THE GRAPE SKINS AND SEED POLYPHENOLIC EXTRACTS
The paper dwells on identification of phenolic compounds and anthocyanins from newly-squeezed grape skins and seed ethanol extracts of Zeibeli and Izabela color grape varieties cultivated in viticulture-winemaking micro-zone of western Georgia, by combined gas chromatography mass-spectrometry, and their determination by method of high-pressure liquid chromatography, but antioxidant activity has been assessed by DPPH method. For the experiment, we used newly-squeezed grape skins and seed without drying, mechanical and thermal treatment. Total phenolic compounds content in grape skins and seed ethanol extracts of Zeibeli variety (>423 mg/100 ml) was greater than in grape skins and seed extracts of Izabela variety (>394.2 mg/100 ml). The same results have been registered when assessing antioxidant activity of extracts. In particular, in the conditions of the same dissolution of extracts, grape skins and seed ethanol extracts of Zeibeli variety had higher antioxidant activity (up to 67-79,4%) than grape skins and seed extracts of Izabela variety (49.5-63.9%). Studies have shown that total phenols and anthocyanins quantitative content correlates with antioxidant activity of extracts. The polyphenolic contents and the antioxidant activity of the skins and pulps of different grape cultivars were estimated using HPLC and DPPH antioxidant assay, respectively. The phenolics and flavonoids identified were quercetin, kaempferol, caffeic acid, p-coumaric acid, cinnamic acid, and (-)-epicatechin. The total phenolic contents were found to be the highest in the grape skin of Flouxa (> 400 mg/100 g), followed by Campbell Early and Tamnara (> 300 mg/100 g), and then by Red Globe and Ruby Seedless (> 250 mg/100 g), and the total phenolic content was the lowest in Italia and Delaware (< 60 mg/100 g). The antioxidant activities of the grape extracts varied from 12.5% (Ruby Seedless) to 60.2% (Hongiseul) for skins, whereas the antioxidant activities of the grape extracts varied from 35.4% (Campbell Early) to 84.5% (Hongiseul) for pulps. The grape pulps have stronger antioxidant activities than those of the grape skins. Our results suggest that the phenolic and flavonoid contents in extracts of grape skins and pulps showed statistically significant correlations with the free radical scavenging activity.