Cold plasma is an emerging non-thermal disinfection and surface modification technology which is chemical free, and eco-friendly. Plasma treatment of water, termed as plasma activated water (PAW), creates an acidic environment which results in changes of the redox potential, conductivity and in the formation of reactive oxygen (ROS) and nitrogen species (RNS). As a result, PAW has different chemical composition than water and can serve as an alternative method for microbial disinfection.This paper reviews the different plasma sources employed for PAW generation, its physico-chemical properties and potential areas of PAW applications. More specifically, the physical and chemical properties of PAW are outlined in relation to the acidity, conductivity, redox potential, and concentration of ROS, RNS in the treated water. All these effects are in microbial nature, so the applications of PAW for microbial disinfection are also summarized in this review. Finally, the role of PAW in improving the agricultural practices, for example, promoting seed germination and plant growth, is also presented.PAW appears to have a synergistic effect on the disinfection of food while it can also promote seedling growth of seeds. The increase in the nitrate and nitrite ions in the PAW could be the main reason for the increase in plant growth. Soaking seeds in PAW not only serves as an anti-bacterial but also enhances the seed germination and plant growth. PAW could potentially be used to increase crop yield and to fight against the drought stress environmental conditions.

Non-thermal plasma has been widely considered to be an effective method for decontamination of foods. Recently, numerous studies report that plasma-activated water (PAW) also has outstanding antibacterial ability. This study presents the first report on the potential of PAW for the inactivation of Staphylococcus aureus (S. aureus) inoculated on strawberries. PAW treatments achieved a reduction of S. aureus ranging from 1.6 to 2.3 log at day-0 storage, while 1.7 to 3.4 log at day-4 storage. The inactivation efficiency depended on the plasma-activated time for PAW generation and PAW-treated time of strawberries inoculated with S. aureus. LIVE/DEAD staining and scanning electron microscopy results confirm that PAW could damage the bacterial cell wall. Moreover, optical emission spectra and oxidation reduction potential results demonstrate the inactivation is mainly attributed to oxidative stress induced by reactive oxygen species in PAW. In addition, no significant change was found in color, firmness and pH of the PAW treated strawberries. Thus, PAW can be a promising alternative to traditional sanitizers applied in the fresh produce industry.

The chemistry, antimicrobial efficacy and energy consumption of plasma-activated water (PAW) was optimized by altering the discharge frequency, ground-electrode configuration, gas flow rate and initial water conductivity for two reactor configurations, i.e., air pin-to-liquid discharge and air plasma-bubble discharge in water. The ratio of NO₂⁻ and NO₃⁻ formation was altered to optimise the antimicrobial effects of PAW, tested against two Gram-negative bacteria. An initial solution conductivity of 0.2 S·m⁻¹ and 2000-Hz discharge frequency with the ground electrode positioned inside the pin reactor showed the highest antimicrobial effect resulting in a 3.99 ± 0.13-log₁₀ reduction within 300 s against Escherichia coli and 5.90 ± 0.24-log₁₀ reduction within 240 s for Salmonella Typhimurium. An excellent energy efficiency of reactive oxygen and nitrogen species (RONS) generation of 10.1 ± 0.1 g·kW⁻¹·h⁻¹ was achieved.Plasma-activated water (PAW) is deemed as an eco-friendly alternative to chemical disinfection because its bactericidal activity is temporary. Optimizing the design and operation of PAW reactors to achieve high inactivation rates of more than 5-log₁₀ reductions, as demonstrated in this work, will support the industrial application of this technology and the scaleup at industrial level.

Engineered water nanostructures (EWNS) synthesized utilizing electrospray and ionization of water, have been, recently, shown to be an effective, green, antimicrobial platform for surface and air disinfection, where reactive oxygen species (ROS), generated and encapsulated within the particles during synthesis, were found to be the main inactivation mechanism. Herein, the antimicrobial potency of the EWNS was further enhanced by integrating electrolysis, electrospray and ionization of de-ionized water in the EWNS synthesis process. Detailed physicochemical characterization of these enhanced EWNS (eEWNS) was performed using state-of-the-art analytical methods and has shown that, while both size and charge remain similar to the EWNS (mean diameter of 13 nm and charge of 13 electrons), they possess a three times higher ROS content. The increase of the ROS content as a result of the addition of the electrolysis step before electrospray and ionization led to an increased antimicrobial ability as verified by E. coli inactivation studies using stainless steel coupons. It was shown that a 45-min exposure to eEWNS resulted in a 4-log reduction as opposed to a 1.9-log reduction when exposed to EWNS. In addition, the eEWNS were assessed for their potency to inactivate natural microbiota (total viable and yeast and mold counts), as well as, inoculated E. coli on the surface of fresh organic blackberries. The results showed a 97% (1.5-log) inactivation of the total viable count, a 99% (2-log) reduction in the yeast and mold count and a 2.5-log reduction of the inoculated E. coli after 45 min of exposure, without any visual changes to the fruit. This enhanced antimicrobial activity further underpins the EWNS platform as an effective, dry and chemical free approach suitable for a variety of food safety applications and could be ideal for delicate fresh produce that cannot withstand the classical, wet disinfection treatments.

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.