Behavior of Escherichia coli O157:H7 and Listeria monocytogenes in Tryptic soy broth subjected to various low temperature treatments

The inactivation and injury of Escherichia coli O157:H7 and Listeria monocytogenes in Tryptic soy broth stored at −5, −18 and −28°C were studied. Regardless of storage temperature, viable populations of E. coli O157:H7 and L. monocytogenes determined with TSA (uninjured and injured cells) or TSAB (uninjured cells), decreased as the storage time increased. However, the least surviving population of both test organisms was noted when stored at −18°C followed by those stored at −28 and −5°C. The viable populations of E. coli O157:H7 determined either with TSA or TSAB, was reduced most drastically during the first day of storage then decreased slowly thereafter. Viable populations of L. monocytogenes declined slightly and gradually during the entire storage period. Furthermore, E. coli O157:H7 was found more susceptible to the freezing storage than L. monocytogenes. After 21-day storage at −18°C, population reduction of E. coli O157:H7 determined with TSA was ca 1.72 log CFU/ml. On the other hand, a population reduction of only 0.64 log CFU/ml was noted with L. monocytogenes. Besides, the surviving population of E. coli O157:H7 contained a larger proportion of injured cells than L. monocytogenes.     

The Effect of pH on Inactivation of Pathogenic Bacteria on Fresh-cut Lettuce by Dipping Treatment with Electrolyzed Water

Fresh‐cut lettuce samples inoculated with S. Typhimurium, E. coli O157:H7 or L. monocytogenes were dipped into 300 ppm electrolyzed water (EW) at pH 4 to 9 and 30 °C for 5 min. The effects of treatment pH on bacterial reduction and visual quality of the lettuce were determined. The treatments at pH 4 and 8 resulted in the most effective inactivation of E. coli O157:H7, but the effect of pH was not significant (P > 0.05) for S. Typhimurium and L. monocytogenes. The treatment at pH 7 retained the best visual quality of lettuce, and achieved a reduction of approximately 2 log CFU/g for above 3 bacteria.     

Behavior of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium in teewurst, a raw spreadable sausage

The fate of Listeria monocytogenes, Salmonella Typhimurium, or Escherichia coli O157:H7 were separately monitored both in and on teewurst, a traditional raw and spreadable sausage of Germanic origin. Multi-strain cocktails of each pathogen (ca. 5.0 log CFU/g) were used to separately inoculate teewurst that was subsequently stored at 1.5, 4, 10, and 21 °C. When inoculated into commercially-prepared batter just prior to stuffing, in general, the higher the storage temperature, the greater the lethality. Depending on the storage temperature, pathogen levels in the batter decreased by 2.3 to 3.4, ca. 3.8, and 2.2 to 3.6 log CFU/g for E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively, during storage for 30 days. When inoculated onto both the top and bottom faces of sliced commercially-prepared finished product, the results for all four temperatures showed a decrease of 0.9 to 1.4, 1.4 to 1.8, and 2.2 to 3.0 log CFU/g for E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively, over the course of 21 days. With the possible exceptions for salt and carbohydrate levels, chemical analyses of teewurst purchased from five commercial manufacturers revealed only subtle differences in proximate composition for this product type. Our data establish that teewurst does not provide a favourable environment for the survival of E. coli O157:H7, S. Typhimurium, or L. monocytogenes inoculated either into or onto the product.     

Efficacy of Neutral pH Electrolyzed Water in Reducing Escherichia coli O157:H7 and Salmonella Typhimurium DT 104 on Fresh Produce Items using an Automated Washer at Simulated Food Service Conditions

The objective of this study was to determine the efficacy of neutral pH electrolyzed (NEO) water (155 mg/L free chlorine, pH 7.5) in reducing Escherichia coli O157:H7 and Salmonella Typhimurium DT 104 on romaine lettuce, iceberg lettuce, and tomatoes washed in an automated produce washer for different times and washing speeds. Tomatoes and lettuce leaves were spot inoculated with 100 μL of a 5 strain cocktail mixture of either pathogen and washed with 10 or 8 L of NEO water, respectively. Washing lettuce for 30 min at 65 rpm led to the greatest reductions, with 4.2 and 5.9 log CFU/g reductions achieved for E. coli O157:H7 and S. Typhimurium respectively on romaine, whereas iceberg lettuce reductions were 3.2 and 4.6 log CFU/g for E. coli O157:H7 and S. Typhimurium respectively. Washing tomatoes for 10 min at 65 rpm achieved reductions greater than 8 and 6 log CFU/tomato on S. Typhimurium and E. coli O157:H7 respectively. All pathogens were completely inactivated in NEO water wash solutions. No detrimental effects on the visual quality of the produce studied were observed under all treatment conditions. Results show the adoption of this washing procedure in food service operations could be useful in ensuring produce safety.     

Inactivation of Escherichia coli O157:H7, Salmonella typhimurium,and Listeria monocytogenes on Stored Iceberg Lettuce by Aqueous Chlorine Dioxide Treatment

ABSTRACT: Inactivation of Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes in iceberg lettuce by aqueous chlorine dioxide (ClO₂) treatment was evaluated. Iceberg lettuce samples were inoculated with approximately 7 log CFU/g of E. coli O157:H7, S. typhimurium, and L. monocytogenes. Iceberg lettuce samples were then treated with 0, 5, 10, or 50 ppm ClO₂ solution and stored at 4 °C. Aqueous ClO₂ treatment significantly decreased the populations of pathogenic bacteria on shredded lettuce (P < 0.05). In particular, 50 ppm ClO₂ treatment reduced E. coli O157:H7, S. typhimurium, and L. monocytogenes by 1.44, 1.95, and 1.20 log CFU/g, respectively. The D₁₀‐values of E. coli O157:H7, S. typhimurium, and L. monocytogenes in shredded lettuce were 11, 26, and 42 ppm, respectively. The effect of aqueous ClO₂ treatment on the growth of pathogenic bacteria during storage was evaluated, and a decrease in the population size of these pathogenic bacteria was observed. Additionally, aqueous ClO₂ treatment did not affect the color of lettuce during storage. These results suggest that aqueous ClO₂ treatment can be used to improve the microbial safety of shredded lettuce during storage.     

Inactivation of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in orange and tomato juice using ohmic heating

The effects of ohmic heating on reduction of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in orange and tomato juice were investigated. Orange and tomato juice inoculated with E. coli O157:H7, Salmonella Typhimurium, and L. monocytogenes were subjected to ohmic heating with selected parameters including electric field strength from 10 to 20 V/cm and treatment times from 0 to 540 s. The number of pathogens was reduced by increasing the electric field strength from 10 to 20 V/cm as well as increasing treatment time. The population of E. coli O157:H7 was reduced more than 5 log after 120, 210, and 540 s of treatment in orange juice with 20, 15, and 10 V/cm electric field strengths, respectively. In tomato juice, levels of E. coli O157:H7 were reduced more than 5 log after 90, 180, and 480 s with the same electric field strengths. Similar phenomena were observed for Salmonella Typhimurium and L. monocytogenes, but E. coli O157:H7 was the most resistant to ohmic heating treatment. These results show that ohmic heating is potentially useful for inactivation of E. coli O157:H7, Salmonella Typhimurium, and L. monocytogenes and that the effect of inactivation depends on applied electric field strength, treatment time, pathogen species, and type of juice.     

Growth and thermal inactivation of Listeria monocytogenes and Escherichia coli O157:H7 in four kinds of traditionally non-fermented soya bean products

This study evaluated growth and thermal inactivation of Listeria monocytogenes and Escherichia coli O157:H7 inoculated in tofu, dougan, qianzhang and doupi which were stored at 4, 25 and 37 °C and heated at 55, 60, 65 and 70 °C. Growth of the two pathogens in four soya bean products increased with temperature or A_w of soya bean products increasing. At the same temperature, lag time (LT) values of L. monocytogenes (16.32–0.94 h) and E. coli O157:H7 (2.66–0.98 h) in tofu which has the highest A_w were the lowest. When inoculated soya bean products were stored at 4 °C, L. monocytogenes grew slowly, while E. coli O157:H7 did not grow but survived for 14 days. With temperature increasing, δ-values of L. monocytogenes and E. coli O157:H7 in the four soya bean products were decreased. With A_w of soya bean products increasing, thermal resistance of L. monocytogenes decreased, while that of E. coli O157:H7 increased. This study could assist retail soya bean products processors and food industry to enhance safety of soya bean products and design thermal processing regimes.     

Inactivation of foodborne pathogens in ready-to-eat salad using UV-C irradiation

To examine the applicability of ultraviolet (UV)-C irradiation on the inactivation of foodborne pathogen in ready-to-eat salad, it was inoculated with Escherichia coli O157:H7 and Listeria monocytogenes and then irradiated with UV-C light. Radiation dose required for 90% reduction (d _R) values of E. coli O157:H7 and L. monocytogenes were determined to be 0.21 and 2.48 J/m², respectively. Foodborne pathogen populations significantly (p<0.05) decreased with increasing UV-C irradiation. UV-C irradiation at 8,000 J/m² reduced the populations of E. coli O157:H7 and L. monocytogenes on ready-to-eat salad by 2.16 and 2.57 log CFU/g, respectively.     

Inactivation of biofilm cells of foodborne pathogens by steam pasteurization

The objective of this study was to evaluate the effect of steam pasteurization on the inactivation of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes biofilms on stainless steel and polyvinyl chloride (PVC). Biofilms were formed on a stainless steel and PVC coupon by using a mixture of three strains each of three foodborne pathogens. Six-day-old biofilms on stainless steel and PVC coupons were treated with steam at 75 and 85 °C for 5, 10, 20, 30, 40, and 50 s. Biofilm cells of E. coli O157:H7, S. Typhimurium, and L. monocytogenes on stainless steel were reduced by more than 6 log CFU/coupon after exposure to steam at 75 °C for 30, 40, and 30 s, respectively, and at 85 °C for 30, 20, and 20 s, respectively. Steam treatment resulted in less reduction in the levels of biofilm cells on PVC coupons. Biofilm cells of E. coli O157:H7, S. Typhimurium, and L. monocytogenes were reduced by 1.78, 2.04, and 1.29 log CFU/coupon, respectively, after 50 s of exposure to steam at 75 °C. Exposure to steam at 85° for 50 s reduced biofilm cells of E. coli O157:H7, S. Typhimurium, and L. monocytogenes by 2.53, 3.01, and 1.70 log CFU/coupon, respectively. The results of this study suggest that steam pasteurization has potential as a biofilm control method by the food industry.     

Incorporation of Essential Oils and Nanoparticles in Pullulan Films to Control Foodborne Pathogens on Meat and Poultry Products

The incorporation of essential oils and nanotechnology into edible films has the potential to improve the microbiological safety of foods. The aim of this study was to evaluate the effectiveness of pullulan films containing essential oils and nanoparticles against 4 foodborne pathogens. Initial experiments using plate overlay assays demonstrated that 2% oregano essential oil was active against Staphylococcus aureus and Salmonella Typhimurium, whereas Listeria monocytogenes and Escherichia coli O157:H7 were not inhibited. Two percent rosemary essential oil was active against S. aureus, L. monocytogenes, E. coli O157:H7, and S. Typhimurium, when compared with 1%. Zinc oxide nanoparticles at 110 nm were active against S. aureus, L. monocytogenes, E. coli O157:H7, and S. Typhimurium, when compared with 100 or 130 nm. Conversely, 100 nm silver (Ag) nanoparticles were more active against S. aureus than L. monocytogenes. Using the results from these experiments, the compounds exhibiting the greatest activity were incorporated into pullulan films and found to inhibit all or some of the 4 pathogens in plate overlay assays. In challenge studies, pullulan films containing the compounds effectively inhibited the pathogens associated with vacuum packaged meat and poultry products stored at 4 °C for up to 3 wk, as compared to control films. Additionally, the structure and cross‐section of the films were evaluated using electron microscopy. The results from this study demonstrate that edible films made from pullulan and incorporated with essential oils or nanoparticles may improve the safety of refrigerated, fresh or further processed meat and poultry products.     

Reductionin Listeria monocytogenes,Salmonella enterica and Escherichia coli O157:H7 in vitro and on tomato by sophorolipid and sanitiser as affected by temperature and storage time

Increased consumption of produce by consumers has been attributed to perceived health benefits of postharvest produce. Pathogen control is crucial because periodic occurrences and contamination of tomato and leafy greens have exacerbated food safety risks for consumers. We investigated the effects of temperatures (5 and 25 °C), storage time (30 min and 24 h) for inactivation of Listeria monocytogenes, Salmonella enterica and Escherichia coli O157:H7 by sophorolipid (SL‐p) produced fermentatively using palmitic acid as a co‐substrate at different concentrations in vitro. Reduction in pathogenic bacteria on grape tomato by SL‐p, sanitiser (Lovit) and combinations of SL‐p and sanitiser was determined. Temperature and storage time significantly (P < 0.05) affected pathogen inactivations by SL‐p as pathogen reductions were greater at 25 °C and 24 h than at 5 °C and 30 min of storage. L. monocytogenes was the most sensitive to SL‐p treatment as reductions of 5 log relative to untreated controls were attained at 0.12% of SL‐p. Significant reductions in S. enterica (1.91–3.85 logs) and E. coli O157:H7 (0.87–4.09 logs) were recorded at 2–5% of SL‐p. Lower populations of Salmonella and E. coli O157:H7 were inactivated than L. monocytogenes. On grape tomato, pathogen populations inactivated increased at higher SL‐p levels at 25 °C. Sanitiser and sanitiser + SL‐p reduced bacterial populations on tomato by 5.29–5.76 logs and 0.71–3.3.66 logs, respectively. These results imply the interactions of temperature, storage time and SL‐p significantly (P < 0.05) affected pathogen strain reductions. The combination of SL‐p with sanitiser led to synergistic effect on E. coli O157:H7, but not L. monocytogenes and S. enterica.     

Inhibition of biofilm formation,adhesion and invasion in Caco-2 cells by foodborne pathogens using phyto-mediated synthesised silver nanoparticles from industrial wastes

Certain foodborne diseases are associated with antibiotic resistance, a significant problem throughout the world. Silver nanoparticles (AgNPs) using industrial waste from Eucalyptus camaldulensis and sericin, a protein derived from Bombyx mori, were synthesised by a one-step approach. Spherical-shaped nanoparticles with the average size of 17.19 nm exhibited strong antioxidant activity. The minimum bactericidal concentrations against foodborne pathogens including Bacillus cereus, Listeria monocytogenes, Staphylococcus aureus, Escherichia coli O157:H7, Klebsiella pneumoniae, Salmonella Typhimurium, Shigella sonnei, Vibrio cholerae and Vibrio parahaemolyticus were between 2.96 and 11.83 µg/mL. Killing against L. monocytogenes and E. coli O157:H7 was observed within 4 h. Treatment with AgNPs at 0.25 – 0.5 × MIC significantly reduced biofilm production in all isolates (P < 0.05). AgNPs significantly impeded adhesion to and invasion of human epithelial Caco-2 cells by L. monocytogenes and E. coli O157:H7 (P < 0.05). Biocompatibility assessment of AgNPs with Caco-2 and human red blood cells demonstrated no toxic effects.     

Effect of juice processing on cranberry antibacterial properties

The effects of the industrial juice process on the ability of neutralized cranberry samples and extracts (polar, apolar and anthocyanins) to inhibit the growth of Enterococcus faecium resistant to vancomycin (ERV), Escherichia coli O157:H7 EDL 933, E. coli ATCC 25922, Listeria monocytogenes HPB 2812, Pseudomonas aeruginosa ATCC 15442, Salmonella Typhimurium SL1344 and Staphylococcus aureus ATCC 29213 were investigated. The juice process appeared to have a general enhancing effect on the antibacterial properties of cranberry polar and anthocyanin extracts. The lowest minimum inhibitory concentrations (MICs) (1.80–7.0 μg phenol/well) were obtained when S. aureus, S. Typhimurium, and ERV were exposed to the juice concentrate. The growth of P. aeruginosa, L. monocytogenes, E. coli ATCC, and E. coli O157:H7 was not inhibited by the juice concentrate, but did show sensitivity (maximal tolerated concentrations of 0.007–0.4 μg phenol/well). The lowest MICs (22.6–90.5 μg phenol/well) for P. aeruginosa, S. aureus, S. Typhimurium, and ERV were observed when they were exposed to the cranberry anthocyanin extract obtained from cranberry pomace. The results also showed a negative effect of the juice process on the antibacterial properties of the cranberry apolar extracts: the one obtained from frozen cranberries was most efficient against P. aeruginosa, S. aureus, L. monocytogenes and S. Typhimirium (MIC of 45.50 μg phenol/well). The tested bacteria showed the greatest resistance toward the cranberry extracts obtained from the mash and the macerated and depectinized mash.     

Combined Effect of Thermosonication and Slightly Acidic Electrolyzed Water to Reduce Foodborne Pathogens and Spoilage Microorganisms on Fresh‐cut Kale

This study evaluated the efficacy of individual treatments (thermosonication [TS+DW] and slightly acidic electrolyzed water [SAcEW]) and their combination on reducing Escherichia coli O157:H7, Listeria monocytogenes, and spoilage microorganisms (total bacterial counts [TBC], Enterobacteriaceae, Pseudomonas spp., and yeast and mold counts [YMC]) on fresh‐cut kale. For comparison, the antimicrobial efficacies of sodium chlorite (SC; 100 mg/L) and sodium hypochlorite (SH; 100 mg/L) were also evaluated. Each 10 g sample of kale leaves was inoculated to contain approximately 6 log CFU/g of E. coli O157:H7 or L. monocytogenes. Each inoculated or uninoculated samples was then dip treated with deionized water (DW; control), TS+DW, and SAcEW at various treatment conditions (temperature, physicochemical properties, and time) to assess the efficacy of each individual treatment. The efficacy of TS+DW or SAcEW was enhanced at 40 °C for 3 min, with an acoustic energy density of 400 W/L for TS+DW and available chlorine concentration of 5 mg/L for SAcEW. At 40 °C for 3 min, combined treatment of thermosonication 400 W/L and SAcEW 5 mg/L (TS+SAcEW) was more effective in reducing microorganisms compared to the individual treatments (SAcEW, SC, SH, and TS+DW) and combined treatments (TS+SC and TS+SH), which significantly (P < 0.05) reduced E. coli O157:H7, L. monocytogenes, TBC, Enterobacteriaceae, Pseudomonas spp., and YMC by 3.32, 3.11, 3.97, 3.66, 3.62, and >3.24 log CFU/g, respectively. The results suggest that the combined treatment of TS+SAcEW has the potential as a decontamination process in fresh‐cut industry.     

Preparation of red algae film containing grapefruit seed extract and application for the packaging of cheese and bacon

Red algae (RA) film containing grapefruit seed extract (GSE) was used as a wrapping film for cheese and bacon. RA film containing 1% GSE was prepared to inhibit the growth of pathogenic bacteria such as Escherichia coli O157:H7 and Listeria monocytogenes. Wrapping of cheese and bacon with the film decreased the populations of E. coli O157:H7 and L. monocytogenes. After 15 days of storage, wrapping of cheese with the RA film reduced the populations of E. coli O157:H7 and L. monocytogenes by 1.21 and 0.85 log CFU/g, respectively, compared to control. Bacon wrapped with the RA film also decreased the populations of E. coli O157:H7 and L. monocytogenes by 0.45 and 0.76 log CFU/g, respectively. Wrapping of bacon with the RA film decreased peroxide and thiobarbituric acid values. These results suggest that RA film containing GSE is a useful wrapping material for extending the shelf lives of cheese and bacon.     

Switchgrass extractives to mitigate Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium contamination of romaine lettuce at pre- and postharvest

The antimicrobial potential of switchgrass extractives (SE) was evaluated on cut lettuce leaves and romaine lettuce in planta, using rifampicin-resistant Escherichia coli O157:H7 and Salmonella Typhimurium strain LT2 as model pathogens. Cut lettuce leaves were swabbed with E. coli O157:H7 or S. Typhimurium followed by surface treatment with 0.8% SE, 0.6% sodium hypochlorite, or water for 1 to 45 min. For in planta studies, SE was swabbed on demarcated leaf surfaces either prior to or after inoculation of greenhouse-grown lettuce with E. coli O157:H7 or S. Typhimurium; the leaf samples were collected after 0, 24, and 48 h of treatment. Bacteria from inoculated leaves were enumerated on tryptic soy agar plates (and also on MacConkey's and XLT4 agar plates), and the recovered counts were statistically analyzed. Cut lettuce leaves showed E. coli O157:H7 reduction between 3.25 and 6.17 log CFU/leaf, whereas S. Typhimurium reductions were between 2.94 log CFU/leaf and 5.47 log CFU/leaf depending on the SE treatment durations, from initial levels of ∼7 log CFU/leaf. SE treatment of lettuce in planta, before bacterial inoculation, reduced E. coli O157:H7 and S. Typhimurium populations by 1.88 and 2.49 log CFU after 24 h and 3 h, respectively. However, SE treatment after bacterial inoculation of lettuce plants decreased E. coli O157:H7 populations by 3.04 log CFU (after 0 h) with negligible reduction of S. Typhimurium populations. Our findings demonstrate the potential of SE as a plant-based method for decontaminating E. coli O157:H7 on lettuce during pre- and postharvest stages in hurdle approaches.     

Viability of multi-strain mixtures of Listeria monocytogenes, Salmonella typhimurium, or Escherichia coli O157:H7 inoculated into the batter or onto the surface of a soudjouk-style fermented semi-dry sausage

The fate of Listeria monocytogenes, Salmonella typhimurium, or Escherichia coli O157:H7 were separately monitored both in and on soudjouk. Fermentation and drying alone reduced numbers of L. monocytogenes by 0.07 and 0.74 log₁₀ CFU/g for sausages fermented to pH 5.3 and 4.8, respectively, whereas numbers of S. typhimurium and E. coli O157:H7 were reduced by 1.52 and 3.51 log₁₀ CFU/g and 0.03 and 1.11 log₁₀ CFU/g, respectively. When sausages fermented to pH 5.3 or 4.8 were stored at 4, 10, or 21 °C, numbers of L. monocytogenes, S. typhimurium, and E. coli O157:H7 decreased by an additional 0.08–1.80, 0.88–3.74, and 0.68–3.17 log₁₀ CFU/g, respectively, within 30 days. Storage for 90 days of commercially manufactured soudjouk that was sliced and then surface inoculated with L. monocytogenes, S. typhimurium, and E. coli O157:H7 generated average D-values of ca. 10.1, 7.6, and 5.9 days at 4 °C; 6.4, 4.3, and 2.9 days at 10 °C; 1.4, 0.9, and 1.6 days at 21 °C; and 0.9, 1.4, and 0.25 days at 30 °C. Overall, fermentation to pH 4.8 and storage at 21 °C was the most effective treatment for reducing numbers of L. monocytogenes (2.54 log₁₀ CFU/g reduction), S. typhimurium (5.23 log₁₀ CFU/g reduction), and E. coli O157:H7 (3.48 log₁₀ CFU/g reduction). In summary, soudjouk-style sausage does not provide a favorable environment for outgrowth/survival of these three pathogens.     

Predicting process lethality of Escherichia coli O157:H7, Salmonella,and Listeria monocytogenes in ground,formulated, and formed beef/turkey links cooked in an air impingement oven

The pathogen thermal lethality in ground and formulated beef/turkey was evaluated for a cocktail of E. coli O157:H7, Salmonella, and Listeria monocytogenes, respectively. At a temperature range of 55–70°C, the heat resistance of L. monocytogenes was not significantly (at α=0.05) different from those of Salmonella. The heat resistance of L. monocytogenes at 55–70°C was 45–81% higher than that of E. coli O157:H7. In this study, a practical approach was developed to predict log₁₀(CFU/g) reduction of E. coli O157:H7, Salmonella, or L. monocytogenes in ground, formulated, and formed beef/turkey links that were cooked in an air impingement oven. The predictions of pathogen thermal kills in the links were verified via the inoculation studies for at least a 7 log₁₀(CFU/g) reduction of E. coli O157:H7, Salmonella, and L. monocytogenes.     

Combined treatment of fumaric acid with aqueous chlorine dioxide or UV-C irradiation to inactivate Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes inoculated on alfalfa and clover sprouts

Effect of fumaric acid, chlorine dioxide (ClO₂), and UV-C treatment was examined on the inactivation of microorganisms in alfalfa and clover sprouts. Clover sprouts were irradiated with UV-C light (1–10 kJ/m²), and the treatment decreased the population of total aerobic bacteria by 1.03–1.45 log CFU/g. Clover sprouts inoculated with pathogenic bacteria were treated with various concentration of fumaric acid, and 0.5 g/100 ml fumaric acid treatment was the most effective. In addition, the combined treatment of fumaric acid (0.5 g/100 ml)/UV-C (1 kJ/m²) reduced the populations of Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes inoculated on clover sprouts by 3.02, 2.88, and 2.35 log CFU/g. Alfalfa sprouts were treated with ClO₂, fumaric acid, and the combination of fumaric acid/ClO₂. The combined treatment was the most effective, and it reduced the total aerobic bacteria by 3.18 log CFU/g as well as the initial populations of E. coli O157:H7, S. typhimurium, and L. monocytogenes inoculated on alfalfa sprouts by 4.06, 3.57, and 3.69 log CFU/g. These results suggest that the combined treatment of fumaric acid with UV-C or ClO₂ can be useful for improving the microbial safety of alfalfa and clover sprouts.     

Inhibitory effects of UV treatment and a combination of UV and dry heat against pathogens on stainless steel and polypropylene surfaces

Abstract: Pathogens that contaminate the surfaces of food utensils may contribute to the occurrence of foodborne disease outbreaks. We investigated the efficacy of UV treatment combined with dry heat (50 °C) for inhibiting 5 foodborne pathogens (Escherichia coli O157:H7, Salmonella Typhimurium, Pseudomonas aeruginosa, Listeria monocytogenes, and Staphylococcus aureus) on stainless steel and polypropylene surfaces in this study. We inoculated substrates with each of the 5 foodborne pathogens cultured on agar surface and then UV treatment alone or a combination of both UV and dry heat (50 °C) was applied for 30 min, 1 h, 2 h, and 3 h. The initial populations of the 5 pathogens before treatment were 8.02 to 9.18 and 8.73 to 9.16 log₁₀ CFU/coupon on the surfaces of stainless steel and polypropylene coupons, respectively. UV treatments for 3 h significantly inhibited S. Typhimurium, L. monocytogenes, and S. aureus on the stainless steel by 3.06, 2.18, and 2.70 log₁₀ CFU/coupon, and S. aureus on the polypropylene by 3.11 log₁₀ CFU/coupon, respectively. The inhibitory effects of the combined UV and dry heat treatment (50 °C) increased as treatment time increased, yielding significant reductions in all samples treated for 3 h, with the exception of S. aureus on polypropylene. The reduction level of E. coli O157:H7 treated for 3 h on the surface of stainless steel and polypropylene treated was approximately 6.00 log₁₀ CFU/coupon. These results indicate that combined UV and dry heat (50 °C) treatments may be effective for controlling microbial contamination on utensils and cooking equipment surfaces as well as in other related environments.