Evaluation of the phenolic profile and antioxidant activity of table grapes and unfermented derivatives

In the last years, the interest in unfermented beverages and table grapes, as potential sources of phenolic compounds, has considerably increased. Among the health-promoting substances contained in these food and beverages, flavonoids seem the most interesting. The aim of this study was the application of in vitro methods for the characterization of the phenolic fraction from different red and white table grapes varieties, and, in parallel, the evaluation of their antioxidant activity. The merhods were: 1) Folin-Cocalteau's assay for the quantification of total polyphenol content; 2) the pH differential method for the quantification of total anthocyanin content; 3) High Performance Thin Layer Chromatography for separation of phenolic substances and assessment of their antioxidant activity. To better understand and support the healthy activity of grapes derivatives, a chromatographic separation and quantification of main active substances was performed by HPLC. Quantitative analysis of the main flavonoids was performed by using a gradient elution and a diode-array detector. The results confirmed that both red and white table grapes contain, in different amount, phenolic compounds with significant antioxidant activity supporting their positive role in the human diet.