## 3 The Influence of Ultrasound on the Physical and Chemical Properties of Juices
[38] in their study, the aim of which was to determine the effect of ultrasound on the physicochemical properties of two types of juices--orange and celery stalk juices. The juice samples were sonicated in the so-called ultrasonic bath (20 kHz, 20 \(\pm\) 5 \({}^{\circ}\)C) for 0, 15, 30, 45, 60, 75 and 90 min. Thereafter, the articles were stored in the dark for 24 h at 4 \({}^{\circ}\)C. After this time, the juices were analysed, showing that the ultrasonic treatment had a significant (\(p<0.05\)) effect on the number of bioactive compounds and antioxidant properties of the juices as early as 15 min into the process. The best results were achieved for 45 min of US treatment, where a 13% increase in the total phenol content, a two-fold increase in the content of flavonoids and a 17% increase in antioxidant activity were observed. The method of processing did not affect some physicochemical properties of juices, such as total soluble solids, pH and titratable acidity. Changes in colour after ultrasonic treatment were observed, showing significant correlations with the increase in the content of bioactive compounds and antioxidant activity. To sum up, properly conducted ultrasonic treatment provides the opportunity to obtain juices with increased health-promoting values. In contrast, a study by Yikmus et al. [37] showed that sonication, compared to other unconventional methods, still needs to be improved. The researchers' analyses were aimed at assessing the impact of the use of high-pressure processing (HPP), ultrasound (US) and pulsed electric field (PEF) on changes in the physicochemical and phytochemical properties of strawberry juice. HPP processing at 300 MPa (1 min), US at 55 \({}^{\circ}\)C (3 min) and PEF at 35 kV/cm (27 \(\mu\)s) were compared to traditional thermal pasteurization (72 \({}^{\circ}\)C, 15 s). No significant differences were observed in total solubles (7.83-8.00\({}^{\circ}\)Brix), titratable acidity (0.79-0.84 g/100 mL) or pH (3.45-3.50; except for sonication) between treated and untreated samples (\(p>0.05\)). In contrast, HPP and PEF technologies significantly increased the retention of total TPC phenol content (4-5%), increased TAC total anthocyanin content (15-17%) and RSA free radical scavenging activity (18-19%) compared to unprocessed strawberry juice samples. In the case of the US process, the positive effects of the research were not so noticeable. No changes in TPC were observed, and the content of TAC and RSA increased by less than 9% and 14%, respectively, compared to the control juice. Hence, the conclusion was that the samples treated with HPP and PEF had similar properties in terms of the content of phytochemicals, which was higher in these samples than in sonicated, thermally pasteurized and untreated samples. More research should be carried out, and different parameters of ultrasonic treatment in juice processing should be used to obtain satisfactory analysis results. Santhirasegaram et al. [39] compared the quality of freshly prepared mango juice after sonication and heat treatment. The product samples were sonicated for 15, 30 and 60 min at 25 \({}^{\circ}\)C, 40 kHz (using an ultrasonic cleaning bath: Branson Model 3510 Ultrasonic Cleaner, CT, USA). Pasteurization was carried out in a covered water bath (Mermmert, Germany) at a temperature of 90 \(\pm\) 1 \({}^{\circ}\)C for 30 s (mild heat pasteurization) and 90 \(\pm\) 1 \({}^{\circ}\)C for 60 s (high-heat pasteurization). The treatments used did not result in any significant changes in pH, total soluble solids or titratable acidity. Interestingly, sonication lasting 15 and 30 min resulted in a significant improvement in selected quality parameters (increase in the extraction of carotenoids and polyphenols), except for the colour and content of ascorbic acid, compared to freshly squeezed (control) juice. In addition, an increase in radical scavenging activity was observed in all sonicated juice samples regardless of the treatment time.