## 4 Conclusions  
Apple leaves are not routinely used in the industry, but their easy availability in Poland and the presence of desirable compounds with antioxidant and health-promoting properties indicate that they are an excellent raw material for use in the food, cosmetics, and pharmaceutical industries. Extracts obtained from apple leaves can be used as antioxidants, protecting food against undesirable oxidative changes. The results obtained in this study clearly indicate that apple leaf extracts are characterised by a high content of polyphenols, comparable to, among others, black tea. Water-alcoholic extracts from apple leaves were characterised by a higher antioxidant capacity and polyphenol content than water extracts. The best solvent was a mixture of water and methanol (80%). The type of solvent and the extraction method used had a significant impact on the content of total polyphenols in apple leaf extracts, while the apple cultivar also had a significant impact on the content of specific phenolic compounds in the extracts. In apple leaf extracts, the dominant phenolic compound was phloridzin. The highest content of phloridzin was found in water-methanol extracts from the leaves of the Ligol cultivar obtained with ultrasound-assisted solvent extraction (UAE). Phloridzin, which is the compound found in the largest amounts in apple leaves, had a positive effect on glucose uptake. Thus, apple leaf extracts have an interesting potential use for the enrichment of food products with phloridzin. They can also be successfully used as an ingredient of dietary supplements, including ones that support weight loss. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14083252/s1](https://www.mdpi.com/article/10.3390/app14083252/s1)]([https://www.mdpi.com/article/10.3390/app14083252/s1](https://www.mdpi.com/article/10.3390/app14083252/s1)), Table S1: Validation parameters of the HPLC-DAD analysis. Conceptualization, A.C. and J.L.P. ; methodology, A.C. and J.L.P. ; software, A.C. and J.L.P. ; validation, A.C. and J.L.P. ; formal analysis, A.C. and J.L.P. ; investigation, A.C., Z.J., and J.L.P. ; resources, A.C.; data curation, J.L.P. ; writing--original draft preparation, A.C.; writing--review and editing, A.C. and J.L.P. ; visualization, J.L.P. ; supervision, A.C.; project administration, A.C.; funding acquisition, A.C. All authors have read and agreed to the published version of the manuscript. Funding: This study received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available on request from the corresponding authors. Conflicts of Interest: The authors declare no conflicts of interest. References  
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