Effect of sonication on viscosity, particle size distribution, turbidity and total phenol of carrot juice

The objective of this work was to investigate the effects of sonication on turbidity, viscosity, particle size distribution and total phenol of carrot juice. Carrot juice samples were sonicated according to a D-optimal design response surface with three factors of sonication temperature (25, 37.5 and 500C), sonication time (10, 20 and 30 min) and sonication power (350, 400w) at a constant frequency of 24 kHz. The results showed that ultrasound temperature (P<0.01) and time (P<0.01) significantly increased the turbidity of carrot juice samples. Also a significant change in particle size distribution was observed in sonicated juice due to cavitation effects. These resultes indicated that the cloud stability of sonicated carrot juice depends not only on pectin methylesteras inactivation but also on particle siz reduction. The highest particle size was observed in heat-treated juices due to heat coagulation of the colloidal materials. Sonication could not make significant alteration in the apparent viscosity of juice at different shear rates ranging between 0.1 and 100s-1, which indicated that the ultrasound or heat treatment juice followed the Newtonian flow behavior. However, the viscosity of heat-treated juice was significantly higher than untreated and sonicated samples. Ultrasound time significantly decreased the total phenolic contents of sonicated samples (P<0.01) but, significant difference was not observed between sonicated and heat-treated or untreated samples. These results suggest that, sonication with mild heat could used to obtain carrot juice with low Particle size and high turbidity, high viscosity and good retention of phenolic component.