Antilisterial activity of selected phenolic acids

Phenolic acids are known to exhibit antimicrobial activity against a variety of micro-organisms. Their influence on the behavior of Listeria monocytogenes, particularly in foods derived from plants, is not well understood. Several phenolic acids including chlorogenic acid and the hydroxycinnamic acids, caffeic acid, p-coumaric acid and ferulic acid, were screened for activity against five strains of L. monocytogenes using a broth dilution method. Minimum inhibitory concentrations ranged between 0.20% and 0.27% (w/vol) for the hydroxycinnamic acids, but chlorogenic acid was ineffective at 1.0% (w/vol). Mixtures of the acids generally exhibited additive antilisterial effects in a checkerboard assay. Growth experiments performed at pH 4.5, 5.5 and 6.5 revealed a strong relationship between pH and activity. All the hydroxycinnamic acids were bactericidal at pH 4.5 and bacteriostatic at higher pH. In contrast, chlorogenic acid inhibited growth of L. monocytogenes only at pH 6.5. The implications of these finding for the ecology of the species in foods are discussed. (C) 2002 Published by Elsevier Science Ltd.