Investigation of nutritional and microbial properties of ultrasound pretreated sour cherry juice

Non-thermal methods can be used to reduce the negative effects of conventional thermal pasteurization on food. In this study current research was to examine the effect of the ultrasonic process on the pasteurized sour cherry juice and compare the optimal sample with the thermally pasteurized one. The effect of non-thermal ultrasonic pasteurization at three powers (10, 105 and 200 W), temperatures (0, 30 and 60°C) and time intervals (2, 6 and 10 min) on the amounts of anthocyanin, pectinase, IC 50 value and microbial load of sour cherry juice was examined, and it was compared with the thermally treated sample (90°C for 30 sec). In order to design, analyze the results and optimize the pasteurization conditions, the response surface method (Box-Behnken) in Minitab ver. 16 was used. The results displayed that by increasing the power of ultrasonic from 10 to 200 W, the temperature from 0 to 60°C and the time from 2 to 10 min, the amounts of anthocyanin and pectinase as well as microbial load of pasteurized sour cherry juice (p≤0.05) decreased significantly and IC 50 increased significantly (p≤0.05). The sour cherry juice pasteurization conditions by ultrasonic technique were optimized to achieve the maximum amount of anthocyanin and pectinase and the minimum IC 50 value and total count at ultrasonic power of 115 W, temperature of 40°C and time of 3 min. Given the obtained results, it could be concluded that the use of ultrasonic waves could reduce the microbial load of sour cherry juice and also preserve the antioxidant properties of the product effectively. Therefore, the ultrasonic process for the pasteurization of fruit juices can be a suitable alternative for conventional heat treatment.