Antimicrobial activities of red wine-based formulations containing plant extracts against Escherichia coli O157:H7 and Salmonella enterica serovar Hadar

- Plant extract powders alone had low antimicrobial activity.
- Tested essential oils were highly active; more so against Salmonella than E. coli.
- Activity was enhanced with temperature, incubation time, and by lower pH.
- Apple extract and lemongrass essential oil combinations showed the highest activity.

We evaluated the antimicrobial activities of three red wine based plant extract/plant essential oil (EO) formulations: olive extract powder/oregano EO, apple skin extract powder/lemongrass EO, and green tea extract powder/bitter almond EO, and their formula permutations against the foodborne pathogens Escherichia coli O157:H7 and Salmonella enterica serovar Hadar. The following parameters that were expected to affect antimicrobial activity were evaluated: pH (3.6 or 7.0), temperature (4, 22, and 37 °C), incubation time (0, 5, 30, and 60 min) and bacterial load (∼104 or ∼109 bacteria/ml). The formulations with oregano, lemongrass, or bitter almond EO inhibited the growth of both pathogens at acidic pH with bacterial loads of ∼104 or ∼109 bacteria/ml. At neutral pH, the formulations were less effective. Although all the 3-component formulations were fast acting; showing significant activity in less than 5 min, only the activity of the lemongrass-containing formulation markedly increased with longer incubation times from 0 to 60 min. Activity also increased for all 3-component formulations with increasing temperature from 4 °C to 37 °C, although the activity of the lemongrass formulation appeared to level off at 22 °C. Of the tested formulations, the lemongrass EO formulations, at pH 3.6, appeared to be the most effective against the tested pathogens, especially against Salmonella. The most active formulations merit evaluation for antimicrobial efficacy in liquid and solid food.