Multiple recalls and outbreaks involving Listeria monocytogenes-contaminated apples have been linked to the post-harvest packing environment where this pathogen can persist in biofilms. Therefore, ...this study assessed L. monocytogenes survival on apples as affected by harvest year, apple cultivar, storage atmosphere, and growth conditions. Unwaxed Gala, Granny Smith, and Honeycrisp apples were dip-inoculated in an 8-strain L. monocytogenes cocktail of planktonic- or biofilm-grown cells (~6.5 log CFU/mL), dried, and then examined for numbers of L. monocytogenes during air or controlled atmosphere (CA) (1.5% O2, 1.5% CO2) storage at 2 °C. After 90 days, air or CA storage yielded similar L. monocytogenes survival (p > 0.05), regardless of harvest year. Populations gradually decreased with L. monocytogenes quantifiable in most samples after 7 months. Apple cultivar significantly impacted L. monocytogenes survival (p < 0.05) during both harvest years with greater reductions (p < 0.05) seen on Gala compared to Granny Smith and Honeycrisp. Biofilm-derived cells survived longer (p < 0.05) on L. monocytogenes-inoculated Gala and Honeycrisp apples compared to cells grown planktonically. These findings should aid in the development of improved L. monocytogenes intervention strategies for apple growers and packers.
As demand for fresh-cut produce increases, minimizing the risk of salmonellosis becomes critical for the produce industry. Sanitizers are routinely used during commercial flume washing of fresh-cut ...produce to minimize cross-contamination from the wash water. This study assessed the efficacy of a novel sanitizer blend consisting of peracetic acid (PAA; OxypHresh 15) with a sulfuric acid-surfactant (SS) antimicrobial (PAA-SS; ProduceShield Plus) against Salmonella during simulated commercial washing of diced tomatoes. Triplicate 9.1-kg batches of Roma tomatoes were dip inoculated in a two-strain avirulent Salmonella cocktail (Salmonella Typhimurium LT2 and MHM112) to achieve 5 to 6 log CFU per tomato and air dried for 2 h. After mechanical dicing, the tomatoes were washed in a pilot-scale processing line for 60 s with or without an added organic load in 90 ppm of PAA-SS (pH 1.8), SS at pH 1.8, 90 ppm of PAA, 5 or 10 ppm of free chlorine or sanitizer-free water as the control. Overall, PAA-SS (1.75 ± 0.75 log CFU/g) was significantly (P ≤ 0.05) more effective than water (0.69 ± 0.42 log CFU/g), chlorine (0.35 ± 0.36 log CFU/g), or SS (0.36 ± 0.19 log CFU/g) in reducing Salmonella. After washing for 20 s, PAA-SS was the only sanitizer to show a significant (P ≤ 0.05) reduction (1.93 ±0.59 log CFU/g) in Salmonella. All wash water samples were negative for Salmonella, except for 5 and 10 ppm of chlorine and the water control. Using PAA-SS with an organic load, yeast and mold populations were below the limit of detection (1.40 log CFU/g) and significantly (P ≤ 0.05) lower on diced tomatoes after 14 days of refrigerated storage compared with the other treatments (8.37 ± 0.08 log CFU/g), with SS at pH 1.8 (3.91 ± 0.93 log CFU/g) most effective against yeast and mold in the absence of an organic load. On the basis of these findings, the safety and shelf life of commercially washed diced tomatoes can be improved with PAA-SS.
Multiple recalls and outbreaks involving Listeria monocytogenes-contaminated apples have been linked to the post-harvest packing environment where this pathogen persists. The research presented here ...addresses the effect of both apple fruit attributes and post-harvest conditions on L. monocytogenes survival. First, L. monocytogenes survival was assessed on apples as affected by harvest year, apple cultivar, storage atmosphere, and growth conditions. The second portion of the study investigated the chemical composition and morphology differences of cuticular wax in Gala and Honeycrisp apples. The influence of natural cuticular wax composition and structure is important to investigate as it impacts apple fruit quality and food safety. Finally, before apple fruit are shipped to market, they are treated with commercial coatings to enhance quality. We assessed L. monocytogenes survival to determine the impact shellac and carnauba surface coatings have during storage in solution or applied to a contaminated surface. On the surface of apples, L. monocytogenes populations gradually decreased but were still quantifiable in most samples after 7 months. Apple cultivar significantly impacted L. monocytogenes survival (p < 0.05) during both harvest years with greater reductions (p < 0.05) seen on Gala compared to Granny Smith and Honeycrisp. Gala apples had more alkanes (g/cm2 of peel) overall for alkane compounds compared to Honeycrisp. In Gala apples the main component of the cuticular wax was nonacosane. Nonacosane content (μg/cm2 of peel) in the cuticular waxes was greater (p < 0.01) on Gala (108.77±0.36) than on Honeycrisp (46.12±4.86). After just 12 hours of storage, in the shellac surface coating solution, L. monocytogenes was no longer detectable, compared to the carnauba surface coating solution which still supported survival (2.4-4.0 log CFU/mL) after 14 days. These findings should aid in the development of improved L. monocytogenes intervention strategies and inform manufacturers looking for natural food safety solutions.
Multiple recalls and outbreaks involving Listeria monocytogenes-contaminated apples have been linked to the post-harvest packing environment where this pathogen can persist in biofilms. Therefore, ...this study assessed L. monocytogenes survival on apples as affected by harvest year, apple cultivar, storage atmosphere, and growth conditions. Unwaxed Gala, Granny Smith, and Honeycrisp apples were dip-inoculated in an 8-strain L. monocytogenes cocktail of planktonic- or biofilm-grown cells (~6.5 log CFU/mL), dried, and then examined for numbers of L. monocytogenes during air or controlled atmosphere (CA) (1.5% Osub.2, 1.5% COsub.2) storage at 2 °C. After 90 days, air or CA storage yielded similar L. monocytogenes survival (p > 0.05), regardless of harvest year. Populations gradually decreased with L. monocytogenes quantifiable in most samples after 7 months. Apple cultivar significantly impacted L. monocytogenes survival (p < 0.05) during both harvest years with greater reductions (p < 0.05) seen on Gala compared to Granny Smith and Honeycrisp. Biofilm-derived cells survived longer (p < 0.05) on L. monocytogenes-inoculated Gala and Honeycrisp apples compared to cells grown planktonically. These findings should aid in the development of improved L. monocytogenes intervention strategies for apple growers and packers.
