## 3 The Influence of Ultrasound on the Physical and Chemical Properties of Juices
Moreover, the results of the research indicate that properly set parameters of the ultrasonic process in cooperation with degassing agents lead to a significant change in the content of naringin in pomelo juice. And as it is well known, naringin is the main flavonoid, having a wide range of pharmacological activity, including increasing lipolysis, lowering cholesterol and anti-inflammatory, anticancer and antiseptic effects [32; 33; 34; 35]. Improving the effectiveness of new cost-effective technologies in preserving the overall quality characteristics and antioxidant properties of fruit juices is of great interest. The team of Margean et al. [36] examined the effect of pasteurization (80 \({}^{\circ}\)C, 2 min) and high-power ultrasonic treatment (50% amplitude--57.5 \(\upmu\)m and 70% amplitude--80.5 \(\upmu\)m for 5 and 10 min) on the quality of red grape juice. The researchers analysed the processed juice in terms of physicochemical aspects, with particular emphasis on the content of phenolic compounds or L-ascorbic acid. In addition, the authors verified the samples in terms of microbiology. The results of the analyses showed that the samples subjected to pasteurization and sonication for 10 min with an amplitude of 70% had a similar level of total phenol content. On the other hand, the sonicated juice was distinguished by a higher content of L-ascorbic acid compared with the thermally preserved juice. Similar results were obtained for pH, total soluble solids and titratable acidity. The conducted analyses also indicated that the US influenced the inactivation of microorganisms, which may be an alternative method to traditional pasteurization in the juice industry. In addition, it has been proven that, compared to pasteurization, ultrasonic treatments with an amplitude of 70% were more effective than those with an amplitude of 50% in terms of inactivating the microorganisms concerned. In general, the authors of this study determined that to achieve higher levels of flavonoids, such as rutin, quercetin, epicatechins, kaempfer and resveratrol, treatment with an amplitude of 70% for 5 min is recommended. On the other hand, the ultrasonic process conducted at an amplitude of 70% for 10 min turned out to be the most effective in reducing microorganisms and achieving the highest content of L-ascorbic acid and total polyphenols, including hydroxycinnamic acids such as ferulic acid and caffe acid. The analyses carried out by Yikmus [37] present similar results and relationships as in the previously described studies. However, in this case, the aim of the experiment was to examine the effect of ultrasonic treatment (4, 8, 12 and 16 min) and pasteurization on pH, titratable acidity, Brix, colour, lycopene, ascorbic acid, total phenol concentration, total flavonoid concentration, antioxidant activity, sensory properties and microbiological safety in red watermelon juice and yellow watermelon juice. And as the research showed, the Brix values and titratable acidity did not change statistically significantly after ultrasonic treatment (\(p>0.05\)). Interestingly, there was an increase in lycopene content, phenol concentration, flavonoid concentration and antioxidant capacity after 16 min of US treatment. The applied ultrasonic process had an unfavourable effect on the concentration of ascorbic acid, reducing its content in comparison to control samples (not subjected to any treatment). However, these losses were not as high as in the case of pasteurization. Importantly, the organoleptic evaluation showed that the juices after ultrasonic treatment did not lose their sensory attractiveness. The growing consumer demand for healthy, natural food products prompts scientists and producers to look for new preservation methods that will preserve the high quality and nutritional value of food, including juices. The positive impact of ultrasonic treatment was presented by Ruiz-De Anda et al.