ANTHOCYANIN PROFILE AND ANTIOXIDANT ACTIVITY OF UNFERMENTED GRAPE DERIVATIVES

Since the first observations of the “French paradox”, numerous studies have been developed to test the antioxidant and health-promoting effects of phenolic compounds present in grapes and wine. These findings, together with the negative campaign against alcoholic beverages, have led to a considerable interest in the evaluation of unfermented grape by-products as skin, seeds and juices. These products are also being employed as ingredients of dietary supplements, but in most cases data about the actual polyphenol content are scarce. To support scientifically the biological activity of unfermented beverages and dietary supplements, it is important to know the associated profile of the active compounds. The aim of this study was to evaluate in parallel the antioxidant activity, the total polyphenol content (TPC) and the HPLC anthocyanin profiles of grape derivatives: fresh grape juices and dietary supplements. The antioxidant activity was measured spectrophotometrically at 517 nm after reaction with 1,1-diphenyl-2-picrylhydrazyl free radical. The TPC was determined with the Folin-Ciocalteu colorimetric assay, measuring the absorbance at 765 nm. Anthocyanins (cyanidin, delphinidin, malvidin, pelargonidin, peonidin, petunidin) were analyzed by HPLC using a gradient elution and a diode-array detector. Anthocyanins were identified and quantified in grape derivatives by comparing their chromatographic behaviour with purified standards (retention times and the UV spectra). Among grape juices, the highest value of TPC was 1570.5±1.60 g GA/L (gallic acid equivalent/L) found in a fresh red grape juice, and the lowest 212.4±6.25 g GA/L in a fresh white grape juice. Our data show that red grape juices show a good polyphenol content justifying their use as an alternative source of antioxidant compounds. Comparison between anthocyanin profiles of grape derivatives and grape-based food supplements will be discussed taking into account data on bioavailability reported in the scientific literature.