Flavanol dimers, absorption

Unlike some classes of polyphenols such as flavonols and flavones, flavanols are almost always present in the nonglycosylated form. Removal of glycoside from flavonoids, usually necessary before the transport across the intestinal barrier, is not required in the case of flavanols [Scalbert and Williamson, 2000]. The absorption of procyanidins by the small intestine was investigated by studying 14C-( + )-catechin, dimer, trimer, and procyanidin polymers permeation through Caco-2 cell cultures [Deprez et al., 2001]. There was little difference in permeability between monomer, dimmer, and trimer, based on the measurement of radioactivity present on the basal side of the cultures, whereas the permeability of the polymers was 10 times lower. The authors reported the absence of catechin metabolism but did not determine whether the radioactivity measured on the basal side of the cultures was from the parent dimers to polymers or from their products of degradation or metabolites, which could have resulted from instability of the parent compounds in the culture... 

The formation of xanthylium pigments may also result from non enzymatic reactions of colorless precursors such as flavanols as previously reported (/yellow derivatives by various oxidation processes. In the presence of tartaric acid and iron or copper ions, yellow pigments with absorption maxima at 440 and 460 nm were formed along with the colorless (+)-catechin carboxymethine bridged dimers 46, 47). These pigments were analysed by ID and 2D NMR and identified as non esterified and esterified xanthylium salts respectively 33, 38, 39, 42) (Figure 5). 

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