## 3 The Influence of Ultrasound on the Physical and Chemical Properties of Juices
However, sometimes the use of ultrasound alone is not effective enough to decontaminate juices, especially those contaminated with pathogenic bacterial flora. In addition, high ultrasound power levels may adversely affect the nutritional and sensory properties of food [77; 78; 79]. Therefore, Kernou et al. [80] evaluated the survival of _Escherichia coli_ ATCC 25922 in orange juice treated with microwaves and/or ultrasounds. Sonication conducted for 60 min at a frequency of 42 kHz had no significant effect on the reduction in survival rates (1.3-log reduction) of the bacteria under consideration. However, it has been established that this method of pretreatment can increase the effectiveness of microwaves to improve the microbiological quality of the juice. More specifically, a significant reduction (by 8.0 log) was achieved via sonication (42 kHz; 20 min) followed by microwave processing (900 W; 30 s) of the orange beverage. Similar relationships were found by Hosseinzadeh Samani et al. [81] after subjecting cherry juice to microwave-ultrasound treatment. Based on response surface modelling (RSM), the optimal processing conditions were microwave output power, 352.21 W; temperature, 49.94 \({}^{\circ}\)C; ultrasound power, 475.13 W; and exposure time, 6 min. Such parameters resulted in a reduction in the number of _E. coli_ bacteria, while maintaining the amount of vitamin C at the level of 142.5 mg per 100 mL. Unfortunately, it was found that each increase in the power of ultrasounds or microwaves and the extension of the exposure time led to a significant reduction in the content of vitamin C due to its increased oxidation, mainly due to the thermal effect. Microwave processing is fast and can significantly reduce the heating time of the juices. And the hydrodynamic effect of ultrasound on microorganisms has great potential to improve the effectiveness of their elimination. This study contributes to the design and control of effective methods for the inactivation of pathogenic microorganisms and food spoilage agents that can be achieved using combined methods. Satisfactory research results were also obtained through combining ultrasonic and pulsed light treatment in order to obtain good microbiological stability of juice prepared from apples [78]; the use of ultraviolet radiation and ultrasonic treatments to inactivate _Alicyclobacillus acidoterrestris_ spores, also in apple juice [82]; the use of pulsed electric field and ultrasounds on the microbiological quality of graprefruit juice [83]; ultrasound and ozone processing to reduce the number of native microflora in cashew apple juice [84]; high-pressure processing and ultrasound for the preservation of strawberry juice [85]; and ultrasonic treatment with high-voltage cold plasma to ensure better quality and greater stability during carrot juice processing [86]. Ultrasound alone or in combination with mild temperatures (<50 \({}^{\circ}\)C in most cases) is a promising alternative technology for juice preservation. Power ultrasound has been shown to be effective against microorganisms contaminating liquid foods and meets the U.S. Food and Drug Administration's 5-log reduction requirement (pasteurization standards) for certain pathogens contaminating fruit and vegetable juices. This technology has the ability to destroy cell membranes due to the high pressure, temperature and shear forces generated during cavitation. In addition, the inhibitory effect of thermal sonication on the population of microorganisms may result from cavitation and the production of free radicals (H+, O2, OH, HOO) formed as a result of the sonolysis of water molecules present in juices. Free radicals are therefore co-responsible for causing oxidative damage, disrupting microbial cell walls and inhibiting microbial growth by inactivating the enzymatic activity of mitochondria [87; 88; 89]. Where ultrasound alone is not sufficiently effective in achieving high microbial reduction, combining it with treatment methods (temperature, pressure, microwave, pulsed light,ultraviolet, HPP, etc.)