Inactivation of E. coli O157:H7 on Rocket Leaves by Eucalyptus and Wild-Thyme Essential Oils

Abstract

Recently, the consumption of fresh produce has been associated with the outbreaks of Escherichia (E.) coli O157:H7, the dangerous foodborne pathogen. Accordingly, the objective of this work was to evaluate the effectiveness of essential oils (EOs) of 24 different plants and herbs in controlling growth of E. coli O157:H7 in rocket leaves model. EOs antibacterial activities and MICs were determined by disk diffusion and micro-dilution methods, respectively. The effectiveness of most active EOs (0.5 and 1 % v/w) were further examined for sanitizing rocket leaves contaminated with 3 log CFU/leaf of E. coli O157:H7 strains cocktail after storage at 4 °C/3 days and 25 °C/24 h. The EOs of Wild-thyme and Eucalyptus had the most (p < 0.05) inhibition activity with Minimal Inhibitory Concentration (MIC) values of 0.32 μL/g. In control rocket leaves samples, E. coli O157:H7 populations increased by 1.16 and 2.60 log cycles after storage at 4 °C/3 days and 25 °C/24 h, respectively. Compared with control samples, sanitizing of rocket leaves stored at 25 °C/24 h with either 0.5 or 1 % of Eucalyptus or Wild-thyme resulted in 1.85, 1.97, 1.95, and 1.98 log cycles reduction in population counts, respectively, whereas sanitizing of samples stored at 4 °C/3 days resulted in 1.82, 1.85, 1.90, and 1.99 log cycles reduction, respectively. Findings showed that EOs of Wild-thyme and Eucalyptus were effective in sanitizing E. coli O157:H7 on rocket leaves at both storage conditions. Our results suggest that these EOs could be used as natural sanitizers in many final produce products, with better safety profile and consumer acceptance compared to chemical sanitizers.