Combined Effect of Ultrasound and Mild Temperatures on the Inactivation of E-coli in Fresh Carrot Juice and Changes on its Physicochemical Characteristics

The combination of ultrasound and mild temperatures to process fruits and vegetables juices is a novel approach that is showing promising results for microbial inactivation and preservation of bioactive compounds and sensory attributes. This study centers on investigating the inactivation of Escherichia coli (ATCC 11755) in carrot juice as a result of the combined effect of ultrasound (24 kHz frequency, 120 m, and 400 W) with temperature (50, 54, and 58 degrees C) and processing time (0 to 10 min). In addition, the possible changes in physicochemical properties and the retention of bioactive compounds after processing were analyzed. Microbial inactivation with ultrasound treatment at 50 degrees C resulted in 3.5 log reduction after 10 min, whereas at 54 degrees C almost 5 log reduction was attained in the same period of time; meanwhile, for treatment at 58 degrees C, no viable cells were detected (> 5 log reduction) after 2 min. There was no significant difference (P > 0.05) on pH (6.80 to 6.82), degrees Brix (8.0 to 8.5), titratable acidity (0.29% to 0.30%), total carotenoid (1774 to 1835 mu g/100 mL), phenolic compounds (20.19 to 20.63 mu g/mL), ascorbic acid (4.8 mg/100 mL), and color parameters between fresh and ultrasound treated samples at the studied temperatures. To predict the inactivation patterns, observed values were tested using 3 different general models: first-order, Weibull distribution, and biphasic. The Weibull and biphasic models show good correlation for inactivation under all processing conditions. Results show ultrasound in combination with mild temperature could be effectively used to process fresh carrot juice providing a safe product without affecting physicochemical characteristics.