IDENTIFICATION AND CHANGES OF FLAVONOIDS IN MERLOT AND CABERNET SAUVIGNON WINES
ABSTRACT Twenty components of an ethyl acetate extract from Merlot and Cabernet Sauvignon wines were isolated by recycle preparative HPLC. A combination of paper chromatography, fluorescence behavior, gas chromatography, reaction with molybdate, reaction with vanillin/HCI, ultraviolet spectrometry and mass spectrometry was used to gain information about the identities of the isolated compounds. Seven of the isolated compounds were catechins, procyanidins or degradation products thereof. Three flavonol glycosides were isolated and one was characterized as an isorhamnetin-3-glycoside. Four compounds were isolated with identical molecular weights and an uncharacteristic blue reaction with vanillin/HCl. These components were interconvertable and thought to be cis-trans isomers of flavenes. The changes in these components during aging of Merlot and Cabernet Sauvignon wines are discussed.
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ABSTRACT: Three commercial extracts of grape phenols (seeds, skin, whole) were used in this study. Each extract was divided by HPLC into five fractions of different polarities, and their free radical-scavenging activities were measured using the DPD (N,N-diethyl-p-phenylenediamine) colorimetric method. Total phenol contents were determined using the Folin-Ciocalteu method to assess their contribution to the antiradical activity. The results showed that there was good correlation between total phenolic compound contents and free radical-scavenging activities of the different grape extracts. Moreover, the seed extract presented the most important free radical-scavenging properties (138 USP/mg extract), whereas the whole extract presented the lowest free radical-scavenging capacity (80.5 USP/mg extract). However, the free radical-scavenging properties, reported on the basis of content of phenolic compounds in each extract, showed that the free radical-scavenging activities of seed and whole extracts were not significantly different (171 versus 162 USP/mg phenol). In addition, free radical-scavenging activities of fractions from seed and skin extracts decreased as their polarities decreased.Food Chemistry. 01/2006;
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ABSTRACT: Three white table wines were treated with additions of purified anthocyanins at 0, 250, and 500 mg/L and 0, 500, and 1000 mg GAE/L of grape-seed tannin in all possible combinations. The results of analyses for polymeric phenols were very consistent with the different wines and show that anthocyanins quickly complex with polymeric phenolic tannins to retain them in solution. The lack of such complexing explains why wines made from white grapes by red vinification methods are deficient in tannins and astringency. These anthocyanin- tannin complexes that form quickly in red wine differ from those produced by aging in remaining relatively adsorbable by Sephadex LH-20. These results have important implications for red wine astringency and other quality and processing characteristics.