Inactivation of Escherichia Coli and Salmonella Using 365 and 395 nm High Intensity Pulsed Light Emitting Diodes

Effectiveness of Ultra-High Irradiance Blue-Light-Emitting Diodes to Control Salmonella Contamination Adhered to Dry Stainless Steel Surfaces

Controlling Salmonella contamination in dry food processing environments represents a significant challenge due to their tolerance to desiccation stress and enhanced thermal resistance. Blue light is emerging as a safer alternative to UV irradiation for surface decontamination. In the present study, the antimicrobial efficacy of ultra-high irradiance (UHI) blue light, generated by light-emitting diodes (LEDs) at wavelengths of 405 nm (841.6 mW/cm2) and 460 nm (614.9 mW/cm2), was evaluated against a five-serovar cocktail of Salmonella enterica dry cells on clean and soiled stainless steel (SS) surfaces. Inoculated coupons were subjected to blue light irradiation treatments at equivalent energy doses ranging from 221 to 1106 J/cm2. Wheat flour was used as a model food soil system. To determine the bactericidal mechanisms of blue light, the intracellular concentration of reactive oxygen species (ROS) in Salmonella cells and the temperature changes on SS surfaces were also measured. The treatment energy dose had a significant effect on Salmonella inactivation levels. On clean SS surfaces, the reduction in Salmonella counts ranged from 0.8 to 7.4 log CFU/cm2, while, on soiled coupons, the inactivation levels varied from 1.2 to 4.2 log CFU/cm2. Blue LED treatments triggered a significant generation of ROS within Salmonella cells, as well as a substantial temperature increase in SS surfaces. However, in the presence of organic matter, the oxidative stress in Salmonella cells declined significantly, and treatments with higher energy doses (>700 J/cm2) were required to uphold the antimicrobial effectiveness observed on clean SS. The mechanism of the bactericidal effect of UHI blue LED treatments is likely to be a combination of photothermal and photochemical effects. These results indicate that LEDs emitting UHI blue light could represent a novel cost- and time-effective alternative for controlling microbial contamination in dry food processing environments.

Effectiveness of Ultra-High Irradiance Blue Light-Emitting Diodes in Inactivating Escherichia coli O157:H7 on Dry Stainless Steel and Cast-Iron Surfaces

The use of blue light-emitting diodes (LEDs) is emerging as a promising dry decontamination method. In the present study, LEDs emitting ultra-high irradiance (UHI) density at 405 nm (842 mW/cm2) and 460 nm (615 mW/cm2) were used to deliver high-intensity photoinactivation treatments ranging from 221 to 1107 J/cm2. The efficacy of these treatments to inactivate E. coli O157:H7 dry cells was evaluated on clean and soiled stainless steel and cast-iron surfaces. On clean metal surfaces, the 405 and 460 nm LED treatment with a 221 J/cm2 dose resulted in E. coli reductions ranging from 2.0 to 4.1 log CFU/cm2. Increasing the treatment energy dose to 665 J/cm2 caused further significant reductions (>8 log CFU/cm2) in the E. coli population. LED treatments triggered a significant production of intracellular reactive oxygen species (ROS) in E. coli cells, as well as a significant temperature increase on metal surfaces. In the presence of organic matter, intracellular ROS generation in E. coli cells dropped significantly, and treatments with higher energy doses (>700 J/cm2) were required to uphold antimicrobial effectiveness. The mechanism of the bactericidal effect of UHI blue LED treatments is likely to be a combination of photothermal and photochemical effects. This study showed that LEDs emitting monochromatic blue light at UHI levels may serve as a viable and time-effective method for surface decontamination in dry food processing environments.

Effects of Electrical Pulse Width and Output Irradiance on Intense Pulse Light Inactivation

The effects of electrical pulse width and output irradiance on the inactivation effect of intense pulse light (IPL) are studied in this paper. The measured radiant efficiency of pulsed xenon lamp can be more than 50%, and its irradiance can reach levels 100-times greater than that of a low-pressure mercury lamp. Staphylococcus aureus is used in inactivation experiments. When the irradiance and dose are both constant, there is no significant difference in inactivation efficiency when the pulse width is changed. However, a narrow pulse width corresponding to high irradiance at the same single-pulsed dose displays better inactivation effect. Experimental results are compared between the xenon lamp and low-pressure mercury lamp. The reduction factor (RF) value of the xenon lamp is more than 1.0 higher under the condition of both the same dose and irradiance. In order to achieve the same RF value, the dose of continuous-wave light must be at least three-times greater than that of pulsed light. The spectral action of the pulsed light is also studied. It is confirmed that UVC plays a major role across the whole spectrum. The experimental results show that extreme high-pulsed irradiance presents the main contributing factor behind the excellent bactericidal effect of IPL.

Comparative Assessment of Pulsed and Continuous LED UV-A Lighting for Disinfection of Contaminated Surfaces

The germicidal efficacy of LED UV-A lighting has scarcely been compared in continuous and pulsed modes for contaminated surfaces. Herein, we compare the disinfection properties of pulsed versus continuous lighting at equal irradiances using a 365 nm LED device that replicates the doses of occupied-space continuous disinfection UV-A products. Representative organisms evaluated in this study included human-infectious enveloped and non-enveloped viruses (lentivirus and adeno-associated virus, respectively), a bacterial endospore (Bacillus atrophaeus), and a resilient gram-positive bacterium (Enterococcus faecalis). Nominal UV-A irradiances were tested at or below the UL standard limit for continuous human exposure (maximum irradiance of 10 W/m2). We observed photoinactivation properties that varied by organism type, with bacteria and enveloped virus being more susceptible to UV-A than non-enveloped virus and spores. Overall, we conclude that continuous-mode UV-A lighting is better suited for occupied-space disinfection than pulsing UV-A at equivalent low irradiances, and we draw comparisons to other studies in the literature.

Antibacterial Efficacy and Mechanisms of Curcumin-Based Photodynamic Treatment against Staphylococcus aureus and Its Application in Juices

Antimicrobial Photodynamic Treatment (aPDT) is a non-thermal sterilization technology, which can inactivate common foodborne pathogens. In the present study, photodynamic inactivation on Staphylococcus aureus (S. aureus) with different concentrations of curcumin and light dose was evaluated and the mechanisms were also investigated. The results showed that curcumin-based aPDT could inactivate S. aureus cells by 6.9 log CFU/mL in phosphate buffered saline (PBS). Moreover, the modified Gompertz model presented a good fit at the inactivation data of S. aureus. Photodynamic treatment caused cell membrane damage as revealed by analyzing scanning electron microscopy (SEM) images. Leakage of intracellular constituents further indicated that cell membrane permeability was changed. Flow cytometry with double staining demonstrated that cell membrane integrity and the activity of nonspecific esterase were destroyed. Compared with the control group, intracellular reactive oxygen species (ROS) levels caused by photodynamic treatment significantly increased. Furthermore, curcumin-based aPDT reduced S. aureus by 5 log CFU/mL in juices. The color of the juices was also tested using a Chromatic meter, and it was found that b* values were the most markedly influenced by photodynamic treatment. Overall, curcumin-based aPDT had strong antibacterial activity against S. aureus. This approach has the potential to remove foodborne pathogens from liquid food.

Salmonella spp. in low water activity food: Occurrence, survival mechanisms, and thermoresistance

The occurrence of disease outbreaks involving low-water-activity (a_w ) foods has gained increased prominence due in part to the fact that reducing free water in these foods is normally a measure that controls the growth and multiplication of pathogenic microorganisms. Salmonella, one of the main bacteria involved in these outbreaks, represents a major public health problem worldwide and in Brazil, which highlights the importance of good manufacturing and handling practices for food quality. The virulence of this pathogen, associated with its high ability to persist in the environment, makes Salmonella one of the main challenges for the food industry. The objectives of this article are to present the general characteristics, virulence, thermoresistance, control, and relevance of Salmonella in foodborne diseases, and describe the so-called low-water-activity foods and the salmonellosis outbreaks involving them.

A review on recent advances in LED-based non-thermal technique for food safety: current applications and future trends

Light-emitting diodes (LEDs) is an eco-friendly light source with broad-spectrum antimicrobial activity. Recent studies have extensively been conducted to evaluate its efficacy in microbiological safety and the potential as a preservation method to extend the shelf-life of foods. This review aims to present the latest update of recent studies on the basics (physical, biochemical and mechanical basics) and antimicrobial activity of LEDs, as well as its application in the food industry. The highlight will be focused on the effects of LEDs on different types (bacteria, yeast/molds, viruses) and forms (planktonic cells, biofilms, endospores, fungal toxin) of microorganisms. The antimicrobial activity of LEDs on various food matrices was also evaluated, together with further analysis on the food-related factors that lead to the differences in LEDs efficiency. Besides, the applications of LEDs on the food-related conditions, packaged food, and equipment that could enhance LEDs efficiency were discussed to explore the future trends of LEDs technology in the food industry. Overall, the present review provides important insights for future research and the application of LEDs in the food industry.

Postharvest Ultraviolet Radiation in Fruit and Vegetables: Applications and Factors Modulating Its Efficacy on Bioactive Compounds and Microbial Growth

Ultraviolet (UV) radiation has been considered a deleterious agent that living organisms must avoid. However, many of the acclimation changes elicited by UV induce a wide range of positive effects in plant physiology through the elicitation of secondary antioxidant metabolites and natural defenses. Therefore, this fact has changed the original UV conception as a germicide and potentially damaging agent, leading to the concept that it is worthy of application in harvested commodities to take advantage of its beneficial responses. Four decades have already passed since postharvest UV radiation applications began to be studied. During this time, UV treatments have been successfully evaluated for different purposes, including the selection of raw materials, the control of postharvest diseases and human pathogens, the elicitation of nutraceutical compounds, the modulation of ripening and senescence, and the induction of cross-stress tolerance. Besides the microbicide use of UV radiation, the effect that has received most attention is the elicitation of bioactive compounds as a defense mechanism. UV treatments have been shown to induce the accumulation of phytochemicals, including ascorbic acid, carotenoids, glucosinolates, and, more frequently, phenolic compounds. The nature and extent of this elicitation have been reported to depend on several factors, including the product type, maturity, cultivar, UV spectral region, dose, intensity, and radiation exposure pattern. Even though in recent years we have greatly increased our understanding of UV technology, some major issues still need to be addressed. These include defining the operational conditions to maximize UV radiation efficacy, reducing treatment times, and ensuring even radiation exposure, especially under realistic processing conditions. This will make UV treatments move beyond their status as an emerging technology and boost their adoption by industry.

Inhibition of bacterial growth through LED (light-emitting diode) 465 and 630 nm: in vitro

Photobiomodulation has been used to inactivate bacterial growth, in different laser or LED protocols. Thus, the aim of this study was to verify the inhibition of Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli, in ATCC strains and bacteria collected from patients with skin burns, after irradiation with LED; 300 μl of saline solution with bacterial suspension was irradiated at a concentration of 0.5-0.63, by the McFarland scale, after five serial dilutions, with evaluation of pre- and post-irradiation pH and temperature control. The cultures were placed in a bacteriological incubator at 37 °C for 24 h for later counting of colony-forming units (CFU). Data were analyzed by Shapiro-Wilk tests and single-factor ANOVA, with Tukey post hoc (p < 0.05). Both wavelengths and energy densities tested showed inhibition of bacterial growth. The comparison of the irradiated groups (ATCC) with the control group showed the following: S. aureus and P. aeruginosa 465 nm (40 J/cm²) and 630 nm (50 J/cm²) and E. coli 465 nm (40 J/cm²) and 630 nm (30 J/cm²). Among the ATCC S. aureus groups, there was a difference for 630 nm (30 J/cm²) and 465 nm (30, 40, 50 J/cm²). The bacteria from the burned patients were S. aureus (30 and 50 J/cm²) and P. aeruginosa (50 J/cm²). We conclude that different bacterial strains were reduced into colony-forming units after LED irradiation.

Ultra-high irradiance (UHI) blue light: highlighting the potential of a novel LED-based device for short antifungal treatments of food contact surfaces

Microbial food spoilage is an important cause of health and economic issues and can occur via resilient contamination of food surfaces. Novel technologies, such as the use of visible light, have seen the light of day to overcome the drawbacks associated with surface disinfection treatments. However, most studies report that photo-inactivation of microorganisms with visible light requires long time treatments. In the present study, a novel light electroluminescent diode (LED)-based device was designed to generate irradiation at an ultra-high power density (901.1 mW/cm²). The efficacy of this technology was investigated with the inactivation of the yeast S. cerevisiae. Short-time treatments (below 10 min) at 405 nm induced a ~4.5 log reduction rate of the cultivable yeast population. The rate of inactivation was positively correlated to the overall energy received by the sample and, at a similar energy, to the power density dispatched by the lamp. A successful disinfection of several food contact surfaces (stainless steel, glass, polypropylene, polyethylene) was achieved as S. cerevisiae was completely inactivated within 5 min of treatments. The disinfection of stainless steel was particularly effective with a complete inactivation of the yeast after 2 min of treatment. This ultra-high irradiance technology could represent a novel cost- and time-effective candidate for microbial inactivation of food surfaces. These treatments could see applications beyond the food industry, in segments such as healthcare or public transport. KEY POINTS : • A novel LED-based device was designed to emit ultra-high irradiance blue light • Short time treatments induced high rate of inhibition of S. cerevisiae • Multiple food contact surfaces were entirely disinfected with 5-min treatments.

Antimicrobial activity and drying potential of high intensity blue light pulses (455 nm) emitted from LEDs

Decontamination of low water activity (a_w) foods, like pet foods is a challenging task. Treatment using light emitting diode (LED) is an emerging decontamination method, that can induce photodynamic inactivation in bacteria. The objective of this study was to understand the effect of selected product and process parameters on the antibacterial efficacy of treatment using light pulses of 455 nm wavelength on dry powdered Salmonella and pet foods equilibrated to 0.75 a_w. The surface temperature increase, weight loss, and a_w decrease in the samples were determined after LED treatments with different doses. S. Typhimurium on pet foods showed better sensitivity to 455 nm LED treatment than the powdered S. Typhimurium. For instance, 455 nm LED treatment with 785.7 J/cm² dose produced a log reduction of 1.44 log (CFU/g) in powdered S. Typhimurium population compared to 3.22 log (CFU/g) on pet food. The LED treatment was less effective against 5-strain cocktail of Salmonella in low a_w pet foods. The treated samples showed significant reduction in weight and a_w showing the heating and drying potential of 455 nm LED treatment. Significant lipid oxidation was observed in the treated pet foods. Overall, the dose, treatment time, and sample type influenced the Salmonella inactivation efficacy of 455 nm LED treatment in low a_w conditions.

Investigating the Use of Ultraviolet Light Emitting Diodes (UV-LEDs) for the Inactivation of Bacteria in Powdered Food Ingredients

The addition of contaminated powdered spices and seasonings to finished products which do not undergo further processing represents a significant concern for food manufacturers. To reduce the incidence of bacterial contamination, seasoning ingredients should be subjected to a decontamination process. Ultraviolet light emitting diodes (UV-LEDs) have been suggested as an alternative to UV lamps for reducing the microbial load of foods, due to their increasing efficiency, robustness and decreasing cost. In this study, we investigated the efficacy of UV-LED devices for the inactivation of four bacteria (Listeria monocytogenes, Escherichia coli, Bacillus subtilis and Salmonella Typhimurium) on a plastic surface and in four powdered seasoning ingredients (onion powder, garlic powder, cheese and onion powder and chilli powder). Surface inactivation experiments with UV mercury lamps, UVC-LEDs and UVA-LEDs emitting at wavelengths of 254 nm, 270 nm and 365 nm, respectively, revealed that treatment with UVC-LEDs were comparable to, or better than those observed using the mercury lamp. Bacterial reductions in the seasoning powders with UVC-LEDs were less than in the surface inactivation experiments, but significant reductions of 0.75-3 log10 colony forming units (CFU) were obtained following longer (40 s) UVC-LED exposure times. Inactivation kinetics were generally nonlinear, and a comparison of the predictive models highlighted that microbial inactivation was dependent on the combination of powder and microorganism. This study is the first to report on the efficacy of UV-LEDs for the inactivation of several different bacterial species in a variety of powdered ingredients, highlighting the potential of the technology as an alternative to the traditional UV lamps used in the food industry.

Lifetime Analysis of Commercial 3 W UV-A LED

The lifetime of ultraviolet high-power light-emitting diodes (UV HP-LEDs) is an open issue due to their high current density, high temperature, and UV radiation. This work presents a reliability study and failure analysis of three high-temperature accelerated life tests (ALTs) for 13,500 h with 3 W commercial UV LEDs of 365 nm at a nominal current in two working conditions: continuous mode and cycled mode (30 s on/30 s off). Arrhenius–Weibull parameters were evaluated, and an equation to evaluate the lifetime (B50) at any junction temperature and other relevant lifetime functions is presented. The Arrhenius activation energy was 0.13 eV for the continuous mode and 0.20 eV for the cycled mode. The lifetime at 50% survival and 30% loss of optical power as a failure definition, working at Ta = 40 °C with a multi-fin heat sink in natural convection, was over 4480 h for the continuous mode and 19,814 h for the cycled mode. The need to add forced convection for HP-LED arrays to achieve these high-reliability values is evidenced. The main source of degradation is the semiconductor device, and the second is the encapsulation silicone break.

Applications of Light-Emitting Diodes (LEDs) in Food Processing and Water Treatment

Light-emitting diode (LED) technology is an emerging nonthermal food processing technique that utilizes light energy with wavelengths ranging from 200 to 780 nm. Inactivation of bacteria, viruses, and fungi in water by LED treatment has been studied extensively. LED technology has also shown antimicrobial efficacy in food systems. This review provides an overview of recent studies of LED decontamination of water and food. LEDs produce an antibacterial effect by photodynamic inactivation due to photosensitization of light absorbing compounds in the presence of oxygen and DNA damage; however, such inactivation is dependent on the wavelength of light energy used. Commercial applications of LED treatment include air ventilation systems in office spaces, curing, medical applications, water treatment, and algaculture. As low penetration depth and high-intensity usage can challenge optimal LED treatment, optimization studies are required to select the right light wavelength for the application and to standardize measurements of light energy dosage.