TOTAL ANTIOXIDANT CAPACITY AND PHENOLIC CONTENTS OF TURKISH HAZELNUT (CORYLUS AVELLANA L.) KERNELS AND OILS

Abstract

Hazelnut (Corylus avellana L.) has an important nutritional value comprising a rich variety monounsaturated fats and vitamins, with a good level of dietary fiber and a high content of minerals. In the present work, phenolics in the aqueous systems were extracted from 15 different dry Turkish hazelnut kernels without skin, cultivated in Ordu province of Turkey, with 80% (v/v) MeOH/H2O. The aqueous methanolic extracts of hazelnut kernels and of oil samples were examined for their phenolic contents (Folin-Ciocalteau), total antioxidant capacities (TAC) (CUPRAC and ABTS/persulfate) and antiradical activities (2,2-diphenyl-1-picrylhydrazyl, DPPH). The individual free phenolic constituents (mainly phenolic and hydroxycinnamic acids) found in hazelnut kernels were also identified and quantified by high-performance liquid chromatography (HPLC). Among the dry hazelnut cultivars, Mincane showed the highest TAC (TACCUPRAC: 2.98 +/- 0.37 mmol TE/g) (n = 3). This work is the first application of the CUPRAC method to Turkish hazelnut antioxidant characterization and of CUPRAC and DPPH assays to hazelnut oils. PRACTICAL APPLICATIONS Hazelnut plays a major role in human nutrition and health because of its fat, protein, carbohydrate, dietary fiber, vitamins, minerals and phenolic content. This paper presents the findings of a comprehensive investigation of phenolic contents, total antioxidant capacities (TAC) and free radical scavenging activities of 15 different dry Turkish hazelnut (Corylus avellana L.) kernels cultivated in Ordu province (in the Black Sea Region) of Turkey for the first time. The TAC and phenolic contents of Turkish hazelnuts reported in this study are believed to contribute to human nutrition and health in the selection of hazelnut-rich diets for natural antioxidant supplementation.