Phenolic profile and antioxidant activity of different raisin (Vitis vinifera L.) samples

In the last years, the interest in non-alcoholic grape products, aa potential alternative sources of phenolic compounds, has considerably increased. Raisins are dried grapes largely consumed in the Mediterranean area for the positive pattern of nutrients, and for recent data describing potential benefits on human health. Among the health-promoting substances contained in raisins, flavonoids seem the most interesting. The aim of this study was the application of in vitro methods for the characterization of the phenolic fraction of five samples of raisins, and, in parallel, the evaluation of their antioxidant activity. The methods were: 1) Folin-Cocalteau's assay for the quantification of total polyphenol content; 2) vanillin assay for the measure of flavan-3-ols content; 3) DPPH (1,1,-diphenil-2-picrylhydrazyl) spectrophotometric assay for the assessment of radical scavenging activity; 4) High Performance Thin Layer Chromatography for separation of phenolic substances and assessment of their antioxidant activity; 5) chromatographic separation and quantification of main active substances was performed by HPLC-DAD. Although raisins showed a high variability in their composition, they can be considered as a promising source of phenolic compounds with a significant antioxidant activity for the human diet.