Sanitization Effectiveness of Alkaline-Dissolved Essential Oils as Organic Produce Washing Solutions

Produce is often rinsed immediately post-harvest to remove dirt and debris. Rinse water can be a point of cross-contamination if no antimicrobials are present. While plant essential oils (EOs) are recognized as antimicrobials, their hydrophobicity makes them difficult to implement in rinsing solutions. In this study, the efficacy of emulsified EOs were examined against Salmonella on the surface of cherry tomatoes and Escherichia coli O157:H7 on the surface of baby spinach. Contaminated produce samples were rinsed in an emulsions of clove bud oil or thyme oil at 0.2 and 0.5% (v/v), as well as free chlorine at 200 ppm and sterile de-ionized water as controls. These treatments were also tested for their vulnerability to organic loading in the system, by adding 1% (w/v) organic load (OL) in the form of blended produce (spinach or tomato). Wash solutions were also tested for their ability to inhibit pathogen transfer onto uninoculated produce samples. To accomplish this, clean produce was immersed in rinse water immediately following contaminated samples. Finally, the wash solutions were enumerated for any viable pathogens.

Emulsified clove bud oil with whey protein at 0.5% was the most effective at reducing levels of Salmonella from tomato surfaces, while 0.5% thyme oil with gum arabic, next most effective, proved more resistant to the influence of 1% organic matter. Chlorine, commonly used as an antimicrobial in the produce industry, lost all measureable effectiveness in an organically loaded system. However, against E. coli O157:H7 on spinach surfaces, 0.5% thyme oil emulsion was the best EO treatment. Although chlorine was more effective in a clean system, 0.5% emulsified thyme oil was the next most effective against E. coli and was not vulnerable to 1% OL, unlike chlorine.

Overall, when testing organically loaded systems that simulate realistic conditions in dump tanks, emulsified EO systems were more effective at reducing pathogen levels and were better at inhibiting pathogen transfer and survival. These data establish potential for these emulsions to be employed as alternative antimicrobials for produce sanitizing systems.