Grape bunch polyphenols, qualitative and quantitative composition, technological stock
The Magarach Institute has been addressing the issue of developing technologies for obtaining functional food products from grapes saturated with grape polyphenols; and of determining main properties and modes of grape polyphenol extraction from potential raw materials (pomace, seeds, crests) for the production of experimental samples of functional products. The aim of the present research was not only to experimentally determine the total stock of polyphenols in pomace, seeds, crests of red and white grape varieties, but also to assess empirically the qualitative and quantitative composition of total polyphenols in pomace, seeds, stems, vines, leaves of red and white grape varieties as functional components of a healthy nutrition. The research has dwelled upon the empiric assessment of the characteristics of grape raw materials (grape must, pomace, seeds, crests) in terms of their technological stock, quantitative and qualitative composition of polyphenols (by HPLC), and the main functional ingredients of the biological activity of grape products. An analysis of the data obtained shows that the aqueous-alcoholic extracts of grape raw materials possess the whole spectrum of polyphenols typical for red grape wines (anthocyanins, flavones, flavan-3-ols, hydroxycinnamic, hydroxybenzoic acids, stilbenes, oligomeric and polymeric procyanidins), however their concentration quantitatively exceeds that found in wines. It has been shown that the total content of water-soluble antioxidants experimentally determined by the amperometric method depends on the content of oligomeric and polymeric procyanidins in the extracts of grape raw materials. Thus, the content of oligomeric procyanidins in the extracts of grape raw materials from the sum of phenolic substances averaged 5.7%; while the content of polymer procyanides went up to 94%. The technological availability of polyphenols of pomace, stalks and grape seeds during water-alcohol extraction in the piled layer without mixing was shown, the equilibrium concentrations of polyphenols transferred into the extract and the potential amounts of polyphenols extracted during single-stage extraction (technological stock) were assessed. The maximum values of technological stock of polyphenols of 29.2-76.02 g/kg dry weight in the stalks of white and red grape varieties were determined.