Antibacterial and antibiofilm performance of low-frequency ultrasound against Escherichia coli O157:H7 and its application in fresh produce.

Ultrasound technology has been focused on due to its unique advantages in biofilm removal compared with traditional antibacterial methods. Herein, the anti-biofilm properties of low-frequency ultrasound (LFUS) were studied against Enterohemorrhagic Escherichia coli O157: H7 (E. coli O157:H7). After ultrasonication (20 kHz, 300 W) for 5 min, the removal rate of biofilm from polystyrene sheets reached up to 99.999 %. However, the bacterial cells could not be inactivated completely even extending the duration of ultrasonic irradiation to 30 min. Fortunately, this study indicated that LFUS could efficiently weaken the metabolic capacity and biofilm-forming ability of bacterial cells separated from biofilm. It could be associated with the removal of cell surface appendages and damage to cell membrane induced by mechanical vibration and acoustic cavitation. Besides, the genetic analysis proved that the transcription level of genes involved in curli formation was significantly down-regulated during ultrasonic irradiation, thus impeding the process of irreversible adhesion and cells aggregation. Finally, the actual application effect of LFUS was also evaluated in different fresh produces model. The results of this study would provide a theoretical basis for the further application of ultrasound in the food preservation.

Inactivation of Escherichia coli O157: H7 in foods by emerging technologies: a review.

Escherichia coli O157: H7 is a representative foodborne pathogen that causes haemorrhagic colitis, bloody diarrhea, and fatal haemolytic uraemic syndrome. Previously, only conventional heat treatment was used to pasteurised food; however, this method decreases food quality, including colour change, denatures proteins, and causes lipid oxidation. Therefore, emerging technologies to inactivate pathogens in food that affect food quality minimally have been researched and developed. This review aims to compile research since 2018 and briefly describe the inactivation mechanisms of emerging technologies such as microwave, radio frequency, ohmic heating, superheated steam, ionising radiation (gamma irradiation, electron beam, and X-rays), high pressure, ultraviolet light, pulsed light, ultrasound, gas treatment, plasma, and combination treatments. Pulsed electric field and electrolysed water were excluded because few research papers were published after 2018. In addition, the shortcomings of emerging technologies in the control of E. coli O157: H7 and the directions for emerging technology research are presented. Taking advantage of emerging technologies with many benefits will significantly improve food safety.

Inactivation of Foodborne Pathogens on Inshell Walnuts by UV-C Radiation.

ABSTRACT: Inshell walnuts can be contaminated with pathogens through direct contact or cross-contamination during harvesting and postharvest hulling, drying, or storage. This study aimed to assess the efficacy of UV-C radiation in inactivating foodborne pathogens on inshell walnut surfaces. Intact inshell walnut surfaces were inoculated separately with Salmonella,Escherichia coli O157:H7, Listeria monocytogenes, and Staphylococcus aureus and then were subjected to UV-C radiation at doses of 29.4, 147.0, 294.0, 588.0, and 882.0 mJ/cm2. UV-C radiation inactivated the inoculated pathogens in a dose-dependent manner, and a tailing effect was observed for the inactivation of pathogens. UV-C radiation at 29.4 and 882.0 mJ/cm2 reduced the populations of Salmonella Enteritidis PT 30, Salmonella Typhimurium, E. coli O157:H7, L. monocytogenes, and S. aureus on inshell walnut surfaces by 0.82 to 1.25 and 1.76 to 2.41 log CFU per walnut, respectively. Scanning electron photomicrographs showed pathogenic bacterial cells in the cracks and crevices of the inshell walnut surface, and the shielding of microorganisms by the cracks and crevices may have contributed to the tailing effect observed during UV-C inactivation. No significant changes (P > 0.05) were found in walnut lipid oxidation following UV-C radiation at doses up to 882.0 mJ/cm2. Together, the results indicate that UV-C radiation could be a potential technology for reducing the populations of various foodborne pathogens on inshell walnut surfaces while maintaining the quality of walnuts.

Growth temperature influences the resistance of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium on lettuce to X-ray irradiation.

This study aimed to investigate the effect of different growth temperatures on the resistance of Escherichia coli O157:H7 and Salmonella Typhimurium to low-energy X-ray irradiation. Irradiation of contaminated phosphate-buffered saline with 0.6 kGy X-ray decreased the counts of E. coli O157:H7 cultured at 37 °C to below the detection limit (<1.0 colony-forming unit (CFU)/mL) and those of E. coli O157:H7 cultured at 25 and 15 °C by 4.82 and 4.45 log CFU/mL, respectively. The viable counts of S. Typhimurium cultured at 37, 25, and 15 °C in phosphate-buffered saline decreased by 3.56, 3.08, and 2.75 log CFU/mL, respectively, after irradiation with 0.6 kGy X-ray. Irradiation of contaminated lettuce with 0.4 kGy decreased the counts of E. coli O157:H7 cultured at 37, 25, and 15 °C by 3.97, 3.45, and 3.10 log CFU/cm2, respectively, and those of S. Typhimurium by 4.41, 3.84, and 3.40 log CFU/cm2, respectively. Growth temperature influenced pathogen resistance to X-ray irradiation by modulating cellular membrane and DNA integrity, intracellular enzyme activity, and efflux pump function. The results of this study suggest that the stress resistance status of pathogenic bacteria cultured at different growth temperatures should be considered for the application of X-ray irradiation for fresh produce sterilization.

Antibacterial Activity of Caffeic Acid Combined with UV-A Light against Escherichia coli O157:H7, Salmonella enterica Serovar Typhimurium, and Listeria monocytogenes.

The aim of this study was to evaluate the antibacterial activity of caffeic acid (CA), which is a natural polyphenol, combined with UV-A light against the representative foodborne bacteria Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes. Data regarding the inactivation of these bacteria and its dependence on CA concentration, light wavelength, and light dose were obtained. E. coli O157:H7 and Salmonella Typhimurium were reduced to the detection limit when treated with 3 mM CA and UV-A for 3 J/cm2 and 4 J/cm2, respectively, and 5 J/cm2 treatment induced 3.10 log reduction in L. monocytogenes. To investigate the mechanism for inactivation of Salmonella Typhimurium and L. monocytogenes, measurement of polyphenol uptake, membrane damage assessment, enzymatic activity assay, and transmission electron microscopy (TEM) were conducted. It was revealed that CA was significantly (P < 0.05) absorbed by bacterial cells, and UV-A light allowed a higher uptake of CA for both pathogens. Additionally, CA plus UV-A treatment induced significant (P < 0.05) cell membrane damage. In the enzymatic activity assay, the activities of both pathogens were reduced by CA, and a greater reduction occurred by use of CA plus UV-A. Moreover, transmission electron microscopy (TEM) images indicated that CA plus UV-A treatment notably destroyed the intercellular structure. In addition, antibacterial activity was also observed in commercial apple juice, which showed results similar to those obtained from phosphate-buffered saline (PBS), resulting in a significant (P < 0.05) reduction for all three pathogens without any changes in color parameters (L*, a*, and b*), total phenolic compounds, and DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging activity. IMPORTANCE Photodynamic inactivation (PDI), which involves photoactivation of a photosensitizer (PS), is an emerging field of study, as it effectively reduces various kinds of microorganisms. Although there are several PSs that have been used for PDI, there is a need to find naturally occurring PSs for safer application in the food industry. Caffeic acid, a natural polyphenol found in most fruits and vegetables, has recently been studied for its potential to act as a novel photosensitizer. However, no studies have been conducted regarding its antibacterial activity depending on treatment conditions and its antibacterial mechanism. In this study, we closely examined the effectiveness of caffeic acid in combination with UV-A light for inactivating representative foodborne bacteria in liquid medium. Therefore, the results of this research are expected to be utilized as basic data for future application of caffeic acid in PDI, especially when controlling pathogens in liquid food processing.

The effect of different ultraviolet-C light doses on microbial reduction and the components of camel milk.

As a result of increasing interest in non-thermal technologies as a possible alternative or complementary to milk pasteurization processing, the objectives of this study were to determine the effects of different ultraviolet-C light doses on the viability of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium and chemical changes to camel milk components. Pasteurized and inoculated camel milk samples were ultraviolet-C treated in a continuous flow system. The viability of E. coli O157:H7 and S. Typhimurium was evaluated with both in vivo imaging system and traditional plate count agar method. Samples subjected to the 4.15, 8.30, and 12.45 mJ/cm2 of ultraviolet-C treatment resulted in 1.9, 3.3, and 3.9-log reductions in E. coli O157:H7 and 0.9, 3, and 3.9-log reductions in S. Typhimurium, respectively. The measurement of secondary lipid peroxidation products (or ThioBarbituric Acid Reactive Substance values) showed no significant (P > 0.05) differences between the raw and ultraviolet-C treated milk samples. Additionally, no changes (P > 0.05) in the protein profiles of αs1-casein, α-lactalbumin, and lactoferrin were observed between both samples. Compared to the untreated raw milk, c9t11 conjugated linoleic acid decreased (P < 0.01) while t10c12 conjugated linoleic acid increased (P < 0.01) in the ultraviolet-C treated milk. Furthermore, three new volatile compounds were identified in the ultraviolet-C treated milk compared to the control. In conclusion, milk treated with the ultraviolet-C light at a dose of 12.45 mJ/cm2 did not meet the Food and Drug Administration (FDA) requirements for the 5-log pathogen reduction. The ultraviolet-C treatment, on the other hand, had minimal effects on camel milk components.

Development and evaluation of a point-of-use UV appliance for fresh produce decontamination.

In-house treatment strategy for fresh produce decontamination has not been emphasized as much as industrial washing. The most common treatment for fresh produce decontamination and cleaning at home and other point-of-use places such as cafeteria is rinsing and/or soaking in a sink. In this study, an appliance utilizing UV and agitated water to decontaminate fresh produce was developed and its effectiveness was investigated in an aim to identify optimum processing parameters. Grape tomato and spinach representing two different surface smoothness were dip-inoculated in a four-strain Salmonella cocktail to reach a final population of 5-8 log CFU/g and air-dried. The produce samples were then washed in 1 gallon tap water under varying conditions, water agitation speed (0-190 RPM), sample size (50-400 g), UV intensity (0-30 mW/cm2) and treatment time (2, 5 and 10 min). In general, increasing the agitation speed and UV intensity enhanced Salmonella inactivation for both grape tomato and spinach. Sample size significantly affected the UV inactivation of Salmonella on grape tomato, but not on spinach. The effect of extending treatment time from 2 to 10 min was insignificant for almost all the UV treatments and the controls. The effect of UV intensity and treatment time on inactivation of Salmonella on spot-inoculated grape tomato and spinach was also determined. The most severe treatment used in this study, 30 mW/cm2 UV for 10 min, resulted in >4 log reductions of Salmonella dip- or spot-inoculated on grape tomato (200 g sample size and 190 RPM agitation speed) and 3.5 log reductions of Salmonella dip- or spot-inoculated on spinach (100 g sample size and 110 RPM agitation speed). We foresee that the UV appliance developed and evaluated in this study could be further fine-tuned and optimized to eventually construct a point-of-use UV appliance that can be used at home, cafeteria, restaurants, and hospitals for fresh produce decontamination and cleaning. The UV appliance could be an inexpensive and effective tool to improve fresh produce safety.

Ultrasound improves the decontamination effect of thyme essential oil nanoemulsions against Escherichia coli O157: H7 on cherry tomatoes.

Development of novel and effective decontamination technologies to ensure the microbiological safety of fresh produce has gained considerable attention, mainly driven by numerous outbreaks. This work presented the first approach regarding to the application of the previously reported hurdle technologies on the sanitization of artificially contaminated cherry tomatoes. Thyme (Thymus daenensis) essential oil nanoemulsion (TEON, 8.28 nm in diameter with a narrow size distribution) was formulated via ultrasonic nanoemulsification, showing remarkably improved antimicrobial activity against Escherichia coli (E. coli) O157:H7, compared to the coarse emulsion. The antimicrobial effect of ultrasound (US), thyme essential oil nanoemulsion (TEON) and the combination of both treatments was assessed against E. coli O157:H7. The remarkable synergistic effects of the combined treatments were achieved, which decontaminated the E. coli populations by 4.49-6.72 log CFU/g on the surface of cherry tomatoes, and led to a reduction of 4.48-6.94 log CFU/sample of the total inactivation. TEON combined with US were effective in reducing the presence of bacteria in wastewater, which averted the potential detrimental effect of cross-contamination resulted from washing wastewater in fresh produce industry. Moreover, the treatments did not noticeably alter the surface color and firmness of cherry tomatoes. Therefore, ultrasound combined with TEON is a promising and feasible alternative for the reduction of microbiological contaminants, as well as retaining the quality characteristics of cherry tomatoes.

Screening of antimicrobial synergism between phenolic acids derivatives and UV-A light radiation.

The objective of this study was to investigate synergistic antibacterial activity based on a combination of UV-A light and three classes of food grade compounds: benzoic acid derivatives, cinnamic acid derivatives, and gallates. By using Escherichia coli O157:H7 as the model strain, it was observed that three cinnamic acid derivatives (ferulic acid, coumaric acid, and caffeic acid) and one benzoic acid derivative (2,5-dihydroxybenzoic acid) presented strong synergistic antibacterial activity with UV-A light radiation, where 1 mM levels of these compounds plus with 15 min of UV-A light (total light dose of 6.1 cm-2) led to more than 7-log CFU mL-1 of bacterial inactivation. In contrast, synergistic antibacterial activity between UV-A light and most benzoic acid derivatives (benzoic acid, gallic acid, vanillic acid, and 2,5-dimethoxybenzoic acid) were only observed after higher concentrations of these compounds were applied (10 mM). Lastly, from the three gallates tested (methyl gallate, ethyl gallate, and propyl gallate), only propyl gallate showed strong antibacterial synergism with UV-A light, where 10 mM of propyl gallate plus 15 min of UV-A light led to approximately 6.5-log of bacterial reduction. Presence of antioxidant compounds mitigated the light-mediated antibacterial activity of gallic acid, 2,5-dihydroxybenzoic acid, and propyl gallate. Similarly, the light-mediated antibacterial activity of these compounds was significantly (P < 0.05) reduced against metabolic-inhibited bacterial cells (sodium azide pretreatment). On the other hand, the antibacterial synergism between ferulic acid and UV-A light was not affected by the presence of antioxidants or the metabolic state of the bacterial cells. Due to the increasing concerns of antimicrobial resistant (AMR) pathogens, the study also investigated the proposed synergistic treatment on AMR Salmonella. Combinations of 1 mM of ferulic acid or 1 mM of 2,5-dihydroxybenzoic acid with UV-A light radiation was able to inactivate more than 6-log of a multi-drug resistant Salmonella Typhimurium strain.

Bactericidal and synergistic effects of X-ray irradiation and gallic acid against foodborne pathogens on lettuce.

The objectives of this study were to evaluate the bactericidal effects of X-ray irradiation and gallic acid (GA) against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on lettuce leaves and in phosphate-buffered saline (PBS). Inoculated PBS and lettuce were exposed to X-rays (0.05, 0.1, and 0.15; 0.1, 0.2, and 0.3 kGy, respectively), and GA was applied to lettuce leaves as a solution and in PBS at concentrations of 0.5% (w/v). Combined treatment with 0.3 kGy and 0.5% GA reduced E. coli O157:H7, S. Typhimurium, and L. monocytogenes cell counts 5.41, 2.57, and 1.36 log CFU/cm2 on lettuce, respectively. Combined treatment with 0.15 kGy X-ray and 0.5% GA reduced counts for the same species by 6.54, 4.24, and 1.51 log CFU/mL in PBS. The combined treatments exerted a synergistic antibacterial effect against E. coli O157:H7 on lettuce, but not against S. Typhimurium or L. monocytogenes. In PBS, the synergistic effect was confirmed in both E. coli O157:H7 and S. Typhimurium cells. Mechanistic investigations indicated that the synergistic antibacterial effect was associated with intracellular reactive oxygen species (ROS) generation and bacterial cell membrane damage. Additionally, the X-ray and GA combination treatment did not adversely affect the color, total phenol content, and texture of lettuce. These findings demonstrate that treatment with X-ray radiation and GA can enhance the microbiological safety of fresh produce.

Synergistic bactericidal effect and mechanism of X-ray irradiation and citric acid combination against food-borne pathogens on spinach leaves.

In this study, we investigated the antimicrobial activity of the X-ray irradiation and citric acid (CA) combination against Escherichia coli O157:H7 and Listeria monocytogenes on the surface of spinach leaves and elucidated the mechanisms underlying their synergistic interaction. Upon treatment with 0.3 kGy X-ray irradiation and 1% CA combination, the cell counts of E. coli O157:H7 and L. monocytogenes reduced by 4.23 and 3.69 log CFU/mL on spinach leaves, respectively. The synergistic reduction in the cell counts of E. coli O157:H7 and L. monocytogenes by the combination treatment was 0.95 and 1.14 log units, respectively. The X-ray and CA combination exerts its antimicrobial effect by damaging the bacterial cell membrane and enhancing the generation of intracellular reactive oxygen species in the pathogens. The enhanced bactericidal effect of the combination treatment may not be due to the loss of intracellular enzyme activity. We also evaluated the effect of the combination treatment on the quality attributes of spinach leaves. The combination treatment did not result in adverse changes in color and texture of spinach leaves. These results demonstrate the potential of citric acid and X-ray irradiation combination for decontaminating foodborne pathogens on fresh produce.

Decontamination of dried whole black peppercorns using ultraviolet-c irradiation.

This study determined the efficacy of UV-C as a decontamination process against some foodborne bacteria in dried whole black peppercorns. Artificially-inoculated Salmonella enterica, Escherichia coli O157:H7, Listeria monocytogenes, Pseudomonas aeruginosa, and Staphylococcus aureus were subjected to UV-C with a surface irradiance of 0.43 mW/cm2 and were all found to exhibit a biphasic inactivation pattern with fast log-linear inactivation followed by a tail. Total log reductions (TLR) ranged from 1.92 (S. aureus) to 3.60 log CFU/g (E. coli O157:H7). Increasing the lamp number from 1 to 5 also linearly (R2 = 0.98) increased the surface irradiance from 0.43 to 1.70 and the TLR of the most resistant S. aureus from 1.92 to 2.62 log CFU/g. Quality evaluation showed very small, variable changes in color coordinates, which were not detected by a same/different test involving a 50-member sensory evaluation panel. Mercury deposition was not detected after a maximum exposure time of 90 min to 0.43 and 1.70 mW/cm2. Finally small, non-significant changes in the innate bacterial microflora of the black peppercorns were determined after 90 min-treatment using 1 lamp and 5 lamps, emphasizing the limitation of utility of UV-C as additional decontamination process for post-process-introduced microorganisms. Good Manufacturing Practices throughout the dried black peppercorn manufacturing process were recommended.

Microwave pasteurization of apple juice: Modeling the inactivation of Escherichia coli O157:H7 and Salmonella Typhimurium at 80-90 °C.

Although due to their acidity some fruit juices are considered safe, several outbreaks have been reported. For processing fruit juices, microwave heating offers advantages such as shorter come-up time, faster and uniform heating, and energy efficiency. Thus, it could be a beneficial alternative to conventional pasteurization. The objective of this study was to study the inactivation kinetics of Escherichia coli O157:H7 and Salmonella Typhimurium under microwave pasteurization at temperatures between 80 and 90 °C, i.e., at conditions that are employed in conventional pasteurization. Inoculated juices were treated at different power levels (600 W, 720 W) and treatment times (5s, 10s, 15s, 20s, 25s). Time-temperature profiles were obtained by fiber-optic sensors in contact with the samples allowing continuous data collection. The log-logistic and Arrhenius equations were used to account for the influence of the temperature history; thus, resulting in two different modeling approaches that were compared in terms of their prediction abilities. Survival kinetics including non-isothermal conditions were described by a non-linear ordinary differential equation that was numerically solved by the Runge-Kutta method (ode45 in MATLAB ®). The lsqcurvefit function (MATLAB®) was employed to estimate the corresponding survival parameters, which were obtained from freshly made apple juice, whereas the prediction ability of these parameters was evaluated on commercial apple juices. Results indicated that inactivation increased with power level, temperature, and treatment time reaching a microbial reduction up to 7 Log10 cycles. The study is relevant to the food industry because it provides a quantitative tool to predict survival characteristics of pathogens at other non-isothermal processing conditions.

Inactivating foodborne pathogens in apple juice by combined treatment with fumaric acid and ultraviolet-A light, and mechanisms of their synergistic bactericidal action.

We evaluated the bactericidal efficacy of the simultaneous application of ultraviolet-A (UV-A) irradiation and fumaric acid (FA) against Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes in apple juice and as well as investigated the effects of this treatment on product quality. Further, we elucidated the mechanisms underlying their synergistic bactericidal action. Simultaneous UV-A light irradiation and 0.1% FA treatment for 30 min resulted in 6.65-, 6.27-, and 6.49-log CFU/ml reductions in E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively, which involved 3.15, 2.21, and 3.43 log CFU reductions, respectively, and these were attributed to the synergistic action of the combined treatments. Mechanistic investigations suggested that the combined UVA-FA treatment resulted in significantly greater bacterial cell membrane damage and intracellular reactive oxygen species (ROS) generation. UVA-FA treatment for 30 min did not cause significant changes to the color, nonenzymatic browning index, pH, and total phenolic content of apple juice. These results suggest that combined UVA-FA treatment can be effectively used to control foodborne pathogens in apple juice without affecting its quality.

Simultaneous Effects of UV-A and UV-B Irradiation on the Survival of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in Buffer Solution and Apple Juice.

The objective of this study was to evaluate the efficacy of simultaneous UV-A and UV-B irradiation (UV-A+B) for inactivating Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in both phosphate-buffered saline (PBS) and apple juice. A cocktail of the three pathogens was inoculated into PBS and apple juice, and then the suspensions were irradiated with UV lamps of 356 nm (UV-A) and 307 nm (UV-B). Significant (P < 0.05) log reductions of the three pathogens in PBS and apple juice were observed after a maximum dose of UV-B alone or the UV-A+B treatment, but few reductions were observed upon UV-A treatment alone. At all irradiation times, antagonistic effects were observed for the application of UV-A+B against in E. coli O157:H7, Salmonella Typhimurium, and L. monocytogenes in PBS and apple juice. The degree of antagonistic effect in apple juice was greater than that in PBS. The results of this study suggest that the combined treatment of commercial UV-A and UV-B lamps would be impractical for disinfecting juice products.

Evaluating a Combined Method of UV and Washing for Sanitizing Blueberries, Tomatoes, Strawberries, Baby Spinach, and Lettuce.

We assessed a fresh produce decontamination system using a combined method of UV and washing (water-assisted UV [WUV]) in different scales. The system used tap water to wash fresh produce while exposing it to UV light. First, the reduction of Salmonella in tap water under UV treatment (1 to 1,740 mJ/cm2) was determined. Increasing the UV dose significantly (P < 0.05) increased the Salmonella reduction in wash water, and UV intensity of more than 2 mW/cm2 could reduce Salmonella in tap water to below 1 CFU/mL given enough processing time (more than 1 min; UV dose of 120 mJ/cm2). Then, the decontamination effectiveness of a small WUV system was tested on blueberries (50 g). Blueberries were spot or dip inoculated with a Salmonella cocktail and treated by the small WUV system (200 mL of water). In general, WUV treatments achieved significantly better Salmonella inactivation than tap water wash; tap water wash (10 min) and 2 mW/cm2 WUV treatment (with a UV dose of 1,200 mJ/cm2) reduced populations of spot-inoculated Salmonella on blueberries by 2.44 and 5.45 log, respectively. Compared with spot-inoculated Salmonella on blueberries, dip-inoculated Salmonella was more difficult to be inactivated by WUV treatments. Then, the decontamination effectiveness of WUV treatments was tested on blueberries (170 g), tomatoes (290 g), strawberries (170 g), baby spinach (60 g), and lettuce (60 g) using a larger WUV system. In general, 10 min of 29 mW/cm2 WUV treatment (a high UV dose of 17,400 mJ/cm2) resulted in significantly better Salmonella inactivation than tap water wash (for 10 min) regardless the inoculation method, agreeing with the results of the small-scale study. For both spot- and dip-inoculated lettuce, no significant difference (P > 0.05) in Salmonella inactivation by WUV treatments was observed when the quantity of lettuce increased from 50 to 100 g.

Ultrasound treatment combined with fumaric acid for inactivating food-borne pathogens in apple juice and its mechanisms.

The purpose of this study was to evaluate the synergistic bactericidal efficacy of combining ultrasound (US) and fumaric acid (FA) treatment against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in apple juice and to identify the synergistic bactericidal mechanisms. Additionally, the effect of combination treatment on juice quality was determined by measuring the changes in color, pH, non-enzymatic browning index, and total phenolic content. A mixed cocktail of the three pathogens was inoculated into apple juice, followed by treatment with US (40 kHz) alone, FA (0.05, 0.1, and 0.15%) alone, and a combination of US and FA for 1, 2, 3, 4, and 5 min. Combined US and 0.15% FA treatment for 5 min achieved 5.67, 6.35, and 3.47 log reductions in E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively, with the 1.55, 2.37, and 0.57 log CFU reductions attributed to the synergistic effect. Although the pH value slightly decreased as FA increased, there were no significant (P > 0.05) differences in color values, browning indices, and phenolic content between untreated and treated samples. To identify the mechanism of this synergistic bactericidal action, membrane integrity, malfunctions in the membrane efflux pump, and intracellular enzyme activity were measured. The analyses confirmed that damage to the cell envelope (membrane integrity and efflux pump) was strongly related to the synergistic microbial inactivation. These results suggest that simultaneous application of US treatment and FA is a novel method for ensuring the microbial safety of apple juice.

Inactivation of Staphylococcus aureus and Escherichia coli O157:H7 on fresh kashar cheese with pulsed ultraviolet light.

Pulsed ultraviolet light is a potential postprocessing decontamination method which is able to reduce pathogens on solid food surfaces. Cheese surfaces may become easily contaminated with pathogens due to improper handling or contact with unhygienic surfaces during or after processing. In this study, the effects of pulsed ultraviolet light on Staphylococcus aureus and Escherichia coli O157:H7 on fresh kashar cheese were investigated. Pulsed ultraviolet light was applied to kashar cheese for different times (5, 15, 30, 45, 60 s) at 5, 8, and 13 cm from the quartz window in a pulsed ultraviolet light system. Based on the inactivation level, time, and visual evaluation, the most favorable treatment was determined as the 45 s-13 cm treatment (∼44 J/cm2). This treatment yielded about 1.62 and 3.02 log10 reductions (cfu/cm2) for S. aureus and E. coli O157:H7, respectively, while did not alter (p>0.05) the pH, lipid oxidation, and moisture content of kashar cheese, except the color parameters. When 0.5 cm thick kashar cheese was treated with pulsed ultraviolet light at a distance of 5 cm from the quartz window, the highest energy transmittance was found to be about 9.16%. These findings demonstrate that pulsed ultraviolet light has the potential for postprocessing decontamination of semi-hard cheese surfaces.

Decontamination Effect of the Spindle and 222-Nanometer Krypton-Chlorine Excimer Lamp Combination against Pathogens on Apples (Malus domestica Borkh.) and Bell Peppers (Capsicum annuum L.).

In this study, we developed a washing system capable of decontaminating fresh produce by combining the Spindle apparatus, which detaches microorganisms on sample surfaces, and a 222-nm krypton-chlorine excimer lamp (KrCl excilamp) (Sp-Ex) and investigated their decontamination effect against Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes on apple (Malus domestica Borkh.) and bell pepper (Capsicum annuum L.) surfaces. Initial levels of the three pathogens were approximately 108 CFU/sample. Both E. coli O157:H7 and S. Typhimurium were reduced to below the detection limit (2.0 log CFU/sample) after 5 and 7 min of treatment on apple and bell pepper surfaces, respectively. The amounts of L. monocytogenes on apple and bell pepper surfaces were reduced by 4.26 and 5.48 logs, respectively, after 7 min of treatment. The decontamination effect of the Sp-Ex was influenced by the hydrophobicity of the sample surface as well as the microbial cell surface, and the decontamination effect decreased as the two hydrophobicity values increased. To improve the decontamination effect of the Sp-Ex, Tween 20, a surfactant that weakens the hydrophobic interaction between the sample surface and pathogenic bacteria, was incorporated into Sp-Ex processing. It was found that its decontamination effect was significantly (P < 0.05) increased by the addition of 0.1% Tween 20. Sp-Ex did not cause significant quality changes in apple or bell pepper surfaces during 7 days storage following treatment (P > 0.05). Our results suggest that Sp-Ex could be applied as a system to control pathogens in place of chemical sanitizer washing by the fresh-produce industry.IMPORTANCE Although most fresh-produce processing currently controls pathogens by means of washing with sanitizers, there are still problems such as the generation of harmful substances and changes in product quality. A combination system composed of the Spindle and a 222-nm KrCl excilamp (Sp-Ex) developed in this study reduced pathogens on apple and bell pepper surfaces using sanitizer-free water without altering produce color and texture. This study demonstrates the potential of the Sp-Ex to replace conventional washing with sanitizers, and it can be used as baseline data for practical application by industry. In addition, implementation of the Sp-Ex developed in this study is expected not only to meet consumer preference for fresh, minimally processed produce but also to reduce human exposure to harmful chemicals while being beneficial to the environment.

Effects of pulsed light and sanitizer wash combination on inactivation of Escherichia coli O157:H7, microbial loads and apparent quality of spinach leaves.

The purpose of this study was to investigate the efficacy of pulsed light (PL), a new formula of sanitizer (HEN) consisting of hydrogen peroxide, EDTA and Nisin, as well as synergy of PL and HEN sanitizer (PL-HEN) wash in inactivating E. coli O157:H7 on spinach. The treatment effect on microbial loads and apparent quality during 13 days storage at 4 °C was also determined. A bacterial cocktail containing three strains of E. coli O157:H7 was used as inoculum based on their association with produce-related outbreaks. Spinach leaves were spot inoculated on surface before treating with PL (1-63J/cm2), HEN sanitizer wash (2 min) or their combinations. PL inactivation was influenced significantly at low doses. Treatment dose of 15.75 J/cm2, equivalent to 15 s intense PL treatment, was found optimal above which adverse quality effect was evident. The optimal PL dose resulted 2.7 log CFU/g reduction of E. coli O157:H7 while a rapid 2 min wash in sanitizer formulation HEN, provided comparatively low, 1.8 log CFU/g, reduction of the pathogen. Two different sequences of PL and HEN treatment combinations were tested. In PL-HEN treatment, inoculated leaves were first treated at optimal PL dose (15.75 J/cm2) followed by 2 min immersion in HEN whereas in HEN-PL treatment, leaves were first washed in HEN before PL exposure. HEN-PL treatment indicated a compound inactivation activity (4.6 logs reduction) while PL-HEN treatment indicated a strong synergistic inactivation as E. coli cells were not detectable after treatment indicating >5 log reduction. The PL-HEN treatment not only significantly reduced spoilage microbial populations on spinach but also slowed their growth during storage. Furthermore, the visual and firmness quality of spinach were not significantly affected by the PL-HEN treatment. Overall, our results demonstrate that integrated PL-HEN technology can be used to enhance microbial safety of spinach.