Condensed tannins (proanthocyanidins, polyflavonoid tannins, catechol-type tannins, pyrocatecollic type tannins, non-hydrolyzable tannins or flavolans) are polymers formed by the condensation of flavans. They do not contain sugar residues.[1]
They are called proanthocyanidins as they yield anthocyanidins when depolymerized under oxidative conditions. Different types of condensed tannins exist, such as the procyanidins, propelargonidins, prodelphinidins, profisetinidins, proteracacinidins, proguibourtinidins or prorobinetidins. All of the above are formed from flavan-3-ols, but flavan-3,4-diols, called (leucoanthocyanidin) also form condensed tannin oligomers, e.g. leuco-fisetinidin form profisetinidin, and flavan-4-ols form condensed tannins, e.g. 3',4',5,7-flavan-4-ol form proluteolinidin (luteoforolor).[2] One particular type of condensed tannin, found in grape, are procyanidins, which are polymers of 2 to 50 (or more) catechin units joined by carbon-carbon bonds. These are not susceptible to being cleaved by hydrolysis.
While many hydrolyzable tannins and most condensed tannins are water-soluble, several tannins are also highly octanol-soluble.[3][4] Some large condensed tannins are insoluble. Differences in solubilities are likely to affect their biological functions.
- ^ Teresa K. Attwood and Richard Cammack (2006). Oxford dictionary of biochemistry and molecular biology. ISBN 0198529171.
- ^ "Phenolics in Food and Nutraceuticals" by Fereidoon Shahidi and Marian Naczk, CRC press, page 44
- ^ Mueller-Harvey, I.; Mlambo, V.; Sikosana, J.L.N.; Smith, T.; Owen, E.; Brown, R.H. (2007). "Octanol-water partition coefficients for predicting the effects of tannins in ruminant nutrition". J. Agric. Food Chem. 55 (14): 5436–5444. doi:10.1021/jf070308a. PMID 17567141.
- ^ Mueller-Harvey, I (2010). "Unravelling the conundrum of tannins in animal nutrition and health". J. Sci. Food Agric. 86 (13): 2006–2037. doi:10.1002/jsfa.2577.