Activity guided fractionation of pomegranate extract and its antioxidant, antidiabetic and antineurodegenerative properties

Pomegranate (Punica granatum L.) peel is a rich source of polyphenols, especially tannins, and concentrations of these compounds may be influenced by extraction processes. This study was aimed to examine phenolic composition and biological activities of pomegranate peel 70% ethanolic extract and its fractions (petroleum ether, ethyl acetate, butanol and water) obtained by liquid/liquid extractions. Fractions were analyzed for polyphenolic content and the highest total phenolic content was obtained in ethyl acetate fraction (200.9 mg gallic acid equivalent/g). This fraction had the highest amounts of gallic acid and ellagic acid, while water fraction contained the highest contents of punicalin and punicalagin. Antioxidant activity was evaluated by four different methods, and butanol and ethyl acetate fractions were the most active in 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis (3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS) assays, whereas water fraction showed the strongest activity in ferric reducing antioxidant power (FRAP) and β-carotene tests. All fractions showed better inhibitory effect on α-glucosidase, with inhibition concentration IC50 = 0.26-4.57 μg/mL, than α-amylase (IC50 = 23.6-284.3 μg/mL), and the most active was ethyl acetate fraction. Antineurodegenerative activity was tested using acetylcholinesterase (AChE) and tyrosinase (TYR) inhibitory activity assays, and the most effective inhibitor of both enzymes was 70% ethanolic extract. Pomegranate peel could be considered as a valuable agro-industrial waste product which could be used as low-cost natural source of biologically active compounds.