Reduction Of Spores Research Articles

장류를 이용하여 제조한 소스류의 총균 및 Bacillus cereus 포자에 대한 줄가열 및 초고압 처리 효과

마리네이드, 간장소스, 된장소스 및 고추장소스를 대상으로 총균수 및 Bacillus cereus 접종포자에 대해 초고압, 줄가열, 항균물질에 단독처리나 hurdle 복합처리에 의한 저감효과를 분석하였다. 줄가열 처리는 된장 및 고추장소스의 총균과 접종포자에 대해서 1.0∼2.0 log 범위의 저감효과를 나타내었다. 한편 J(85℃), A(EtOH 3.0%) 및 P(550 Mpa, 5분)를 허들로 설정하였을 경우 된장소스의 총균수는 JA 처리구가 0.35 log, JP 처리구가 0.92 log 및 JAP 처리구가 1.21 log 감소하였고, 고추장소스의 총균수는 JA 처리구가 1.26 log, JP 처리구가 1.7 log 및 JAP 처리구가 1.47 log 감소하였다. 포자의 경우 된장소스는 AP 처리구가 0.50 log, JP와 JAP 처리구는 각각 1.42 log 및 1.38 log로 감소효과가 증가하였고, 고추장소스는 AP 처리구가 0.47 log, JA 처리구가 3.3 log, JP와 JAP 처리구가 모두 3.45 log만큼 크게 감소하였다. 상기 소스의 총균과 포자에 대한 처리구는 30℃에서 8주간 저장 시 대조구 대비 유사하거나 낮은 수준을 유지하였다. 따라서 소스류 중에서 고추장소스와 된장소스는 줄가열과 초고압을 연계한 허들처리를 통해 총균수와 B. cereus 포자를 제어할 수 있을 것으로 기대된다.

Sporicidal properties from surface micro-discharge plasma under different plasma conditions at different humidities

In the current study, bacterial endospores of Geobacillus stearothermophilus are exposed to the surface micro-discharge plasma for 5 min and the humidity and power consumption are varied. At the low humidity of 5.5 ± 0.5 g m−3, almost no sporicidal effect (<0.5 log) is observed. At the high humidity of 17.9 ± 0.6 g m−3, the spore reduction increases monotonically up to 3.5 log with increasing power consumption. At a humidity of 10.4 ± 0.6 g m−3, the spores are inactivated in a limited range of power consumption with a maximum reduction of ∼2.5 log. The survival curves show a single-slope decrease of the spores. The contribution of heat and UV to the sporicidal effect as well as the inactivation of spores by the short-lived species from the plasma are ruled out. The concentration of ozone, one indicator for the long-lived species, is measured and no correlation with the sporicidal effect is found. In conclusion, water-related reactive species, e.g. hydrogen peroxide, appear to be responsible for the sporicidal effect under the investigated conditions. Furthermore, condensation of water at high humidity enables the plasma-activated water containing both long-lived and short-lived reactive species to contribute to the sporicidal effect.

Influence of high voltage atmospheric cold plasma process parameters and role of relative humidity on inactivation of Bacillus atrophaeus spores inside a sealed package

Non-thermal plasma has received much attention for elimination of microbial contamination from a range of surfaces. This study aimed to determine the effect of a range of dielectric barrier discharge high voltage atmospheric cold plasma (HVACP) parameters for inactivation of Bacillus atrophaeus spores inside a sealed package. A sterile polystyrene Petri dish containing B.atrophaeus spore strip (spore population 2.3×10(6)/strip i.e. 6.36 log10/strip) was placed in a sealed polypropylene container and was subjected to HVACP treatment. The HVACP discharge was generated between two aluminium plate electrodes using a high voltage of 70kVRMS. The effects of process parameters, including treatment time, mode of exposure (direct/indirect), and working gas types, were evaluated. The influence of relative humidity on HVACP inactivation efficacy was also assessed. The inactivation efficacy was evaluated using colony counts. Optical absorption spectroscopy (OAS) was used to assess gas composition following HVACP exposure. A strong effect of process parameters on inactivation was observed. Direct plasma exposure for 60s resulted in ≥6 log10 cycle reduction of spores in all gas types tested. However, indirect exposure for 60s resulted in either 2.1 or 6.3 log10 cycle reduction of spores depending on gas types used for HVACP generation. The relative humidity (RH) was a critical factor in bacterial spore inactivation by HVACP, where a major role of plasma-generated species other than ozone was noted. Direct and indirect HVACP exposure for 60s at 70% RH recorded 6.3 and 5.7 log10 cycle reduction of spores, respectively. In summary, a strong influence of process parameters on spore inactivation was noted. Rapid in-package HVACP inactivation of bacterial spores within 30-60s demonstrates the promising potential application for reduction of spores on medical devices and heat-sensitive materials.

Study of the inactivation of spoilage microorganisms in apple juice by pulsed light and ultrasound

The aim of this study was to evaluate the effect of ultrasound (US) (600 W, 20 kHz and 95.2 μm wave amplitude; 10 or 30 min at 20, 30 or 44 ± 1 °C) and pulsed light (PL) (Xenon lamp; 3 pulses/s; 0.1 m distance; 2.4 J/cm2–71.6 J/cm2; initial temperature 2, 30, 44 ± 1 °C) on the inactivation of Alicyclobacillus acidoterrestris ATCC 49025 spores and Saccharomyces cerevisiae KE162 inoculated in commercial (pH: 3.5; 12.5 °Brix) and natural squeezed (pH: 3.4; 11.8 °Brix) apple juices. Inactivation depended on treatment time, temperature, microorganism and matrix. Combination of these technologies led up to 3.0 log cycles of spore reduction in commercial apple juice and 2.0 log cycles in natural juice; while for S. cerevisiae, 6.4 and 5.8 log cycles of reduction were achieved in commercial and natural apple juices, respectively. In natural apple juice, the combination of US + 60 s PL at the highest temperature build-up (56 ± 1 °C) was the most effective treatment for both strains. In commercial apple juice, US did not contribute to further inactivation of spores, but significantly reduced yeast population. Certain combinations of US + PL kept on good microbial stability under refrigerated conditions for 15 days.

Synergistic sporicidal effect of ethanol on a combination of orthophthalaldehyde and didecyldimethylammonium chloride.

The objective of this study was to evaluate the potential synergistic effect of ethanol on a combination of orthophthalaldehyde (OPA) and didecyldimethylammonium chloride (DDAC) against the spores of Bacillus subtilis var. Niger. The quantitative carrier test for sporicidal testing of high-level disinfectants according to the guideline of China (Technical Standard for Disinfection 2002) was used as method. Considerable synergistic effect was observed after a 30-min treatment at 20°C. There was an augment in mean log reduction as the concentration of DDAC was increased ranging from 0·2 to 3gl(-1) in combination with 6gl(-1) OPA. Ten and 20% ethanol in combination with 6gl(-1) OPA and 2gl(-1) DDAC caused more than a 3-log reduction while either 6gl(-1) OPA, 2gl(-1) DDAC and 20% ethanol alone or a combination of two of the three agents produced less than a 1-log reduction. Further, 40-min exposure time of combination of OPA, DDAC and 20% ethanol led to greater than a 5-log reduction in spores, and no spore growth was observed following 60- and 90-min exposures. Orthophthalaldehyde (OPA) is very effective at concentrations far lower than its recommended in-use concentration of 0·5% (w/v) and is equally effective against both the gram-negative and gram-positive bacteria. However, it shows lower activity against spores. The synergistic sporicidal effect exhibited by ethanol on a combination of OPA and DDAC can be considered to enhance sporicidal activity for using in situations of sterilization, to reduce in-use concentration of OPA used alone, which may minimize its side effect. OPA may be a more satisfactory and the first-choice agent to replace glutaraldehyde (GTA) as a high-level disinfectant for medical devices.

Combined effects of high pressure, moderate heat and pH on the inactivation kinetics of Bacillus licheniformis spores in carrot juice

The objective of this research was to evaluate the combined effect of high pressure processing (temperature, pressure and time) and product (pH) related variables on destruction kinetics of spores of Bacillus licheniformis in carrot juice. A 3-level factorial experimental design was used with the microbial spores inoculated into carrot juice at the natural pH (6.2) and acidified pH (4.5 and 5.5), pressure (400, 500 or 600MPa), temperature (40, 50, and 60°C) and time (0–40min) conditions. D values found varied from 0.6 to 14.1min based on the temperature, pressure and pH level combinations. The corresponding temperature and pressure dependency of D values were in the range 23.3 to 31°C and 241 to 465MPa, respectively. The destruction pattern was also dependent on pH, with lower pH contributing to higher destruction rate. Conventional log-linear model and Weibull model were used to describe the survivor curves and for predicting processing time to achieve a 5D spore reduction. The survivor curves exhibited slightly upward concavity and therefore better described by a Weibull than the log-linear model. Treatment combinations showed significant (p≤0.05) effects on D and z values of log-linear model and rate parameter (α) of Weibull model. The 5D spore count reduction times estimated using Weibull model parameters were longer than those from the log-linear model, generally demonstrating an over-treatment. Overall, the pH reduction of low acid foods showed a significant enhancement of rate of destruction of B. licheniformis spores.

Inactivation of Alicyclobacillus acidoterrestris Spores in Apple and Orange Juice Concentrates by Gamma Irradiation

The objective of this study was to evaluate the effect of different concentrations of reconstituted apple and orange juice on reduction of Alicyclobacillus acidoterrestris spores by gamma irradiation. Spores of A. acidoterrestris were inoculated into three concentrations of apple (18, 36, and 72 °Brix) and orange (11, 33, and 66 °Brix) juice and subjected to five radiation doses (1, 3, 5, 7, and 10 kGy). No significant reductions (P > 0.05) in spores were observed after the 1-kGy treatment for all apple and orange concentrations. Spores in 18, 36, and 72 °Brix apple juice concentrates subjected to 10 kGy were reduced to 4.34, 3.9, and 3.84 log CFU/ml, respectively. Similar results were observed for orange juice. When 10 kGy was applied to 11 °Brix orange juice, populations of spores were reduced by 5 log CFU/ml. The reduction of spores in 33 and 66 °Brix orange juice concentrates exposed to 10-kGy gamma irradiation was 4.54 and 3.85 log CFU/ml, respectively. Juice concentration did not affect (P > 0.05) the number of surviving A. acidoterrestris spores from the same kGy treatment. Gamma irradiation treatment did not change the pH or water activity of the juice (P > 0.05).

A selective sweep in a microsporidian parasite Nosema‐tolerant honeybee population, Apis mellifera

Nosema is a microsporidian parasite of the honeybee, which infects the epithelial cells of the gut. In Denmark, honeybee colonies have been selectively bred for the absence of Nosema over decades, resulting in a breeding line that is tolerant toward Nosema infections. As the tolerance toward the Nosema infection is a result of artificial selection, we screened chromosome 14 for a selective sweep with microsatellite markers, where a major quantitative trait locus (QTL) had been identified to be involved in the reduction in Nosema spores in the honeybees. By comparing the genetic variability of 10 colonies of the selected honeybee strain with a population sample from 22 unselected colonies, a selective sweep was revealed within the previously identified QTL region. The genetic variability of the swept loci was not only reduced in relation to the flanking markers on chromosome 14 within the selected strain but also significantly reduced compared with the same region in the unselected honeybees. This confirmed the results of the previous QTL mapping for reduced Nosema infections. The success of the selective breeding may have driven the selective sweep found in our study.

Showering BSL-4 Suits to Remove Biological Contamination

Positive pressure suits are widely used at BSL-4 to protect operators from contact with microbiological agents. As there is the potential for the outside of the suits to become contaminated during use, they must be decontaminated prior to final exit from the high-containment laboratory. Chemical showers are used to remove biological material from suits, and the shower effluent is collected for subsequent treatment by heat or chemicals. The efficacy of showering to clean/remove biological materials from two different BSL-4 suits (ILC Dover and Delta) was studied using Bacillus atrophaeus spores dried directly onto the suit surface as a surrogate contaminant, with a 4 log colony forming unit (cfu) reduction pass criterion required. Initial studies using water alone, without disinfectant, achieved a 1–2 log cfu reduction in the microbial contamination. However, direct scrubbing, using a lightweight brush combined with relatively short cycle times (6 minutes) and low water volumes (<45 L per cycle) achieved an average spore reduction of 3.4 log cfu from the suit. The log cfu reduction was dependent on suit type, position of the contamination on the suit surface, and suit fit. Higher reductions (mean 4.2 log cfu) were achieved with the ILC Dover suit than the Delta suit (mean 3.6 log cfu) when the tests were undertaken using experienced staff who had been matched to the suit size. The study highlights that assumptions cannot be made about the efficacy of shower decontamination systems for BSL-4 facilities and that familiarization with decontamination improves the efficacy of removal of biological material during showering.

Effectiveness of a peracetic acid-based disinfectant against spores of Bacillus cereus under different environmental conditions

A peracetic acid based disinfectant was tested for its efficacy against spores of different Bacillus cereus -strains (DSM 318, 4312, 4313 and 4384). To determine the influence of different factors like exposure-time, temperature and presence of protein quantitative and qualitative suspension tests were performed. Spore suspensions of B. cereus were treated with various concentrations of a representative peracetic acid based disinfectant at three temperatures (10, 15 and 20 °C), with protein load and with different exposure times (5, 30 and 60 min). Temperature, level of concentration and exposure-time had a significant influence on reduction of spores of B. cereus (p < 0.05). The susceptibility of spores of different strains greatly differed. A treatment of spores of DSM 4384 with 2.0% for 30 min even at 10 °C inactivated all present spores (initial number 6.18–6.71 log CFU/ml). Spores of B. cereus strain DSM 4313 had only reductions of 0.16–0.97 log CFU/ml at same treatment conditions. The presence of inactivated bovine serum as interfering substance had no significant influence on reduction (p > 0.05).

Effects of lysozyme on Alicyclobacillus acidoterrestris under laboratory conditions

SummaryThis research was aimed at investigating the bioactivity of lysozyme towards Alicyclobacillus acidoterrestris. Lysozyme (0.1–20 ppm) was tested towards five different strains; the experiments were performed on both spores and vegetative cells using a microdilution approach to assess the minimal inhibitory concentration (MIC). Thereafter, spore viability of two selected strains was evaluated through the traditional plate count. Finally, an experiment was run to assess the role of lysozyme on the complex phenomenon of spore germination. The MIC of lysozyme towards vegetative cells varied from 0.1 to 6 ppm, while for the spores, it was from 0.1 to 3 ppm. Concerning spore viability, the effect of lysozyme relied upon its amount on the broth, as at MIC it caused a slight reduction in spores (approximately 1 log cfu ml−1) after 24 h; otherwise, higher concentrations caused a decrease in spore level below the detection limit. Concerning spore germination, lysozyme exerted a promoting effect on this phenomenon and reduced the optical density by 66%.

Novel Strategies for Enhanced Removal of Persistent Bacillus anthracis Surrogates and Clostridium difficile Spores from Skin

BackgroundRemoving spores of Clostridium difficile and Bacillus anthracis from skin is challenging because they are resistant to commonly used antimicrobials and soap and water washing provides only modest efficacy. We hypothesized that hygiene interventions incorporating a sporicidal electrochemically generated hypochlorous acid solution (Vashe®) would reduce the burden of spores on skin.MethodsHands of volunteers were inoculated with non-toxigenic C. difficile spores or B. anthracis spore surrogates to assess the effectiveness of Vashe solution for reducing spores on skin. Reduction in spores was compared for Vashe hygiene interventions versus soap and water (control). To determine the effectiveness of Vashe solution for removal of C. difficile spores from the skin of patients with C. difficile infection (CDI), reductions in levels of spores on skin were compared for soap and water versus Vashe bed baths.ResultsSpore removal from hands was enhanced with Vashe soak (>2.5 log10 reduction) versus soap and water wash or soak (~2.0 log10 reduction; P <0.05) and Vashe wipes versus alcohol wipes (P <0.01). A combined approach of soap and water wash followed by soaking in Vashe removed >3.5 log10 spores from hands (P <0.01 compared to washing or soaking alone). Bed baths using soap and water (N =26 patients) did not reduce the percentage of positive skin cultures for CDI patients (64% before versus 57% after bathing; P =0.5), whereas bathing with Vashe solution (N =21 patients) significantly reduced skin contamination (54% before versus 8% after bathing; P =0.0001). Vashe was well-tolerated with no evidence of adverse effects on skin.ConclusionsVashe was safe and effective for reducing the burden of B. anthracis surrogates and C. difficile spores on hands. Bed baths with Vashe were effective for reducing C. difficile on skin. These findings suggest a novel strategy to reduce the burden of spores on skin.

Nonthermal inactivation of heterogeneous and superdormant spore populations of Bacillus cereus using ozone and high pressure processing

Superdormant spores are those which germinate extremely slowly compared to the majority of the spore population. The development of a method to isolate large quantities of superdormant spores in a laboratory setting has allowed for further study of these hardy organisms. In this study, the ability of nonthermal processing technologies, including a combined hurdle technology of aqueous ozone and high pressure processing (HPP), to inactivate superdormant spore populations of mesophilic and psychrotolerant isolates of Bacillus cereus was investigated. Superdormant spores were approximately 20% more resistant to ozone treatment than heterogeneous spore populations (p = 0.02) and psychrotolerant species were approximately 31.9% more resistant than mesophilic species (p = 0.004). The combined ozone-HPP hurdle technology achieved a maximum 2.67-log CFU/mL reduction of superdormant spores. Nonthermal processing technologies including high pressure processing (HPP) and ozone have high implications for reducing the number of spores in foods; however, these technologies are not widely utilized in the industry due to their inability to completely inactivate all the spores within a product. The spores that do not germinate as easily as the majority of a spore population are known as superdormant spores. This study demonstrates that an ozone-HPP combined hurdle technology may be able to effectively reduce the number of superdormant spores, specifically psychrotolerant sporeforming toxin-producing species such as B. cereus and Bacillus weihenstephanensis , in refrigerated food products such as RPFEDs and reduce the risk of foodborne illness. • Inactivation of superdormant spores using nonthermal technologies is investigated. • Superdormant spores were more resistant to ozone than heterogeneous populations. • Psychrotolerant sporeformers were more resistant to ozone than mesophilic species. • Ozone and HPP combined treatment achieved a 2.67-log CFU/mL reduction.

Evidence that contaminated surfaces contribute to the transmission of hospital pathogens and an overview of strategies to address contaminated surfaces in hospital settings

Evidence that contaminated surfaces contribute to the transmission of hospital pathogens comes from studies modeling transmission routes, microbiologic studies, observational epidemiologic studies, intervention studies, and outbreak reports. This review presents evidence that contaminated surfaces contribute to transmission and discusses the various strategies currently available to address environmental contamination in hospitals.

Factors influencing the inactivation of Alicyclobacillus acidoterrestris spores exposed to high hydrostatic pressure in apple juice

Alicyclobacillus acidoterrestris, a thermoacidophilic and spore-forming bacterium, survives the typical pasteurization process and can cause the spoilage of juices, producing compounds associated with disinfectant-like odour (guaiacol, 2,6 – dibromophenol, 2,6 – dichlorophenol). Therefore, the use of other more effective techniques such as high hydrostatic pressure (HHP) is considered for preserving juices. The aim of this study was to search for factors affecting the resistance of A. acidoterrestris spores to HHP. The baroprotective effect of increased solute concentration in apple juice on A. acidoterrestris spores during high pressure processing was observed. During the 45 min pressurization (200 MPa, 50°C) of the spores in concentrated apple juice (71.1°Bx), no significant changes were observed in their number. However, in the juices with a soluble solids content of 35.7, 23.6 and 11.2°Bx, the reduction in spores was 1.3–2.4 log, 2.6–3.3 log and 2.8–4.0 log, respectively. No clear effect of age of spores on the survival under high pressure conditions was found. Spores surviving pressurization and subjected to subsequent HHP treatment showed increased resistance to pressure, by even as much as 2.0 log.

Effect of Packaging Systems and Pressure Fluids on Inactivation of Clostridium botulinum Spores by Combined High Pressure and Thermal Processing

Several studies have been published on the inactivation of bacterial spores by using high pressure processing in combination with heat. None of the studies investigated the effect of the packaging system or the pressurizing fluid on spore inactivation. The objective of this study was to select and validate an appropriate packaging system and pressure transfer fluid for inactivation of Clostridium botulinum spores by using high pressure processing in combination with thermal processing. Inactivation of spores packaged in three packaging systems (plastic pouches, cryovials, and transfer pipettes) was measured in two pressure test systems (laboratory-scale and pilot-scale) at 700 MPa and >105°C. Total destruction (>6.6-log reduction) of the spores packaged in the graduated tube part of transfer pipettes was obtained after processing for up to 10 min at 118°C and 700 MPa in both pressure test systems, compared with the spores packaged either in plastic pouches or cryovials. Reduction of spores packaged in plastic pouches was lowest (<4.8 log) for both pressure test systems when processed at the same conditions (i.e., 700 MPa and 118°C). Within the pilot-scale pressure system, increasing the process temperature from 118 to 121°C at 700 MPa for 10 min resulted in only a small increase in spore reduction (<5.1 log) for spores packaged in plastic pouches, whereas there were no recoverable spores for either of the other two packaging systems. Use of plastic pouches for packaging spores in inactivation kinetic studies could lead to erroneous conclusions about the effect of high pressure in combination with heat. BioGlycol is the pressure-heat transfer fluid of choice, as compared with Duratherm oil, to maximize the temperature response rate during pressurization within the laboratory-scale pressure test system.

Evaluation of peracetic acid fog for the inactivation of Bacillus anthracis spore surrogates in a large decontamination chamber

The purpose of this study was to evaluate the sporicidal (inactivation of bacterial spores) effectiveness and operation of a fogging device utilizing peracetic acid/hydrogen peroxide (PAA). Experiments were conducted in a pilot-scale 24m3 stainless steel chamber using either biological indicators (BIs) or bacterial spores deposited onto surfaces via aerosolization. Wipe sampling was used to recover aerosol-deposited spores from chamber surfaces and coupon materials before and after fogging to assess decontamination efficacy. Temperature, relative humidity, and hydrogen peroxide vapor levels were measured during testing to characterize the fog environment. The fog completely inactivated all BIs in a test using a 60mL solution of PAA (22% hydrogen peroxide/4.5% peracetic acid). In tests using aerosol-deposited bacterial spores, the majority of the post-fogging spore levels per sample were less than 1 log colony forming units, with a number of samples having no detectable spores. In terms of decontamination efficacy, a 4.78 log reduction of viable spores was achieved on wood and stainless steel. Fogging of PAA solutions shows potential as a relatively easy to use decontamination technology in the event of contamination with Bacillus anthracis or other spore-forming infectious disease agents, although additional research is needed to enhance sporicidal efficacy.

Influence of Long Chain Free Fatty Acids on the Thermal Resistance Reduction of Bacterial Spores

Aims: The objective of this study was to investigate the effect of free fatty acid length chain and unsaturated bond number on the heat resistance and recovery media of bacterial spores. Methods and results: For 6 species, bacterial spore heat resistances were estimated at different free fatty acid concentrations added to heating media or in recovery media. The addition of free fatty acids to heating media has a slight influence on the heat resistance of bacterial spores whatever the species or type of acid studied. On the contrary, the addition of free fatty acids to the recovery medium after the heat treatment greatly reduces the ability to bacterial spores to recover and form colonies. This effect varies depending on chain length, unsaturated bond number of fatty acid and on the bacterial strain studied. Conclusion: The presence of free acids in the recovery media is an additive stress which decreases the capability of injured spores to germinate and grow thereafter. Significance and impact of this study: The impact of free fatty acids presented in this study can be taken into account to reduce the thermal intensity of food sterilization in relation to their availability in food matrix.

Inactivation of Bacillus sporothermodurans LTIS27 spores by high hydrostatic pressure and moderate heat studied by response surface methodology

Bacillus sporothermodurans is a milk spoilage bacterium producing resistant endospores that survive ultra-high temperature treatment. The inactivation of B. sporothermodurans LTIS27 spores by combined hydrostatic pressure and heat treatments was studied. A central composite experimental design was used to evaluate the effect of pressure (300–500 MPa), temperature (30–50 °C), and pressure-holding time (10–30 min) on the inactivation of spores in distilled water and skim milk. The inactivation observed was shown to fit well with the values predicted by the quadratic equation, since Radj2 were 0.970 and 0.977 in distilled water and milk, respectively. By analyzing the response surface plots, the inactivation was shown to be higher in distilled water than in milk under all the conditions tested. This was probably due to a protective effect of milk against inactivation by pressure. The optimum process parameter values for a 5-log cycle reduction of spores were calculated as 477 MPa/48 °C for 26 min and 495 MPa/49 °C for 30 min in water and in milk, respectively. This study shows the efficiency of hydrostatic pressure in combination with moderate temperature to inactivate B. sporothermodurans spores. Such treatments could be applied by the dairy industry to ensure the commercial sterility of UHT milk.

Inactivation of Penicillium aerosols by atmospheric positive corona discharge processing

Microbial infection, especially from mold aerosols inside storage facilities, is an important cause of the short-term deterioration of horticultural products. As a novel non-thermal sterilization technology, atmospheric positive corona discharge (APCD) is an efficient method for introducing low-temperature plasma to inactivate pathogens in horticultural cold-storage environments. Here, APCD was investigated for the inactivation of Penicillium expansum aerosols. Scanning electron microscopy and transmission electron microscopy revealed noticeable changes in the morphology and interior of P. expansum spores on agar plates after exposure to low-temperature plasma generated by APCD. A first-order kinetics model better supported the survival curves of P. expansum aerosols exposed to low-temperature plasma than other models such as Weibull and simplified Baranyi distribution. The D-value (the time taken to achieve a 10-fold reduction in fungal spores in first-order kinetics) varied from 70 to 204min at various conditions of discharge-power (0.65–1.65VA) and air-flow (300–900L/h). A model was constructed using response surface methodology to describe the relationship between sterilization efficiency in terms of the D-value and the key parameters (discharge-power and air-flow) under conditions of temperature and relative humidity at 3±1°C and 90±5%. The kinetics description of the inactivation of P. expansum aerosols will be instructive for the potential application of APCD in horticultural cold storage.