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

Inactivation of Desiccation-Resistant Salmonella on Apple Slices Following Treatment with ε-Polylysine, Sodium Bisulfate, or Peracetic Acid and Subsequent Dehydration

Salmonella is capable of surviving dehydration within various foods, such as dried fruit. Dried fruit, including apple slices, have been the subject of product recalls due to contamination with Salmonella. A study was conducted to determine the fate of Salmonella on apple slices, following immersion in three antimicrobial solutions (viz., ε-polylysine [epsilon-polylysine or EP], sodium bisulfate [SBS], or peracetic acid [PAA]), and subsequent hot air dehydration. Gala apples were aseptically cored and sliced into 0.4 cm thick rings, bisected, and inoculated with a five-strain composite of desiccation-resistant Salmonella, to a population of 8.28 log CFU/slice. Slices were then immersed for 2 min in various concentrations of antimicrobial solutions, including EP (0.005, 0.02, 0.05, and 0.1%), SBS (0.05, 0.1, 0.2, and 0.3%), PAA (18 or 42 ppm), or varying concentrations of PAA + EP, and then dehydrated at 60°C for 5 h. Salmonella populations in positive control samples (inoculated apple slices washed in sterile water) declined by 2.64 log after drying. In the present study, the inactivation of Salmonella, following EP and SBS treatments, increased with increasing concentrations, with maximum reductions of 3.87 and 6.20 log (with 0.1 and 0.3% of the two compounds, respectively). Based on preliminary studies, EP concentrations greater than 0.1% did not result in lower populations of Salmonella. Pretreatment washes with either 18 or 42 ppm of PAA inactivated Salmonella populations by 4.62 and 5.63 log, respectively, following desiccation. Combining PAA with up to 0.1% EP induced no greater population reductions of Salmonella than washing with PAA alone. The addition of EP to PAA solutions appeared to destabilize PAA concentrations, reducing its biocidal efficacy. These results may provide antimicrobial predrying treatment alternatives to promote the reduction of Salmonella during commercial or consumer hot air drying of apple slices.

Impact of preculture temperature on peracetic acid-induced inactivation and sublethal injury of L. monocytogenes and subsequent growth potential of single cells

The disinfectant peracetic acid (PAA) that is used in the food industry can cause sublethal injury in L. monocytogenes. The effect of preculture temperature on the inactivation and sublethal injury of L. monocytogenes cells due to PAA was evaluated by plating on non-selective and selective agar medium supplemented with 5 % (w/v) NaCl. L. monocytogenes cells were precultured at 30 °C, 20 °C or 4 °C, and the former was used as reference temperature. Preculture of cells at 20 °C or 4 °C and subsequent exposure to PAA at the respective growth temperatures caused higher injury compared to cells grown at 30 °C and exposed to PAA 20 °C and PAA 4 °C, respectively. Survival was also affected by the preculture temperature; 20 °C-grown cultures resulted in lower survival at PAA 20 °C. Nevertheless, preculture at 4 °C resulted in a similar number of surviving cells when exposed to PAA 4 °C compared to cells precultured at 30 °C and exposed to PAA at 4 °C. Flow cytometry was subsequently used to quantify outgrowth capacity of stressed and sublethal damaged populations following sorting of single cells in nutrient rich medium (Tryptone soy broth supplemented with yeast extract [TSBY]). PAA treatment affected the outgrowth of L. monocytogenes at single-cell level resulting in increased outgrowth-times reflecting higher single cell heterogeneity. To conclude, the response of L. monocytogenes when exposed to PAA depended on the preculture conditions, and the highly heterogeneous outgrowth potential of PAA-injured cells may affect their detection accuracy and pose a food safety risk.

Enhancing the efficacy of peracetic acid against Listeria monocytogenes and Listeria innocua on fresh apples using commercial acidic and alkaline cleaners

Peracetic acid (PAA) is a commonly used antimicrobial in brush-bed spray bar interventions during apple packing. Prior to sanitizer application on the brush-bed, specific fruit cleaners, such as Acidex Duo (AD), EpiClean (EC), Nature's Shield 220-ACL (NS 220), or Nature's Shield 330-ALK (NS 330), are used to remove of soil, debris, and natural wax from the surfaces of apples. This study evaluated the effectiveness of commonly used cleaners in the apple industry to improve the antimicrobial efficacy of PAA against Listeria monocytogenes on apple surfaces during brush-bed spray bar interventions. Granny Smith apples, 48 h post-inoculation, underwent submersion treatment with different cleaners, as well as PAA alone or in combination with the cleaners. A 30-sec treatment of 5.0% AD, 4.2% EC, 10.0% NS 220, and 10.0% NS 330 resulted in 0.65, 0.50, 0.68, and 0.51 log10 CFU/apple reduction of L. monocytogenes on apples, respectively. Incorporating AD, NS 220, and EC significantly enhanced the antimicrobial efficacy of an 80 ppm PAA intervention. The enhancing effects were not impacted whether the cleaner was applied consecutively with PAA (sequentially) or in combination with PAA (simultaneously), nor were they impacted by a post-treatment water rinse. A 30-120 s wash of 80 ppm PAA with AD, EC, and NS 220 at their suggested concentration resulted in 2.46-2.55, 1.87-2.03, and 2.34-2.48 log10 CFU/apple reduction of L. monocytogenes, respectively, compared to 1.39-1.64 log10 CFU/apple in PAA treatment alone. The inclusion of AD or NS 220 in 80 ppm PAA solution resulted in a reduction of 1.51-1.63 log10 CFU/apple of Listeria after 30-60 s brush-bed spray wash. This enhancement in efficacy was significant compared to the treatment with 80 ppm PAA alone, which resulted in a reduction of 0.94-1.03 log10 CFU/apple. This study demonstrated that using certain commercially available cleaners along with PAA can enhance the effectiveness of PAA in reducing L. monocytogenes on fresh apples.

The Effect of Water Hardness and pH on the Efficacy of Peracetic Acid and Sodium Hypochlorite against SARS-CoV-2 on Food-Contact Surfaces

Sodium hypochlorite (NaOCl) and peracetic acid (PAA) are commonly used disinfectants with a maximum recommended concentration of 200 ppm for food-contact surfaces. The objectives of this study were to assess the effect of pH and water hardness on NaOCl and PAA efficacy against SARS-CoV-2 on stainless steel (SS). The two disinfectants were prepared at 200 ppm in water of hardness 150 or 300 ppm with the final pH adjusted to 5, 6, 7, or 8. Disinfectants were applied to virus-contaminated SS for one minute at room temperature following the ASTM E2197 standard assay. SARS-CoV-2 infectivity was quantified using TCID50 assay on Vero-E6 cells. In general, increasingly hard water decreased the efficacy of NaOCl while increasing the efficacy of PAA. Hard water at 300 ppm significantly increased virus log reduction with PAA at pH 8 by ~1.5 log. The maximum virus log reductions were observed at pH 5 for both NaOCl (~1.2 log) and PAA (~2 log) at 150 and 300 ppm hard water, respectively. In conclusion, PAA performed significantly better than NaOCl with harder water. However, both disinfectants at 200 ppm and one minute were not effective (≤3 log) against SARS-CoV-2 on contaminated food-contact surfaces, which may facilitate the role of these surfaces in virus transmission.

Efficacy of Power Ultrasound-Based Hurdle Technology on the Reduction of Bacterial Pathogens on Fresh Produce

Minimally processed produce is frequently contaminated with foodborne bacterial pathogens. Power ultrasound is a non-thermal and cost-effective technology that can be combined with other chemical sanitization methods. This study investigated the reduction of Listeria monocytogenes and Salmonella Newport on grape tomato, romaine lettuce, and spinach washed with water, chlorine, or peroxyacetic acid alone or in combination with 25 or 40 kHz power ultrasound for 1, 2, or 5 min. Produce items were inoculated with either pathogen at 10 log CFU/g, dried for 2 h, and treated. Combined treatment of ultrasound and sanitizers resulted in 1.44-3.99 log CFU/g reduction of L. monocytogenes and 1.35-3.62 log CFU/g reduction of S. Newport, with significantly higher reductions observed on grape tomato. Synergistic effects were achieved with the hurdle treatment of power ultrasound coupled with the chemical sanitizers when compared to the single treatments; an additional 0.48-1.40 log CFU/g reduction of S. Newport was obtained with the addition of power ultrasound on grape tomato. In general, no significant differences were observed in pathogen reductions between the ultrasound frequencies, the sanitizers, or the treatment lengths. Results from this study suggest that incorporation of power ultrasound into the current washing procedure may be beneficial for the reduction, but not elimination, of bacterial pathogens on certain produce items, including tomatoes.

Listeria monocytogenes Outbreaks Related to Commercially Produced Caramel Apples: Developments in Sanitation, Product Formulation, and Packaging: A Review

ABSTRACT

Prior to a deadly 2014 listeriosis outbreak, caramel apples were not thought to be vehicles for the foodborne pathogen Listeria monocytogenes. The purpose of this review article is to summarize what has been learned from research prompted by this outbreak. This overview includes descriptions of the two L. monocytogenes infection outbreaks related to prepackaged caramel apples and a brief discussion of apple sanitation, the production processes used to make caramel apples, and research on ways to prevent future outbreaks associated with caramel apples. A qualitative analysis of the literature and interviews with current caramel apple manufacturers were conducted. Sanitation, packaging, and storage procedures used by manufacturers in the past may not effectively inactivate L. monocytogenes from contaminated product. Novel apple sanitation methods and product formulations to control L. monocytogenes on caramel apples have been developed and, in some cases, implemented in commercial production.

HIGHLIGHTS

The Efficacy of Conventional Spray, Electrostatic Spray, and Dip with a Combination of Hydrogen Peroxide and Peroxyacetic Acid To Inactivate Listeria monocytogenes on Apples

ABSTRACT

This study aimed to evaluate the efficacy of a hydrogen peroxide (H2O2) and peroxyacetic acid (PAA) mixer delivered by conventional garden spray (GS), electrostatic spray (ES), and dip methods to inactivate Listeria monocytogenes on apples. Organic Honeycrisp, Fuji, and Pink Lady apples were dip inoculated with L. monocytogenes (two strains, serotype 1/2b), which were then kept untreated (control), sprayed with water only, or treated with the H2O2-PAA mixer (0.0064, 0.1, 0.25, and 0.50%) for 20 s via GS, ES, or dip, followed by draining (for 2 min) on aluminum foil. Surviving bacteria were recovered on modified Oxford agar. Atomic force microscopy was used to detect the structural changes of inactivation of L. monocytogenes in broth medium by the H2O2-PAA mixer solution. Data (two replicates, with six samples per replicate) were analyzed using the mixed model procedure of SAS (P = 0.05). Initial counts of L. monocytogenes on untreated apples were 6.80 to 6.90 log CFU per apple. The dip method was the most effective treatment (P < 0.05) for pathogen reductions (2.31 to 2.41 log CFU per apple), followed by GS (1.44 to 1.70 log CFU per apple) and then ES (0.84 to 1.20 log CFU per apple). Reductions of L. monocytogenes were greatest (P < 0.05) when apples were treated with H2O2-PAA mixer -0.25 and -0.50%. Atomic force microscopy analyses indicated that inactivation of L. monocytogenes cells in H2O2-PAA mixer solutions resulted from disruption of the outer membrane. The H2O2-PAA mixer-treated cells had increased width and height and decreased roughness compared with the untreated cells. Results suggested that applying a H2O2-PAA mixer by dip or GS methods is better for pathogen reduction than ES on apples.

HIGHLIGHTS

Examining the antimicrobial efficacy of granulated tetraacetylethylenediamine derived peracetic acid and commercial peracetic acid in urban wastewaters

The ever-increasing need for access to safe water has meant that alternative water sources and innovative water reclamation approaches are often required to meet the global water demand. As a result, many wastewater treatment facilities have faced regulatory pressure to seek alternative disinfection methods that ensure public health safety, while adhering to regulations that set limits on carcinogenic disinfection by-products (DBPs). Peracetic acid (PAA) is an emerging wastewater disinfectant in the United States that has been widely used in other industries such as food sanitization and does not produce carcinogenic DBPs. However, several factors such as transport, storage, and physical and chemical effects have stymied its widespread use in wastewater markets. Therefore, the purpose of this study was to examine the antimicrobial efficacy of an on-site generated PAA compared against a commercially available PAA. Antimicrobial efficacy was assessed using standard fecal contamination indicators (i.e., total coliforms and Escherichia coli) in six urban wastewater treatment facilities ranging in size and treatment processes. Overall, few statistical differences were found between the antimicrobial efficacies of on-site generated PAA and commercially available PAA; however, before becoming more widely utilized, the on-site PAA should be tested against emerging fecal contamination indicators (e.g., human norovirus and enterovirus) and be assessed in terms of economic and sustainability impacts. PRACTITIONER POINTS: Alternative Ct approaches should be considered when using disinfectants like PAA. On-site generated PAA can achieve the same level of disinfection as commercial PAA. On-site generation of PAA may help further its use as a wastewater disinfectant.

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% CO_2, 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.

In vitro virulence potential, surface attachment and transcriptional response of sublethally injured Listeria monocytogenes following exposure to peracetic acid

The disinfectant Peracetic acid (PAA) can cause high levels of sublethal injury to L. monocytogenes. This study aims to evaluate phenotypic and transcriptional characteristics concerning surface attachment and virulence potential of sublethally injured L. monocytogenes ScottA and EGDe after exposure to 0.75 ppm PAA for 90 min at 4°C and subsequent incubation in TSBY at 4°C. Results showed that injured L. monocytogenes cells (99% of total population) were able to attach (after 2 and 24h) on stainless steel coupons at 4°C and 20°C. In vitro virulence assays using human intestinal epithelial Caco-2 cells showed that injured L. monocytogenes could invade host cells but could not proliferate intracellularly. In vitro virulence response was strain-dependent; injured ScottA was more invasive than EGDe. Assessment of PAA-injury at the transcriptional level showed upregulation of genes (motB, flaA) involved in flagellum motility and surface attachment. The transcriptional response of L. monocytogenes EGDe and ScottA was different; only injured ScottA demonstrated upregulation of the virulence genes inlA and plcA. Downregulation of the stress-related genes fri and kat, and upregulation of lmo0669 was observed in injured ScottA. The obtained results indicate that sublethally-injured L. monocytogenes cells may retain part of their virulence properties as well as their ability to adhere on food processing surfaces. Transmission to food products and introduction of these cells in the food chain is therefore a plausible scenario that is worth taking into consideration in terms of risk assessment. Importance L. monocytogenes is the causative agent of listeriosis a serious food-borne illness. Antimicrobial practices, such as disinfectants used for the elimination of this pathogen in food industry can produce a sublethally injured population fraction. Injured cells of this pathogen, that may survive an antimicrobial treatment, may pose a food safety-risk. Nevertheless, knowledge regarding how sublethal injury may impact important cellular traits and phenotypic responses of this pathogen is limited. This work suggests that sublethally injured L. monocytogenes cells maintain the virulence and surface attachment potential and highlights the importance of the occurrence of sublethally injured cells regarding food safety.

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.

Practical in-storage interventions to control foodborne pathogens on fresh produce

Although tremendous efforts have been made to ensure fresh produce safety, various foodborne outbreaks and recalls occur annually. Most of the current intervention strategies are evaluated within a short timeframe (less than 1 h), leaving the behavior of the remaining pathogens unknown during subsequent storages. This review summarized outbreak and recall surveillance data from 2009 to 2018 obtained from government agencies in the United States to identify major safety concerns associated with fresh produce, discussed the postharvest handling of fresh produce and the limitations of current antimicrobial interventions, and reviewed the intervention strategies that have the potential to be applied in each storage stage at the commercial scale. One long-term (up to 12 months) prepacking storage (apples, pears, citrus among others) and three short-term (up to 3 months) postpacking storages were identified. During the prepacking storage, continuous application of gaseous ozone at low doses (≤1 ppm) is a feasible option. Proper concentration, adequate circulation, as well as excess gas destruction and ventilation systems are essential to commercial application. At the postpacking storage stages, continuous inhibition can be achieved through controlled release of gaseous chlorine dioxide in packaging, antimicrobial edible coatings, and biocontrol agents. During commercialization, factors that need to be taken into consideration include physicochemical properties of antimicrobials, impacts on fresh produce quality and sensory attributes, recontamination and cross-contamination, cost, and feasibility of large-scale production. To improve fresh produce safety and quality during storage, the collaboration between researchers and the fresh produce industry needs to be improved.

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.

Assessing the survival and sublethal injury kinetics of Listeria monocytogenes under different food processing-related stresses

The foodborne pathogen L. monocytogenes can be present in food processing environments where it is exposed to various stressors. These antimicrobial factors, which aim to eliminate the pathogen, can induce sub-lethal injury to the bacterial cells. In the present study, we investigated the efficacy of different treatments (stresses) relevant to food processing and preservation as well as sanitation methods, in generating sub-lethal injury at 4 °C and 20 °C to two L. monocytogenes strains, ScottA and EGDe. Additionally, we evaluated the survival and extent of L. monocytogenes injury after exposure to commonly used disinfectants (peracetic acid and benzalkonium chloride), following habituation in nutrient-deprived, high-salinity medium. Each stress had a different impact on the survival and injury kinetics of L. monocytogenes. The highest injury levels were caused by peracetic acid which, at 4 °C, generated high populations of injured cells without loss of viability. Other injury-inducing stresses were lactic acid and heating. Long-term habituation in nutrient-limited and high salinity medium (4 °C) and subsequent exposure to disinfectants resulted in higher survival and injury in benzalkonium chloride and increased survival, yet with lower injury levels, in peracetic acid at 20 °C. Taken together, these results highlight the potential food safety risk emerging from the occurrence of injured cells by commonly used food processing methods. Consequently, in order to accurately assess the impact of an antimicrobial method, its potential of inducing sublethal injury needs to be considered along with lethality.

Microbial and physicochemical assessment of irrigation water treatment methods

AIMS

The presence of foodborne pathogens in preharvest agricultural water has been identified as a potential contamination source in outbreak investigations, driving markets and auditing bodies to begin requiring water treatment for high-risk produce. Therefore, it is essential that we identify water treatment methods which are effective as well as practical in their application on farm.

METHODS AND RESULTS

In this work, we evaluated two sanitizers which are most prominent in preharvest agricultural water treatment (calcium hypochlorite (free chlorine: 3-5 ppm) and peracetic acid (PAA: 5 ppm)), an EPA registered antimicrobial device (ultraviolet light (UV)), in addition to a combination approach (chlorine + UV, PAA + UV). Treatments were evaluated for their ability to inactivate total coliforms and generic Escherichia coli and consistency in treatment efficacy over 1 h of operation. Physicochemical variables were measured along with microbial populations at 0, 5, 15, 30, 45 and 60 min of operation. Escherichia coli and coliform counts showed a significant (P < 0·05) reduction after treatment, with combination and singular treatments equally effective at inactivating E. coli and coliforms. A significant increase (P < 0·05) in oxidation-reduction potential was seen during water treatment (Chlorine; UV + Chlorine), and a significant reduction (P < 0·05) in pH was seen after PAA and PAA + UV treatments (60 min).

CONCLUSION

Overall, the results indicate that all treatments evaluated are equally efficacious for inactivating E. coli and coliforms present in surface agricultural water.

SIGNIFICANCE AND IMPACT OF THE STUDY

This information when paired with challenge studies targeting foodborne pathogens of interest can be used to support grower decisions when selecting and validating a preharvest agricultural water treatment programme.

Impact of gas micro-nano-bubbles on the efficacy of commonly used antimicrobials in the food industry

AIM

To study the impact of incorporating micro-nano-bubbles (MNBs) in commonly used food antimicrobials (AMs) against Escherichia coli O157:H7 (EC) and Listeria monocytogenes (LM).

METHODS AND RESULTS

Air, carbon dioxide (CO₂ ) and nitrogen (N₂ ) were used to incorporate MNBs in city water. AM solution (with or without MNBs) of 9 ml was individually taken into sterile test tubes and mixed with 1 ml of inoculum grown in brain heart infusion (BHI) broth to get the net AM concentrations of 28·4 ppm peracetic acid (PAA), 200 ppm chlorine (Cl₂ ), 5·4% citric acid (CA) and 4·5% lactic acid (LA). After treatment time of 1·5 and 3·0 min, 1 ml of sample was neutralized using Dey-Engley neutralizing broth and plated on BHI agar. For EC, Cl₂ -CO₂ solutions resulted in significantly greater log reductions (5·2 logs) compared to that of Cl₂ solutions without MNBs (3·8 logs). For LM, PAA-CO₂ solutions resulted in significantly greater log reductions (4·4 logs) compared to that of PAA solutions without MNBs (1·7 logs).

CONCLUSIONS

This study demonstrated that the efficacy of Cl₂ and PAA AM solutions could be increased by incorporating CO₂ -MNBs against EC and LM in microbiological growth medium.

SIGNIFICANCE AND IMPACT OF THE STUDY

Incorporation of CO₂ -MNBs in AM solutions could increase the efficacy of AMs against pathogens on/in food matrices, which should be tested in future research.

The efficacy of sodium acid sulfate on controlling Listeria monocytogenes on apples in a water system with organic matter

During fresh apple packing, wash water in the dump tank and flume systems is reused during daily production, resulting in high levels of organic matter in the wash water. This study evaluated the antimicrobial efficacy of sodium acid sulfate (SAS), a Generally Recognized as Safe compound, against Listeria monocytogenes on fresh apples in a water system with high organic load. SAS at 1.0% reduced L. monocytogenes population in water with 1000 ppm chemical oxygen demand (COD) by more than 5.0 Log₁₀ CFU/ml in 5 min, 2.0-3.0% SAS reduced L. monocytogenes to undetectable levels (10 CFU/ml) within 2 min regardless of organic levels. When applied on apples, a 2-min wash with SAS at 1.0, 1.5, 2.0, and 3.0% reduced L. monocytogenes by ~1.3, 1.9, 2.3, and 3.0 Log₁₀ CFU/apple in clean water, respectively. High organic load in wash water up to 4000 ppm COD had no impact on the bactericidal effect of SAS against L. monocytogenes on fresh apples regardless of SAS concentrations. Shortening the contact time from 2 min to 30 s significantly reduced the antimicrobial efficacy of 25 ppm chlorine and 1.0-2.0% SAS but not that of 3.0% SAS. In addition, SAS at 1.0% demonstrated a better efficacy than 25 ppm chlorine in reducing fruit-to-water cross-contamination regardless of organic matter. SAS also showed a comparable efficacy as 25 ppm chlorine in reducing fruit-to-fruit cross-contamination in water with organic matter. The collective data indicate that SAS, as an enviroment-friendly compound, has the potential to be used as an alternative antimicrobial washing aid in dump tank process water intervention in apple packing facilities.

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.

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.