## 3 Results and Discussion
### Content of TPC Using the Folin-Ciocalteu Reagent Method
#### 3.1.4 Comparison of the Extracts Tested
Based on the available standards, the following were identified and quantified: epicatechin, rutin, hyperoside, isoquercitrin, phloridzin, and phloretin (Figure 4). Additionally, 4 other quercetin glycosides were identified, including quercetin as well as phloretin xyloglucide and naringenin. According to [PERSON] et al. [46], among quercetin glycosides, in addition to rutin, hyperoside, isoquercitrin, and quercetin, avicularin may also be present in apple leaves. [PERSON] et al. [5] determined phloridzin, phloretin, chlorogenic acid, rutin, and quercetin in methanol extracts of 13 cultivars of apple leaves. [PERSON] et al. [51] observed the phenolic composition (phloridzin,  
Figure 3: Content of total polyphenols in apple leaf extracts obtained using various extraction methods. Abbreviations: SSE—Shaking Solvent Extraction; UAE—Ultrasound-Assisted Extraction; ASE—Accelerated Solvent Extraction. phloretin, chlorogenic acid, and rutin) of the individual parts of apple trees during the vegetation period. [PERSON] et al. [6] determined the following in apple leaf extracts: quercetin, isoquercitrin, rutin, hyperoside, phloridzin, p-hydroxybenzoic acid, and chlorogenic acid. [PERSON] et al. [46], in addition to quercetin, phloretin, phloridzin, and epicateching glycosides, detected catechin, chlorogenic acid, and caffe acid. Additionally, [PERSON] et al. [41] identified neochlorogenic and dicaffeic acid, flavian-3-ols (gallocatechin-glucoside and epigallocatechin), and chalcone, 3-hydroxyphloridine, in apple leaves. [PERSON] et al. [52] also determined another derivative of phloretin among apple leaf chalcones, i.e., phloretin xyloglucoside, which was found in the highest concentration right after quercetin-3-rhamoside. However, in all other works, as well as in [PERSON] et al. [19] and in this study, phloridzin was by far the most abundant among all identified polyphenic compounds in apple leaves. All previously mentioned authors also determined quercetin glycosides, which, after phloridzin, were the most abundant in apple leaves. Among the phenolic compounds identified on the basis of the standard and quantitatively determined, phloridzin was the most abundant in apple leaf extracts, approximately 91.8% (Table 2). Next was quercetin glycoside, isoquercitrin (approx. 4.3%), phloretin (approx. 2.4%), and then epicatechin (approx. 0.7%) and hyperoside (approx. 0.6%). Rutin was the least abundant among the compounds determined (approx. 0.2%). The content of these compounds in the extracts was significantly influenced by the extraction method used, the cultivar of apple leaves, and the type of extract (Tables 2-4). Figure 4: Sample chromatogram of apple leaf extract (at 254 nm). Peaks: 1—(-) epicatechin, 2—rutin, 3—hyperoside, 4—isoquercitrin, 5, 7, 8—quercetin glycosides, 6—phloretin xyloglucide, 9—quercitrin, 10—phloridzin, 11—naringen, 12—phloretin. The content of all phenolic compounds, quantitatively determined using HPLC, was the highest in extracts obtained using ASE. The reason for this was probably the special conditions of this extraction, i.e., high pressure, increasing the extraction efficiency, and the nitrogen atmosphere, which could prevent the oxidation of polyphenols. Indeed, the least discussed phenolic compounds were extracted using the SSE method, by shaking with a solvent. The exception was hyperoside, which was significantly least determined in the extracts obtained using UAE. The longer exposure time of oxygen to the extracted samples (greater exposure to polyphenol oxidation) in the SSE method compared to ultrasound-assisted extraction (UAE) could have resulted in obtaining such results. Differences were observed in the quantitative and qualitative composition of individual polyphenic extracts obtained from different cultivars of apple leaves. This is partly due to genetic conditions and the differences that usually occur between cultivars.