Flavanols small

A dual-electrode liquid chromatography-electrochemistry (LCEC) system used in the detection and identification of flavanols and procyanidins in wines and grape seeds is a valuable tool (30). Voltammetric behavior of phenolic compounds by LCEC could provide information that cannot be obtained using HPLC with UV detection, for which the identification is usually based on a comparison of the retention time with that of standard compounds, especially for the identification of catechins and procyanidins with a small amount of sample available (30). Figure 10 shows the procyanidins commonly found in wines. 

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... 

Flavanols, snch as catechins and ohgomeric proanthocyanidins, are largely unglycosylated and occur naturally as the aglycone form. Proanthocyanidins are stable in the stomach in humans in vivcf but break down in vitro at pH 2 over several hours to monomeric flavanols and unidentified compounds. Most of the ingested proanthocyanidins and catechins therefore reach the small intestine intact. 

New products have been isolated from the photolysis of 3-flavonols in methanol for example, 3-arylphthalides (172) were minor products and were derived from the diketones (170). Some flavanols also gave small amounts of the keto-ester (171), but photolysis was inhibited in the presence of some metal ions, " e.g. Cu ", Ni ", Fe , Co, and Be . 

Small flavanols mainly monomers, dimers and trimers. The aqueous extract was deposited on Sephadex LH20, swollen with water, then rinsed with water, phosphate buffer 0.05 M at pH 6.7 and water again. All of the flavanols were eluted with an acetone/H20 (70/30) mixture. Once the acetone had been eliminated by evaporation, the small flavanols were extracted from the aqueous residue using ethyl acetate. 

During digestion and transfer across the small intestine, and in the liver, flavanols are rapidly metabolized in phase I and phase II biotransformations to various 0-sulfated, <9-glucuronidated and (7-methylated forms. Various UGT isozymes, expressed in the intestine and in the Uver, have been identified to catalyze the glucuronidation of flavonoids. In humans consuming cocoa, plasma levels of non-methylated epicatechins such as epicatechin-7-sulfate and methylated metabolites such as 3 -0-methylepicatechin have been reported to occur in micromolar concentrations within 1 h after intake. Metabolic studies have confirmed the presence of these conjugates in the plasma and urine of rodents and humans, as well as in the bile and brain of rats. It has been reported that colonic microflora can break flavonoids flavan structure to form simple phenolics and rig-flssion metabolites that may be physiologically relevant. 

Most flavanol absorption is thought to occur in the small intestine. The mechanism of catechin and epicatechin absorption has been investigated by using intestinal perfusion models in the rat. Both catechin and epicatechin appear to be efficiently absorbed by the jejunum and ileum. Extensive metabolism also occurs within the small intestine, demonstrating that these flavanols are absorbed into intestinal cells, and not by the paraceUular route [49,50]. 

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