Ultrasonic Cellular Disruption of Yeast in Water-based Suspensions

Abstract

This study examines the qualitative and quantitative properties of water-based suspensions and the effect on the occurrence and threshold levels of ultrasonic phenomena, standing wave, acoustic streaming and especially cavitation. Commercial pressed (hydrated) and lyophilised (dehydrated) baker's yeast (Saccharomyces cerevisiae), and a dolomite suspension that has the same average particle size as that of the yeast were used. The experiments were conducted in the specially designed and constructed ultrasonic treating vessel under conditions of 1·117 MHz frequency and 30–120 kW m−2 ultrasound output power. The levels of particle concentration, expressed in g l−1, in the ultrasound field that were needed to terminate cavitation (that is the cavitation threshold concentration), and the length of time that passed from the start of the experiment until the restart of cavitation, which is the time period required for the formation of cavitation, were examined. The experiments aimed at determining the time period required for the formation of cavitation was carried out at concentration levels that were 1·5 times higher than the cavitation threshold concentrations. The acoustic phenomena taking place in the ultrasound field, and through these, the effects of ultrasound can be characterised by these two measures. Under the conditions of an output power of 90 kW m−2, it was found that a concentration of 3·2 g l−1 lyophilised Saccharomyces cerevisiae baker's yeast stopped cavitation in the ultrasound field. Then, by using multiples of the aforementioned concentration, the acoustic phenomena occurring in the ultrasound field were monitored and, simultaneously, the survival dynamics of the yeast cells were examined. Physical parameters of the ultrasound field had an essential effect on the acoustic phenomena formed in the sound field and on the threshold levels of their formation.