Nonthermal plasma for pesticide and microbial elimination on fruits and vegetables: an overview

Nonthermal plasma (NTP) is defined in terms of partly ionised gas which overall temperature is quite low because the stored energy is mostly in free electrons. Applications of NTP have been expanded to new areas of food applications such as the microbial inactivation and also the elimination of pesticide and toxic chemical residues in food such as fruits and vegetables while nutritional content and key characteristics are still preserved. Plasma treatment has successfully decreased the concentrations of pesticides by about 45‐71%. In this article, NTP technologies as well as investigations about applying of NTP for removing pesticide residues and improving microbial safety in fresh produce are described. Potential applications of NTP in food processing together with some of their challenges and limitations are also discussed.     

Nonthermal plasma-activated water: A comprehensive review of this new tool for enhanced food safety and quality

Nonthermal plasma (NTP) is an advanced technology that has gained extensive attention because of its capacity for decontaminating food from both biological and chemical sources. Plasma-activated water (PAW), a product of NTP's reaction with water containing a rich diversity of highly reactive oxygen species (ROS) and reactive nitrogen species (RNS), is now being considered as the primary reactive chemical component in food decontamination. Despite exciting developments in this field recently, at present there is no comprehensive review specifically focusing on the comprehensive effects of PAW on food safety and quality. Although PAW applications in biological decontamination have been extensively evaluated, a complete analysis of the most recent developments in PAW technology (e.g., PAW combined with other treatments, and PAW applications in chemical degradation and as curing agents) is nevertheless lacking. Therefore, this review focuses on PAW applications for enhanced food safety (both biological and chemical safeties) according to the latest studies. Further, the subsequent effects on food quality (chemical, physical, and sensory properties) are discussed in detail. In addition, several recent trends of PAW developments, such as curing agents, thawing media, preservation of aquatic products, and the synergistic effects of PAW in combination with other traditional treatments, are also presented. Finally, this review outlines several limitations presented by PAW treatment, suggesting several future research directions and challenges that may hinder the translation of these technologies into real-life applications.     

Preservation effect of plasma-activated water (PAW) treatment on fresh walnut kernels

Fresh walnuts exhibit unique flavor and multiple biological activities, but they are highly perishable due to the lack of practical and cost-effective postharvest preservation technique. In this paper, the quality of fresh walnut kernels treated with deionized water, water containing ClO₂, and plasma-activated water (PAW) for 15 min were monitored during 4 °C storage. Results showed that 100-s PAW treatment reduced the total viable count by 1.15 log CFU/g immediately after treatment. The bactericidal and bacteriostatic effects of PAW was superior to 4 mg/L ClO₂. PAW-treated samples retained their flavor during 12d storage at 4 °C, while other samples generated odor at 6d. Moreover, PAW treatment could prevent nutritional loss, browning, and rancidity. The increases of peroxidase, polyphenol oxidase, and lipase activities were inhibited after PAW treatment. Hence, PAW treatment can be applied for the preservation of fresh walnut kernels due to its effect on microbial inhibition and quality maintenance.Industry relevanceNon-thermal plasma is an emerging non-thermal food processing technology due to its advantages of non-destructive, pollution-free, high efficiency and short treatment periods. In this study, plasma-activated water (PAW) was applied in the preservation of fresh walnut kernels, and inhibited flavor changes, nutritional loss, microbial growth, browning, and oxidation reaction. When approaching food preservation technologies, especially for heat-sensitive materials, PAW treatment as a novel technique appears to have far-reaching implications for increasing markets by antimicrobial properties, and avoiding the negative impacts on quality attributes.     

Effect of plasma activated water (PAW) on rocket leaves decontamination and nutritional value

Plasma Activated Water (PAW) obtained by exposing water to cold atmospheric pressure plasma, has recently emerged as a promising alternative for food decontamination, compared to the use of traditional chemical sanitizers. The aim of the study was to evaluate the efficacy of PAW treatments for rocket salad decontamination. Washing with PAW for 2, 5, 10 and 20 min was assessed against different endogenous spoilage microorganisms and compared to untreated water and hypochlorite solution. The chemical composition of PAW as a function of treatment and delay time was characterized and the effect on product quality and nutritional parameters was evaluated.Results showed that PAW allowed an average reduction of 1.7–3 Log CFU/g for total mesophilic and psychrotrophic bacteria and Enterobacteriaceae following 2–5 min washing with minimal variation of qualitative and nutritional parameters. Overall, experimental results highlighted the potentiality of PAW treatments as a promising alternative to chlorine having the advantage of a minor adverse impact on environment and consumers' health.Industrial relevanceTo meet consumers demand, the minimally processed fruit and vegetable industry needs to find sustainable solutions as alternative to the use of traditional chemical sanitizers that allow to increase product shelf-life and preserve safety, qualitative and nutritional characteristics.Plasma activated water represents a promising strategy for food decontamination, but its effects on foods have been only limitedly investigated. The present research is the first study on the use of plasma activated water on fresh rocket leaves, providing new and important information on microbial inactivation and quality of the fresh cut product.     

等离子体活化水在食品工业中应用研究进展

等离子体活化水(Plasma-activated water,PAW)具有活性组分含量高、低pH和氧化还原电位较高等特点,具有杀菌、抗生物被膜、促进种子萌发和幼苗生长等功能。作为一种新型的环境友好型非热加工技术,PAW在食品工业中的潜在应用前景受到广泛关注。本文综述了PAW在食品杀菌保鲜、肉制品护色、细菌生物被膜控制等领域中的应用研究,为PAW技术在食品工业中的广泛应用提供参考。     

Recent advancements in the application of non-thermal plasma technology for the seafood industry

Abstract

Non-thermal plasma (NTP) is one of the most promising minimal processing methods for the food industry. However up until recently there are limited studies which would report the application and effect of NTP on processed seafood. The objective of this review is to highlight the recent findings and advancements in the application of NTP within the fish and other seafood industry, including direct application of fresh and dried fish and seafood with as well as indirect application of plasma activated water and seafood industry wastewater purification. The article also summarizes the effect of plasma treatment on microbiological quality, physicochemical and sensory properties and oxidation rate of treated fish and seafood. NTP has high potential to be used within various fields of seafood industry. It is especially effective in treatment of dried seafood products, but the use of plasma activated water during various processing steps such as seafood washing could be also beneficial. Moreover NTP could also be used as a cost effective and environmentally friendly method for seafood wastewater purification.     

Understanding the Impact of Nonthermal Plasma on Food Constituents and Microstructure—A Review

Nonthermal plasma (NTP) is superior to thermal technologies as a technique that provides a satisfactory microbial safety and maintains reasonable standards in food quality attributes. Currently, the effects of NTP on some food components is regarded as beneficial, such as effects on starch and protein modification. For other food components, such as lipid oxidation, NTP is regarded as an undesirable treatment because it leads to quality deterioration and formation of off-flavor. An overview of the basic principles of NTP and food microstructure in relation to NTP-treated food and the underlying mechanisms are discussed. The review further highlights the latest research on plasma application in food and the related impact on food matrices. Efforts were made to outline the research findings in terms of NTP application on foods with an emphasis on the impacts on the food microstructure and their related qualities. In this review, the industrial capacity of NTP to improve the functional properties of starch, proteins, and lipids as well as provide little or no alteration in food quality compared to other technologies are emphasized. Some oxidative breakdown in relation to starch, proteins, and lipids are discussed and documented in this paper as a review of representative available publications.     

Diagnostics of plasma reactive species and induced chemistry of plasma treated foods

Cold plasma is a promising technique that has been tested as a process technology for a range of food commodities, mainly to destroy microorganisms, but also aimed at toxin degradation, enzyme inactivation, residual pesticide degradation and functionalization of food properties. Plasma has already been employed by industry for food packaging material sterilization and surface modification. As most of the current literature on cold plasma in the field of food science is focused on microbial inactivation efficacy, the information about its chemical influences on food is sparse. To better understand the chemical interactions of with plasma, this review focuses on plasma chemistry diagnostics techniques available to characterize the plasma reactive species generated. Equally important is the detection of induced chemistry in the food and here we present approaches to analyze likely reactions with key food bio-molecules. Such analysis will support mechanistic insights involved in these complex chemical reactions (i.e., DNA, lipid and protein) along with potential physical modifications of the food structure. For successful adoption of plasma as a food processing aid it is critical to elucidate these interactions as they have an important role in demonstrating the technology’s safety as a food processing technique along with understanding any effect on food nutrients.     

Pulsed Light Treatments for Food Preservation. A Review

Consumers demand high-quality processed foods with minimal changes in nutritional and sensory properties. Nonthermal methods are considered to keep food quality attributes better than traditional thermal processing. Pulsed light (PL) is an emerging nonthermal technology for decontamination of food surfaces and food packages, consisting of short time high-peak pulses of broad spectrum white light. It is considered an alternative to continuous ultraviolet light treatments for solid and liquid foods. This paper provides a general review of the principles, mechanisms of microbial inactivation, and applications of PL treatments on foods. Critical process parameters that are needed to be optimized for a better efficiency of PL treatments are also discussed. PL has considerable potential to be implemented in the food industry. However, technological problems need to be solved in order to avoid food overheating as well as to achieve better penetration and treatment homogeneity. In addition, a more extensive research is needed to understand how PL affects quality food attributes.     

Effects of Nonthermal Plasma Technology on Functional Food Components

Understanding the impact of nonthermal plasma (NTP) technology on key nutritional and functional food components is of paramount importance for the successful adoption of the technology by industry. NTP technology (NTPT) has demonstrated marked antimicrobial efficacies with good retention of important physical, chemical, sensory, and nutritional parameters for an array of food products. This paper presents the influence of NTPT on selected functional food components with a focus on low‐molecular‐weight bioactive compounds and vitamins. We discuss the mechanisms of bioactive compound alteration by plasma‐reactive species and classify their influence on vitamins and their antioxidant capacities. The impact of NTP on specific bioactive compounds depends both on plasma properties and the food matrix. Induced changes are mainly associated with oxidative degradation and cleavage of double bonds in organic compounds. The effects reported to date are mainly time‐dependent increases in the concentrations of polyphenols, vitamin C, or increases in antioxidant activity. Also, improvement in the extraction efficiency of polyphenols is observed. The review highlights future research needs regarding the complex mechanisms of interaction with plasma species. NTP is a novel technology that can both negatively and positively affect the functional components in food.     

Nonthermal Processes for Shelf‐Life Extension of Seafoods: A Revisit

For the past two decades, consumer demand for minimally processed seafoods with good sensory acceptability and nutritive properties has been increasing. Nonthermal food processing and preservation technologies have drawn the attention of food scientists and manufacturers because nutritional and sensory properties of such treated foods are minimally affected. More importantly, shelf‐life is extended as nonthermal treatments are capable of inhibiting or killing both spoilage and pathogenic organisms. They are also considered to be more energy‐efficient and to yield better quality when compared with conventional thermal processes. This review provides insight into the nonthermal processing technologies currently used for shelf‐life extension of seafoods. Both pretreatments such as acidic electrolyte water and ozonification and processing technologies, including high hydrostatic pressurization, ionizing radiation, cold plasma, ultraviolet light, and pulsed electric fields, as well as packaging technology, particularly modified atmosphere packaging, have been implemented to lower the microbial load in seafood. Thus, those technologies may be the ideal approach for the seafood industry, in which prime quality is maintained and safety is assured for consumers.     

Effects of bubble and reactor shape on cold plasma yeast inactivation

Cold plasma is a promising non-thermal technology for inactivating pathogenic and spoilage microorganisms in food by generating various reactive species that damage and inactivate the microorganisms. In this study, a mathematical model was established using COMSOL software to quantitatively describe the process of yeast inactivation by cold plasma under different treatment conditions. The study investigated the effects of discharge voltage, bubble size, and reactor shape on the efficiency of yeast inactivation in apple juice. The results revealed that the discharge voltage significantly influenced yeast inactivation, with a 0.4-fold voltage increase leading to a 53% reduction in inactivation time, achieving a 4-log reduction within 12 min at 21 kV. However, bubble size and reactor shape had no significant impact on the inactivation. The developed model can help to predict the cold plasma inactivation yeast in apple juice, facilitating the design and optimization of plasma-based microbial inactivation in liquid food processing.     

Evaluating the effects of plasma-activated slightly acidic electrolyzed water on bacterial inactivation and quality attributes of Atlantic salmon fillets

In this study, an intervention non-thermal processing technology plasma-activated slightly acidic electrolyzed water (PASW) was developed to better preserve salmon fillets. Compared to the plasma-activated water (PAW) and slightly acidic electrolyzed water (SAEW), PASW treatment was found to be more effective in inactivating microorganisms. After PAW, SAEW, or PASW treatment for 120 s, the population of Shewanella putrefaciens (S. putrefaciens) was reduced by 2.04, 2.62 and 2.08 Log CFU/mL (P < 0.05) using plate counts, respectively. The test for the leakage of nucleic acids and protein in intracellular contents confirmed that PASW caused serious damage to the microbial cell structural integrity compared to that alone PAW or SAEW. Meanwhile, scanning electron microscopic observations also showed that PASW caused apparent bacterial structural changes. Besides, the PASW treatment did not alter color and textural properties of salmon fillets, and restrained lipid oxidation as compared to the control and SAEW treatments. In all, this study compared the bacterial inactivation mechanisms for PAW, SAEW, and PASW, and suggested that PASW was effective in inactivating S. putrefaciens of salmon fillets.Industrial relevancePlasma-activated slightly acidic electrolyzed water, an emerging technology in food processing, can be a potential green technology for the processing of aquatic food products. PASW treatment had higher disinfection efficacy than that of SAEW or PAW treatment alone, and no adverse effect on the quality of Atlantic salmon fillets. These results boost knowledge in the food preservation field, as well as the application of non-thermal processing in the food industry.     

Dielectric barrier discharge cold atmospheric plasma: Influence of processing parameters on microbial inactivation in meat and meat products

Decontamination of meat is commonly practiced to get rid of or decrease the microbial presence on the meat surface. Dielectric barrier discharge cold atmospheric plasma (DBD-CAP) as innovative technology is a food microbial inactivation technique considered in high regard by food scientists and engineers in present times. However, cold atmospheric plasma application is at the experimental stage, due to lack of sufficient information on its mode of action in inactivating microbes, food shelf-life extensibility, whereas, the nutritional value of food is preserved. In this review, we have appraised recent work on DBD-CAP concerning the decontamination treatment of meat products, highlighting the processing value results on the efficacy of the DBD-CAP microbial inactivation technique. Also, the paper will review the configurations, proposed mechanisms, and chemistry of DBD-CAP. Satisfactory microbial inactivation was observed. In terms of DBD-CAP application on sensory evaluation, inferences from reviewed literature showed that DBD has no significant effect on meat color and tenderness, whereas in contrast, TBARS values of fresh and processed meat are affected. DBD seems economically efficient and environmentally sustainable.     

Nonthermal Food Processing Alternatives and Their Effects on Taste and Flavor Compounds of Beverages

Food drinks are normally processed to increase their shelf-life and facilitate distribution before consumption. Thermal pasteurization is quite efficient in preventing microbial spoilage of many types of beverages, but the applied heat may also cause undesirable biochemical and nutritious changes that may affect sensory attributes of the final product. Alternative methods of pasteurization that do not include direct heat have been investigated in order to obtain products safe for consumption, but with sensory attributes maintained as unchanged as possible. Food scientists interested in nonthermal food preservation technologies have claimed that such methods of preserving foods are equally efficient in microbial inactivation as compared with conventional thermal means of food processing. Researchers in the nonthermal food preservation area also affirm that alternative preservation technologies will not affect, as much as thermal processes, nutritional and sensory attributes of processed foods. This article reviews research in nonthermal food preservation, focusing on effects of processing of food drinks such as fruit juices and dairy products. Analytical techniques used to identify volatile flavor-aroma compounds will be reviewed and comparative effects for both thermal and nonthermal preservation technologies will be discussed.     

等离子体活化水对沙门氏菌的灭活作用及机制研究

等离子体活化水（Plasma-activated water,PAW）是一种新兴的非热杀菌技术,在食品保鲜等领域具有广泛的应用前景。本文研究了PAW处理对沙门氏菌（S. typhimurium）的杀灭效果及其作用机制。将经等离子体放电30、60和90 s得到的PAW分别记为PAW30、PAW60和PAW90。结果表明,PAW对S. typhimurium的杀菌效果随放电时间的延长而逐渐增强。当初始浓度为7.91 lg CFU/mL时,PAW60处理10 min后S. typhimurium活菌数减少了4.22 lg CFU/mL。扫描电镜（Scanning electron microscope,SEM）结果表明,PAW60处理后S. typhimurium细胞形态发生明显变化。经PAW60处理后,S. typhimurium胞外核酸和蛋白含量均显著（P<0.05）升高,表明其细胞膜通透性显著（P<0.05）增强。此外,PAW60处理破坏了S. typhimurium细胞外膜完整性,造成胞内活性氧水平显著（P<0.05）升高。以上实验结果表明,PAW处理能够有效灭活S. typhimurium,其作用机理可能与其破坏细胞结构、增强细胞膜通透性等有关。研究结果为PAW在食品杀菌保鲜中的应用提供了科学理论依据。     

Mechanism characterization of bacterial inactivation of atmospheric air plasma gas and activated water using bioluminescence technology

We assessed the efficacy of bacterial inactivation using a dielectric barrier discharge in three different plasma setups: plasma gas (PG), and direct and indirect plasma activated water (PAW), where deionized water was placed either between or away from the electrodes, respectively. We used bioluminescent Escherichia coli K12 lux as a model bacteria in a biosensor format to study the inactivation kinetics and mechanism of action of produced PG and PAW. The results showed that uninterrupted application of PG decreased bioluminescence rapidly by 1-log within the first minute and 3.6-log after 10 min of treatment. Exposing the bacterial culture with a sublethal dose of PAW (1 mL) rapidly decreased the bioluminescence; however, luminescence slowly recovered after exposure. Subsequent treatment with PAW decreased the bioluminescence to a lesser extent. In addition, direct PAW induced a greater decrease in bioluminescence compared to indirect treatments for both single and multiple exposures. In contrast to the PG, PAW treatments induced a lower bactericidal effect with 0.11 to 0.22-log reduction for indirect PAW and 0.2 to 0.32-log for direct PAW. Our results also indicate that antimicrobial activity of PAW decreased slowly within 20 min of its preparation. The rapid decrease in bioluminescence followed by a partial recovery in a repeatable pattern suggests an incomplete inactivation, and that the reducing power of the cell helps them to survive. Moreover, the complete and partial oxidation of NADH solutions in vitro by PG and PAW, respectively, strongly suggest that the lux fluorophore FMNH₂ and other reducing cofactors could be the target of such treatment before other cell components. This hypothesis was supported by the tendency to recover luminescence by potentially replenishing the pool of FMNH₂ after plasma treatment. It is also important to consider that the reducing power of the cell (NADH, NADPH, and FMNH₂) is crucial for cell viability mostly due to reducing potential for critical metabolic reactions. Therefore, in situ bioluminescence monitoring technology can potentially serve as a unique approach to elucidate the mechanism of bacteria inactivation in real time.Industrial relevanceThe present study developed three dielectric barrier discharge (DBD) plasma setups to produce plasma gas and plasma activated water, which can disinfect both food products and their contact surfaces regardless of geometry. Our in situ bioluminescent technology elucidated bacterial inactivation mechanisms of plasma treatments, which may potentially suggest sufficient exposures to plasma resulting in safe food products without deteriorating their quality. The results will help food manufacturers apply new plasma-based disinfection methods with appropriate treatments.     

非热杀菌技术杀灭食品中芽孢效能及机理研究进展

传统热杀菌会对食品品质产生不利影响,造成食品颜色变化、产生异味、营养损失等不良后果;非热杀菌技术是食品工业新型加工技术,处理过程中可以保持相对较低的温度,对食品的色、香、味以及营养成分影响较小;同时有利于保持食品中各种功能成分的生理活性,可以满足消费者对高品质食品的要求。芽孢在加工过程中抗性强,在食品中萌发和生长的潜力较大,因此,利用低热或非热灭菌技术对芽孢进行灭活是当前食品工业面临的严峻挑战和重要课题。本文综述现有非热杀菌技术（如高静压技术、高压CO2技术、低温等离子体技术、紫外辐射技术、高压脉冲电场技术等）独立处理或与其他处理技术相结合对芽孢灭活的效果及其机理,着重讨论其在食品行业中的应用以及芽孢灭活的分子机制,以期为生产安全食品、减少不同种类食品中微生物污染提供解决方案。     

等离子体活化水对腐败希瓦氏菌杀菌效果及机理

为探究等离子体活化水（plasma activated water,PAW）对水产品中常见的腐败希瓦氏菌（Shewanella putrefaciens）的杀菌效果及其作用机制。本实验通过平板计数、荧光染色、扫描电子显微镜等方法,研究了PAW对Shewanella putrefaciens的杀菌作用以及对其细胞形态、细胞膜通透性、细胞膜电位和细胞内容物泄漏情况等指标的影响。结果表明：PAW能显著降低Shewanella putrefaciens的数量（P＜0.05）,经等离子体放电120 s的活化水（PAW120）处理6.0 min后,菌落数对数值减少了7.44（lg（CFU/mL））,细菌形态发生皱缩和破裂,内膜和外膜通透性分别增加了989.31%和474.51%,胞内核酸、蛋白等大分子发生泄漏,电导率显著升高（P＜0.05）;傅里叶变换红外光谱分析结果显示,经PAW120处理后细菌细胞脂质和蛋白质结构发生变化。综上所述,PAW能够通过破坏细胞壁从而使细胞膜通透性增大、细胞内蛋白和核酸流出,最终导致细胞死亡。本研究可为PAW在水产品保鲜中的应用提供理论依据。     

低温等离子体技术在肉品保藏及加工中的应用研究进展

低温等离子体作为一种新兴的非热能技术已成为研究热点,该技术具有安全、温和、操作简便以及成本较低等优点,在食品非热加工领域具有广泛的应用前景。低温等离子体在激发过程中能够产生臭氧、单线态氧、超氧阴离子自由基、羟自由基、氮氧化物等活性物质,对肉品中微生物的抑制和亚硝酸盐的产生具有独特的作用。本文概述了低温等离子体的产生方式,分析了其工作效率和影响因素,并在此基础上从抑制微生物生长和替代亚硝酸钠两方面,介绍了低温等离子体技术在肉品保藏及加工中的应用研究进展,同时探讨了低温等离子体对肉品脂肪氧化的影响,并对其应用前景进行展望,为推动低温等离子体技术在肉品研究中的应用和推广提供理论参考。