Extraction of natural antioxidants from hazelnut (Corylus avellana L.) shell and skin wastes by long maceration at room temperature

The feasibility of obtaining antioxidant phenolic extracts from hazelnut by-products was investigated by long maceration at room temperature. The hard shells and defatted skins of both whole and chopped roasted hazelnut kernels were studied. Three solvent systems were employed and these included aqueous methanol, ethanol and acetone. Extraction yields as well as phenolic contents varied according to the by-product and the solvent used. Among the studied samples, the skin of whole roasted hazelnuts gave remarkably high extraction yields (about 30%) and extracts with the richest phenolic content (up to 502 mg/g, expressed as gallic acid equivalents).Extracts were screened for antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH)-induced oxidation of linoleic acid in vitro model systems. The extracts from the skin of whole roasted hazelnuts manifested the strongest antioxidant activity, similar or superior to butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) and α-tocopherol, at equivalent concentrations. The presence of hazelnut fragments in the skin residue lowered the yield and the antioxidant activity of the extract. All the extracts were found to be very rich in tannins.