Phenolic profile and antioxidant capacity of leaves, berry skins and seeds of Gohér white (Vitis vinifera L.)

Abstract

Polyphenols fulfil a variety of roles in plants including antioxidant and UV-protective functions, and are also known to possess beneficial human health effects. In addition to the consumption of berries and vine making, Vitis vinifera leaves are also being used as food and for treating medical disorders. Leaf polyphenols are also key components in ensuring development and growth of the whole plant even under adverse environmental conditions. Our research was to measure the amount of different groups of polyphenolics and their antioxidant capacities in a Hungarian grapevine cultivar, Gohér white. The study evaluates the effect of sunlight exposure on the accumulation of polyphenolic compounds in shaded and fully sun exposed leaves and also includes measurements of berry skins and seeds harvested in late summer. Relative amounts of total phenolics and compound groups such as flavonols or flavan-3-ols were measured using photometric assays in leaves, skins and seeds. Intact glycoconjugate forms were profiled, identified and quantified by high performance liquid chromatography – mass spectrometry (HPLC-MS) in leaves. In addition, total antioxidant capacities (TAC) were also compared. We found that berry skins contained less phenolic components and had less TAC values than sunny or even shaded leaves. Berry seeds contained the highest amount of polyphenolics providing the highest TAC values. HPLC-MS analyses confirmed the presence of a number of quercetin- and kaempferol-glycosides, and the main phenolic acid, the caftaric acid in leaves and also provided quantitative data regarding these compounds. Our results emphasize the high impact of natural sunlight on the accumulation of these secondary metabolites.