Masuzawa N., Katayama K.

Food processing with lactic acid bacteria has been made in various ways. Yogurt and kefir are representative and are paid to attention recently because they are good for health. By adding lactic acid bacteria to milk, yogurt and kefir are produced by lactic acid fermentation. We have studied promotion effect of ultrasonic irradiation in the fermentation process. In the previous studies, it was proven that ultrasonic irradiation was extremely effective to promote fermentation of yogurt and kefir and that degree of increase of promotion with ultrasonic frequency is slight. In this study, considering the change of degree of increase of promotion with frequency is larger in audio frequency range, we expanded the measurement range from ultrasonic frequency to audio frequency of 5kHz. Since we could not find appropriate vibrating system in audio frequency range on the market, we made and used vibrating systems with ultrasonic transducer to both ends of which metal pieces adhered in order to decrease resonant frequency. From the measurement result of wide frequency range, it was found that degree of increase of promotion was changed abruptly in the audio frequency range as expected and that the change was exponential.