Ultraviolet Inactivation Research Articles

Evaluating the Performance of UV Disinfection across the 222-365 nm Spectrum against Aerosolized Bacteria and Viruses.

Bioaerosols play a significant role in the transmission of many infectious diseases, especially in enclosed indoor environments. Ultraviolet (UV) disinfection has demonstrated a high efficacy in inactivating microorganisms suspended in the air. To develop more effective and efficient UV disinfection protocols, it is necessary to evaluate and optimize the effectiveness of UV disinfection against aerosolized bacteria and viruses across the entire UV spectrum. In this study, we evaluated the performance of UV disinfection across the UV spectrum, ranging from 222 to 365 nm, against aerosolized bacteria and viruses, including Escherichia coli, Staphylococcus epidermidis, Salmonella enterica, MS2, P22, and Phi6. Six commonly available UV sources, including gas discharge tubes and light-emitting diodes with different emission spectra, were utilized, and their performance in terms of inactivation efficacy, action spectrum, and energy efficiency was determined. Among these UV sources, the krypton chloride excilamp emitting at a peak wavelength of 222 nm was the most efficient in inactivating viral bioaerosols. A low-pressure mercury lamp emitting at 254 nm performed well on both inactivation efficacy and energy efficiency. A UV light-emitting diode emitting at 268 nm demonstrated the highest bacterial inactivation efficacy, but required approximately 10 times more energy to achieve an equivalent inactivation level compared with that of the krypton chloride excilamp and low-pressure mercury lamp. This study provides insights into UV inactivation on bioaerosols, which can guide the development of effective wavelength-targeted UV air disinfection technologies and may significantly help reduce bioaerosol transmission in public areas.

A novel Helicoverpa armigera Nucleopolyhedrovirus (HearNPV-IR18 isolate) formulation on hemocyte cultures of cotton bollworm (Helicoverpa armigera Hübner)

The Helicoverpa armigera nucleopolyhedrovirus (HearNPV) is the active ingrediant biopesticide used to manage larvae. However, the effectiveness of HearNPV is limited by ultraviolet (UV) radiation. This study was conducted to develop a new formulation of HearNPV that is more tolerant to UV without compromising its efficiency. A microencapsulated formulation of HearNPV was increase its resistance to UV. For this, the virus was produced using cell lines established from H. armigera hemocytes in two media (Grace’s and EX-CELL 420). The microencapsulated formulation consisted of two different formulas. Formula A included cotton seed kernel extract, boric acid, glycerol, egg white, Bran, and sugar and Formula B included sodium alginate, gelatin, molasses and starch. The results showed that the microencapsulated formulation B exhibited higher photostability with an efficacy (84. 7 ± 4 %) and an original activity remaining (OAR) of 91.31 ± 2. 9 % after 72 h of exposure to UV by 385 nm. The average percentage of OAR in control HearNPV and formulation A was 10. 22 ± 1. 8 % and 45. 33 ± 3. 6 % respectively, after 72 h of UV exposure, with no significant statistical differences between control and formulation A. The evaluated microencapsulation mixture B had good potential to protect HearNPVs microparticles against UV inactivation. Furthermore, in EX-CELL 420 medium, virulence of the HearNPV close to that of OBs grow in the insect, with a LC50 of 6.58 × 105 OBs/mL. Therefore, the current study aimed to establish a novel and more stable pathogenic formulation in order to manage the cotton bollworm in the field.

Transcription profiles and phenotype reveal global response of Staphylococcus aureus exposed to ultrasound and ultraviolet stressors

Ultrasound and ultraviolet light have good inactivation performance against pathogens in sewage. In this study, the inactivation mechanisms of 60 kHz ultrasound and ultraviolet radiation against Staphylococcus aureus (S. aureus) were studied from the perspectives of cell phenotype and transcriptome for the first time. The results showed that both ultrasound and ultraviolet treatments had adverse impacts on the cellular morphology of S. aureus to varying degrees at cellular level. The transcriptomic analysis revealed that there were 225 and 1077 differentially expressed genes (DEGs) in the ultrasound and ultraviolet treatments, respectively. The result revealed that both ultrasound and ultraviolet could interfere with the expression of the genes involved in ABC transporters, amino acid and fatty acid metabolism to influence the membrane permeability. Besides the membrane permeability, ultraviolet also could disturb the ATP synthesis, DNA replication and cell division through restraining the expression of several genes related to carbohydrate metabolism, peptidoglycan synthesis, DNA-binding/repair protein synthesis. Compared with the single inactivation pathway of ultrasound, ultraviolet inactivation of S. aureus is multi-target and multi-pathway. We believe that the bactericidal mechanisms of ultrasound and ultraviolet radiation presented by this study could provide theoretical guidance for the synergistic inactivation of pathogens in sewage by ultrasound and ultraviolet radiation in the future.

Interspecific Hybridization between Ganoderma lingzhi and G. resinaceum by PEG-Induced Double-Inactivated Protoplast Fusion

Ganoderma lingzhi is an important medicinal fungus, and it is particularly important to select strains with high yields and active substance contents. In this study, protoplasts of G. lingzhi were thermally inactivated to destroy intracellular enzyme proteins and preserve DNA. The DNA of G. resinaceum was damaged by ultraviolet (UV) radiation, and other components of the protoplasm except DNA were preserved. Then, the protoplast was induced using polyethylene glycol (PEG) for fusion. The results showed that the optimal thermal inactivation conditions for G. lingzhi were 30 min in a 45 °C water bath, and the optimal UV inactivation conditions for G. resinaceum were 70 s of irradiation using a 20 W UV lamp at a vertical distance of 15 cm. Antagonistic tests, internal transcribed space (ITS) and mitochondrial DNA identification, intersimple sequence repeat (ISSR) molecular markers and morphology were used to distinguish the parents from the fusants. Four true fusants were obtained, and the yield was 2.5%. The fruiting body yield of the fusants was significantly higher than that of G. lingzhi, and the polysaccharide and triterpene contents of the RAD-64 fusant were significantly higher than those of G. lingzhi. The results presented in this paper show that protoplast fusion technology can effectively improve G. lingzhi varieties and support the breeding of new varieties.

Wavelength dependence of ultraviolet light inactivation for SARS-CoV-2 omicron variants

Ultraviolet (UV) irradiation offers an effective and convenient method for the disinfection of pathogenic microorganisms. However, UV irradiation causes protein and/or DNA damage; therefore, further insight into the performance of different UV wavelengths and their applications is needed to reduce risks to the human body. In this paper, we determined the efficacy of UV inactivation of the SARS-CoV-2 omicron BA.2 and BA.5 variants in a liquid suspension at various UV wavelengths by the 50% tissue culture infection dose (TCID50) method and quantitative polymerase chain reaction (qPCR) assay. The inactivation efficacy of 220 nm light, which is considered safe for the human body, was approximately the same as that of health hazardous 260 nm light for both BA.2 and BA.5. Based on the inactivation rate constants determined by the TCID50 and qPCR methods versus the UV wavelength, the action spectra were determined, and BA.2 and BA.5 showed almost the same spectra. This result suggests that both variants have the same UV inactivation characteristics.

Possible repair of UV-damaged Spodoptera littoralis nucleopolyhedrovirus DNA via generation of mutant carrying photolyase gene with DNA repair activity

BackgroundBaculoviruses can be inactivated by ultraviolet (UV) light, which limits their application as an efficient biopesticide. In an attempt to enhance virus resistance to UV inactivation, a photolyase gene, isolated from Spodoptera litura granulovirus (SpliGV), was expressed in a photolyase deficient Spodoptera littoralis nucleopolyhedrovirus (SpliNPV) and the infectivity of recombinant virus expressing phr gene was determined after exposure to UV irradiation.ResultsExpression of the photolyase resulted in a fivefold resistance of virus occlusion bodies of the recombinant virus (vSpli-phr) compared to the wild type SpliNPV upon exposure to UV irradiation as measured by LC50 value when fed on S. littoralis neonate. Furthermore, the recombinant virus expressing phr showed a significant decrease in the time required for lethality than the control virus with about 22 h, as measured by ST50 value. Hence, expression of photolyase via vSpli-phr relatively may rescue the viral DNA damage caused by UV irradiation.ConclusionsThis study provided the evidence that the generated recombinant virus encoding a functioning photolyase, which may have implications for the development of a new generation of baculoviruses with enhanced insect pest management capabilities.

Time-dose reciprocity mechanism for the inactivation of Escherichia coli explained by a stochastic process with two inactivation effects

There is a great demand for developing and demonstrating novel disinfection technologies for protection against various pathogenic viruses and bacteria. In this context, ultraviolet (UV) irradiation offers an effective and convenient method for the inactivation of pathogenic microorganisms. The quantitative evaluation of the efficacy of UV sterilization relies on the simple time-dose reciprocity law proposed by Bunsen-Roscoe. However, the inactivation rate constants reported in the literature vary widely, even at the same dose and wavelength of irradiation. Thus, it is likely that the physical mechanism of UV inactivation cannot be described by the simple time-dose reciprocity law but requires a secondary inactivation process, which must be identified to clarify the scientific basis. In this paper, we conducted a UV inactivation experiment with Escherichia coli at the same dose but with different irradiances and irradiation durations, varying the irradiance by two to three orders of magnitude. We showed that the efficacy of inactivation obtained by UV-light emitting diode irradiation differs significantly by one order of magnitude at the same dose but different irradiances at a fixed wavelength. To explain this, we constructed a stochastic model introducing a second inactivation rate, such as that due to reactive oxygen species (ROS) that contribute to DNA and/or protein damage, together with the fluence-based UV inactivation rate. By solving the differential equations based on this model, the efficacy of inactivation as a function of the irradiance and irradiation duration under the same UV dose conditions was clearly elucidated. The proposed model clearly shows that at least two inactivation rates are involved in UV inactivation, where the generally used UV inactivation rate does not depend on the irradiance, but the inactivation rate due to ROS does depend on the irradiance. We conclude that the UV inactivation results obtained to date were simply fitted by one inactivation rate that superimposed these two inactivation rates. The effectiveness of long-term UV irradiation at a low irradiance but the same dose provides useful information for future disinfection technologies such as the disinfection of large spaces, for example, hospital rooms using UV light, because it can reduce the radiation dose and its risk to the human body.

Radiation source with enhanced virucide effectiveness based on a mixture of helium and iodine vapor

Subject of study. A source of spontaneous emission (a lamp) in the ultraviolet spectral range excited by a capacitive discharge was investigated. Iodine vapor and mixtures of iodine vapor with inert gases were used as the operating gas medium of the lamp. Conditions for enhancements in specific output parameters of the lamp emission were investigated. Excitation conditions under which the lamp emits predominantly at the iodine atomic line with a wavelength of 206.16 nm were determined. Aim of study. The primary aim of the study was to investigate the spectral and energy characteristics of the lamp based on the iodine vapor, which is promising for the development of a radiation source with enhanced virucidal effectiveness for ultraviolet disinfection of a human environment contaminated with pathogenic microorganisms including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Method. In this study, the composition and pressure of the operating medium were optimized. In addition, the excitation mode of the lamp emission was optimized by changing the repetition rate of voltage pulses. Main results. At a specific excitation power of approximately 1.3mW/cm3 and partial pressures of iodine vapor and helium of approximately 2.5 and 7 Torr, respectively, the line of an iodine atom with a wavelength of 206.16 nm dominates in the output lamp spectrum, and the specific emission power at the outer surface of the lamp tube is approximately 3mW/cm2. Practical significance. The emission of the investigated lamp is in the spectral range of 200–225 nm, which is promising in terms of developing technology for safe ultraviolet inactivation of pathogenic microorganisms including SARS-CoV-2.

Ultrafast-UV laser integrating cavity device for inactivation of SARS-CoV-2 and other viruses

Ultraviolet (UV) irradiation-based methods used for viral inactivation have provided an important avenue targeting severe acute respiratory-syndrome coronavirus-2 (SARS-CoV-2) virus. A major problem with state-of-the-art UV inactivation technology is that it is based on UV lamps, which have limited efficiency, require high power, large doses, and long irradiation times. These drawbacks limit the use of UV lamps in air filtering systems and other applications. To address these limitations, herein we report on the fabrication of a device comprising a pulsed nanosecond 266 nm UV laser coupled to an integrating cavity (LIC) composed of a UV reflective material, polytetrafluoroethylene. Previous UV lamp inactivation cavities were based on polished walls with specular reflections, but the diffuse reflective UV ICs were not thoroughly explored for virus inactivation. Our results show that LIC device can inactivate several respiratory viruses including SARS-CoV-2, at ~ 1 ms effective irradiation time, with > 2 orders of magnitude higher efficiency compared to UV lamps. The demonstrated 3 orders of magnitude cavity enhancement relative to direct exposure is crucial for the development of efficient real-time UV air and water purification systems. To the best of our knowledge this is the first demonstration of LIC application for broad viral inactivation with high efficiency.

Genotype-dependent kinetics of enterovirus inactivation by free chlorine and ultraviolet (UV) irradiation

Inactivation kinetics of enterovirus by disinfection is often studied using a single laboratory strain of a given genotype. Environmental variants of enterovirus are genetically distinct from the corresponding laboratory strain, yet it is poorly understood how these genetic differences affect inactivation. Here we evaluated the inactivation kinetics of nine coxsackievirus B3 (CVB3), ten coxsackievirus B4 (CVB4), and two echovirus 11 (E11) variants by free chlorine and ultraviolet irradiation (UV). The inactivation kinetics by free chlorine were genotype- (i.e., susceptibility: CVB5 < CVB3 ≈ CVB4 < E11) and genogroup-dependent and exhibited up to 15-fold difference among the tested viruses. In contrast, only minor (up to 1.3-fold) differences were observed in the UV inactivation kinetics. The differences in variability between the two disinfectants could be rationalized by their respective inactivation mechanisms: inactivation by UV mainly depends on the genomic size and composition, which was similar for all viruses tested, whereas free chlorine targets the viral capsid protein, which exhibited critical differences between genogroups and genotypes. Finally, we integrated the observed variability in inactivation rate constants into an expanded Chick-Watson model to estimate the overall inactivation of an enterovirus consortium. The results highlight that the distribution of inactivation rate constants and the abundance of each genotype are essential parameters to accurately predict the overall inactivation of an enterovirus population by free chlorine. We conclude that predictions based on inactivation data of a single variant or reference pathogen alone likely overestimate the true disinfection efficiency of free chlorine.

A sequential utilization of the UV-A (365 nm) fluence rate for disinfection of water, contaminated with Legionella pneumophila and Legionelladumoffii

Legionella species are the etiological agent of Legionnaires' disease, a pathology easily contracted from water circuits and by the inhalation of aerosol droplets. This bacterium mainly proliferates in water: Legionella pneumophila is the most commonly isolated specie in water environments and consequently in water system, although further Legionella species have frequently been isolated, including Legionella dumoffii. The simultaneous presence of the two species in the water system can therefore lead to the simultaneous infection of several people, giving rise to harmful outbreaks. Ultraviolet inactivation of waterborne microorganisms offers a rapid and effective treatment technique and recently is getting more attention mostly to eliminate unsafe level of contamination. To tackle the issue, the inactivation of the two species of Legionella spp., namely L. pneumophila and L. dumoffii, by means of UV-A light emitting diodes (UV-A LED) system is explored. We used a commercially available UV-A LED at 365 nm wavelength, and the UV-A dose is given incrementally to the Legionellae with a concentration of 106 CFU/mL in 0.9% NaCl (aq) solution. In this study, with a UV-A-dose of 1700 mJ/cm2, the log-reduction of 3-log (99.9% inactivation) for L. pneumophila and 2.1-log (99.1% inactivation) for L. dumoffii of the contaminated water are achieved. The Electrical Energy per Order (EEO) is evaluated and showed this system is more economic and efficient in comparison with UV-C and UV-B LEDs. Following the support of this preliminary study with additional tests, aiming to validate the technology, we expect this device may be installed in water plants such as cooling systems or any water purification station in either industrial or home scales to reduce the risk of this infectious disease, preventing consumers' health.

Mitigation of Airborne PRRSV Transmission with UV Light Treatment: Proof-of-Concept

Proper treatment of infectious air could potentially mitigate the spread of airborne viruses such as porcine reproductive and respiratory syndrome virus (PRRSV). The objective of this research is to test the effectiveness of ultraviolet (UV) in inactivating aerosolized PRRSV, specifically, four UV lamps, UV-A (365 nm, both fluorescent and LED-based), “excimer” UV-C (222 nm), and germicidal UV-C (254 nm), were tested. The two UV-C lamps effectively irradiated fast-moving PRRSV aerosols with short treatment times (&lt;2 s). One-stage and two-stage UV inactivation models estimated the UV doses needed for target percentage (%) reductions on PRRSV titer. UV-C (254 nm) dose needed for 3-log (99.9%) reduction was 19.43 and 2.44 mJ/cm2, respectively, based on one-stage and two-stage models. UV-C (222 nm) doses needed for a 3-log reduction 2.81 and 1.04 mJ/cm2, based on one-stage and two-stage models, respectively. However, the cost of 222 nm excimer lamps is still economically prohibitive for scaling-up trials. The UV-A (365 nm) lamps could not reduce PRRSV titers for tested doses up to 4.11 mJ/cm2. Pilot-scale or farm-scale testing of UV-C on PRRSV aerosols simulating barn ventilation rates are recommended based on its effectiveness and reasonable costs comparable to HEPA filtration.

Improving the microalgae inactivating efficacy of ultraviolet ballast water treatment in combination with hydrogen peroxide or peroxymonosulfate salt

Due to the increasing number of ecosystem invasions with the introduction of exogenous species via ballast water, the International Maritime Organization adopted the Ballast Water Convention (BWMC). The BWMC establishes standards for the concentration of viable organisms in a ballast water discharge. Ultraviolet (UV) irradiation is commonly used for treating ballast water; however, regrowth after UV irradiation and other drawbacks have been reported. In this study, improvement in UV treatment with the addition of hydrogen peroxide or peroxymonosulfate salt was investigated using the microalgae Tetraselmis suecica as the target organism. Results reported that each of these reagents added in a concentration of 10 ppm reduced the concentration of initial cells by more than 96%, increased the UV inactivation rate, and enabled reaching greater level of inactivation with the treatment. These improvements imply a reduction of the UV doses required for a consistent compliance with the BWMC standards.

Viricidal and bactericidal exciplex barrier-discharge lamps

A brief review is presented of investigations performed in 2002 – 2020 on ultraviolet inactivation of bacteria, vital cells, and viruses by using excilamps. The excilamp models that have been developed at the Institute of High-Current Electronics, SB RAS are briefly described. Scientific data acquired by now show that excilamps on KrCl*, KrBr*, and XeBr* molecules are an alternative to low-pressure mercury lamps with respect to optical parameters. These sources of optical radiation exhibit a bactericidal effect, and emission of KrCl and KrBr excilamps demonstrates viricidal action. The latter is actual due to expansion of coronavirus disease.

Peracetic acid (PAA) and low-pressure ultraviolet (LP-UV) inactivation of Coxsackievirus B3 (CVB3) in municipal wastewater individually and concurrently

Domestic wastewater (WW) contains a large number of pathogenic viruses that are not significantly reduced in most WW treatment processes and are found in high numbers in the effluent of conventionally disinfected WW. In this study, secondary WW effluent bench-scale disinfection efficacy experiments with two different peracetic acid (PAA) formulations (15 and 22% peracetic acid) and low-pressure ultraviolet irradiation (LP-UV) were carried out using Coxsackievirus B3 (CVB3) as a clinically relevant surrogate for enteric viruses and Escherichia coli (E. coli) as the disinfection efficacy control. Efficacy experiments were done in a test matrix of medium-pressure UV (MP-UV) decontaminated secondary WW effluent under representative PAA doses and LP-UV fluences used at wastewater treatment plants (WWTP). Membrane filtration technique was used to determine Log10 CFU reductions of E. coli and a tissue culture infectious dose 50% assay (TCID50) for Log10 TCID50 reduction of CVB3. The CVB3 proved to be quite resistant to PAA with ≤1 Log10 TCID50 reduction to concentrations ≤50 mg/L at a contact time of 15 min, and highly susceptible to LP-UV at 20 mJ/cm2. Concurrent use of both formulations of 3 mg/L PAA with 20 mJ/cm2 LP-UV achieved ∼4 Log10 TCID50 reduction. The E. coli results showed ˃5 Log10 CFU reductions at a contact time of 15 min with both 3 mg/L PAA formulations, 20 mJ/cm2 LP-UV treatment alone, and combined with both 1.5 mg/L PAA formulations. The E. coli efficacy data were consistent with that reported in the literature and showed to be comparable to conventional chlorine disinfection. The CVB3 efficacy data has shown that PAA alone may not be suitable for the reduction of enteric viruses in secondary wastewater effluent, but this is also the case for chlorine-based disinfectants. The results from this study showed that the use of PAA with LP-UV at reasonable concentrations (1.5 mg/L) and fluence (20 mJ/cm2) can significantly reduce the PAA use and meet wastewater disinfection goals for both E. coli and CVs. However, the concurrent use of PAA with LP-UV did not lead to significant synergy in disinfection efficacy in wastewater.

Aluminum based reflective nanolens arrays to improve the effectiveness of ultraviolet inactivation of Escherichia coli O157:H7 and Listeria monocytogenes in water and a sucrose solution.

Aluminum based reflective nanolens arrays were developed via a series of aluminum electropolishing and anodization steps with subsequent selective dissolution of anodic aluminum oxide (AAO). The diameter of nanolenses (d) on arrays can be controlled by altering electrolytes and voltages used for aluminum anodization. The d values of arrays produced by anodization in 0.3M oxalic acid at 40, 60, and 80V, and in 1.0M phosphoric acid at 100, 110, and 120V were 71.94, 121.90, and 161.53nm, and 220.16, 252.06, and 274.78nm, respectively. The effectiveness of UV (254nm) inactivation of Escherichia coli O157:H7 and Listeria monocytogenes at concentrations of 5-6 log CFU/mL in water and in a 10% (w/v) sucrose solution was improved using a nanolens array having a d value of 252.06nm.

The cluster model of ultraviolet disinfection explains tailing kinetics.

To develop a new mathematical model derived from first principles to define the kinetics of ultraviolet disinfection and to explain the phenomenon known as tailing. The theory presented interprets tailing as the result of photoprotection due to cumulative Mie scattering effects in clustered populations of micro-organisms. Mie scattering effects at ultraviolet wavelengths are used to compute a shielding constant for each micro-organism based on the average projected diameter. An intrinsic rate constant, hypothesized to be a characteristic property of the microbial genome alone, is computed. The cluster model is fitted to tailing data from 30 ultraviolet inactivation studies and results are compared with the classic two stage multihit model. The cluster model demonstrates a statistically significant improvement in the mean adjusted R2 values of the tested data sets (P<0·0001). Tailing in survival curves is the direct consequence of the Gaussian distribution of cluster sizes and the intrinsic rate constant is a real and critical parameter that defines ultraviolet susceptibility. The ultraviolet dose-response behaviour of micro-organisms can now be explained in terms of parameters that have physical meaning and provide deep insight into the disinfection process.

Use of 254 nm ultraviolet light for decontamination of fresh produce and wash water

Fresh produce has been identified as the transmission vehicle for many foodborne illness outbreaks every year. They could be contaminated by pathogens at any point within the farm-to-fork food chain. Washing is often used to remove dirt and pathogens on fresh produce. Moreover, an effective decontamination method is required for wash water to prevent cross-contamination. Our group developed a water-assisted ultraviolet (UV) decontamination system (WUV) which combined washing and UV treatments. We evaluated the influence of turbidity (0–100 NTU) and chemical oxygen demand (COD; 0–2500 ppm) on UV inactivation of Salmonella in simulated wash water with different produce extracts. In the worst condition tested (turbidity of 100 NTU and COD of 2500 ppm), Salmonella in simulated wash water could be eliminated by UV (23–28 mW/cm2; wavelength peak at 254 nm) in 90 s (>6 log CFU/mL reduction), indicating the potential of UV for fresh produce wash water disinfection. Within the ranges tested, the effectiveness of UV inactivation of Salmonella was significantly decreased with increasing COD, but not with turbidity. In addition, ultraviolet lamps were installed in different locations (above and/or in the washing tank).Three WUV configurations showed similar Salmonella reduction on blueberries (1.8–2.0 log) and tomatoes (2.4–2.9 log). However, the Overhead and Dual WUV configurations reduced significantly (P < 0.05) more Salmonella on lettuce than the Submersible WUV configuration.

Inactivation of Bacillus and Clostridium Spores in Coconut Water by Ultraviolet Light.

Bacterial spores are generally more resistant than vegetative bacteria to ultraviolet (UV) inactivation. The UV sensitivity of these spores must be known for implementing UV disinfection of low acid liquid foods. UV inactivation kinetics of bacterial spores in coconut water (CW) and distilled sterile water was studied. Populations of Bacillus cereus and Clostridium sporogenes dormant spores were reduced by more than 5.5 log10 at the UV-C photon fluence of 1142 μE·m-2 and 1919 μE·m-2 respectively. C. sporogenes spores showed higher UV-C resistance than B. cereus, with the photon fluence 300 μE·m-2 required for one log inactivation (D10) and 194 μE·m-2, respectively. No significant difference was observed in D10 values of spores suspended in the two fluid types (p > 0.05). The inactivation kinetics of microorganisms were described by log linear models with low root mean square error and high coefficient of determination (R2 > 0.98). This study clearly demonstrated that high levels of inactivation of bacterial spores can be achieved in CW. The baseline data generated from this study will be used to conduct spore inactivation studies in continuous flow UV systems. Further proliferation of the technology will include conducting extensive pilot studies.

Ultraviolet inactivation of bacteria and model viruses in coconut water using a collimated beam system.

This study investigated the effect of ultraviolet-C irradiation on the inactivation of microorganisms in coconut water, a highly opaque liquid food (1.01 ± 0.018 absorption coefficient). Ultraviolet-C inactivation kinetics of two bacteriophages (MS2, T1UV) and three surrogate bacteria (Escherichia coli, Salmonella Typhimurium, Listeria monocytogenes) in 0.1% (w/v) peptone and coconut water were investigated. Ultraviolet-C irradiation at 254 nm was applied to stirred samples, using a collimated beam device. A series of known ultraviolet-C doses (0-40 mJ cm-2) were applied for ultraviolet-C treatment except for MS2 where higher doses were delivered (100 mJ cm-2). Inactivation levels of all organisms were proportional to ultraviolet-C dose. At the highest dose of 40 mJ cm-2, three surrogates of pathogenic bacteria were inactivated by more than 5-log10 (p < 0.05) in 0.1% (w/v) peptone and coconut water. Results showed that ultraviolet-C irradiation effectively inactivated bacteriophage and surrogate bacteria in highly opaque coconut water. The log reduction kinetics of microorganisms followed log-linear and exponential models with higher R2 (>0.95) and low root mean square error values. The D10 values of 3, 5.48, and 4.58 mJ cm-2 were obtained from the inactivation of E. coli, S. Typhimurium, and L. monocytogenes, respectively. Models for predicting log reduction as a function of ultraviolet-C irradiation dose were found to be significant (p < 0.05). Fluid optics were the key controlling parameters for efficient microbial inactivation. Therefore, the ultraviolet-C dose must be calculated not only from the incident ultraviolet-C intensity but must also consider the attenuation in the samples. The results from this study imply that adequate log reduction of vegetative cells and model viruses is achievable in coconut water and suggested significant potential for ultraviolet-C treatment of other liquid foods.