Apple Tree Leaves (Malus domestica Borkh) as a Valuable Source of Polyphenolic Compounds with a High Antioxidant Capacity

Abstract

The aim of the study was to compare the antioxidant activity and polyphenol content in extracts prepared from freeze-dried leaves of three apple cultivars: Ligol, Gala, and Gloster, using different solvents and extraction methods. The content of total polyphenols was determined using the Folin–Ciocâlteu reagent method, and a qualitative and quantitative analysis of polyphenols was performed using the HPLC method. The antioxidant capacity of the extracts was determined using the DPPH radical method. The colour parameters (in the CIEL*a*b system) of the obtained extracts were also determined. The antioxidant activity of apple leaf extracts increased with increasing polyphenol content. Water–alcoholic extracts from apple leaves were characterised by a significantly higher antioxidant capacity and polyphenol content in comparison with water extracts. The best solvent was a mixture of water and methanol (80%). Among the phenolic compounds identified in the extracts, the most common was phloridzin. The highest content of phloridzin (105.0 mg/1 g of dry weight) was found in water–methanol extracts from the leaves of the Ligol variety obtained with ultrasound-assisted extraction. The extracts with the highest antioxidant activity (131.2 μmol of Trolox/1 g of dry weight) and polyphenol content (81.9 mg GAE/1 g of dry weight) were water–methanol from the leaves of the Ligol cultivar, obtained by shaking them with a solvent.