## 1 Introduction
[18], which showed that apple leaves infected with _Venturia inaequalis_ fungi, causing apple scab, had a 6-fold higher concentration of flavonoids and chlorogenic acid compared to uninfected leaves. Also, [PERSON] et al. [16] showed that after the inoculation of _Erwinia amylovora_, the phloretin content increased at a higher rate in resistant cultivars, although the initial concentrations of phloridzin and phloretin in the leaves were similar. The type of crop used is also important. Apple leaves from organic farming have a 10-20% higher total polyphenol content than leaves from trees in an integrated farming system. Apples from organic production also have a higher content of polyphenols, including hydroxycinnamic acid, flavanols, dihydrochalcones, and quercetin, than fruits grown in integrated cultivation [19]. Phloridzin is the dominant component of polyphenols in apple leaves. It constitutes approximately 80% of all identified phenolic compounds in this raw material. Phloridzin has a wide range of biological effects: it inhibits the growth of cancer cells [20], improves memory [21], and helps prevent bone fractures [22]. One of the most important and beneficial properties of phloridzin is the possibility of using it for the prevention and treatment of type 2 diabetes. The activity of phloridzin in this case involves inhibiting the absorption of glucose in the small intestine, which reduces its concentration in the plasma. This process has no effect on the level of insulin in the blood. All this contributes to weight loss, which is one of the most important factors in preventing diabetes [23; 24; 25]. Phloridzin belongs to the group of dihydrochalcones and is formed from phloretin as a result of the glycosylation reaction caused by the enzyme dihydrochalcone 2-O-glucosyltransferase [26]. The content of phloretin in apple leaves is much lower than that of phloridzin, but compared to its glucoside, it has an antioxidant effect that is up to 18 times stronger. It inhibits inflammatory processes and lipid oxidation to a much greater extent, but to a lesser extent, it inhibits the transport of glucose into cells [27]. In addition to flavonoids, the polyphenol composition of apple leaves also includes phenolic acids. Among them, chlorogenic acid is the most abundant [1; 3; 10]. Chlorogenic acid has strong antioxidant, anti-inflammatory, anti-atherosclerotic, and cholesteric properties, and it also inhibits the growth of fungi and bacteria. Additionally, chlorogenic acid has antiviral activity and prevents the negative effects of UV radiation and is important in the chemoprevention of cancer [28]. Its undoubted advantage is the inhibition of both the initiation and progression of cancer, while, for example, quercetin only prevents the initiation [29]. It is worth paying attention to the possibility of using chlorogenic acid in the treatment of mental illnesses. Studies have been conducted on mice that have shown that chlorogenic acid has a neuroprotective effect. It protects against anxiolytic and depressive processes and also increases communication between neurons, thus preventing neurodegenerative diseases, e.g., Alzheimer's disease [30]. For each raw material and substance that we want to extract, the extraction method, the appropriate solvent, and the detailed parameters of the entire process must be matched [31]. When extracting polyphenols from plant raw materials, the best results are achieved by using a mixture of solvents, e.g., water with ethanol and an increased extraction temperature. However, it is crucial to limit the access of oxygen as much as possible because polyphenols are easily oxidised [32]. Data collected by [PERSON] et al. [1] show that the yields of phenolic compounds recovered through extraction are significantly dependent on the extraction procedure, but they also vary between different cultivars. There are various methods for extracting phenolic compounds, such as leaching-out extraction [33].