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.     

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.     

Evaluation of electrolyzed water as cleaning and disinfection agent on stainless steel as a model surface in the dairy industry

In the dairy industry, cleaning and disinfection of surfaces are important issues and development of innovative strategies may improve food safety. This study was aimed to optimize the combined effect of alkaline electrolyzed water (AEW) and neutral electrolyzed water (NEW) as alternative cleaning and disinfection procedure on stainless steel plates (SSP) with and without electropolishing. NEW at 10 ppm total available chlorine (TAC), achieved a ˃5 log CFU/mL reduction of milk spoilage bacterial suspension, grown in trypticase soy broth (8.7 log CFU/mL of each bacterial strain: Pseudomonas aeruginosa, Enterococcus faecalis and Micrococcus luteus) contacted for 30 s. An optimal design of experiments was used to assess the combined effect of cleaning with AEW, followed by disinfection with NEW (40 ppm TAC, contact time 3 min). Tested factors were contact time (10, 20 and 30 min), concentration of AEW (100, 200 and 300 mg NaOH/L), temperature (30, 40 and 50 °C), and surface type (304-2B SSP with or without electropolishing), using sixteen treatments with two replicates. The response variable was bacterial cells removal (log CFU/cm²). All main effects, two factors interactions and a quadratic term significantly influenced cells removal, and were modeled using a second order polynomial. Best cleaning procedures were significantly affected by surface roughness; electropolished SSP required 10 min, 100 mg/L AEW at 30 °C, whereas SSP without modification required 30 min, 300 mg/L AEW at 30 °C. From confirmatory tests cells removed were 3.90 ± 0.25 log CFU/cm² for electropolished SSP, and 3.20 ± 0.20 log CFU/cm² for SSP without modification. NEW is non-corrosive, and can be advantageously used for environmentally friendly cleaning and disinfection processes.     

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.     

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.     

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.     

Effects of electrolyzed oxidizing water and ice treatments on reducing histamine-producing bacteria on fish skin and food contact surface

This study investigated efficacy of electrolyzed oxidizing water (EO water) and ice (EO ice) treatments in reducing histamine-producing bacteria (Enterobacter aerogenes, Enterobacter cloacae, Klebsiella pneumoniae, Morganella morganii and Proteus hauseri) on food contact surfaces (ceramic tile and stainless steel) and fish skin (Atlantic salmon and yellowfin tuna). Soaking ceramic tile and stainless steel in EO water (50 ppm chlorine) for 5 min inactivated inoculated bacteria on the surface (>0.92 to >5.4 log CFU/cm² reductions). E. cloacae, K. pneumoniae and P. hauseri did not survive well on fish skin. Soaking salmon skin in EO water (100 ppm chlorine) for 120 min resulted in 1.3 and 2.2 log CFU/cm² reductions of E. aerogenes and M. morganii, respectively. A treatment of EO ice (100 ppm chlorine) for 24 h was capable of reducing E. aerogenes and M. morganii on tuna skin by 2.4 and 3.5 log CFU/cm², respectively. EO water and EO ice can be used as post-harvest treatments for reducing histamine-producing bacteria on food contact surfaces and fish skin.     

Real-time PCR with internal amplification control for the detection of Cronobacter spp. (Enterobacter sakazakii) in food samples

Cronobacter spp. (Enterobacter sakazakii) is an opportunistic pathogen and is linked with life-threatening infections in neonates. The organism has been isolated from a wide variety of foods and environments. In this study, a Taqman real-time PCR assay incorporating an internal amplification control (IAC) was developed and evaluated for specific detection of Cronobacter spp. in foods. Previously reported macromolecular synthesis (MMS) operon sequence was selected for specificity, and 67 bacterial strains, including four strains of Cronobacter spp., were evaluated. All Cronobacter strains were successfully identified, however no cross-reactivity was observed with non-Cronobacter strains. Detection limit of the assay in pure culture and formula infant without enrichment was 1.2 × 10³ CFU/ml (1.2 × 10¹ CFU/assay). After 24 h enrichment in broth, as few as 10⁰ CFU/ml or g of Cronobacter could be detected in artificially contaminated food samples (infant formula, sterilized milk and chicken meat). The detection limit of the real-time PCR assay however remained unaffected in the presence of 10⁸ CFU/ml Salmonella typhimurium in another analysis. A total of 92 food samples were analyzed for the presence of Cronobacter, out of which two pork samples were found as positive by real-time PCR, whereas only one was detected by the ISO standard method. The adjusted real-time PCR assay can be adopted to rapidly detect Cronobacter spp. in food samples with high specificity and sensitivity, and can prevent false negative results by using the IAC.     

Effects of HACCP on process hygiene in different types of Serbian food establishments

This paper presents results from a research that analyzed effects of implementing HACCP on process hygiene in food establishments in Serbia. Process hygiene indicators were microbial profiles of 73,428 samples from food contact surfaces, hands of food handlers and cooling facilities collected from 1707 food establishments during a period of seven years. The study covered two periods during the observed period, 41 months before and 43 months after the implementation of the new Food Safety Law in Serbia requiring HACCP. Overall results presented in this paper confirm post-HACCP process hygiene improvement expressed as reduction of at least 0.7 log₁₀ CFU/cm² for food contact surfaces to over 1 log₁₀ CFU/cm² for cooling facilities. Our research confirms that after requiring HACCP, the main differences in process hygiene in respect to food contact surfaces were observed between takeaways (as food establishment with poorest hygiene) and other categories of food establishments. Institutional food services were the best scored establishments. Regarding food handlers' hygiene, results show similar level of hygiene improvements in all types of establishments.     

Adhesion of Staphylococcus aureus and Staphylococcus xylosus to materials commonly found in catering and domestic kitchens

The aim of this work was to investigate the adhesion of Staphylococcus aureus and Staphylococcus xylosus on marble, granite, polypropylene, stainless steel 304 and stainless steel 316. The results showed that S. aureus adhered to all substratums. The maximum was observed on marble (30 10⁶ CFU/cm²) and, on polypropylene (30,2 10⁶ CFU/cm²). The results showed also that S. xylosus revealed a high ability to adhere to all substratum. This strains adhere more on marble (32.8 10⁶ CFU/cm²) and granite (16,3 10⁶ CFU/cm²) than to others substratum. The highest extent of adhesion of S. aureus and S. xylosus occurred to marble, polypropylene and granite. A correlation between substratum physicochemical properties and bacterial adhesion was also examined. A good correlation was observed between S. xylosus adhesion and their acid-base character. The topography of substratum surface was investigated using AFM. A good correlation was obtained between roughness and bacterial adhesion.     

Development of a multiplexed PCR assay combined with propidium monoazide treatment for rapid and accurate detection and identification of three viable Salmonella enterica serovars

Salmonella is the leading pathogenic bacteria in food and contaminated water. The aim of this study was to develop a rapid and reliable technique for simultaneous detection of the main three serotypes (Salmonella enterica serovars Typhimurium, Paratyphi B and Typhi) of Salmonella. Primers were designed to amplify the genes specific to each of these three serotypes for simultaneous detection using polymerase chain reaction (PCR). To ensure the detection of only viable cells, propidium monoazide (PMA) was applied to selectively suppress the DNA signal from dead cells. Results showed that the PMA-multiplexed PCR (PMA-mPCR) assay always gave negative results for heat-killed Salmonella at concentrations up to 1 × 10⁶ CFU/ml in pure culture or 1 × 10⁶ CFU/g in spiked food products (tomato, chicken, beef and ham). Results showed that the detection limits of the PMA-mPCR assay were approximately 10² CFU/ml (4.3 × 10² CFU/ml for S. Typhimurium, 3.7 × 10² CFU/ml for S. Paratyphi B, 7.2 × 10² CFU/ml for S. Typhi) in pure culture and 10³ CFU/g (4.3 × 10³ CFU/g for S. Typhimurium, 3.7 × 10³ CFU/g for S. Paratyphi B, 7.2 × 10³ CFU/g for S. Typhi) in food produce. These results demonstrated that the PMA-mPCR assay can simultaneously detect and identify viable S. Typhimurium, Paratyphi B and Typhi in a short period of time, even in food produce.     

Uneven distribution of microorganisms on the surface of field-grown cantaloupes

Cantaloupes have been implicated in a number of foodborne illness outbreaks due to contamination with human pathogens. However, we have limited understanding on the potential microbial contamination routes, especially in the production fields. We hypothesized that the soil upon which cantaloupe fruit rest can be a source of microbial contamination. Microbial populations on the surfaces of field-grown cantaloupes were enumerated and the effect of washing on the removal of microorganisms from the cantaloupe surfaces was evaluated. The microbial populations on the lower surface (in direct contact with soil) of the cantaloupes were significantly higher (p < 0.05), averaging 2.21 log CFU/cm² (aerobic bacteria); 1.62 log CFU/cm² (coliforms); and 2.02 log CFU/cm² (molds and yeasts), compared to those on the upper surface (exposed to the air). Washing significantly reduced only the populations of yeasts and molds on the lower surfaces of cantaloupes. Scanning electron micrographs showed more microbe-like bodies on the lower surface of cantaloupe than on the top. This study revealed an uneven distribution of microbial populations on the surfaces of field-grown cantaloupes, suggesting that direct contact with soil can be a major source of microbial contamination to fruits. Field production practices that minimize direct contact of cantaloupes with the soil may serve as a control strategy for ensuring a safer product. Also, more effective surface cleaning methods should be explored.     

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.     

Quantification and variability of Escherichia coli and Staphylococcus aureus cross-contamination during serving and consumption of cooked thick porridge in Lungwena rural households, Malawi

The study investigated bacterial transfer to cooked thick porridge via ladles and hands during serving in 29 households in Lungwena, rural Malawi. Household stored water used for hand and ladle washing, was contaminated with Escherichia coli and Staphylococcus. aureus from hands of members of the household or from contaminated ladles used in food preparation. The results showed that hands became contaminated with E. coli and S. aureus cells in the range 0.6–3.7 and 2.2–4.3 log₁₀ CFU/cm², respectively, following washing with the contaminated water. Ladles became contaminated with 0.9–3.2 log₁₀ CFU/cm² of E. coli cells whereas contamination with S. aureus on ladles ranged between 1.9 and 4.6 log₁₀ CFU/cm². Bacterial transfer from hands to food ranged from <1 to 3.6 log₁₀ CFU/g for E. coli and 2.1 to 4.2 log₁₀ CFU/g for S. aureus. Ladle surfaces transferred from 1.3 to 3.1 and from 1.2 to 4.3 log₁₀ CFU/g of E. coli and S. aureus, respectively, on to the food. Contamination of food by hands was significantly (p < 0.05) higher than that of ladles and transfer of S. aureus was significantly (p < 0.05) higher than that of E. coli. The amount of bacteria transferred to the recipient depended on the wash water type and bacteria type. The study has demonstrated that although the traditional cooking of thick porridge inactivates S. aureus and E. coli, the porridge can be contaminated with bacteria during consumption using hands and serving on to a plate with wooden ladles.     

Development of a quantitative real-time PCR assay for viable Salmonella spp. without enrichment

Propidium monoazide (PMA) combined with molecular quantitative real-time PCR (qPCR) has been widely used for only detection of viable bacteria. However, recent studies indicated PMA did not fully inhibit the detection of dead Salmonella. In this study, we developed a more effective PMA Taqman-based qPCR than previous studies to quantify viable Salmonella spp. in raw shrimp. This method has high specificity by using 60 strains belonging to 23 species. The optimization of the PMA concentration showed that 100 μM was considered optimal to effectively inhibit 10⁶ CFU/mL dead cells, while only 10³–10⁴ CFU/mL dead cells could be inhibited in previous reports. This assay could detect viable Salmonella spp. at as low as 36 CFU/mL in pure culture and 100 CFU/g in raw shrimp. By comparing with PMA-qPCR, qPCR and plate counting for quantifying Salmonella in samples, this PMA-qPCR was obviously superior to qPCR and had good agreement with plate counting. In conclusion, this effective method can be used as an available tool to quantify viable Salmonella spp. in raw shrimp.     

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.     

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.     

Factors impacting microbial load of food refrigeration equipment

Our aim was to determine factors that have an impact on the bacterial load of inner surfaces of food refrigeration equipment to develop recommendations that should be made to consumers. We investigated 23 domestic refrigerators (DRs) and, for comparison, six serve-over counters (SOCs). Several zones were studied for aerobic mesophilic counts (AMC) presumptive Bacillus cereus and coagulase-positive staphylococci. In addition, for each DR sample, we collected data on the condition of the sampled surface and refrigeration practices. In DRs, there was no correlation between AMC and temperature, relative humidity, pH or cleaning frequency. AMC counts in SOCs, which are cleaned and disinfected weekly, were similar to the figures from the less frequently cleaned DRs, but B. cereus and coagulase-positive Staphylococus were less frequently found in SOCs. In DRs, the highest AMC counts were reached when both condensation and food traces were visible, i.e. when growth conditions were met, resulting in a mean of 10⁴ CFU/cm² against of mean of 32 CFU/cm² on clean surfaces and dry surfaces with food traces. Consequently, two recommendations for consumers are (1) to avoid condensation and (2) to clean up food spills as soon as possible.     

Influence of processing parameters on the pulsed-light inactivation of Penicillium expansum in apple juice

The objective of this study was to evaluate the efficiency of pulsed light treatments on the inactivation of Penicillium expansum inoculated in apple juice. Different critical processing parameters, namely fluence (0.2 and 0.4 J/cm² per pulse), number of pulses (5, 10, 15, 20, 30 and 40 flashes applied from opposite product sides), depth of the juice layer (6, 8, 10 mm) and inoculation level (2.3 × 10⁴ CFU/mL and 3 × 10⁵ CFU/mL) were studied regarding their effect on microbial inactivation. Moulds inactivation increased with increasing number of pulses and fluence. Treatments led to microbial reductions of up to 3.76 log CFU/mL. Inactivation levels achieved with treatments performed on thin layers of juice (6 mm) were substantially higher than those observed after applying the same treatments on deeper layers of 8 or 10 mm. As well, P. expansum inactivation in juice samples with lower initial counts was greater than in samples with higher counts. Minor changes were noticed after PL treatments regarding juice pH and soluble solids; however, apple juice colour slightly darkened after applying and overall fluence of 32 J/cm² (40 pulses of 0.4 J/cm² from both upper and bottom sides). The obtained results suggest that PL-technology can be applied to efficiently reduce P. expansum counts in apple juice while maintaining the product quality.