Oligomeric catechins

An efficient separation of apple procyanidins (oligomeric catechins) was performed by high-speed counter-current chromatography (HSCCC) in a one-step operation from an apple condensed tannins fraction using a hydrophilic two-phase solvent system composed of methylacetate-water (1 1, v/v). In further matrix-assisted laser desorption initiation-time-of-flight mass spectrometry (MALDI-TOF-MS) analyses of the solute oligomers, the elution order of the procyanidins in the HSCCC was coincident with their degree of polymerization. 

Polyhedral oligomeric silsesquioxane (POSS) has been extensively studied as starting substrate to construct nanocomposites with precise control of nanoarchitecture and properties. Octahedral derivatives are the most representative ones of this family. It was reported that the HRP-catalyzed conjugation of catechin on amine-substituted octahedral silsesquioxane amplified the beneficial physiological property of flavonoids. The POSS-catechin conjugate exhibited great... 

Recently published literature described either the improvement of the strategies devoted to the synthesis of either catechins derivatives or oligomeric proanthocyanidins or the use of a synthetic program as a way to obtain... 

Steynberg, J.P. et al.. Oligomeric fiavanoids. Part 4. Base-catalyzed conversions of (—)-fisetinidol-(+)-catechin profisetinidins with 2,3-trflwj-3,4-cw-flavan-3-ol constituent units, J. Chem. Soc., Perkin Trans. 1, 1331, 1988. 

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). 

The phenolic composition of apple consists of cinnamic acids, flavonols, dihydrochalcones, and flavan-3-ols (50,56). In the apple fruit processing industry, hydroxycinnamic acid derivatives and flavan-3-ols are important due to their contribution to the astringency, haze, and browning in apple juice and cider. Chlorogenic acid represents the major hydroxycinnamic acid derivative. The flavan-3-ols (catechins) are present in the monomeric form as well as in oligomeric and polymeric forms (procyanidins) in apple and apple products (56). 

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. 

Flavan-3-ols represent the most common flavonoid consumed in the American and, most probably, the Western diet and are regarded as functional ingredients in various beverages, whole and processed foods, herbal remedies, and supplements. Their presence in food affects quality parameters such as astringency, bitterness, sourness, sweetness, salivary viscosity, aroma, and color formation [Aron and Kennedy, 2007]. Flavan-3-ols are structurally the most complex subclass of flavonoids ranging from the simple monomers ( + )-catechin and its isomer (—)-epicatechin to the oligomeric and polymeric proanthocyanidins (Fig. 1.10), which are also known as condensed tannins [Crozier et al., 2006b]. 

Flavanols consist of catechin and epicatechin monomers together with oligomeric tannins, which comprise the most abundant class of flavonoids in the... 

The profile (%) of polyphenolics in tamarind pericarp was dominated by proan-thcyanidins in various forms, such as (+)-catechin, procyanidin B2, (-)-epicatechin (9.4), procyanidin trimer (11.3), procyanidin tetramer (22.2), procyanidin pentamer (11.6) and procyanidin hexamer (12.8), along with taxifolin (7.4), apigenin (2.0), eriodictyol (6.9), luteolin (5.0) and naringenin (1.4) of total phenols, respectively. Tamarind seeds comprised procyanidins only, represented (%) mainly by oligomeric procyanidin tetramer (30.2), procyanidin hexamer (23.8), procyanidin trimer (18.1), procyanidin pen-tamer (17.6), with lower amounts of procyanidin B2 (5.5) and (-)-epicatechin (Sudjaroen et al., 2005). 

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. 

Ascorbate oxidase is a dimer containing two identical subunits, and appears to be accompanied by smaller amounts of oligomeric forms (64-66). This compound contains 8-10 atoms of copper and is blue colored. The copper may be removed to give an inactive apoenzyme. Ascorbate oxidase contains Cu " in three different environments (63, 67,68). The enzyme also catalyzed the oxidation of o-catechols, although the Km is less favorable than that for AA Km, ( + )-catechin, 3.08 mM Km, l-AA, 0.24 mM (69). The role of ascorbate oxidase in plants is not known. 

Jordao, A.M., Ricardo da Silva, J.M. and Laureano, O. (2001) Evolution of catechins and oligomeric procyanidins during grape maturation of Castelao Frances and Touriga Francesa, Am. J. Enol. Vitic., 52(3), 230-234. 

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