Phenolic Acidshydroxycinnamates And Hydroxybenzoates

The phenolic acids are generally the lowest molecular weight polyphenol compounds. Hydroxycinnamates (Fig. 2) are a core class of polyphenols and are central to the biosynthetic pathways of polyphenols. Caffeic and quinic acids combine to form chlorogenic acid, which is found in many types of fruit and in high concentrations in coffee (20). Ferulic acid is the most abundant phenolic acid found in grains and may constitute the main dietary source of this compound. Hydroxybenzoic acids (Fig. 2) are less abundant in plants but are often found in red fruits, black radishes and onions. Tea is an important source of gallic acid containing 4.5 g/kg fresh weight tea leaves (21), whilst ellagic acid is a major polyphenol in some berry fruits. Hydroxybenzoic acids are also important components of complex hydrolysable tannins such as gallotannins in mangoes and ellagitannins in red fruits, hazelnuts, walnuts, pomegranates, and oak aged wines (from the barrels) (22-25).

Human bioavailability studies for hydroxycinnamates reveal that between 0.3 and 25% of ingested dose is excreted in urine (12). Chlorogenic acid (ingested as coffee) has been detected at low concentrations in urine samples (26,27) along with a range of smaller molecular weight secondary metabolites including ferulic acid, isoferulic acid, dihydroferulic acid, vannilic acid, 3,4-dihydroxyphenylpropionic acid, 3-hydroxyhippuric acid, and hippuric acid (27-29). One third of ingested chlorogenic acid is absorbed in the

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