Microbial Inactivation Kinetics Research Articles

Thermosonication process of sour cherries: Microbial inactivation kinetics, experimental and computational fluid dynamics simulation

In this study, the inactivation of Listeria monocytogenes PTCC 1302 and Shigella sonnei PTCC 1974 of sour cherries by thermosonication (37 kHz, 300 W; 50and 60°C; 0–12 min) was evaluated. Several statistical models including polynomial, Weibull, and biphasic linear models were implemented to obtain the variation of microorganism population through time. The coupled non-linear Westervelt and heat transfer equations were solved to determine the acoustic pressure and thermal fields using computational fluid dynamics (CFD). According to the obtained results, average inactivation improvements of 15.47 and 17.13% were obtained when the temperature level was increased for both S. sonnei and L. monocytogenes, respectively. S. sonnei was more affected by the sonication procedure at the initial stages, while similar behavior was also found for L. monocytogenes but at the final stages. The maximum and minimum pressure level was obtained at ∼380 and −230 kPa, respectively. In the beginning, the hot spot was formed near the bottom of the simulated sour cherry, where the acoustic intensity was higher. Although, with the elapse of time, the temperature field became more uniform, and the hot spot moved toward the center of the sour cherry.

Hurdle approaches using conventional thermal, microwave heating and ginger essential oil in vegetable juice mixture: Heat transfer modeling and microbial inactivation kinetics

In this study, microwave (1000 W; 30 s) and conventional thermal treatments were used in combination with ginger essential oil (EO; 1, 2, 3 % (v/v)) to inactivate Salmonella Typhi and Listeria monocytogenes in a mixture of vegetable (lettuce, spinach, celery, and parsley) juice. The momentum, heat, and Maxwell equations were solved to obtain the electromagnetic and thermal fields simultaneously. Besides, the Weibull model was implemented to simulate microorganisms' inactivation and determine the initiation time and rate. Based on the results, microwave heating with 3% EO reduced the inactivation initiation time by 9.82 and 8.87 s for S. Typhi and L. monocytogenes, respectively (compared to 0 % EO). At the initial stages of heating, where the temperature level has not increased to the desired value, the addition of EO can effectively initiate the inactivation process. The maximum value of resistive losses was reported to be approximately 28 MW/m3. Microwave heating lowered the required process time from 240 to 30 s and 67 % of the consumed power compared to the conventional method. Using microwave and EO in combination can synergistically affect the inactivation of microorganisms.

Maximizing the disinfection effectiveness of 254 nm UV-C light with a special design unit: simulation and experimental approaches

We propose a special design enclosure device that promotes isotropic distribution of germicidal UV-C light for the effective disinfection of difficult to reach surfaces. We used experimental and computational approaches to investigate the disinfection efficacy of this device against Escherichia coli and Listeria innocua. Stainless steel, Copper metal, and a Copper polymer were used as solid substrates of varying roughness and hydrophobicity. Bacteria reductions of up to 6.9 log CFU were achieved at various locations relative to the UV-C source after 3 min of treatment (20–990 mJ/cm2 cumulative fluence depending on the location). Inactivation kinetics was nonlinear and followed the Weibull model (0.77 ≤ R2 ≤ 0.97). Optical ray tracing simulation was used to generate maps of spatial light distribution, which were then coupled with microbial inactivation kinetics to create spatial maps of inactivation. The modeling approach used accurately predicted microbial inactivation at various locations, with only small discrepancies (±8%) between predicted and experimental data. These findings demonstrate that the proposed device is suitable for disinfecting various hard to reach surfaces, with numerous possible applications in the food and healthcare industries. Additionally, the modeling approach used here can be used to aid in the design of a highly effective Ultraviolet treatment system.

Effect of electron beam irradiation on sliced Korean cabbage (Brassica rapa L. ssp. pekinensis) kimchi: Kinetics of microbial inactivation and changes in physiochemical and microbial quality

Ensuring microbial safety and controlled kimchi fermentation without thermal sterilization is challenging owing to the background microbiota present in raw materials of kimchi. In this study, we investigated the effect of electron beam (EB) irradiation on naturally occurring microbiota and physicochemical characteristics of sliced Korean cabbage kimchi (KCK). In addition, the inactivation kinetics of natural microbes during EB irradiation were evaluated. The total aerobic bacteria (TAB) and total lactic acid bacteria (TLAB) counts in sliced KCK significantly decreased (p < 0.05) with an increase in EB irradiation. In particular, the total coliform (TC) count in unripened and optimally ripened kimchi was reduced to below the detection limit (1 log CFU/g) following 4 kGy EB irradiation. In contrast, no significant difference was observed in the physicochemical characteristics, viz., pH, titratable acidity, salinity, electrical conductivity, and reducing sugar content between the non-irradiated and irradiated slices of KCK. These results imply that EB irradiation effectively controlled microorganisms i.e., TC without adversely affecting the quality of kimchi. Furthermore, we determined that the Gompertz model was relatively more suitable for predicting the inactivation of TAB, TLAB, TC, or yeast and molds in sliced KCK than the linear model.

Pulsed light treatment of table grape juice: Influence of matrix pH on microbial and enzyme inactivation kinetics

The influence of pulsed light (PL) treatment and matrix pH was tested in the case of green table grape juice. Escherichia coli, Listeria monocytogenes, and Saccharomyces cerevisiae were inoculated into the table grape juices with matrix pH levels of 3.0, 3.5, and 4.0. Further, the juice was treated at 378–3186 J/cm2. The Weibull model better explained the microbial inactivation data. The shape parameters (β) from the Weibull model for E. coli, L. monocytogenes, and S. cerevisiae are 0.95 ± 0.02, 0.55 ± 0.04, and 0.40 ± 0.03, respectively. A lesser δ-value (scale parameter in J/cm2) was obtained for each microorganism at a lower pH. PL exposure resulted in a lack of cell visibility, cell wall, and cell membrane disruption in bacterial cells. The inactivation of polyphenol oxidase (PPO), peroxidase (POD), and pectin methyl esterase (PME) was studied at an elevated fluence level of 1152–3186 J/cm2. Enzymes in the juice were less sensitive to PL than microorganisms. The enzyme inactivation of >90% was achieved at 3186 J/cm2; thus, the juice was adjudged as the microbially safe and enzymatically stable pasteurized sample. The PL-induced enzyme inactivation followed nth-order kinetics with an inactivation order (n) of 1.1, 1.15, and 0.85 for PPO, POD, and PME, respectively. The enzyme inactivation rate was higher at a low pH. The PL-treated pasteurized juice at pH 3.5 showed the highest sensory acceptance (7.4 out of 9), with a minimal color change, a 7% loss in total phenolics, and a 12% loss in vitamin C and flavonoids.

Pasteurization of tender coconut water by pulsed light treatment: Microbial safety, enzymatic inactivation, and impact on physicochemical properties

The study investigated the potential of pulsed light (PL) in the pasteurization of tender coconut water (TCW). The initial counts of E. coli, B. cereus and L. monocytogenes in the inoculated TCW were 7.00, 9.14 and 7.8 log10 cfu mL−1, respectively. For a PL fluence of 465 J cm−2, E. coli, B.cereus and L. monocytogenes exhibited a log reduction of 5.12, 2.97 and 3.40, respectively. Bacillus cereus and Listeria monocytogenes exhibited greater resistance than Escherichia coli in the TCW. Peroxidase (POD) was more sensitive to PL treatments than polyphenoloxidase (PPO) in TCW. Weibull model and nth order model exhibited excellent fit for microbial inactivation (R2 > 0.96) and enzyme inactivation (R2 > 0.97) kinetics, respectively. While 5-log10 reduction of B. cereus and L. monocytogenes was achieved at 2.5 kV|2.5 min (1073 J cm−2), PPO was inactivated by greater than 99% at 2.9 kV| 5 min (2988 J cm−2). While the total reducing sugars increased, the changes in color (0.49 < ΔE* < 1.51), pH, total soluble solids, and acidity were insignificant after the PL pasteurization. The PL condition of 2.9 kV|5 min preserved 21 and 24% more phenolics and ascorbic acid in TCW, along with greater sensory scores than the thermal treatment (90 °C|3 min). Industrial significanceThe outcome of this study determined the intensity (fluence of 2988 J/cm2) and penetration depth (4–5 mm) required for the pasteurization of tender coconut water (TCW). On an industrial scale of large processing volumes, continuous pulsed light (PL) pasteurization of TCW can be undertaken in an annular flow reactor or thin film flat bed chamber. The thickness of the film can be mimicked from this study to ensure adequate penetration of PL in the sample to achieve adequate lethality.

Novel pulsed infrared radiation: Effect on microbial, chemical and sensory properties of saffron (Crocus sativus L.).

In this study, the effect of pulsed infrared (PIR) irradiation on saffron microbial, chemical and sensory properties were evaluated. The PIR power (250, 350 and 450 W), the distance of sample with irradiation source (10, 20 and 30 cm), irradiation time (0-20 min) and PIR pulse (1, 2 and 3 pulse/s) were investigated. Decontamination of total bacteria and total mould and yeast flora and microbial inactivation kinetics were determined. Saffron quality by FTIR and HPLC and sensory attributes were also measured. The highest reduction of the total bacterial count (2.203 log10 CFU per g) and total mould and yeast counts (2.194 log10 CFU per g) were obtained in Sargol Negin saffron at 350 W PIR power, 10cm distance, 1.5min treatment time and 3 pulse/s. The Double Weibull model is the best-fit model for the prediction of the microbial population. Until now, there have been no reports of application for PIR in food processing and decontamination. According to the results, it can be concluded that PIR can be used as a safe method of saffron processing. Utilization of a proper decontamination method for spices especially saffron as the most expensive agricultural product is challengeable. It is recommended to use the PIR method for food processing because due to the reduction of microbial population, it can maintain foodstuff quality at an acceptable level.

Protective effects of whey protein hydrolysate on Bifidobacterium animalis ssp. lactis Probio-M8 during freeze-drying and storage.

We evaluated the potential of whey protein hydrolysate as a lyoprotectant for maintaining the cell viability of Bifidobacterium animalis ssp. lactis Probio-M8 during freeze-drying and subsequent storage. The moisture content and water activity of the lyophilized samples treated by different concentrations of whey protein hydrolysate were ≤5.23 ± 0.33 g/100 g and ≤0.102 ± 0.003, respectively. During storage at 25°C and 30°C, whey protein hydrolysate had a stronger protective effect on B. lactis Probio-M8 than the same concentration of whey protein. Using the Excel tool GinaFit, we estimated the microbial inactivation kinetics during storage. Whey protein hydrolysate reduced cell damage caused by an increase in temperature. Whey protein hydrolysate could protect cells by increasing the osmotic pressure as a compatible solute. Whey protein hydrolysate improved cell membrane integrity and reduced the amounts of reactive oxygen species and malondialdehyde produced. The findings indicated that whey protein hydrolysate was a novel antioxidant lyoprotectant that could protect probiotics during freeze-drying and storage.

The Biochemical Mechanisms of Antimicrobial Photodynamic Therapy†.

The unbridled dissemination of multidrug-resistant pathogens is a major threat to global health and urgently demands novel therapeutic alternatives. Antimicrobial photodynamic therapy (aPDT) has been developed as a promising approach to treat localized infections regardless of drug resistance profile or taxonomy. Even though this technique has been known for more than a century, discussions and speculations regarding the biochemical mechanisms of microbial inactivation have never reached a consensus on what is the primary cause of cell death. Since photochemically generated oxidants promote ubiquitous reactions with various biomolecules, researchers simply assumed that all cellular structures are equally damaged. In this study, biochemical, molecular, biological and advanced microscopy techniques were employed to investigate whether protein, membrane or DNA damage correlates better with dose-dependent microbial inactivation kinetics. We showed that although mild membrane permeabilization and late DNA damage occur, no correlation with inactivation kinetics was found. On the other hand, protein degradation was analyzed by three different methods and showed a dose-dependent trend that matches microbial inactivation kinetics. Our results provide a deeper mechanistic understanding of aPDT that can guide the scientific community toward the development of optimized photosensitizing drugs and also rationally propose synergistic combinations with antimicrobial chemotherapy.

Inactivation kinetics of different flexible packing materials for decontamination of yellowfin tuna Thunnus albacares using pulsed light technology

Comparative efficiency of three different packing materials for post-packaging decontamination of yellowfin tuna Thunnus albacares steaks using pulsed light (PL) technology was investigated during the study. The packing materials used were 300 gauge low density polyethylene (LDPE), 12 µ polyester 300 guage polyethylene (PEST/PE) and 300 gauge cast polypropylene (CPP). Inactivation curves were plotted separately for each material for pulsed light exposure time ranging from 0 to 12 s. The curves were fitted with three different models viz, (i) log-linear, (ii) log-linear with Geeraerd and (iii) log-linear with Weibull model and corresponding goodness-of-fit statistics were estimated. Considering the least treatment time for achieving log microbial reduction, CPP was found to be the ideal choice among the three packaging materials. Among the three models, considering the lowest root-mean-square error values (0.0291, 0.0210 and 0.0141 for samples packed in LDPE, PEST/PE and CPP respectively), Weibull model was found to be most appropriate for describing the inactivation curves in all sample cases. Therefore, inactivation curves of steaks packed in CPP was validated with the Weibull model. The corresponding root-mean-square error (0.1036) and correlation coefficient (0.9974) showed that this model can be effectively utilised for modelling the microbial inactivation kinetics using pulsed light technology.Keywords: Cast polypropylene, Inactivation kinetics, Non-thermal processing, Pulsed light technology, Statistical modelling, Yellowfin tuna

Pulsed light treatment reduces microorganisms and mycotoxins naturally present in red pepper (Capsicum annuum L.) powder

AbstractThe impact of pulsed light (PL) treatment on naturally occurring microorganisms, mycotoxins, and on physicochemical properties in red pepper powder was investigated. Powder samples were exposed to different PL treatments up to 61 pulses, with fluence ranging from 1.0 to 9.1 J/cm2. The highest fluence applied (9.1 J/cm2, 61 pulses, 20 s) resulted in 2.7, 3.1, and 4.1 log CFU/g reduction of yeasts, molds, and total plate counts (TPC), where initial microbial loads were 4.6, 5.5, and 6.5 log CFU/g, respectively. At the same fluence intensity, a maximum reduction of 67.2, 50.9, and 36.9% of aflatoxin B1 (AFB1), total aflatoxins (AF), and ochratoxin A (OTA) were detected, respectively. Proportional increase in temperature of the samples was observed from the absorbed PL energy, reaching maximum of 59.8°C. The inactivation of investigated microorganisms and mycotoxins followed first‐order kinetics (R2 &gt; 0.95). The fluence intensity at 6.9 and 9.1 J/cm2 did not cause degradation, but rather a significant (p &lt; .05) and apparent increase of total phenols. Total color difference (ΔE*) revealed only “slight differences,” compared to the untreated sample. In conclusion, higher reduction of microbial load and mycotoxins in red pepper powder could be achieved, when higher treatment intensity was applied. This suggests the PL as a potential technology for decontamination of red pepper powder and other spice powders.Practical ApplicationsPulsed light could be used for the decontamination of foods and reduce variety of spoilage and pathogenic microorganisms. Exposure of red pepper powder to different levels of doses proposed in this study demonstrates alternative approaches for microbial inactivation and mycotoxins degradation of the product. Moreover, pulsed light treatment is a young technology using short treatment times with potential feasibility. The technique can be of great interest for the scientific and industrial R&amp;D community dealing with pulsed light technology, microbial, and mycotoxins inactivation kinetics, food safety, and quality control.

The effect of ultrasound treatment in combination with nisin on the inactivation of Listeria innocua and Escherichia coli

Ultrasound, alone or in combination with natural antimicrobials, is a novel food processing technology of interest to replace traditional food decontamination methods, as it is milder than classical sterilisation (heat treatment) and maintains desirable sensory characteristics. However, ultrasound efficacy can be affected by food structure/composition, as well as the order in which combined treatments are applied. More specifically, treatments which target different cell components could result in enhanced inactivation if applied in the appropriate order. The microbial properties i.e. Gram positive/Gram negative can also impact the treatment efficacy.This work presents a systematic study of the combined effect of ultrasound and nisin on the inactivation of the bacteria Listeria innocua (Gram positive) and Escherichia coli (Gram negative), at a range of cavitation conditions (44, 500, 1000 kHz). The order of treatment application was varied, and the impact of system structure was also investigated by varying the concentration of Xanthan gum used to create the food model systems (0 – 0.5% w/v). Microbial inactivation kinetics were monitored, and advanced microscopy and flow cytometry techniques were utilised to quantify the impact of treatment on a cellular level.Ultrasound was shown to be effective against E. coli at 500 kHz only, with L. innocua demonstrating resistance to all frequencies studied. Enhanced inactivation of E. coli was observed for the combination of nisin and ultrasound at 500 kHz, but only when nisin was applied before ultrasound treatment. The system structure negatively impacted the inactivation efficacy. The combined effect of ultrasound and nisin on E. coli was attributed to short-lived destabilisation of the outer membrane as a result of sonication, allowing nisin to penetrate the cytoplasmic membrane and facilitate cell inactivation.

Heating of milk powders at low water activity to 95°C for 15 minutes using hot air-assisted radio frequency processing achieved pasteurization

Salmonella persistence in milk powders has caused several multistate foodborne disease outbreaks. Therefore, ways to deliver effective thermal treatment need to be identified and validated to ensure the microbial safety of milk powders. In this study, a process of hot air-assisted radio frequency (HARF) followed by holding at high temperatures in a convective oven was developed for pasteurization of milk powders. Heating times were compared between HARF and a convection oven for heating milk powders to a pasteurization temperature, and HARF has been shown to considerably reduce the come-up time. Whole milk powder (WMP) and nonfat dry milk (NFDM) were inoculated with a 5-serotype Salmonella cocktail and equilibrated to a water activity of 0.10 to simulate the worst case for the microbial challenge study. After heating the sample to 95°C using HARF, followed by 10 and 15 min of holding in the oven, more than 5 log reduction of Salmonella was achieved in WMP and NFDM. This study validated a HARF-assisted thermal process for pasteurization of milk powder based on previously collected microbial inactivation kinetics data and provides valuable insights to process developers to ensure microbial safety of milk powder. This HARF process may be implemented in the dairy industry to enhance the microbial safety of milk powders.

Mechanistic modeling of peracetic acid wastewater disinfection using computational fluid dynamics: Integrating solids settling with microbial inactivation kinetics

While the impact of suspended solids on chemical disinfection kinetics has been widely recognized, a detailed modeling framework for assessing their contribution on disinfection efficiency in municipal contact tanks is yet unavailable. In this paper, we conducted experimental and modeling studies to mechanistically describe the interplay between suspended solids (not removed by gravity settling in secondary clarifiers) and disinfection performance of an emerging disinfectant, peracetic acid, operated in a municipal contact tank. Specifically, we developed an integrated computational fluid dynamics (CFD) model to simultaneously predict the fate and transport of suspended solids, Escherichia coli and peracetic acid in a hypothetical reactor using an exposure-based (i.e., CT-based) inactivation rate expression. The integrated CFD model, calibrated against laboratory data, was used to gain insights on the vertical distribution and local PAA decay effect associated with solids settling and their impact on disinfectant decay and microbial inactivation. Results indicated that: (a) solids settling in contact tanks is a significant phenomenon that cannot be neglected, which can substantially impact disinfection efficiency under low flow conditions; (b) vertical solids distribution and stratification in contact tanks can strongly affect Escherichia coli inactivation by peracetic acid, as highlighted by the CFD modeling studies; (c) Escherichia coli settling is experimentally measurable, and strongly correlated with solids settling. These phenomena can be successfully integrated into a CFD model to obtain a comprehensive description of the PAA disinfection process in presence of changes in secondary effluent quality and flow, a situation typically encountered in municipal contact tanks operated in full scale wastewater treatment plants.

Microbial Inactivation on a Processed Cheese Surface by UV-A Light

Ultraviolet (UV) light has exhibited antimicrobial effects, with recent studies looking at UV-A light in particular. The objective of this study was to determine the antimicrobial mechanism and microbial inactivation kinetics of UV-A light on processed cheese. Processed cheese was inoculated with Escherichia coli K12 and Listeria innocua to yield a final concentration of ∼5 log[colony-forming units (CFU)/g] and then exposed to UV-A light for 0–60 min to determine the kinetics of microbial inactivation. The experimental data were fitted with the Weibull model of inactivation kinetics. To achieve an ∼6 log(CFU/g) decrease, UV-A light exposure for ∼70 min was required for E. coli K12 and ∼130 min for L. innocua L2. The processed cheese was analyzed using infrared spectroscopy after UV-A exposure for 0 and 60 min and showed no apparent changes in the surface chemistry. A decrease in the moisture content was noted, which caused an increase in the concentration of lipids on the surface. A statistically significant (P < 0.05) effect was observed in the color of the cheese after UV-A light exposure for 60 min. The effect of UV-A light exposure on the oxidative stress and membrane damage of both bacteria was analyzed through fluorometric techniques. A significant (P < 0.05) increase in oxidative stress and membrane damage was observed for both bacteria, which was more pronounced for E. coli K12. Our findings suggest the UV-A light could prove to be a suitable alternative for surface decontamination of dairy products.

Influence of electron beam treatment on naturally contaminated red pepper (Capsicum annuum L.) powder: Kinetics of microbial inactivation and physicochemical quality changes

This study reported the impact of electron beam (e-beam) treatment on microbiota and mycotoxins naturally present in red pepper powder and physicochemical quality changes. Treatment at 6 kGy indicated significant (p < 0.05) decontamination of yeasts and molds by 3.0 and 4.4 log CFU/g, respectively. A reduction of 4.5 log CFU/g of total plate counts (TPC) was observed at 10 kGy for 23 s. Fungal inactivation followed first-order kinetics while TPC better fitted with Gompertz function (R2 = 0.9912). E-beam treatment was not efficient for the degradation of aflatoxins but indirectly controlled their production by inactivation of mycotoxigenic molds. Indeed, reduction of 25% ochratoxin A was recorded at 30 kGy retaining >85% of total phenols, carotenoids and antioxidants activity. Moreover, treatment impact on total color difference (ΔE*) indicated ‘slight differences’. Overall, e-beam treatments up to 10 kGy were efficient in decontaminating the natural microbiota without detrimental effects on the physicochemical qualities of red pepper powder.

Microbial Modeling Needs for the Nonthermal Processing of Foods

Year 2019 marked the 20th anniversary of the Nonthermal Processing Division (NPD) of the Institute of Food Technologists (IFT). The first 20 years served to understand the extents and limitations of nonthermal food processing technologies (NTP) that evolved from emerging trends to well-established commercial operations. It is now time for a new generation of contributors to rise up to the challenge of establishing safe harbors for NTP and deepening food safety regulations that meet industrial practices, where the development of simple, reliable kinetic models plays a major role. The review presents evidence against the still accepted assumption of linear microbial inactivation kinetics modeling in NTP, and questions the contributions of traditional kinetic parameters derived from this belief like the decimal reduction time (D) and z-values, in the development of NTP guidelines. Moreover, research findings continue to support the Weibull model and derived mathematical expressions as simple, reliable equations to predict microbial inactivation in thermal and NTP, allowing the reinterpretation of some kinetic parameters (D, z) within the Weibullian context. The review also aims to serve as a starting point for readers interested in mathematical modeling by summarizing related guidelines and statistical criteria, which goes beyond simply fitting equations to experimental data. Mathematical modeling is an integral approach involving careful experimental planning, knowledge of model properties and assumptions, data visualization, evaluation of model performance, assessment of model parameter estimate uncertainty and inherent data variability, model selection, and most importantly, critical judgment and common sense to provide the model a practical context.

Microbial Inactivation by Non-equilibrium Short-Pulsed Atmospheric Pressure Dielectric Barrier Discharge (Cold Plasma): Numerical and Experimental Studies

Microbial inactivation efficacy of plasma generated by a custom-made floating electrode dielectric barrier discharge (FE-DBD) or cold plasma at three different frequencies (1 kHz, 2 kHz, and 3.5 kHz) was experimentally evaluated for its inactivation of the pathogen surrogate Enterobacter aerogenes on a glass surface to obtain inactivation kinetics. COMSOL Multiphysics® was used to numerically simulate the amount and the distribution of reactive species within an FE-DBD system. Microbial inactivation kinetics was predicted using species concentrations and microbial inactivation rates from the literature and compared with experimental data. The results showed that the FE-DBD plasma treatment achieved a microbial reduction of 4.3 ± 0.5 log CFU/surface at 3.5 kHz, 5.1 ± 0.09 log CFU/surface at 2 kHz, and 5.1 ± 0.05 log CFU/surface at 1 kHz in 2 min, 3 min, and 6 min, respectively. The predicted values were 4.02 log CFU/surface, 4.10 log CFU/surface, and 4.56 log CFU/surface at 1 kHz, 2 kHz, and 3.5 kHz, respectively. A maximum 1 log difference was observed between numerical predictions and the experimental results. The difference might be due to synergistic interactions between plasma species, UV component of FE-DBD plasma, and/or the electrical field effects, which could not be included in the numerical simulation.

Microbial inactivation by high pressure processing: principle, mechanism and factors responsible.

High-pressure processing (HPP) is a novel technology for the production of minimally processed food products with better retention of the natural aroma, fresh-like taste, additive-free, stable, convenient to use. In this regard safety of products by microbial inactivation is likely to become an important focus for food technologists from the research and industrial field. High pressure induces conformational changes in the cell membranes, cell morphology. It perturbs biochemical reactions, as well as the genetic mechanism of the microorganisms, thus ensures the reduction in the microbial count. Keeping in view the commercial demand of HPP products, the scientific literature available on the mechanism of inactivation by high pressure and intrinsic and extrinsic factors affecting the efficiency of HPP are systematically and critically analyzed in this review to develop a clear understanding of these issues. Modeling applied to study the microbial inactivation kinetics by HPP is also discussed for the benefit of interested readers.

Inactivation kinetics of waterborne virus by ozone determined by a continuous quench flow system

Ozone has a strong oxidation power that allows effective inactivation of waterborne viruses. Few studies have accurately measured the kinetic relationship between virus inactivation and ozone exposure, because the high reactivity of ozone makes it difficult to measure them simultaneously. A continuous quench flow system (CQFS) is a possible solution for analyzing such a fast reaction; however, previous studies reported that CQFS provided different results of inactivation rate constants from the batch system. The objectives of this study were (1) to develop a CQFS to evaluate the kinetics of microbial inactivation accurately, (2) to evaluate the inactivation rate constants of waterborne virus by ozone, and (3) to compare the results with previous studies. The results indicated that the simple plug flow assumption in the reaction tube of CQFS led to underestimation of the rate constants. The accurate measurement of rate constants was achieved by the pseudo-first-order reaction model that takes the residence time distribution (RTD; i.e., the laminar flow assumption) into account. The results of inactivation experiments suggested that the resistance of viruses were getting higher in the following order: Qβ < MS2, fr, GA < CVB5 Faulkner, φX-174, PV1 Sabin, CVB3 Nancy. The environmental isolates of CVB3 and CVB5 had a 2-fold higher resistance compared with their lab strains. Predicted CT values for 4-log inactivation ranged from 0.018 mg sec L−1 (Qβ) to 0.31 mg sec L−1 (CVB3 Environmental strain). The required CT values for 4-log PV1 inactivation was 0.15 mg sec L−1, which was 166-fold smaller than those reported in the United States Environmental Protection Agency guidance manuals. The overestimation in previous studies was due to the sparse assumption of RTD in the reactor. Consequently, the required ozone CT values for virus inactivation should be reconsidered to minimize the health risks and environmental costs in water treatment.