Epicatechin belongs to the colorless flavanols, which are a subgroup of flavonoids. These are classified as secondary plant compounds (bioactive substances with potential health-promoting effects).Chemically, epicatechin has a similar structure to catechin. It is composed of two benzene rings, in the middle of which an O-heterocyclic pyran ring is found. On the pyran ring, the second and third carbon are connected with a single bond. In addition, there is a hydroxy group on the 3rd carbon. Based on the stereocenter at the 2nd carbon, epicatechin and catechin differ. Epicatechin has a cis-configuration and catechin has a trans-configuration. The molecular formula is also C15H14O6.Epicatechin is found, for example, in chocolate and in the skins of apples.
Synthesis
As a secondary plant substance, epicatechin is synthesized (produced) only by plants and is found here in the marginal layers and in the outer leaves. Therefore, epicatechin is found primarily in plant foods, with levels varying depending on how the food is grown, the season, and the variety of the food. In 100 g of baking cocoa powder, there is a high amount of epicatechin, 196.43 mg. Dark grapes contain 8.68 mg of epicatechin per 100 g. In the plant organism, flavonoids such as epicatechin occur predominantly in bound form as a glycoside (binding to glucose) and to a lesser extent in free form as an aglycone (without a sugar compound).
Absorption
The nutritively (dietary) absorbed free and glycoside-bound flavonoids enter the small intestine. The flavonoid aglycones are absorbed into enterocytes (cells of the small intestinal epithelium) via passive diffusion. Some of the flavonoid glycosides are absorbed (taken up) via the sodium/glucose cotransporter-1 (SGLT-1). This transports sodium ions together with glucose into the cell by means of a symport (rectified transport). In this way, the flavonoid glycosides reach the mucosa epithelium (intestinal mucosa) intact. The flavonoid glycosides that are not absorbed in the small intestine are transformed into free phenolic acids and flavonoid aglycones by the microorganisms of the colon (large intestine). While some of these flavonoids passively enter the colonic epithelium, the other part continues to be degraded by the microflora and excreted in the feces (stool). Flavonoids are well bioavailable at > 15%. Brewing in water can result in a 50% loss of water-soluble flavonoids. To brew green tea optimally, a temperature of 85 °C is suitable. In a study it was found that the contents of epicatechin, epicatechin gallate, epigallocatechin and epigallocatechin gallate increase within the first 3 to 5 minutes. As the brewing time increases, their content in green tea decreases. In contrast, the contents of catechin, gallocatechin and gallocatechin gallate increase continuously with the duration of infusion. Also on the basis of sensory points, green tea performs best after a brewing time of 3 to 5 minutes. The longer the green tea steeped, the more bitter the taste as well as the aroma.
Transport and distribution in the body
Absorbed flavonoids are transported to the liver via the portal vein. Here, conjugation or methylation with glucuronic acid or sulfate occurs via phase II reactions. Subsequently, elimination via bile occurs.
