Inactivation Of Bacterial Spores Research Articles

Mechanistic insight into roles of α/β-type small acid-soluble proteins, RecA, and inner membrane proteins during bacterial spore inactivation by ohmic heating.

Ohmic heating (OH) (i.e. heating by electric field) more effectively kills bacterial spores than traditional wet heating, yet its mechanism remains poorly understood. This study investigates the accelerated spore inactivation mechanism using genetically modified spores. We investigated the effects of OH and conventional heating (CH) on various genetically modified strains of Bacillus subtilis: isogenic PS533 (wild type_1), PS578 [lacking spores' α/β-type small acid-soluble proteins (SASP)], PS2318 (lacking recA, encoding a DNA repair protein), isogenic PS4461 (wild type_2), and PS4462 (having the 2Duf protein in spores, which increases spore wet heat resistance and decreases spore inner membrane fluidity). Removal of SASP brought the inactivation profiles of OH and CH closer, suggesting the interaction of these proteins with the field. However, the reemergence of a difference between CH and OH killing for SASP-deficient spores at the highest tested field strength suggested there is also interaction of the field with another spore core component. Additionally, RecA-deficient spores yielded results like those with the wild-type spores for CH, while the OH resistance of this mutant increased at the lower tested temperatures, implying that RecA or DNA are a possible additional target for the electric field. Addition of the 2Duf protein markedly increased spore resistance both to CH and OH, although some acceleration of killing was observed with OH at 50V/cm. In summary, both membrane fluidity and interaction of the spore core proteins with electric field are key factors in enhanced spore killing with electric field-heat combinations.

Inactivation of microorganisms by high hydrostatic pressure: A literature review

The use of high hydrostatic pressure is intended to perform non-thermal inactivation of microorganisms in food products, to ensure their freshness and to prevent foodborne infections. These infections impact the healthcare system, the food industry, and consumers directly. This study aims to analyse the literature on the effectiveness of high hydrostatic pressure against pathogenic and opportunistic microorganisms transmitted through the consumption of contaminated food. Scientific publications for 2011-2023 were selected for the review. A total of 44 scientific publications were selected, the information from which was critically analysed, systematised and presented in the form of a literature review. The mechanisms of high hydrostatic pressure’s effect on microbial cells are described. To illustrate the effectiveness of high hydrostatic pressure against microorganisms, data from selected publications regarding efficiency and treatment parameters are presented in tables. The inactivation of such clinically important microorganisms as Bacillus cereus, Campylobacter jejuni, Clostridium perfringens, Escherichia coli, Listeria monocytogenes, Salmonella spp., Staphylococcus aureus and Toxoplasma gondii in liquids and food has been demonstrated. High-pressure treatment has been shown to be a non-thermal food processing method, which distinguishes this method from traditional thermal processing methods such as boiling or pasteurization. One of the notable advantages of using high hydrostatic pressure is the non-thermal inactivation of various microorganisms, which preserves the nutritional and flavour properties of the processed product. It is also noted that food products can be processed in the final packaging, which reduces the risk of microbial contamination at the post-processing stages. The main disadvantages are the impossibility of complete inactivation of bacterial spores and the high cost of high-pressure processing equipment. Combining high-pressure treatment with other methods, such as heat treatment, can overcome the limitations of spore inactivation

Post-high-pressure temperature and time — Overlooked parameters in high pressure treatment of bacterial spores

High pressure (HP) processing has high potential for bacterial spore inactivation with minimal thermal input. To advance HP germination and subsequent inactivation of spores, this study explored the physiological state of HP-treated spores using flow cytometry (FCM). Bacillus subtilis spores were treated at 550 MPa and 60 °C (very HP (vHP)) in buffer, incubated after the HP treatment, and stained for FCM analysis with SYTO16 indicating germination and propidium iodide (PI) indicating membrane damage. FCM subpopulations were analyzed depending on the HP dwell time (≤20 min), post-HP temperature (ice, 37 °C, 60 °C) and time (≤4 h), germination-relevant cortex-lytic enzymes (CLEs) and small-acid-soluble-proteins-(SASP)-degrading enzymes by using deletion strains. The effect of post-HP temperatures (ice, 37 °C) was additionally studied for moderate HP (150 MPa, 38 °C, 10 min).Post-HP incubation conditions strongly influenced the prevalence of five observed FCM subpopulations. Post-HP incubation on ice did not or only slowly shifted SYTO16-positive spores to higher SYTO16 levels. At 37 °C post-HP, this shift accelerated, and a shift to high PI intensities occurred depending on the HP dwell time. At 60 °C post-HP, the main shift was from SYTO16-positive to PI-positive subpopulations. The enzymes CwlJ and SleB, which are CLEs, seemed both necessary for PI or SYTO16 uptake, and to have different sensitivities to 550 MPa and 60 °C. Different extents of SASP degradation might explain the existence of two SYTO16-positive subpopulations. Shifts to higher SYTO16 intensities during post-HP incubation on ice or at 37 °C might rely on the activity and recovery of CLEs, SASP-degrading enzymes or their associated proteins from reversible HP-induced structural changes. These enzymes seemingly become active only during decompression or after vHP treatments (550 MPa, 60 °C). Based on our results, we provide a refined model of HP germination-inactivation of B. subtilis spores and an optimized FCM method for quantification of the safety-relevant subpopulation, i.e., vHP (550 MPa, 60 °C) superdormant spores.This study contributes to the development of mild spore inactivation processes by shedding light on overlooked parameters: post-HP incubation conditions. Post-HP conditions significantly influenced the physiological state of spores, likely due to varying enzymatic activity. This finding may explain inconsistencies in previous research and shows the importance of reporting post-HP conditions in future research. Furthermore, the addition of post-HP conditions as HP process parameter may open up new possibilities to optimize HP-based inactivation of spores for potential industrial applications in the food industry.

Identification of the Kinetic Parameters of Thermal Micro-Organisms Inactivation

A mathematical model for estimating the characteristics of the process of thermal inactivation of vegetative bacterial cells and their spores is presented. The model relates the change rate of the number of living cells as a nonlinear kinetic dependence of the p-th order, and the temperature constant of their inactivation rate is the Arrhenius function. A method for solving the inverse kinetic problem of identifying the parameters of this model from experimental data is proposed. The method is implemented through the minimization of the original functional, which reduces the number of variable parameters. The solution results of inverse problems for determining the kinetic model parameters based on the experimental data of thermal inactivation of bacterial spores B. subtilis and B. anthracis are presented. The obtained parameters are used to solve the direct problems of the dynamics of micro-organism inactivation. The calculation results represent the dependence on the time of the change number of inactivated micro-organisms, and the thermal exposure time for 99% of their deaths at different temperatures. A comparison of the results with other authors’ calculations and experimental data confirms the adequacy of the model, the high accuracy of the new solution method and the algorithm for its implementation. The developed model of thermal sterilization can be used for the selective deactivation of pathogens in the food products.

Efficacy of Dry Heat Treatment against Clostridioides difficile Spores and Mycobacterium tuberculosis on Filtering Facepiece Respirators.

The COVID-19 pandemic has required novel solutions, including heat disinfection of personal protective equipment (PPE) for potential reuse to ensure availability for healthcare and other frontline workers. Understanding the efficacy of such methods on pathogens other than SARS-CoV-2 that may be present on PPE in healthcare settings is key to worker safety, as some pathogenic bacteria are more heat resistant than SARS-CoV-2. We assessed the efficacy of dry heat treatment against Clostridioides difficile spores and Mycobacterium tuberculosis (M. tb) on filtering facepiece respirator (FFR) coupons in two inoculums. Soil load (mimicking respiratory secretions) and deionized water was used for C. difficile, whereas, soil load and PBS and Tween mixture was used for M. tb. Dry heat treatment at 85 °C for 240 min resulted in a reduction equivalent to 6.0-log10 CFU and 7.3-log10 CFU in C. difficile spores inoculated in soil load and deionized water, respectively. Conversely, treatment at 75 °C for 240 min led to 4.6-log10 CFU reductions in both soil load and deionized water. C. difficile inactivation was higher by >1.5-log10 CFU in deionized water as compared to soil load (p < 0.0001), indicating the latter has a protective effect on bacterial spore inactivation at 85 °C. For M. tb, heat treatment at 75 °C for 90 min and 85 °C for 30 min led to 8-log10 reduction with or without soil load. Heat treatment near the estimated maximal operating temperatures of FFR materials (which would readily eliminate SARS-CoV-2) did not achieve complete inactivation of C. difficile spores but was successful against M. tb. The clinical relevance of surviving C. difficile spores when subjected to heat treatment remains unclear. Given this, any disinfection method of PPE for potential reuse must ensure the discarding of any PPE, potentially contaminated with C. difficile spores, to ensure the safety of healthcare workers.

Photocatalytic Inactivation of Bacillus subtilis Spores by Natural Sphalerite with Persulfate under Visible Light Irradiation

Bacterial spores are highly resistant to be inactivated by conventional water disinfection methods. In this study, the inactivation efficiency and mechanisms of Bacillus subtitles (B. subtilis) spores by natural sphalerite (NS) with persulfate (PS) under visible light (Vis) irradiation were investigated for the first time. The NS was composed of ZnS doped with trace amounts of metal ions, including As, Fe, Cd, and Mn. The results showed that 7 log of B. subtilis spores could be completely inactivated within 5 h in the Vis/NS/PS photocatalytic system, and the inactivation efficiency was about four and seven times higher than that of the NS/PS system and the Vis/PS system, respectively. The photo-generated electrons are generated by the excitation of NS under the illumination activated PS to form PS radicals (∙SO4−) and hydroxyl radicals (∙OH), which are the main active species for spore inactivation. Mechanism studies further showed that spore inactivation was related to physiological responses, including the increase in intracellular reactive oxygen species, the change of induced antioxidant enzyme activity, and the change of total protein. Furthermore, the dynamic changes of cells during spore inactivation were observed by SEM. These results not only clarify the relationship between the cell physiological stress response and inactivation mechanism of spores, but also reveal the interaction between minerals and PS under Vis, which provides technical methods for the inactivation of bacterial spores in the field of water disinfection.

A UV-LED module that is highly effective at inactivating human coronaviruses and HIV-1

Ultraviolet (UV) light has previously been established as useful method of disinfection, with demonstrated efficacy to inactivate a broad range of microorganisms. The advent of ultraviolet light-emitting diodes provides advantages in ease of disinfection, in that there can be delivery of germicidal UV with the same light unit that delivers standard white light to illuminate a room. Herein we demonstrate the efficacy and feasibility of ultraviolet light-emitting diodes as a means of decontamination by inactivating two distinct virus models, human coronavirus 229E and human immunodeficiency virus. Importantly, the same dose of ultraviolet light that inactivated human viruses also elicited complete inactivation of ultraviolet-resistant bacterial spores (Bacillus pumilus), a gold standard for demonstrating ultraviolet-mediated disinfection. This work demonstrates that seconds of ultraviolet light-emitting diodes (UV-LED) exposure can inactivate viruses and bacteria, highlighting that UV-LED could be a useful and practical tool for broad sanitization of public spaces.

Heat Activation and Inactivation of Bacterial Spores: Is There an Overlap?

Heat activation at a sublethal temperature is widely applied to promote Bacillus species spore germination. This treatment also has the potential to be employed in food processing to eliminate undesired bacterial spores by enhancing their germination and then inactivating the less-heat-resistant germinated spores at a milder temperature. However, incorrect heat treatment could also generate heat damage in spores and lead to more heterogeneous spore germination. Here, the heat activation and heat damage profile of Bacillus subtilis spores was determined by testing spore germination and outgrowth at both population and single-spore levels. The heat treatments used were 40 to 80°C and for 0 to 300 min. The results were as follows. (i) Heat activation at 40 to 70°C promoted l-valine- and l-asparagine-glucose-fructose-potassium (AGFK)-induced germination in a time-dependent manner. (ii) The optimal heat activation temperatures for AGFK and l-valine germination via the GerB plus GerK or GerA germinant receptors were 65°C and 50 to 65°C, respectively. (iii) Heat inactivation of dormant spores appeared at 70°C, and the heat damage of molecules essential for germination and growth began at 70 and 65°C, respectively. (iv) Heat treatment at 75°C resulted in both activation of germination and damage to the germination apparatus, and 80°C treatment caused more pronounced heat damage. (v) For the spores that should withstand adverse environmental temperatures in nature, heat activation seemed functional for a subsequent optimal germination process, while heat damage affected both germination and outgrowth. IMPORTANCE Bacterial spores are thermal-stress-resistant structures that can thus survive food preservation strategies and revive through the process of spore germination. The more heat resistant spores are, the more heterogeneous their germination upon the addition of germinants. Upon germination, spores can cause food spoilage and food intoxication. Here, we provide new information on both heat activation and inactivation regimes and their effects on the (heterogeneity of) spore germination.

Inactivation of multidrug-resistant bacteria and bacterial spores and generation of high-potency bacterial vaccines using ultrashort pulsed lasers.

Multidrug-resistant organisms (MDROs) represent a continuing healthcare crisis with no definitive solution to date. An alternative to antibiotics is the development of therapies and vaccines using biocompatible physical methods such as ultrashort pulsed (USP) lasers, which have previously been shown to inactivate pathogens while minimizing collateral damage to human cells, blood proteins, and vaccine antigens. Here we demonstrate that visible USP laser treatment results in bactericidal effect (≥3-log load reduction) against clinically significant MDROs, including methicillin-resistant Staphylococcus aureus and extended spectrum beta-lactamase-producing Escherichia coli. Bacillus cereus endospores, which are highly resistant to conventional chemical and physical treatments, were also shown to be effectively inactivated by USP laser treatment, resulting in sporicidal (≥3-log load reduction) activity. Furthermore, we demonstrate that administration of USP laser-inactivated E. coli whole-cell vaccines at dosages as low as 105 cfu equivalents without adjuvant was able to protect 100% of mice against subsequent lethal challenge. Our findings open the possibility for application of USP lasers in disinfection of hospital environments, therapy of drug-resistant bacterial infections in skin or bloodstream via pheresis modalities, and in the production of potent bacterial vaccines.

Cycling versus Continuous High Pressure treatments at moderate temperatures: Effect on bacterial spores?

The advantage of using high pressure (HP) cycling treatment compared with continuous HP treatment was investigated for the inactivation of bacterial spores. The effects of parameters such as pulse number, pressure level, treatment temperature, compression and decompression rates, and time between pulses were evaluated. For this purpose, Bacillus subtilis and B. cereus spores (108 and 106 CFU/mL respectively) were suspended in 2-(N-morpholino) ethanesulfonic acid (MES) buffer solution, tryptone salt (TS) buffer solution, or infant milk and treated by HP cycling at 300–400 MPa, at 38–60 °C, for 1–5 pulses. Pressure cycling reduced the number of viable spores by 1.8 and 5.9 log respectively for B. subtilis and B. cereus species. Continuous HP treatments were performed at the same pressure and temperature for similar treatment durations. Our results showed that the spore inactivation ratio was correlated with the cumulative exposure time to pressure rather than to effects of the cycling process. Greater spore inactivation caused by HP cycling was observed only when faster compression and decompression rates were applied, probably due to adiabatic heating. A three-step kinetic model was developed, which seemed to support our hypothesis regarding the mechanisms of inactivation by pressure cycling and continuous HP treatments. Industrial relevanceThe resistance of bacterial spores to HP limits the industrial applications to refrigerated food products. In this study, we investigated the use of pressure cycling as a means to improve spore baroinactivation at moderate temperatures (T < 60 °C). We showed that cycling pressure does not significantly increase bacterial spore inactivation in comparable treatment duration, but certainly increases material fatigue in HP vessels. Thus, under moderate temperature, cycling pressure treatment is not industrially relevant.

A Computational Fluid Dynamics (CFD) model to simulate the inactivation of Geobacillus stearothermophilus spores in different moist heat sterilization environments

The aim of this study was to develop a Computational Fluid Dynamics (CFD) model to simulate the inactivation of bacterial spores of Geobacillus stearothermophilus inside a Peritoneal Dialysis Bag System (PDBS). The presented CFD model has three significant modifications in comparison to current state-of-the-art simulations of sterilization processes. (i) The CFD simulation can be used to consider the multiphase flow (water, steam, different dialysis solutions, non-condensable gases (NCGS)) inside the PDBS, the natural convection as well as the steam penetration. (ii) Experimentally obtained inactivation kinetics were added to the CFD code to enable simulation of the inactivation of G. stearothermophilus spores. (iii) The inactivation process of G. stearothermophilus spores was simulated in different sterilization environments which are present inside a PDBS. The CFD model was verified with measurements using Biological Indicators (BIs). Results showed that on the pre-CFD-simulated “worst case locations” CFD simulations and the BI-based verification were in well accordance.By using the presented CFD model, the simulation of a moist heat sterilization process can be performed for any given sterilization cycle. In addition, the model is a powerful tool that can be used to optimize steam sterilization processes and guarantee a high level of sterilization efficiency and product safety.

Combination of supercritical CO2 and high-power ultrasound for the inactivation of fungal and bacterial spores in lipid emulsions

For the first time, this study addresses the intensification of supercritical carbon dioxide (SC-CO2) treatments using high-power ultrasound (HPU) for the inactivation of fungal (Aspergillus niger) and bacterial (Clostridium butyricum) spores in oil-in-water emulsions. The inactivation kinetics were analyzed at different pressures (100, 350 and 550 bar) and temperatures (50, 60, 70, 80, 85 °C), depending on the microorganism, and compared to the conventional thermal treatment. The inactivation kinetics were satisfactorily described using the Weibull model.Experimental results showed that SC-CO2 enhanced the inactivation level of both spores when compared to thermal treatments. Bacterial spores (C.butyricum) were found to be more resistant to SC-CO2 + HPU, than fungal (A.niger) ones, as also observed in the thermal and SC-CO2 treatments. The application of HPU intensified the SC-CO2 inactivation of C.butyricum spores, e.g. shortening the total inactivation time from 10 to 3 min at 85 °C. However, HPU did not affect the SC-CO2 inactivation of A.niger spores. The study into the effect of a combined SC-CO2 + HPU treatment has to be necessarily extended to other fungal and bacterial spores, and future studies should elucidate the impact of HPU application on the emulsion’s stability.

Efficient reduction in vegetative cells and spores of Bacillus subtilis by essential oil components-coated silica filtering materials.

Inactivation of bacterial spores is a key objective for developing novel food preservation technologies. In this work, the removal properties of filtering materials based on silica microparticles functionalized with essential oil components (EOCs) (carvacrol, eugenol, thymol, and vanillin) against Bacillus subtilis, a spore-forming bacterium, in two liquid matrices were investigated. The viability of vegetative cells and spores after treatment was also evaluated. The results exhibited marked removal effectiveness against B. subtilis vegetative cells and spores after filtration with the different silica supports coated with EOCs in either sterile water or nutrient broth, with reductions of 3.2 to 4.9 log units and 3.7 to 5.0 log units for vegetative cells and spores, respectively. The fluorescent viability images revealed the poor viability of the treated B. subtilis vegetative cells and spores due to damage to the cell envelope when coming into contact with the immobilized antimicrobials. The culture counts results revealed the great inhibitory capacity of the EOC-functionalized silica microparticles against B. subtilis vegetative cells and spores after a single filtration. Hence, the present work suggests the feasibility of using EOC-functionalized supports as filtering aids to enhance the microbial quality of liquid matrices with spore-forming microorganisms. PRACTICAL APPLICATION: The developed antimicrobial-coated filters have shown remarkable removal properties against an important spore-forming bacterium in food industry. These filters may be used as a potential sterilization technique for preservation of different beverages alone or in combination with other mild-thermal or nonthermal techniques.

Bacterial Spore Inactivation in Orange Juice and Orange Peel by Ultraviolet-C Light.

Spore-forming bacteria are a great concern for fruit juice processors as they can resist the thermal pasteurization and the high hydrostatic pressure treatments that fruit juices receive during their processing, thus reducing their microbiological quality and safety. In this context, our objective was to evaluate the efficacy of Ultraviolet-C (UV-C) light at 254 nm on reducing bacterial spores of Alicyclobacillus acidoterrestris, Bacillus coagulans and Bacillus cereus at two stages of orange juice production. To simulate fruit disinfection before processing, the orange peel was artificially inoculated with each of the bacterial spores and submitted to UV-C light (97.8–100.1 W/m2) with treatment times between 3 s and 10 min. The obtained product, the orange juice, was also tested by exposing the artificially inoculated juice to UV-C light (100.9–107.9 W/m2) between 5 and 60 min. A three-minute treatment (18.0 kJ/m2) reduced spore numbers on orange peel around 2 log units, while more than 45 min (278.8 kJ/m2) were needed to achieve the same reduction in orange juice for all evaluated bacterial spores. As raw fruits are the main source of bacterial spores in fruit juices, reducing bacterial spores on fruit peels could help fruit juice processors to enhance the microbiological quality and safety of fruit juices.

Ultrasonic-assisted supercritical CO2 inactivation of bacterial spores and effect on the physicochemical properties of oil-in-water emulsions

A combined supercritical carbon dioxide and high power ultrasound treatment (SC-CO2 + HPU) to inactivate spores while minimizing the physicochemical changes in emulsions was investigated. The inactivation kinetics were obtained for Bacillus subtilis, Bacillus pumilus and Geobacillus stearothermophilus spores and the effect of the treatment conditions on the quality of the emulsions was explored using response surface methodology. The treatment for 20 min at 95 °C and 350 bar was effective at inactivating B. subtilis and B. pumilus. Treated emulsions showed, in general, minimal changes in density and good stability, although the pH decreased and the droplet size increased. The treatment at 600 bar, 95 °C and 12.5 min permitted satisfactory B. subtilis and B. pumilus inactivation with minimal physicochemical changes in the emulsions. Therefore, the use of SC-CO2 + HPU could be a viable alternative for the preservation of emulsions using temperatures lower than those of thermal treatments.

Short Wave Ultraviolet Light (UV-C) Effectiveness in the Inactivation of Bacterial Spores Inoculated in Turbid Suspensions and in Cloudy Apple Juice

Liquid foods might present interferences in their optical properties that can reduce the effectiveness of short-wave ultraviolet radiation (UV-C) treatments used for sterilization purposes. The effect of turbidity as UV-C interference factor against the inactivation of bacterial spores was analysed by using phosphate-buffered saline solutions (PBS) of different turbidity values (2000, 2500, and 3000 NTU) which were adjusted with the addition of apple fibre. These suspensions were inoculated with spores of Bacillus subtilis and Alicyclobacillus acidoterrestris. While higher UV-C doses increased the inactivation rates of spores, these were reduced when turbidity values increased; a dose of 28.7 J/mL allowed inactivation rates of B. subtilis spores of 3.96 Log in a 2000-NTU suspension compared with 2.81 Log achieved in the 3000-NTU one. Spores of B. subtilis were more UV-C-resistant than A. acidoterrestris. Cloudy apple juice inoculated with A. acidoterrestris spores was processed by UV-C at different doses in a single pass and with recirculation of the matrix through the reactor. Inactivation increased significantly with recirculation, surpassing 5 Log after 125 J/mL compared with 0.13 Log inactivation after a single-pass treatment at the same UV-C dose. UV-C treatments with recirculation affected the optical properties (absorption coefficient at 254 nm and turbidity) of juice and increased browning as UV-C doses became higher.

Bacterial spore inactivation by non-thermal technologies: resistance and inactivation mechanisms

Thermal processing remains the major technology in food industry while it inevitably destructs sensory, nutrition and functional ingredients of food. In recent years, there has been a growing interest in non-thermal process. Spores are the dormant state of vegetative cells and have unique multilayers structure. A lot of research focused on the inactivation of spores due to its extremely resistance. This review focused on the inactivation effects and mechanisms of spores by non-thermal processing. High-pressure processing inactivated spores by two step pathways. First moderate high pressure induced the germination of spores, and the resistance decreased rapidly. Then the germinated spores inactivated as followed. Some non-thermal techniques such as ultrasound and ultraviolet radiation had synergistic effects and were usually applied as hurdle technologies.

Application of ohmic heating for the inactivation of microbiological hazards in food products

AbstractOhmic heating has long been used to inactivate pathogens in food products. Several research investigations on the use of ohmic heating technology in the inactivation of microbial hazards in food products are discussed in this review. These studies are discussed under the following sub‐headings: (a) inactivation of microbiological hazards, (b) in combination treatments with other sanitizing technologies, and (c) mathematical modeling, all of which are of long‐standing interest. In this review, we evaluate ohmic heating as a rapid and volumetric heating process that inactivates microbiological hazards in food products. We also examine ohmic heating‐based combination treatments as promising methods to maximize microbial inactivation efficacy and minimize the quality deterioration of food products. We first highlight the fact that most researchers had an interest in the inactivation of vegetative pathogens, whereas only a few focused on the inactivation of bacterial spores. In general, significantly higher treatment conditions were needed to inactivate bacterial spores (&gt;95°C) than vegetative pathogens (&gt;50°C). Studies on the inactivation of viral pathogens by ohmic heating are limited, and further research is needed in this field. In the first part of this review, the nonthermal effects of ohmic heating are also discussed, which is a popular topic in the food industry. Cumulatively, research suggests that that these nonthermal effects are dependent on the treatment conditions and the electrical conductivity of different food samples. Therefore, we suggest that focus should be on the thermal rather than the nonthermal effects of ohmic heating when considering the application of this technology to inactivate pathogens. Finally, we introduced combination technology based on ohmic heating and mathematical modeling, which are of interest recently.

Enhancing the Inactivation of Bacterial Spores during Pressure-Assisted Thermal Processing

High pressure treatments have been the best pasteurization alternative to thermal processing due its capacity to reduce microbial safety risks and increase shelf life by inactivating microorganisms and key food spoilage–causing enzymes while retaining food freshness. In spite of these advantages, an important drawback limiting a wider application of this technology is its inability to inactivate bacterial spores which are resistant to several stress conditions, including high pressure. An approach to pressure-mediated spore inactivation is to promote spore germination which reduces their resistance to inactivation treatments. However, the germination response, and thus the spore inactivation rate achieved by these treatments, is strongly dependent on the food matrix, process conditions, spore physiology factors, and also on their interactions. Statistical experimental designs, such as the use of the central composite design as an optimization tool to identify effective PATP treatments as opposed to one-factor-at-a-time experimental designs, can reveal the importance of the effect of individual and combined factors on the inactivation response. A general review of these factors and examples of agents that could lower the severity of pressure treatments required to inactivate spores is here presented including the modelling of germination as affected by these factors.

Effect of pulsed electric field with moderate heat (80°C) on inactivation, thermal resistance and differential gene expression inB. cereusspores

Bacillus cereus spores pose a challenge to the food industry owing to their ability to germinate in food during storage and produce toxins. The objective of the current study was to investigate the effect of pulsed electric field (PEF) at low electric field strength (i.e., 7.3, 8.1, 8.8 and 9.4 kV/cm) and moderate temperatures (65, 70, 75 and 80°C) on B. cereus spores. PEF treatment at 9.4 kV/cm at 80°C (pulse width of 20 μs and frequency of 300 Hz) led to a 3.1 log CFU/ml reduction in the number of B. cereus spores and importantly, the D88°C values of the surviving spores were reduced by 12 min. Differential gene expression revealed the upregulation of the gene (BC1768) encoding for chitooligosaccharide deacetylase involved in peptidoglycan degradation in PEF treated spores. The gene (BC2729) encoding for a penicillin-binding protein required for septation during sporulation was downregulated in PEF treated spores. Practical applications PEF treatment is an emerging food processing technology that has gained attention owing to its potential to provide high-quality foods. However, to date the inactivation of bacterial spores by PEF has only been partially successful and then only when combined with high heat. The effect of PEF on the thermal stability of spores has not previously been reported. The current work bridges these gaps by providing insight into differential gene expression associated with the PEF treatment of B. cereus spores. The study indicates the potential for PEF to be incorporated into a hurdle regime targeting spore inactivation and provides data on specific genes that may help to provide a better understanding of the stress induced in B. cereus spores by PEF treatment.