Abstract
Recent multistate outbreaks and recalls of fresh apples due to Listeria monocytogenes contamination have increased consumer concerns regarding fresh and processed apple safety. This study aimed to evaluate the antimicrobial efficacy of two sanitizers, mineral oxychloride (JC9450) and neutral electrolyzed water (NEW), for inactivation of L. monocytogenes on fresh apples. A 2-min treatment of 0.125% (v/v) JC9450 with 100 ppm free available chlorine (FAC) or NEW with 110 ppm FAC caused 0.9–1.2 log10 CFU/apple reduction of L. monocytogenes on both Granny Smith and Fuji apples 24 h post-inoculation. Increasing JC9450 concentration to 0.25 and 0.50% significantly improved its bactericidal effect and reduced L. monocytogenes on Granny Smith apples by ~2.0 and 3.8 log10 CFU/apple, respectively, after a contact time of 2 min. At a shorter contact time of 30 sec, the inactivation efficacy of chlorine and 0.25–0.50% JC9450 against L. monocytogenes on apples was significantly reduced compared with the respective 2-min wash. Furthermore, no L. monocytogenes was recovered in deionized water prepared antimicrobial wash solution or on non-inoculated apples post-NEW with 110 ppm FAC or 0.125–0.5% JC9450 washes, indicating their ability to prevent cross-contamination. In addition, a 2-min exposure to NEW with 110 ppm FAC and 0.50% JC9450 reduced apple native microbiota including total plate count by 0.14 and 0.65 log10 CFU/apple, respectively, and yeast and mold counts by 0.55 and 1.63 log10 CFU/apple, respectively. In summary, L. monocytogenes attached on apples was difficult to eliminate. JC9450 and NEW demonstrated a dose-dependent reduction in L. monocytogenes on apples and successfully prevented cross-contamination, indicating their application potential in post-harvest washes of apples.
Highlights
Listeria monocytogenes is a major foodborne pathogen, which causes more than 1,500 illnesses annually in the United States with a high mortality rate of ~16% (Scallan et al, 2011)
Multistate outbreaks attributed to contamination of L. monocytogenes on caramel apples (CDC, 2015) and recalls of fresh apples (FDA, 2016, 2017b) and sliced apples (CFIA, 2015) due to potential L. monocytogenes contamination highlight the importance of preventive control programs directed at L. monocytogenes on fresh apples
Antimicrobial efficacy of JC9450 and neutral electrolyzed water (NEW) was first assessed and compared against L. monocytogenes on Granny Smith apples (GSA), the variety associated with a recent listeriosis caramel apple outbreak (CDC, 2015), and Fuji apple, which is a commercially important variety and has a different surface structure than GSA (Hall, 1966)
Summary
Listeria monocytogenes is a major foodborne pathogen, which causes more than 1,500 illnesses annually in the United States with a high mortality rate of ~16% (Scallan et al, 2011). Typically in the form of sodium/calcium hypochlorite, is the most commonly used antimicrobial in the fresh produce industry (Banach et al, 2015). Chlorine at commonly used concentration, 50–200 ppm (Suslow, 2005), has a limited efficacy against L. monocytogenes on fresh produce (Prado-Silva et al, 2015). A 1-min spray of sodium hypochlorite solution with 200 ppm FAC reduced L. monocytogenes inoculated on whole Red Delicious apples at ~1.7 log CFU/cm by ~0.9 log CFU/cm (Beuchat et al, 1998). Chemical and fresh produce industries have been seeking for alternative antimicrobial sanitizers with an improved efficacy and convenience. P values of less than 0.05 were considered statistically significant. Three spent water samples were collected in each independent crosscontamination study, a total of nine samples per treatment
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