Comparison of the effect of ultrasonic and thermal pasteurization on total phenol content and microbial load of sour cherry juice

Non-thermal methods can be used to reduce the adverse effects of conventional thermal pasteurization on food. The purpose of this study was to investigate the ultrasound method regarding the effect of the three variables of ultrasound power (10, 105, and 200 watts), ultrasound temperature (0, 30, and 60 °C), and ultrasound duration (2, 6 and 10 min) on microbial load as well as total phenol content of sour cherry juice. According to the results, the most effective treatment in preserving the quality characteristics and the highest phenol content of all sour cherry juice samples was the pasteurized treatment by ultrasonic method with 10-watt power, 0 °C, and 6 min. It was assumed that by increasing the ultrasound power from 10 to 200 watts, the ultrasound temperature from 0 to 60 °C, and the ultrasound duration from 2 to 10 min, the total microbial count and the populations of coliforms, and mold and yeast decreased significantly (p <0.05) in the pasteurized cherry juice. Ultrasound pasteurization of cherry juice at the power of 109 watts, 60 °C and 9.5 min had the best results in terms of preserving phenolic compounds and reducing microbial load. The results revealed no significant difference between the microbial load of pasteurized cherry juice with the two methods. In terms of bioactive compounds and quality properties, the optimal ultrasonic treatment was more favorable than the pasteurized sample at 90 °C for 30 seconds.