Inactivation Efficiency Research Articles

Inactivation Efficiency of Bacillus atrophaeus Spores on Seeds of Barley, Wheat, Lupine and Rapeseed by Direct Cold Atmospheric Pressure Plasma

The objective of this study was to evaluate the antimicrobial effect of direct cold atmospheric plasma (CAPP) treatment for pre-harvest application using four different crop species: Hordeum vulgare L. (barley), Triticum aestivum L. (wheat), Brassica napus L. (rapeseed) and Lupinus angustifolius L. (lupine). The model bacterium Bacillus atrophaeus served as a proxy for spore-forming plant pathogens on the seed surface. After semi-dry inoculation of spores onto the seeds, treatment with two different plasma sources, a volume-dielectric barrier discharge and a corona discharge, and different exposure times was carried out. Subsequently, recovery of viable spores from the seeds’ surfaces was performed. Moreover, seed viability was determined based on maximum germination, as well as water contact angle as a measure for seed surface hydrophilicity. Direct CAPP treatment was efficient in reducing viable spores of B. atrophaeus with no significant differences between the plasma sources, reaching a mean inactivation of 1 log10 CFU/mL across all treatment times and crops species. Maximum germination of seeds was not negatively affected under any treatment condition. Seed hydrophilicity was increased for both plasma sources tested. Overall, this study provides valuable information on the efficiency of direct CAPP treatment of seeds with the purpose of seed hygienization with the premise of unaltered seed vitality and evaluates the potential application in comparison with previous investigated CAPP methods.

Enhanced photocatalytic properties of visible light-responsive ZnS/FeWO4 composites for degradation of tetracycline and Escherichia coli inactivation

The development of highly efficient visible light-driven photocatalysts for the removal of diverse pollutants is crucial for wastewater treatment. In this study, a series of ZnS/FeWO4 composites were prepared via a facile hydrothermal method combined with in situ calcination. The photocatalytic properties of the resulting ZnS/FeWO4 composites were evaluated for the degradation of tetracycline (TC) and the inactivation of Escherichia coli (E. coli), considering the environmental persistence and potential carcinogenicity of these pollutants. The optimized ZnS/FeWO4-1:2 photocatalyst demonstrated outstanding activity in the degradation of TC, achieving a degradation efficiency of 91.7 % (k = 0.0230 min⁻¹), which is significantly higher than that of pristine FeWO4 (67.5 %) and ZnS (53.4 %). Kinetic studies confirmed that the degradation process followed a pseudo-first-order kinetic model. Furthermore, the as-prepared photocatalyst exhibited excellent stability after five cycles. Additionally, the ZnS/FeWO4-1:2 composites showed potent inactivation efficiency, achieving approximately 96 % inactivation of 7.0 × 106 CFU/mL E. coli. These superior photocatalytic capabilities are attributed to the effective integration of FeWO4 with ZnS and the formation of optimal heterojunction structures. This incorporation leads to a delay in electron-hole recombination within the nanocomposites. Moreover, the enhancement mechanisms of photocatalytic TC degradation over ZnS/FeWO4-1:2 composites were discussed. The findings of this study provide valuable insights into the multi-application potential of ZnS/FeWO4-1:2 composites and demonstrate an effective approach to designing photocatalysts for wastewater treatment.

Light increases resistance of thylakoid membranes to thermal inactivation.

In the region of slightly acidic pH (рН 5.7), the manganese cluster in oxygen-evolving complex of photosystem II (PSII) is more resistant to exogenous reductants. The effect of such pH on the heat inactivation efficiency of the electron transport chain (O2 evolution and 2,6-dichlorophenolindophenol reduction) in PSII membranes and thylakoid membranes was investigated. Under thylakoid membranes illumination accompanied by lumen acidification, their resistance to heat inactivation increases. In the presence of protonophores, the rate of heat inactivation increases, which seems to be associated not with the protonophore mechanism, but with structural and/or functional changes in membranes. In PSII membrane preparations, the efficiency of the oxygen evolution inhibition at pH 5.7 is also lower than at pH 6.5. The role of reactive oxygen species in thermal inactivation of photosynthetic membranes was investigated using a lipophilic cyclic hydroxylamine ESR spin probe.

Improving gel properties of low-salt silver carp surimi through single-mode microwave-assisted processing

Surimi, a product derived from low-value fish, is widely used to produce high-value items such as imitation crabsticks and fish balls. However, surimi from freshwater fish like silver carp generally exhibits inferior gel properties compared to marine fish. This study investigated the effects of 915 MHz single-mode microwave-assisted processing on the gel properties of low-salt silver carp surimi. Traditional water bath processing served as the control for comparison. Gel strength, texture, water-holding capacity (WHC), whiteness, protein secondary structure, and microstructure, along with thermal processing efficiency for microbial inactivation were evaluated. The results demonstrated that single-mode microwave processing significantly improved gel properties compared to water bath processing. Compared with the optimal water bath treatment, the gel strength of microwave processed samples increased significantly from 479.32 g·cm to 821.74 g·cm, while WHC increased from 0.77 to 0.87. The microwave processed surimi exhibited a more uniform microstructure. Because it enhanced the dissolution and cross-linking of myofibrillar proteins, leading to superior gel formation characterized by a lower α-helix content (10.31%) and higher β-sheet content (61.70%). Furthermore, microwave processing achieved faster heating rates, reducing the time spent in the critical gel deterioration temperature range, thereby improving overall gel quality. Single-mode microwave-assisted gelation also provided better thermal processing uniformity and efficiency, achieving pasteurization standards. The study highlights the potential of 915 MHz single-mode microwave processing to produce high-quality, low-salt surimi products, meeting contemporary health and convenience demands. These findings offer valuable insights for the industrial application of single-mode microwave technology in surimi production, promoting the development of innovative processing techniques to enhance the quality of surimi-based food products.

Microwave-assisted CuO-modified porous ZnO nanosheet for photocatalytic degradation of organic pollutants and antibacterial inactivation

The present study investigated the development of a porous ZnO/CuO photocatalyst for photocatalytic dye degradation and antibacterial inactivation of bacteria. Porous ZnO nanosheets are prepared by calcinating inorganic-organic ZnS(en)0.5. Further, CuO was integrated on a porous ZnO nanosheet using the microwave (MW)-assisted synthesis technique. Additionally, the effect of CuO at different concentrations on the photocatalytic activity of CuO/ZnO was investigated. Under 1.5G light illumination, an optimized ZnO/CuO-5 photocatalyst exhibited higher degradation efficiencies of 99.3%, 98%, and 99% for orange II dye, methylene blue (MB), and Eosin-Y respectively. The optimized photocatalyst exhibited inactivation efficiencies of 98% and 90% towards Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria, after 3h. The enhanced photocatalytic activity was attributable to a porous structure, extended visible light responsiveness, and delayed electron-hole recombination in nanostructured CuO/ZnO photocatalysts. Moreover, radical scavenger tests confirmed that superoxide radicals (•O2−) accompanied most degradation, followed by holes (h+) as minor factors. Our work suggests a simple photocatalytic interfacial engineering technique based on porous ZnO/CuO nanostructures to decompose organic chemicals and inactivate microorganisms in wastewater sources.

Modelling of radiation and flow fields in in-duct ultraviolet germicidal irradiation systems with and without ribs

In-duct ultraviolet germicidal irradiation systems (ID-UVs) is a promising technology for the development of biosecure buildings. This study explored the Computational Fluid Dynamics (CFD) method for accurately predicting the inactivation efficiency of ID-UVs. The results showed that the setting of ‘Divisions’ is crucial to the accuracy of radiation field modelling, and 15 × 15 was considered to be a reasonable value in this study. In addition, residence time and deposition ratio are two crucial parameters determining the average UV dose (AD) received by microbial particles, thereby influencing the inactivation efficiency. For ID-UVs without ribs, the Renormalization Group (RNG) [Formula: see text] model largely overestimated these two parameters, while the Reynolds Stress Model (RSM) with correcting fluctuation velocity improved the predictive accuracy of AD by 10.0%. For ID-UVs with ribs, the RNG [Formula: see text] model overestimated the eddy size and AD by 28.6% and 12.0%, respectively. The RSM model provided results closer to the Large Eddy Simulation. Adding 0.10 H (H: duct height) ribs increased the inactivation efficiency for MS2 Bacteriophage by 19.0%–64.3%, with an additional pressure drop of only 3.3 Pa. These findings contributed to a reliable CFD framework and provided novel ideas for improving inactivation efficiency.

Electrochemical flow-through disinfection of Escherichia coli versus Staphylococcus aureus: Identifying impacts of flow patterns on efficiency

While Ti4O7 reactive electrochemical membrane (REM) treatment exhibits high efficiency in inactivating bacteria, it remains obscure about the disinfection and antifouling mechanism. Herein, we highlighted the decisive impact of flow patterns on the electrochemical inactivation of both Escherichia coli and Staphylococcus aureus during dead-end filtration mode. Specifically, 5.22 and 5.47 log removal for E. coli and S. aureus were achieved by a single pass under anode-to-cathode (AC) flow pattern at 7 mA cm−2 respectively, while the inactivation rates immediately decreased to less than one log for cathode-to-anode (CA) flow pattern. Further analysis demonstrated that the remarkable inactivation efficiency in neutral condition, the complete inactivation of E. coli and S. aureus in the parallel plate batch mode were achieved in 15 min and 30 min at 7 mA cm−2 respectively, was significantly inhibited during alkaline and acidic exposure, thereby which explained the slow disinfection rates in CA flow pattern due to the formed alkaline experiment near anodic reaction section. The disinfection efficiency and comparative differences of E. coli and S. aureus were also affected by their hydraulic condition and cell wall structure. Functional groups model substances experiments and molecular dynamics simulation elucidated that the response changes of cell structure especially denser membrane protein complex under alkaline and acidic exposure resisted electrooxidation attack to the membrane structure. These findings here provide insights into the application of Ti4O7 REM technologies in controlling waterborne disease transmission.

Ozone processing of milk and milk products: a review of applications, quality effect and implementation challenges

Abstract The impact on the natural characteristics of dairy products during thermal processing warrants the investigation of non-thermal techniques. Ozone has proved to be an effective and sustainable processing technology for the dairy processing sector. This review delves into the effect of ozone processing on the microbiological, physiochemical, nutri-functional, and sensory quality of milk and milk products. Alongside this, the other ozone applications in the dairy processing sector (storage room disinfection, wastewater treatment, benefits in Clean-in-Place (CIP) system, toxin reduction) have been discussed. Current regulatory and industrial status, and safety requirements in the facility have also been highlighted. Overall, ozone treatment has lower microbial inactivation efficiency in milk and milk products than thermal treatment. Further, safety precautions are needed in the processing areas due to its potential health hazard concerns.

Deactivation of harmful green tide using Ag/SiO2 and Ag/Al2O3 coatings on low-density porous materials

Nowadays harmful bloom tides affect greatly the economy of coastal states. For this reason, the present communication reports on a practical method for synthesizing SiO2 and γ-alumina nanospheres, immobilized by sonochemistry on low-density porous foams and perlite granules, as a solution to this problem. A biostatic AgNP effect was incorporated into both materials, achieving AgSi and AgAl. The green-tide inactivation was performed by using Tetraselmis suecica under aqueous conditions. AgAl/FWGS displayed the best inactivation efficiency performance (94 %). Additionally, foams have significant buoyancy and are easy to handle, being an option for T. suecica inactivation for their easy recovering.

Catalyst-free regeneration of plasma-activated water via ultrasonic cavitation: Removing aggregation concealment of antibiotic-resistant bacteria with enhanced wastewater sustainability

Aggregation is a crucial factor in bacterial biofilm formation, and comprehending its properties is vital for managing waterborne antibiotic-resistant bacteria. In this study, we examined Methicillin-resistant Staphylococcus aureus (MRSA) cell aggregation under varying conditions and assessed the inactivation efficiency of a novel disinfection method, micro-nano bubbles plasma-activated water via ultrasonic stirring cavitation (MPAW-US), on aggregated MRSA cells. Aggregation efficiency increased over time and at low salt concentrations but diminished at higher concentrations. Elevated MRSA cell aggregation in actual water samples represented significant real-life biohazard risks. Unlike conventional disinfection, MPAW-US treatment exhibited minimal change in the inactivation rate constant despite protective outer layers. Enhanced inactivation efficiency results from the synergistic effects of increased intracellular oxidative stress damage and extracellular substance disruption, triggered by ultrasound-activated micro-nano bubbles that improve PAW reactivity and applicability. This approach neither induced MRSA cross-resistance to unfavorable conditions nor increased toxicity or regrowth potential of aggregative MRSA, utilizing ATP levels as potential regrowth capability indicators. Ultimately, this energy-efficient disinfection technology functions effectively across diverse temperature ranges, showcasing exceptional sterilization and nutritional bean sprout production after cyclic filtering, thereby promoting wastewater sustainability amidst carbon emission concerns.

Efficacy of Atmospheric Non‐thermal Plasma Corona Discharge Under Dry and Wet Conditions on Decontamination of Food Packaging Film Surfaces

ABSTRACTFood packaging materials must be sterilized to prevent cross‐contamination of the product. Non‐thermal plasma (NTP) corona discharge can be an effective alternative sterilization method for packaging films. The inactivation efficiency atmospheric NTP corona discharge under dry and wet conditions against vegetative cells of Escherichia coli, Staphylococcus aureus and Bacillus subtilis, spores of B. subtilis and Clostridium sporogenes and fungal spores of Candida albicans, Penicillium expansum and Aspergillus niger on polymeric packaging films were studied. The maximum inactivation of these microorganisms was 5.58, 0.54, 1.51, 1.06, 2.47, 1.73, 2.80, 3.20 and 3.50 log, respectively. Microbial inactivation by the treatments was greatly enhanced under wet conditions. Gram‐negative bacteria were found to be more sensitive to NTP, but spores were more resistant than vegetative bacterial cells. Although fungi were less susceptible than bacteria in dry treatments, they became more sensitive than the Gram‐positive bacteria in wet treatments. Overall, plasma treatments under wet conditions achieved higher microbial inactivation and would be favourable over the dry treatment.

Application of antioxidants in cold plasma treatment of fish oil

As a mild non-thermal treatment technology, cold plasma can lead to lipid oxidation when applied to products with high lipid content. This study focuses on the physical and chemical properties of fish oil with cold plasma treatment and to explore the potential of Curcumin, Tea polyphenols, Vitamin E and β-Carotene in inhibit the oxidation process. Following treatment, the peroxide value and malondialdehyde value of the fish oil significantly increased, while the content of unsaturated fatty acids decreased and the singlet oxygen content rose (p < 0.0 5). However, the introduction of antioxidants during treatment yielded diminished peroxide and malondialdehyde values in the fish oil, thereby effectively curbing the presence of singlet oxygen. Notably, fish oil enriched with vitamin E exhibited the most robust antioxidant activity among the tested compounds. This study offers insights into strategies for enhancing the stability of high-fat foods subjected to cold plasma treatment. Industrial relevanceFish oil has long been essential in the processing of food, pharmaceuticals, and animal feed, making its quality crucial. This study revealed that cold plasma treatment accelerated the oxidation of fish oil; however, the addition of antioxidants effectively mitigated this effect. In industrial settings, cold plasma technology is favored in the food industry for its low-temperature operation and high efficiency in microbial inactivation. Despite these advantages, the reactive species produced during the process can cause lipid peroxidation and alter amino acids in proteins. This research offered critical insights into optimizing process parameters to minimize lipid oxidation. It also lays the groundwork for developing more efficient and safer food processing technologies and offers new approaches to extending the shelf life of fish oil and other lipid-rich foods during cold plasma treatment.

Near infrared photothermal inactivation of Candida albicans assisted by plasmonic nanorods

The use of photothermal processes has been proven effective in the control of microbial infections. Simultaneously, the localized surface plasmon resonance phenomena in metallic nanoparticles have been explored as an alternative strategy to achieve highly efficient localized heating. In this work, we propose the use of selected nanoheaters to improve the efficiency of fungal photothermal inactivation of Candida albicans through size optimization of plasmonic gold nanorods. Here, the optical heating of polyethylene glycol coated gold nanorods of varying sizes is evaluated, both theoretically and experimentally. A size-dependent computational approach was applied to identify metallic nanorods with maximized thermal performance at 800 nm, followed by the experimental comparison of optimal and suboptimal nanoheaters. Comparison among samples show temperatures of up to 53.0 °C for 41×10 nm gold nanorods against 32.3 °C for 90×25 nm, a percentage increase of ∼63% in photothermal inactivation assessments. Our findings reveal that gold nanorods of 41×10 nm exhibit superior efficiency in near-infrared (800 nm) photothermal inactivation of fungi, owing to their higher light-thermal conversion efficiency. The identification of high performance metallic nanoheaters may lead to the reduction of the nanoparticle dose used in plasmonic-based procedures and decrease the laser exposure time needed to induce cell death. Moreover, our results provide insights to better exploit plasmonic nanoparticles on photothermal inactivation protocols.

Effect of biofilm physical characteristics on their susceptibility to antibiotics: impacts of low-frequency ultrasound

Biofilms are highly resistant to antimicrobials, often causing chronic infections. Combining antimicrobials with low-frequency ultrasound (LFU) enhances antimicrobial efficiency, but little is known about the underlying mechanisms. Biofilm physical characteristics, which depend on factors such as growth conditions and age, can have significant effects on inactivation efficiency. In this study, we investigated the susceptibility of Pseudomonas aeruginosa biofilms to tobramycin, with and without LFU treatment. The biofilms were grown under low and high fluid shear to provide different characteristics. Low-shear biofilms exhibited greater thickness, roughness, and porosity and lower density, compared to high-shear biofilms. The biofilm matrix of the high-shear biofilms had a three times higher protein-to-polysaccharide ratio, suggesting greater biofilm stiffness. This was supported by microrheology measurements of biofilm creep compliance. For the low-shear biofilms without LFU, the viability of the biofilms in their inner regions was largely unaffected by the antibiotic after a 2-hour treatment. However, when tobramycin was combined with LFU, the inactivation for the entire biofilm increased to 80% after 2 h. For the high-shear biofilms without LFU, higher LFU intensities were needed to achieve similar inactivation results. Microrheology measurements revealed that changes in biofilm inactivation profiles were closely related to changes in biofilm mechanical properties. Modeling suggests that LFU changes antibiotic diffusivity within the biofilm, probably due to a “decohesion” effect. Overall, this research suggests that biofilm physical characteristics (e.g., compliance, morphology) are linked to antimicrobial efficiency. LFU weakens the biofilm while increasing its diffusivity for antibiotics.

The Antibacterial Efficacy of Far-UVC Light: A Combined-Method Study Exploring the Effects of Experimental and Bacterial Variables on Dose-Response.

Far-ultraviolet C light, with a wavelength of 200-230 nm, has demonstrated broad-spectrum germicidal efficacy. However, due to increased interest in its use as an alternative antimicrobial, further knowledge about its fundamental bactericidal efficacy is required. This study had two objectives. Firstly, it investigated experimentally the Far-UVC dose-response of common bacteria suspended at various cell densities in transparent buffer, ensuring no influence from photosensitive suspending media. Increasing doses of Far-UVC were delivered to Enterococcus faecium, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus in PBS at 101, 102, 103, 105 and 107 CFU·mL-1, with surviving colony-forming units enumerated (n ≥ 3). Secondly, through a systematised literature review, this work sought to explore the impact of genus/species, Gram type, cell form, cell density and irradiance on dose-response. The screening of 483 publications was performed with 25 included in the study. Data for 30 species were collated, analysed and compared with the experimental results. Overall, Gram-positive species showed greater resilience to Far-UVC than Gram-negative; some inter-species and inter-genera differences in resilience were identified; endospores were more resilient than vegetative cells; the results suggested that inactivation efficiency may decrease as cell density increases; and no significant correlation was identified between irradiance and bactericidal dose effect. In conclusion, this study has shown Far-UVC light to be an effective decontamination tool against a vast range of bacterial vegetative cells and endospores.

Synthesis of activated carbon-supported nano copper oxide and its inactivation performance on Escherichia coli in water

Copper oxide (CuO) is limited in inactivating bacteria due to the deficiency of active Cu(I) that can catalyze dissolved oxygen to produce reactive oxygen radicals. A novel sterilization agent was developed to inactivate Escherichia coli (E. coli) by loading nano copper oxide onto activated carbon (nCuO/AC) with a facile impregnation method. Surface techniques proved that CuO with a size of 100–200 nm was evenly loaded on AC surface, which improved its dispersity and reactivity. XPS analysis further revealed a cycle of surface-bonded Cu(II) to Cu(I) in the nCuO matrix that was driven by reducing groups on AC surface such as hydroxyl. The resultant Cu(I) activated dissolved oxygen to produce reactive oxygen species for bacterial inactivation. Superoxide radical (•O2–) was proved to be the primarily oxidative species during the sterilization process by EPR analysis and quenching investigations. Therefore, the nCuO/AC achieved an enhanced inactivation efficiency of 6.0 log CFU/mL as compared to those of 1.1 and 0.4 log CFU/mL by the nCuO and AC, respectively. The above sterilization reaction was pH-dependent and high inactivation efficiency could be achieved under neutral conditions. Additionally, the nCuO/AC exhibited excellent stability with an inactivation efficiency of 5.4 log CFU/mL after 4 cycles. Spent nCuO/AC showed great potential in renewability because it could inactivate 5.5 log CFU/mL of E. coli by peeling off residual nCuO on AC surface with sulfuric acid and reloading new nCuO through impregnation, with a regeneration rate up to 97.2 %. The above results demonstrated that nCuO/AC could be a promising bactericidal material for water treatment.

Intensifying inactivation strategies: Insights into the role of ultrasound on the inactivation of antibiotic resistant Acinetobacter baumannii via Photo-Fenton reaction

Improvisation of the contemporary water treatment technologies is critical not only to prevent water borne diseases but also to augment the available water sources. Here, a systematic study is effectuated to comprehend the upswing in the inactivation efficiency of Photo-Fenton (PF) chemistry induced by ultrasound (US) against antibiotic resistant (ABR) Acinetobacter baumannii (A. baumannii). Inactivation of A. baumannii (≈5×106 CFU/mL) was noticed within 75 and 105 min of US assisted PF (SPF) and PF processes respectively using 20 mg/L of H2O2 and 2 mg/L of Fe2+. It was interesting to notice that the PF reaction was effective under weak acidic condition (pH=3 and 5.5) whereas SPF process was realized over a wide pH range (3, 5.5, 7 and 9). No reactivation of the bacteria was found in both the processes till 96 h suggesting the impairment of not only the bacterial cell membrane but also the intracellular components. Experimental results although has suggested the generation of several reactive oxygen species (ROS), the inactivation mechanism was suggested to be dominated by the H2O2 and •OH. The damage caused to the bacterial cell membranes by the synergistic role of US and ROS was observed in the electron microscopy images. Comparative transcriptomic analysis has indicated the upregulation of genes regulating the LPS assembly proteins (Lpt A, B, C) and Pls B, Pgs A and Pal genes regulating the phospholipid synthesis which are known to regulate the stress induced response in bacteria. The SPF process was further validated with real water samples and the treated water was not found to have remarkable toxic effect on the in-vivo animal which endorse its candidature for future applications.

Gaseous ozone inactivation of Bacillus atrophaeus spores on ceramic and porcelain tiles

In this study, we investigated the ozone inactivation efficiency of Bacillus atrophaeus spores attached to various tile surfaces. Eight different types of tiles were employed, considering factors such as porosity (ceramic, porcelain), color (white, black), and glossiness (matte, glossy). Inactivation was performed by exposing the spore-loaded tiles to ozone gas for a specified duration. The inactivation efficiencies of ozone gas on different tile surfaces were compared by analyzing the colony-forming units of desorbed Bacillus atrophaeus cultured in a growth medium. Results revealed a reduction in colony counts with increasing ozone exposure time, indicating a proportional enhancement in inactivation effectiveness on ozone exposure time. After exposure to ozone gas for 30 min or longer, more than 90% of spores on each tile were inactivated. Regarding porosity, ceramic tiles exhibited slightly superior inactivation effects compared to porcelain tiles. Additionally, in terms of glossiness, glossy tiles demonstrated better inactivation effects than matte tiles. However, no significant differences were observed in inactivation effects based on the color of the tiles.

Indoor air disinfection by non thermal atmospheric pressure plasma: a comparative study of performance in low and high humidity environments

Atmospheric pressure plasma (APP) has intrigued the interest of researchers for various applications such as disinfection, air purification, etc. In this context, a deeper understanding of the correlation between APP’s characteristics like discharge parameters, active species composition, and eradication of airborne microorganisms with varying relative humidity (RH) has been examined using a dielectric barrier discharge based atmospheric pressure plasma (DBD-APP) source. One of the electrodes of the developed DBD-APP source has been coated with TiO2 nanoparticles to enhance the generation of reactive species during the discharge process. The results show that, even with the same peak-to-peak applied voltage, the peak-to-peak current and discharge power decrease with increasing RH. Optical emission spectroscopy (OES) is used to determine the relative emission intensity of the reactive species, whereas spectrophotometry is used to quantify the reactive species produced by the plasma at various parameters. Instead of UV radiation, the plasma-produced highly energetic electrons activates the TiO2 nanoparticles for electron–hole pair generation. The geometry of the plasma device has played an important role in generating high energy electrons. From the developed DBD-APP source, the airborne microorganism’s disinfection efficiency of ∼95.8% and ∼98.7% has been achieved in the total bacterial counts (TBCs) and total fungal counts (TFCs) at an RH range of 70%–90%, in just 20 min of continuous operation. However, in the RH range of 20%–40%, the inactivation efficiency dropped to ∼78.8% and ∼87.5% for the TBCs and TFCs, respectively. The outcome indicates that higher humidity levels are better for indoor air purification using DBD-APP sources and that plasma with a circulation system can effectively disinfect indoor environments.

Efficacy, kinetics, inactivation mechanism and application of cold plasma in inactivating Alicyclobacillus acidoterrestris spores

As spores of Alicyclobacillus acidoterrestris can survive traditional pasteurization, this organism has been suggested as a target bacterium in the fruit juice industry. This study aimed to investigate the inactivation effect of cold plasma on A. acidoterrestris spores and the mechanism behind the inactivation. The inactivation effect was detected by the plate count method and described by kinetic models. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), the detection of dipicolinic acid (DPA) release and heat resistance detection, the detection and scavenging experiment of reactive species, and cryo-scanning electron microscopy were used to explore the mechanism of cold plasma inactivation of A. acidoterrestris. The results showed that cold plasma can effectively inactivate A. acidoterrestris spores in saline with a 3.0 ± 0.3 and 4.4 ± 0.8 log reduction in CFU/mL, for 9 and 18 min, respectively. The higher the voltage and the longer the treatment time, the stronger the overall inactivation effect. However, a lower gas flow rate may increase the probability of spore contact with reactive species, resulting in better inactivation results. The biphasic model fits the survival curves better than the Weibull model. SEM and TEM revealed that cold plasma treatment can cause varying degrees of damage to the morphology and structure of A. acidoterrestris spores, with at least 50 % sustaining severe morphological and structural damage. The DPA release and heat resistance detection showed that A. acidoterrestris spores did not germinate but died directly during the cold plasma treatment. 1O2 plays the most important role in the inactivation, while O3, H2O2 and NO3− may also be responsible for inactivation. Cold plasma treatment for 1 min reduced A. acidoterrestris spores in apple juice by 0.4 ± 0.0 log, comparable to a 12-min heat treatment at 95 °C. However, as the treatment time increased, the survival curve exhibited a significant tailing phenomenon, which was most likely caused by the various compounds in apple juice that can react with reactive species and exert a physical shielding effect on spores. Higher input power and higher gas flow rate resulted in more complete inactivation of A. acidoterrestris spores in apple juice. What's more, the high inactivation efficiency in saline indicates the cold plasma device provides a promising alternative for controlling A. acidoterrestris spores during apple washing. Overall, our study provides adequate data support and a theoretical basis for using cold plasma to inactivate A. acidoterrestris spores in the food industry.