Effect of sonication on colour, ascorbic acid and yeast inactivation in tomato juice

Power ultrasound is recognised as a potential non-thermal technique to inactivate micro-organisms pertinent to fruit juices. In this study tomato juice was sonicated at different amplitude levels (24.4–61.0 μm) at a constant frequency of 20 kHz for treatment times (2–10 min) and pulse durations of 5 s on and 5 s off. Hunter colour values ( L ∗, a ∗ and b ∗), pH, °Brix, titratable acidity, ascorbic acid and yeast inactivation were measured. No significant differences ( p < 0.05) in pH, °Brix or titratable acidity were observed. Regression modelling was used to investigate the main effects of amplitude level and treatment time. Prediction models were found to be significant ( p < 0.05) with low standard errors and high coefficients of determination ( R 2 ). Model predictions for critical quality parameters of Hunter colour values ( L ∗, a ∗ and b ∗), ascorbic acid and yeast inactivation were closely correlated with the experimental results obtained.