The potential application of plant essential oils as natural preservatives against Escherichia coli O157:H7.

Investigation were carried out to compare the efficiency of three plant essential oils; Zataria multiflora, Carum carvi and Mentha piperita as natural food preservatives. The effect of these plant essential oils at concentrations of 0.0, 0.3, 0.6 and 1% was studied against inoculated Escherichia coli O157:H7 (10(5) cfu mL(-1)) in prepared commercial chicken soup stored at 8 and 35 degrees C over seven (168 h) and three (72 h) days, respectively by plate count technique on CT-SMAC agar. Zataria multiflora was the most effective essential oil against the bacterium in all concentrations, followed by Mentha piperita and Carum carvi. The maximum inhibitory effects of all essential oils were seen at 1% concentration. The inhibitory effects were affected by the incubation temperature as well as by the type and concentrations of essential oils. The 1% concentration of Mentha piperita and 0.6 and 1% concentrations of Zataria multiflora essential oil showed bacteriostatic effect on growth of Escherichia coli O157:H7 at 35 degrees C. Also 1% concentration of Carum carvi, 0.6 and 1% concentrations of Mentha piperita and 0.6% concentration of Zataria multiflora essential oil had bacteriostatic effect while 1% concentration of Zataria multiflora essential oil showed bactericidal effect on the bacteria during the incubation period at 8 degrees C. It is concluded that selected plant essential oils have promising inhibitory effects on Escherichia coli O157:H7 in chicken soup and could be considered as natural food preservatives. This is especially relevant at a time when there is an increasing interest in finding more natural alternatives to many existing preservatives.