It was reported that the glucoamylase activity of rice-koji prepared with sound-irradiated conidiospores of yellow-koji, Aspergillus oryzae, at 16 kHz was decreased as compared with that of conidiospores that had not been sound irradiated. To reveal why the glucoamylase activity was changed, we observed the changes of the expression level of glaB encoding glucoamylase. We also determined to observe how the germination ratio of conidiospores and the hyphal weight of rice-koji were changed by sound waves. When conidiospores were irradiated with sound waves at 16 kHz, the expression level of glaB was decreased and the correlation between the expression level of glaB and glucoamylase activity was confirmed. When steamed rice was inoculated by sound-irradiated conidiospores, the conidial germination ratio 8 h after inoculation was 1.4 times higher than that of conidiospores that had not been sound irradiated, and the hyphal weight of rice-koji was 1.2 times higher than that of conidiospores that had not been sound irradiated. The correlation between the germination ratio and hyphal weight was also confirmed.
Key words: Aspergillus oryzae RIB40, glucoamylase activity, rice-koji; sound waves.
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