ABSTRACT
Intestine and Colon ............................................................ 127 6.3.2 Sites of Metabolism and Metabolic Processes ................................. 128
6.3.2.1 Gastrointestinal Tract ......................................................... 128 6.3.2.2 Liver ................................................................................... 133 6.3.2.3 Biliary Excretion and Efux Mechanisms ........................ 133
6.3.3 Bioavailability ................................................................................... 134 6.3.3.1 Effect of Bound Hydroxycinnamic Acids and
Esterication on Their Bioavailability ............................... 135 6.3.3.2 Effect on Absorption .......................................................... 135 6.3.3.3 Effect on Metabolism ......................................................... 138
6.4 Bioavailability of Chlorogenic Acids ........................................................... 139 6.4.1 Absorption throughout the Gastrointestinal Tract ............................ 139 6.4.2 Identication of Metabolites in Plasma and Urine ........................... 140 6.4.3 Bioavailability of Intact Chlorogenic Acids ..................................... 140 6.4.4 Biphasic Pharmacokinetic Prole of Absorption ............................. 143 6.4.5 Sites of Metabolism .......................................................................... 144 6.4.6 Extensive Methylation, Sulfation, and Isomerization of
Chlorogenic Acid Metabolites .......................................................... 144
Hydroxycinnamic acids are a class of (poly)phenolic compounds with a C6-C3 skeleton structure of trans-phenyl-3-propenoic acid, with one or more hydroxyl groups attached to the phenyl moiety, some of which may be methylated. The main hydroxycinnamic acids in the diet are p-coumaric, caffeic, ferulic, and sinapic acids, usually found as glycosides or esters of quinic acid, shikimic acid, or tartaric acid (Clifford 2000; Manach et al. 2004), as well as ether-and ester-linked to polysaccharides forming the structure of plant cell walls (Sun et al. 2002). Structures of major hydroxycinnamic acids in the diet are shown in Figure 6.1. Quinic esters of mono-and dihydroxycinnamic acids (chlorogenic acids) are found in abundance in coffee beverage, artichoke, cherries, blueberries, aubergine, and apples (Herrmann 1989; Clifford 2000; Manach et al. 2004); mono-and dicaffeoyl and p-coumaroyl tartaric acids can be found in wine; endives, and spinach (Singleton et al. 1978; Herrmann 1989); glycosylated hydroxycinnamic acids are found in kale leaf, spinach, and tomatoes (Herrmann 1989); malic acid esters are found in radishes and chicory (Herrmann 1989); and rosmarinic acid, which is 3-(3′,4′-dihydroxyphenyl)lactic acid ester of caffeic acid, is commonly found in rosemary, oregano, thyme, and sage (Herrmann 1989).
