Since 2014, fresh apples have been linked to outbreaks and recalls associated with postharvest cross-contamination with the foodborne pathogen L. monocytogenes . These situations drive both public health burden and economic loss and underscore the need for continued scrutiny of packinghouse management to eliminate potential Listeria spp. niches.

There is a need for effective postharvest controls capable of inactivating bacterial foodborne pathogens, which can be applied to the organic and conventional apple industries. This study evaluated the efficacy of natural antimicrobials (essential oils or cultured dextrose) when incorporated into carnauba wax and applied to apples. Organic Gala apples were spot inoculated with a five strains/serovars cocktail (∼9 Log CFU/mL) of Listeria monocytogenes, Shiga-toxigenic E. coli O157:H7, or Salmonella. Inoculated apples were coated with organic carnauba wax containing a 1% and 2% (v/v) mixture of essential oils (EOs) in equal proportions (oregano, clove bud, cinnamon bark, and coriander seed) or commercially cultured dextrose at 0.5% (w/v). Apples coated with carnauba wax only and uncoated apples were used as control treatments. Apples were stored at 20 °C and sampled for up to 40 days. Five treatments with three biological replicates and three samples per replicate were used for each treatment (n = 9). A sensory discrimination test was used to identify differences between waxed apples for treatments with the greatest efficacy. Carnauba wax containing 2% EOs was the most effective treatment for inactivating target foodborne pathogens inoculated on apples for 40 days. This treatment showed 4.05, 1.38 and 2.81 Log CFU/apple reduction in L. monocytogenes, E. coli O157:H7, and Salmonella, respectively, compared to uncoated apples. Carnauba wax containing 2% EOs showed significantly (P ≤ 0.001) lower populations of L. monocytogenes and Salmonella compared with 1% EOs, 0.5% cultured dextrose, or wax-only control. In contrast, there were no significant differences (P > 0.05) for E. coli O157:H7. Sensory evaluation showed that panelists could detect differences for apples treated with wax containing 2% EOs, but not for 1% EOs compared to wax-only control. This study provides information to the organic and conventional apple industry about the efficacy of antimicrobial waxes to inactivate bacterial foodborne pathogens.