Phenolic compound quantification and antioxidant activity determination in ethanol extracts of apple pulp and peels

Apple (Malus domestica Borkh.) is one of the most important fruit crops in temperate regions of the world. [11] The worldwide production of apples is increasing and in 2012 it reached 76.38 t. of apple crop a year [4]. Apples are a potential source of carbohydrates, minerals, dietary fibers and phenolic compounds. Phenolics that are found in apples are organic substances, which possess antioxidative properties which are particularly beneficial to human health. Epidemiologic research links apple consumption with decreased incidence of various forms of cancer, cardiovascular disorders, asthma and diabetes [2, 3, 6]. The aim of this research was to evaluate the total content of phenolic compounds, flavonoids, proanthocyanidins and the antioxidant activity in apple peels and pulp of six apple cultivars (‘Ligol’, ‘Connel Red’, ‘Aldas’, ‘Auksis’, ‘Rajka’, ‘Lodel’) by using spectrophotometric methods. Apple peels and pulp were separated, cut into pieces, lyophilized and ground to a powder. Extraction was performed for 20 min with 70 % (v/v) ethanol at 40°C using ultrasound assisted extraction [7]. In order to determine the total amount of phenolic compounds Folin-Ciocalteu method [9] was used. The total flavonoid content of apple peels and pulp was evaluated by using the reaction with aluminum (III) chloride [10]. The DMCA assay [5] was used to quantify proanthocyanidins. To determine the antioxidant activity of the ethanolic extracts, FRAP [1] and ABTS [8] spectrophotometric methods were used. The total soluble phenolic compound concentration was expressed as milligrams of gallic acid equivalents (GAE) per gram of absolutely dried lyophylisate. It varied from 19.24 mg GAE/g in pulp of cultivar (cv.) ‘Rajka’ to 26.03 mg GAE/g in pulp of cv....[...].