Low frequency thermo-ultrasonication of Saccharomyces cerevisiae suspensions: Effect of temperature and of ultrasonic power

The combined effect of low frequency ultrasound (20 kHz) with temperature on the survival of a strain of Saccharomyces cerevisiae suspended in water was studied. The treatment temperatures tested were 45 degrees C, 50 degrees C and 55 degrees C; the actual ultrasonic powers tested were 50 W, 100 W and 180 W. Application of ultrasonic waves at a non-lethal temperature did not display a deactivating action; a higher effect of ultrasound at higher temperatures was observed, and the synergy between ultrasound and temperature was confirmed. These results proved that the ultrasonic waves do not destroy the yeast's cells; they damage them, thus increasing their sensitivity to heat. The existence of an optimal ultrasonic power for a maximal deactivating effect was shown, and was found to have a value of around 100 W (actual power). (C) 1997 Elsevier Science S.A.