Listeria monocytogenes cross-contamination during apple waxing and subsequent survival under different storage conditions.

This study evaluated Listeria monocytogenes cross-contamination between inoculated fruits, waxing brush, and uninoculated fruits during apple wax coating and investigated the fate of L. monocytogenes on wax-coated apples introduced via different wax coating schemes. There were 1.8-1.9 log10 CFU/apple reductions of L. monocytogenes on PrimaFresh 360, PrimaFresh 606, or Shield-Brite AP-450 coated apples introduced before wax coating after 6 weeks of ambient storage (22 °C and ambient relative humidity). L. monocytogenes showed a similar trend (P > 0.05) on waxed apples under cold storage (1 °C and ∼ 90% relative humidity); there were 1.8-2.0 log10 CFU/apple reductions of L. monocytogenes during the 12 weeks of cold storage regardless of wax coating type. For cross-contamination study, a waxing brush was used to wax one inoculated apple (6.2 log10 CFU/apple); then, this brush was used to wax five uninoculated apples in a sequence. There were 3.7, 3.5, 3.3, 2.9, and 2.7 log10 CFU/apple and 3.6 log10 CFU/brush of L. monocytogenes transferred from the inoculated apple to uninoculated apple 1 to apple 5, and the waxing brush, respectively. The die-off rate of L. monocytogenes on wax-coated apples contaminated during wax coating was not significantly different from that contaminated on apples before wax coating, and 1.8-1.9 log10 CFU/apple reductions were observed during the 12 weeks of cold storage. The application of wax coatings, regardless of wax coating type, did not impact the survival of endogenous yeasts and molds on apples during ambient or cold storage. L. monocytogenes transferred onto waxing brushes during wax coating remained relatively stable during the 2-week ambient holding. Fungicide application during wax coating reduced (P < 0.05) yeast and mold counts but had a minor impact (P > 0.05) on the survival of L. monocytogenes on apples after 12 weeks of cold storage. Collectively, this study indicated that a high cross-contamination risk of L. monocytogenes during apple waxing, and L. monocytogenes on wax-coated apples introduced via different scenarios is stable during subsequent cold storage, highlighting the need for potential intervention strategies to control L. monocytogenes on wax-coated apples.

Effects of 1-methylcyclopropene and gaseous ozone on Listeria innocua survival and fruit quality of Granny Smith apples during long-term commercial cold storage.

This study evaluated the impact of 1-methylcyclopropene (1-MCP), an ethylene synthesis inhibitor, followed by long-term commercial cold storage with low-dose gaseous ozone on the microbiological safety and quality of fresh apples. Granny Smith apples were inoculated with or without Listeria innocua, treated with or without 1.0 mg/L 1-MCP for 24 h, then subjected to commercial cold storage conditions including refrigerated air (RA, 0.6 °C, control), controlled atmosphere (CA, 2% O2, 1% CO2, 0.6 °C), and CA with 51-87 µg/L ozone gas for up to 36 weeks. RA storage reduced L. innocua on apples by up to 3.6 log10 CFU/apple. CA had no advantage over RA in controlling Listeria. Continuous ozone gas application resulted in an additional ∼2.0 log10 CFU/apple reduction of L. innocua (total reduction up to 5.7 log10 CFU/apple) and suppressed native bacteria and fungi. Treatment with 1-MCP had a minor impact on survival of L. innocua or background microbiota on apples, while it significantly delayed fruit ripening and reduced the incidence of superficial scald and internal browning. In summary, 1-MCP treatment followed by CA storage with low-dose continuous ozone gas can effectively control Listeria on fresh apples and delay fruit ripening.

Prevalence of Listeria Species on Food Contact Surfaces in Washington State Apple Packinghouses.

The 2014 caramel apple listeriosis outbreak was traced back to cross-contamination between food contact surfaces (FCS) of equipment used for packing and fresh apples. For Washington state, the leading apple producer in the United States with 79% of its total production directed to the fresh market, managing the risk of apple contamination with Listeria monocytogenes within the packing environment is crucial. The objectives of this study were to determine the prevalence of Listeria spp. on FCS in Washington state apple packinghouses over two packing seasons and to identify those FCS types with the greatest likelihood to harbor Listeria spp. Five commercial apple packinghouses were visited quarterly over two consecutive year-long packing seasons. A range of 27 to 50 FCS were swabbed at each facility to detect Listeria spp. at two sample times, (i) postsanitation and (ii) in-process (3 h of packinghouse operation), following a modified protocol of the FDA's Bacteriological Analytical Manual method. Among 2,988 samples tested, 4.6% (n = 136) were positive for Listeria spp. Wax coating was the unit operation from which Listeria spp. were most frequently isolated. The FCS that showed the greatest prevalence of Listeria spp. were polishing brushes, stainless steel dividers and brushes under fans/blowers, and dryer rollers. The prevalence of Listeria spp. on FCS increased throughout apple storage time. The results of this study will aid apple packers in controlling for contamination and harborage of L. monocytogenes and improving cleaning and practices for sanitation of the FCS on which Listeria spp. are the most prevalent.IMPORTANCE 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 niches. This research assesses the prevalence of Listeria spp. on FCS in apple packinghouses and identifies those FCS most likely to harbor Listeria spp. Such findings are essential for the apple-packing industry striving to further understand and exhaustively mitigate the risk of contamination with L. monocytogenes to prevent future listeriosis outbreaks and recalls.

Verification of peroxyacetic acid treatment against L. monocytogenes on fresh apples using E. faecium NRRL B-2354 as a surrogate in commercial spray-bar operations.

Peroxyacetic acid (PAA) is a commonly used antimicrobial in apple spray bar interventions during post-harvest packing. However, limited information is available about its efficacy against foodborne pathogens on fresh apples under commercial packing conditions. In this study, the practical efficacies of PAA against Listeria monocytogenes on fresh apples during spray bar operation at ambient and elevated temperature were validated in three commercial packing facilities using Enterococcus faecium NRRL B-2354 as a surrogate strain. Apples were inoculated with E. faecium at ~6.5 Log10 CFU/apple and subjected to PAA spray bar interventions per commercial packing line practice. At each temperature and contact time intervention combination, 20-24 inoculated apples were processed together with 72-80 non-inoculated apples. Applying 80 ppm PAA at ambient temperature (17-21 °C) achieved a similar log reduction (P > 0.05) of E. faecium on Granny Smith apples (GSA) in three apple packing facilities, which caused 1.12-1.23 and 1.18-1.32 Log10 CFU/apple reductions of E. faecium on GSA for 30-sec and 60-sec intervention, respectively. Increasing the temperature of the PAA solution to 43-45 °C enhanced its bactericidal effect against E. faecium, causing 1.45, 1.86 and 2.19 Log10 CFU/apple reductions in three packing facilities for a 30-sec contact, and 1.50, 2.24, and 2.29 Log10 CFU/apple reductions for a 60-sec contact, respectively. Similar efficacies (P > 0.05) of PAA at both ambient and elevated temperature were also observed on Fuji apples. Spraying PAA on apples at ambient or elevated temperature reduced the level of E. faecium cross-contamination from inoculated apples to non-inoculated apples but could not eliminate cross-contamination. Data from this study provides valuable technical information and a reference point for the apple industry in controlling L. monocytogenes and verifying the effectiveness of their practices.

Survival of Listeria innocua on Fuji apples under commercial cold storage with or without low dose continuous ozone gaseous.

This study evaluated the fate of Listeria innocua, a non-pathogenic species closely related to Listeria monocytogenes, on Fuji apple fruit surfaces during commercial cold storage with and without continuous low doses of gaseous ozone. Unwaxed Fuji apples of commercially acceptable maturity were inoculated with 6.0-7.0 Log10 CFU L. innocua/apple, and subjected to refrigerated air (RA, 33 °F), controlled atmosphere (CA, 33 °F, 2% O2, 1% CO2), or CA with low doses of ozone gas (50.0 -87.0 ppb ) storage in a commercial facility for 30 weeks. A set of uninoculated apples was simultaneously subjected to the above storage conditions for total plate count and yeasts and molds enumeration. L. innocua survival under RA and CA storage was similar, which led to 2.5-3.0 Log10 CFU/apple reduction during storage. Continuous gaseous ozone application decreased L. innocua population on Fuji apples to ∼1.0 Log10 CFU/apple after 30-week storage, and suppressed apple native flora. CA storage delayed apple fruit ripening through reduction of apple firmness and titratable acidity loss, and low dose gaseous ozone application had no negative influence on apple visual quality, including both external and internal disorders. In summary, L. innocua decreased on Fuji apple surfaces during commercial long-term RA and CA storage. Ozone gas has the potential to be used as a supplemental intervention method to control Listeria spp. and to ensure fresh apple safety.

Gene expression and metabolism preceding soft scald, a chilling injury of 'Honeycrisp' apple fruit.

BACKGROUND: 'Honeycrisp' is an apple cultivar that is susceptible to soft scald, a chilling injury expressed as necrotic patches on the peel. Improved understanding of metabolism associated with the disorder would improve our understanding of soft scald and contribute to developing more effective management strategies for apple storage. It was expected that specific gene expression and specific metabolite levels in the peel would be linked with soft scald risk at harvest and/or specific time points during cold storage. RESULTS: Fruit from nine 'Honeycrisp' apple orchards that would eventually develop different incidences of soft scald between 4 and 8 weeks of cold air storage were used to contrast and determine differential transcriptomic and metabolomic changes during storage. Untargeted metabolic profiling revealed changes in a number of distinct pathways preceding and concurrent with soft scald symptom development, including elevated γ-aminobutryic acid (GABA), 1-hexanol, acylated steryl glycosides, and free p-coumaryl acyl esters. At harvest, levels of sesquiterpenoid and triterpenoid acyl esters were relatively higher in peel of fruit that did not later develop the disorder. RNA-seq driven gene expression profiling highlighted possible involvement of genes and associated metabolic processes with soft scald development. These included elevated expression of genes involved in lipid peroxidation and phenolic metabolism in fruit with soft scald, and isoprenoid/brassinosteroid metabolism in fruit that did not develop soft scald. Expression of other stress-related genes in fruit that developed soft scald included chlorophyll catabolism, cell wall loosening, and lipid transport while superoxide dismutases were up-regulated in fruit that did not develop the disorder. CONCLUSIONS: This study delineates the sequential transcriptomic and metabolomic changes preceding soft scald symptom development. Changes were differential depending on susceptibility of fruit to the disorder and could be attributed to key stress related and mediating pathways.

Chilling-related cell damage of apple (Malus × domestica Borkh.) fruit cortical tissue impacts antioxidant, lipid and phenolic metabolism.

'Soggy breakdown' (SB) is an internal flesh disorder of 'Honeycrisp' apple (Malus × domestica Borkh.) fruit that occurs during low temperature storage. The disorder is a chilling injury (CI) in which visible symptoms typically appear after several weeks of storage, but information about the underlying metabolism associated with its induction and development is lacking. The metabolic profile of flesh tissue from wholly healthy fruit and brown and healthy tissues from fruit with SB was characterized using gas chromatography-mass spectrometry (GC-MS) and liquid chromatograph-mass spectrometry (LC-MS). Partial least squares discriminant analysis (PLS-DA) and correlation networks revealed correlation among ester volatile compounds by composition and differences in phytosterol, phenolic and putative triacylglycerides (TAGs) metabolism among the tissues. anova-simultaneous component analysis (ASCA) was used to test the significance of metabolic changes linked with tissue health status. ASCA-significant components included antioxidant compounds, TAGs, and phytosterol conjugates. Relative to entirely healthy tissues, elevated metabolite levels in symptomatic tissue included γ-amino butyric acid, glycerol, sitosteryl (6'-O-palmitoyl) ß-d-glucoside and sitosteryl (6'-O-stearate) ß-d-glucoside, and TAGs containing combinations of 16:0, 18:3, 18:2 and 18:1 fatty acids. Reduced metabolite levels in SB tissue included 5-caffeoyl quinate, ß-carotene, catechin, epicatechin, α-tocopherol, violaxanthin and sitosteryl ß-d glucoside. Pathway analysis indicated aspects of primary metabolism differed according to tissue condition, although differences in metabolites involved were more subtle than those of some secondary metabolites. The results implicate oxidative stress and membrane disruption processes in SB development and constitute a diagnostic metabolic profile for the disorder.

Persistence of Listeria innocua on Fresh Apples during Long-Term Controlled Atmosphere Cold Storage with Postharvest Fungal Decay.

ABSTRACT: Recent apple-related recall and outbreak events have exposed a need for better food safety controls along the supply chain. Following harvest, apples can be stored under a controlled atmosphere for up to 1 year after harvest before packing and distribution, making the crop susceptible to many opportunities for contamination that increase the quantity of postharvest losses. Botrytis cinerea and Penicillium expansum cause significant rot-associated losses to the apple industry. These fungi can colonize and destroy apple tissue as storage duration increases, which may also impact the growth of saprophytic foodborne pathogens like Listeria monocytogenes. Thus, the objective of this study was to observe population changes of Listeria innocua as a surrogate for L. monocytogenes on apples inoculated with B. cinerea or P. expansum under long-term controlled atmosphere cold storage conditions to identify the effect of postharvest mold growth on growth patterns of a microorganism relevant to food safety. 'Gala' and 'WA 38' apples (n = 1,080) were harvested, treated with pyrimethanil, and inoculated with L. innocua only or with L. innocua and one of the mold species on wounded and unwounded portions of the apple equator. Apples were treated with 1-methylcyclopropene and stored at a controlled atmosphere (2 kPa O2, 1 kPa CO2, 1°C) for 1 week and 1, 3, 6, 9, and 11 months before enumeration. After 3 months, L. innocua consistently fell below the limit of detection (2.35 Log CFU/g), and samples were enriched following a modified Bacteriological Analytical Manual method with PCR confirmation. Listeria persistence was dependent on the storage duration and type of fungal contamination (P ≤ 0.05). Surface wounding may impact these trends, depending on the apple variety. Prevalence of L. innocua was greater in Gala apples. Future studies should more closely examine the interactions on the fruit surface that occur during the seemingly critical time frame of 3 to 6 months in storage.

Utility of rapid tests to assess the prevalence of indicator organisms (Aerobic plate count, Enterobacteriaceae, coliforms, Escherichia coli, and Listeria spp.) in apple packinghouses.

The 2014 listeriosis outbreak caused by caramel-coated apples was linked to apples cross-contaminated within an apple packing facility. This outbreak has increased the focus on effective cleaning and sanitation methods that must be validated and monitored during apple packing. Thus, rapid and reliable testing methods are necessary for assessing cleanliness in the apple packing industry. The objectives of this study were to assess the prevalence of common indicator organisms [Aerobic plate count (APC), Enterobacteriaceae, coliforms, Escherichia coli, and Listeria spp.] on food contact surfaces (zone 1) in apple packinghouses and to evaluate the utility and accuracy of currently used rapid tests (ATP and glucose/lactose residue swabs). Food contact surfaces were sampled over a 100 cm2 area in five commercial apple packinghouses to evaluate populations of indicator organisms APC, Enterobacteriaceae, coliforms, E. coli (n = 741), and rapid test readings (n = 659). Petrifilm plates were used for the quantification of APC, Enterobacteriaceae, and coliform/E. coli. Rapid tests [ATP swabs (UltraSnap) and glucose/lactose residue swabs (SpotCheck Plus)] were processed on-site. A larger area (0.93 m2) was sampled for the detection of Listeria spp. (n = 747), following a modified protocol of the FDA's Bacteriological Analytical Manual method, and confirmed with PCR and gel electrophoresis via the iap gene. No significant association was found between either rapid test and populations of APC, Enterobacteriaceae, coliforms, E. coli, and Listeria spp. detection. However, recovery of APC (log CFU/100 cm2) was higher with a failed glucose/lactose residue swab surface hygiene result (3.1) than a passed result (2.9) (p = 0.03). Populations of APC, Enterobacteriaceae, and coliforms were significantly different at each unit operation during the packing process (p ≤ 0.05). This study concluded that ATP and glucose/lactose residue rapid tests were poorly suited for determining microbial load since they were not related to populations of any common indicator organisms or the detection of Listeria spp. These findings emphasize the need to utilize a rapid test, which can be a good indicator of residual matter on a surface, along with traditional microbiological methods to assess cleaning and sanitation practices in apple packinghouses.

Synergistic Effects of Lauric Arginate and Peracetic Acid in Reducing Listeria monocytogenes on Fresh Apples.

Apples are naturally coated with a water-repelling hydrophobic wax layer, which may limit the antimicrobial efficacies of surface sanitizer solutions. Lauric arginate (LAE) is a cationic surfactant with antimicrobial efficacy against Listeria monocytogenes. In this study, we investigated the antimicrobial and the wettability effects of LAE in enhancing anti-L. monocytogenes efficacy of peracetic acid (PAA) and further verified the optimized treatment combinations in a pilot spray-bar brush bed system. Apples after 48 h of inoculation were treated with PAA surface sanitation in combination with different concentrations of LAE at 22 or 46°C. The effectiveness of PAA with LAE solutions in decontaminating L. monocytogenes significantly increased with the increased concentration of PAA (60-80 ppm) or LAE (0.01-0.05%) or the treatment temperature (from 22 to 46°C). A 30-120-sec wash by 80 ppm PAA with 0.01 and 0.05% LAE at 22°C reduced L. monocytogenes on apples by 2.10-2.25 and 2.48-2.58 log10 CFU/apple, respectively. Including LAE in the PAA solution decreased contact angles on apple surfaces. However, the increased wettability of the sanitizer solution may not be the main contributor to the enhanced antimicrobial efficacy of the PAA solution, given that the addition of Tween 80 or Tween 85 only slightly boosted the anti-L. monocytogenes efficacy of PAA solutions though both increased the wettability of the PAA solutions. The synergistic effects of PAA and LAE were further validated in a pilot spray-bar brush bed packing system, where a 30-sec spray wash with 80 ppm PAA and 0.05% LAE at 22 and 46°C caused 1.68 and 2.08 log reduction of Listeria on fresh apples, respectively. This study provides an improved PAA process/preventive strategy for ensuring microbial food safety of fresh apples that is applicable to commercial apple packing lines.

Effectiveness of Low-Dose Continuous Gaseous Ozone in Controlling Listeria innocua on Red Delicious Apples During 9-Month Commercial Cold Storage.

This study aimed to investigate the effects of low-dose continuous ozone gas in controlling Listeria innocua and quality attributes and disorders of Red Delicious apples during long-term commercial cold storage. Red Delicious apples were inoculated with a three-strain L. innocua cocktail at ∼6.2 log10 CFU/apple, treated with or without 1-methylcyclopropene, and then subjected to controlled atmosphere (CA) storage with or without continuous gaseous ozone in a commercial facility for 36 weeks. Uninoculated Red Delicious apples subjected to the above storage conditions were used for yeast/mold counts and quality attributes evaluation. The 36 weeks of refrigerated air (RA) or CA storage caused ∼2.2 log10 CFU/apple reduction of L. innocua. Ozone gas application caused an additional > 3 log10 CFU/apple reduction of L. innocua compared to RA and CA storage alone. During the 36-week CA storage, low-dose continuous gaseous ozone application significantly retarded the growth of yeast/mold, delayed apple firmness loss, and had no negative influence on ozone burn, lenticel decay, russet, CO2 damage, superficial scald, and soft scald of Red Delicious apples compared to CA-alone storage. In summary, the application of continuous low-dose gaseous ozone has the potential to control Listeria on Red Delicious apples without negatively influencing apple quality attributes.

Hurdle Effect of Hot Air Impingement Drying and Surfactant-Sanitizer Wash on Removal of Listeria innocua from Fresh Apples.

ABSTRACT: This study investigated the decontamination efficacy of washing treatments for whole fresh apples by using washes containing surfactants, lauric arginate, sodium dodecyl sulfate, and Tween 20, combined with peracetic acid (PAA), followed by hot air impingement drying. Whole fresh apples of selected varieties (Gala and Granny Smith) were inoculated with Listeria innocua (7 log CFU/mL) by using a dipping method, and then dried and subjected to wash treatments with selected washing solutions (H2O, PAA, PAA-lauric arginate, PAA-sodium dodecyl sulfate, and PAA-Tween 20), followed by hot air impingement drying at two different temperature and time conditions, 93°C for 60 s or 121°C for 25 s. The H2O and PAA wash followed by hot air impingement drying led to a maximum 1.5-log reduction of L. innocua on the fruit surface. Adding surfactants increased the effectiveness of washing and drying treatments, resulting in an approximate 2.2-log reduction. Surfactants increased the spreadability and evaporation rate of the washing solutions. Posttreatment changes in apple firmness were assessed during a 21-day storage at 4 and 21°C. The hot air impingement drying had no adverse effect on the firmness of the apples and did not show any further reduction in L. innocua. Washing apples with solutions containing surfactants combined with PAA followed by hot air impingement drying helped to reduce the microbial loads to some extent and may help to reduce drying times significantly.

Efficacy of Surfactant Combined with Peracetic Acid in Removing Listeria innocua from Fresh Apples.

Large amounts of water used in the apple packing process, the presence of organic matter, and difficult-to-clean equipment are vectors for contaminating apples with foodborne pathogens, such as Listeria monocytogenes. There is a need to develop new cleaning methods for fresh apples and evaluate their antimicrobial efficacy. A series of surfactants of different chemical properties (cationic lauric arginate [LAE], anionic sodium dodecyl sulfate [SDS], and nonionic Tween 20 [T20]) alone and combined with peracetic acid (PAA) were evaluated for their efficiency in the removal of L. innocua, a surrogate of L. monocytogenes, from fresh apples. Whole fresh apples were inoculated with L. innocua (7 log CFU/mL) by a dipping method, dried, and subjected to wash treatments with selected cleaning solutions (water, PAA, PAA-LAE, PAA-SDS, and PAA-T20). The contact angle between the cleaning solutions and the surface of the apples was measured. The antimicrobial activity of the cleaning solutions and the efficacy of the cleaning treatment were evaluated by enumeration of L. innocua from treated apples and visualized by scanning electron microscopy. Stem bowl and calyx cavities of the apple harbored higher bacteria concentrations (∼4.82 log CFU per apple), compared with the equatorial section (∼2.66 log CFU per apple). Addition of 0.1% of selected surfactants led to a significant decrease in surface tension of cleaning solutions and allowed better spreading on the apple surface. Surfactants combined with PAA solution resulted in higher L. innocua reduction compared with PAA alone; however, their efficacy was limited. The most effective cleaning solution was PAA-T20, with reduction of approximately 2.2 log. Scanning electron microscopy imaging confirmed that most bacteria were harbored inside the surface irregularities. PAA alone and with surfactants caused damage and deformation of bacteria cells. Cleaning apples with PAA combined with surfactants may improve microbial safety in whole apples; however, the efficiency of the decontamination treatment can be reduced because of variations in apple morphology.

Enhanced Efficacy of Peroxyacetic Acid Against Listeria monocytogenes on Fresh Apples at Elevated Temperature.

Peroxyacetic acid (PAA) is the most commonly used antimicrobial in spray bar antimicrobial treatment during fresh apple packing and processing. However, there are limited data regarding its practical efficacy against Listeria monocytogenes on fresh apples. This study evaluated the antimicrobial activity of PAA against L. monocytogenes on fresh apples applicable to current industry practice, and further examined practical parameters impacting its efficacy to maximize the biocidal effects. Apples were inoculated with a three-strain L. monocytogenes cocktail at ~6.0 Log10 CFU/apple and then subjected to comparative antimicrobial treatments after 48 h post-inoculation. An 80 ppm PAA treatment, at 30-s and 2-min exposure, reduced L. monocytogenes on fresh apples by ~1.3 or 1.7 Log10 CFU/apple, respectively. The anti-Listeria efficacy of PAA was not affected by the water hardness and pH of PAA solution, while it improved dramatically when applied at elevated temperature. A 2-min exposure of 80 ppm PAA at 43 and 46°C resulted in a 2.3 and 2.6 Log10 CFU/apple reduction, respectively. A 30-s contact time of 80 ppm PAA at 43-46°C reduced L. monocytogenes on apples by 2.2-2.4 Log10 CFU/apple. Similarly, PAA intervention at elevated temperatures significantly strengthened its effectiveness against naturally occurring apple microbiota. PAA treatment at 43-46°C can provide a vital method to improve antimicrobial efficacy against both L. monocytogenes and indigenous microbiota on fresh apples. Our data provide valuable information and reference points for the apple industry to further validate or verify process controls.

Evaluation of JC9450 and Neutral Electrolyzed Water in Controlling Listeria monocytogenes on Fresh Apples and Preventing Cross-Contamination.

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.

Efficacy of Ozonated Water, Chlorine, Chlorine Dioxide, Quaternary Ammonium Compounds and Peroxyacetic Acid Against Listeria monocytogenes Biofilm on Polystyrene Surfaces.

Listeria monocytogenes contaminated processing equipment and the general packing environment have been implicated in deadly foodborne listeriosis outbreaks, highlighting the significance of proper sanitization and disinfection of food contact surfaces. This study aims to comprehensively evaluate antimicrobial efficacy of commercially available, economical sanitizers at practical concentrations against L. monocytogenes biofilm formed on polystyrene surfaces under different conditions. Ozonated water 1-min treatment at 1.0, 2.0, and 4.0 ppm resulted in ∼0.9, 3.4, and 4.1 log reduction of L. monocytogenes single strain biofilm grown on polystyrene surfaces, respectively. However, its efficacy was dramatically diminished in multi-strain L. monocytogenes biofilm and was further compromised by aged biofilm and in the presence of organic matter. Quaternary ammonium compounds (QAC) at 100/400 ppm, chlorine at 100/200 ppm, chlorine dioxide at 2.5/5.0 ppm and peroxyacetic acid (PAA) at 80/160 ppm resulted in 2.4/3.6, 2.0/3.1, 2.4/3.8, and 3.6/4.8 log reduction of L. monocytogenes single strain biofilm, respectively. Antimicrobial efficacies of all tested sanitizers against 7-day-old biofilm were much lower when compared to 2-day-old biofilm, with PAA being the least influenced by the age of the biofilm. Organic matter conditioning with diluted milk or apple juice dramatically impacted the antimicrobial efficacy of all sanitizers. PAA treatment of 1 min at 160-200 ppm resulted in a 3.2-3.5 log reduction against 7-day-old biofilm in the presence of organic matter, thus showing its effectiveness in eradicating L. monocytogenes biofilm on polystyrene surface. Collectively, data highlight the importance of timely and thoroughly cleaning food contact surfaces before disinfection and provides practical information and guidance for the food industry in selecting the most effective sanitizer in their sanitizing regimes to eliminate L. monocytogenes biofilm.

Fate of Listeria monocytogenes on Fresh Apples under Different Storage Temperatures.

Fresh apples are typically stored for up to 1 year commercially; different apple varieties require different storage temperatures to maintain their quality characteristics. There is sparse information available about Listeria monocytogenes survival on fresh apples under various storage temperatures. The objective of this study was to comprehensively evaluate the effect of storage temperature on apple fruit decay and L. monocytogenes survival. Unwaxed apple fruits of selected varieties (Fuji and Granny Smith) were dip inoculated in a three-strain L. monocytogenes cocktail to establish ∼3.5 and 6.0 Log10 CFU/apple. Twenty-four hours post-inoculation, apples were subjected to 1, 4, 10, or 22°C storage for up to 3 months. Apples under the different storage treatments were sampled at 1-, 4-, 7- and 14-day for short-term storage under all four tested temperatures, and 2-, 4-, 8-, and 12-week for long-term storage at 1, 4, and 10°C. A set of uninoculated and unwaxed apples were simultaneously subjected to the previously mentioned storage temperatures and sampled biweekly for their total bacterial count (TPC) and yeasts/molds (Y/M) count. During the 2-week short-term storage, L. monocytogenes population on organic Granny Smith apples stored at 1, 4, or 10°C was reduced by 0.2-0.3 Log. When apples were stored at 22°C, there was a 0.5-1.2 Log10 CFU/apple reduction 14-day post storage dependent on the initial inoculation level. During the 12-week cold storage under 1, 4, and 10°C, L. monocytogenes count on organic Granny Smith apples decreased by 0.5-1.5 Log10 CFU/apple for both inoculation levels. L. monocytogenes had similar survival pattern on conventional Granny Smith and Fuji apples with 0.8-2.0 Log10 CFU/apple reduction over a 3-month cold storage period. Interestingly, both TPC and Y/M count were stable regardless of apple variety or cultivation practice during the 12-week storage at all tested temperatures. In summary, while L. monocytogenes did not proliferate on apple surfaces during 12 weeks of refrigerated storage, only a limited reduction of L. monocytogenes was observed in this study. Therefore, the apple industry cannot rely on cold storage alone to control this pathogen. Additional interventions are needed to eradicate Listeria on fresh apples during long-term cold storage.