•460 nm LEDs acted against Salmonella spp. on fresh-cut pineapple slices.•This effect was bactericidal at 7 and 16 °C but growth inhibitory at 25 °C.•An adapted Weibull model best described the antibacterial kinetics.•Temperature influenced the antibacterial effect, but irradiance level did not.Blue light emitting diodes (LEDs) have emerged as an intervention against Salmonella, which colonizes and grows on fresh-cut fruits. This study evaluated their efficacy on fresh-cut pineapples. Pineapple slices were surface-inoculated with a Salmonella cocktail and illuminated with 460 nm LEDs at different irradiances (92, 147.7 and 254.7 mW/cm2) and temperatures (7, 16 and 25 °C). The resulting differences in the populations of control and illuminated samples were modeled to determine the antibacterial effect. The color of the slices was also measured. Bactericidal action was observed at 7 and 16 °C and growth inhibition at 25 °C. An adapted Weibull model best described the inactivation, with the D values ranging from 15 to 27 kJ/cm2. Temperature influenced the antibacterial effect but the irradiance had no significant effect (P ≥ 0.05). Though the illuminated pineapple slices tended to be bleached, this study demonstrated the potential of 460 nm LEDs against Salmonella on fresh-cut pineapple slices.

•405 nm LED was much more effective in inactivating bacteria compared to 520 nm LED.•Hom model proved most apt in describing the photodynamic inactivation curves.•Bacterial inactivation by LED varied with treatment temperatures and their Gram nature.•Gram-positives were more susceptible to LED treatment compared to Gram-negatives.•Coproporphyrin content was higher in Gram-positives compared to Gram-negatives.Photodynamic inactivation studies of microbial pathogens have focused on the use of an external photosensitizer or a precursor compound to eliminate bacteria. The present study investigated the inactivation kinetics of six bacterial pathogens by a 405 nm light emitting diode (LED) without the addition of any external compound. The role of endogenous coproporphyrin on the bacterial susceptibility to LEDs was also examined. Pathogens were illuminated with LEDs at 25, 10 and 4 °C for 9 h and the inactivation curves were modeled using six different equations. Endogenous coproporphyrin was quantified using an HPLC system equipped with a fluorescence detector. At a dose of 306 J/cm2, the 405 nm LED brought about 4.0, 2.1 and 1.9 log reductions in the populations of Staphylococcus aureus at 25, 10 and 4 °C, respectively. At all three temperatures, the population of Bacillus cereus and Listeria monocytogenes reduced by approximately 2.3 and 1.9 log respectively. Salmonella Typhimurium and Escherichia coli O157:H7 showed moderate susceptibility to 405 nm LED while Pseudomonas aeruginosa was most resistant. Of the six models tested, Hom model proved most suitable. This study demonstrated that 405 nm LEDs can be useful in the inactivation of bacterial pathogens with the aid of endogenous coproporphyrin alone.

•The 405 nm illumination inactivated the selected Gram-positive pathogens.•Staphylococcus aureus was the most resistant strain to the LED illumination.•The inactivation by LED might be due to physical damage to bacterial membrane.•405 nm LED may be a promising technology in eliminating these pathogens on foods.This study investigated the antibacterial effect of 405 ± 5 nm light emitting diode (LED) on Bacillus cereus, Listeria monocytogenes, and Staphylococcus aureus, and examined its antibacterial mechanism by determining the bacterial membrane and DNA damages. A 405 ± 5 nm LED illuminated the Gram-positive pathogens until 486 J/cm2 at 4 °C. Weibull model was used to calculate reliable life (tR) to compare bacterial sensitivities to LED illumination. The membrane damage was determined by NaCl and LIVE/DEAD® assay, while comet assay and DNA ladder analysis were conducted to determine DNA degradation. The illumination resulted in 1.9, 2.1, and 1.0 log reductions for B. cereus, L. monocytogenes, and S. aureus at 486 J/cm2, respectively. The comparison of tR values revealed that L. monocytogenes was identified as the most susceptible strain to LED illumination. The percentage of the bacterial sensitivity to NaCl remarkably increased in LED-illuminated cells compared to non-illuminated cells. Moreover, loss of membrane integrity was confirmed for LED-illuminated cells by LIVE/DEAD® assay, whereas no DNA breakage was indicated by comet assay and DNA ladder analysis. Thus, these findings suggest that the antibacterial effect of 405 ± 5 nm LED illumination on these pathogens might be due to physical damage to bacterial membrane rather than DNA degradation.

•460 nm LED illumination effectively reduced the populations of foodborne pathogens.•In general, inactivation rate in PBS was higher at 25 °C compared to 4 and 10 °C.•LED illumination induced significant sub-lethal injury into foodborne pathogens.•Several ROS precursors and scavengers were differentially regulated in bacteria.The objective of this study was to investigate the effect of 460 nm light-emitting diode (LED) on the inactivation of foodborne bacteria. Additionally, the change in the endogenous metabolic profile of LED illuminated cells was analyzed to understand the bacterial response to the LED illumination. Six different species of bacteria (Bacillus cereus, Listeria monocytogenes, Staphylococcus aureus, Escherichia coli O157:H7, Pseudomonas aeruginosa and Salmonella Typhimurium) were illuminated with 460 nm LED to a maximum dose of 4080 J/cm2 at 4, 10 and 25 °C. Inactivation curves were modeled using Hom model. Metabolic profiling of the non-illuminated and illuminated cells was performed using a Liquid chromatography–mass spectrometry system. Results indicate that the 460 nm LED significantly (p < 0.05) reduced the populations of all six bacterial species. For example, the population of S. aureus reached below detection limit within 7 h. B. cereus was most resistant to photo-inactivation and exhibited about 3-log reduction in 9 h. Metabolic profiling of the illuminated cells indicated that several metabolites e.g. 11-deoxycortisol, actinonin, coformycin, tyramine, chitobiose etc. were regulated during LED illumination. These results elucidate the effectiveness of 460 nm LED against foodborne bacteria and hence, its suitability as a novel antimicrobial control method to ensure food safety.

•Denser biofilms were observed in PW and EW compared to those in WE and EY.•Chlorine treatment failed to eradicate biofilms formed in egg media.•Biofilm formed in EW was more chlorine tolerant than those in EY, WE, and PW.•Organic materials of growth media greatly affected biofilm morphology.•Hot water treatment was more effective in eliminating biofilms formed in egg media.This study investigated the biofilm formation by three S. Enteritidis strains in a simulated liquid egg processing environment using 0.1% peptone water (PW) (control), 10% whole eggs (WE), 10% egg yolks (EY) and 10% egg whites (EW) as growth media, and evaluated the effectiveness of chlorine (200 ppm, 5 min) and hot water (71 °C, 30 s) treatments against S. Enteritidis biofilms. The results showed that S. Enteritidis formed significantly (P < 0.05) denser biofilms in PW and EW compared to those in WE and EY. However, biofilms formed in PW were less resistant to chlorine treatment than those formed in WE, EY, and EW, with average log reductions of 6.34, 2.28, 0.67 and 0.95 CFU/cm2, respectively. Microscopic observation showed that biofilm morphology was greatly affected by the growth medium, and the egg matrices might act as protective barriers, contributing to the greater chlorine resistance. All biofilms were very sensitive to hot water treatment, which reduced the cell populations by 4.30–7.08 log CFU/cm2. This study could advance our understanding towards the biofilm forming abilities of S. Enteritidis in liquid egg processing environments and the effectiveness of sanitation methods against S. Enteritidis biofilms, which may aid in the development of better sanitation strategies.

•The antimicrobial effect of LEDs was enhanced at acidic and alkaline conditions.•Escherichia coli O157:H7 and Salmonella Typhimurium were more susceptible to LEDs at an alkaline pH.•Listeria monocytogenes was more susceptible to LEDs at an acidic pH.•Results suggest that the LED should be applied selectively to foods.Light emitting diodes (LEDs) with their antibacterial effect present a novel method for food preservation. This effect may be influenced by environmental conditions such as the pH of the food contaminated by the pathogen. Thus, it is necessary to investigate the influence of pH on the antibacterial effect of LEDs before their application to real food matrices. Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes in trypticase soy broth were illuminated using 10-W 461 (22.1 mW/cm2) and 521 nm (16 mW/cm2) LEDs at pH values of 4.5, 6.0, 7.3, 8.0 and 9.5 for 7.5 h at 15 °C. Using the 461 nm LEDs, the populations of E. coli O157:H7 decreased by 2.1 ± 0.02, 1.2 ± 0.08 and 4.1 ± 0.42 log CFU/ml at pH 4.5, 7.3 and 9.5 respectively, after a dosage of 596.7 J/cm2. For L. monocytogenes, approximately a 5.8 ± 0.03 log reduction was observed after 238.7 J/cm2 at pH 4.5 using the 461 nm LEDs, while the bacterial concentration was reduced by 1.8 ± 0.01 log at pH 9.5 after 596.7 J/cm2. Bacterial inactivation using the 521 nm LEDs showed similar trends to the 461 nm LEDs at both acidic and alkaline pH conditions but with lower (1–2 log CFU/ml) reductions after 432 J/cm2. Lower D-values were observed for L. monocytogenes when exposed to LEDs at acidic pH values, while the sensitivity of E. coli O157:H7 and S. Typhimurium to LED was markedly increased at an alkaline pH. Regardless of the pH at which the cultures were illuminated, the percentage of sublethal injury increased with the treatment time. These results highlight the enhanced antibacterial effect of the 461 nm LED under acidic and alkaline pH conditions, proving its potential to preserve foods as well as to have synergistic effect with acidic and alkaline antimicrobials.

The aim of the present study was to determine the survival of Salmonella Typhimurium adapted with sodium lactate (NaL), potassium lactate/sodium acetate mixture (KL/NaA) or sodium acetate (NaA) in simulated gastric fluid (SGF) and during heat treatment. NaL-, KL/NaA- and NaA-adapted cells were prepared by incubating in tryptic soy broth (TSB) containing these salts at 5, 5 and 3% (w/v) concentration levels, respectively, for 24 h at 37 °C. The Baranyi model was used to compare the growth kinetic parameters of adapted cells. The acid and heat resistance of adapted cells were determined by incubating in SGF (pH 2.04) at 37 °C and in TSB at 55.8, 57.8 and 59.8 °C, respectively. Adapted cells had significantly (P < 0.05) longer lag phase duration (LPD) and slower maximum growth rate (MGR) than non-adapted cells. The acid resistance of KL/NaA-adapted cells was not significantly (P > 0.05) different from that of non-adapted cells. NaL-adapted cells were more susceptible to the low pH environment, whereas NaA-adapted cells showed enhanced acid resistance compared to non-adapted and other adapted cells. Unlike acid resistance, both NaL- and NaA-adapted cells showed enhanced heat resistance with increased D-values, regardless of treatment temperatures. Thus, this study indicates that adaptation of S. Typhimurium to 5% NaL or 3% NaA could enhance their ability to survive thermal processes or in the human stomach, possibly increasing the risk of Salmonella outbreaks.Highlights► Sodium lactate-adapted S. Typhimurium showed enhanced heat resistance. ► Adaptation to sodium acetate increased heat and acid resistance of S. Typhimurium. ► Adaptation to KL/NaA did not affect their resistance to heat and acid. ► A mixture of KL/NaA may be effective technique in controlling Salmonella spp.

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

•405 nm LED illumination inactivated Salmonella on fresh-cut papaya.•Antibacterial effect of LED might result from oxidation of bacterial DNA.•LED illumination did not negatively influence the quality of cut papaya.•LED at refrigeration could preserve cut fruits, minimizing risk of salmonellosis.This study evaluated the antibacterial effect of 405 ± 5 nm light emitting diode (LED) illumination against four Salmonella serovars on fresh-cut papaya and on fruit quality at various storage temperatures. To determine the antibacterial mechanism of LED illumination at 0.9 kJ/cm2, oxidative damage to DNA and membrane lipids of Salmonella in phosphate-buffered saline solution was measured. The populations of Salmonella on cut fruits were significantly (P < 0.05) reduced by 0.3–1.3 log CFU/cm2 at chilling temperatures following LED illumination for 36–48 h (1.3–1.7 kJ/cm2). However, at room temperature, bacterial populations increased rapidly to 6.3–7.0 log CFU/cm2 following LED illumination for 24 h (0.9 kJ/cm2), which was approximately 1.0 log lower than the number of colonies on non-illuminated fruits. Levels of bacterial DNA oxidation significantly increased, whereas lipid peroxidation in bacterial membrane was not observed, suggesting that DNA oxidation contributes to photodynamic inactivation by LED illumination. LED illumination did not adversely affect the physicochemical and nutritional qualities of cut papaya, regardless of storage temperature. These results indicate that a food chiller equipped with 405 ± 5 nm LEDs can preserve fresh-cut papayas in retail stores without deterioration, minimizing the risk of salmonellosis.

•A 405 nm LED illumination inactivated pathogens on fresh-cut mango at 4 and 10 °C.•Long-term LED illumination did not affect physicochemical quality of cut mango.•405 nm LEDs in a food chiller might be used to preserve cut fruits.To investigate a potential of 405 ± 5 nm light emitting diode (LED) as a novel technology for food preservation, the antibacterial effect of 405 ± 5 nm LED on Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. on the surface of fresh-cut mango and its influence on fruit quality were evaluated at different storage temperatures. LED-illumination inactivated 1.0–1.6 log CFU/cm2 of populations at 4 and 10 °C for 36–48 h (total dose, 2.6–3.5 kJ/cm2) regardless of bacterial species, while those on non-illuminated mange remained unchanged or slightly increased during storage. At 20 °C for 24 h (total dose, 1.7 kJ/cm2), non-illuminated E. coli O157:H7 and Salmonella gradually grew, whereas LED-illumination reduced 1.2 log of Salmonella and inhibited the growth of E. coli O157:H7. Unlike these, non-illuminated L. monocytogenes cells rapidly increased to 7.3 log, while illuminated cells reached 4.6 log, revealing that LED-illumination delayed their growth. There were no significant (P > 0.05) differences in color, antioxidant capacity, ascorbic acid, β-carotene, and flavonoid between non-illuminated and illuminated cut mangoes, regardless of storage temperature. These results suggest that 405 ± 5 nm LEDs in combination with chilling temperatures could be applied to preserve fresh-cut fruits without deterioration of physicochemical quality of fruits at food establishments, minimizing the risk of foodborne disease.

•PCR-IMS and PCR-cen were evaluated for Salmonella detection for mung bean sprouts.•PCR-IMS and PCR-cen showed similar LOD, which was more sensitive than PCR alone.•Enrichment of 10 h was sufficient to detect Salmonella on sprouts by both methods.•PCR-cen might be more cost-effective over PCR-IMS for rapid Salmonella detection.Fresh mung bean sprouts have been identified as a source of many Salmonella outbreaks worldwide. The aim of this study was to develop a rapid and accurate detection methodology for low levels of healthy and sanitizer-injured Salmonella on mung bean sprouts using real-time PCR coupled with either immunomagnetic separation (PCR-IMS) or centrifugation (PCR-cen). Initially, three parameters of IMS; specificity/sensitivity, bacterial concentration and bead incubation time were optimized. Secondly, limit of detection (LOD) was determined for the optimized PCR-IMS and PCR-cen. These two methods were compared against PCR alone (PCR) and the standard culture method (ISO) for their ability to detect Salmonella using inoculated and uninoculated sprouts. Under optimum IMS conditions (105 CFU/ml for 30 min), capture efficiency of Salmonella in sprout suspensions was lower than 40%, most probably due to the non-specific binding of the background microbiota. PCR-IMS and PCR-cen had a similar LOD at 103 CFU/ml, which was one log unit lower than PCR. Enrichment of 10 h was sufficient to detect 100% of the inoculated sprouts with both PCR-IMS and PCR-cen, which was significantly faster compared to PCR and the ISO method. Moreover, the validation study using uninoculated sprouts revealed that PCR-IMS and PCR-cen were equally effective on Salmonella detection, showing 98.3% accuracy. These results suggest that PCR-cen would be the effective and less costly method for the detection of both healthy and sanitizer-injured Salmonella on mung bean sprouts.

•Cells grown at 37 and 42 °C were most acid and heat resistant, respectively.•Membrane fluidity decreased as temperature increased from 10 to 42 °C.•The expression of rpoS and rpoH was induced at 10 or 25 °C and 42 °C, respectively.•Most of the virulence genes were upregulated in cells cultivated at 42 °C.The influence of growth temperature (10, 25, 37, and 42 °C) on the survival of Salmonella Enteritidis in simulated gastric fluid (SGF; pH = 2.0) and during heat treatment (54, 56, 58, and 60 °C), on the membrane fatty acid composition, as well as on stress-/virulence-related gene expression was studied. Cells incubated at temperatures lower or higher than 37 °C did not increase their acid resistance, with the maximum D-value of 3.07 min in cells grown at 37 °C; while those incubated at higher temperature increased their heat resistance, with the maximum D60 °C-values of 1.4 min in cells grown at 42 °C. A decrease in the ratio of unsaturated to saturated fatty acids was observed as the growth temperature increased. Compared to the control cells grown at 37 °C, the expression of rpoS was 16.5- and 14.4-fold higher in cells cultivated at 10 and 25 °C, respectively; while the expression of rpoH was 2.9-fold higher in those cultivated at 42 °C. The increased expression of stress response gene rpoH and the decreased ratio of unsaturated to saturated fatty acids correlated with the greater heat resistance of bacteria grown at 42 °C; while the decreased expression of stress response gene rpoS at 42 °C might contribute to the decrease in acid resistance. Virulence related genes-spvR, hilA, avrA-were induced in cells cultivated at 42 °C, except sefA which was induced in the control cells. This study indicates that environmental temperature may affect the virulence potential of S. Enteritidis, thus temperature should be well controlled during food storage.

•461 and 521 nm LEDs produced a bactericidal effect at 10 and 15 °C but not 20 °C.•642 nm LED did not show bactericidal or bacteriostatic effect at any temperature.•The Gram nature of the strains did not influence the susceptibility to the LEDs.•LEDs combined with chilling could be used as a novel food preservation technology.The antibacterial effect of light emitting diodes (LEDs) in the visible region (461, 521 and 642 nm) of the electromagnetic spectrum was investigated on Escherichia coli O157:H7, Salmonella typhimurium, Listeria monocytogenes and Staphylococcus aureus. The irradiances of the 461, 521 and 642 nm LEDs were 22.1, 16 and 25.4 mW/cm2, respectively. Bacterial cultures suspended in tryptic soy broth were illuminated by 10-watt LEDs at a distance of 4.5 cm for 7.5 h at 20, 15 and 10 °C. Regardless of the bacterial strains, bacterial inactivation was observed with the range of 4.6–5.2 log CFU/ml at 10 and 15 °C after illumination with the 461 nm LED, while illumination with the 521 nm LED resulted in only 1.0–2.0 log reductions after 7.5 h. On the other hand, no antibacterial effect was observed using the 642 nm LED treatment. The photodynamic inactivation by 461 and 521 nm LEDs was found to be greater at the set temperatures of 10 and 15 °C than at 20 °C. The D-values for the four bacterial strains at 10 and 15 °C after the illumination of 461 nm LED ranged from 1.29 to 1.74 h, indicating that there was no significant difference in the susceptibility of the bacterial strains to the LED illumination between 10 and 15 °C, except for L. monocytogenes. Regardless of the illumination temperature, sublethal injury was observed in all bacterial strains during illumination with the 461 and the 521 nm LED and the percentage of injured cells increased as the treatment time increased. Thus, the results show that the antibacterial effect of the LEDs was highly dependent on the wavelength and the illumination temperature. This study suggests the potential of 461 and 521 nm LEDs in combination with chilling to be used as a novel food preservation technology.

•Real-time PCR with IMS was optimized for Salmonella detection on duck wings.•Among three primers, Sal primer showed lower LOD and higher PCR efficiency.•PCR–IMS decreased LOD and shortened the enrichment time for healthy Salmonella.•Longer enrichment time was needed for heat-injured Salmonella detection.•PCR–IMS could provide rapid and accurate detection for Salmonella on duck wings.Conventional culture detection methods are time consuming and labor-intensive. For this reason, an alternative rapid method combining real-time PCR and immunomagnetic separation (IMS) was investigated in this study to detect both healthy and heat-injured Salmonella Typhimurium on raw duck wings. Firstly, the IMS method was optimized by determining the capture efficiency of Dynabeads® on Salmonella cells on raw duck wings with different bead incubation (10, 30 and 60 min) and magnetic separation (3, 10 and 30 min) times. Secondly, three Taqman primer sets, Sal, invA and ttr, were evaluated to optimize the real-time PCR protocol by comparing five parameters: inclusivity, exclusivity, PCR efficiency, detection probability and limit of detection (LOD). Thirdly, the optimized real-time PCR, in combination with IMS (PCR–IMS) assay, was compared with a standard ISO and a real-time PCR (PCR) method by analyzing artificially inoculated raw duck wings with healthy and heat-injured Salmonella cells at 101 and 100 CFU/25 g. Finally, the optimized PCR–IMS assay was validated for Salmonella detection in naturally contaminated raw duck wing samples. Under optimal IMS conditions (30 min bead incubation and 3 min magnetic separation times), approximately 85 and 64% of S. Typhimurium cells were captured by Dynabeads® from pure culture and inoculated raw duck wings, respectively. Although Sal and ttr primers exhibited 100% inclusivity and exclusivity for 16 Salmonella spp. and 36 non-Salmonella strains, the Sal primer showed lower LOD (103 CFU/ml) and higher PCR efficiency (94.1%) than the invA and ttr primers. Moreover, for Sal and invA primers, 100% detection probability on raw duck wings suspension was observed at 103 and 104 CFU/ml with and without IMS, respectively. Thus, the Sal primer was chosen for further experiments. The optimized PCR–IMS method was significantly (P = 0.0011) better at detecting healthy Salmonella cells after 7-h enrichment than traditional PCR method. However there was no significant difference between the two methods with longer enrichment time (14 h). The diagnostic accuracy of PCR–IMS was shown to be 98.3% through the validation study. These results indicate that the optimized PCR–IMS method in this study could provide a sensitive, specific and rapid detection method for Salmonella on raw duck wings, enabling 10-h detection. However, a longer enrichment time could be needed for resuscitation and reliable detection of heat-injured cells.