of ketones, and an ester were identified. The production of volatile compounds was affected by the oxygen concentration, and aldehydes and ketones increased significantly with a deficiency of oxygen. The production of most of the volatile compounds was maximum at the middle stage of growth, and decreased thereafter. The tendency of 1-octen-3-ol was different from other volatile compounds ; it increased with the cultivation time and did not decrease.
社団法人日本生物工学会の論文
1993-03-25

麹菌の米粒上での増殖特性に関する研究

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