Tannins and anthocyanins

Salas, E. et al.. Reactions of anthocyanins and tannins in model solutions. J. Agric. Food Chem. 51, 7951, 2003. 

Table V. Anthocyanins and Tannins of Red Wines of Different Vintages from Two Vineyards of the Bordeaux Region"...

Table VII. Development of Anthocyanins and Tannins as Fruit Matures...

Table VII shows the development of anthocyanins and tannins from the beginning of ripening to maturity. There are three stages first, a rapid increase in all the substances second, a slowing in the production...

These tables show larger differences between years than between varieties. The comparison between the two vineyards, both cultivated by traditional methods, does not show significant differences. These experiments demonstrate the importance of the year and climatic conditions on the anthocyanin and tannin content. These variations are much more important than those of other chemical constituents (sugars and acids). 

Calculation of the theoretical levels of anthocyanins and tannins in wines is possible, assuming complete extraction of these compounds from the parts of the cluster. Thus one sees only 20-30% of the possible grape pigments in wine. 

Respective Roles of Anthocyanins and Tannins. The mediation of tannins and anthocyanins in the color of red wine, covered in our work (38) has been conducted in model solutions (17). The procedure is as follows. 

Table XV. Anthocyanin and Tannin Coloration of Model Solutions, Analytical Results...

The mixture of anthocyanins and tannins kept from air are a color reminiscent of young wines (tube 6). Upon oxidation they take on an orange-brown hue reminiscent of old wine. Again in this case Fe3+ catalyzes the oxidation (compare tubes 6, 3, and 9). 

As a first approximation, this experiment represents the evolution of the coloring matter in red wines during aging. It confirms the large role of tannins in the color of old wines and thus shows that tannins play an important part in the color of young wines. Taken as another point, the possibility of a reaction between the anthocyanins and tannins already postulated (50) is accurately described. 

Red wine color does not depend exclusively on the anthocyanin and tannin levels the physicochemical state of these pigments also exerts an influence. Related wine types, especially those of the same age, can have colors which may not be interpreted solely on the basis of anthocyanin and tannin levels. 

Pigments, such as anthocyanins and tannins, may protect against viruses and inhibit the formation of dental plaque. 

Moderate consumption of red wine may decrease the risk of heart disease and certain cancers. The pigments found in grapes, such as anthocyanins and tannins, may protect against viruses and inhibit the formation of dental plaque. 

The fermentation usually is complete within 30 or 40 days. During this period additional anthocyanins are extracted from pomace and the color stabilizes due to polymerization between the anthocyanins and tannins. Winemakers call this process pomace "maturation". Moreover, due to the increasing alcohol concentration, many other metabolites are extracted from the pomace. In addition, yeast metabolites contribute to the aromatic complexity of the wine. 

Phenolic compounds, anthocyanins and tannins, are considered among the most important substances extracted from the grape pomace. 

Microoxygenation is a technique that involves the addition of small and controlled quantities of oxygen to the wine. This technique is mainly used to stabilize the colour of red wines, since oxygen in small quantities favours polymerization reactions among anthocyanins and tannins (Atanasova et al. 2002). Globally, total anthocyanins decrease, but what is formed, combined with tannins, leads to a product which is more intensely coloured and more stable over time than the initial compounds. 

Hallas, C. A., The Anthocyanin and Tannin Content of Cocoa, BFMIRA Research Rept. 13... 

Since it appears that anthocyanins and tannins condense in wine to form secondary wine pigments, the nature of the linkage between these compounds has been the focus of many investigations. There are a large number of possibilities but this chapter will discuss only two for historical purposes. Others will be discussed by other authors in this book. Based upon the structure of a natural compound, Jurd synthesized a dimer from catechin and a synthetic anthocyanidin (Figure 1). The flavylium form of the anthocyanidin has an electrophilic carbon at C-4 that will condense with the phloroglucinol ring of catechin. The new product, a flavene, will be oxidized by a second flavylium... 

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