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<p style="text-align: justify;">The various analysis required for the measure of the red wines color are discussed and explained : absorbance at 420, 520 and 620 nm, determination of anthocyanins, p.v.p. and ionisation index.</p><p style="text-align: justify;">The part played in the absorbance at 520 nm by the free anthocyanins and the tannins-anthocyanins complex is investigated.</p><p style="text-align: justify;">The study of two red wines from two vinifications and stored in barrels for six months is carried out as an application.</p>

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Polyphenolic nonahydroxyterphenoyl-containing C-glycosidic oak ellagitannins are found in wine as a result of the aging of this beverage in oak-made barrels. Once in the slightly acidic wine (pH approximately 3-4), some of these complex natural products such as (-)-vescalagin (1), but not its C-1 epimer (-)-castalagin (2), can capture grape-derived nucleophilic entities such as ethanol, the flavanols catechin (10a) and epicatechin (10b), the anthocyanin oenin (13b), and the thiolic glutathione (16) to furnish condensation products with retention of configuration at the C-1 locus. A computer-aided rationale of this high diastereoselectivity is given. These condensation products can contribute to the modulation of organoleptic properties of the wine, as evidenced by the 23 nm bathochromic shift color absorbance observed with the novel oenin-based anthocyano-ellagitannin (15b). Hydrolysis of 1 under solvolytic conditions furnished another novel compound that we refer to as vescalene (21), in addition to the known (-)-vescalin (18). Of pharmacological importance is the fact that most of these found-in-wine water-soluble ellagitannin derivatives are much more potent than etoposide (VP-16) at inhibiting top2-mediated DNA decatenation in vitro (top2=topoisomerase II)). The known (-)-vescalin (18) and the novel vescalene (21) fully inhibited top2 at 10 microM concentration!

<p style="text-align: justify;">The study covers the equilibria of a mixture of five free anthocyanins from Cabernet Sauvignon skins, depending on the solvent, the tanin content, the pH, and the S0₂ concentration of the medium. The various constants of the proton transfer, cular extinction of the two coloured forms are determined using the technique of chemical relaxation of these molecules applied to the pH jump ; from these results, the constant of the reaction of the anthocyanins with the S0₂ on the one hand, and the calculation of the colour of the solutions of these molecules on the other hand, can be determined. From the same study with combinations between tanins and anthocyanins, it is possible to explain the influence of their structure on the stabilization of colour in the solutions. In the light of these results, the chemical origin of the wine colour and its variations are discussed.</p>