Combining essential oils and olive extract for control of multi-drug resistant Salmonella enterica on organic leafy greens

Authors: RADA, XEEROY - University Of Arizona; TODD, JENNIFER - University Of Arizona; Friedman, Mendel; Patel, Jitu; JARONI, DIVYA - Oklahoma State University; RAVISHANKAR, SADHANA - University Of Arizona

Submitted to: Journal of Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2016
Publication Date: 2/22/2016
Publication URL: https://handle.nal.usda.gov/10113/6961223
Citation: Rada, X., Todd, J., Friedman, M., Patel, J.R., Jaroni, D., Ravishankar, S. 2016. Combining essential oils and olive extract for control of multi-drug resistant Salmonella enterica on organic leafy greens. Journal of Food Science and Technology. 1(2):1-9.

Interpretive Summary: Non – typhoidal Salmonella species are associated with foodborne illnesses, causing approximately 11% of domestically acquired cases, 35% of hospitalizations, and 28% of deaths. Salmonella serotypes isolated from human infections include Typhimurium, Enteritidis, and Newport. S. Newport is resistant to seven antibiotics and has become increasingly frequent. In 2010, S. Newport was attributed to a massive, multistate outbreak associated with raw alfalfa sprouts which led to product recalls. S. Typhimurium and S. Newport caused an outbreak due to contaminated cantaloupes that resulted in 261 cases and 3 deaths in 2012. The risk of pathogen transmission from contaminated produce is greater as most produce is consumed raw with very little processing or terminal treatment. Safety considerations become even more important because of the increased demand by consumers for organic produce. The objective of this collaborative study supported by a USDA-NIFA grant was to assess the effectiveness of cinnamon oil and olive extract and oregano oil and olive extract combinations as a wash treatment against antibiotic-resistant S. Newport on organic leafy greens. The combination treatments demonstrated strong antimicrobial properties in both laboratory media and large scale experiments. The advantages of utilizing two plant antimicrobials at lower concentrations are important to maintain sensory attributes of leafy greens.

Technical Abstract: We investigated the combined antimicrobial effects of plant essential oils and olive extract. Organic baby spinach, mature spinach, romaine lettuce, and iceberg lettuce were inoculated with the pathogen and then dip-treated in phosphate buffered saline (PBS) control, 3.0% hydrogen peroxide, a 0.1% cinnamon oil and 3.0% olive extract or a 0.1% oregano oil and 3.0% olive extract combination treatments. Samples were collected on days 0, 1, and 3 for enumeration of survivors. In addition, in a large scale study, nonpathogenic Escherichia coli K12 was used to inoculate iceberg lettuce, and then treated with 3.0% hydrogen peroxide and a 3.0% olive extract and 1.0% oregano oil treatment. Treatment with both antimicrobials induced up to 4 log CFU/g reductions in the leafy greens. Similarly, these treatments reduced Salmonella by 3 log CFU/g in mature spinach. For romaine lettuce, there was a 3.0 log CFU/g reduction for the cinnamon oil and olive extract combination, and a 4.0 log CFU/g reduction for the oregano oil and olive extract combination. The cinnamon oil and olive extract treatment yielded a 2.75 log CFU/g reduction, while the oregano oil and olive extract treatment yielded a 3.5 log CFU/g reduction in iceberg lettuce. Compared to previously reported treatment with individual antimicrobials, the combination treatment induced a synergistic effect against the pathogen on romaine lettuce, baby spinach and mature spinach, and an additive effect on mature spinach. Against E. coli K12, the 0.1% oregano oil and 3% olive extract yielded an initial 3.0 log CFU/g reduction on organic iceberg lettuce, which increased to no detectable survivors (<1.0 log CFU/g) after three days of storage. The hydrogen peroxide control yielded an initial 1.0 log CFU/g, which remained consistent after three days. These results show that combination treatments involving essential oils and olive extract are a potential option for use as wash to decontaminate organic produce.