Effect of neutral electrolyzed water on lux-tagged Listeria monocytogenes EGDe biofilms adhered to stainless steel and visualization with destructive and non-destructive microscopy techniques

The presence of Listeria monocytogenes in food processing environment is a risk of food contamination by persistent cells due to their ability to attach to stainless steel and other surfaces. We aimed to study biofilms formation of lux-tagged L. monocytogenes EGDe on stainless steel surfaces and their control using neutral electrolyzed water (NEW), where biofilms development was monitored using destructive and non-destructive microscopy techniques. The development of biofilms was monitored for 5 days on stainless steel chips. We used two sources of NEW, commercial (NEW-1) and from a prototype (NEW-2) for treatments of free and biofilm L. monocytogenes EGDe cells. Complete inhibition of L. monocytogenes EGDe free cells was observed after 1 min contact time for both NEW sources, but NEW-1 concentration used (9 mg/L total available chlorine, TAC) was 1.8 times higher. Cells within biofilms were more resistant to NEW compared to planktonic cells. Same concentration of both NEW sources (70 mg/L TAC) exhibited complete inhibition of biofilm cells after 3 min contact time. However, using a sub-lethal dose of 40 mg/L TAC, NEW-2 reduced about 2 log CFU/cm² biofilm cells while NEW-1 inhibited 0.3 log CFU/cm² only. Biofilms formation and antagonistic effect of NEW could be visualized by epifluorescence and scanning electron microscopy, revealing significant biofilms structure. The disinfectant effect of NEW may be attributed to the combined antimicrobial effect of available chlorine and high ORP exhibited by its oxidizing compounds. NEW does not promote metal equipment corrosion due to its neutral pH, and is also environmentally friendly.     

Growth of Escherichia coli,Salmonella enterica and Listeria spp., and their inactivation using ultraviolet energy and electrolyzed water,on ‘Rocha’ fresh-cut pears

The present study aimed at evaluating the growth of Escherichia coli, Salmonella enterica, and Listeria spp. and studying the efficacy of Ultraviolet-C (UV-C) irradiation, acidic electrolyzed (AEW) and neutral electrolyzed (NEW) waters in the reduction of these bacteria on ‘Rocha’ pear. Fresh-cut pieces were inoculated and incubated at 4–20 °C for 8 days. Inoculated pears were treated with UV-C (2.5–10 kJ/m²), AEW, NEW and sodium hypochlorite (SH) and microbiological and quality parameters were evaluated. The three bacteria, inoculated at 6.1–6.2 log cfu/g, grew on the pear at high growth rates at 12 and 20 °C reaching populations of 8.1–8.6 log cfu/g, in 24 h. At 8 °C the microorganisms increased their populations by at least 1 log cfu/g in three days. At 4 °C adaptation phases of less than 24 h for Listeria spp. were measured before exponential growth occurred and the enterobacteria did not grow despite having survived for 8 days. AEW and NEW caused microbial reductions similar to SH, of approximately 1 log cfu/g, while the best UV-C dose (7.5 kJ/m²) of at least 2.4 log cfu/g. Fresh-cut pears were a good substrate for foodborne bacteria emphasizing the importance of preventing contaminations and cross contaminations. The UV-C was more effective than the chemical decontaminations, as it provided superior microbial reductions without greatly affecting the quality of pears.     

Combining basic electrolyzed water pretreatment and mild heat greatly enhanced the efficacy of acidic electrolyzed water against Vibrio parahaemolyticus on shrimp

The objective of this study was to investigate the efficacy of acidic electrolyzed water (AEW) against Vibrio parahaemolyticus on shrimp. The shrimp was initially inoculated with V. parahaemolyticus(7-8 log CFU/g), and treated with AEW (AEW1 containing 51 mg/L of chlorine or AEW2 containing 78 mg/L of chlorine) or organic acids (2% AA and 2%LA) for 1 min or 5 min under different treated conditions. The effect of AEW was better than that of organic acids, the number of survival V. parahaemolyticus cells on shrimp was reduced by 0.9 log CFU/g after treatment for 5 min with AEW without vibration, while 1.0 log CFU/g bacteria cells reduced with vibration. No significant difference (p > 0.05) was observed between AEW and organic acids in the bactericidal activity with or without vibration. The effective order of temperatures on bactericidal activities of AEW was 50 °C > 20 °C > 4 °C, and a 3.1 log CFU/g reduction of V. parahaemolyticus cells on shrimp was detected with treatment of AEW at 50 °C. Mild heat greatly enhanced efficacy of electrolyzed water against V. parahaemolyticus. Basic electrolyzed water (BEW) (50 °C) pretreatment combined with AEW (50 °C) treatment remarkably reduced bacterial cells by 5.4 log CFU/g on shrimp after treatment for 5 min. There was a significant change in physicochemical properties (pH, ORP, ACC) of AEW, after it was used to wash shrimp (P < 0.05). This study suggests that BEW (50 °C) pretreatment followed by AEW (50 °C) treatment could be a possible method to effectively control V. parahaemolyticus contamination on shrimp.     

Effects of bacterial concentrations and centrifugations on susceptibility of Bacillus subtilis vegetative cells and Escherichia coli O157:H7 to various electrolyzed oxidizing water treatments

This study discussed the effects of different bacterial concentrations and centrifugations on the antimicrobial efficacy of electrolyzed oxidizing (EO) water on Bacillus subtilis and Escherichia coli O157:H7. Overnight grown bacterial cultures were centrifuged 1 to 3 times and bacterial concentrations were adjusted to approximately 9 (high), 7 (medium), or 5 (low) log₁₀ CFU/mL. Antimicrobial efficacy of acidic EO water (AEW) and neutral pH EO water (NEW) containing 0.25–30 mg/L available chlorine was determined. In order to ascertain the effects of AEW and NEW on targeted pathogens, cellular properties at bio-molecular levels were also studied. The results showed that the susceptibility of both pathogens decreased significantly with increasing bacterial concentrations. AEW with 10, 0.25 and 0.25 mg/L and NEW with 30, 0.5 and 0.25 mg/L available chlorine were needed for high, medium and low bacterial concentrations, respectively to non-detectable levels by direct plating for E. coli O157:H7. B. subtilis was found more resistant to both EO water treatments and only 4.1 and 3.8 log reductions were achieved for AEW and NEW containing 30 mg/L available chlorine. On the other hand, it was observed that as centrifugation time increased, both bacteria became significantly more sensitive to EO water treatments. When centrifugation period increased from 1 to 3 times, additional 2.67 and 3.38 log E. coli O157:H7 reductions were observed for AEW and NEW treatments, respectively. A similar trend was observed for B. subtilis. DNA and protein leakage increased when pathogens were treated by AEW and NEW with increasing available chlorine concentration, but decreased DNA and protein leakage were observed with increased centrifugation times. These results indicate that initial bacterial concentration and the centrifugation time are two important factors and should be carefully considered in chlorine-based antimicrobial efficacy testing.     

Microbial load reduction of sweet basil using acidic electrolyzed water and lactic acid in combination with mild heat

Sweet basil has been used worldwide as an ingredient for several cuisines. However, it can be contaminated with pathogens; especially Escherichia coli and Salmonella spp. are mainly introduced by poor hygiene during harvesting, cleaning, packaging and distribution. This study aimed to study the efficacy of lactic acid (LA) and acidic electrolyzed water (AEW) against mesophilic bacteria on sweet basil. In addition, a combination treatment was also investigated, using mild heat with the selected sanitizer to disinfect sweet basil inoculated with S. Typhimurium and E. coli. The 2% LA treatment showed high efficiency in microbial decontamination, and mesophilic bacteria were reduced by about 3 log CFU/g. Additionally, the decontamination efficacy of LA increased when combined with mild heat. The use of 2% LA at 50 °C showed the highest microbial reduction in sweet basil, in which mesophilic bacteria, S. Typhimurium, and E. coli were reduced by 4.62, 3.80 and 3.61 log CFU/g, respectively. These findings indicate that LA can be more effective than AEW in disinfection and provides greater efficiency when combined with mild 50 °C heat.     

Removal of Listeria monocytogenes, Staphylococcus aureus and Escherichia coli O157:H7 biofilms on stainless steel using scallop shell powder

Biofilms on steel surfaces containing Listeria monocytogenes, Staphylococcus aureus and Escherichia coli O157:H7 continue to threaten dairy and meat processors. In this study, the ability of scallop shell powder (SSP) to remove biofilms formed by these three pathogens on stainless steel plates was examined. Whey powder solution (WPS) and bench wash water (BWW) provided by dairy and meat factories, respectively, were inoculated with L. monocytogenes, S. aureus or E. coli O157:H7 (9 log₁₀ CFU/ml). Stainless steel plates (10 cm²) were placed in the inoculated fluids and incubated at 20 °C at 48 h to form biofilms. After drying and washing in sterile water, the plates were treated with 0.0, 0.25, or 0.50% (w/v) SSP slurries for 1, 5, or 10 min and then quantitatively examined for the three pathogens. Both 0.25 and 0.50% SSP reduced L. monocytogenes on the plates by 4 log CFU/cm² with a 1 min exposure to 0.50% SSP decreasing S. aureus by 5 logs CFU/cm². After 1 min in 0.25 and 0.50% SSP, E. coli O157:H7 populations in WPS and BWW biofilms decreased 4 and 6 log CFU/cm² and 3 and 5 log CFU/cm², respectively. Increasing the concentration of SSP led to significantly increased efficacy against the tested pathogens (P < 0.05). In conclusion, this study showed that SSP slurries could significantly reduce the numbers of L. monocytogenes, S. aureus and E. coli O157:H7 in biofilms on stainless steel surfaces.     

Influence of food soiling matrix on cleaning and disinfection efficiency on surface attached Listeria monocytogenes

Cleaning and disinfection are essential steps in preventing contamination of foods with pathogenic and spoilage bacteria. The efficacy of cleaning and disinfection products differ depending on target bacteria and type of soiling. We evaluated the effectiveness of cleaning and disinfecting products against Listeria monocytogenes attached on food soiled inert surfaces in a laboratory model. The number of bacteria on surfaces before and after treatment was quantified using indirect conductometric measurements. L. monocytogenes attached to stainless steel surfaces in fish broth systems reached approx. 10⁴ CFU/cm². However, all cleaning and disinfection products were equally effective in this system since all bacteria were removed or killed. When the steel disks were immersed in a fish or meat emulsions, a level of approx. 10⁵–10⁶ L. monocytogenes per cm² was reached after 2–3 days at 20 °C. In this case, 2–3 log were removed or killed by alkaline cleaning products (MC103 or FC140). Direct use of a peracetic acid based disinfectant (Oxivit Active Plus) killed all bacteria when attached in salmon emulsions, whereas only 1–2 log were removed or killed in the meat emulsion system. Thus, the efficiency of cleaning and disinfection products against L. monocytogenes is strongly influenced by the food matrix.     

Inactivation of Listeria monocytogenes and natural microbiota on raw salmon fillets using acidic electrolyzed water,ultraviolet light or/and ultrasounds

The objective of this study was to investigate the effectiveness of various decontamination treatments of raw salmon fillets, namely acidic electrolyzed water (AEW), ultraviolet light (UV), ultrasound (US), and their combinations against Listeria monocytogenes and natural microbiota including total viable count (TVC), total coliforms, Escherichia coli, and yeasts and molds. The changes in quality and sensory parameters of treated salmon samples were also evaluated. The combined treatments: UV + US and UV + US + AEW showed significantly (P ≤ 0.05) higher reduction in L. monocytogenes of 0.79 and 0.75 log CFU/g, respectively, compared to control (0.17 log CFU/g) washed with sterile distilled water (dH₂O). TVC was reduced by 0.59 and 0.64 log CFU/g after UV + US and UV + US + AEW treatments, respectively. The color and odor of salmon were significantly affected after combined treatments, but the texture and firmness of tissue were not significantly (P > 0.05) changed. These results indicate that UV + US and UV + US + AEW were the most effective at reducing the populations of L. monocytogenes and natural microbiota on raw salmon fillets. The AEW treatment by itself was found to be ineffective for raw salmon sanitation. However, these combined treatments should be improved by optimizing other factors such as treatment temperature, time and the distance between UV and food sample to enhance their anti-listerial or antimicrobial effects.     

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.     

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.     

Application of disinfectant sprays after chilling to reduce the initial microbial load and extend the shelf-life of chilled chicken carcasses

The objective of this study was to evaluate the effects of various disinfectant sprays on initial microbial load and conduct a shelf-life study of chilled chicken carcasses. Chilled chicken carcass samples obtained after chilling were sprayed for 15 s in a purpose-built spray rig with sodium hypochlorite (SH, 50 & 100 mg/L), chlorine dioxide (CD, 50 & 100 mg/L), lactic acid (LA, 1 & 2%), acid electrolyzed oxidizing water (AEOW) and slightly acid electrolyzed oxidizing water (SAEOW). Untreated carcasses were used as the control. Back, leg and breast skin were removed from each carcass after treatment to determine the total viable counts (TVC) and total coliforms. Sprays of 2% LA, AEOW and SAEOW were the most effective treatments with reductions of 0.47–0.83 log CFU/cm² and 0.49–0.96 log MPN/cm² in TVC and total coliforms, respectively. Samples treated with AEOW and SAEOW had 2 days of microbial shelf-life extension compared to the controls, which exceeded the TVC limit of 7 log CFU/cm² at day 6. Even longer extension was obtained for the 2% LA treated samples. The total coliforms, pH and total volatile basic nitrogen (TVBN).TVBN values of the 2% LA, AEOW and SAEOW treated samples were significantly (P < 0.05) lower than those of the controls during storage. Predominantly, the TBARS values of the AEOW and SAEOW treated samples were not statistically different from those of the controls (P > 0.05); however, the 2% LA treatment accelerated lipid oxidization, manifested as the highest TBARS value (2.09 mg MDA/kg) at day 8. Conclusively, this study indicated that the application of AEOW and SAEOW sprays to chilled chicken carcasses after chilling can reduce initial microbial load and maintain quality attributes during refrigerated storage.     

Efficacy of acidic and alkaline electrolyzed water for inactivating Escherichia coli O104:H4, Listeria monocytogenes,Campylobacter jejuni,Aeromonas hydrophila,and Vibrio parahaemolyticus in cell suspensions

This study investigated the effect of electrolyzed water on pathogenic bacteria cell suspensions. Specifically, we evaluated the efficacy of strong and weak acidic electrolyzed waters (SACEW, WACEW) and strong and weak alkaline electrolyzed waters (SALEW, WALEW) on Vibrio parahaemolyticus, Listeria monocytogenes, Aeromonas hydrophila, Campylobacter jejuni, and Escherichia coli O104:H4 in suspensions of (10⁷–10⁹ CFU/mL) in 1% NaCl. SACEW and WACEW were applied at available chlorine concentrations (ACC) of 20 and 10 mg/mL, pH 3.1 and 3.55 and oxidation-reduction potentials (ORP) of 1150 and 950 mV, respectively. Results show that no viable cells were recovered for V. parahaemolyticus, L. monocytogenes, A. hydrophila, C. jejuni within 2 min at 20 °C. However, E. coli O104:H4 was significantly more resistant to ALEW compared to ACEW. Results also show that the bactericidal activity of SACEW (20 mg/mL ACC) was more effective than WACEW (10 mg/mL ACC) in terms of inactivating E. coli O104:H4. Alkaline-electrolyzed waters were found to reduce cell numbers by 1–3 log (P < 0.05). However, alkaline electrolyzed water was less effective (P < 0.05) than acidic electrolyzed treatment.     

Photodynamic inactivation of Salmonella enterica Enteritidis by 405 ± 5-nm light-emitting diode and its application to control salmonellosis on cooked chicken

A 405 ± 5-nm LED illumination was evaluated for its antibacterial effect against Salmonella Enteritidis in phosphate buffered saline (PBS) and on the surface of cooked chicken. Its antibacterial mechanism was also elucidated by determining the injury of cellular components using metabolic inhibitors. LED illuminated three S. Enteritidis strains in PBS at doses as high as 0.45 kJ/cm² (for 7.5 h) and on cooked chicken at doses of 1.58–3.80 kJ/cm² (for 20–48 h) at 4, 10, and 20 °C. Results showed that illumination inactivated 1.4–2.1 log CFU/ml of populations in PBS at 0.45 kJ/cm², indicating that S. Enteritidis 130 was more susceptible to illumination than 124 and 125 strains. At 4 °C, Salmonella populations on illuminated cooked chicken decreased by 0.8–0.9 log CFU/cm² at 3.80 kJ/cm², whereas bacterial growth inhibition and delay were observed by illumination at 10 and 20 °C, respectively, regardless of bacterial strain. These results indicate that illumination temperature significantly (P ≤ 0.05) influenced the antibacterial effect of LED on cooked chicken. LED illumination at 4 °C resulted in the incapability of Salmonella cells to repair cellular damage related to metabolism of DNA, RNA, protein, and cell wall. These results suggest that 405 ± 5-nm LEDs under refrigeration conditions could control Salmonella linked to cooked chicken.     

Efficacy of electrolyzed oxidizing water as a pretreatment method for reducing Listeria monocytogenes contamination in cold-smoked Atlantic salmon (Salmo salar)

Listeria monocytogenes contamination in ready-to-eat (RTE) fish products, in particular in cold-smoked salmon is an important food safety concern. This study evaluated the antimicrobial activity of electrolyzed oxidizing (EO) water as a pretreatment method during the process of cold-smoked salmon to inactivate L. monocytogenes. In addition, the effect of EO water treatment on the sensory and textural quality of the final product was also evaluated. Raw Atlantic salmon (Salmo salar) fillets were inoculated with L. monocytogenes (with an approximately cell number of 6 × 10⁵ CFU/g L. monocytogenes ATCC 19114) and treated with EO water at three different temperatures (20, 30, and 40 °C) and at three different exposure time of 2, 6, and 10 min before the cold-smoking process. A combination of EO water and a mild temperature (40 °C) had reduced L. monocytogenes populations by 2.85 log₁₀ CFU/g. The sensory as evaluated by a consumer panel (N = 71) and texture, which was measured by texture analysis showed no significant changes between EO and mild temperature treated samples and the control.     

Disinfection efficacy and mechanism of slightly acidic electrolyzed water on Staphylococcus aureus in pure culture

Slightly acidic electrolyzed water (SAEW), considered as a broad-spectrum and high-performance bactericide are increasingly applied in the food industry. However, its disinfection mechanism has not been completely elucidated. This study aims to examine the disinfection efficacy and mechanism of SAEW on Staphylococcus aureus, compared with that of sodium hypochlorite (NaClO) and hydrochloric acid (HCl). SAEW treatment significantly reduced S. aureus by 5.8 log CFU/mL in 1 min, while 3.26 and 2.73 log reductions were obtained with NaClO and HCl treatments, respectively. A series of biological changes including intracellular potassium leakage, TTC-dehydrogenase relative activity and bacterial ultrastructure destruction were studied following disinfection treatment of S. aureus. The results showed that SAEW decreased the relative activity of TTC-dehydrogenase by 65.84%. Comparing intracellular potassium leakage, the SAEW treatment caused a greater percent of protein leakage (108.34%) than the NaClO (18.75%) or HCl (0.84%) treatments. These results demonstrated the potent impact SAEW had on the permeability of cell membranes. In addition, the ranking of partly agglutinated cellular inclusion formation was HCl > SAEW > NaClO. It appeared that HCl, along with its low pH value, are responsible for most of the cytoplasmic disruptions. Overall, this study demonstrated that the disinfection mechanism of SAEW was disrupting the permeability of cell membrane and the cytoplasmic ultrastructures in S. aureus cells.     

Combined effect of acidic electrolyzed water (AcEW) and alkaline electrolyzed water (AlEW) on the microbial reduction of fresh-cut cilantro

In the present study, the disinfection efficacy on fresh-cut cilantro of the combination of strongly acidic electrolyzed water (AcEW) and alkaline electrolyzed water (AlEW) was evaluated, in comparison with single slightly acidic electrolyzed water (SAEW) and single AcEW treatments. The populations of E. Coli O78 on inoculated cilantro treated by AlEW 5 min + AcEW 5 min, was not detected while 3.43 and 3.73 log₁₀ CFU/g in the AlEW 2.5 min + AcEW 2.5 min and AcEW 2 min + AlEW 2 min + AcEW 2 min treatments respectively. Our results implied that the bactericidal abilities of the combination of AlEW and AcEW treatments were higher than that of single AcEW and SAEW, which also was demonstrated microscopically by scanning electron microscopy (SEM). Moreover, the efficacy of combination of AcEW and AlEW in reducing natural micro flora on fresh-cut cilantro was also evaluated compared with single AcEW and SAEW. The results showed that the combination of AlEW and AcEW had stronger sterilization ability than single AcEW and SAEW. Considering the utilizations of AlEW and disinfection efficacy, we suggest that the combination of AlEW and AcEW may also be a better choice in fresh-cut produce.     

Photocatalytic TiO2 coating of plastic cutting board to prevent microbial cross-contamination

Kitchen cutting boards are one common source of microbial cross-contamination in foods. In this study, a method was developed to create an antimicrobial coating on HDPE cutting board using UV-activated TiO₂ nanoparticles (NPs). The antimicrobial efficacy of the developed coatings was tested against E. coli O157: H7 for 3 h at 0.5 ± 0.05 mW/cm² UVA light intensity. In addition, the effect of NP loading (0.0125, 0.0625, and 0.125 mg/cm²), and surface treatment of coatings by oxygen plasma for 1–15 min on the bactericidal efficacy was investigated. Further, the bactericidal efficacy of the TiO₂ coated cutting board on repeated use (i.e. 1, 2, 3 and 5 times) was also evaluated. The results showed that by increasing the NP loading from 0 to 0.125 mg/cm² has increased the log reduction from 0.37 to 1.18 CFU/cm². However, no significant difference (P > 0.05) in the reduction was observed between NP loadings at 0.0625 and 0.125 mg/cm². Oxygen plasma treatment of the coated surfaces for 5–15 min significantly increased (P ≤ 0.05) the log reduction compared to control sample without plasma treatment. Under the tested conditions, TiO₂ coating with 0.0625 mg/cm² NP loading followed by oxygen plasma treatment for 5 min was found to achieve the greatest reduction up to 2.67 log CFU/cm². Also, the coated-surfaces were found to retain the original bactericidal property even after up to 5 times washing treatment. The developed TiO₂ coating on cutting board showed promise to mitigate the risk of microbial cross-contamination by providing a stable antimicrobial activity for extended use. Plasma treatment further enhanced the bactericidal property of the developed coatings without affecting physical stability.     

Catering services and HACCP: Temperature assessment and surface hygiene control before and after audits and a specific training session

Proper application of HACCP in catering services involves monitoring decisive critical points. The purpose of this study was to assess food temperatures and surface hygiene control in two catering services in Navarra (Spain) at two different time periods: the first one after implementation of the HACCP system and the second period, after the initial supervision through audits and a specific training session regarding temperatures of products and hygienic conditions of surfaces and equipment because the majority of detected nonconformities were related to these parameters. The recorded temperatures of 650 cooked food products within the first period showed that only 65.1% of the hot dishes had a temperature higher than 65 °C, in accordance with Spanish legislation, and 12.9% of them showed a risky holding temperature (<55 °C). However, the percentage of noncomplying dishes was reduced by a half after the training session (p < 0.001). Since the significant differences observed in recorded temperatures were related to the type of meal (with or without sauces) and the type of cooking procedure, a lower safe criterion for the retention of hot dishes was suggested if the temperature is continuously maintained over 55 °C until serving. With regard to cleaning and disinfection, 18.3% of the 600 analyzed surfaces did not meet the established cleaning criterion (≤100 CFU/25 cm²) in the first period, while in the second period this percentage was reduced to 13.6% in both catering businesses (p = 0.021). The dirtiest surfaces were equipment such as cutting boards and meat slicing machines (>26%) compared to utensils for distribution (12.0%). As the impact of dirty surfaces on the hygienic quality of a finished product will depend on which step was being taken during dish elaboration when equipment or utensil was used, it is suggested that more restrictive limits be established regarding utensils and equipment that are in direct contact with the finished product (≤1 CFU/cm²). Results of the study demonstrate that a specific training session on these items has improved the temperature control of prepared meals and the effectiveness of cleaning and disinfection, essentials for guaranteeing the hygienic quality of prepared foods.     

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.     

Effect of ozone and ultraviolet light on Listeria monocytogenes populations in fresh and spent chill brines

The efficacy of ozone and ultraviolet light (UV) treatment as hurdles against Listeria monocytogenes suspended in fresh (9% NaCl, 91.86% transmittance) and spent brines (20.5% NaCl, 0.01% transmittance) was evaluated. Brines were inoculated with a cocktail of L. monocytogenes-strains N1-227, N3-031, and R2-499. Ozonation was performed by sparging gaseous ozone into brine. This was followed by UV irradiation (253.7 nm) of the brine in sterile quartz cuvettes. Enumeration was performed by spread plating on modified Oxford medium and Trypticase Soy agar supplemented with yeast extract. In fresh brines containing L. monocytogenes, 10 min of ozonation lead to a 7.44 ± 0.13 log CFU/ml mean reduction and 10 min of UV radiation caused a 1.95 ± 0.41 log CFU/ml mean reduction. Sequential exposure of 10 min of ozonation and UV resulted in >9 log CFU/ml reduction in L. monocytogenes populations in fresh brine. Sixty minutes of ozonation of spent brines resulted in a 4.85 ± 0.61 log CFU/ml mean reduction of L. monocytogenes populations. Ten minutes of UV exposure in spent brines resulted in 0.49 ± 0.14 log CFU/ml mean reduction in L. monocytogenes. A sequential treatment of 60 min ozonation and 10 min UV resulted in an excess of 5 log CFU/ml reduction in L. monocytogenes cells in spent brine. Ozonation did not cause a significant increase in the transmittance of the spent brine to aid UV penetration but resulted in color change. Sequential treatments of Ozonation and UV maybe effective in reducing L. monocytogenes in chill brines.