The effects of ultrasound application durations on the rheological properties of tomato (Lycopersicon Esculentum) juice

In this study, effects of ultrasound application durations on the rheological properties of tomato juice were investigated. Tomato juice having 6.18 +/- 0.04 % soluble solid contents was ultrasonicated using a 1500 W ultrasonic processor at a constant frequency of 20 kHz for different application durations (0, 5 and 10 min). The empirical data for tomato juice samples obtained from the viscometer (Brookfield LVDV II Pro, USA) were converted into viscosity function. Rheological properties of juice at 20 degrees C were determined by fitting shear stress-shear rate data to some rheological models (Newtonian, Bingham, Power Law, Herschel Bulkley). It was found that samples showed Non-Newtonian fluid (pseudoplastic) behavior. As the ultrasonic application duration increased the apparent viscosity of the tomato juice increased. Herschel Bulkley model was the best model for all application durations investigated (For raw juice and chi-square (chi(2)) 0.203, root mean square error (RMSE) 0.045, Regression coefficient (R-2) 0.995; for 5 min: chi(2) = 0.219, RMSE = 0.053, R-2 = 0.994 and for 10 min: chi(2) = 0.225, RMSE = 0.056, R-2 = 0.994). Rheological data obtained in this study showed the importance of ultrasonic application duration. Application time should be optimized for ultrasonic processing of tomato juices by considering pumping requirements and changes on quality attributes.