Rice-koji is an important agent for the saccharification of fermented food production in Japan. In koji-making, temperature, humidity, light and oxygen are important environmental factors. However, there is no report of koji-making controlled by sound wave. In this study, focusing on the enzyme activity of rice-koji, we confirmed the relationship between enzyme activity and frequency of sound waves. Here, the enzyme activities of rice-koji cultured with no sound and sound waves at seven different frequencies (1.0, 2.5, 6.3, 8.0, 10.0, 12.5 and 16.0 kHz) were compared. Using two types of polished rice from different production areas, the activities were investigated. In this study, we investigated the enzyme activity of four types of rice-koji and found frequencies where the enzyme activity was significantly different to activity with no sound. In particular, the frequency of significant difference was investigated to confirm both rice. In the results, due to the irradiation frequency of 6.3 kHz, glucoamylase activity of both rice-koji decreased significantly (P<0.01) compared to the silent control. Further, due to the irradiation frequency of 1.0 kHz, acid protease activity confirmed a significant difference between the silent control and a frequency of 1.0 kHz (P<0.01). That is, as the activity of one of rice-koji increased, that of another rice-koji decreased. However, the activity of α-amylase and acid carboxypeptidase was not affected at any frequency. These results suggest that sound waves, particularly at frequencies of 1.0 and 6.3 kHz, have marked effects on the specific enzymatic activity of rice-koji.

 

Key words: Frequency of sound waves, sound wave, rice-koji, enzyme activity, koji-making.