High Levels Of Inactivation Research Articles

Impact of plasma activated water (PAW) at different temperatures on Alicyclobacillus acidoterrestris spores

This study aimed to determine the impact of plasma activated water (PAW) combined with heating on the Alicyclobacillus acidoterrestris spores’ inactivation. For this, viable spore counts were determined after contact with PAW at 20–90 °C/5–150 min and inactivation kinetic parameters were determined at 90 °C by fitting Bigelow and Weibull models. Results showed that A. acidoterrestris spores were resistant to PAW at room temperature (reduction <0.8 log CFU/mL after 2h of exposure), while PAW at 80 and 90 °C for 30 min inactivated 2.8 and 3.6 log CFU/mL, respectively, showing a synergistic effect (p < 0.05). Moreover, Weibull model fitted the data better (R2 ≥ 0.95) than Bigelow (R2 ≥ 0.90), due to the tail behavior observed. Although PAW sanitation is insufficient to guarantee high levels of inactivation of A. acidoterrestris spores, its association with mild temperatures reduces 1–2 log CFU/mL, potentially improving the shelf life of fruit products.

Occurrence and Treatment of Antibiotic-Resistant Bacteria Present in Surface Water.

According to the World Health Organization, antibiotic resistance is one of the main threats to global health. The excessive use of several antibiotics has led to the widespread distribution of antibiotic-resistant bacteria and antibiotic resistance genes in various environment matrices, including surface water. In this study, total coliforms, Escherichia coli and enterococci, as well as total coliforms and Escherichia coli resistant to ciprofloxacin, levofloxacin, ampicillin, streptomycin, and imipenem, were monitored in several surface water sampling events. A hybrid reactor was used to test the efficiency of membrane filtration, direct photolysis (using UV-C light emitting diodes that emit light at 265 nm and UV-C low pressure mercury lamps that emit light at 254 nm), and the combination of both processes to ensure the retention and inactivation of total coliforms and Escherichia coli as well as antibiotic-resistant bacteria (total coliforms and Escherichia coli) present in river water at occurrence levels. The membranes used (unmodified silicon carbide membranes and the same membrane modified with a photocatalytic layer) effectively retained the target bacteria. Direct photolysis using low-pressure mercury lamps and light-emitting diode panels (emitting at 265 nm) achieved extremely high levels of inactivation of the target bacteria. The combined treatment (unmodified and modified photocatalytic surfaces in combination with UV-C and UV-A light sources) successfully retained the bacteria and treated the feed after 1 h of treatment. The hybrid treatment proposed is a promising approach to use as point-of-use treatment by isolated populations or when conventional systems and electricity fail due to natural disasters or war. Furthermore, the effective treatment obtained when the combined system was used with UV-A light sources indicates that the process may be a promising approach to guarantee water disinfection using natural sunlight.

Can quarantine plant-parasitic nematodes within wastes be managed by useful tools in a circular economy approach?

Seen as an integral part of sustainable development, circular economy represents a model of production and consumption notably based on the limitation of both resource wastage and environmental impact. Laboratories and commercial companies working on plant pathogens, in particular quarantine species, must effectively disinfect their waste to avoid disseminating these organisms. The methods used for waste disinfection can however incur high energy costs or pose environmental and human health hazards. Here, we tested the effectiveness of five disinfection methods — chlorination, heat treatment, composting, mesophilic methanation and waste stabilization ponds — on plant-parasitic nematodes belonging to the genera Globodera and Meloidogyne. For the widely used chlorination and heat treatment methods, we showed that they can be very effective in inactivating nematodes at relatively low chlorine doses and temperatures (60 °C–3 min and 50 °C–30 min), respectively. For the three other disinfection methods tested, initially designed for waste recycling, we obtained different levels of efficiency. Composting and mesophilic methanation (based on cattle or pig slurry) both led to the complete elimination of nematodes, even for short treatment durations. However, waste stabilization ponds showed contrasting results, ranging from virtually no effect to high levels of inactivation of nematodes. Our study demonstrates that it is possible to use more environmentally friendly disinfection methods to control plant-parasitic nematodes. In particular, this finding paves the way towards the treatment of infected plant materials using composting or methanation, providing that disinfection is still reached under other (real-life) treatment conditions, especially with other kinds of waste. Both composting and methanation recycle and thus valorize infected waste; they are viable alternatives to landfilling or incineration, thereby demonstrating the usefulness of a circular economy approach.

Combination of vaporized ethyl pyruvate and non-thermal atmospheric pressure plasma for the inactivation of bacteria on lettuce surfaces

The effect of vaporized ethyl pyruvate (EP) and atmospheric pressure plasma (APP) treatments on the inactivation of total viable counts of bacteria on fresh lettuce leaves samples after treatment and during storage (1 and 3 days) at 6 and 25 °C was studied. For this purpose, freshly grown B. cereus and Escherichia coli were inoculated on the lettuce leaves prior to treatments. Combination of EP (at a concentration of around 10 μL dm−3) with APP was more effective on inactivation of bacteria when compared to EP and APP treatments separately, reducing the total viable counts nearly 5 CFU cm−2 compared to control. The use of EP and APP together led to around 2.5 more log (CFU cm−2) reductions when compared to the sole use of EP and APP separately. B. cereus cells were almost three times more susceptible to APP treatment than E. coli. Growth inhibition increased after storing the treated samples at 25 °C by around 2.5 and 1.5 logs for E. coli and B. cereus, respectively, compared to 6 °C. APP treatment time (30 and 60 s) and storage time (1 and 3 days) did not significantly affect the inactivation levels. E. coli was more effectively inactivated after EP + O2 treatment followed by storage at 25 °C. The highest level of inactivation was noted as nearly 5 log reductions. Slight differences in the peak intensities of FTIR spectra of treated lettuce samples were observed compared to control, indicating slight modifications on the chemical structure on the lettuce leaves. Industrial relevanceThe microbial load influences the quality, safety, and shelf-life of fresh produce such as lettuce. Current decontamination techniques may cause some unwanted effects such as odor, discoloration, and decreased nutritional value. This study shows that the use of the APP-EP hurdle represents a promising strategy to improve the decontamination efficiency and hence, enhance the shelf-life of freshly cut vegetables. The data obtained contribute to a better understanding of APP-EP-induced effects on the quality and shelf-life of fresh-cut lettuce and provide a scientific basis for industrial implementation.

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.

UV‐C treatment on the safety of skim milk: Effect on microbial inactivation and cytotoxicity evaluation

AbstractThe efficacy of UV‐C irradiation as a nonthermal processing method for skim milk (SM) was investigated. SM inoculated with two surrogate viruses (MS2 and T1UV), and three bacteria (Escherichia coli ATCC 25922, Salmonella enterica serovar Typhimurium ATCC 13311, and Listeria monocytogenes ATCC 19115) was treated with Deanflow UV‐C irradiation, a spiral reactor with the fluid pumped around a central low‐pressure mercury UV lamp (40 W) emitting at 254 nm wave‐length. A series of known UV doses (0–168.33 mJ·cm2) were delivered to the samples. The microbial loads of MS2, T1UV, E. coli, Salmonella, and Listeria were reduced by more than 5 log10. The inactivation kinetics of all microorganisms were best described by log linear models with a low RMSE and higher coefficient of determination (R2 &gt; 0.95). This study demonstrated that high levels of inactivation of pathogenic particles can be achieved in SM.Practical applicationsThis scientific study provides evidence based data on the advantages of UV‐C light in achieving microbial reduction in skim milk. The irradiated skim milk did not show any toxicity on mice liver and intestinal cells. UV‐C irradiation is an efficient food preservation technology and offers opportunities for dairy and food processing industries to meet the growing demand from consumers for safer foods. This exploration would provide methodological evidence for commercialization of UV‐C processing of milk and dairy based beverages.

Microbial inactivation and cytotoxicity evaluation of UV irradiated coconut water in a novel continuous flow spiral reactor

A continuous-flow UV reactor operating at 254nm wave-length was used to investigate inactivation of microorganisms including bacteriophage in coconut water, a highly opaque liquid food. UV-C inactivation kinetics of two surrogate viruses (MS2, T1UV) and three bacteria (E. coli ATCC 25922, Salmonella Typhimurium ATCC 13311, Listeria monocytogenes ATCC 19115) in buffer and coconut water were investigated (D10 values ranging from 2.82 to 4.54mJ·cm−2). A series of known UV-C doses were delivered to the samples. Inactivation levels of all organisms were linearly proportional to UV-C dose (r2>0.97). At the highest dose of 30mJ·cm−2, the three pathogenic organisms were inactivated by >5 log10 (p<0.05). Results clearly demonstrated that UV-C irradiation effectively inactivated bacteriophage and pathogenic microbes in coconut water. The inactivation kinetics of microorganisms were best described by log linear model with a low root mean square error (RMSE) and high coefficient of determination (r2>0.97). Models for predicting log reduction as a function of UV-C irradiation dose were found to be significant (p<0.05) with low RMSE and high r2. The irradiated coconut water showed no cytotoxic effects on normal human intestinal cells and normal mouse liver cells. Overall, these results indicated that UV-C treatment did not generate cytotoxic compounds in the coconut water. This study clearly demonstrated that high levels of inactivation of pathogens can be achieved in coconut water, and suggested potential method for UV-C treatment of other liquid foods. Industrial relevanceThis research paper provides scientific evidence of the potential benefits of UV-C irradiation in inactivating bacterial and viral surrogates at commercially relevant doses of 0–120mJ·cm−2. The irradiated coconut water showed no cytotoxic effects on normal intestinal and healthy mice liver cells. UV-C irradiation is an attractive food preservation technology and offers opportunities for horticultural and food processing industries to meet the growing demand from consumers for healthier and safe food products. This study would provide technical support for commercialization of UV-C treatment of beverages.

Efficacy of ultraviolet (UV‐C) light in reducing foodborne pathogens and model viruses in skim milk

The efficacy of low wavelength ultraviolet light (UV-C) as a disinfection process for a scattering fluid such as skim milk was investigated in this study. UV-C inactivation kinetics of two surrogate viruses (bacteriophages MS2 and T1UV) and three bacteria Escherichia coli ATCC 25922, S. Typhimurium ATCC 13311, Listeria monocytogenes ATCC 19115 in buffer and skim milk were investigated. UV-C irradiation was applied to stirred samples, using a collimated beam operating at 253.7 nm wavelength. A series of known UV-C doses (0–40 mJ·cm−2) were delivered to the samples except MS2 where higher doses (0–150 mJ·cm−2) were delivered. Biodosimetry, utilizing D values of viruses inactivated in buffer, was carried out to verify and calculate reduction equivalent dose. At the highest dose of 40 mJ·cm−2, the three pathogenic organisms were inactivated by more than 5 log10 (p < .05). Results provide evidence that UV-C irradiation effectively inactivated bacteriophage and pathogenic microbes in skim milk. The inactivation kinetics of microorganisms was well described by log linear and exponential models with a low root mean squared error and high coefficient of determination (r2 > 0.96). Models were validated and parameterized for predicting log reduction as a function of UV-C irradiation dose (p < .05). This study clearly demonstrated that high levels of inactivation of pathogens can be achieved in skim milk, and suggests significant potential for UV-C treatment of treating fluids that exhibit significant scattering. Practical application This research paper provides scientific evidence of the potential use of UV technology in inactivating pathogenic bacteria and model viruses in skim milk. UV-C doses were validated and verified using biodosimetry. UV-C irradiation is an attractive food preservation technology and offers opportunities for dairy and food processing industries to meet the growing demand from consumers for safer food products. This study clearly shows the potential for using UV-C treatment for treating highly scattering fluid such as skim milk. Results from this work will be used to further develop continuous flow-through UV-C systems based on dean or turbulent flow patterns.

Inactivation of Fungi in Treated Surface Water by Chloramination

This study evaluated the efficacy of chloramination to inactivate fungi isolates (Aspergillus fumigatus, Aspergillus terreus, Cladosporium tenuissimum, Penicillium citrinum, and Phoma glomerata) reported to occur in drinking water sources with different compositions. Inactivation rate constants were determined for laboratory‐grade water and real treated surface water samples, with higher rate constants than are often reported in laboratory‐grade water. The effects of conducting disinfection at different temperatures were also evaluated. Results showed that the Penicillium and Aspergillus species tested were more resistant to inactivation using chloramines than were the Cladosporium and Phoma species. Higher inactivation levels were observed at higher temperatures, especially for the Cladosporium and Phoma species tested. The degree of sensitivity of fungi to chloramination varied among the different genera. Water treatment plants applying chloramination can expect inactivation efficiency similar to free chlorine for most of the selected fungi isolates tested.

Pulsed light for the inactivation of fungal biofilms of clinically important pathogenic Candida species.

Microorganisms are naturally found as biofilm communities more than planktonic free-floating cells; however, planktonic culture remains the current model for microbiological studies, such as disinfection techniques. The presence of fungal biofilms in the clinical setting has a negative impact on patient mortality, as Candida biofilms have proved to be resistant to biocides in numerous in vitro studies; however, there is limited information on the effect of pulsed light on sessile communities. Here we report on the use of pulsed UV light for the effective inactivation of clinically relevant Candida species. Fungal biofilms were grown by use of a CDC reactor on clinically relevant surfaces. Following a maximal 72 h formation period, the densely populated biofilms were exposed to pulsed light at varying fluences to determine biofilm sensitivity to pulsed-light inactivation. The results were then compared to planktonic cell inactivation. High levels of inactivation of C. albicans and C. parapsilosis biofilms were achieved with pulsed light for both 48 and 72 h biofilm structures. The findings suggest that pulsed light has the potential to provide a means of surface decontamination, subsequently reducing the risk of infection to patients. The research described herein deals with an important aspect of disease prevention and public health.

Inactivation of Escherichia coli in fresh water with advanced oxidation processes based on the combination of O3, H2O2, and TiO2. Kinetic modeling.

The purpose of this work was to study the efficiency of different treatments, based on the combination of O3, H2O2, and TiO2, on fresh surface water samples fortified with wild strains of Escherichia coli. Moreover, an exhaustive assessment of the influence of the different agents involved in the treatment has been carried out by kinetic modeling of E. coli inactivation results. The treatments studied were (i) ozonation (O3), (ii) the peroxone system (O3/0.04mM H2O2), (iii) catalytic ozonation (O3/1g/L TiO2), and (iv) a combined treatment of O3/1g/L TiO2/0.04mM H2O2. It was observed that the peroxone system achieved the highest levels of inactivation of E. coli, around 6.80log after 10min of contact time. Catalytic ozonation also obtained high levels of inactivation in a short period of time, reaching 6.22log in 10min. Both treatments, the peroxone system (O3/H2O2) and catalytic ozonation (O3/TiO2), produced a higher inactivation rate of E. coli than ozonation (4.97log after 10min). While the combination of ozone with hydrogen peroxide or titanium dioxide thus produces an increase in the inactivation yield of E. coli regarding ozonation, the O3/TiO2/H2O2 combination did not enhance the inactivation results. The fitting of experimental values to the corresponding equations through non-linear regression techniques was carried out with Microsoft® Excel GInaFiT software. The inactivation results of E. coli did not respond to linear functions, and it was necessary to use mathematical models able to describe certain deviations in the bacterial inactivation processes. In this case, the inactivation results fit with mathematical models based on the hypothesis that the bacteria population is divided into two different subgroups with different degrees of resistance to treatments, for instance biphasic and biphasic with shoulder models. Graphical abstract ᅟ.

Ballast Waters Treatment Using UV/(H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt;+O&lt;sub&gt;3&lt;/sub&gt;) Advanced Oxidation Process with &lt;i&gt;Heterosigma akashiwo&lt;/i&gt;, &lt;i&gt;Pyramimimonas sp&lt;/i&gt;., and &lt;i&gt;Escherichia coli&lt;/i&gt; as Indicator Microorganism

Introducing invasive species through ballast water is a specific pollution problem and has recently identified as one of the main concerns of Maritime Organizations. UV/(H2O2/O3) advanced oxidation process is a technological alternative to prevent this maritime pollution. In this present study, inactivation efficiency of the UV/(H2O2/O3) processes for ballast water treatment using Heterosigma akashiwo, Pyramimimonas sp. and Escherichia coli as indicator microorganisms was investigated. Compared with individual or combined two units processes using UV, H2O2 and O3, the UV/(H2O2+O3) process yield the highest levels of inactivation due to synergistic effects. In order to study the dynamic inactivation efficiency of equipment for stimulated ballast water treatment, the effects tests of the hydraulic residence time were conducted. The results indicated that the shorter hydraulic residence time had better inactivation efficiency. These findings have implications for the ballast water treatment.

Sublethally damaged cells of Escherichia coli by Pulsed Electric Fields: The chance of transformation and proteomic assays

The present research work comprised: (i) Escherichia coli DH5α inactivation by Pulsed Electric Field (PEF) technology (E=15–30kV/cm; t=0–9000μs); (ii) a study of sublethally damaged cells generated by PEF; (iii) a quantitative and qualitative proteomic study after PEF treatment (15kV/cm–700μs); and (iv) the determination of the occurrence of electrotransformant cells, based on pUC19 plasmid ampicillin resistance. All analyses were carried out with PEF inlet temperatures of 7, 16, 24, 30 and 38°C. According to the results, a maximum of 16% of the PEF-treated population was sublethally damaged by 15kV/cm–700μs PEF treatment (30°C). In the [7–24]°C temperature range, electroporation was directly affected by temperature and directly related with the sublethally damaged population. In the temperature range [16–24]°C, a transformation frequency in the range [3–23]×10−9transformants/total CFU was observed after 15kV/cm–700μs PEF treatment. PEF treatments combined with 38°C showed no electrotransformant generation and low levels of sublethal damage, associated with the highest levels of inactivation. Proteomic studies revealed a significant change in the expression of some structural and metabolic proteins (ompA, gmhA, ClpA, RS6, Dut, FtnA, TufB, ftsH, putA, atpA, and sdhA) due to PEF treatment and temperature.

Computational fluid dynamics (CFD) modeling of UV disinfection in a closed-conduit reactor

The use of ultraviolet (UV) disinfection in water treatment is governed by several factors, including flow field, fluence rate field, and microbial inactivation kinetics. In this study, a computational fluid dynamics (CFD) model was developed for UV disinfection in a closed-conduit reactor where an improved low-Reynolds number k– ε model was used to calculate flow field and a modified P-1 model was employed to obtain the fluence rate field. The Chick–Watson model was adopted to characterize the inactivation of microorganisms. Commercial CFD software FLUENT 6.3 was employed to solve the governing equations. The predicted flow field agreed well with experimental data obtained by digital particle image velocimetry (DPIV) ( Liu et al., 2007) in terms of velocity field. The proposed CFD model was also evaluated by comparing current predictions to bioassay test data, and reasonable agreement was obtained in terms of effluent log inactivation. The impact of wall reflection of the light on the fluence rate field and the viable microorganism concentration field was investigated. The effect of wall reflection of the light on effluent log inactivation was also investigated under different water qualities and lamp power conditions. The results showed that at higher inactivation levels, the effect of wall reflection was more influential.

SWNT−MWNT Hybrid Filter Attains High Viral Removal and Bacterial Inactivation

We describe the concept and demonstrate the efficacy of a novel SWNT-MWNT hybrid filter for the removal and inactivation of microbial pathogens from water. The filter is composed of a thin SWNT layer (0.05 mg cm(-2)) on top of a thicker MWNT layer (0.27 mg cm(-2)) supported by a microporous support membrane. The SWNT-MWNT filter exhibits high log removal of several model viruses (MS2, PRD1, and T4 bacteriophages) by depth filtration, which predominantly takes place in the thicker and more uniform MWNT layer. The filter removes all bacteria by a sieving mechanism, with the top SWNT layer providing high levels of inactivation of model bacteria (Escherichia coli K12 and Staphylococcus epidermidis), as well as microbes from river water and treated wastewater effluent. The dual-layer SWNT-MWNT filter lays the framework for new possibilities in point-of-use water filtration.

Biofouling control in water by various UVC wavelengths and doses

UV light irradiation is being increasingly applied as a primary process for water disinfection, effectively used for inactivation of suspended (planktonic) cells. In this study, the use of UV irradiation was evaluated as a pretreatment strategy to control biofouling. The objective of this research was to elucidate the relative effectiveness of various targeted UV wavelengths and a polychromatic spectrum on bacterial inactivation and biofilm control. In a model system using Pseudomonas aeruginosa, the inactivation spectra corresponded to the DNA absorption spectra for all wavelengths between 220 and 280 nm, while wavelengths between 254 nm and 270 nm were the most effective for bacterial inactivation. Similar wavelengths of 254-260-270 nm were also more effective for biofilm control in most cases than targeted 239 and 280 nm. In addition, the prevention of biofilm formation by P. aeruginosa with a full polychromatic lamp was UV dose-dependent. It appears that biofilm control is improved when larger UV doses are given, while higher levels of inactivation are obtained when using a full polychromatic MP lamp. However, no significant differences were found between biofilms produced by bacteria that survived UV irradiation and biofilms produced by control bacteria at the same microbial counts. Moreover, the experiments showed that biofilm prevention depends on the post-treatment incubation time and nutrient availability, in addition to targeted wavelengths, UV spectrum and UV dose.

Disinfection of Waterborne Coliform Bacteria by Neem Oil

Abstract This study assessed the ability of Neem oil to disinfect an Escherichia coli isolate in pure laboratory-grade water and total and fecal coliform bacteria in two unfiltered surface waters. Neem oil doses as low as 2.13 g·L−1 with 5 min of mixing time achieved high levels of inactivation of the E. coli in pure laboratory-grade water (>99% inactivation). However, the disinfection of total and fecal coliforms in the unfiltered surface waters was variable and limited to <70% inactivation typically. Increasing the Neem oil dose and mixing time generally resulted in an increase in the mean inactivation of total coliform bacteria but not always of fecal coliform bacteria. The inactivation of total coliforms was consistently greater than the inactivation of fecal coliforms, suggesting a potential range of sensitivities to Neem oil among coliform bacteria. Reduced effectiveness of the Neem oil in the unfiltered surface waters compared to the pure laboratory-grade water suggests a possible interference by n...

Synergistic effect of Pulsed Electric Fields and CocoanOX 12% on the inactivation kinetics of Bacillus cereus in a mixed beverage of liquid whole egg and skim milk

With a view to extending the shelf-life and enhancing the safety of liquid whole egg/skim milk (LWE–SM) mixed beverages, a study was conducted with Bacillus cereus vegetative cells inoculated in skim milk (SM) and LWE–SM beverages, with or without antimicrobial cocoa powder. The beverages were treated with Pulsed Electric Field (PEF) technology and then stored at 5 °C for 15 days. The kinetic results were modeled with the Bigelow model, Weibull distribution function, modified Gompertz equation, and Log-logistic models. Maximum inactivation registered a reduction of around 3 log cycles at 40 kV/cm, 360 µs, 20 °C in both the SM and LWE–SM beverages. By contrast, in the beverages supplemented with the aforementioned antimicrobial compound, higher inactivation levels were obtained under the same treatment conditions, reaching a 3.30 log 10 cycle reduction. The model affording the best fit for all four beverages was the four-parameter Log-logistic model. After 15 days of storage, the antimicrobial compound lowered Bacillus cereus survival rates in the samples supplemented with CocoanOX 12% by a 4 log cycle reduction, as compared to the untreated samples without CocoanOX 12%. This could indicate that the PEF-antimicrobial combination has a synergistic effect on the bacterial cells under study, increasing their sensitivity to subsequent refrigerated storage.

Combined effect of temperature and pulsed electric fields on pectin methyl esterase inactivation in red grapefruit juice (Citrus paradisi)

Pulsed electric fields (PEF) were applied to freshly prepared grapefruit juice using a laboratory scale continuous PEF system to study the feasibility of inactivating pectin methyl esterase (PME). Square wave PEF using different combinations of pre-treatment temperature, electric field strength and treatment time were evaluated in this study. Inactivation curves for the enzyme were plotted for each parameter and inactivation kinetics were calculated. Results showed that the highest level of inactivation (96.8%) was obtained using a combination of preheating to 50 °C, and a PEF treatment time of 100 μs at 40 kV/cm. Inactivation of grapefruit PME activity could be described using an exponential decay model. Calculated D-values following a 50 °C preheat were 77.5, 76.0 and 70.4 μs at 20, 30 and 40 kV/cm, respectively. The activation energy for the inactivation of PME by PEF was 36.2 kJ/mol.

Pulsed electric field treatment as a potential method for microbial inactivation in scaffold materials for tissue engineering: the inactivation of bacteria in collagen gel

To investigate the effectiveness of pulsed electric field (PEF) treatment as a new method for inactivation of micro-organisms in complex biomatrices and to assess this by quantifying the inactivation of Escherichia coli seeded in collagen gels. PEF was applied to E. coli seeded collagen gels in static (nonflowing) chambers. The influence of electric field strength, pulse number and seeded cell densities were investigated. The highest level of inactivation was obtained at the maximum field strength of 45 kV cm(-1). For low levels of E. coli contamination (10(3) CFU ml(-1)), PEF treatment resulted in no viable E. coli being recovered from the gels. However, PEF treatment of gels containing higher cell densities (>or=10(4) CFU ml(-1)) did not achieve complete inactivation of E. coli. PEF treatment successfully inactivated E. coli seeded in collagen gels by 3 log(10) CFU ml(-1). Complete inactivation was hindered at high cell densities by the tailing effect observed. PEF shows potential as a novel, nondestructive method for decontamination of collagen-based matrices. Further investigation is required to ensure its compatibility with other proteins and therapeutic drugs for tissue engineering and drug delivery applications.