No abstract

Cold plasma generated in a gliding arc was applied to outbreak strains of Escherichia coli O157:H7 and Salmonella Stanley on agar plates and inoculated onto the surfaces of Golden Delicious apples. This novel sanitizing technology inactivated both pathogens on agar plates, with higher flow rate (40 liters/min) observed to be more efficacious than were lower flow rates (20 liters/min), irrespective of treatment time (1 or 2 min). Golden Delicious apples were treated with various flow rates (10, 20, 30, or 40 liters/min) of cold plasma for various times (1, 2, or 3 min), applied to dried spot inoculations. All treatments resulted in significant (P < 0.05) reductions from the untreated control, with 40 liters/min more effective than were lower flow rates. Inactivation of Salmonella Stanley followed a time-dependent reduction for all flow rates. Reductions after 3 min ranged from 2.9 to 3.7 log CFU/ml, close to the limit of detection. For E. coli O157:H7, 40 liters/min gave similar reductions for all treatment times, 3.4 to 3.6 log CFU/ml. At lower flow rates, inactivation was related to exposure time, with 3 min resulting in reductions of 2.6 to 3 log CFU/ml. Temperature increase of the treated apples was related to exposure time for all flow rates. The maximum temperature of any plasma-treated apple was 50.8 degrees C (28 degrees C above ambient), after 20 liters/min for 3 min, indicating that antimicrobial effects were not the result of heat. These results indicate that cold plasma is a nonthermal process that can effectively reduce human pathogens inoculated onto fresh produce.

Numerous outbreaks of salmonellosis by Salmonella Poona have been associated with the consumption of cantaloupe. Commercial washing processes for cantaloupe are limited in their ability to inactivate or remove this human pathogen. Our objective was to develop a commercial-scale surface pasteurization process to enhance the microbiological safety of cantaloupe. Populations of indigenous bacteria recovered from cantaloupes that were surface pasteurized at 96, 86, or 76 degrees C for 2 to 3 min were significantly (P < 0.05) lower than those of the controls. Whole cantaloupes, surface inoculated with Salmonella Poona RM 2350 or Escherichia coli ATCC 25922 to a final cell concentration of ca. 5 log CFU/cm2 were stored at 4 degrees C or room temperature (RT = 19+/-1 degrees C) for up to 72 h before processing. Treatments at 76 degrees C for 2 to 3 min at 24 h postinoculation resulted in a reduction in excess of 5 log CFU/cm2 of Salmonella Poona and E. coli populations. Cantaloupes that were surface pasteurized and stored at 4 degrees C for 21 days retained their firmness qualities and had no visible mold growth compared with the controls, which became soft and moldy. These results indicate that surface pasteurization will enhance the microbiological safety of cantaloupes and will extend the shelf life of this commodity as well. Storage of untreated inoculated cantaloupes at RT for 24 to 72 h postinoculation caused a significant (P < 0.05) increase in Salmonella Poona and E. coli populations compared with storage at 4 degrees C. This indicates that cantaloupes should be refrigerated as soon as possible following harvest to suppress the growth of any possible contaminant on the rind.

No abstract

Viruses are currently the leading cause of foodborne outbreaks, most of which are associated with foods consumed raw. Cold plasma (CP) is an emerging novel nonthermal technology that can be used to surface decontaminate foods. This study investigated CP technology for the nonthermal inactivation of human norovirus surrogates, Tulane virus (TV) and murine norovirus (MNV), on the surface of blueberries. Blueberries (5 g) were weighed into sterile 4 oz. glass jars and inoculated with TV, 5 log PFU/g. Samples were treated with atmospheric CP for 0, 15, 30, 45, and 60 s at a working distance of 7.5 cm with 4 cubic feet/minute (cfm) of CP jet. Temperature readings were taken with an infrared camera prior to, and immediately following, CP treatments. In order to establish the impact of air flow during CP treatment (4 cfm), an additional 7 cfm jet of room temperature air was introduced from a separate nozzle. The experiment was repeated with 90 and 120 s as additional treatment time points. Viral titers were measured immediately after each treatment with a plaque assay using LLC-MK2 cells (TV) or RAW 264.7 cells (MNV). TV was significantly reduced 1.5 PFU/g compared to the control after treatment time of 45s, which was achieved regardless of temperature conditions. With the addition of 7 cfm of ambient air, the maximum log reduction for TV was 3.5 log PFU/g after 120s of treatment. MNV was significantly reduced by 0.5 log PFU/g compare to the control at 15s, and further treatment of MNV with ambient air brought the log reduction to greater than 5 log PFU/g at 90 s of treatment (Fig. 3). These results demonstrate that CP viral inactivation does not rely on thermal inactivation, and is therefore nonthermal in nature. With further optimization, CP may be used by food processors as a means of nonthermal inactivation of foodborne viruses.

Ultraviolet Light (254 nm) is a U.S. Food and Drug Administration‐approved nonthermal intervention technology that can be used for decontamination of food surfaces. In this study, the use of ultraviolet light (UV‐C) at doses of 0.5–4.0 J/cm2 to inactivate a cocktail of Salmonella spp., Listeria monocytogenes and Staphylococcus aureus that were surface‐inoculated on frankfurters, bratwurst, shell eggs, chicken drumsticks, boneless skinless chicken breasts, boneless pork chops, tomatoes and jalapeno peppers was investigated. The pathogens displayed similar sensitivities to UV‐C on individual food products. Pathogen reductions ranged from approximately 0.5 log/g on raw meat and poultry to almost 4 log/g on tomatoes, while the pathogens were not recovered from stainless steel at a UV‐C dose of 0.4 J/cm2. Use of UV‐C light should be given serious consideration as a technology for routine surface decontamination of food contact surfaces and appropriate food products. PRACTICAL APPLICATIONS Ultraviolet light (UV‐C) is an U.S. Food and Drug Administration‐approved intervention technology that can be used to inactivate pathogenic bacteria in liquid foods and water, food contact surfaces, and food surfaces. This work indicates than UV‐C would be an effective technology for inactivation of foodborne pathogens on the surfaces of frankfurters and sausages immediately prior to packaging, shell eggs immediately prior to cracking in the production of liquid egg products, and smooth skinned produce such as tomatoes and jalapeno peppers prior to further processing. This work provides pathogen inactivation kinetics for food processors and government regulatory agencies.

Pathogens such as Salmonella can form chemical-resistant biofilms, making them difficult to remove from food contact surfaces. A 15 s treatment with cold plasma reduced mature Salmonella biofilms by up to 2.13 log CFU/mL (99.3%). This contact-free, waterless method uses no chemical sanitizers. Cold plasma may therefore have a practical application for conveyor belts, equipment, and other food contact surfaces where a rapid, dry antimicrobial process is required.

Efficacy of 1% hydrogen peroxide (H 2 O 2 ) in decontaminating apples and cantaloupes containing human pathogens was investigated. Apples inoculated with Escherichia coli (ATCC 25922) were washed with 1% H 2 O 2 at 20 or 40 °C for 15 or 30 min. Population reductions approaching 3 logs were obtained with all treatments. Comparable reductions were obtained with apples inoculated with 3 strains of E. coli O157:H7, associated with cider outbreaks, and a 5-strain cocktail. The 1% H 2 O 2 treatment was ineffective against E. coli 766 (ATCC 9637; similar to Salmonella Poona) on inoculated cantaloupes. Treatment of apples with 1% H 2 O 2 was carried out successfully in a wet dump tank.