Pulsed UV Light Research Articles

Inactivation of Salmonella spp. in wheat flour by 395 nm pulsed light emitting diode (LED) treatment and the related functional and structural changes of gluten.

Salmonella spp. is one of the top foodborne pathogens associated with low-moisture foods and they exhibit significant resistance to conventional thermal treatments. UV light pulses emitted from light emitting diode (LED) has shown antimicrobial potential in high-moisture foods and water. However, limited information is available about the antimicrobial potential of UV light with different wavelengths, including 395 nm in low-moisture foods. The objectives of this study were to investigate the antimicrobial potential of 395 nm pulsed LED light in wheat flour and the resulting quality changes. This study demonstrated a maximum 2.91 log reduction of Salmonella cocktail in wheat flour treated with 395 nm pulsed LED for 60 min in a semi-closed system. Oxidation occurred in wheat flour after 30 and 60 min exposure to the 395 nm LED, which subsequently led to bleaching, and polymerization of gluten components through disulphide linkage. The water holding capacity of gluten was reduced by oxidation, and the contents of secondary structures were altered significantly after pulsed LED treatment, but the rheological properties were not deteriorated. The disulfide bond formation naturally happens during dough formation and the oxidation triggered by pulsed LED treatment may play a role on accelerating this process. The 395 nm pulsed LED treatment could be a promising decontamination technology for wheat flour with an additional benefit of bleaching of the flour without chemicals. INDUSTRIAL RELEVANCE: A number of foodborne outbreaks and recalls have been related to low-moisture foods in these decades and recently several outbreaks were reported due to the occurrence of Salmonella in wheat flour. However, it is difficult to solve this problem through conventional thermal approaches because of the increased thermal resistance of Salmonella at low water activity environment. The emerging LED light source can produce light with monochromatic wavelengths without the use of mercury vapor lamps. It also has high durability, low heat generation, and is relatively easy to be adapted in an existing production line. Therefore, there is a great potential of using certain UV wavelengths emitted from LED to disinfect the low-moisture foods in food industries. To the best of our knowledge, no research was conducted on decontamination of wheat flour by using LEDs and only limited studies are available on the influence of pulsed LED treatment on food quality. The aim of this study was to explore the possibility of using 395 nm pulsed LED treatment as a novel tool for decontamination of Salmonella in a low-moisture food product (wheat flour) with industrial feasibility, and investigate the influence of the pulsed LED treatment on quality changes in the product.

Transformation of Radiation-Induced Molecular Point Defects and Color Centers in LiF Crystals under Influence of Light

The influences of UV light and integral light pulses from lamps on γ-irradiated LiF crystals with impurities of hydroxyl and magnesium ions have been investigated. The optical absorption and luminescence of color centers in different bleaching stages are studied depending on the crystal exposure time under UV light or on the number of light pulses. IR spectra of molecular hydrogen-bonded complexes and hydroxyl ions in different bleaching stages are presented. The transformation of strong hydrogen-bonded complexes under illumination into complexes with weak hydrogen bond (and vice versa) is studied. It is shown how molecular hydrogen-bonded complexes involving hydroxyl affect the transformation of color centers during the crystal bleaching.

Inactivation of Escherichia coli and Salmonella in liquid egg white by pulsed UV light and its effects on quality

AbstractThis study evaluated the pulsed UV light treatment for the inactivation of Escherichia coli K12 and Salmonella Enteritidis in liquid egg white. Three parameters (treatment time, volume of liquid egg white, and distance from the sample to the pulse UV strobe) have been optimized for log reductions of microorganisms using response surface methodology. The maximum log reductions obtained after 40 s of treatment time at a 5 cm of distance (the energy dose equals 45.6 J/cm2) were 1.28 log CFU/ml of E. coli K12 and 1.98 log CFU/ml of S. Enteritidis in 5 ml of fresh liquid egg white. A significant temperature increase of the egg white sample (from 24 to 70°C) was observed at the extreme treatment condition (5 cm, 40 s). Quality evaluations indicate that pulsed UV light does not change foaming ability or foam stability of liquid egg white. However, the changes in pH, lipid oxidation, turbidity, and color of the egg white were correlated with the intensity of the treatment.Practical applicationsHeat pasteurization is currently being used to decontaminate liquid egg white. However, alternative methods are desired to improve decontamination as well as maintain the quality of liquid egg white. This study demonstrated the potential of pulsed UV light for the inactivation of pathogens in liquid egg white.

Low-Power Graphene/ZnO Schottky UV Photodiodes with Enhanced Lateral Schottky Barrier Homogeneity.

The low-power, high-performance graphene/ZnO Schottky photodiodes were demonstrated through the direct sputter-growth of ZnO onto the thermally-cleaned graphene/SiO2/Si substrate at room temperature. Prior to the growth of ZnO, a thermal treatment of the graphene surface was performed at 280 °C for 10 min in a vacuum to desorb chemical residues that may serve as trap sites at the interface between graphene and ZnO. The device clearly showed a rectifying behavior with the Schottky barrier of ≈0.61 eV and an ideality factor of 1.16. Under UV illumination, the device exhibited the excellent photoresponse characteristics in both forward and reverse bias regions. When illuminating UV light with the optical power density of 0.62 mW/cm2, the device revealed a high on/off current ratio of >103 even at a low bias voltage of 0.1 V. For the transient characteristics upon switching of UV light pulses, the device represented a fast and stable photoresponse (i.e., rise time: 0.16 s, decay time: 0.19 s). From the temperature-dependent current–voltage characteristics, such an outstanding photoresponse characteristic was found to arise from the enhanced Schottky barrier homogeneity via the thermal treatment of the graphene surface. The results suggest that the ZnO/graphene Schottky diode holds promise for the application in high-performance low-power UV photodetectors.

Lighting up the new order.

Irradiating a PbTiO3/SrTiO3 superlattice with ultrafast UV light pulses modifies elastic and electrostatic interactions, resulting in the formation of a stable complex 3D supercrystal.

Преобразования радиационно-наведенных молекулярных точечных дефектов и центров окраски в кристаллах LiF под воздействием света

The effect of UV light and light pulses of the integral light of lamps on γ-irradiated LiF crystals with impurities of hydroxyl ions and magnesium were investigated. The optical absorption and luminescence of color centers at different stages bleaching depending on the exposure time of the crystal under UV light or from the number of light pulses were studied. IR spectra of molecular complexes with hydrogen bond and hydroxyl ions at different stages of bleaching are present. The transformation of complexes with a strong hydrogen bond in complexes with a weak hydrogen bond, and vice versa under the action of light are shown. It is presented as molecular complexes with hydrogen bond affect transformations color centers in the process of crystal bleaching.

A quantitative study of the effect of flow on the photopolymerization of fibers.

Pulsed-UV light in the continuous flow of a photo-crosslinkable liquid can result in gelation and is a useful method to produce soft microfibers with uniform sizes. With modeling and experiments, we characterize some aspects of this fiber fabrication process. We model the spatial concentration profiles of radical species and molecular oxygen in the flow direction during light exposure, and predict the critical conditions for the onset of fiber formation and compare these predictions with experimental observations. We also characterize the different regimes of microfiber production (no polymerization, non-uniform fibers, and uniform microfibers), qualitatively characterize the rigidity of the fibers, and demonstrate that we can predictably control the length of the produced microfibers for a range of process parameters.

Drying of mangoes (Mangifera indica L.) applying pulsed UV light as pretreatment

High-intensity pulsed UV light is a non-thermal treatment used in the sanitization of fruits. As a secondary effect to sanitization, the energy of the pulses is absorbed by the fruit and converted into internal energy, which results in partial evaporation of the water of the fruit. In this work, we have applied high-intensity pulsed UV light as a pretreatment for convective air-drying evaluating its advantages and disadvantages on the drying process and nutritional quality of the dried product. Mangoes were subjected to pulses of UV light and dried in a convective oven-drier. The pulsed UV light pretreatment reduced the water content in the samples but did not affect the kinetics or apparent water diffusivity of the subsequent drying process. The concentration of vitamin C and carotenoids in dried mangoes subjected to fluences between 3.6 and 10.8J/cm2 in the pretreatment were between 10 and 40% higher than the untreated dried mango. The concentration of vitamins B1, B3 and B5 increased by 10 to 25% in dried mangoes subjected to fluences between 3.6 and 7.2J/cm2, in comparison with the untreated dried mango. Vitamin B6 was highly affected by pulsed UV light decreasing by 40 to 50% in the pretreated mangoes.

Inactivation efficiency of Bacillus endospores via modified flow-through PUV treatment with comparison to conventional LPUV treatment

Water is a fragile resource, consequently there is a pressing need to develop sustainable environmental-friendly disinfection technologies. This constitutes the first study to compare efficacy of continuous low-pressure UV (LPUV) to that of pulsed UV light (PUV) for UV disinfection performance in flow-through water systems. Bacillus endospores were used as these are frequently deployed as biodosimeters for drinking water UV reactor validation protocols. Results showed a PUV system output of 2,052 mJ/cm2 (energy below 300 nm) was required for a 2 log inactivation of B.pumilus endospores, whereas a lower LPUV system output of 12 mJ/cm2 produced a similar level of disinfection. Measurements of dose incident to the samples (which were 10.75 cm from the PUV light source) showed supplementation of cultivation media with manganese sulphate monohydrate (MnSO4.H2O) employed to enhance the rate of endospore formation for propagation was shown to increase the UV resistance of different Bacillus spp. to both irradiation approaches (P < 0.05). Conventional LPUV light that is commonly-used by the drinking water industry is a reliable and superior approach to PUV which requires substantial modification for effective disinfection of continuous flow-through water. Caution must also be exercised when manipulating media formulation to propagate endospores as this may lead to inconsistencies in reporting efficacy of intervention treatments with implications for validation and environmental evaluation.

Degradation kinetics of anthocyanin and physicochemical changes in fermented turnip juice exposed to pulsed UV light

In this study, the effects of pulsed UV (PUV) light on the degradation kinetics of anthocyanins and physicochemical properties of turnip juice were investigated. PUV light was applied to turnip juice at 3 different distances (5, 8, 13cm) from the quartz window of the xenon lamp for 5 different times (5, 15, 30, 45, 60s). The pH, total acidity (% lactic acid), monomeric anthocyanin content, color density, hue, brightness, and percent color components (yellow, red, and blue) of turnip juice changed significantly after PUV-light treatments at each level. The maximum degradation of anthocyanin after PUV-light treatments was found to be about 63%. The anthocyanin degradation, brightness, yellow and blue color (%) increased, while red color (%) decreased with longer treatment time and shorter distance. The degradation of monomeric anthocyanins in turnip juice exposed to PUV light was described by the Weibull model (R2 0.982-0.998, RMSE 0.087-0.133) more accurately than the first-order kinetics (R2 0.906-0.992, RMSE 0.071-0.192).

Resistance of Listeria monocytogenes to Stress Conditions Encountered in Food and Food Processing Environments.

Listeria monocytogenes is a human food-borne facultative intracellular pathogen that is resistant to a wide range of stress conditions. As a consequence, L. monocytogenes is extremely difficult to control along the entire food chain from production to storage and consumption. Frequent and recent outbreaks of L. monocytogenes infections illustrate that current measures of decontamination and preservation are suboptimal to control L. monocytogenes in food. In order to develop efficient measures to prevent contamination during processing and control growth during storage of food it is crucial to understand the mechanisms utilized by L. monocytogenes to tolerate the stress conditions in food matrices and food processing environments. Food-related stress conditions encountered by L. monocytogenes along the food chain are acidity, oxidative and osmotic stress, low or high temperatures, presence of bacteriocins and other preserving additives, and stresses as a consequence of applying alternative decontamination and preservation technologies such high hydrostatic pressure, pulsed and continuous UV light, pulsed electric fields (PEF). This review is aimed at providing a summary of the current knowledge on the response of L. monocytogenes toward these stresses and the mechanisms of stress resistance employed by this important food-borne bacterium. Circumstances when L. monocytogenes cells become more sensitive or more resistant are mentioned and existence of a cross-resistance when multiple stresses are present is pointed out.

Pulse UV light effect on microbial biomolecules and organic pollutants degradation in aqueous solutions

This study present assessed the effect of UV pulsed light (PL) on microbial and organic pollutants using two spiral lamps were used, i.e., PL1 and PL2 lamps, with wavelength cut-offs of 190 and 240 nm, respectively. Overall, our study demonstrated that pulsed UV light impacts several microbial biomolecules and degrades polycyclic aromatic hydrocarbons (PAHs) in aqueous solution. In microbial inactivation by PL2, temporary changes of bacterial cellular components, specifically proteins, were observed, but the compositional changes of bacteria that were exposed to PL1 were permanent due to ozonolysis. PL1 irradiation caused greater deactivation of the bacteria than PL2 irradiation due to the generation of ozone. The higher efficacy of PL1 in terms of membrane disruption, reduction of respiration rate, and reduction of growth rate was due to the production of ozone during the irradiation period. The bacteria that were irradiated with both PL lamps regrew due to photoreactivation, such as an enzymatic DNA-repair mechanism.The PAH degradation kinetics indicate that higher molecular weights degraded faster than those with lower molecular weights. For both lamps, the degradation of naphthalene and fluorene was first order, whereas second order for pyrene and anthracene. Any effect of ozonolysis on the PAH degradation rates was not apparent, which indicated that photolysis was the primary degradation pathway. PAH solutions treated with both pulsed UV lamps did not result in a toxicity effect on the bacteria.

Reductions of Listeria monocytogenes on cold-smoked and raw salmon fillets by UV-C and pulsed UV light

Abstract Salmon is the food most frequently reported in the RASFF (Rapid Alert System for Food and Feed) database in conjunction with Listeria monocytogenes and consumption of cold-smoked salmon have led to severe outbreaks of listeriosis infections. UV-C and pulsed UV light were investigated for their ability to reduce L. monocytogenes on salmon. Cold-smoked and raw salmon were spiked with a mix of ten L. monocytogenes strains (104 CFU/sample) and subsequently exposed to UV-C light (0.0075–0.6 J/cm2) or high intensity pulsed UV light (1.3–10.8 J/cm2). Reductions of L. monocytogenes on smoked salmon were 0.7–1.3 log, depending on the fluence. Corresponding reductions for raw salmon muscle side and skin side were 0.2–0.9 log and 0.4–1.1 log, respectively. Generally, reductions using UV-C and pulsed UV light were within the same range, but with some treatments statistically different. L. monocytogenes surviving UV treatments on smoked and raw salmon grew at the same rate as controls during storage at 4 °C, but reached the levels of the controls 13 and 7 days later, respectively. No sensory changes were detected in UV-C treated (0.05 J/cm2) smoked salmon. Industrial relevance Due to the lack of critical control points in salmon production, it is not possible to ensure products that are consistently free from L. monocytogenes in the absence of mitigation strategies. Taking into account the reported generally low levels of L. monocytogenes on contaminated salmon, UV treatments should be considered important tools for the industry to contribute to lower prevalence and levels of Listeria. The present work on microbial and quality effects of UV-C and pulsed UV light treatments performed under industry relevant conditions on raw and cold-smoked salmon provides important information to the salmon industry for implementation of UV-light as risk reducing mitigation tools. This has key relevance for industry and consumers and will contribute to enhanced food safety, reduction of costly recalls and longer shelf-life.

Adaptation of a visible wavelength fluorescence microplate reader for discovery of near-infrared fluorescent probes.

We present an inexpensive, generalizable approach for modifying visible wavelength fluorescence microplate readers to detect emission in the near-infrared (NIR) I (650-950 nm) and NIR II (1000-1350 nm) tissue imaging windows. These wavelength ranges are promising for high sensitivity fluorescence-based cell assays and biological imaging, but the inaccessibility of NIR microplate readers is limiting development of the requisite, biocompatible fluorescent probes. Our modifications enable rapid screening of NIR candidate probes, using short pulses of UV light to provide excitation of diverse systems including dye molecules, semiconductor quantum dots, and metal clusters. To confirm the utility of our approach for rapid discovery of new NIR probes, we examine the silver cluster synthesis products formed on 375 candidate DNA strands that were originally designed to produce green-emitting, DNA-stabilized silver clusters. The fast, sensitive system developed here discovered DNA strands that unexpectedly stabilize NIR-emitting silver clusters.

Ultrahigh-Density Spin-Polarized H and D Observed via Magnetization Quantum Beats.

We measure nuclear and electron spin-polarized H and D densities of at least 10^{19} cm^{-3} with ∼10 ns lifetimes, from the photodissociation of HBr and DI with circularly polarized UV light pulses. This density is ∼6 orders of magnitude higher than that produced by conventional continuous-production methods and, surprisingly, at least 100 times higher than expected densities for this photodissociation method. We observe the hyperfine quantum beating of the H and D magnetization with a pickup coil, i.e.,the respective 0.7 and 3ns periodic transfer of polarization from the electrons to the nuclei and back. The 10^{19} cm^{-3} spin-polarized H and D density is sufficient for laser-driven ion acceleration of spin-polarized electrons, protons, or deuterons, the preparation of nuclear-spin-polarized molecules, and the demonstration of spin-polarized D-T or D-^{3}He laser fusion, for which a reactivity enhancement of ∼50% is expected.

Rapid Photoactuation of a DNA Nanostructure using an Internal Photocaged Trigger Strand.

A reconfigurable DNA nano-tweezer is reported that can be switched between a closed and open state with a brief pulse of UV light. In its initial state, the tweezer is held shut using a hairpin with a single-stranded poly-A loop. Also incorporated in the structure is a poly-T trigger strand bearing seven photocaged residues. Upon illumination with 365 nm light, the cages are removed and the trigger strand hybridizes to the loop, opening the tweezer and increasing the distance between its arms from 4 to 18 nm. This intramolecular process is roughly 60 times faster than adding an external trigger strand, and provides a mechanism for the rapid interconversion of DNA nanostructures with light.

Rapid Photoactuation of a DNA Nanostructure using an Internal Photocaged Trigger Strand

AbstractA reconfigurable DNA nano‐tweezer is reported that can be switched between a closed and open state with a brief pulse of UV light. In its initial state, the tweezer is held shut using a hairpin with a single‐stranded poly‐A loop. Also incorporated in the structure is a poly‐T trigger strand bearing seven photocaged residues. Upon illumination with 365 nm light, the cages are removed and the trigger strand hybridizes to the loop, opening the tweezer and increasing the distance between its arms from 4 to 18 nm. This intramolecular process is roughly 60 times faster than adding an external trigger strand, and provides a mechanism for the rapid interconversion of DNA nanostructures with light.

Using the Transient Response of WO₃ Nanoneedles under Pulsed UV Light in the Detection of NH₃ and NO₂.

Here we report on the use of pulsed UV light for activating the gas sensing response of metal oxides. Under pulsed UV light, the resistance of metal oxides presents a ripple due to light-induced transient adsorption and desorption phenomena. This methodology has been applied to tungsten oxide nanoneedle gas sensors operated either at room temperature or under mild heating (50 °C or 100 °C). It has been found that by analyzing the rate of resistance change caused by pulsed UV light, a fast determination of gas concentration is achieved (ten-fold improvement in response time). The technique is useful for detecting both oxidizing (NO2) and reducing (NH3) gases, even in the presence of different levels of ambient humidity. Room temperature operated sensors under pulsed UV light show good response towards ammonia and nitrogen dioxide at low power consumption levels. Increasing their operating temperature to 50 °C or 100 °C has the effect of further increasing sensitivity.

ИССЛЕДОВАНИЕ МИКОБАКТЕРИЦИДНОЙ АКТИВНОСТИ ИМПУЛЬСНОГО УЛЬТРАФИОЛЕТОВОГО ИЗЛУЧЕНИЯ СПЛОШНОГО СПЕКТРА

The article presents the experimental studies results of continuous spectrum pulsed UV light mycobactericidal activity against the laboratory strain of Mycobacterium terrae and clinical strains of Mycobacterium tuberculosis with multiple and extensive drug resistance. A pulsed xenon lamp of a mobile “Alfa-01” unit for air decontamination was used as ultraviolet light source. The experiments showed high activity of pulsed UV light against all studied strains, which does not depend on the distance to the treated surface (up to 4 m). The efficiency of contaminated surfaces disinfection reached 100%. Exposing contaminated objects to pulsed xenon UV lamps’ light leads to multiple molecular genetic changes in DNA macromolecules with complete loss of drug resistance to rifampicin and partial loss of drug resistance to isoniazid.

Photoactivatable Sensors for Detecting Mobile Zinc.

Fluorescent sensors for mobile zinc are valuable for studying complex biological systems. Because these sensors typically bind zinc rapidly and tightly, there has been little temporal control over the activity of the probe after its application to a sample. The ability to control the activity of a zinc sensor in vivo during imaging experiments would greatly improve the time resolution of the measurement. Here, we describe photoactivatable zinc sensors that can be triggered with short pulses of UV light. These probes are prepared by functionalizing a zinc sensor with protecting groups that render the probe insensitive to metal ions. Photoinduced removal of the protecting groups restores the binding site, allowing for zinc-responsive changes in fluorescence that can be observed in live cells and tissues.