The Effect of Thermal Sonication on the Chemical Properties of Red Grape Juice Compared to the usual Pasteurization Method

Thermal pasteurization destroys bioactive compounds. Therefore, there is a need for a technique that provides microbial stability and stability while preserving biologically active compounds in grape juice. In recent years, the application of ultra-sonication in food processing has been considered for its ability to deactivate microorganisms with very little or no effect on bioactive compounds and nutritional properties of food. Ultrasound is considered as one of the potential non-thermal pasteurization techniques in the production of juices and is an effective method for maintaining the qualitative properties of juices. These properties have the advantage of thermal pasteurization. The purpose of this study was to investigate the effect of thermal ultrasound in comparison with the usual pasteurization method on bioactive compounds and some characteristics of red grape juice (Brix, pH, acidity, vitamin C, phenolic content, antioxidant properties and anthocyanin content).

In this research, the red grape juice was prepared from the fruit. The treatments were: controlled sample (without treatment), pasteurized sample (90 °C,30˝), heated sample at 60 °C for 4,8,12 min, ultrasound sample without heating for 4,8,12 min with amplitudes of 24.4, 42.7, 61 μm, ultrasound sample with heating (60 °C) for 4,8,12 min with 24.4, 42.7 and 61 μm amplitudes. The effect of treatments on Brix, pH and acidity, phenilic content, ascorbic acid content, antioxidant activity and anthocyanin content of the samples were investigated.

According to the results, the treatments did not have a significant effect on the pH, pH, and acidity of red grape juice. Pasteurization treatment caused the greatest reduction in the qualitative characteristics of the samples. The highest percentage of degradation of ascorbic acid content in red grape juice was 28.2% which was related to pasteurization treatment, and high temperatures at 60 ° C and long duration also had the most significant decrease in ascorbic acid compared to other treatments. The highest phenolic content was observed in treatment with temperature of 25 ° C and duration of 4 minutes with intensity 61 μm. The antioxidant activity of juice was significantly reduced by pasteurization and high temperatures with high levels. The highest antioxidant activity was related to treatment at 25 ° C for 8 minutes and 61 μm intensity, which increased antioxidant activity compared to control sample of 16.4%. Pasteurization treatment reduced 7.4% of the anthocyanin content of red grape juice and at high levels of sonication, increasing the duration and treatment temperature had a negative effect on the content of anthocyanin and reduced it to 7.9%.

According to the results of this study, it can be stated that pasteurization treatment in most cases had a negative effect on the qualitative traits of red grape juice and by using thermosonication in producing red juice at lower temperatures than pasteurization, higher qualitative traits can be achieved. Therefore, the use of average values of ultrasound intensity (42.7 μm) at 60 ° C for red grape juice is recommended.