Modelling of yeast inactivation in sonicated tomato juice.

Power ultrasound is recognised as a potential non thermal technique to inactivate microorganisms pertinent to fruit juices. In this study, the effect of sonication on the resistance of yeast (Pichia fermentans) in tomato juice was investigated. Tomato juice samples were sonicated at amplitude levels ranging from 24.4 to 61.0mum at a constant frequency of 20kHz for different treatment times (2 to 10min) and pulse durations of 5s on and 5s off. Significant reductions (p<0.05) were observed at higher amplitudes and processing times. Yeast inactivation was found to follow the Weibull model with a high regression coefficient (R(2)>0.98) and low RMSE (<0.51). The desired 5 log reductions (D(5) value) and shape factors were found to correlate exponentially with amplitude level. Results presented in this study show that sonication alone is an effective process to achieve the desired level of yeast inactivation in tomato juice.