Effect of binder on the physical stability and bactericidal property of titanium dioxide (TiO2) nanocoatings on food contact surfaces

TiO₂ is a promising photocatalyst for use in food processing environment as an antimicrobial coating. The purpose of this study was to determine the effect of different binding agents on the physical stability and bactericidal property of TiO₂ nanocoatings created on stainless steel surfaces. A total of six different coating suspensions were prepared by mixing TiO₂ (Aeroxide^® P-25) nanoparticles (NPs) with three different types of binders (Shellac (A), polyuretahne (B), and polycrylic (C)) at a 1:4 to 1:16 NP to binder weight ratio. Bactericidal activity of these TiO₂ coatings against Escherichia coli O157:H7 (5-strain) was determined at three different UV-A light intensities (0.25, 0.50 and 0.75 mW/cm²) for 3 h. The type of binder used in the coating had a significant effect on the log reduction of E. coli O157:H7. TiO₂ coatings with binder C showed highest reduction (>4 log CFU/cm²) followed by TiO₂ coating with binder B and A. Increasing the binder concentration in the formulation from a 1:4 to 1:16 weight ratio decreased the log reduction of E. coli O157:H7. Increasing the UV-A light intensity from 0.25 to 0.75 mW/cm² increased the log reduction of bacteria for all the TiO₂ coatings. The physical stability of the TiO₂ coatings was determined using ASTM procedures. TiO₂ coatings with binder B showed highest adhesion strength and scratch hardness when compared to coatings with other binders. However, on repeated use experiments (1, 3, 5, and 10 times), TiO₂ coatings with binder C were found to be physically more stable and able to retain their original bactericidal property. The results of this study showed promise in developing durable TiO₂ coatings with strong photocatalytic bactericidal property on food contact surfaces using appropriate binding agents to help ensure safe food processing environment.     

Antimicrobial films and coatings for inactivation of Listeria innocua on ready-to-eat deli turkey meat

Edible antimicrobial coating solutions incorporating chitosan, lauric arginate ester (LAE) and nisin were developed to reduce foodborne pathogen contamination on ready-to-eat (RTE) meats. RTE deli meat samples were directly coated with the solutions, or treated with solution-coated polylactic acid (PLA) films. The antimicrobial efficacy of the coatings and films against Listeria innocua inoculated onto the surface of RTE meat samples was investigated. Antimicrobial coatings with 1.94 mg/cm² of chitosan and 0.388 mg/cm² of LAE reduced L. innocua by ca. 4.5 log CFU/cm². Nisin (486 IU/cm²) showed less effectiveness than LAE (0.388 mg/cm²) and addition of nisin to the antimicrobial coatings or films containing LAE (0.388 mg/cm²) did not enhance the total antimicrobial effectiveness. Combining antimicrobial coatings or films with flash pasteurization (FP), which uses short burst of steam under pressure, further reduced L. innocua, achieving over a 5 log reduction. There was no significant difference in the effectiveness of antimicrobial films versus the coatings (p > 0.05). These data show the potential use of antimicrobial packaging alone, or in combination with FP, in preventing foodborne illness due to post-processing contamination of RTE meat products.     

A risk assessment of salmonellosis linked to chicken meals prepared in households of China

A quantitative microbiological risk assessment model was used to quantify the risk of salmonellosis caused by bacterial growth and cross-contamination of chicken meals prepared in households of China. Chinese data on initial loads of Salmonella in chicken carcasses sold at retail, storage time and handling of raw chicken meat in household kitchens and confirmatory transfer rates of Salmonella among different kitchen objects were collected. Only one third of Chinese families in our sample separated the cutting board between raw and ready-to-eat foods. The cross-contamination of ready-to-eat foods from chicken meals via the cutting board, the knife and cooks’ hands increased the frequency of pathogen ingestion and the risk of salmonellosis. A significant decrease in the risk of salmonellosis could be achieved by reducing the cross-contamination when handling raw chicken meat and ready-to-eat foods. Decreasing the prevalence of Salmonella contamination to 8.8% or removing chicken carcasses with contamination densities higher than 100 MPN/100 g at retail was less effective. Using transfer rates of Salmonella from raw chicken meat to the wooden cutting board instead of that from references, a statistically higher risk of salmonellosis per serve due to the cross-contamination in households was observed. The present study validated values of hygiene practices in China to reduce the risk of salmonellosis from contaminated raw chicken meat at retail. Deliberate surveys for cooking behaviors and transfer rates of Salmonella from and to different objects including wooden cutting boards were needed.     

The incidence of significant foodborne pathogens in domestic refrigerators

The interior surfaces of household refrigerators are at risk of becoming contaminated with foodborne pathogens, increasing the risks of cross-contamination to other food items, including higher risk ready-to-eat foods. This study determined the incidence of a number of significant foodborne pathogens, and the general hygienic status (as estimated by total viable counts (TVCs), and total coliform counts (TCCs)) on the interior surfaces of domestic refrigerators (n = 342). Campylobacter spp., Salmonella spp. and Escherichia coli O157:H7 were not recovered from any refrigerators, but Staphylococcus aureus was recovered from 6.4%, Listeria monocytogenes and E. coli from 1.2% and Yersinia enterocolitica from 0.6% of examined refrigerators. As the recovered species can survive and grow under refrigeration or conditions of mild temperature abuse, such pathogens may transfer to (and develop to clinically significant numbers in) food in domestic fridges. Such risks are of particular concern in relation to “ready-to-eat” foods, which will not receive further bactericidal treatments (cooking) before consumption. The study estimated TVCs ranging from 2.91 log₁₀ cfu/cm² to 8.78 log₁₀ cfu/cm² and TTCs ranging from 0.045 log₁₀ cfu/cm² to 5.96 log₁₀ cfu/cm² indicating very poor standards of consumer refrigerator management and hygiene, and posing risks to consumer health. The study findings highlight the importance of adequate temperature control and thorough, regular cleaning of domestic refrigerators to ensure food safety, and of effective cooking as the last link in the domestic food service chain.     

Simulation of decontamination and transmission of Escherichia coli O157:H7, Salmonella Enteritidis,and Listeria monocytogenes during handling of raw vegetables in domestic kitchens

Epidemiological data indicates that a large number of foodborne illnesses are attributed to cross-contamination during food preparation in the domestic kitchen. The objectives of this study were to evaluate the efficiency of household washing practices in removing Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Enteritidis on artificially contaminated lettuce and to determine the transfer rate of these three foodborne pathogens from contaminated lettuce to wash water, tomato, cabbage, and cutting boards during washing and cutting processes. Washing under the running tap water with scrubbing for 60 s was the most effective method in reducing pathogen populations by 1.86–2.60 log₁₀ CFU/g. Also, final rinsing and scrubbing practices were found to enhance the efficiency of washing treatment. In this study, the transfer rates of S. Enteritidis, E. coli O157:H7, and L. monocytogenes from cutting board to cabbage and tomato via cutting process (17.5–31.7%) were higher (P < 0.05) than from wash water to cabbage and tomato (0.8–23.0%) during washing treatment. Overall, our findings suggest that wash water and cutting board can be potential vehicles in the dissemination of foodborne pathogens. Therefore, there is a need to promote consumer awareness for proper handling practices in the kitchen to minimise the risk of foodborne infection.     

Hygiene and good practices in school meal services: Organic matter on surfaces,microorganisms and health risks

The aim of this study was to evaluate and classify the sanitation and hygiene conditions in Porto Alegre/Rio Grande do Sul (RS) public schools using an analysis of surfaces that come in contact with food and a food safety checklist validated for the school environment. The following mesophilic heterotrophic bacteria count medians were observed on each piece of equipment or utensil studied: countertops, 27.3 Colony-Forming Units (CFU)/cm²; cutting boards, 15 CFU/cm²; blenders, 14.5 CFU/cm²; dishes, 2 CFU/cm²; and refrigerators, 1 CFU/cm². The median of the surface measurements analyzed by adenosine triphosphate (ATP) bioluminescence was less than 40 Relative Light Units (RLU)/100 cm² for all equipment and utensils, except for the countertop surface, which had a median of 52.5 RLU/100 cm². The data from 120 schools showed that 33, 64 and 3% were classified as high, regular and low health risk, respectively. The results showed that most schools were exposed to cross-contamination with failures especially with regard to environmental hygiene and procedures. Failures related to both factors potentially raise the risk of outbreaks in this environment. The scores used enabled the classification of school meal services and the identification of the points that need more attention. Intervention strategies that target different aspects of food handling, not only knowledge, may be promising in this scenario, which may address problems that mainly involve the food handler and promote changes in food handling practices.     

Photocatalytic degradation of methylene blue and inactivation of Gram-negative bacteria by TiO2 nanoparticles in aqueous suspension

The photocatalytic degradation of methylene blue (MB) and inactivation of Gram-negative bacteria Escherichia coli (generic) and Pseudomonas aeruginosa by TiO₂ nanoparticles in aqueous suspension were studied. TiO₂ resulted in significant reduction in MB absorption and a shift of MB absorption peak from 664 nm to 658 nm after a short time of irradiation. The maximum degradation of MB was observed when the concentration of TiO₂ in the aqueous suspension was 0.5 g L⁻¹. TiO₂ was also very effective with inhibiting growth of both Gram-negative bacteria E. coli and P. aeruginosa, although it took more than 60 min to observe the inactivation effects. The photocatalytic inactivation toward E. coli and P. aeruginosa by TiO₂ showed a similar trend with much higher effectiveness toward E. coli under the same experimental conditions. The inactivation kinetic behaviors could be explained by the modified Langmuir–Hinshelwood model, and well fitted to a pseudo-first order kinetic equation. The reaction rate constant for E. coli and P. aeruginosa were 7.768 × 10⁶ cfu mL⁻¹ min⁻¹ and 5.655 × 10⁶ cfu mL⁻¹ min⁻¹, respectively. The adsorption equilibrium constant for E. coli was 1.053 × 10⁻⁸ mL cfu⁻¹, while it was 1.438 × 10⁻⁸ mL cfu⁻¹ for P. aeruginosa. These results further demonstrate that in an aqueous system, TiO₂ nanoparticles can effectively both degrade organic compounds and inhibit Gram-negative bacteria under UVA light. Compared with the degradation activity of TiO₂ toward organic compounds, its antimicrobial activity against Gram-negative bacteria would be delayed by 60 min. The antimicrobial activity of TiO₂ against Gram-negative bacteria could vary with bacterial species.     

Antimicrobial coatings for controlling Listeria monocytogenes based on polylactide modified with titanium dioxide and illuminated with UV-A

The anti-listerial properties of biodegradable polylactide coatings modified with titanium dioxide have been studied. Free standing films were prepared by casting solutions prepared from titanium dioxide and previously extruded polylactide. It was demonstrated that polylactide alone could support 2.84 ± 0.10 log CFU reduction of Listeria monocytogenes when incubated at 23 °C for 2 h. However, the log reduction for Listeria could be increased to >4 log CFU with titanium dioxide:polylactide composites illuminated with UV-A. The inactivation kinetics of L. monocytogenes followed a diphasic die-off with an initial 30 min lag period then a progressive decline in bacterial levels over a further 90 min period. The anti-listeria effect of polylactide:titanium dioxide films was dependent on illumination with UV-A but independent on the concentration of TiO₂ incorporated in the film within the range of 1–5% w/w. The mode of L. monocytogenes inactivation was via direct contact of the pathogen with the polylactide, in addition to the generation of oxygen radicals produced by excitation of the titanium dioxide. The composite film illuminated with UV-A was equally effective against Salmonella Typhimurium and Shiga toxin producing Escherichia coli. The coating was stable to 5 repeated sanitation cycles consisting of detergent and sodium hypochlorite rinses. The polylactide-titanium dioxide coating shows potential as an antimicrobial coating although further work is required to assess if the protective film can function under commercial conditions.     

Antimicrobial efficacy of vacuum impregnation washing with malic acid applied to whole paprika,carrots, king oyster mushrooms and muskmelons

Antimicrobial effect of vacuum impregnation (VI) applied to organic acid washing against Salmonella Typhimurium, Escherichia coli O157:H7 and Listeria monocytogenes on paprika fruit, carrots, king oyster mushrooms and muskmelons was investigated. Samples were treated with intermittent VI with 21.3 kPa and compared with dipping washing in 2% malic acid. The initial sample pathogen levels were approximately 10⁵–10⁷ CFU/cm². Enumerations of the three pathogens on paprika and carrots treated with VI washing were reduced to below the detection limit (= 1 log₁₀ CFU/cm²) after 3–5 min and 15–20 min, respectively. For each time point where populations of the three pathogens were reduced to below the detection limit by VI treatment, populations of 1.2–1.9 log CFU/cm² and 2.5 to 2.8 log CFU/cm² survived on paprika and carrots, respectively, when subjected to dipping treatment. After 20 min of dipping treatment, surviving populations of the three pathogens ranged from 3.5 to 4.1 and 3.3 to 4.4 log CFU/cm² on king oyster mushrooms and muskmelons, respectively. After 20 min of VI treatment, surviving populations of the three pathogens ranged from 3.0 to 3.6 log and 3.1 to 4.1 log CFU/cm², respectively, on king oyster mushrooms and muskmelons. Additionally, there were no significant (P ≥ 0.05) differences in pathogen reductions between dipping and VI treatment for both king oyster mushrooms and muskmelons. King oyster mushrooms (R_a = 6.02 ± 1.65 μm) and muskmelons (R_a = 11.43 ± 1.68 μm) had relatively large roughness values compared to those of paprika (R_a = 0.60 ± 0.10 μm) and carrots (R_a = 2.51 ± 0.50 μm). Scanning electron photomicrographs showed many deep protected sites in king oyster mushrooms and muskmelons with many microbes located deep in these sites following VI treatment. Instrumental color, texture and titratable acidity values of paprika and carrots subjected to VI washing treatment with 2% malic acid for 5 and 20 min were not significantly (P ≥ 0.05) different from those of untreated control samples during 7 day storage.     

Disinfecting efficacy of a plastic container covered with photocatalyst for postharvest

The simplification of the cleaning process of plastic containers used in the storage and/or distribution of fruits or vegetables is important. We coated a plastic container with an apatite-coated titanium dioxide photocatalyst (TiO₂–Ap container), and examined its disinfecting efficacy under UV irradiation from black light. The disinfecting efficacy of the TiO₂–Ap container on diluted drops evaporated from spinach (suspension) was examined. Changes in the microbial populations of the total aerobic bacteria, coliform bacteria, and moulds and yeasts in the TiO₂–Ap container were assayed at 25 °C for 24 h (UV-A intensity of 0.2 and 0.4 mW cm⁻²). The results showed that all of the microbial populations in the TiO₂–Ap container decreased with irradiation time and then reduced to uncountable levels. It was found that the increase in UV-A intensity enhanced the disinfecting efficacy.     

Effects of Quillaja saponaria extract and Nα-lauroyl-l-arginine ethyl ester on reducing selected foodborne pathogens in vitro and maintaining quality of fresh-cut endive (Cichorium endivia L.) at pilot plant scale

The aim of the present study was to evaluate the applicability of Quillaja saponaria extract (QSE) and N^α-lauroyl-l-arginine ethyl ester (LAE) as antimicrobial wash water additives in fresh-cut lettuce processing. Antibacterial activities of LAE and QSE against selected strains of the foodborne pathogens Salmonella enterica, Bacillus cereus, Staphylococcus aureus, Pseudomonas aeruginosa, and Listeria monocytogenes were examined in vitro. Minimum inhibitory concentrations determined by broth microdilution assay demonstrated that LAE exhibited a strong antimicrobial activity with MICs between 4 and 32 μg/mL against all tested strains, whereas QSE showed a weaker antimicrobial activity with MICs >512 μg/mL. On a pilot-plant scale, the effects of warm water washing at 45 °C for 120 s with and without 40 mg/L QSE or 100 mg/L LAE as well as cold water washing at 4 °C for 120 s with QSE or LAE, respectively, of shredded endive (Cichorium endivia L.) were investigated regarding microbiological and sensory quality as well as physiological properties. Samples were analyzed for headspace O₂ and CO₂ levels, phenylalanine-ammonia-lyase activity and contents of nitrite and nitrate during nine days of cold storage at 4 °C. By analogy to its antimicrobial effect against the foodborne pathogens in vitro, LAE allowed up to 4 log₁₀ cfu/mL reduction of the microbial load in the washing water of the pilot plant, and might therefore reduce cross-contamination while saving water. The addition of LAE to warm washing water impaired sensory properties of fresh-cut endive during storage, which was predicted by chlorophyll fluorescence imaging analyses. QSE treatment combined with warm water washing best retained sensory appearance throughout our study, being possibly suitable for the production of premium products.     

The effect of pulsed UV light on Escherichia coli O157:H7, Listeria monocytogenes,Salmonella Typhimurium,Staphylococcus aureus and staphylococcal enterotoxin A on sliced fermented salami and its chemical quality

Pulsed UV light (PL) applied at a fluence of 3 J/cm² was effective to reduce Listeria monocytogenes, Escherichia coli 0157:H7, Salmonella Typhimurium and Staphylococcus aureus for 2.24, 2.29, 2.25 and 2.12 log CFU/g on the surface of dry fermented salami. Further increase in the fluence of PL treatment did not increase levels of microbial inactivation. However, the time interval between the contamination and PL treatment was found to have a significant impact on the efficacy of PL treatment and should be kept as short as possible. After initial PL treatment slices of fermented salami were packed in vacuum or in 80%CO₂/20%N₂ modified atmosphere and stored at 4 °C to investigate the effect of PL treatment on protein and lipid oxidation as the shelf life of fermented salami is not usually limited by microbial deterioration, but by chemical and sensory alterations. In this study observed lipid oxidation values for PL treated vacuum and modified atmosphere packed fermented salami slices fall within the acceptable threshold for the rancid odor, except for the sample treated with the highest fluence tested (15 J/cm²), packed in modified atmosphere and kept in cold storage for 9 weeks (1.23 mg MDA/kg). All values were below the threshold for rancid flavor, too. The significant rise in protein oxidation of PL treated fermented salami slices, perceived as 28% increase of carbonyl content compared to untreated samples, was observed only after 9 weeks of cold storage in both vacuum and modified atmosphere packed samples. The results of chemical analysis are in agreement with previously published results of sensory analysis. Current results show the applicability of PL to improve microbial safety of sliced fermented salami that are prone to cross-contamination without affecting quality attributes by lipid and protein oxidation.     

Use of chemical treatments applied alone and in combination to reduce Campylobacter on raw poultry

Research focussing on the use of chemicals to decontaminate poultry carcasses to reduce pathogenic and spoilage organisms has increased in recent years. The objective of this study was to evaluate the efficacy of 12% (w/v) trisodium phosphate (TSP), 2% (w/v) citric acid (CA) and 5% (w/v) capric acid sodium salt (CP) in reducing Campylobacter, total viable counts and total Enterobacteriaceae counts on poultry. These chemicals were also used in various combinations (TSP + CA, TSP + CP and CA + CP) to determine if sequential treatments would enhance microbial reductions. TSP (1.9–2.3 log₁₀ cfu cm²) and CP (2.2–2.4 log₁₀ cfu cm²) gave the largest Campylobacter jejuni reductions while TSP was the most effective at reducing TVC (0.9 log₁₀ cfu cm²) and TEC (0.9 log₁₀ cfu cm²). TSP + CP was the most effective combination treatment (2.9 log₁₀ cfu cm²) for reducing C. jejuni counts and was significantly (P < 0.05) greater than any of the single chemical treatments, with the exception of CP treatment against strain 1146 (2.4 log₁₀ cfu cm²). The TVC and TEC populations proved more resistant to combination treatments as only TSP + CP showed a significantly (p < 0.05) enhanced reductive efficacy in comparison to single CP treatment. This study provides further data on the efficacy of a number of potential chemicals used alone and in combination for the decontamination of raw poultry.     

Evaluation of a novel antimicrobial solution and its potential for control Escherichia coli O157:H7, non-O157:H7 shiga toxin-producing E. coli,Salmonella spp., and Listeria monocytogenes on beef

The goal of this study was to evaluate the efficacy of a novel antimicrobial solution made with chitosan, lauric arginate ester, and organic acids on Escherichia coli O157:H7, Salmonella spp., Listeria monocytogenes, and non-O157 shiga toxin-producing E. coli cocktails and to test its potential to be used as a marinade for raw beef. Fresh beef top round steaks were surface-inoculated with the pathogen cocktails at approximately 2.5 or 4.5 Log CFU/cm², marinated with the antimicrobial solution (AMS), and then stored at 4 °C for 6, 24, and 48 h. Three commercially available marinades were used for comparison. Results revealed that AMS had the most antimicrobial effect regardless of the type or inoculation level of pathogens (P < 0.05). After 6 h, the AMS marination reduced all pathogens to levels below the limit of detection (<1 Log CFU/cm²), resulting in a 3.5 Log CFU/cm² reduction. When AMS was diluted with autoclaved distilled water by 5 times (AMS 1:5) or 10 times (AMS 1:10), its antimicrobial efficacy was impacted by marination time, the inoculated pathogens, and the inoculation levels. This study demonstrates that the developed antimicrobial solution has a great potential to be used during marination by consumers to ensure better food safety.     

Effectiveness of a phage cocktail as a biocontrol agent against L. monocytogenes biofilms

Listeria monocytogenes can persist and form biofilms in a food environment which are difficult to eradicate because biofilms are inherently resistant to a variety of antimicrobial treatments. Therefore, alternative approaches such as bacteriophages have been suggested as a promising biocontrol agent against biofilms. The aim of this study was to evaluate the efficacy of a cocktail bacteriophage product (ListShield™) against L. monocytogenes biofilms. These biofilms were established on lettuce, stainless steel, rubber, and a MBEC biofilm device and exposed to the ListShield™ phage preparation (1 × 10⁸ PFU/mL) for 2 h. ListShield™ had sufficient potency to significantly reduce the biofilm (P < 0.05) in all cases. Biofilm reduction achieved after ListShield™ treatment on the stainless steel coupon was 1.9–2.4 log CFU/cm² and on the rubber surface approximately 1.0 log CFU/cm². Phage application on lettuce inactivated biofilm bacteria up to 0.7 log CFU/cm². These results suggest that bacteriophage preparation ListShield™ is an effective tool for the inactivation of L. monocytogenes biofilms in the food industry.     

Degradation of cypermethrin,malathion and dichlorovos in water and on tea leaves with O3/UV/TiO2 treatment

The main aims of the present study were to study the efficacy and mechanisms of removing three pesticides (cypermethrin, malathion, dichlorovos) from fresh tea leaves and water by O₃/UV/TiO₂ treatment, and to explore the optimal conditions for the removal. The results indicated that the removal rates of pesticides on tea leaves were not affected by water pH, whereas the removal rates of pesticides from water were affected.Eliminating rates of cypermethrin and malathion from tea leaves by O₃/UV/TiO₂ were significantly higher than that by water rinsing treatment (P < 0.05). The O₃/UV/TiO₂ treatment resulted in an 80% removal rate for cypermethrin (initial residue content 5.8 mg/kg) and 78% for malathion (initial residue content 2.2 mg/kg). It could be concluded that O₃/UV/TiO₂ treatment was especially effective for the removal of insoluble pesticides (e.g. cypermethrin) from tea leaves, with a 250% enhancement over the water rinsing treatment.     

Transmission of Listeria monocytogenes from raw chicken meat to cooked chicken meat through cutting boards

Listeria monocytogenes (L. monocytogenes) is a food-borne pathogen contaminating poultry products. Ready-to-eat (RTE) cooked chicken meat can easily be contaminated with L. monocytogenes in post-processing activities. This study aimed to determine transmission of L. monocytogenes from raw chicken meat to hot and cooled chicken meat through polyethylene and wooden cutting boards. Raw chicken breast samples were purchased from retail markets and were artificially contaminated with L. monocytogenes at concentration of 7.35 ± 0.22 log CFU/ml. Contaminated raw samples were placed on polyethylene and wooden cutting boards to simulate bacterial transfer to cutting boards. Cooked chicken samples (hot and cooled) were then placed on the same cutting boards to simulate transfer of bacteria from cutting boards to cooked meat. L. monocytogenes successfully attached to polyethylene and wooden cutting boards and recovered after holding time up to 1 h. Transmissions of L. monocytogenes to cooled cooked samples from both types of cutting boards were relatively higher than hot cooked samples. Moreover, transfer rates of L. monocytogenes from wooden cutting boards at holding time of 1 h to both cooled and hot cooked samples were lower than those from polyethylene cutting board. It is recommended to use different cutting boards for raw and cooked materials and apply detergents and hot water for cleaning procedure to eliminate L. monocytogenes attached to the cutting boards and prevent cross-contamination of final products.     

Synergistic effect of a combination of ultraviolet–C irradiation and sodium hypochlorite to reduce Listeria monocytogenes biofilms on stainless steel and eggshell surfaces

The present study demonstrates the synergistic effect of treatment with a combination of ultraviolet (UV)C (300, 600, 1200, and 1800 mWs/cm²) irradiation and sodium hypochlorite (NaOCl) (50, 100, 150, and 200 ppm) on Listeria monocytogenes ATCC 19113 biofilms formed on stainless steel and eggshell surfaces. The synergistic effect was not dependent on the dose of UV–C irradiation or the concentration of NaOCl. Synergistic reductions of biofilms after UV–C/NaOCl treatment on stainless steel and eggshells were 0.95–3.68 log CFU/cm² and –0.22 to 1.02 log CFU/cm², respectively. The largest synergistic reductions of biofilms were 3.68 log CFU/cm² using 1800 mWs/cm² UV–C and 200 ppm NaOCl on stainless steel, and 1.02 CFU/cm² using 600 mWs/cm² UV–C and 50 ppm NaOCl on eggshells. The Hunter colors of L*, a*, and b* were not significantly (P > 0.05) changed on eggshell surfaces treated with all single and combined treatments. The results in this study indicate that the combination treatment of 1800 mWs/cm² UV–C/200 ppm NaOCl could be feasible for use on stainless steel surfaces in industrial kitchens, facilities, and restaurants. In addition, the combination of 600 mWs/cm² UV–C/500 ppm NaOCl could possibly be used in egg production, processing, and distribution processes to enhance food safety without causing changes to the eggshell surface color.     

Suboptimal growth conditions induce heterologous ultraviolet-C adaptation in Salmonella enterica in orange juice

This study was conducted to determine the effects of single and simultaneous physicochemical stress exposures on the subsequent resistance of Salmonella spp. to ultraviolet-C (UV–C) in orange juice (pH 3.1, 11.5 °Brix, 0.63% citric acid). Seven strains of the test bacterium were individually subjected to suboptimal growth conditions (24 h), including gradual acidification (final pH 4.5), abrupt desiccation (a_w 0.96), heat stress by incubation at high temperature (40 °C), and combinations of acid + desiccation (pH 4.5, a_w 0.96), acid + heat (pH 4.5, 40 °C), and desiccation + heat (a_w 0.96, 40 °C). Cocktail of the different strains previously exposed to specific stress were then subjected to UV–C inactivation. The UV–C resistance of Salmonella enterica was expressed in terms of D and D_UV–C values, which correspond to the unit time of exposure and UV–C energy necessary to reduce the population by 1 log cycle (90%), respectively. Results showed that in all treatments, S. enterica exhibited logarithmic linear or first-order UV inactivation kinetics, indicating that the cells had homogenous responses towards the environmental stresses and the eventual kill step. Except for heat, all prior stress exposures resulted in cells more resistant to UV–C than the control (D = 12.7 s, D_UV–C = 63.56 mJ/cm²). Cells previously exposed to desiccation were most resistant to UV–C with a D and D_UV–C values of 16.6 s and 83.20 mJ/cm², respectively. Combining desiccation with acid (D = 16.2 s, D_UV–C = 80.88 mJ/cm²) and heat (D = 15.0 s, D_UV–C = 75.16 mJ/cm²) also resulted in relatively more resistant cells, with D and D_UV–C values greater than those exposed to acid (D = 14.9 s, D_UV–C = 74.56 mJ/cm²), acid + heat (D = 14.4 s, D_UV–C = 72.00 mJ/cm²), and heat stresses (D = 11.9 s, D_UV–C = 59.67 mJ/cm²). All (D ratio = D stress/D control >1.0) but those previously exposed to heat stress (D ratio <1.0) exhibited heterologous adaptation against UV–C in orange juice. These results provide additional evidences of the induction of heterologous UV–C tolerance response in S. enterica from environmental stresses commonly encountered by cells in food and food processing ecologies.     

Low-amperage pulsating direct current has a bactericidal effect on marine fish pathogens in circulating seawater

The bactericidal effect of pulsating direct current (PC) generated at a very low amperage (0.01 A) with a frequency of 5 Hz or 14 kHz against two marine fish pathogens, Edwardsiella tarda and Vibrio parahaemolyticus, in circulating seawater at 15 and 25 °C in comparison with the effect of direct current (DC) of the same amperage was investigated. The bactericidal effect was directly correlated with the generation of active chlorine species (ACS) and the treatment duration. PC treatment at 14 kHz resulted in complete bacterial inactivation when the ACS level reached 0.11–0.12 mg/L after 45–60 min of treatment. PC treatment at 5 Hz required generation of only 0.03–0.07 mg/L ACS to achieve complete bacterial inactivation, although a slightly longer treatment duration (60–90 min) was needed. DC treatment resulted in complete disinfection within a shorter time (30 min) due to greater ACS production. The bactericidal effect and ACS generation were weaker at the higher temperature (25 °C) due to more rapid evaporation of Cl₂ gas. The pH of the seawater maintained at ∼8.0. A disinfection study in circulating non-chloride Na₂SO₄ solution at pH 8.0 showed that the electric pulsation did not have notable bactericidal effect up to 14 kHz at 0.2 A.