*2.2. Polyphenol Extraction*

Polyphenols were extracted from hazelnut skin as described by Locatelli et al. [6]. Prior to extraction, the hazelnut skin was defatted with *n*-hexane using the method described by Özdemir et al. [12]. Defatted hazelnut skins (2 g) were extracted with 50 mL of pure ethanol at 22 ◦C for 1 h in the dark using a VDRL 711 orbital shaker under constant rotatory agitation at 60 rpm. The extract was centrifugated at 2800× *g* for 10 min at 4 ◦C. The solid residue was re-extracted for 30 min with 25 mL of pure ethanol and then centrifuged. The two supernatants were mixed, filtered through a 0.45 μm nylon membrane, and stored in amber vials at −18 ◦C until analysis. All extractions were performed in triplicate.
