Condensed tannins, occurrence

Rhus coriaria L. is a shrab, which reaches 3M p in high in the wild. Its powdered leaves were used as a tanning agent for its high tannin content [10]. Tannins are found in the leaves, fmit, barks, roots and wood of trees. They can be classified into two groups condensed tannins and hydroly sable tannins [11]. The co-occurrence of both kinds of tannins in the same plant or plant tissue is often observed [12]. The main compounds present mRhus coriaria L. are hydrolysable gallatonnins. 

The information in Table I reveals differences between sane of the inportant types of tannin. Tannic acid is unique for its occurrence in all reports of diet-induced gut lesion and gastrointestinal damage (vertebrate or invertebrate) it is also the only tannin for which metabolism and excretion are reported. By contrast condensed tannins are not thought to leave the gut lumen. Thus,in comparison with tannic acid condensed tannins would not be espected to drain 1-carbon metalx>lism, notably methionine resources. However, the reports by Elkin (] ) and Ford ( ) of corrective methionine treatment for chicks fed a condensed-tannin diet, indicate that sane condensed tannin may enter the body or that methionine can react with tannin in the gut, so perhaps the position is once again not clear cut on tannin structure and its impact on methionine levels. The conclusion can, however, be made that despite its hydrolyzability, tannic acid does exert an allelochemical effect which is not abolished by hydrolysis. 

The term, complex tannin, appears to be established as descriptor for the class of polyphenols in which a flavan-3-ol unit, representing a constituent unit of the condensed tannins (proanthocyanidins), is connected to a hydrolyzable (gallo-or ellagi-) tannin through a carbon-carbon linkage. Since the first demonstration of their natural occurrence, a considerable number of these unique secondary metabolites have been reported. " New additions (Table 11.17) to this series of compounds come exclusively from the groups of Nonaka and Nishioka, and Okuda and Yoshida in Japan. 

Foo L Y 1984 Condensed tannins Co-occurrence of procyanidins, prodelphinidins and pro-fisetinidins in the heartwood of Acacia baileyana. Phytochemistry 23 2915-2918... 

Table 7.7.4. Occurrence of deoxyflavanoid condensed tannins in woody plants... 

There are now a number of well authenticated examples of the occurrence of gallate esters of monomeric flavan-3-ols and proanthocyanidins. Recently Haslam suggested that, in view of the apparently similar function and properties of hydrolyzable and condensed tannins, there is some form of metabolic link between these two complex polyphenols (58). Further, he observed that where gallate esters of flavan-3-ols occur, they are accompanied by only low concentrations of proanthocyanidins. 

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. 

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