D. COUTEAU, A.L. McCARTNEY, G.R. GIBSON, G. WILLIAMSON AND C.B. FAULDS. 2001.

Aims: Conjugated hydroxycinnamates, such as chlorogenic acid (caffeoyl‐quinic acid), are widely consumed in a Western diet, coffee being one of the richest sources. Ingested hydroxycinnamate esters can reach the large intestine essentially unaltered, and may then be hydrolysed by esterases produced by the indigenous microflora. This study is aimed at identifying bacterial species responsible for the release of natural antioxidants, such as hydroxycinnamic acids, in the human large intestine.

Methods and Results: Thirty‐five isolates recovered after anaerobic batch culture incubation of human faecal bacteria in a chlorogenic acid‐based medium were screened for cinnamoyl esterase activity. Six isolates released the hydroxycinnamate, ferulic acid, from its ethyl ester in a plate‐screening assay, and these were identified through genotypic characterization (16S rRNA sequencing) as Escherichia coli (three isolates), Bifidobacterium lactis and Lactobacillus gasseri (two strains). Chlorogenic acid hydrolysing activities were essentially intracellular. These cinnamoyl esterase‐producing organisms were devoid of other phenolic‐degrading activities.

Conclusions: The results show that certain gut bacteria, including some already recognized as potentially health‐promoting (i.e. species belonging to the genera Bifidobacterium and Lactobacillus), are involved in the release of bioactive hydroxycinnamic acids in the human colon.

Significance and Impact of the Study: Free hydroxycinnamates, including caffeic, ferulic and p‐coumaric acids, exhibit antioxidant and anticarcinogenic properties both in vitro and in animal models. Given that the gut flora has a major role in human nutrition and health, some of the beneficial effects of phenolic acids may be ascribed to the microflora involved in metabolism.