Synergetic antibacterial efficacy of cold nitrogen plasma and clove oil against Escherichia coli O157:H7 biofilms on lettuce

Determination of the combined effect of grape seed extract and cold atmospheric plasma on foodborne pathogens and their environmental stress knockout mutants

The study aimed to explore the antimicrobial efficacy of grape seed extract (GSE) and cold atmospheric plasma (CAP) individually or in combination against L. monocytogenes and E. coli wild type (WT) and their isogenic mutants in environmental stress genes. More specifically, we examined the effects of 1% (wt/vol) GSE, 4 min of CAP treatment, and their combined effect on L. monocytogenes 10403S WT and its isogenic mutants ΔsigB, ΔgadD1, ΔgadD2, ΔgadD3, as well as E. coli K12 and its isogenic mutants ΔrpoS, ΔoxyR, and ΔdnaK. In addition, the sequence of the combined treatments was tested. A synergistic effect was achieved for all L. monocytogenes strains when exposure to GSE was followed by CAP treatment. However, the same effect was observed against E. coli strains, only for the reversed treatment sequence. Additionally, L. monocytogenes ΔsigB was more sensitive to the individual GSE and the combined GSE/CAP treatment, whereas ΔgadD2 was more sensitive to CAP, as compared to the rest of the mutants under study. Individual GSE exposure was unable to inhibit E. coli strains, and individual CAP treatment resulted in higher inactivation of E. coli in comparison to L. monocytogenes with the strain ΔrpoS appearing the most sensitive among all studied strains. Our findings provide a step toward a better understanding of the mechanisms playing a role in the tolerance/sensitivity of our model Gram-positive and Gram-negative bacteria toward GSE, CAP, and their combination. Therefore, our results contribute to the development of more effective and targeted antimicrobial strategies for sustainable decontamination.IMPORTANCEAlternative approaches to conventional sterilization are gaining interest from the food industry, driven by (i) the consumer demand for minimally processed products and (ii) the need for sustainable, environmentally friendly processing interventions. However, as such alternative approaches are milder than conventional heat sterilization, bacterial pathogens might not be entirely killed by them, which means that they could survive and grow, causing food contamination and health hazards. In this manuscript, we performed a systematic study of the impact of antimicrobials derived from fruit industry waste (grape seed extract) and cold atmospheric plasma on the inactivation/killing as well as the damage of bacterial pathogens and their genetically modified counterparts, for genes linked to the response to environmental stress. Our work provides insights into genes that could be responsible for the bacterial capability to resist/survive those novel treatments, therefore, contributing to the development of more effective and targeted antimicrobial strategies for sustainable decontamination.

Integrated in-package treatment of hydrogen peroxide and cold plasma for microbial inactivation of cabbage slices

The efficacy of an in-package microbial inactivation method, combining H2O2 and atmospheric dielectric barrier discharge cold plasma (ADCP) treatments (H2O2-ADCP), in reducing contamination of Brassica oleracea (cabbage) slices was investigated. Cabbage slices were placed in a polyethylene terephthalate container with a H2O2-soaked polypropylene pad attached to the inside of the lid, followed by subjecting the closed container to ADCP treatment. The H2O2-ADCP treatment inactivated Escherichia coli O157:H7 and Listeria monocytogenes, resulting in reductions of 1.8 and 2.0 log CFU/g, respectively, which were greater than the sum of the inactivation effects observed with each individual treatment. The combined treatment decreased the count of Bacillus cereus spores and indigenous bacteria by 1.0 log spores/g and 1.3 log CFU/g, respectively. Moreover, the in-package method did not alter the moisture content or texture of cabbage slices. These results demonstrate the potential of H2O2-ADCP as a microbial decontamination method for packaged cabbage slices.

Elucidation of heavy metal content, phenolic profiles, and antioxidant activities of kale (Brassica oleracea L. var. acephala) and arugula (Brassica eruca L.) grown in urban gardens in Istanbul

This study was conducted to evaluate the effect of two distances: close (0-10 m) and far (60 m) from the heavy traffic roadside, at three different cultivation sites (MS: Mevlanakapi-Silivrikapi, SB: Silivrikapi-Belgradkapi, and BY: Belgradkapi-Yedikule kapi) along the road line. First, the phenolic compounds, antioxidant activity, and physicochemical properties in kale and arugula vegetables were examined. Second, heavy metal concentrations in vegetables, soil, and irrigated water were investigated. In both vegetables, the highest total phenolic content was detected in samples obtained from far distance in SB site (3880.3 mg/kg) for kale and in BY site (1459.9 mg/kg) for arugula, whereas the lowest content was found at the close distance in MS site for both kale (448.5 mg/kg) and arugula (586.4 mg/kg). The antioxidant activity values [mg Trolox/kg (dw)] ranged from 366.74 to 586.10 and 2349.00 to 3757.4 for kale and from 520.00 to 945.60 and 3323.00 to 5814.70 for arugula in 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) and 2,2-diphenyl-1-picrylhydrazyl methods, respectively. The levels of Cd and Hg in kale and arugula and Fe content in arugula exceeded FAO/WHO permissible limits, making them unsafe for human consumption. Meanwhile, the Pb content in kale and arugula and Fe content in kale were observed to be within acceptable limits set by FAO/WHO. In the irrigated water, the Pb value was below the permissible limit, whereas the Cd value was above it and no Hg and Fe were detected. In the soil samples, the Pb and Fe values were below the limit, whereas the Cd and Hg values were higher.

Insights into Cold Plasma Treatment on the Cereal and Legume Proteins Modification: Principle, Mechanism, and Application

Cereal and legume proteins, pivotal for human health, significantly influence the quality and stability of processed foods. Despite their importance, the inherent limited functional properties of these natural proteins constrain their utility across various sectors, including the food, packaging, and pharmaceutical industries. Enhancing functional attributes of cereal and legume proteins through scientific and technological interventions is essential to broadening their application. Cold plasma (CP) technology, characterized by its non-toxic, non-thermal nature, presents numerous benefits such as low operational temperatures, lack of external chemical reagents, and cost-effectiveness. It holds the promise of improving proteins' functionality while maximally retaining their nutritional content. This review delves into the pros and cons of different cold plasma generation techniques, elucidates the underlying mechanisms of protein modification via CP, and thoroughly examines research on the application of cold plasma in augmenting the functional properties of proteins. The aim is to furnish theoretical foundations for leveraging CP technology in the modification of cereal and legume proteins, thereby enhancing their practical applicability in diverse industries.

On the evaluation of the antimicrobial effect of grape seed extract and cold atmospheric plasma on the dynamics of Listeria monocytogenes in novel multiphase 3D viscoelastic models

The demand for products that are minimally processed and produced in a sustainable way, without the use of chemical preservatives or antibiotics have increased over the last years. Novel non-thermal technologies such as cold atmospheric plasma (CAP) and natural antimicrobials such as grape seed extract (GSE) are attractive alternatives to conventional food decontamination methods as they can meet the above demands. The aim of this study was to investigate the microbial inactivation potential of GSE, CAP (in this case, a remote air plasma with an ozone-dominated RONS output) and their combination against L. monocytogenes on five different 3D in vitro models of varying rheological, structural, and biochemical composition. More specifically, we studied the microbial dynamics, as affected by 1 % (w/v) GSE, CAP or their combination, in three monophasic Xanthan Gum (XG) based 3D models of relatively low viscosity (1.5 %, 2.5 % and 5 % w/v XG) and in a biphasic XG/Whey Protein (WPI) and a triphasic XG/WPI/fat model. A significant microbial inactivation (comparable to liquid broth) was achieved in presence of GSE on the surface of all monophasic models regardless of their viscosity. In contrast, the GSE antimicrobial effect was diminished in the multiphasic systems, resulting to only a slight disturbance of the microbial growth. In contrast, CAP showed better antimicrobial potential on the surface of the complex multiphasic models as compared to the monophasic models. When combined, in a hurdle approach, GSE/CAP showed promising microbial inactivation potential in all our 3D models, but less microbial inactivation in the structurally and biochemically complex multiphasic models, with respect to the monophasic models. The level of inactivation also depended on the duration of the exposure to GSE. Our results contribute towards understanding the antimicrobial efficacy of GSE, CAP and their combination as affected by robustly controlled changes of rheological and structural properties and of the biochemical composition of the environment in which bacteria grow. Therefore, our results contribute to the development of sustainable food safety strategies.

Cold plasma application to fresh green leafy vegetables: Impact on microbiology and product quality

Fresh green leafy vegetables (FGLVs) are consumed either garden-fresh or by going through very few simple processing steps. For this reason, foodborne diseases that come with the consumption of fresh products in many countries have prioritized the development of new and reliable technologies to reduce food-related epidemics. Cold plasma (CP) is considered one of the sustainable and green processing approaches that inactivate target microorganisms without causing a significant temperature increase during processing. This review presents an overview of recent developments regarding the commercialization potential of CP-treated FGLVs, focusing on specific areas such as microbial inactivation and the influence of CP on product quality. The effect of CP differs according to the power of the plasma, frequency, gas flow rate, application time, ionizing gases composition, the distance between the electrodes and pressure, as well as the characteristics of the product. As well as microbial decontamination, CP offers significant potential for increasing the shelf life of perishable and short-shelf-life products. In addition, organizations actively involved in CP research and development and patent applications (2016-2022) have also been analyzed.

Antibacterial mechanism of vanillin against Escherichia coli O157: H7

Vanillin, a plant-derived antimicrobial volatile substance, has potential microbial control applications in the food industry. However, the effect of vanillin on the food-borne pathogen Escherichia coli (E. coli) O157:H7 has not been well studied. This study aims to explore the antibacterial mechanism of vanillin against E. coli O157:H7. The minimum inhibitory concentration (MIC) and antibacterial effect of vanillin were determined by microdilution. Scanning electron microscopy (SEM) was used to observe the damage of vanillin to the cell membrane, while cell membrane potential and the leakage of nucleic acid protein were measured to explore the effect of vanillin on the membrane system. Confocal laser scanning and intracellular adenosine triphosphate (ATP) concentration determination were utilized to investigate the effects of vanillin on the energy, life, and death of E. coli. Finally, transcriptome sequencing was conducted to investigate the gene expression differences induced by vanillin treatment. The results showed that vanillin treatment effectively controlled E. coli O157:H7 with an MIC of 2 mg/mL. After treatment, damage to the membrane system, depolarization of the membrane, and leakage of nucleic acid and protein were observed. Meanwhile, vanillin treatment caused decreased ATP content and cell death. Transcriptome analysis showed that vanillin treatment significantly affected the expression of genes involved in cell membrane formation, tricarboxylic acid (TCA) cycling pathway, and oxidative phosphorylation pathway in E. coli O157:H7. In conclusion, membrane damage and energy metabolism disruption are important mechanisms of vanillin's inhibitory effect on E. coli O157:H7. This study provides new insights into the molecular reaction mechanism of vanillin against E. coli O157:H7, highlighting its potential as an antibacterial substance for preventing E. coli contamination in the food industry.

Effect of Dielectric Barrier Discharge Plasma against Listeria monocytogenes Mixed-Culture Biofilms on Food-Contact Surfaces

Listeria monocytogenes is a major foodborne pathogen. Various methods can be used to control biofilms formed by foodborne pathogens. Recently, the food industry has become interested in plasma, which can be used as a non-thermal technology with minimum changes to product quality. In this study, the effects of dielectric barrier discharge (DBD) plasma on L. monocytogenes mixed-culture biofilms formed on stainless steel (SS), latex hand glove (HG), and silicone rubber (SR) were investigated. DBD plasma effectuated reductions of 0.11-1.14, 0.28-1.27 and 0.37-1.55 log CFU/cm², respectively. Field emission scanning electron microscopy (FE-SEM) demonstrated that DBD plasma cuts off intercellular contact and induces cell decomposition to prevent the development of biological membranes. It was confirmed that the formed biofilms collapsed and separated into individual bacteria. Our findings suggest that DBD plasma can be used as an alternative non-heating sterilization technology in the food industry to reduce biofilm formation on bacterial targets.

Quaternary Ammonium Salt Strategy and Molecular Docking Studies of Novel 5-Acyl-8-(Arylamino)-Quinolines by Acetyl and Methanesulfonyl Chloride for Dual Evaluation Bioactivity

Six quinoline derivatives containing quaternary ammonium salts and acyl chloride groups were synthesized from ethyl 8-chloro-[1,3]dioxolo[4,5-g]quinoline-7-carboxylate in several step. With berberine as the positive control, three human cancer cell lines (HCT-116, Hela and A549) and human normal liver L-02 cell lines were used to evaluate the cytotoxicity of the newly synthesized compounds in vitro. Compound (V-X) showed good antitumor activity, and the test result of compound (VII) was better than that of positive control group. In terms of antibacterial activity, compound (V-X) has obvious inhibitory effect on Staphylococcus aureus (ATCC 29213) and Escherichia coli (ATCC 8739), and its antibacterial activity is about 1-4 times that of positive control amoxicillin and 1-2 times that of ciprofloxacin. Among them, the most effective compounds (VII) and (X) have 4-fold the antibacterial activity of amoxicillin and 2-fold the antibacterial activity of ciprofloxacin.

Supplementary Information

The online version contains supplementary material available at 10.1134/S1068162023020097.

Pepsin and Trypsin Treatment Combined with Carvacrol: An Efficient Strategy to Fight Pseudomonas aeruginosa and Enterococcus faecalis Biofilms

Biofilms consist of microbial communities enclosed in a self-produced extracellular matrix which is mainly responsible of biofilm virulence. Targeting this matrix could be an effective strategy to control biofilms. In this work, we examined the efficacy of two proteolytic enzymes, pepsin and trypsin, to degrade P. aeruginosa and E. faecalis biofilms and their synergistic effect when combined with carvacrol. The minimum dispersive concentrations (MDCs) and the contact times of enzymes, as well as the minimal inhibitory concentrations (MICs) and contact times of carvacrol, were determined against biofilms grown on polystyrene surfaces. For biofilms grown on stainless steel surfaces, the combined pepsin or trypsin with carvacrol treatment showed more significant reduction of both biofilms compared with carvacrol treatment alone. This reduction was more substantial after sequential treatment of both enzymes, followed by carvacrol with the greatest reduction of 4.7 log CFU mL−1 (p < 0.05) for P. aeruginosa biofilm and 3.3 log CFU mL−1 (p < 0.05) for E. faecalis biofilm. Such improved efficiency was also obvious in the epifluorescence microscopy analysis. These findings demonstrate that the combined effect of the protease-dispersing activity and the carvacrol antimicrobial activity could be a prospective approach for controlling P. aeruginosa and E. faecalis biofilms.

Hurdle technology based on the use of microencapsulated pepsin, trypsin and carvacrol to eradicate Pseudomonas aeruginosa and Enterococcus faecalis biofilms

The biofilm lifestyle plays a major role in the resistance and virulence of Pseudomonas aeruginosa and Enterococcus faecalis. In this study, two microencapsulated proteases (pepsin ME-PEP and trypsin ME-TRYP) were evaluated for their biofilm dispersal activity and their synergistic effect with microencapsulated carvacrol (ME-CARV). Spray-drying was used to protect enzymes and essential oil and enhance their activities. Cell count analysis proved the synergistic activity of enzymes and carvacrol treatment as biofilms were further reduced after combined treatment in comparison to ME-CARV or enzymes alone. Furthermore, results showed that sequential treatment in the order ME-TRYP - ME-PEP - ME-CARV resulted in more efficient biofilm removal with a maximum reduction of 5 log CFU mL^-1 for P. aeruginosa and 4 log CFU mL^-1 for E. faecalis. This study proposes that the combination of microencapsulated proteases with ME-CARV could be useful for the effective control of P. aeruginosa and E. faecalis biofilms.

Insights into antibiofilm mechanisms of phytochemicals: Prospects in the food industry

The recalcitrance of microbial aggregation or biofilm in the food industry underpins the emerging antimicrobial resistance among foodborne pathogens, exacerbating the phenomena of food spoilage, processing and safety management failure, and the prevalence of foodborne illnesses. The challenges of growing tolerance to current chemical and disinfectant-based antibiofilm strategies have driven the urgency in finding a less vulnerable to bacterial resistance, effective alternative antibiofilm agent. To address these issues, various novel strategies are suggested in current days to combat bacterial biofilm. Among the innovative approaches, phytochemicals have already demonstrated their excellent performance in preventing biofilm formation and bactericidal actions against resident bacteria within biofilms. However, the diverse group of phytochemicals and their different modes of action become a barrier to applying them against specific pathogenic biofilm-formers. This phenomenon mandates the need to elucidate the multi-mechanistic actions of phytochemicals to design an effective novel antibiofilm strategy. Therefore, this review critically illustrates the structure - activity relationship, functional sites of actions, and target molecules of diverse phytochemicals regarding multiple major antibiofilm mechanisms and reversal mechanisms of antimicrobial resistance. The implementation of the in-depth knowledge will hopefully aid future studies for developing phytochemical-based next-generation antimicrobials.

Control Measurements of Escherichia coli Biofilm: A Review

Escherichia coli (E. coli) is a common pathogen that causes diarrhea in humans and animals. In particular, E. coli can easily form biofilm on the surface of living or non-living carriers, which can lead to the cross-contamination of food. This review mainly summarizes the formation process of E. coli biofilm, the prevalence of biofilm in the food industry, and inhibition methods of E. coli biofilm, including chemical and physical methods, and inhibition by bioactive extracts from plants and animals. This review aims to provide a basis for the prevention and control of E. coli biofilm in the food industry.

A comprehensive study on decontamination of food-borne microorganisms by cold plasma

Food-borne microorganisms are one of the biggest concern in food industry. Food-borne microorganisms such as Listeria monocytogenes, Escherichia coli, Salmonella spp., Vibrio spp., Campylobacter jejuni, Hepatitis A are commonly found in food products and can cause severe ailments in human beings. Hence, disinfection of food is performed before packaging is performed to sterilize food. Traditional methods for disinfection of microorganisms are based on chemical, thermal, radiological and physical principles. They are highly successful, but they are complex and require more time and energy to accomplish the procedure. Cold plasma is a new technique in the field of food processing. CP treatments has no or very low effect on physical, chemical and nutritional properties of food products. This paper reviews the effect of plasma processing on food products such as change in colour, texture, pH level, protein, carbohydrate, and vitamins. Cold plasma by being a versatile, effective, economical and environmentally friendly method provides unique advantages over commercial food processing technologies for disinfection of food.

Microencapsulation of Natural Food Antimicrobials: Methods and Applications

The global demand for safe and healthy food with minimal synthetic preservatives is continuously increasing. Some natural food antimicrobials with strong antimicrobial activity and low toxicity have been considered as alternatives for current commercial food preservatives. Nonetheless, these natural food antimicrobials are hardly applied directly to food products due to issues such as food flavor or bioavailability. Recent advances in microencapsulation technology have the potential to provide stable systems for these natural antibacterials, which can then be used directly in food matrices. In this review, we focus on the application of encapsulated natural antimicrobial agents, such as essential oils, plant extracts, bacteriocins, etc., as potential food preservatives to extend the shelf-life of food products. The advantages and drawbacks of the mainly used encapsulation methods, such as molecular inclusion, spray drying, coacervation, emulsification, supercritical antisolvent precipitation and liposome and alginate microbeads, are discussed. Meanwhile, the main current applications of encapsulated antimicrobials in various food products, such as meat, dairy and cereal products for controlling microbial growth, are presented.

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.

Nanoemulsified Carvacrol as a Novel Washing Treatment Reduces Escherichia coli O157:H7 on Spinach and Lettuce

ABSTRACT

Fresh produce continues to be the main source of foodborne illness outbreaks in the United States, implicating bacterial pathogens such as Escherichia coli O157:H7 (EHEC). The efficacy of nanoemulsified carvacrol (NCR) as a washing treatment in reducing EHEC on fresh produce was investigated. Fresh baby spinach, romaine lettuce, and iceberg lettuce leaves (2.5-cm-diameter cores) were spot inoculated with a five-strain cocktail of nalidixic acid-resistant EHEC at ∼6 log CFU/cm2. After air drying for 1 h, 20 pieces of each inoculated produce leaf were immersed in water-based treatment solutions (200 mL per group), including water alone, 25 or 50 ppm of free chlorine, and 0.25 or 0.75% NCR for 2 min. Inoculated produce leaves without any treatment served as baseline. Produce leaves were stored at 10°C, and surviving EHEC populations were enumerated on days 0, 2, 7, and 14. The viability of EHEC following NCR treatments on the fresh produce was visualized under a fluorescence microscope. NCR treatment at 0.75% immediately reduced EHEC populations on iceberg lettuce by 1.3 log CFU/cm2 as compared with the produce treated with water alone (P < 0.05). Antimicrobial activity of NCR against EHEC was comparable to chlorine treatments on day 0 for all produce (P > 0.05). After 14 days of storage at 10°C, populations of EHEC on 0.75% NCR-treated romaine lettuce were reduced by 2.3 log CFU/cm2 compared with the recovery from 50 ppm of chlorine-treated samples (P < 0.05). Microscopic images revealed that EHEC cells were observed to be clustered on the baseline samples, indicating the development of cell aggregation, compared with the scattered cells seen on NCR-treated leaf surfaces. Treatments with NCR did not significantly affect the color of the fresh produce leaves during 14 days of storage at 10°C. Results of this study support the potential use of NCR as a water-soluble natural antimicrobial wash treatment for controlling EHEC on fresh produce.

HIGHLIGHTS

Impact of cold plasma on the biomolecules and organoleptic properties of foods: A review

Cold plasma is formed by the nonthermal ionization of gas into free electrons, ions, reactive atomic and molecular species, and ultraviolet (UV) radiation. This cold plasma can be used to alter the surface of solid and liquid foods, and it offers multiple advantages over traditional thermal treatments, such as no thermal damage and increased output variation (due to the various input parameters gas, power, plasma type, etc.). Cold plasma appears to have limited impact on the sensory and color properties, at lower power and treatment times, but there has been a statistically significant reduction in pH for most of the cold plasma treatments reviewed (p < 0.05). Carbohydrates (cross linking and glycosylation), lipids (oxidation), and proteins (secondary structure) are more significantly impacted due to cold plasma at higher intensities and longer treatment times. Although cold plasma treatments and food matrices can vary considerably, this review has identified the literary evidence of some of the influences and impacts of the vast array of cold plasma treatment parameters on the biomolecular and organoleptic properties of these foods. Due to the rapidly evolving nature of the field, we have also identified that authors prioritize the presentation of different information when publishing from different research areas. Therefore, we have proposed a number of key physical and chemical cold plasma parameters that should be considered for inclusion in all future publications in the field.

Beef-Based Medium Influences Biofilm Formation of Escherichia coli O157:H7 Isolated from Beef Processing Plants

ABSTRACT

Beef-based medium beef extract (BE) and standard medium tryptic soy broth (TSB) are used as minimally processed food models to study the effects on Escherichia coli O157:H7 biofilm formation. The effects of temperatures (4, 10, 25, 37, and 42°C), pH values (4.5, 5.0, 5.5, 6.0, 7.0, and 8.0), strain characteristics, and the expression of functional genes on the biofilm formation ability of the bacteria were determined. The three tested E. coli O157:H7 strains produced biofilm in both media. Biofilm formation was greater in BE than in TSB (P < 0.05). The strongest biofilm formation capacity of E. coli O157:H7 was achieved at 37°C and pH 7.0. Biofilm formation was significantly inhibited for three tested strains incubated at 4°C. Biofilm formation ability was correlated with swarming in TSB. Biofilm formation was significantly and positively correlated with autoaggregation or hydrophobicity in BE (P < 0.05). At the initial stage of biofilm formation, the expressions of luxS, sdiA, csgD, csgA, flhC, adrA, and rpoS were significantly higher in BE than in TSB (P < 0.05). At the maturity stage, the expressions of luxS, sdiA, csgD, csgA, flhC, csrA, adrB, adrA, iraM, and rpoS were significantly higher in TSB than in BE (P < 0.05). Such information could help in the development of effective biofilm removal technologies to deal with risks of E. coli O157:H7 biofilms in the beef industry.

HIGHLIGHTS

The antimicrobial efficacy of remote cold atmospheric plasma effluent against single and mixed bacterial biofilms of varying age

Cold atmospheric plasma (CAP) is a minimal food processing technology of increasing interest in the food industry, as it is mild in nature compared to traditional methods (e.g. pasteurisation) and thus can maintain the food's desirable qualities. However, due to this mild nature, the potential exists for post-treatment microbial survival and/or stress adaptation. Furthermore, biofilm inactivation by CAP is underexplored and mostly studied on specific foods or on plastic/polymer surfaces. Co-culture effects, biofilm age, and innate biofilm-associated resistance could all impact CAP efficacy, while studies on real foods are limited to the food product investigated without accounting for structural complexity. The effect of a Remote and Enclosed CAP device (Fourth State Medicine Ltd) was investigated on Escherichia coli and Listeria innocua grown as planktonic cells and as single or mixed bacterial biofilms of variable age, on a biphasic viscoelastic food model of controlled rheological and structural complexity. Post-CAP viability was assessed by plate counts, cell sublethal injury was quantified using flow cytometry, and biofilms were characterised and assessed using total protein content and microscopy techniques. A greater impact of CAP on planktonic cells was observed at higher air flow rates, where the ReCAP device operates in a mode more favourable to reactive oxygen species than reactive nitrogen species. Although planktonic E. coli was more susceptible to CAP than planktonic L. innocua, the opposite was observed in biofilm form. The efficacy of CAP was reduced with increasing biofilm age. Furthermore, E. coli produced much higher protein content in both single and mixed biofilms than L. innocua. Consequently, greater survival of L. innocua in mixed biofilms was attributed to a protective effect from E. coli. These results show that biofilm susceptibility to CAP is age and bacteria dependent, and that in mixed biofilms bacteria may become less susceptible to CAP. These findings are of significance to the food industry for the development of effective food decontamination methods using CAP.

Understanding of food biofilms by the application of omics techniques

Biofilms constitute a protective barrier for foodborne pathogens to survive under stressful food processing conditions. Therefore, studies into the development and control of biofilms by novel techniques are vital for the food industry. In recent years, foodomics techniques have been developed for biofilm studies, which contributed to a better understanding of biofilm behavior, physiology, composition, as well as their response to antibiofilm methods at different molecular levels including genes, RNA, proteins and metabolic metabolites. Throughout this review, the main studies where foodomics tools used to explore the mechanisms for biofilm formation, dispersal and elimination were reviewed. The data summarized from relevant studies are important to design novel and appropriate biofilm elimination methods for enhancing food safety at any point of food processing lines.

Effectiveness and mechanisms of essential oils for biofilm control on food-contact surfaces: An updated review

Microbial biofilms represent a constant source of contamination in the food industry, being also a real threat for human health. In fact, most of biofilm-producing bacteria are becoming resistant to sanitizers, thus arousing the interest in natural alternatives to prevent biofilm formation on foods and food-contact surfaces. In particular, studies on biofilm control by essential oils (EOs) application are increasing, being EOs characterized by unique mixtures of compounds able to impair the mechanisms of biofilm development. This review reports the anti-biofilm properties of EOs in bacterial biofilm control (inhibition, removal and prevention of biofilm dispersion) on food-contact surfaces. The relationship between EOs effect and composition, concentration, involved bacteria, and surfaces is discussed, and the possible sites of action are also elucidated. The findings prove the high biofilm controlling capability of EOs through the regulation of genes and proteins implicated in motility, Quorum Sensing and exopolysaccharides (EPS) matrix. Moreover, incorporation in nanosized delivery systems, formulation of blends and combination of EOs with other strategies can increase their anti-biofilm activity. This review provides an overview of the current knowledge of the EOs effectiveness in controlling bacterial biofilm on food-contact surfaces, providing valuable information for improving EOs use as sanitizers in food industries.

The impact of food model system structure on the inactivation of Listeria innocua by cold atmospheric plasma and nisin combined treatments

Novel processing methods such as cold atmospheric plasma (CAP) and natural antimicrobials like nisin, are of interest to replace traditional food decontamination approaches as, due to their mild nature, they can maintain desirable food characteristics, i.e., taste, texture, and nutritional content. However, the microbial growth characteristics (planktonic growth/surface colonies) and/or the food structure itself (liquid/solid surface) can impact the inactivation efficacy of these novel processing methods. More specifically, cells grown as colonies on a solid(like) surface experience a completely different growth environment to cells grown planktonically in liquid, and thus could display a different response to novel processing treatments through stress adaptation and/or cross protection mechanisms. The order in which combined treatments are applied could also impact their efficacy, especially if the mechanisms of action are complementary. This work presents a fundamental study on the efficacy of CAP and nisin, alone and combined, as affected by food system structure. More specifically, Listeria innocua was grown planktonically (liquid broth) or on a viscoelastic Xanthan gum gel system (1.5% w/v) and treated with CAP, nisin, or a combination of the two. Both the inactivation system, i.e., liquid versus solid(like) surface and the growth characteristics, i.e., planktonic versus colony growth, were shown to impact the treatment efficacy. The combination of nisin and CAP was more effective than individual treatments, but only when nisin was applied before the CAP treatment. This study provides insight into the environmental stress response/adaptation of L. innocua grown on structured systems in response to natural antimicrobials and novel processing technologies, and is a step towards the faster delivery of these food decontamination methods from the bench to the food industry.

Inactivation of foodborne pathogens by the synergistic combinations of food processing technologies and food-grade compounds

There is a need to develop food processing technologies with enhanced antimicrobial capacity against foodborne pathogens. While considering the challenges of adequate inactivation of pathogenic microorganisms in different food matrices, the emerging technologies are also expected to be sustainable and have a minimum impact on food quality and nutrients. Synergistic combinations of food processing technologies and food-grade compounds have a great potential to address these needs. During these combined treatments, food processes directly or indirectly interact with added chemicals, intensifying the overall antimicrobial effect. This review provides an overview of the combinations of different thermal or nonthermal processes with a variety of food-grade compounds that show synergistic antimicrobial effect against pathogenic microorganisms in foods and model systems. Further, we summarize the underlying mechanisms for representative combined treatments that are responsible for the enhanced microbial inactivation. Finally, regulatory issues and challenges for further development and technical transfer of these new approaches at the industrial level are also discussed.

Cold plasma enhances the efficacy of aerosolized hydrogen peroxide in reducing populations of Salmonella Typhimurium and Listeria innocua on grape tomatoes, apples, cantaloupe and romaine lettuce

In the present study, we investigated whether cold plasma activation affected the efficacy of aerosolized hydrogen peroxide against S. Typhimurium and L. innocua. Stem scars and smooth surfaces of grape tomatoes, surfaces of Granny Smith apples and Romaine lettuce (both midrib and upper leaves) and cantaloupe rinds were inoculated with two-strain cocktails of S. Typhimurium and 3-strain cocktails of L. innocua. The inoculated samples were treated with 7.8% aerosolized H2O2 with and without cold plasma for various times. For all fresh produce items and surfaces, cold plasma significantly (P < 0.05) improved the efficacy of aerosolized H2O2 against Salmonella and L. innocua. Without cold plasma activation, H2O2 aerosols only reduced populations of Salmonella by 1.54-3.17 log CFU/piece while H2O2 with cold plasma achieved 2.35-5.50 log CFU/piece reductions of Salmonella. L. innocua was more sensitive to the cold plasma-activated H2O2 than Salmonella. Cold plasma activated H2O2 aerosols reduced Listeria populations by more than 5 log CFU/piece on all types and surfaces of fresh produce except for the tomato stem scar area. Without cold plasma, the reductions by H2O2 were only 1.35-3.77 log CFU/piece. Overall, our results demonstrated that cold plasma activation significantly enhanced the efficacy of H2O2 mist against bacteria on fresh produce.

Super-antibiofilm effect of N2 plasma treated buffer (NPB) against plant pathogenic bacterium

Controlling of biofilms formation in numerous pathogenic bacteria is one of the most difficult tasks in the control of bacterial diseases. Plasma has attracted extensive attention due to their potential applications for effective inhibiting of biofilm. Recently, plasma-activated water (PAW) has developed as an alternative method for bacterial inactivation and disinfection of foods owing to advantages of more convenient and efficient storage and transportation than direct plasma application. However, most previous studies about PAW have only focused on the improvement of its antibacterial effect instead of antibiofilm activity. Therefore, we report the development of N₂ plasma treated buffer (NPB) and the super-antibiofilm effect of NPB against Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) as a plant pathogenic bacterium. Scavenger assays using various antioxidants revealed that reactive oxygen species were involved in the inhibitory cellular actions of NPB, with H₂O₂ and singlet oxygen proving essential for bacterial death. Intensive analysis of NPB, stored at different periods and temperatures, showed that the antimicrobial efficacy was well maintained for 3 months at − 80 °C. Importantly, further studies showed that NPB effectively inhibited not only the growth of planktonic Pst DC3000 but also biofilm formation. The remarkable inhibition on the biofilm was analyzed and visualized using LIVE/DEAD viability assays and confocal laser scanning microscopy (CLSM) imaging. The 3D CLSM imaging data revealed that the bactericidal activity of NPB was permeable enough to affect the cells embedded inside the biofilm. This prominent permeability could be a crucial feature of NPB contributing to effective super-antibiofilm.

Cold Plasma-Mediated Treatments for Shelf Life Extension of Fresh Produce: A Review of Recent Research Developments

Fresh produce, like fruits and vegetables, are important sources of nutrients and health-promoting compounds. However, incidences of foodborne outbreaks associated with fresh produce often occur; it is thus important to develop and expand decay-control technologies that can not only maintain the quality but can also control the biological hazards in postharvest, processing, and storage to extend their shelf life. It is under such a situation that plasma-mediated treatments have been developed as a novel nonthermal processing tool, offering many advantages and attracting much interest from researchers and the food industry. This review summarizes recent developments of cold plasma technology and associated activated water for shelf life extension of fresh produce. An overview of plasma generation and its physical-chemical properties as well as methods for improving plasma efficiency are first presented. Details of using the technology as a nonthermal agent in inhibiting spoilage and pathogenic microorganisms, inactivating enzymes, and modifying the barrier properties or imparting specific functionalities of packaging materials to extend shelf life of food produce are then reviewed, and the effects of cold plasma-mediated treatment on microstructure and quality attributes of fresh produce are discussed. Future prospects and research gaps of cold plasma are finally elucidated. The review shows that atmospheric plasma-mediated treatments in various gas mixtures can significantly inhibit microorganisms, inactive enzyme, and modify packaging materials, leading to shelf life extension of fresh produce. The quality attributes of treated produce are not compromised but improved. Therefore, plasma-mediated treatment has great potential and values for its application in the food industry.

A Review on Non-thermal Atmospheric Plasma for Food Preservation: Mode of Action, Determinants of Effectiveness, and Applications

Non-thermal Atmospheric Plasma (NTAP) is a cutting-edge technology which has gained much attention during the last decade in the food-processing sector as a promising technology for food preservation and maintenance of food safety, with minimal impact on the quality attributes of foods, thanks to its effectiveness in microbial inactivation, including of pathogens, spoilage fungi and bacterial spores, simple design, ease of use, cost-effective operation, short treatment times, lack of toxic effects, and significant reduction of water consumption. This review article provides a general overview of the principles of operation and applications of NTAP in the agri-food sector. In particular, the numerous studies carried out in the last decade aimed at deciphering the influence of different environmental factors and processing parameters on the microbial inactivation attained are discussed. In addition, this review also considers some important studies aimed at elucidating the complex mechanism of microbial inactivation by NTAP. Finally, other potential applications of NTAP in the agri-food sector, apart from food decontamination, are briefly described, and some limitations for the immediate industrial implementation of NTAP are discussed (e.g., impact on the nutritional and sensory quality of treated foods; knowledge on the plasma components and reactive species responsible for the antimicrobial activity; possible toxicity of some of the chemical species generated; scale-up by designing fit-for-purpose equipment).

Disinfectant Resistance Profiles and Biofilm Formation Capacity of Escherichia coli Isolated from Retail Chicken

Disinfectant resistance and biofilm formation capacity are two important characteristics that contribute to the persistence of microorganisms in food processing environments and contamination of food products. This study investigated the susceptibility of 510 Escherichia coli isolates against 5 disinfectants and the prevalence of 10 disinfectant-resistant genes in these isolates. The biofilm formation capacity of 194 isolates was determined, and the correlation between disinfectant resistance and biofilm formation was analyzed. The minimal inhibitory concentrations (MICs) of cetyltrimethylammonium bromide (CTAB), benzalkonium chloride (BC), cetylpyridinium chloride, and chlorhexidine (CHX) against isolates were 32-512, 16-256, 32-256, and 2-32 mg/L, respectively. The MICs of triclosan against 88.43% of isolates were 8-1,024 mg/L, while the MICs for the rest of isolates exceed 2,048 mg/L. The presence of ydgE, ydgF, and qacF genes was significantly correlated with the CHX resistance of E. coli isolates, while the presence of qacF and qacEΔ1 genes was significantly correlated with CTAB and BC resistance, respectively. The biofilm formation capacity (adjusted optical density value) was positively correlated with BC resistance (r = 0.201, p < 0.01) and showed no correlation with other disinfectants. The presence of sugE(p) was positively correlated with biofilm formation, while four genes were negatively correlated with biofilm formation. This study provides useful data on disinfectant resistance and biofilm formation capacity of E. coli contaminating poultry products, which could be helpful in guiding proper disinfectant usage and establishing effective biofilm eradication strategy in food industry.

A Critical Review on Selected External Physical Cues and Modulation of Cell Behavior: Magnetic Nanoparticles, Non-thermal Plasma and Lasers

Physics-based biomedical approaches have proved their importance for the advancement of medical sciences and especially in medical diagnostics and treatments. Thus, the expectations regarding development of novel promising physics-based technologies and tools are very high. This review describes the latest research advances in biomedical applications of external physical cues. We overview three distinct topics: using high-gradient magnetic fields in nanoparticle-mediated cell responses; non-thermal plasma as a novel bactericidal agent; highlights in understanding of cellular mechanisms of laser irradiation. Furthermore, we summarize the progress, challenges and opportunities in those directions. We also discuss some of the fundamental physical principles involved in the application of each cue. Considerable technological success has been achieved in those fields. However, for the successful clinical translation we have to understand the limitations of technologies. Importantly, we identify the misconceptions pervasive in the discussed fields.

Fabrication and Release Behavior of Microcapsules with Double-Layered Shell Containing Clove Oil for Antibacterial Applications

In this study, double-layer polyurethane/poly(urea-formaldehyde) (PU/PUF) shell microcapsules containing clove oil with antibacterial properties were successfully synthesized via in situ and interfacial polymerization reactions in an oil-in-water emulsion. The morphology, core-shell structure, and composition of the microcapsules were investigated systematically. Additionally, the release behaviors of microcapsules synthesized under different reaction parameters were studied. It was found that the release rate of clove oil can be controlled by tuning the amount of PU reactants and the length of PUF deposition time. The release profile fitted well against the Baker-Lonsdale model, which indicates diffusion as the primary release mechanism. Experimental results based on the ASTM E2315 time kill test revealed that the fabricated microcapsules have great antibacterial activities against the marine bacteria Vibrio coralliilyticus, Escherichia coli, Exiguobacterium aestuarii, and marine biofilm-forming bacteria isolated from the on-site contaminated samples, showing their great potential as an eco-friendly solution to replace existing toxic antifouling agent.

Co-loaded proteinase K/thyme oil liposomes for inactivation of Escherichia coli O157:H7 biofilms on cucumber

E. coli O157:H7 is a bacterium frequently found on vegetable surfaces, such as cucumber, that can pose a significant threat to consumers. In the present work, proteinase K (PK) and thyme oil (TO) were used to inactivate E. coli O157:H7 biofilms. Both PK and TO were encapsulated in liposomes to improve their chemical stability and to allow for a controlled release. The optimal PK/TO-loaded liposomes (particle size of 170.4 nm, polydispersity index of 0.309, zeta potential of -29.8 mV and entrapment efficiency of 33.2%) were engineered. The antibacterial activities of the PK/TO liposomes against E. coli O157:H7 biofilms in vitro and on the cucumber were observed. Compared to free PK, free TO, and free PK/TO and TO liposome treatments, PK/TO-liposomes exhibited a higher antibiofilm activity and longer action duration. Specifically, the counts of viable E. coli O157:H7 on cucumbers were reduced by 1.23, 2.32 and 2.44 Logs after treatment with 400 mg mL^-1 of PK/TO liposomes for 3 d, at 5, 15 and 25 °C, respectively. Colorimetric analysis and sensory tests showed that the PK/TO-liposome treatment had almost no impact on food quality after 1 d.