Effect of thermosonication treatment on quality parameters and shelf life of apple juice

In the present study, ultrasound process (thermosonication) was applied to apple juice at different temperatures (55, 65 and 75°C), 24 kHz frequency and 85 μm amplitude level. The change in quality parameters of apple juice during 12 weeks was investigated. Quality parameters of apple juice considered in the present study were polyphenol oxidase activity, turbidity, pH, brix, colour properties, phenolic content and antioxidant activity. Polyphenol oxidase (PPO) enzyme was completely inactivated by the ultrasound application carried out at 75°C. Regarding the process performed at 65°C, PPO enzymes lost their activity exactly after 6 week storage of the samples. Ultrasound process performed at 65°C for 12 min caused to remarkable increase in turbidity level (92 times higher than control samples) and turbidity stability (9 times higher than control sample) when compared with the those of control sample which was produced without ultrasound process. Ultrasound process applied at temperature and time levels higher than 65°C and 12 min, respectively. It was also observed that higher level of temperature and time applications resulted in slight decrease in turbidity quality of the samples. Ultrasound process applied at 65°C and 12 min caused to increase in L* value of the sample approximately 19% times comparing with the sample and chroma value significantly increased (25% times). Also the total phenolic content and antioxidant activities of the apple juices which are applied by ultrasound are higher than apple juices which are applied by conventional heat treatment. The results of the present study indicated that the quality and functional parameters of apple juice were positively influenced by ultrasound process and the effectiveness of the process was depend on the temperature level. Combining ultrasound with temperature is up-and-coming process for the fruit juice industry.