Procyanidin condensed tannin

Procyanidin (condensed tannin) Vitis vinifera (Vitaceae) LELA (4 pM) [88]]... 

Procyanidins (condensed tannins, polymers of catechin and epicatechin)... 

Components The phytochemistry of the individual classes varies enormously [for components of the clubmosses and horse tails, see the appropriate entries]. The true ferns (Filicatae) contain saccharose as the main carbohydrate. Large amounts of C2o-poly-enoic acids, see also arachidonic acid, and fatty acids with 21 - 30 C atoms are found among the lipids. Ferns produce a great variety of secondary products such as procyanidins, condensed tannins, flavan derivatives, benzoic and cinnamic acid derivatives, acylphloroglucinols, cyanogenic glycosides, pter-osins, di- and triterpenes as well as phytoecdysone (see ecdysteroids). Alkaloids have not yet been detected. 

Fig. 3. The regular structure of a procyanidin-type condensed tannin showing characteristic 4,8 interflavonoid bonds linking the flavonoid units.

Proanthocyanidins (PAs), also known as condensed tannins, are oligomeric and polymeric flavan-3-ols. Procyanidins are the main PAs in foods however, prodelphinidins and propelargonidins have also been identified (Gu and others 2004). The main food sources of total PAs are cinnamon, 8084 mg/100 g FW, and sorghum, 3937 mg/100 g FW. Other important sources of PAs are beans, red wine, nuts, and chocolate, their content ranging between 180 and 300 mg/100 g FW. In fruits, berries and plums are the major sources, with 213.6 and 199.9 mg/100 g FW, respectively. Apples and grapes are intermediate sources of PAs (60 to 90 mg/100 g FW), and the content of PAs in other fruits is less than 40 mg/100 g FW. In the majority of vegetables PAs are not detected, but they can be found in small concentrations in Indian squash (14.8 mg/ 100 g FW) (Gu and others, 2004 US Department of Agriculture, 2004). 

Flavanols and procyanidins Flavanols, or flavan-3-ols, are synthesized via two routes, with (+) catechins formed from flavan-3,4-diols via leucoanthocyanidin reductase (LAR), and (—) epicatechins from anthocyanidins via anthocyanidin reductase (ANR) (see Fig. 5.4). These flavan-3-ol molecules are then polymerized to condensed tannins (proanthocyanidins or procyanidins), widely varying in the number and nature of their component monomers and linkages (Aron and Kennedy 2008 Deluc and others 2008). It is still not known whether these polymerization reactions happen spontaneously, are enzyme catalyzed, or result from a mixture of both. 

Flavan-3-ols (catechins, proanthocyanidins, and condensed tannins) can often be extracted directly with water. However, the composition of the extract does vary with the solvent — whether water, methanol, ethanol, acetone, or ethyl acetate. For example, it is claimed that methanol is the best solvent for catechins and 70% acetone for procyanidins. ... 

Delcour, J.A., Ferreira, D., and Roux, D.G., Synthesis of condensed tannins part 9. The condensation sequence of leucocyanidin with (-l-)-catechin and with the resultant procyanidins. J. Chem. Soc. Perkin Trans. /1711, 1983. 

McGraw, G.W., Steynberg, J.P., and Hemingway, R.W., Condensed tannins a novel rearrangement of procyanidins and prodelphinidins in thiolytic cleavage. Tetrahedron Lett., 34, 987, 1993. 

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). 

Condensed tannins are also referred to as proanthocyanidins. They are oligomeric or polymeric flavonoids consisting of flavan-3-ol (catechin) units. Hydrolysis under harsh conditions, such as heating in acid, yields anthocyanidins. An example of a condensed tannin is procyanidin B2 (epicatechin-(4 3—>8 )-epicatechin 1.90). In this case the interflavanyl linkage is between C4 of the lower unit, and C8 of the upper unit. The linkage can also be between C4 of one unit and C6 of the second unit. 

Some recent evidences have shown that a basic PRP binds condensed tannins much more effectively than a-amylase. In Figure 16.10, it can be seen that the light-scattering intensity caused by aggregation increases with the concentration of procyanidins until a maximum after which the light scattered intensity remains constant even with a further increase in tannin concentration. 

Procyanidin B-2 3,3 -di-0-gallate (condensed tannin) Rheum palmatum (Polygonaceae) ACE (2 pM) [SlF... 

Nonhydrolyzable or condensed tannins are also named proanthocyanidins. These are polymers of flavan-3-ols, with the flavan bonds most commonly between C4 and C8 or C6 (Figure 6-23) (Macheix et al. 1990). Many plants contain tannins that are polymers of (+)-catechin or (-)-epicatechin. These are hydrogenated forms of flavonoids or anthocyanidins. Other monomers occupying places in condensed fruit tannins have trihydroxylation in the B-ring (+)-gallocat-echin and (-)-epigallocatechin. Oligomeric and polymeric procyanidins are formed by addition of more flavan-3-ol units and result in the formation of helical structures. These structures can form bonds with proteins. 

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