Modification of red wine vinification process: addition of white grape seeds, skins and ethanol causes changes in biochemical properties and vasodilatatory activity in vitro

Introduction. Beneficial effects of moderate red wine intake on human health have been attributed primarily to the high content of polyphenols (like catechin), strong antioxidants in red wine. White wine contains significantly less polyphenols than red wine, due to different wine making technique. Skins and seeds of white grapes are excluded from fermentation, and white grape juice is the only source of polyphenols in white wine. Technological and biological potential of white grapes skins and seeds is mainly overlooked and insufficiently exploited. The aim of this study was to determine how addition of white grape seeds, skins and ethanol to the red grape marc before and during fermentation, might influence biochemical properties and vasodilatatory activity in vitro of the obtained beverages. Materials and Methods. Basic red wine was made with grapes of Merlot variety. Chardonnay variety was used as a source of white grapes skins and seeds. Five different beverages were produced: 1. control red wine (CRW), from 20 kg of Merlot grapes by standard enological practices, with no additional intervention ; 2. modified wine (W40), by adding skins and seeds from separately crushing and pressing of 40 kg of Chardonnay grapes to CRW prior fermentation ; 3. modified wine (W40+E), the same as W40, with addition of ethanol to halt fermentation and to increase extraction of polyphenols into the wine. The final ethanol concentration was 25% vol. ; 4. modified wine (W80), the same as W40, with doubled amount of added skins and seeds (from 80 kg of grapes) ; 5. modified wine (W80+E), the same as W40+E, but with doubled amount of added skins and seeds (from 80 kg of grapes). All five beverages were analyzed for their total content of ethanol, sugars, phenols, catechins, flavonoids, anthocyanins, antioxidant capacity, and in vitro vasodilatatory activity on isolated rings (n = 15 per beverage) from rat aorta. Results. Addition of white grape seeds and skins resulted in related changes of total phenolic content (1.01, 1.35, 1.32, 1.75 and 1.77 g/L gallic acid equivalents) and total catechins content (388, 610, 452, 625, 681 mg/L) for CRW, W40, W40+E, W80 and W80+E, respectively. Antioxidant capacity of the beverages, measured by ferric reducing antioxidant power (FRAP), was 5.89, 7.77, 6.66, 8.79, and 8.43 mmol/L Trolox equivalents for CRW, W40, W40+E, W80 and W80+E, respectively. FRAP values generally correlated with the phenolic content of the beverages. All modified beverages were more potent vasodilators than CRW but did not differ between each other. Conclusion. This study confirms that white grapes skins and seeds are valuable unused plant materials with significant biological potential. Modification of red wine vinification by adding white grape seeds and skins might prove useful from economical and biomedical point of view.