Fundamental Characteristics of Deep-UV Light-Emitting Diodes and Their Application To Control Foodborne Pathogens

Cell density and extracellular matrix composition mitigate bacterial biofilm sensitivity to UV-C LED irradiation

Ultraviolet-C light-emitting diodes (UV-C LEDs) are an emerging technology for decontamination applications in different sectors. In this study, the inactivation of bacterial biofilms was investigated by applying an UV-C LED emitting at 280 nm and by measuring both the influence of the initial cell density (load) and presence of an extracellular matrix (biofilm). Two bacterial strains exposing diverging matrix structures and biochemical compositions were used: Pseudomonas aeruginosa and Leuconostoc citreum. UV-C LED irradiation was applied at three UV doses (171 to 684 mJ/cm2) on both surface-spread cells and on 24-h biofilms and under controlled cell loads, and bacterial survival was determined. All surface-spread bacteria, between 105 and 109 CFU/cm2, and biofilms at 108 CFU/cm2 showed that bacterial response to irradiation was dose-dependent. The treatment efficacy decreased significantly for L. citreum surface-spread cells when the initial cell load was high, while no load effect was observed for P. aeruginosa. Inactivation was also reduced when bacteria were grown under a biofilm form, especially for P. aeruginosa: a protective effect could be attributed to abundant extracellular DNA and proteins in the matrix of P. aeruginosa biofilms, as revealed by Confocal Laser Scanning Microscopy observations. This study showed that initial cell load and exopolymeric substances are major factors influencing UV-C LED antibiofilm treatment efficacy. KEY POINTS: • Bacterial cell load (CFU/cm2) could impact UV-C LED irradiation efficiency • Characteristics of the biofilm matrix have a paramount importance on inactivation • The dose to be applied can be predicted based on biofilm properties.

Cleaning technologies integrated in duct flows for the inactivation of pathogenic microorganisms in indoor environments: A critical review of recent innovations and future challenges

Pathogenic microorganisms are a major concern in indoor environments, particularly in sensitive facilities such as hospitals, due to their potential to cause nosocomial infections. This study evaluates the concentration of airborne bacteria and fungi in the University Hospital Complex of Albacete (Spain), comparing the results with recent literature. Staphylococcus is identified as the most prevalent bacterial genus with a percentage distribution of 35%, while Aspergillus represents the dominant fungal genus at 34%. The lack of high Technology Readiness Levels (TRL 6, TRL 7) for effective indoor air purification requires research efforts to bridge this knowledge gap. A screening of disinfection technologies for pathogenic airborne microorganisms such as bacteria and fungi is conducted. The integration of filtration, irradiation or and (electro)chemical gas treatment systems in duct flows is discussed to enhance the design of the air-conditioning systems for indoor air purification. Concerns over microbial growth have led to recent studies on coating commercial fibrous air filters with antimicrobial particles (silver nanoparticles, iron oxide nanowires) and polymeric materials (polyaniline, polyvinylidene fluoride). Promising alternatives to traditional short-wave UV-C energy for disinfection include LED and Far-UVC irradiation systems. Additionally, research explores the use of TiO2 and TiO2 doped with metals (Ag, Cu, Pt) in filters with photocatalytic properties, enabling the utilization of visible or solar light. Hybrid photocatalysis, combining TiO2 with polymers, carbon nanomaterials, or MXene nanomaterials, enhances the photocatalytic process. Chemical treatment systems such as aerosolization of biocidal agents (benzalkonium chloride, hydrogen peroxide, chlorine dioxide or ozone) with their possible combination with other technologies such as adsorption, filtration or photocatalysis, are also tested for gas disinfection. However, the limited number of studies on the use of electrochemical technology poses a challenge for further investigation into gas-phase oxidant generation, without the formation of harmful by-products, to raise its TRL for effectively inactivating airborne microorganisms in indoor environments.

Skin optical properties from 200 to 300 nm support far UV-C skin-safety in vivo

The growing threat of multi-drug resistant pathogens and airborne microbial diseases has highlighted the need to improve or develop novel disinfection methods for clinical environments. Conventional ultraviolet C (UV-C) lamps effectively inactivate microorganisms but are harmful to human skin and eyes upon exposure. The use of new 233 nm far UV-C LEDs as an antiseptic can overcome those limitations. In this research, the light penetration into the skin was elucidated for the UV-C region (<300 nm) by measuring the scattering and absorption of skin layers and inverse Monte Carlo simulation, and further confirmed by the first clinical pilot trial in which healthy volunteers were irradiated with a dose of 60 mJ/cm2 at 233 nm. The radiation is strongly absorbed in the stratum corneum, resulting in minimal skin damage without inducing inflammatory responses. The results suggest that 233 nm far UV-C light emitting diodes (LEDs) could effectively inactivate microorganisms, while being safe and soft for the skin.

Study on disinfection effect of a 222-nm UVC excimer lamp on object surface

Effective disinfection of contaminated surfaces is essential for preventing the transmission of pathogens. In this study, we investigated the UV irradiance and wavelength distribution of a 222-nm ultraviolet C (UVC) excimer lamp and its disinfection efficacy against microorganisms in laboratory conditions. By using a carrier quantitative germicidal test with stainless steel sheets as carriers, we examined the disinfection effect of the 222-nm UVC lamp on three standard strains-Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. We tested the disinfection efficacy under different conditions by adjusting irradiation time, as well as the state and temperature of the stainless steel carriers. Our results indicated that a bacterial suspension in PBS and not-dried stainless steel carriers yielded better disinfection than in TSB and dried carriers. Additionally, carrier temperature had no significant impact on disinfection efficacy. When utilizing a bacterial suspension in PBS and non-dried carriers at a temperature of 20 °C, the three bacteria were eliminated by 222-nm UVC excimer lamp irradiation in just 15 s. In contrast, when using a bacterial suspension in TSB and dried carriers at temperatures of 20 °C, 4 °C, or - 20 °C, the three bacteria were eradicated by 222-nm UVC excimer lamp irradiation in 60 s. Comparatively, the LPM lamp required more than 10 min to achieve the same disinfection effect. Our data demonstrate that the 222-nm UVC excimer lamp has higher irradiance and a more potent microbial disinfection effect than the LPM lamp, requiring significantly less irradiation time to achieve the same disinfection effect under identical conditions. Furthermore, the 222-nm UVC excimer lamp exhibited a substantial disinfection effect on bacterial propagules at low temperatures. Our findings support the optimization of "tunnel-type" cold-chain goods disinfection devices, providing an alternative, highly efficient, and practical tool to combat the spread of SARS-CoV-2 through cold-chain systems.

Blue 405 nm LED light effectively inactivates bacterial pathogens on substrates and packaging materials used in food processing

This study investigates the antimicrobial effectiveness of 405 nm light emitting diodes (LEDs) against pathogenic Escherichia coli O157:H7, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Typhimurium, and Staphylococcus aureus, in thin liquid films (TLF) and on solid surfaces. Stainless steel (SS), high density polyethylene (HDPE), low density polyethylene (LDPE), and borosilicate glass were used as materials typically encountered in food processing, food service, and clinical environments. Anodic aluminum oxide (AAO) coupons with nanoscale topography were used, to evaluate the effect of topography on inactivation. The impact of surface roughness, hydrophobicity, and reflectivity on inactivation was assessed. A 48 h exposure to 405 nm led to reductions ranging from 1.3 (E. coli) to 5.7 (S. aureus) log CFU in TLF and 3.1 to 6.3 log CFU on different solid contact surfaces and packaging materials. All inactivation curves were nonlinear and followed Weibull kinetics, with better inactivation predictions on surfaces (0.89 ≤ R2 ≤ 1.0) compared to TLF (0.76 ≤ R2 ≤ 0.99). The fastest inactivation rate was observed on small nanopore AAO coupons inoculated with L. monocytogenes and S. aureus, indicating inactivation enhancing potential of these surfaces. These results demonstrate significant promise of 405 nm LEDs for antimicrobial applications in food processing and handling and the healthcare industry.

Effects of solvent environment on the spectroscopic properties of tylosin, an experimental and theoretical approach

Tylosin is a commonly used antibiotic in animal medicine. However, it remains unclear how tylosin impacts the broader ecosystem once the host animal has excreted it. One of the main concerns is that it can lead to the development of antibiotic resistance. Therefore, there exists a need to develop systems that remove tylosin from the environment. Utilizing UV irradiation to destroy pathogens is one technique often deployed by scientists and engineers. However, for light-based techniques to be efficient, it is necessary to understand the spectral properties of the material being removed. Steady-state spectroscopy and density functional theory were used to analyze the electronic transitions of tylosin responsible for its strong absorbance in the mid-UV region. It was observed that the absorbance peak of tylosin stems from two transitions in the conjugated region of the molecule. Moreover, these transitions stem from an electronegative region of the molecule, which would allow them to be manipulated by changing solvent polarity. Finally, a polariton model has been proposed, which can be used to initiate the photodegradation of tylosin without the need for direct irradiation of the molecule with UV-B light.

Microbial inactivation kinetics of UV LEDs and effect of operating conditions: A methodological critical analysis

Tiny ultraviolet (UV) light-emitting diodes (LED)s that are replacing the conventional energy-intensive mercury UV lamps have gained interest since the early 2000's because of their promising advantages. In the context of microbial inactivation (MI) of waterborne microbes, disinfection kinetics of those LEDs exhibited variations among studies, in terms of varying the UV wavelength, the exposure time, power, and dose (UV fluence) as well as other operational conditions. While reported results may appear contradictory when examined separately, they probably are not when analyzed collectively. As such, in this study, we carry out a quantitative collective regression analysis of the reported data to shed light on the kinetics of MI by the emerging UV LEDs technology alongside the effects of varying operational conditions. The main goal is to identify dose response requirements for UV LEDs and to compare them to traditional UV lamps in addition to ascertaining optimal settings that could help in achieving the optimal inactivation outcome for comparable UV doses. The analysis showed that kinetically, UV LEDs are as effective as conventional mercury lamps for water disinfection, and at times more effective, especially for UV resistant microbes. We defined the maximal efficiency at two wavelengths, 260-265 nm and 280 nm, among a wide range of available LED wavelengths. We also defined the UV fluence per log inactivation of tested microbes. At the operational level, we identified existing gaps and developed a framework for a comprehensive analysis program for future needs.

Porcine embryo development and inactivation of microorganisms after ultraviolet-C irradiation at 228 nm

It is important to prevent contamination inside the incubator as a method of preventing microbial infections during the embryo culture. In the present study, we examined the effects of ultraviolet-C (UV-C) irradiation, used for microorganism inactivation, on embryo development and the growth of bacteria, including Escherichia coli and Staphylococcus aureus, and the fungus Cladosporium cladosporioides. In the embryo irradiation experiment, we examined the effects of the plastic lid of the culture dish, irradiation distances (10, 20, and 25 cm), and different irradiation wavelengths (228 and 260 nm) during embryo culture for 7 days on the development and quality of porcine in vitro-fertilized embryos. None of the embryos cultured in dishes without plastic lids developed into blastocysts after irradiation with 228 nm UV-C. When porcine embryos were cultured in a culture dish with lids, the 228 nm UV-C irradiation decreased blastocyst formation rates of the embryos but not their quality, irrespective of the UV-C irradiation distance. Moreover, irradiation with 260 nm UV-C, even with plastic lids, had more detrimental effects on embryo development than irradiation with 228 nm UV-C. Investigation of the inactivating effects of UV-C irradiation at 228 nm and 260 nm on the growth of the bacteria and fungus showed that 260 nm UV-C reduced the viability to a greater extent than 228 nm UV-C. Moreover, the disinfection efficacy for the bacteria increased when the irradiation duration increased and the distance decreased. In conclusion, porcine embryos can develop into blastocysts without loss of quality even after continuous long-duration irradiation (7 days) with 228 nm UV-C, which can inactivate the growth of bacteria and the tested fungus; however, the development rate of the embryo is reduced.

Shedding a light on ultraviolet-C technologies in the hospital environment

Ultraviolet (UV)-C light for disinfection has experienced a surge in popularity since the outbreak of COVID-19. Currently, many different UV-C systems, with varied properties that impact disinfection performance, are available on the market. Therefore this review aims to bundle the available information on UV-C disinfection to obtain an overview of its advantages, disadvantages, and performance-influencing parameters. A literature search was performed using the snowball search method in Google Scholar and PubMed with the following keywords: UV-C disinfection, UV-C dose, UV-C light source, UV-C repair mechanism, UV-C photoreactivation, and UV-C disinfection standards. The main parameters of UV-C disinfection are wavelength, dose, relative humidity, and temperature. There is no consensus about their optimal values, but, in general, light at a high dose and a spectrum of wavelengths containing 260 nm is preferred in an environment at room temperature with low relative humidity. This light can be generated by mercury-vapour, light-emitting diode (LED), pulsed-xenon, or excimer lamps. Multiple factors are detrimental to disinfection performance such as shadowing, a rough surface topography, a high level of contamination, repair mechanisms, and the lack of standardization. Also, there are health and safety risks associated with the UV-C technology when used in the proximity of people. UV-C disinfection systems have promising features and the potential to improve in the future. However, clarifications surrounding the different parameters influencing the technologies' effectiveness in hospital environment are needed. Therefore UV-C disinfection should currently be considered for low-level rather than high-level disinfection.

Optimized parameters for effective SARS-CoV-2 inactivation using UVC-LED at 275 nm

The spread of SARS-CoV-2 infections and the severity of the coronavirus disease of 2019 (COVID-19) pandemic have resulted in the rapid development of medications, vaccines, and countermeasures to reduce viral transmission. Although new treatment strategies for preventing SARS-CoV-2 infection are available, viral mutations remain a serious threat to the healthcare community. Hence, medical devices equipped with virus-eradication features are needed to prevent viral transmission. UV-LEDs are gaining popularity in the medical field, utilizing the most germicidal UVC spectrum, which acts through photoproduct formation. Herein, we developed a portable and rechargeable medical device that can disinfect SARS-CoV-2 in less than 10 s by 99.9%, lasting 6 h. Using this device, we investigated the antiviral effect of UVC-LED (275 nm) against SARS-CoV-2 as a function of irradiation distance and exposure time. Irradiation distance of 10-20 cm, < 10 s exposure time, and UV doses of > 10 mJ/cm2 were determined optimal for SARS-CoV-2 elimination (≥ 99.99% viral reduction). The UVC-LED systems have advantages such as fast-stabilizing intensity and insensitivity to temperature, and may contribute to developing medical devices capable of containing SARS-CoV-2 infection. By demonstrating SARS-CoV-2 inactivation with very short-term UVC-LED irradiation, our study may suggest guidelines for securing a safer medical environment.

Retention and Inactivation of Quality Indicator Bacteria Using a Photocatalytic Membrane Reactor

The development of effective disinfection treatment processes is crucial to help the water industry cope with the inevitable challenges resulting from the increase in human population and climate change. Climate change leads to heavy rainfall, flooding and hot weather events that are associated with waterborne diseases. Developing effective treatment technologies will improve our resilience to cope with these events and our capacity to safeguard public health. A submerged hybrid reactor was used to test the efficiency of membrane filtration, direct photolysis (using ultraviolet-C low-pressure mercury lamps, as well as ultraviolet-C and ultraviolet-A light-emitting diodes panels) and the combination of both treatment processes (membrane filtration and photolysis) to retain and inactivate water quality indicator bacteria. The developed photocatalytic membranes effectively retained the target microorganisms that were then successfully inactivated by photolysis and advanced oxidation processes. The new hybrid reactor could be a promising approach to treat drinking water, recreational water and wastewater produced by different industries in small-scale systems. Furthermore, the results obtained with membranes coated with titanium dioxide and copper combined with ultraviolet-A light sources show that the process may be a promising approach to guarantee water disinfection using natural sunlight.

Non-thermal Processing Technologies for Dairy Products: Their Effect on Safety and Quality Characteristics

Thermal treatment has always been the processing method of choice for food treatment in order to make it safe for consumption and to extend its shelf life. Over the past years non-thermal processing technologies are gaining momentum and they have been utilized especially as technological advancements have made upscaling and continuous treatment possible. Additionally, non-thermal treatments are usually environmentally friendly and energy-efficient, hence sustainable. On the other hand, challenges exist; initial cost of some non-thermal processes is high, the microbial inactivation needs to be continuously assessed and verified, application to both to solid and liquid foods is not always available, some organoleptic characteristics might be affected. The combination of thermal and non-thermal processing methods that will produce safe foods with minimal effect on nutrients and quality characteristics, while improving the environmental/energy fingerprint might be more plausible.

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.

Review of air disinfection approaches and proposal for thermal inactivation of airborne viruses as a life-style and an instrument to fight pandemics

COVID-19 (Coronavirus Disease 2019) pandemic highlighted the importance of air biosecurity because SARS-CoV-2 is mainly transmitted from person to person via airborne droplets. Preventing infectious droplets from entering the body is one of the best ways to protect against infection. This paper reviews the transmission patterns of airborne pathogens and air disinfection methods. A particular emphasis is put on studies devoted to the thermal inactivation of viruses. These reviews reveal that air heat treatment has not been seriously considered as a possible air disinfection approach. Simple calculations show that the energy input required for thermal disinfection of human's air daily consumption is almost the same as for daily water consumption (by heat treatment from room temperature to 100 °C). Moreover, it is possible to organize a continuous heat recovery from the air already heated during disinfection to the inlet air, thus significantly increasing the energy efficiency. Therefore, I propose a solution for the thermal inactivation of airborne pathogens based on air heating and its subsequent cooling in a heat exchanger with heat recovery. Such a solution could be used to create mobile personal and stationary indoor air disinfectors, as well as heating, ventilation, and air conditioning systems. Thermal disinfection of air to breathe might one day be part of people's daily life like thermal disinfection of drinking water. Aside from limiting infectious disease transmission, thermal inactivation might be the basis for developing inhaled vaccines using thermally inactivated whole pathogens.

Study on the Light Field Regulation of UVC-LED Disinfection for Cold Chain Transportation

In this paper, the pain point that cold chain transportation urgently needs for an efficient disinfection method is pointed out. Thus, this work aims at solving the problems and improving the disinfection efficiency in cold chain transportation. While Ultraviolet-C (UVC) irradiation is an effective method by which to kill viruses, it is difficult to apply the commonly used UVC-LED disinfection light source to ice-covered cold chain transportation due to its uneven light field distribution. Thus, the light field regulation of UVC-LED disinfection for cold chain transportation is studied. A UVC-LED chip with a wavelength of 275 nm was used as a light source, and parallel light was obtained by collimating lenses. Then, microlens array homogenization technology was used to shape the UVC light into a uniform light spot, with an energy space uniformity rate of 96.4%. Moreover, a simulation was conducted to compare the effects of the ice layer on the absorption of UVC light. Finally, an experiment was carried out to verify that the disinfection efficiency can be increased nearly by 30% with the proposed system by disinfecting E. coli (Escherichia coli), and the results indicate that the proposed system is an effective disinfection solution during cold chain transportation.

UV Light Application as a Mean for Disinfection Applied in the Dairy Industry

Thermal treatment is the most popular decontamination technique used in the dairy industry to ensure food protection and prolong shelf life. But it also causes nutrient and aroma degradation, non-enzymatic browning, and organoleptic changes of dairy products. Non-thermal solutions, on the other hand, have been extensively explored in a response to rising market demand for more sustainable and safe goods. For a long time, the use of ultraviolet (UV) light in the food industry has held great promise. Irradiation with shortwave UV light has excellent germicidal properties, which can destroy a variety of microbial pathogens (for example bacteria, fungi, molds, yeasts, and viruses), at low maintenance and installation costs with minimal use of energy to preserve food without undesirable effects of heat treatment. The purpose of this review is to update the studies made on the possibilities of UV-C radiation while also addressing the essential processing factors involved in the disinfection. It also sheds light on the promise of UV light-emitting diodes (UV-LEDs) as a microbial inactivation alternative to conventional UV lamps.

Effects of Combined Aerosolization with Ultraviolet C Light-Emitting Diode on Enterohemorrhagic Escherichia coli and Staphylococcus aureus Attached to Soft Fresh Produce

Washing soft fresh produce such as strawberries, baby leaves, and sliced onions with sanitizing agents is challenging due to their fragile texture. Thus, treatments like aerosolization using slightly acidic electrolyzed water (SAEW) and ultraviolet C light-emitting diode (UVC LED) irradiation may be good alternatives. In the present study, the reduction effects of a combined treatment of aerosolization using SAEW and UVC LED irradiation on enterohemorrhagic Escherichia coli (EHEC) and Staphylococcus aureus attached to strawberries, baby leaves, and sliced onions were investigated. The behaviours of EHEC and S. aureus, moisture loss, colour measurement, and visual appearance were also analyzed at 10 and 15 °C for 7 days. The reduction effect of the combined treatment with 100 SAEW and UVC LED was higher (0.53–0.92 log CFU g⁻¹) than a single aerosolization treatment (0.11–0.41 log CFU g⁻¹), regardless of samples or pathogens. A greater effect on EHEC and S. aureus reduction was observed in strawberries (0.74 and 0.92 log CFU g⁻¹) than in baby leaves (0.62 and 0.53 log CFU g⁻¹) and sliced onions (0.55 and 0.62 log CFU g⁻¹). The combined treatment further reduced the EHEC and S. aureus populations in strawberries during 7 days of storage at 10 and 15 °C. However, the EHEC and S. aureus populations were maintained in baby leaves and sliced onions at 10 °C for 7 days. Additionally, the greatest effect on the maintenance of colour and appearance was obtained in the combined treatment. Since the combined treatment reduces EHEC and S. aureus populations and preserves visual quality, it could be expected to extend the shelf life of soft fresh produce at the retailer stage of the supply chain.

Bactericidal effect of ultraviolet C light-emitting diodes: Optimization of efficacy toward foodborne pathogens in water

The elimination of bacterial pathogens from water using ultraviolet C light-emitting diodes (UVC-LEDs) is a critical technology in terms of hygiene and sanitation. This technology has several advantages, such as low energy consumption, no heating requirements, and high effectiveness. Although several studies have reported the bactericidal effect of UVC-LEDs, little information is available on their bactericidal effect on water reservoirs contaminated with microorganisms. Therefore, the aim of this study was to optimize the bactericidal effects of UVC-LED irradiation, particularly at a wavelength of 278 nm, against major foodborne gram-positive and gram-negative pathogenic bacteria, such as Escherichia coli, Staphylococcus aureus, Bacillus cereus, Salmonella Typhimurium, and Listeria monocytogenes. The efficiency of the bactericidal effect of UVC-LED irradiation was determined based on three variables: exposure time (A, 0-60 min), stirring speed (B, 0-100 rpm), and volume of water (C, 400-1200 mL). To optimize the conditions, the operation of the designed model and results analysis were carried out using Box-Behnken design (BBD) and response surface method (RSM). The final conditions optimized for an effective bactericidal activity included a 60 min exposure time, a 100 rpm stirring speed, and 400 mL of liquid volume. Furthermore, the validation of the optimized model using the predicted values was calculated by the program, which was conducted by matching the actual values within standard deviations. The present study revealed that the optimization of a UVC-LED irradiation model is a promising approach for effectively controlling the contamination of water reservoirs by bacterial pathogens.

UV-C LED Irradiation Reduces Salmonella on Chicken and Food Contact Surfaces

Ultraviolet (UV-C) light-emitting diode (LED) light at a wavelength of 250–280 nm was used to disinfect skinless chicken breast (CB), stainless steel (SS) and high-density polyethylene (HD) inoculated with Salmonella enterica. Irradiances of 2 mW/cm² (50%) or 4 mW/cm² (100%) were used to treat samples at different exposure times. Chicken samples had the lowest Salmonella reduction with 1.02 and 1.78 Log CFU/cm² (p ≤ 0.05) after 60 and 900 s, respectively at 50% irradiance. Higher reductions on CB were obtained with 100% illumination after 900 s (>3.0 Log CFU/cm²). Salmonella on SS was reduced by 1.97 and 3.48 Log CFU/cm² after 60 s of treatment with 50% and 100% irradiance, respectively. HD showed a lower decrease of Salmonella, but still statistically significant (p ≤ 0.05), with 1.25 and 1.77 Log CFU/cm² destruction for 50 and 100% irradiance after 60 s, respectively. Longer exposure times of HD to UV-C yielded up to 99.999% (5.0 Log CFU/cm²) reduction of Salmonella with both irradiance levels. While UV-C LED treatment was found effective to control Salmonella on chicken and food contact surfaces, we propose three mechanisms contributing to reduced efficacy of disinfection: bacterial aggregation, harboring in food and work surface pores and light absorption by fluids associated with CB.

Ultraviolet germicidal irradiation (UVGI) for in-duct airborne bioaerosol disinfection: Review and analysis of design factors

The rapid increase in global cases of COVID-19 illness and death requires the implementation of appropriate and efficient engineering controls to improve indoor air quality. This paper focuses on the use of the ultraviolet germicidal irradiation (UVGI) air purification technology in HVAC ducts, which is particularly applicable to buildings where fully shutting down air recirculation is not feasible. Given the poor understanding of the in-duct UVGI system regarding its working mechanisms, designs, and applications, this review has the following key research objectives:•Identifying the critical parameters for designing a UVGI system, including the characterization of lamp output, behavior of the target microbial UV dose-response, and evaluation of the inactivation performance and energy consumption.•Elucidating the effects of environmental factors (air velocity, air temperature, and humidity) on the UVGI system design parameters and optimization of the in-duct UVGI design.•Summarizing existing UVGI system designs in the literature and illustrating their germicidal and energy performance in light of COVID-19 mitigation.

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.

Control Measures of Pathogenic Microorganisms and Shelf-Life Extension of Fresh-Cut Vegetables

We investigated the combined effect of using slightly acidic electrolyzed water (SAEW), ultrasounds (US), and ultraviolet-C light-emitting diodes (UV-C LED; 275 nm) for decreasing pathogenic Escherichia coli and Staphylococcus aureus (SEA) in fresh-cut vegetables, including carrots, celery, paprika, and cabbage. Survival of pathogenic E. coli and SEA and quality properties of fresh-cut vegetables at 5 and 15 °C for 7 days were also investigated. When combined treatment (SAEW + US + UV-C LED) was applied to fresh-cut vegetables for 3 min, its microbial reduction effect was significantly higher (0.97~2.17 log CFU/g) than a single treatment (p < 0.05). Overall, the reduction effect was more significant for SEA than for pathogenic E. coli. At 5 °C, SAEW + US and SAEW + US + UV-C LED treatments reduced populations of pathogenic E. coli and SEA in all vegetables. At 15 °C, SAEW + US + UV-C LED treatment inhibited the growth of both pathogens in carrot and celery and extended the shelf life of fresh-cut vegetables by preventing color changes in all vegetables. Although the effects of treatments varied depending on the characteristics of the vegetables and pathogens, UV-C LED can be suggested as a new hurdle technology in fresh-cut vegetable industry.

Efficacy of light-emitting diodes emitting 395, 405, 415, and 425 nm blue light for bacterial inactivation and the microbicidal mechanism

We investigated the bactericidal effects against Escherichia coli O157:H7 of light-emitting diodes (LEDs) emitting blue light of four different peak wavelengths ranging from 395 to 425 nm in water. Furthermore, we investigated inactivation in the presence of reactive oxygen species (ROS) scavengers to elucidate the contribution of bacterial inactivation. An aluminum chamber was constructed and coated in carbon to block exterior light, and a single blue light LED with a rear heat sink was attached to the chamber lid. Effective inactivation of the pathogen was observed for all blue light LED irradiation at 305, 405, 415, and 425 nm. The log-linear with shoulder and tail model and log-linear model described the survival of the bacteria after blue light LED treatments. Not just the effects of ROS but also photophysical effects were shown with the addition of mannitol, a ROS scavenger. The integrity of the cell membrane was damaged regardless of the presence of ROS, which indicates that photophysical effects were sufficient to induce damage to the cell membrane. In addition, activity of succinate-coenzyme Q reductase, which participates in respiratory metabolism to generate energy, decreased in the absence of ROS and decreased further in the presence of ROS.

Antimicrobial Effect of UVC Light-Emitting Diodes against Saccharomyces cerevisiae and Their Application in Orange Juice Decontamination

ABSTRACT

UVC light-emitting diodes (UVC-LEDs) are a novel eco-friendly alternative source of UV light. This study evaluated the inactivation and membrane damage of spoilage yeast Saccharomyces cerevisiae by UVC-LEDs and their application in orange juice pasteurization. The results demonstrated that the antimicrobial effect of UVC-LED treatment against S. cerevisiae was enhanced by increased radiation dose. When the dose of UVC-LED radiation was 1,420 mJ/cm2, the population of S. cerevisiae in yeast extract peptone dextrose broth was reduced by 4.86 log CFU/mL. Through scanning electron microscopy and fluorescent staining, the structure and function of plasma membrane was observed to be severely damaged by UVC-LED treatment. The inactivation efficacy of UVC-LEDs against S. cerevisiae in orange juice also increased with increasing radiation dose. Radiation at 1,420 mJ/cm2 greatly reduced S. cerevisiae in orange juice by 4.44 log CFU/mL and did not induce remarkable changes in pH, total soluble solids, titratable acidity, and color parameters. However, the total phenolic content in orange juice was found to be significantly decreased by UVC-LEDs. These findings contribute to a better comprehension of UVC-LED inactivation and provide theoretical support for its potential application in fruit and vegetable juice processing.

HIGHLIGHTS

Inactivation of Bacillus anthracis and Bacillus atrophaeus spores on different surfaces with ultraviolet light produced with a low-pressure mercury vapor lamp or light emitting diodes

AIMS

To obtain quantitative efficacy data of two ultraviolet light (UVC) technologies for surface inactivation of Bacillus anthracis Ames and Bacillus atrophaeus spores.

METHODS AND RESULTS

Spores were deposited onto test coupons and controls of four different materials, via liquid suspension or aerosol deposition. The test coupons were then exposed to UVC light from either a low-pressure mercury vapor lamp or a system comprised of light emitting diodes, with a range of dosages. Positive controls were held at ambient conditions and not exposed to UVC light. Following exposure to UVC, spores were recovered from the coupons and efficacy was quantified in terms of log₁₀ reduction (LR) in the number of viable spores compared to that from positive controls.

CONCLUSIONS

Decontamination efficacy varied by material and UVC dosage (efficacy up to 5·7 LR was demonstrated). There was no statistical difference in efficacy between the two species or between inoculation methods. Efficacy improved for the LED lamp at lower relative humidity, but this effect was not observed with the mercury vapor lamp.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study will be useful in determining whether UVC could be used for the inactivation of B. anthracis spores on different surface types.

Inactivation of Listeria and E. coli by Deep-UV LED: effect of substrate conditions on inactivation kinetics

Irradiation with deep-ultraviolet light-emitting diodes (DUV LEDs) is emerging as a low energy, chemical-free approach to mitigate microbial contamination, but the effect of surface conditions on treatment effectiveness is not well understood. Here, inactivation of L. innocua and E. coli ATCC25922, as examples of Gram-positive and Gram-negative bacteria, respectively, by DUV LED of 280 nm wavelength was studied. Surface scenarios commonly encountered in environmental, clinical or food processing environments were used: nutrient rich surfaces, thin liquid films (TLF), and stainless steel surfaces (SS). DUV LED exposure achieved 5-log reduction for both strains within 10 min in most scenarios, except for TLF thicker than 0.6 mm. Inactivation kinetics in TLF and on dry SS followed the Weibull model (0.96 ≤ R2 ≤ 0.99), but the model overestimated inactivation by small-dose DUV on wet SS. Confocal microscopy revealed in situ that bacteria formed a dense outer layer at the liquid-air interface of the liquid droplet, protecting the cells inside the droplet from the bactericidal DUV. This resulted in lower than anticipated inactivation on wet SS at small DUV doses, and deviation from the Weibull model. These findings can be used to design effective DUV LED disinfection strategies for various surface conditions and applications.

Moving from the traditional paradigm of pathogen inactivation to controlling antibiotic resistance in water - Role of ultraviolet irradiation

Ultraviolet (UV) irradiation has proven an effective tool for inactivating microorganisms in water. There is, however, a need to look at disinfection from a different perspective because microbial inactivation alone may not be sufficient to ensure the microbiological safety of the treated water since pathogenic genes may still be present, even after disinfection. Antibiotic resistance genes (ARGs) are of a particular concern since they enable microorganisms to become resistant to antibiotics. UV irradiation has been widely used for disinfection and more recently for destroying ARGs. While UV lamps remain the principal technology to achieve this objective, UV light emitting diodes (UV-LEDs) are novel sources of UV irradiation and have increasingly been reported in lab-scale investigations as a potential alternative. This review discusses the current state of the applications of UV technology for controlling antibiotic resistance during water and wastewater treatment. Since UV-LEDs possess several attractive advantages over conventional UV lamps, the impact of UV-LED characteristics (single vs combined wavelengths, and operational parameters such as periodic or pulsed and continuous irradiation, pulse repetition frequencies, duty cycle), type of organism, and fluence response, are critically reviewed with a view to highlighting the research needs for addressing future disinfection challenges. The energy efficiency of the reported UV processes is also evaluated with a focus on relating the findings to disinfection efficacy. The greater experience with UV lamps could be useful for investigating UV-LEDs for similar applications (i.e., antibiotic resistance control), and hence identification of future research directions.