Epicatechin monomers

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

Flavanols cof HO., Epicatechin (monomer) Apple Chocolate Red wine Black tea 5-15 20-400 2-45 7-35... 

Seeds of Theobroma cacao are worldwide in use for production of cocoa butter and confectionary products. The production of raw cocoa from fresh seeds is based on a complex fermentation process, which leads to the aroma precursors. This process enhances the amount of peptides and free amino acids in the seeds, but it also reduces the amount of phenolic compounds, especially the proantho-cyanidins. These antioxidative compounds are mostly composed of catechin and epicatechin monomers and oligomers up to decamers. The fermentation has to take into account that both factors, production of aroma precursors as well as... 

Chocolate is a rich source of epicatechin monomer in addition to its high procyanidin content [96]. Several studies have fed chocolate samples and determined the total amount of glucuronide and sulfate conjugates in plasma [8-10,97]. Epicatechin levels in the experimental chocolate samples ranged from 35 to 164 mg. Average maximal levels of epicatechin in plasma in these studies ranged from 36 nM to 700 nM. 

Figure 5.3. Flavanol monomers (catechins, epicatechins, and their gallates) and pro-cyanidins. C catechin GC, gallocatechin EC, epicatechin EGC, epigallocatechin CG, catechin gallate GCG, gallocatechin gallate ECG, epicatechin gallate, EGCG, epigallocatechin gallate.

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. 

Fig. 2.115. Mass chromatograms of catechin monomers (m/z 289) and procyanidin oligomers (dimer through hexamers m/z 577 to 1729). C, ( + )-catechin, EC, ( — )-epicatechin, and PB2, procyanidin B2 as identified by the retention times of authentic standard. Reprinted with permission from J. Wollgast et al. [256].

Recent studies performed using this method have shown that flavanol bitterness decreases from monomer to trimer. Epicatechin was perceived more bitter than catechin and the C4-C6-linked catechin dimer more bitter than other procyanidin dimers with C4-C6 linkages. This may be due to the higher lipophilic character of these molecules facilitating their diffusion to the gustatory receptor. Bitterness of procyanidin fractions in 5% ethanol decreased with their... 

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). 

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]. 

Figure 2.1 Structure of flavan-3-ol monomers and dimers. (A)(—)-Epicatechin with = OH and R2 = H or ( + )-catechin with Ri = H and R2 = OH , (B) procyanidin (4p - 8)-dimer (C) procyanidin (4p -> 6)-dimer.

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. 

As expected, k2 for catechin and epicatechin are the same, since the reaction rate would be expected to be independent of C-ring stereochemistry. The comparatively smaller rate constants observed for the two procyanidins could be explained by the fact that they possess fewer reaction sites per monomer unit than catechin or epicatechin and also by steric effects. 

---