Phenolic acids in the aglycone form are generally absorbed in the upper part of the gastrointestinal tract (Saura-Calixto and others 2007). Recently, it was shown that the stomach constitutes an active absorption site of numerous phenolic acids as gallic caffeic,ferulic, coumaric, and also chlorogenic acids can be absorbed from the stomach (Konishi and others 2006; Lafay and others 2006; Lafay and Gil-Izquierdo 2008a). This fact explains the rapid absorption of these compounds ranging from 1 to 2 h after intake of fruits and vegetables. The small intestine constitutes another absorption site. However, aglycone phenolic acids can be absorbed to different degrees—19.1% compared with 56.1% for caffeic and
ferulic acids, respectively. In general, when the phenolic acids are esterified, the bioavailability decreases, reaching only 0.3% to 0.4% absorbed from the original intake. This is because esterified phenolic acids must be hydrolyzed in the enterocytes before reaching the blood circulation and the enzymatic machinery of these intestinal cells is not efficient enough to hydrolyze the ester bonds (Adam and others 2002; Lafay and others 2006).