UV-C Dose Research Articles

Impact of UV-C Assisted Drying Treatment on the Quality of Malaysian Stingless Bee Honey

Stingless bee honey (SBH) has been the focus of various drying studies with the aim of lowering the moisture content to an acceptable limit of less than 20%. The low moisture level of SBH has been found to slow yeast development and hinder the fermentation process, thereby prolonging its shelf-life. Conventionally, SBH is treated using thermal treatment to lower its moisture content. Due to issues with quality degradation of thermal-treated SBH, other alternatives are being explored. Non-thermal treatment, namely ultraviolet (UV-C) assisted drying, has been proposed in this study with the expectation of replacing conventional heat treatment. The UV-C closed system, when properly employed, will provide enough radiation energy (below 40°C) to evaporate the moisture bound in the honey. Hence, this study was aimed at determining and correlating the effects of the UV-C assisted drying process on the quality of UV-C treated SBH. The experiment was carried out on SBH (Heterotrigona itama) under UV-C treatment with the stated parameters; wavelength: 254 nm, power: 7 W, UV-C dose: 8 mJ/cm2, thickness of SBH: 3 mm for 0, 30, 50, 75, and 120 minutes in a controlled environment (35 ± 5% relative humidity and 25 ± 5 °C temperature). The results of this study showed that the moisture level of SBH was below the critical moisture content of 20%, with the lowest moisture content recorded at 17.42% after 120 minutes of UV-C treatment time (moisture loss: 3.5%) and the highest moisture content of 18.40% after 30 minutes of treatment time (moisture loss: 2.21%). However, the value of 5-HMF obtained in this study was significantly high (above 80 mg/ kg), might be due to the high content of fructose to glucose ratio in SBH. Nevertheless, while it has been demonstrated that UV-C assisted drying was be able to lower the moisture content of SBH, further study is necessary to evaluate its effectiveness without compromising on the quality of SBH.

Systematical Investigations on Disinfection Effectiveness of Far-UVC (222 nm) irradiation: From Laboratory Study to Field Tests

The spread of pathogenic microorganisms in public spaces poses a great threat to human health. Far-UVC irradiation is regarded as an efficient method for inactivating most pathogenic microorganisms. Nevertheless, most of the studies on it have been done in laboratory, and there is still little knowledge about the disinfection effectiveness of far-UVC irradiation in real life. Here, systematic investigations were conducted to shed light on the disinfection effectiveness of far-UVC irradiation with laboratory studies and field tests in a real operating public lift cabin. The results of the laboratory study demonstrated that far-UVC irradiation can markedly promote the inactivation of the selected 7 types of microorganisms (including bacteria, viruses and fungus species) on steel surface compared to that on the glass surface, due to the synergistic effect of direct and reflected far-UVC light. This improvement was identified in the field test by employing the far-UVC device for disinfecting the surfaces of the lift cabin which are mostly made of stainless steel. Furthermore, the long-term field test of about 4 months also suggested that both environmental temperature and relative humidity (RH) affect the far-UVC disinfection effectiveness, where the best inactivation efficiency (99.9%) on the surface of lift button and handrail was achieved in the environmental temperature range of 23.5-25.5°C and the RH range of 60-70% at a low UVC dose of 5.2 mJ/cm2. In addition, >99.9% of airborne bacteria were inactivated in a chamber at a far-UVC dose of 15 mJ/cm2, showing a better performance of far-UVC for air disinfection compared to other technologies. This study systematically investigates the performance of far-UVC irradiation for surface and air disinfection in an actual environment, which provides helpful guidance for controlling the spread of pathogenic microorganisms in public spaces, especially in the ongoing COVID-19 pandemic.

Efficacy of single pass UVC air treatment for the inactivation of coronavirus, MS2 coliphage and Staphylococcus aureus bioaerosols

There is strong evidence that SARS-CoV-2 is spread predominantly by airborne transmission, with high viral loads released into the air as respiratory droplets and aerosols from the infected subject. The spread and persistence of SARS-CoV-2 in diverse indoor environments reinforces the urgent need to supplement distancing and PPE based approaches with effective engineering measures for microbial decontamination – thereby addressing the significant risk posed by aerosols. We hypothesized that a portable, single-pass UVC air treatment device (air flow 1254 L/min) could effectively inactivate bioaerosols containing bacterial and viral indicator organisms, and coronavirus without reliance on filtration technology, at reasonable scale. Robust experiments demonstrated UVC dose dependent inactivation of Staphylococcus aureus (UV rate constant (k) = 0.098 m2/J) and bacteriophage MS2, with up to 6-log MS2 reduction achieved in a single pass through the system (k = 0.119 m2/J). The inclusion of a PTFE diffuse reflector increased the effective UVC dose by up to 34% in comparison to a standard Al foil reflector (with identical lamp output), resulting in significant additional pathogen inactivation (1-log S. aureus and MS2, p < 0.001). Complete inactivation of bovine coronavirus bioaerosols was demonstrated through tissue culture infectivity (2.4-log reduction) and RT-qPCR analysis – confirming single pass UVC treatment to effectively deactivate coronavirus to the limit of detection of the culture-based method. Scenario-based modelling was used to investigate the reduction in risk of airborne person-to-person transmission based upon a single infected subject within the small room. Use of the system providing 5 air changes per hour was shown to significantly reduce airborne viral load and maintain low numbers of RNA copies when the infected subject remained in the room, reducing the risk of airborne pathogen transmission to other room users. We conclude that the application of single-pass UVC systems (without reliance on HEPA filtration) could play a critical role in reducing the risk of airborne pathogen transfer, including SARS-CoV2, in locations where adequate fresh air ventilation cannot be implemented.

Physical, Chemical and Microbiological Properties during Storage of Red Prickly Pear Juice Processed by a Continuous Flow UV-C System

The effects of pH (3.6 and 7.0) and irradiation UV-C dose irradiation (0, 9.81, 15.13, and 31.87 mJ/cm2) on the physicochemical properties and natural microbiota of red prickly pear juice were evaluated during processing and storage. Thermal treatments were used as the control applying high temperatures for a short time (HTST 80 °C/30 s) or ultra-high temperature (UHT 130 °C/3 s). UV-C treatments applied to juices with both pHs inactivated coliforms and mesophiles with the same efficacy as thermal treatments. Yeasts and molds were inactivated at a dose of &gt;15.13 mJ/cm2 at both pHs. The UV-C doses showed no differences in betalains, polyphenols, or antioxidant activity. However, a decrease in these compounds was observed during storage. The lowest reductions in betacyanins (11.1–16.7%) and betaxanthins (2.38–10.22%) were obtained by UV-C treatment at pH 3.6. Thermal treatments (HTST and UHT) caused a reduction greater than UV-C irradiation in betacyanins, betaxanthins, polyphenols, and antioxidant activity after treatment. However, after storage at pH 3.6, the contents of these compounds reached those of the UV-C treatments, except for polyphenols. In specific pigments, betanin retention was highest at pH 3.6 (62.26–87.24%), and its retention decreases with UV-C dose increase and storage. The indicaxanthin retentions were higher (75.85–92.27%) than those of betanin, and the reduction was mainly due to storage. The physical properties (pH, acidity, and °Brix) were not affected by treatments, except for the color. The results suggest that a dose of 15.13 mJ/cm2 of a continuous UV-C system is a non-thermal alternative for the processing of red prickly pear juice at pH 3.6, preserving its properties.

Prompt Inactivation of Coronavirus Using a 280 nm Light-Emitting Diode Cluster Device.

Objective: We report on the development and characterization of a UV-C light-emitting diode (LED) 280 nm cluster prototype device designed for the rapid disinfection of SARS-CoV-2 coronaviruses. The device was evaluated against the Betacoronavirus mouse hepatitis virus-3 strain, and its virucidal capacity was probed as a function of different applied UV-C doses versus different situations concerning irradiation distances. Background: UV-C LEDs are light emitters that offer advantages over low-pressure mercury lamps, such as quasimonochromaticity, lower electrical power consumption, instant on/off with the instant full-power operation, unlimited on/off cycles for disinfection schemes, and a much longer lifetime operation, in addition to portability aspects, as well as UV-C LEDs do not contain heavy metal in its composition such as mercury, found in ultraviolet germicidal irradiation (UVGI) lamps. Results: This novel device reached a 99.999% elimination rate at a distance of 9 cm at all the tested irradiation times (dose dependence), demonstrating that it took only 30 sec to achieve this inactivation rate. Its virucidal effectivity in rapid virus inactivation was demonstrated. Conclusions: We conclude that the HHUVCS cluster device (λp = 280 nm) provides a rapid virucidal effect against the SARS-CoV-2 coronavirus. The current research should encourage further advances in UV-C LED-based devices designed for the inactivation of SARS-CoV-2 virus on surfaces, in air, and in liquids.

Autonomous Environment Disinfection Based on Dynamic UV-C Irradiation Map.

The COVID-19 pandemic has become a worldwide concern and has motivated the entire scientific community to join efforts to fight it. Studies have shown that SARS-CoV-2 remains viable onsurfaces for days, increasing the chances of human infection. Environmental disinfection is thus an important action to prevent the transmission of the virus. Despite the valuable contribution of the research community to the field of UV-C disinfection by robots, there still lacks a disinfection system that is fully autonomous and computes its trajectory in real-time and in unknown environments. To meet this need, we propose an autonomous UV-C disinfection strategy for indoor environments based on a dynamic Irradiation Map that indicates the amount of energy applied in each region. Our method was tested in different scenarios and compared with other disinfection strategies. Experiments show that our approach delivers better results, especially when targeting high ideal UV-C doses.

Hydroxyl-radical activated water for inactivation of Escherichia coli O157:H7, Salmonella and Listeria monocytogenes on germinating mung beans

The following reports on the generation of hydroxyl-radical activated water prepared by passing a hydrogen peroxide solution containing Fe(III) catalyst through a UV-C reactor. The activated water was subsequently evaluated for antimicrobial activity against Escherichia coli O157:H7 in suspension or when inoculated onto mung beans. Hydroxyl-radical generation was assessed through the oxidation of methylene blue when reacted with activated water prepared from solutions of different pH (4–10), UV-C dose (32–128 mJ/cm2), hydrogen peroxide (0–1000 mg/L) and Fe(III) concentration (0–100 mg/L). Methylene blue oxidation was associated with high concentrations of each reactant with a positive correlation with Fe(III) concentration. Inactivation curves of E. coli O157:H7 in activated water were diphasic with an initial slow rate that increased after 15 min contact time. In contrast to the methylene blue assay, the antimicrobial action of activated water was associated with high hydrogen peroxide (500 mg/mL) and low Fe(III) catalyst (1 mg/L) with no significant interaction with UV-C dose. Evidence would suggest that the mode-of-inactivation was through a radical propagation reaction that is rate-limited by the reduction of Fe (III) to Fe (II). Here, the initial activation process via UV-C illumination results in photo-reduction of Fe(III) and propagates the formation of hydroxyl-radicals. Fe(III) to Fe(II) cycling continues with oxidation of cell structures that ultimately leads to loss of viability due to accumulation of cellular damage. When activated water was used to soak mung beans inoculated with E. coli O157:H7 a 1 log reduction was obtained with a 19% increase in germinated beans and 8.5% higher sprout yield relative to controls. The oxidation reduction potential decreased from 477 mV to 288 mV and pH increased from 3.97 to 5.47, over the 24 h mung bean soak period. The reduction of Salmonella and Listeria monocytogenes on mung beans soaked in activated water was <1 log CFU/g with all three pathogens growing back over the sprouting period. From the results it can be concluded that activated water can enhance the germination of mung beans along with sprout yield but has limited capacity when applied alone as a seed disinfection method.

Short UV-C treatments extend the shelf-life of fresh-cut strawberries (Fragaria x ananassa Duch cv. Camarosa)

In recent years there has been a marked increase in the demand for fresh-cut fruit. Although these products have high user convenience, they are extremely perishable. Consequently, they must be marketed within a very short period. A number of studies have shown that brief UV-C irradiation prior to storage may reduce postharvest deterioration in whole fruit. Herein, we evaluated the influence of different UV-C dose and intensity combinations on the quality and shelf-life of fresh-cut strawberries. Fresh berries were cut in wedges and subjected to brief UV-C treatments having different combinations of radiation intensity (0, 9, or 36 W m-2) and dose (0, 2, or 4 kJ m-2). Treatments with a dosage of 4 kJ m-2 at an intensity of 36 W m-2 decreased decay, juice leakage, dehydration softening, and yeasts and mold counts. UV-C treated berries also scored better in freshness color and overall acceptability in consumer tests. The treatments did not affect the acidity, soluble solids, or phenolic compounds. Results suggest that short UV-C treatment could be useful to supplement cold storage, extending the shelf-life of fresh-cut strawberries.

Effect of high-dose 290 nm UV-B on resveratrol content in grape skins.

UV-C irradiation increases resveratrol content in grape skins, but it reaches a maximum at a certain UV-C dose. In contrast, UV-B has a weak resveratrol-enhancing effect at low doses, but it has not been investigated at high doses. In this study, we investigated the effect of high-dose UV-B on resveratrol contents in grape skins. Irradiation of Muscat Bailey A with 290 nm UV-B LED at 22500 and 225000 µmol m-2 increased the resveratrol contents in the grape skins by 2.1- and 9.0-fold, respectively, without significant increases in other phenolic compounds. The effect was also confirmed for 2 other cultivars: Shine Muscat and Delaware. Transcriptome analysis of the grape skins of Muscat Bailey A immediately after irradiation with UV-B at 225000 µmol m-2 showed that genes related to biotic and abiotic stresses were upregulated. Hence, it was suggested that high-dose UV-B irradiation induces a stress response and specifically activates resveratrol biosynthesis.

Rapid disinfection of radiology treatment rooms using an autonomous ultraviolet germicidal irradiation robot

BackgroundUltraviolet germicidal irradiation (UVGI) technologies have emerged as a promising adjunct to manual cleaning, however, their potential to shorten cleaning times remains unexplored. MethodsA <10-minute disinfection procedure was developed using a robotic UVGI platform. The efficacy and time to perform the UVGI procedure in a CT scan treatment room was compared with current protocols involving manual disinfection using biocides. For each intervention, environmental samples were taken at 12 locations in the room before and after disinfection on seven distinct occasions. ResultsThe mean UVC dose at each sample location was found to be 13.01 ± 4.36 mJ/cm2, which exceeded published UVC thresholds for achieving log reductions of many common pathogens. Significant reductions in microbial burden were measured after both UVGI (P≤.001) and manual cleaning (P≤.05) conditions, with the UVGI procedure revealing the largest effect size (r = 0.603). DiscussionThese results support the hypothesis that automated deployments of UVGI technology can lead to germicidal performance that is comparable with, and potentially better than, current manual cleaning practices. ConclusionsOur findings provide early evidence that the incorporation of automated UVGI procedures into cleaning workflow could reduce turnaround times in radiology, and potentially other hospital settings.

Adaptation of O157:H7 and non-O157 Escherichia coli strains in orange juice and subsequent resistance to UV-C radiation

This study assessed the acid-adaptation of pathogenic and non-pathogenic strains of Escherichia coli in orange juice and the microbial resistance to the subsequent UV-C radiation treatment. Nine Shiga toxin-producing E. coli (STEC) and one strain of a non-pathogenic surrogate E. coli were used in this study. Each E. coli strain was inoculated in orange juice, following pre-exposure during 0, 1, 2, and 3 h at 10 °C. Then, the inoculated juices with the ten different strains separately were exposed to 0 and 2 J/cm2 of UV-C radiation. The D value (i.e., the UV-C dose in J/cm2 required to cause a one-log reduction in the target microorganism) was calculated. Further, the resistance coefficient [RC; i.e., the ratio between the D-values for the control condition (D0h) and each pre-exposure tested time (D1h,D2h, D3h)] were determined. The results indicated that the resistance of E. coli was influenced by the pre-exposure period in the orange juice, with increased resistance to UV-C observed for periods >2 h. Furthermore, the sensitivity of cells to subsequent UV-C treatment was found to be strain-dependent. The results may allow the development of more reliable UV-C radiation processes for orange juice processing aiming the inactivation of pathogenic E. coli.

Ultraviolet-C Irradiation, Heat, and Storage as Potential Methods of Inactivating SARS-CoV-2 and Bacterial Pathogens on Filtering Facepiece Respirators.

The arrival of SARS-CoV-2 to Aotearoa/New Zealand in February 2020 triggered a massive response at multiple levels. Procurement and sustainability of medical supplies to hospitals and clinics during the then upcoming COVID-19 pandemic was one of the top priorities. Continuing access to new personal protective equipment (PPE) was not guaranteed; thus, disinfecting and reusing PPE was considered as a potential alternative. Here, we describe part of a local program intended to test and implement a system to disinfect PPE for potential reuse in New Zealand. We used filtering facepiece respirator (FFR) coupons inoculated with SARS-CoV-2 or clinically relevant multidrug-resistant pathogens (Acinetobacter baumannii Ab5075, methicillin-resistant Staphylococcus aureus USA300 LAC and cystic-fibrosis isolate Pseudomonas aeruginosa LESB58), to evaluate the potential use of ultraviolet-C germicidal irradiation (UV-C) or dry heat treatment to disinfect PPE. An applied UV-C dose of 1000 mJ/cm2 was sufficient to completely inactivate high doses of SARS-CoV-2; however, irregularities in the FFR coupons hindered the efficacy of UV-C to fully inactivate the virus, even at higher UV-C doses (2000 mJ/cm2). Conversely, incubating contaminated FFR coupons at 65 °C for 30 min or 70 °C for 15 min, was sufficient to block SARS-CoV-2 replication, even in the presence of mucin or a soil load (mimicking salivary or respiratory secretions, respectively). Dry heat (90 min at 75 °C to 80 °C) effectively killed 106 planktonic bacteria; however, even extending the incubation time up to two hours at 80 °C did not completely kill bacteria when grown in colony biofilms. Importantly, we also showed that FFR material can harbor replication-competent SARS-CoV-2 for up to 35 days at room temperature in the presence of a soil load. We are currently using these findings to optimize and establish a robust process for decontaminating, reusing, and reducing wastage of PPE in New Zealand.

Inactivation of Escherichia coli, Salmonella enterica and Listeria monocytogenes on apple peel and apple juice by ultraviolet C light treatments with two irradiation devices

Following the market trends, the consumption of fresh and cold-pressed juice in Europe is increasing. However, a primary concern – particularly in apple juice – is the related outbreaks caused by food-borne pathogens. One of the challenges is to find methods able to reduce pathogenic loads while avoiding deterioration of nutritional properties and bioactive compounds that occur in thermal pasteurization processes. In this study, the inactivation of Escherichia coli, Salmonella enterica and Listeria monocytogenes was evaluated under different ultraviolet C (UVC254nm) light treatments (up to 10,665.9 ± 28.1 mJ/cm2), in two different steps of the production chain (before and after juice processing): on apple peel discs and in apple juice. The systems proposed were a horizontal chamber with UVC254nm emitting lamps treating the product disposed at a distance of 12 cm, and a tank containing UVC254nm lamps and in which the product is immersed and agitated. Final reductions ranged from 3.3 ± 0.5 to 5.3 ± 0.4 logarithmic units, depending on the microorganism, matrix and used device. The survival curves were adjusted to Weibull and biphasic models (R2-adj ≥ 0.852), and UVC doses needed for the first decimal reduction were calculated, being lower for the apple peel discs (0.20 to 83.83 mJ/cm2) than they were for apple juice (174.60 to 1273.31 mJ/cm2), probably for the low transmittance of the apple juice compared to the surface treatment occurring on the peels. Within the treatments evaluated, the UVC254nm irradiation of apple peels immersed in water was the best option as it resulted in a reduction of the tested microorganisms of ca. 2–3 log units at lower UVC254nm doses (< 500 mJ/cm2) when compared to those occurring in apple peel treated with the UVC chamber and in juice. As contamination can proceed from apples, the sanitization of these fruit prior to juice production may be helpful in reducing the safety risks of the final product, reducing the drawbacks related to the poor transmittance of the fruit juices.

UVC, UVB and UVA susceptibility of Phi6 and its suitability as a SARS-CoV-2 surrogate.

For SARS-CoV-2 disinfection systems or applications that are based on UVC, UVB or UVA irradiation, it would be desirable to have a SARS-CoV-2 surrogate for tests and development, which does not require a laboratory with a high biosafety level. The bacteriophage Phi 6, an enveloped RNA virus like coronaviruses, is an obvious candidate for such a surrogate. In this study, UVC, UVB and UVA log-reduction doses for Phi6 are determined by plaque assay. Log-reduction doses for SARS-CoV-2 are retrieved from a literature research. Because of a high variability of the published results, median log-reduction doses are determined for defined spectral ranges and compared to Phi6 data in the same intervals. The measured Phi6 log-reduction doses for UVC (254 nm), UVB (311 nm) and UVA (365 nm) are 31.7, 980 and 14 684 mJ/cm2, respectively. The determined median log-reduction doses for SARS-CoV-2 are much lower, only about 1.7 mJ/cm2 within the spectral interval 251–270 nm. Therefore, Phi6 can be photoinactivated by all UV wavelengths but it is much less UV sensitive compared to SARS-CoV-2 in all UV spectral ranges. Thus, Phi6 is no convincing SARS-CoV-2 surrogate in UV applications.

Antarctic-derived yeasts: taxonomic identification and resistance to adverse conditions.

Antarctic harsh conditions favor the development of microbial adaptations. In this study, a molecular approach was applied to identify/refine the taxonomy of five yeasts isolated from different Antarctic samples, which were tested against ranges of temperature, UV radiations, salinity, and pH. Based on sequencing and phylogenetic analysis, strain CRM 1839 was confirmed as Naganishia sp., and strains CRM 1874, CRM 1565, CRM 2571, and CRM 2576 were identified as Goffeauzyma gilvescens, Goffeauzyma gastrica, Candida atlantica, and Camptobasidium sp., respectively, being this last one possibly a new species. Growth at different temperatures indicates that these yeasts are psychrotolerant, with the exception of Camptobasidium sp., which presents psychrophilic characteristics. G. gastrica recovered from marine sediment showed the best results of resistance to UV radiation, being able to grow even after the exposure to UVB dose of 9144 J/m² and UVC dose of 6102 J/m². C. atlantica isolated from glacier soil showed high cellular growth from 3 to 10% NaCl. The majority of the strains produced higher biomass at pH 7; nevertheless, G. gilvescens showed higher biomass production at pH 9. The studied Antarctic-derived yeasts have adaptations to extreme conditions, which makes them useful for biotechnological applications and studies of extremophiles.

Impact of ultraviolet-C and peroxyacetic acid against murine norovirus on stainless steel and lettuce

The aim of this study was to evaluate the efficacy of the representative method of physical (ultraviolet-C [UV-C] irradiation) and chemical disinfectant treatment (peroxyacetic acid, PAA) against murine norovirus (MNV-1) in suspension and on a food-contact surface (stainless steel) and food (lettuce). Stainless steel and lettuce displayed less than 1 log10 reduction at the highest UV-C doses. More than 1 log10 reduction was possible on stainless steel and lettuce treated with the highest concentration of PAA. For sequential treatment with UV-C doses of 0–600 mJ/cm2 and a fixed PAA concentration (75 ppm for 1, 3, and 5 min) on lettuce, the MNV-1 titer was significantly decreased with increased doses of UV-C (p < 0.05). However, sequential treatment did not show any synergistic effect on MNV-1 reduction in this study. Therefore, single UV or PAA treatment had effective virucidal activities on a fresh vegetable sample.

Effects of UV Radiation on the Chlorophyte Micromonas polaris Host-Virus Interactions and MpoV-45T Virus Infectivity.

Polar seas are under threat of enhanced UV-radiation as well as increasing shipping activities. Considering the ecological importance of marine viruses, it is timely to study the impact of UV-AB on Arctic phytoplankton host–virus interactions and also test the efficacy of ballast water (BW) UV-C treatment on virus infectivity. This study examined the effects of: (i) ecologically relevant doses of UV-AB radiation on Micromonas polaris RCC2258 and its virus MpoV-45T, and (ii) UV-C radiation (doses 25–800 mJ cm−2) on MpoV-45T and other temperate algal viruses. Total UV-AB exposure was 6, 12, 28 and 48 h (during the light periods, over 72 h total). Strongest reduction in algal growth and photosynthetic efficiency occurred for 28 and 48 h UV-AB treatments, and consequently the virus production rates and burst sizes were reduced by more than half (compared with PAR-only controls). For the shorter UV-AB exposed cultures, negative effects by UV (especially Fv/Fm) were overcome without impacting virus proliferation. To obtain the BW desired log−4 reduction in virus infectivity, a UV-C dose of at least 400 mJ cm−2 was needed for MpoV-45T and the temperate algal viruses. This is higher than the commonly used dose of 300 mJ cm−2 in BW treatment.

Pre-oxidation of spent lettuce wash water by continuous Advanced Oxidation Process to reduce chlorine demand and cross-contamination of pathogens during post-harvest washing

A continuous Photo-Fenton Advanced-Oxidation-Process (AOP) for reducing the chlorine-demand of spent lettuce wash water was developed based on the generation of hydroxyl-radicals from the UV-C degradation of hydrogen peroxide in the presence of ferric-catalyst. It was found that an interaction between UV-C and hydrogen peroxide or ferric-catalyst concentration was associated with high hydroxyl-radical generation as determined from the oxidation of methylene blue. The optimal AOP treatment was identified as 320 mJ/cm2 UV-C dose, 9.6 mg/L H2O2, and 9 mg/L ferric-catalyst. When the treatment was applied to simulated lettuce spent wash water (6.6 g romaine lettuce per liter of distilled water containing 100 mg bentonite; pH 6.9) the chlorine demand was reduced from 150 ppm to 130 ppm. The chlorination of AOP treated water did not result in a greater log reduction of pathogens (Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella) on lettuce but did reduce cross-contamination between batches during washing. The chlorinated byproducts formed in AOP treated water exhibited higher antimicrobial activity compared to untreated controls. Although the treatment was successful in reducing cross-contamination of lettuce batches the cytotoxicity of disinfection byproducts requires to be assessed.

Vapor-Phase Hydroxyl or Chlorine Radical Treatment for Inactivating Listeria monocytogenes on Mushrooms (Agaricus bisporus) without Negatively Affecting Quality or Shelf Life

Processes based on generating vapor-phase hydroxyl radicals or chlorine radicals were developed for inactivating Listeria monocytogenes on mushrooms without negatively affecting quality. Antimicrobial radicals were generated from the UV-C degradation of hydrogen peroxide or hypochlorite and ozone gas. Response surface modeling was used to identify the interaction among the operating parameters for the hydroxyl radical process: UV-C254nm intensity, hydrogen peroxide concentration, and ozone delivered. There was an inverse relationship between hydrogen peroxide concentration and UV-C intensity in terms of the log reduction of L. monocytogenes. The independent parameters for the chlorine radical process were hypochlorite concentration, pH, and UV-C intensity. From predictive models, the optimal hydroxyl radical treatment was found to be 5% (v/v) H2O2, 2.86 mW/cm2 UV-C intensity (total UV-C dose 144 mJ/cm2), and 16.5 mg of ozone. The optimal parameters for the chlorine radical process were 10 ppm of hypochlorite (pH 3.0), 11.0 mg of ozone, and 4.60 mW/cm2 UV-C intensity. When inoculated mushrooms were treated with the optimal hydroxyl radical and chlorine radical processes, the reduction of L. monocytogenes was found to be 2.42 ± 0.42 and 2.61 ± 0.30 log CFU, respectively, without any negative effects on mushroom quality (weight loss and Browning index during 14 days of storage at 4°C). These reductions were significantly greater than those from application of the individual elements of the radical processes and those in the control process, which used a 90-s dip in 1% (v/v) hydrogen peroxide. The study has demonstrated that hydroxyl radical and chlorine radical vapor-phase treatments are equally effective at inactivating L. monocytogenes on mushrooms and can be considered as a preventative control step.

Rapid, dose-dependent and efficient inactivation of surface dried SARS-CoV-2 by 254 nm UV-C irradiation

Background: The COVID-19 pandemic urges for cheap, reliable, and rapid technologies for disinfection and decontamination. One frequently proposed method is ultraviolet (UV)-C irradiation. UV-C doses necessary to achieve inactivation of high-titre SARS-CoV-2 are poorly defined.Aim: We investigated whether short exposure of SARS-CoV-2 to UV-C irradiation sufficiently reduces viral infectivity and doses necessary to achieve an at least 6-log reduction in viral titres.Methods: Using a box and two handheld systems designed to decontaminate objects and surfaces, we evaluated the efficacy of 254 nm UV-C treatment to inactivate surface dried high-titre SARS-CoV-2.Results: Drying for 2 hours did not have a major impact on the infectivity of SARS-CoV-2, indicating that exhaled virus in droplets or aerosols stays infectious on surfaces for at least a certain amount of time. Short exposure of high titre surface dried virus (3–5*10^6 IU/ml) with UV-C light (16 mJ/cm2) resulted in a total inactivation of SARS-CoV-2. Dose-dependency experiments revealed that 3.5 mJ/cm2 were still effective to achieve a > 6-log reduction in viral titres, whereas 1.75 mJ/cm2 lowered infectivity only by one order of magnitude.Conclusions: SARS-CoV-2 is rapidly inactivated by relatively low doses of UV-C irradiation and the relationship between UV-C dose and log-viral titre reduction of surface residing SARS-CoV-2 is nonlinear. Our findings emphasize that it is necessary to assure sufficient and complete exposure of all relevant areas by integrated UV-C doses of at least 3.5 mJ/cm2 at 254 nm. Altogether, UV-C treatment is an effective non-chemical option to decontaminate surfaces from high-titre infectious SARS-CoV-2.