Antimicrobial efficacy of plant phenolic compounds against Salmonella and Escherichia Coli

Hayriye Cetin-Karaca, Melissa C. Newman

Abstract

The present study evaluated the antimicrobial efficacy of natural phenolic compounds (PC) extracted from vegetables, fruits, herbs and spices; to inhibit the growth of Gram-negative foodborne bacteria which is defined as the minimum inhibitory concentration (MIC).

Strains of Escherichia coli and Salmonella species were treated with natural PCs including; chlorogenic acid, curcumin, (−) epicatechin, eugenol, myricetin, quercetin, rutin, thymol, thymoquinone, and xanthohumol. Concentrations of 5, 10, 15, and 20 ppm of each compound were evaluated by a broth micro-dilution method and the MICs were determined by using optical density after 24 and 60 h of incubation. Structural alterations in treated bacteria were observed via scanning electron microscopy.

For E. coli, thymoquinone showed the highest inhibition, followed by rutin, (−) epicatechin and myricetin (MIC<20 ppm for all), while Salmonella was most sensitive to (−) epicatechin (MIC<15 ppm), followed by thymoquinone, rutin and myricetin (MIC<20 ppm for all) following 60 h of incubation. The results demonstrated that the PCs have varying antimicrobial activities against foodborne pathogens following 24 and 60 h incubation periods. Natural sources of PCs contain major antibacterial components and have great potential to be used as natural antimicrobials and food preservatives, during long term storage.

This study highlighted the antimicrobial efficacy of some novel PCs which may replace chemical antimicrobials and preservatives in food or pharmaceutical industry to partially or completely inhibit the growth of bacteria.

Keywords: Foodborne pathogen; Phenolic compounds; Minimum inhibitory concentration (MIC); Antimicrobial activity.