# Effect of Extraction Method and Thermosonication on Apple Juice Quality
## 1 Introduction  
Apples (_Malus domestica_) are a source of numerous valuable phenolic compounds with documented antioxidant, antibacterial, antiviral, anti-inflammatory, antiallergic, and even anticancer properties [1, 2]. This fruit is typically consumed fresh or processed into juice. Under industrial conditions, juices are preserved primarily with the help of thermal methods. Research has demonstrated that the use of these method influences the degradation of polyphenols and reduces nutritional value [3]. An interest by consumers in high-quality foods with minimal processing has been observed in recent years. Juices with several-day best-before dates are an example of this kind of food. Eliminating microbial hazards creates an issue in the production of several-day juices. In order to preserve these juices, light pasteurization, a pulsed electric field, and combined methods are used [4]. Despite the systems of food safety assurance in use, cases of poisoning caused by juice consumption are still recorded around the world [5, 6, 7]. Considering the low degree of processing, juice can form reservoirs of natural microfloraand be a carrier of undesirable microorganisms. Microbial contamination occurs at the raw material cultivation stage, where there is exposure to contamination from soil, water, and even air, as well as during transport and storage [8]. It has been proven that increased use of natural fertilizer, commonly in the cultivation of fruits and vegetables on organic farms, is the source of pathogens in numerous cases. The list of microorganisms present will differ depending on the season and climatic changes [9]. Ultrasound has been increasingly used in food processing in recent years [10; 11]. High-intensity and high-power active ultrasound techniques have the capacity to interact with raw material (matter) and can modify the course of physical or chemical processes. Ultrasound can be used to increase pressing efficacy [11], to support the process of extracting different components (herb extracts, polyphenols, aromatic compounds, polysaccharides) [12; 13; 14], and to improve the quality of obtained products [15]. Some authors have studied the potential of ultrasound for use in the preservation of fruit juice [16; 17]. However, some researchers have suggested that ultrasonic treatment at low temperatures is not very efficient for inactivation of some microorganisms [18]. Therefore, in many cases ultrasound is combined with moderate heat, a process known as thermosonication [19; 20]. This method increases the inactivation of microorganisms by the combined effects of heat and cavitation [21; 22; 23; 24]. The efficiency of sonication can also be enhanced through gamma irradiation [25], the use of high pressure [26], or the introduction of additional substances [25]. Despite numerous studies, knowledge on the application of active ultrasound (US) to preserve fresh juice is insufficient. From a practical standpoint, the method of thermosonication is rather expensive, and researchers have attempted to increase, reduce, or stabilize juice temperature by introducing an additional cooling-heating system [22; 27]. In our study, we propose using the heat generated by ultrasound to heat tested juice samples, which in industrial practice would considerably reduce the costs associated with the energy consumption of the thermosonication process. Another issue in the production of minimally processed fruit juices is selecting the method of obtaining them. Typical methods include pressing with the use of piston presses, cylinder presses, screw presses, or centrifuges (decanters). The obtained juice is characterized by variable physical and chemical properties, which may influence the presence and development of microflora. Thus far, no studies have been carried out on the influence of the extraction method on the microorganism content in juice.