Screening of 21 Vitis vinifera L. leaf and grape skin extracts for antioxidant capacity and phenolic content

Polyphenols are of secondary plant metabolites, naturally present in fruit, vegetables and herbs. In last two decades the number of publications on the potential health benefits of these compounds has increased enormously. The aim of this study is to determine and compare polyphenolic profile and related antioxidative properties of Vitis vinifera leaf and grape berry skin extracts. The research includes 21 grape varieties (White: Bogdanusa, Debit, Grk, Kuc, Malvasija, Marastina, Medna, Prc, Posip, Trebbiano toscano, Vugava and Žlahtina ; Red: Babica, Babic, Cabernet sauvignon, Dobricic, Glavinusa, Nincusa, Plavac mali, Plavina and Vranac). Plant material was collected at the stage of the grape technological maturity. Phenolic profile of plant extracts (total phenols, flavonoids, non-flavonoids, catechins and flavanols) were determined using spectrophotometric methods. Antioxidant capacity of plant extracts was estimated by Ferric Reducing/Antioxidant Power (FRAP) assay. The research of polyphenolic profile of berry skin and grape leaves extracts has shown difference in the mass amounts of total phenols among selected grape cultivars, as expected. The high antioxidant capacity of tested extracts has been observed and related to the presence of a mixture of polyphenolic compounds with good antioxidant properties. Significant linear correlation between total phenol content, or main phenolic subgroups, and FRAP was confirmed. To make practical comparison of relative antioxidant potential of phenolics extracted from berry skins and grape leaves, the phenol antioxidant coefficient (PAC) was calculated for each extract. PAC values ranged from 4.54-13.05 for grape skin extracts, and from 8.42-12.13 for grape leaves extracts. It can be concluded that grape skin extracts, as well as leaves extracts, can be a good source of phenolics with good antioxidant properties.