Insight in the phenolic composition and antioxidative properties of Vitis vinifera leaves extracts

Abstract

In the present investigation, leaf ethanolic extracts of Vitis vinifera were assayed for their polyphenolic composition and antioxidative properties. The leaves were collected during lush vegetation period (May leaves) and after the harvest (September leaves). Air dried plant material was homogenized and the polyphenolic constituents were extracted using conventional solvent extraction procedure. Total phenolics, flavonoids, non-flavonoids, catechins and flavanols were determined using spectrophotometric methods. Both extracts were very rich in phenolic compounds. The concentration of total phenols in September leaves extract was about 30 % higher compared to May leaves extract, due to the increase of flavonoid (catechin) fraction. Non-flavonoid compound content was almost equal in both extracts. The amount of flavanols, determined with p-dimethylaminocinnamaldehyde method, was taken as indicator of flavan-3-ol monomers, while high catechin content determined by vanillin method, indicated the presence of polymeric fraction. The total catechin content in September leaves extract was more than 3 folds higher in comparison to May leaves extract. Principal phenolic compounds were separated by high pressure liquid chromatography on reverse phase. Antioxidant properties, determined as: 2,2-diphenyl-1-picrylhydrazyl radical and 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonate) radical cation scavenging ability, ferric reducing/antioxidant power, Fe2+ chelating activity, and using β-carotene bleaching assay, were total phenol concentration dependent. September leaves extract had better free radical scavenging capacity, higher reducing power, and was more efficient in protecting the oxidation of emulsified linoleic acid, in comparison with May leaves extract which showed better chelating ability. The presence of active phenolic compounds: phenolic acids (3-hydroxybenzoic acid, caffeic acid, gallic acid, vanillin acid), flavonoids ((+)-catechin, (-)-epicatechin, apigenin, myricetin, quercetin, quercetin-4'-glucoside, rutin), and stilbenes (trans-resveratrol and resveratrol derivatives) was confirmed in both extracts. According to the results achieved, vine leaf extracts can be considered rich natural source of polyphenols with significant antioxidant properties.