Effect of atmospheric pressure plasma jet on the foodborne pathogens attached to commercial food containers

Recent advances on the formation, detection, resistance mechanism, and control technology of Listeria monocytogenes biofilm in food industry

Listeria monocytogenes is an important foodborne pathogen that causes listeriosis, a severe and fatal condition. Biofilms are communities of microorganisms nested within a self-secreted extracellular polymeric substance, and they protect L. monocytogenes from environmental stresses. Biofilms, once formed, can lead to the persistence of L. monocytogenes in processing equipment and are therefore considered to be a major concern for the food industry. This paper briefly introduces the recent advancements on biofilm formation characteristics and detection methods, and focuses on analysis of the mechanism of L. monocytogenes biofilm resistance; Moreover, this paper also summarizes and discusses the existing different techniques of L. monocytogenes biofilm control according to the physical, chemical, biological, and combined strategies, to provide a theoretical reference to aid the choice of effective control technology in the food industry.

Advances in emerging technologies for the decontamination of the food contact surfaces

Foodborne pathogens could be transferred to food from food contact surfaces contaminated by poor hygiene or biofilm formation. The food processing industry has various conditions favouring microbes' adherence, such as moisture, nutrients, and the microbial inoculums obtained from the raw material. The function of the ideal antimicrobial surface is preventing initial attachment of the microbes, killing the microbes or/and removing the dead bacteria. This review article provides detail about the challenges food industries are facing with respect to food contact materials. It also summarises the merits and demerits of several sanitizing methods developed for industrial use. Furthermore, it reviews the new and emerging techniques that enhance the efficiency of reducing microbial contamination. Techniques such as surface functionalisation, high-intensity ultrasound, cold plasma technologies etc. which have high potential to be used for the decontamination of food contact surfaces are discussed. The emerging designs of antibacterial surfaces provide the opportunity to reduce or eradicate the adhesion of microorganisms. The most important purpose of these surfaces is to prevent the attachment of bacteria and to kill the bacteria that come in contact. These emerging technologies have a high potential for developing safe and inert food contact materials for the food industry.

Influence of Plasma Treatment on the Polyphenols of Food Products—A Review

The consumption of bioactive compounds, especially phenolic compounds, has been associated with health benefits such as improving the health status and reducing the risk of developing certain diseases such as cancer, cardiovascular diseases, and neurodegenerative disorders. However, the preservation of natural bioactive compounds in food products is a major challenge for the food industry. Due to the major impact of conventional thermal processing, nonthermal technologies such as cold plasma have been proposed as one of the most promising solutions for the food industry. This review will cover the current knowledge about the effects of cold plasma in polyphenols found in food products. The increasing number of studies in the last years supports the continuous search for specific treatment conditions for each type of food and the central role of plasma treatments as a food-processing technology.

Efficacy of cold plasma in producing Salmonella-free duck eggs: effects on physical characteristics, lipid oxidation, and fatty acid profile

Concerns related to foodborne pathogens necessitate the decontamination of avian eggs. Conventional decontamination methods, such as egg washing, usually use health-threatening chemicals (e.g. chlorine). Hence, innovative chemical-free decontamination approaches are interesting for the food industry, especially to decontaminate commonly Salmonella infected products such as duck eggs. The present study is the first attempt to evaluate the effectiveness of cold plasma against Salmonella enterica inoculated on the surface of duck eggshell. In this regard, Salmonella-contaminated duck eggs were treated by arc plasma for 10, 20, 30, and 40 s. The bacteria count, eggshell strength, color, pH, Haugh unit, acid value (AV), thiobarbituric acid reactive substances (TBARS), and fatty acid profile of the plasma-treated samples were then compared with those of untreated sample. According to the results, all the plasma treatments significantly decreased the Salmonella population and longer treatment times enhanced the bactericidal effects of plasma. A maximum bacterial reduction of 4.1 log cycle was observed when plasma was applied for 40 s. Furthermore, plasma treatments did not deteriorate the quality parameters of eggs such as eggshell strength, eggshell color, yolk color, Haugh unit, AV, and TBARS. These findings introduced arc plasma as an emerging tool for improving the safety of duck eggs with good potential for industrial application.

Impact of atmospheric non-thermal plasma and hydrothermal treatment on bioactive compounds and microbial inactivation of strawberry juice: A hurdle technology approach

The aim of this study was to investigate the hurdle effect of combining atmospheric cold plasma (ACP) with hydrothermal treatment on ascorbic acid, individual polyphenolic compounds, total phenolic content, and microbial inactivation of strawberry juice. Strawberry juice was treated with ACP for 10 and 15 min using dielectric barrier discharge at 60 kV with the input voltage of 260 V. The ascorbic acid concentration was retained maximum only in ACP treatment followed by ACP + hydrothermal treatment. Furthermore, ACP treatment for 10 min coupled with hydrothermal treatment resulted in the higher concentration of gallic acid, epigallocatechin, phloretin, naringin, hyprin, and 4-O-caffeoylquinic acid with respect to control ( p < 0.05). In addition, ACP treatment for 10 min at 60 kV in combination with hydrothermal treatment resulted in increased total phenolic content ( p < 0.05). Moreover, a 2-log microbial reduction was found in processed strawberry juice with ACP coupled-hydrothermal treatment in comparison to control juice ( p < 0.05). Therefore, ACP treatment of 10 min followed by hydrothermal treatment was found to be advantageous processing for strawberry juice to retain nutritional quality and decrease microbial load. Moreover, further optimization of ACP or hydrothermal processing with utilization of preservatives could be achieved for desired microbial inactivation for an industrial process.

Microplasma Bubbles: Reactive Vehicles for Biofilm Dispersal

Interactions between effects generated by cold atmospheric-pressure plasmas and water have been widely investigated for water purification, chemical and nanomaterial synthesis, and, more recently, medicine and biotechnology. Reactive oxygen and nitrogen species (RONS) play critical roles in transferring the reactivity from gas plasmas to solutions to induce specific biochemical responses in living targets, e.g., pathogen inactivation and biofilm removal. While this approach works well in a single-organism system at a laboratory scale, integration of plasma-enabled biofilm removal into complex real-life systems, e.g., large aquaculture tanks, is far from trivial. This is because it is difficult to deliver sufficient concentrations of the right kind of species to biofilm-covered surfaces while carefully maintaining a suitable physiochemical environment that is healthy for its inhabitants, e.g., fish. In this work, we show that underwater microplasma bubbles (generated by a microplasma-bubble reactor that forms a dielectric barrier discharge at the gas-liquid interface with the applied voltage of 4.0 kV) act as transport vehicles to efficiently deliver reactive plasma species to the target biofilm sites on artificial and living surfaces while keeping healthy water conditions in a multispecies system. The as-generated air microplasma bubbles and plasma-activated water (PAW) both can effectively reduce the existing pathogenic biofilm load by ∼83 and 60%, respectively, after 15 min of discharge at 40 W and prevent any new biofilm from forming. The generation of underwater microplasma bubbles in a custom-made fish tank for less than a minute per day (20 s per time, twice daily) can introduce sufficient quantities of RONS into PAW to reduce the biofilm-infected area by ∼80-90% and improve the health status of Cichlasoma synspilum × Cichlasoma citrinellum blood parrot cichlid fish. Species generated include hydrogen peroxide, ozone, nitrite, nitrate, and nitric oxide. Using mimicked chemical solutions, we show that the plasma-induced nitric oxide acts as a critical bioactive species that triggers the release of cells from the biofilm and their inactivation.

Plasma-Induced Degradation of Quercetin Associated with the Enhancement of Biological Activities

Nonthermal plasma is a promising technology to improve the safety and to extend the shelf-life of various minimally processed foods. However, research on plasma-induced systemic degradation related to changes in chemical structure and biological activity is still very limited. In this study, the enhancement of biological activity and the mechanism of degradation of the most common type of flavonol, quercetin, induced by a dielectric barrier discharge (DBD) plasma were investigated. Quercetin is dissolved in methanol and exposed to nonthermal DBD plasma for 5, 10, 20, and 30 min. The quercetin treated with the plasma for 20 min showed rapidly increased α-glucosidase inhibitory and radical scavenging activities compared to those of parent quercetin. The structures of the degradation products 1-3 from the quercetin treated with the plasma for 20 min were isolated and characterized by interpretation of their spectroscopic data. Among the generated products, (±)-alphitonin (1) exhibited significantly improved antidiabetic and antioxidant properties compared to those of the parent quercetin. The antidiabetic and antioxidant properties were measured by α-glucosidase inhibition and 1,1-diphenyl-2-picrylhydrazyl radical scavenging assays. These results suggested that structural changes in quercetin induced by DBD plasma might be attributable to improving the biological activity.

Potential applications of nonthermal plasmas against biofilm-associated micro-organisms in vitro

Biofilms as complex microbial communities attached to surfaces pose several challenges in different sectors, ranging from food and healthcare to desalination and power generation. The biofilm mode of growth allows microorganisms to survive in hostile environments and biofilm cells exhibit distinct physiology and behaviour in comparison with their planktonic counterparts. They are ubiquitous, resilient and difficult to eradicate due to their resistant phenotype. Several chemical-based cleaning and disinfection regimens are conventionally used against biofilm-dwelling micro-organisms in vitro. Although such approaches are generally considered to be effective, they may contribute to the dissemination of antimicrobial resistance and environmental pollution. Consequently, advanced green technologies for biofilm control are constantly emerging. Disinfection using nonthermal plasmas (NTPs) is one of the novel strategies having a great potential for control of biofilms of a broad spectrum of micro-organisms. This review discusses several aspects related to the inactivation of biofilm-associated bacteria and fungi by different types of NTPs under in vitro conditions. A brief introduction summarizes prevailing methods in biofilm inactivation, followed by introduction to gas discharge plasmas, active plasma species and their inactivating mechanism. Subsequently, significance and aspects of NTP inactivation of biofilm-associated bacteria, especially those of medical importance, including opportunistic pathogens, oral pathogenic bacteria, foodborne pathogens and implant bacteria, are discussed. The remainder of the review discusses majorly about the synergistic effect of NTPs and their activity against biofilm-associated fungi, especially Candida species.

Effects of minimal exposures to atmospheric pressure plasma on the activity of Salmonella Typhimurium: Deactivation of bacterial motility and suppression of host-cell invasion

Atmospheric pressure plasma (APP) has been shown effective in sterilization by reducing the number of viable microbes during surface cleaning, food processing, or human tissue treatment. For safe conduct, the majority of previous research focused on complete abolition of microbes, which may require severe treatments. Our aim is to investigate the minimal treatment conditions necessary for effective inactivation of bacteria in such a manner that the APP treated bacteria would not be able to harm the host cells. For this, we ought to identify the objective criteria to make the bacteria dysfunctional. We choose the motile properties and the host-cell invasion capability as two measures to quantify the pathogenic state of bacteria. In this paper, we investigated how the APP treatment in a minimal dosage affects the activity of Salmonella Typhimurium. At 100 W and 15 kHz for 20 s, the APP treatment effectively suppressed active "run and tumble" type motility and induced formation of abnormally long structures. With 20 s exposure, the bacterial cells failed to cause pyroptosis in the host cells with >90% survival after 12 h of co-incubation. Our results suggest novel measures to evaluate the functional pathogenic state for identifying safe APP treatment conditions.