Chlorogenic Acid
Chlorogenic acids are a family of esters formed between quinic and trans-cinnamic acids, which are an important group of dietary phenols (Figure 4). 18 The most common individual chlorogenic acid is 5-O-caffeoylquinic acid, which is still often called chlorogenic acid. For those who drink it, coffee represents the richest dietary source of chlorogenic acids and cinnamic acids (caffeic acid). The chlorogenic acid content of a 200 ml (7-oz) cup of coffee has been reported to range from 70–350 mg, which would provide about 35–175 mg of caffeic acid. 18 Studies in colostomy patients indicate that about 33% of ingested chlorogenic acid and 95% of caffeic acid are absorbed intestinally. 19 Thus, about two–thirds of ingested chlorogenic acid reaches the colon where it may be metabolized by the colonic microflora. 20 In the colon, chlorogenic acid is likely hydrolyzed to caffeic acid and quinic acid. The presence of bacterial metabolites of chlorogenic acid in the urine suggests that they are absorbed in the colon. Although chlorogenic acid and caffeic acid have antioxidant activity in vitro, 21 it is unclear how much antioxidant activity they contribute in vivo because they are extensively metabolized, and the metabolites often have lower antioxidant activity than the parent compounds.