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

Organic fresh produce sales have been increasing in recent years and ensuring safety of produce is important. We investigated the combined antimicrobial effects of plant essential oils and olive extract against Salmonella on organic leafy greens. Organic baby spinach, mature spinach, romaine lettuce, and iceberg lettuce were inoculated with antibiotic-resistant Salmonella Newport and dip-treated in phosphate buffered saline, 3.0% hydrogen peroxide, 0.1% cinnamon leaf oil and 3.0% olive extract or 0.1% oregano oil and 3.0% olive extract combination treatments. Leaves were sampled on days 0, 1, and 3 for enumeration of survivors. Treatment with both antimicrobials induced reductions in Salmonella population of up to 3.5-4 logs, 3-logs and 3-4.4 logs CFU/g on baby spinach, mature spinach and romaine lettuce, respectively. Cinnamon leaf oil and olive extract treatment yielded about 3.0 logs, while oregano oil and olive extract treatment yielded about 3.5 logs CFU/g reduction on iceberg lettuce. Compared to previously reported treatments with individual antimicrobials, the combination treatments had greater antimicrobial effect. The results showed that combination treatments involving essential oils and olive extract are a potential option for use in the wash water for organic leafy greens.