Bioactive compounds in different hazelnut varieties and their skins

Bioactive profiles of hazelnut skins belonging to fourteen hazelnut varieties were identified. Concentration of phenolic compounds, flavonoids and phenolic acids in soluble free, conjugated soluble and insoluble bound fractions together with their total concentrations were presented. In addition, tocopherol content and total antioxidant capacity of hazelnuts and their skins were revealed. Concentration of total phenolic compounds ranged between 51.9 and 203.1 mg gallic acid equivalent/g of skin among varieties, which is in accordance with the total antioxidant capacity. Total flavonoid content was almost 60% of the total phenolic compounds. Flavonoids and phenolic acids were found to be concentrated mostly in the conjugated soluble fraction. Tocopherol contents of hazelnut skins ranged from 226 to 593 mu g/g, and alpha-tocopherol was the most abundant. Total antioxidant capacity was between 309 and 1375 mu mol Trolox equivalent/g of hazelnut skins, which is more than 100 times higher than for hazelnuts without the skins. (C) 2015 Elsevier Inc. All rights reserved.