The study of the phenolic complex composition and the antioxidant activity of white grape cultivars

Grape plants are rich in antioxidants of phenolic nature which are used in the production of food products and have addition functional actions. Phenolic substances having different antioxidant activity and functional orientation are unevenly distributed in different parts of the grape plants, and their qualitative and quantitative composition depends on grape cultivar. A comparative study of the phenolic complex and the antioxidant activity of must, aqueous-alcoholic extracts of peel and one-year-old vine shoots (next-shoots) from six white grape cultivars was conducted. The phenolic complex of must was represented mainly by flavan-3-ols, procyanidins (76-81%) and hydroxycinnamic acids (17-20%). The flavan-3-ols concentration in must was higher than its concentration in extracts of peel and shoots in 2.2-3.8 times, hydroxycinnamic acids - in 1.9-12 times. But must had low antioxidant activity (0.09-0.43 mg L^-1 Trolox). A distinctive feature of the complex phenolic antioxidant of peel extract is it is enriched in comparison with must and shoot extract flavonols (quercetin, kaempferol and its glycosides), epicatechin and dimers procyanidins (B1, B6, B8), gallic acid. Antioxidant activity of the peel extract is from 6.46 to 9.91 mg L^-1 Trolox, and the highest was observed in the grape cultivars 'Riesling Magaracha', 'Aligote', 'Tsitronnyi Magaracha'. The concentration of stilbenes (piceid, resveratrol, ε- and α-viniferin) in extracts of shoots was exceeded in 61 times its concentration in peel extracts and in 42 times NDASH in must. Largest total concentration of stilbene (63.53-81.2 mg L^-1) was presented in cultivars 'Podarok Magaracha', 'Riesling of the Rhine', 'Aligote'. The antioxidant activity of shoot extract was 0.39-0.85 mg L^-1 Trolox. Thus, polyphenolic extracts from different parts of the grape plant can be used to enrich beverages with antioxidants of stilbene groups (shoot extract); flavonols, procyanidins (peel extract).