IN VITRO AND IN VIVO ANTIOXIDANT POTENTIAL OF PHENOLIC EXTRACTS OBTAINED FROM HAZELNUT SKIN BY-PRODUCTS

Recently, a growing interest in replacing synthetic antioxidants with natural ones has fostered research on the screening of plant materials in order to evaluate new antioxidants. Phenolic compounds are the major plant metabolites with antioxidant properties; many of these can be potentially exploited as antioxidant agents and nutraceuticals. The aim of this research was to evaluate the antioxidant potential of a crude phenolic extract obtained with 80% ethanol from hazelnut (Corylus avellana L.) skin by-products by means of an improved extraction procedure. The extract was screened for in vitro antiradical, reducing and chelating activity. Moreover, an in vivo test carried out on rats was performed. The long-term stability of the extract dissolved in ethanol was tested during storage for six months at room temperature and under refrigerated conditions. The results showed that the defatted hazelnut skin by-product is an excellent source of phenolic antioxidants which are natural and very efficient. The defatted skins provided a high yield in the crude extract (over 30%). The extract was characterized by a very high phenolic content (743.5 mg gallic acid equivalent/g d.w.), high antiradical efficiency (superior to pure BHT, BHA, Trolox and -Tocopherol), Fe(III) reducing activity and Fe(II) chelating capacity. The in vivo study showed an evident biological activity of the extract, which was able to improve the antioxidant potential of plasma in rats. The results of the storage tests demonstrated that the hazelnut skin extract can be kept at room temperature for several months maintaining its antioxidant capacity at a high level. Because of their potential antioxidant and nutraceutical properties, phenolic extracts derived from hazelnut skin could satisfy the demand for new natural products in the preparation of innovative foods and beverages with a high dietetic/functional value.