Condensed tannin

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. 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. 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). 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. Some large condensed tannins are insoluble. Differences in solubilities are likely to affect their biological functions. Tannins of tropical woods tend to be of a catechin nature rather than of the gallic type present in temperate woods. Condensed tannins can be recovered from Lithocarpus glaber or can be found in Prunus sp. The bark of Commiphora angolensis contains condensed tannins. Commercial sources of condensed tannins are plants such as quebracho wood (Schinopsis lorentzii), mimosa bark (Acacia mollissima), grape seeds (Vitis vinifera), pine barks and spruce barks. Condensed tannins are formed in tannosomes, specialized organelles, in Tracheophytes, i.e. vascular plants. Pycnogenol is a dietary supplement derived from extracts from maritime pine bark, is standardised to contain 70% procyanidin and is marketed with claims it can treat many conditions; however, according to a 2012 Cochrane review, the evidence is insufficient to support its use for the treatment of any chronic disorder. Condensed tannins can be characterised by a number of modern techniques including depolymerisation, asymmetric flow field flow fractionation, small-angle X-ray scattering and MALDI-TOF mass spectrometry. Their interactions with proteins can be studied by isothermal titration calorimetry and this provides information on the affinity constant, enthalpy and stoichiometry in the tannin-protein complex.