The Effect of High Power Ultrasound and Cold Gas-Phase Plasma Treatments on Selected Yeast in Pure Culture

High power ultrasound (US) and cold gas-phase plasma (CP) are non-thermal processing technologies that maybe used in food processing industry. The main objective of this research was to study the effect of both treatments on selected yeasts (Rhodotorula spp. 74 and Candida spp. 86) in pure culture. Samples were treated by ultrasound with 57.50-, 86.25- or 115-mu m amplitude, for 3, 6 or 9 min at 20 A degrees C, and 40 or 60 A degrees C in the case of thermosonication. For cold gas-phase plasma treatments, samples were treated at a gas flow of 0.75, 1 or 1.25 L min(-1), treatment time of 3, 4 or 5 min, and sample volume of 2, 3 or 4 mL. Each technology has its own advantages and is able to give the best effect on the desired target product. The experiment was designed using central composite design (CCD), and results were analysed and presented using response surface methodology (RSM). The greatest reduction of yeasts was observed after ultrasound treatments at 60 A degrees C (thermosonication) and after plasma treatments, after the longest treatment time (5 min) and the lowest sample volume (2 mL). For high power ultrasound treatment, reduction in the number of yeast cells (N) can be attributed to elevated temperature (60 A degrees C), cavitation and free radical formation. For plasma treatment, the inactivation can be attributed to UV radiation and plasma reactive oxygen species (ROS).