Clove Bud Oil, Its Active Component and Combination Treatments with Plant Extracts Inactivate Multi-Drug Resistant Salmonella Newport on Organic Leafy Greens

Introduction: Nearly 40% of foodborne outbreaks involving Salmonella are linked to fresh produce. The USDA-NOP mandates for chemical-free production practices have left the organic industry with few treatment options.  Plant essential oils and extracts have shown notable antimicrobial activity against foodborne pathogens in vitro, are generally recognized as safe (GRAS) by the FDA, and may provide an effective treatment alternative for the organic produce industry. 

Purpose: Developing natural alternative treatments is necessary for reducing contamination by foodborne pathogens. We investigated the antimicrobial activity of clove bud oil, its active component eugenol, and combination treatments consisting of a plant extract and the essential oil (combinations A and B) against multi-drug resistant Salmonella enterica serovar Newport on organic leafy greens. 

Methods: Iceberg lettuce, romaine lettuce, bunched mature spinach and baby spinach were dip inoculated with Salmonella Newport, treated with either PBS, 3% H₂O₂, 0.1 - 0.5% essential oil or its active component and combination A or B (5% plant extract and 0.1% essential oil) for 2 min and stored at 4°C.  Samples were taken for enumeration on day 0, 1 and 3.  

Results: Reductions in Salmonella populations for all treatments ranged from 0.36 - 3.7 log CFU/g on all four leafy greens, with the essential oil (0.5%), its active component (0.5%) and combination B being most effective on bunched mature spinach with reductions of 3.7, 3.7 and 3.6 log CFU/g, respectively. Reductions from individual treatments of essential oil (0.1%) and plant extract (5%) ranged from 0.40 - 2.5 log CFU/g and were less effective than the combination treatments (0.87 - 3.6 log CFU/g). Hydrogen peroxide yielded a maximum reduction of 1.7 log CFU/g showing no residual activity during storage, whereas plant antimicrobials showed residual activity that was concentration- and storage time-dependent. 

Significance: This data supports the potential use of plant antimicrobials as alternative sanitizers to reduce the microbial burden of organic leafy greens.