Effect of temperature, pH and presence of nisin on inactivation of Salmonella Typhimurium and Escherichia coli O157:H7 by pulsed electric fields

Pulsed electric field technology in vegetable and fruit juice processing: A review

The worldwide market for vegetable and fruit juices stands as a thriving sector with projected revenues reaching to $81.4 billion by 2024 and an anticipated annual growth rate of 5.27% until 2028. Juices offer a convenient means of consuming bioactive compounds and essential nutrients crucial for human health. However, conventional thermal treatments employed in the juice and beverage industry to inactivate spoilage and pathogenic microorganisms, as well as endogenous enzymes, can lead to the degradation of bioactive compounds and vitamins. In response, non-thermal technologies have emerged as promising alternatives to traditional heat processing, with pulsed electric field (PEF) technology standing out as an innovative and sustainable choice. In this context, this comprehensive review investigated the impact of PEF on the microbiological, physicochemical, functional, nutritional, and sensory qualities of vegetable and fruit juices. PEF induces electroporation phenomena in cell membranes, resulting in reversible or irreversible changes. Consequently, a detailed examination of the effects of PEF process variables on juice properties is essential. Monitoring factors such as electric field strength, frequency, pulse width, total treatment time, and specific energy is important to ensure the production of a safe and chemically/kinetically stable product. PEF technology proves effective in microbial and enzymatic inactivation within vegetable and fruit juices, mitigating factors contributing to deterioration while maintaining the physicochemical characteristics of these products. Furthermore, PEF treatment does not compromise the content of substances with functional, nutritional, and sensory properties, such as phenolic compounds and vitamins. When compared to alternative processing methods, such as mild thermal treatments and other non-thermal technologies, PEF treatment consistently demonstrates comparable outcomes in terms of physicochemical attributes, functional properties, nutritional quality, and overall safety.

Phages for treatment of Escherichia coli infections

Diseases due to infections by pathogenic Escherichia coli strains are on the rise and with the growing antimicrobial resistance among bacterial pathogens, including this group. Thus, alternative therapeutic options are actively investigated. Among these alternatives is phage therapy. In the case of E. coli, the combination of the well understood biology of this species and its bacteriophages represents a good guiding example for the establishment of phage therapy principles against this and other pathogenic bacteria. In this chapter, the procedures toward the development of phage therapy against pathogenic E. coli with the use of T-even group of phages are discussed. These steps involve the isolation, purification, characterisation and large-scale production of these phages, with formulation of phage cocktails for in vitro and in vivo studies. The main emphasis is made on phage therapy of enteropathogenic E. coli O157:H, which is one of the prominent human pathogens but persists as a commensal bacterium in many food animals. The implementation of phage therapy against E. coli O157:H within the One Health framework in carrier animals and for treatment of meat, vegetables, fruits and other agricultural produce thus would allow controlling and interrupting the transmission routes of this pathogen to the human food chain and preventing human disease. Examples of successful control and elimination of E. coli O157:H are given, while the problems encountered in phage treatment of this pathogen are also discussed.

Pulsed electric field processing as an alternative to sulfites (SO2) for controlling saccharomyces cerevisiae involved in the fermentation of Chardonnay white wine

The use of sulfites (SO₂) for microbial control in the winemaking process is currently being questioned due to its potential toxicity. Pulsed Electric Fields (PEF) are capable of inactivating microorganisms at low temperatures, thus avoiding the negative effects of heat on food properties. In this study, the capacity of PEF technology for the decontamination of yeasts involved in the fermentation process of Chardonnay wine from a winery was evaluated. PEF treatments at 15 kV/cm of low (65 µs, 35 kJ/kg) and higher intensity (177 µs 97 kJ/kg) were selected for evaluating the microbial stability, physicochemical and volatile composition of wine. Even with the least intense PEF-treatment, Chardonnay wine remained yeast-free during 4 months of storage without sulfites. PEF-treatments did not affect the wine's oenological parameters or its aroma during storage. This study, therefore, reveals the potential of PEF technology as an alternative to sulfites for the microbiological stabilization of wine.

Microbial Decontamination of Red Wine by Pulsed Electric Fields (PEF) after Alcoholic and Malolactic Fermentation: Effect on Saccharomyces cerevisiae, Oenococcus oeni, and Oenological Parameters during Storage

New techniques are required to replace the use of sulfur dioxide (SO₂) or of sterilizing filtration in wineries, due to those methods' drawbacks. Pulsed electric fields (PEF) is a technology capable of inactivating microorganisms at low temperatures in a continuous flow with no detrimental effect on food properties. In the present study, PEF technology was evaluated for purposes of microbial decontamination of red wines after alcoholic and malolactic fermentation, respectively. PEF combined with SO₂ was evaluated in terms of microbial stability and physicochemical parameters over a period of four months. Furthermore, the effect of PEF on the sensory properties of red wine was compared with the sterilizing filtration method. Results showed that up to 4.0 Log₁₀ cycles of S. cerevisiae and O. oeni could be eradicated by PEF and sublethal damages and a synergetic effect with SO₂ were also observed, respectively. After 4 months, wine treated by PEF after alcoholic fermentation was free of viable yeasts; and less than 100 CFU/mL of O. oeni cells were viable in PEF-treated wine added with 20 ppm of SO₂ after malolactic fermentation. No detrimental qualities were found, neither in terms of oenological parameters, nor in the sensory parameters of wines subjected to PEF after storage time.

Biocontrol Approaches against Escherichia coli O157:H7 in Foods

Shiga-toxin-producing Escherichia coli O157:H7 is a well-known water- and food-borne zoonotic pathogen that can cause gastroenteritis in humans. It threatens the health of millions of people each year; several outbreaks of E. coli O157:H7 infections have been linked to the consumption of contaminated plant foods (e.g., lettuce, spinach, tomato, and fresh fruits) and beef-based products. To control E. coli O157:H7 in foods, several physical (e.g., irradiation, pasteurization, pulsed electric field, and high-pressure processing) and chemical (e.g., using peroxyacetic acid; chlorine dioxide; sodium hypochlorite; and organic acids, such as acetic, lactic, and citric) methods have been widely used. Although the methods are quite effective, they are not applicable to all foods and carry intrinsic disadvantages (alteration of sensory properties, toxicity, etc.). Therefore, the development of safe and effective alternative methods has gained increased attention recently. Biocontrol agents, including bacteriophages, probiotics, antagonistic bacteria, plant-derived natural compounds, bacteriocins, endolysins, and enzymes, are rapidly emerging as effective, selective, relatively safe for human consumption, and environmentally friendly alternatives. This paper summarizes advances in the application of biocontrol agents for E. coli O157:H7 control in foods.

Electroporation as an Efficacy Potentiator for Antibiotics With Different Target Sites

Antibiotic resistance is a global health threat, and there is ample motivation for development of novel antibacterial approaches combining multiple strategies. Electroporation is among the promising complementary techniques – highly optimizable, effective against a broad range of bacteria, and largely impervious to development of resistance. To date, most studies investigating electroporation as an efficacy potentiator for antibacterials used substances permissible in food industry, and only few used clinical antibiotics, as acceptable applications are largely limited to treatment of wastewaters inherently contaminated with such antibiotics. Moreover, most studies have focused mainly on maximal achievable effect, and less on underlying mechanisms. Here, we compare Escherichia coli inactivation potentiation rates for three antibiotics with different modes of action: ampicillin (inhibits cell wall synthesis), ciprofloxacin (inhibits DNA replication), and tetracycline (inhibits protein synthesis). We used concentrations for each antibiotic from 0 to 30× its minimum inhibitory concentration, a single 1-ms electric pulse with amplitude from 0 to 20 kV/cm, and post-pulse pre-dilution incubation either absent (≲1 min) or lasting 60 min, 160 min, or 24 h. Our data show that with incubation, potentiation is significant for all three antibiotics, increases consistently with pulse amplitude, and generally also with antibiotic concentration and incubation time. With incubation, potentiation for ampicillin was rather consistently (although with weak statistical significance) superior to both ciprofloxacin and tetracycline: ampicillin was superior to both in 42 of 48 data points, including 7 with significance with respect to both, while at 60- and 160-min incubation, it was superior in 31 of 32 data points, including 6 with significance with respect to both. This suggests that electroporation potentiates wall-targeting antibiotics more than those with intracellular targets, providing motivation for in-depth studies of the relationship between the mode of action of an antibiotic and its potentiation by electroporation. Identification of substances permissible in foods and targeting the cell wall of both Gram-negative and Gram-positive bacteria might provide candidate antibacterials for broad and strong potentiation by electroporation applicable also for food preservation.

Optimization of the In Vitro Bactericidal Effect of a Mixture of Chlorine and Sodium Gallate against Campylobacter spp. and Arcobacter butzleri

ABSTRACT

Campylobacter spp. and Arcobacter butzleri are foodborne pathogens associated with the consumption of contaminated raw chicken meat. At the industry level, the combination of new and common antimicrobials could be used as a strategy to control the presence of pathogens in chicken carcasses. The objective of this study was to determine the bacteriostatic and bactericidal effects of a mixture of chlorine (Cl) and sodium gallate (SG) on a mixture of two Campylobacter species (Campylobacter jejuni and Campylobacter coli) and A. butzleri. Using a central composite experimental design, it was established that the optimum inhibitory SG-Cl concentration for Campylobacter spp. was 44 to 45 ppm. After 15 h of incubation, Campylobacter species growth was reduced by 37.5% and the effect of Cl was potentiated by SG at concentrations above 45 ppm. In the case of A. butzleri, optimum levels of 28 and 41 ppm were observed for SG and Cl, respectively; no synergism was reported, as this bacterium was more sensitive to lower Cl concentrations than Campylobacter. After a 20-min pretreatment with peracetic acid (50 ppm), the optimum condition to achieve a >1.0-Log CFU/mL reduction of Campylobacter spp. was exposure to 177 ppm of Cl and 44 ppm of SG for 56 min. As A. butzleri showed lower resistance to the bacteriostatic effect of the Cl-SG combination, it was assumed that optimum bactericidal conditions for Campylobacter spp. were effective to control the former; this was confirmed with subsequent validation of the model. The SG-Cl combination has bactericidal properties against Campylobacter and A. butzleri, and it may be a useful strategy to improve sanitary practices applied in the poultry industry.

HIGHLIGHTS

Effects of Ultrahigh Temperature Pasteurization on the Liquid Components and Functional Properties of Stored Liquid Whole Eggs

Ultrahigh temperature (UHT) pasteurization is often used to sterilize liquid whole eggs in egg processing enterprises in China. Although this treatment generates satisfactory sterilization effect, there are few studies on the processing characteristics and physical and chemical properties of the liquid whole eggs treated by UHT pasteurization. We compared the physical and chemical properties (i.e., foaming ability and stability, emulsification ability and stability, viscosity, thiol content, gel strength, and color) of unsterilized eggs and liquid whole eggs pasteurized with UHT over five weeks of storage. The emulsifying properties of sterilized liquid whole eggs were initially low and decreased further with the storage time. The emulsification stability index of UHT-pasteurized liquid whole eggs was higher than that of unsterilized eggs and increased by 21.9%, from 7.850 to 9.567. The foaming ability of UHT-pasteurized and unsterilized liquid whole eggs increased by 33.38% and 15.48%, respectively. The viscosity, gel strength, and soluble protein content were higher in UHT-pasteurized liquid whole eggs than those in unsterilized liquid whole eggs and increased further with storage time. Our results demonstrate that UHT pasteurization preserves and improves the processing characteristics and shelf life of liquid whole eggs.

Modular Serial Flow Through device for pulsed electric field treatment of the liquid samples

In biotechnology, medicine, and food processing, simple and reliable methods for cell membrane permeabilization are required for drug/gene delivery into the cells or for the inactivation of undesired microorganisms. Pulsed electric field treatment is among the most promising methods enabling both aims. The drawback in current technology is controllable large volume operation. To address this challenge, we have developed an experimental setup for flow through electroporation with online regulation of the flow rate with feedback control. We have designed a modular serial flow-through co-linear chamber with a smooth inner surface, the uniform cross-section geometry through the majority of the system’s length, and the mesh in contact with the electrodes, which provides uniform electric field distribution and fluid velocity equilibration. The cylindrical cross-section of the chamber prevents arching at the active treatment region. We used mathematical modeling for the evaluation of electric field distribution and the flow profile in the active region. The system was tested for the inactivation of Escherichia coli. We compared two flow-through chambers and used a static chamber as a reference. The experiments were performed under identical experimental condition (product and similar process parameters). The data were analyzed in terms of inactivation efficiency and specific energy consumption.

Severely Heat Injured Survivors of E. coli O157:H7 ATCC 43888 Display Variable and Heterogeneous Stress Resistance Behavior

Although minimal food processing strategies aim to eliminate foodborne pathogens and spoilage microorganisms through a combination of mild preservation techniques, little is actually known on the resistance behavior of the small fraction of microorganisms surviving an inimical treatment. In this study, the conduct of severely heat stressed survivors of E. coli O157:H7 ATCC 43888, as an indicator for the low infectious dose foodborne enterohemorrhagic strains, was examined throughout their resuscitation and outgrowth. Despite the fact that these survivors were initially sublethally injured, they were only marginally more sensitive to a subsequent heat treatment and actually much more resistant to a subsequent high hydrostatic pressure (HHP) shock in comparison with unstressed control cells. Throughout further resuscitation, however, their initial HHP resistance rapidly faded out, while their heat resistance increased and surpassed the initial heat resistance of unstressed control cells. Results also indicated that the population eventually emerging from the severely heat stressed survivors heterogeneously consisted of both growing and non-growing cells. Together, these observations provide deeper insights into the particular behavior and heterogeneity of stressed foodborne pathogens in the context of food preservation.

Effect of Pulsed Electric Field on Membrane Lipids and Oxidative Injury of Salmonella typhimurium

Salmonella typhimurium cells were subjected to pulsed electric field (PEF) treatment at 25 kV/cm for 0–4 ms to investigate the effect of PEF on the cytoplasmic membrane lipids and oxidative injury of cells. Results indicated that PEF treatment induced a decrease of membrane fluidity of Salmonella typhimurium (S. typhimuriumi), possibly due to the alterations of fatty acid biosynthesis-associated gene expressions (down-regulation of cfa and fabA gene expressions and the up-regulation of fabD gene expression), which, in turn, modified the composition of membrane lipid (decrease in the content ratio of unsaturated fatty acids to saturated fatty acids). In addition, oxidative injury induced by PEF treatment was associated with an increase in the content of malondialdehyde. The up-regulation of cytochrome bo oxidase gene expressions (cyoA, cyoB, and cyoC) indicated that membrane damage was induced by PEF treatment, which was related to the repairing mechanism of alleviating the oxidative injury caused by PEF treatment. Based on these results, we achieved better understanding of microbial injury induced by PEF, suggesting that micro-organisms tend to decrease membrane fluidity in response to PEF treatment and, thus, a greater membrane fluidity might improve the efficiency of PEF treatment to inactivate micro-organisms.

Comparative Resistance of Bacterial Foodborne Pathogens to Non-thermal Technologies for Food Preservation

In this paper the resistance of bacterial foodborne pathogens to manosonication (MS), pulsed electric fields (PEFs), high hydrostatic pressure (HHP), and UV-light (UV) is reviewed and compared. The influence of different factors on the resistance of bacterial foodborne pathogens to these technologies is also compared and discussed. Only results obtained under harmonized experimental conditions have been considered. This has allowed us to establish meaningful comparisons and draw significant conclusions. Among the six microorganisms here considered, Staphyloccocus aureus is the most resistant foodborne pathogen to MS and HHP and Listeria monocytogenes to UV. The target microorganism of PEF would change depending on the treatment medium pH. Thus, L. monocytogenes is the most PEF resistant microorganism at neutral pH but Gram-negatives (Escherichia coli, Salmonella spp., Cronobacter sakazakii, Campylobacter jejuni) would display a similar or even higher resistance at acidic pH. It should be noted that, in acidic products, the baroresistance of some E. coli strains would be comparable to that of S. aureus. The factors affecting the resistance of bacterial foodborne pathogens, as well as the magnitude of the effect, varied depending on the technology considered. Inter- and intra-specific differences in microbial resistance to PEF and HHP are much greater than to MS and UV. Similarly, both the pH and aw of the treatment medium highly condition microbial resistance to PEF and HHP but no to MS or UV. Growth phase also drastically affected bacterial HHP resistance. Regarding UV, the optical properties of the medium are, by far, the most influential factor affecting its lethal efficacy. Finally, increasing treatment temperature leads to a significant increase in lethality of the four technologies, what opens the possibility of the development of combined processes including heat. The appearance of sublethally damaged cells following PEF and HHP treatments could also be exploited in order to design combined processes. Further work would be required in order to fully elucidate the mechanisms of action of these technologies and to exhaustively characterize the influence of all the factors acting before, during, and after treatment. This would be very useful in the areas of process optimization and combined process design.

Ziziphora clinopodioides Essential Oil and Nisin as Potential Antimicrobial Agents against Escherichia coli O157:H7 in Doogh (Iranian Yoghurt Drink)

The aim of the present study was to evaluate the effects of Ziziphora clinopodioides essential oil (0.1 and 0.2%) and nisin (250 and 500 IU/mL) separately and in combination on survival of Escherichia coli O157:H7 inoculated in Doogh (Iranian yoghurt drink) during storage under refrigerated temperature (4 ± 1°C) for 9 days. Viability of Lactobacillus casei at different concentrations of Z. clinopodioides essential oil (0.1 and 0.2%) in Doogh was also examined. The major components were carvacrol (64.22%), thymol (19.22%), γ-terpinene (4.63%), and p-cymene (4.86%). There was no significant difference (p > 0.05) between samples treated with nisin and those of untreated samples. Samples treated with both concentrations of the essential oil (0.1 and 0.2%) showed populations of E. coli O157:H7 significantly (p < 0.05) lower than those of untreated samples. The essential oil of Z. clinopodioides in combination with nisin had a potential synergistic effect against E. coli O157:H7 in Doogh samples after 5 days. The count of L. casei was not inhibited by different concentrations of the Z. clinopodioides essential oil. It is concluded that the leaf essential oil of Z. clinopodioides in combination with nisin can be applied as alternative antimicrobial agents in Doogh to inhibit the growth of E. coli O157:H7.

Pulsed electric field processing of egg products: a review

Thermal processing ensures safety and enhances the shelf-life of most of the food products. It alters the structural-chemical composition, modifies heat labile components, as well as affects the functional properties of food products. This has driven the development of non-thermal food processing techniques, primarily for extending the shelf-life of different food products. These techniques are currently also being evaluated for their effects on product processing, quality and other safety parameters. Pulsed electric field (PEF) is an example of non-thermal technique which can be applied for a variety of purpose in the food processing industry. PEF can be used for antimicrobial treatment of various food products to improve the storability or food safety, for extraction and recovery of some high-value compounds from a food matrix or for stabilization of various food products through inactivation of some enzymes or catalysts. Research on the application of PEF to control spoilage or pathogenic microorganisms in different egg products is being currently focused. It has been reported that PEF effectively reduces the activity of various microorganisms in a variety of egg products. However, the PEF treatment also alters the structural and functional properties to some extent and there is a high degree of variability between different studies. In addition to integrating findings, the present review also provides several explanations for the inconsistency in findings between different studies related to PEF processing of egg products. Several specific recommendations for future research directions on PEF processing are well discussed in this review.