Tannin condensed

There are two categories of tannins condensed and hydrolyzable tannins. The polymerization of flavonoid molecules produces condensed tannins, which are commonly found in woody plants (Fig. 3.9). Hydrolyzable tannins are also polymers, but they are a more heterogeneous mixture of phenolic acids (especially gallic acid) and simple sugars. Though widely distributed, their highest concentration is in the bark and galls of oaks. 

In the adsorption of some metal ion by tannin adsorbents [16], tannins are widely distributed in nature and have multiple adjacent phenolic hydroxyl groups and exhibit specific chelation ability toward metal ions [17]. According to the chemical stractures of tannins, they can usually be classified into hydrolyzable tannins, condensed tannins and complex tannins. Hydrolyzed tannins yield galhc acid or ellagic acid when hydrolyzed by acid, base or some enzymes [18]. Turkish sumac tannin (hydrolyzable tannin) is illustrated in Fig. 28.1 whose basic stracture is of flavan-3-ols. 

Complex phenolics Coumarins, phenolic quinones, lignins, flavonoids, stilbenes, hydrolyzable tannins, condensed (or catechin) tannins, phenolic lipids... 

Two different types of tannin, condensed and hydrolysable tannins, play important roles. 

Condensed tannins (= proanthocyanidins) unlike hydrolysable tannins, condensed tannins are polymeric flavans that are not readily hydrolysable. They often consist of molecules of catechin and epicatechin joined by carbon-carbon bonds. Hence catechin and epicatechin are referred to as monomers oligomers containing 2-4 (epi)catechin units are referred to as oligomeric procyanidins (OPC). 

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... 

Other studies have described similar results to those found in our research, that is, that ellagitannins are more abundant in French oak (26) and therefore, in wines matured in French oak barrels. So, the presence of ellagitannins enhances the color of wine and increases absorbance at 620 nm by fevoring anthocyanin-procyanidin type tannin condensations with acetaldehyde (purple pigments) and that foct also helps to explain the higher PVPP index values of wines fix)m new French oak barrels. They also prevent the development of brick-yellow color by preventing the oxidation of phenolic compounds (24). 

Since Somers published his first observations on anthocyanin-tannin condensations, many advances have been made in the identification of new... 

Both xanthylium salts shown in Figure 5 have been detected in wine stored with no care to avoid oxidation, supporting the occurrence of the above described pathways (33, SO, 51), This constitutes an in5)ortant support to the occurrence of the above described pathways, since the xanthylium salts is expected to result from anthocyanin-tannin condensation have never been detected. 

Tannin condensation Anthocyanin (T-A). One of the characteristics of procyanidins is that they form a carbocation after protonation of the molecule, and react with nucleophilic sites, such as nodes 6 and 8 of anthocyanin molecules as carbinol bases (neutral) (Figure 6.31). 

Compared with other beverages prepared by fermentation, wines are very acidic (their pH value is within 2.8 to 3.8, and tartaric acid is a major carrier of sour taste) and they have a relatively high ethanol content. Ethanol has a significant influence on the nature of the taste. Its content is related to sugar content in the must, and therefore it is related to the degree of grape ripeness and the extent of the fermentation. For the red wine taste, tannins, condensation products of catechins and other flavonoid molecules are important compounds. Ethanol corrects their bitter and astringent taste. 

Botha, J. J., D. Ferreira, D. G. Roux, and W. E. Hull Condensed tannins Condensation mode and sequence during formation of synthetic and natural tri-flavanoids. J. Chem. Soc. Chem. Commun. 1979, 510. 

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