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The involvement of plasma produced species in the reduction of silver ions at the plasma–liquid interface is investigated using a well-characterized radio-frequency driven atmospheric pressure plasma jet. The absolute gas phase H density was measured using two photon absorption laser induced fluorescence in the free jet. Broadband absorption and transmission electron microscopy were used to study the synthesis of silver nanoparticles (AgNPs). It is shown that fructose, an often used surfactant/stabilizer for AgNP synthesis, also acts as a reducing agent after plasma exposure. Nonetheless, surfactant free AgNP synthesis is observed. Several experimental findings indicate that H plays an important role in the reduction of silver ions for the plasma conditions in this study. Vacuum ultraviolet photons generated by the plasma are able to reduce silver ions in the presence of fructose. Adding H2 to the argon feed gas leads to the production of a large amount of AgNPs having a particle size distribution with a maximum at a diameter of 2–3 nm, which is not observed for argon plasmas. This finding is consistent with a smaller concentration of reducing species at the plasma–liquid interface for Ar with the H2 admixture plasma. The smaller flux of reactive species to the liquid is in this case due to a less strong interaction of the plasma with the liquid. The formation of the nanoparticles was observed even at a distance of 6–7 mm below the tip of the plasma plume, conditions not favoring the injection of electrons.

Minimal food-processing methods are not effective against foodborne viruses, such as human norovirus (NV). It is important, therefore, to explore novel nonthermal technologies for decontamination of foods eaten fresh, minimally processed and ready-to-eat foods, and food contact surfaces. We studied the in vitro virucidal activity of cold atmospheric gaseous plasma (CGP) against feline calicivirus (FCV), a surrogate of NV. Factors affecting the virucidal activity of CGP (a socalled radio frequency atmospheric pressure plasma jet) were the plasma generation power, the exposure time and distance, the plasma feed gas mixture, and the virus suspension medium. Exposure to 2.5-W argon (Ar) plasma caused a 5.55 log 10 unit reduction in the FCV titer within 120 s. The reduction in the virus titer increased with increasing exposure time and decreasing exposure distance. Of the four plasma gas mixtures studied (Ar, Ar plus 1% O 2 , Ar plus 1% dry air, and Ar plus 0.27% water), Ar plus 1% O 2 plasma treatment had the highest virucidal effect: more than 6.0 log 10 units of the virus after 15 s of exposure. The lowest virus reduction was observed with Ar plus 0.27% water plasma treatment (5 log 10 unit reduction after 120 s). The highest reduction in titer was observed when the virus was suspended in distilled water. Changes in temperature and pH and formation of H 2 O 2 were not responsible for the virucidal effect of plasma. The oxidation of viral capsid proteins by plasma-produced reactive oxygen and nitrogen species in the solution was thought to be responsible for the virucidal effect. In conclusion, CGP exhibits virucidal activity in vitro and has the potential to combat viral contamination in foods and on food preparation surfaces. Foodborne illnesses continue to plague public health, as well as world economies, costing approximately $152 billion in the United States alone (1). Enteric viruses, particularly human norovirus (NV) and hepatitis A virus (HAV), are the leading causes of viral foodborne illnesses (2). Human NV, one of the top five pathogens with respect to the total cost of foodborne illnesses in the United States, belongs to the family Caliciviridae and is a wellknown cause of "winter vomiting disease" or "stomach flu" (3). NV causes 19 to 21 million cases of acute gastroenteritis annually in the United States and leads to 1.7 to 1.9 million outpatient visits, 400,000 emergency room visits, 56,000 to 71,000 hospitalizations, and 570 to 800 deaths, mostly among young children (4). More than half of all foodborne disease outbreaks due to a known cause reported to the CDC from 2006 to 2010 were attributed to NV. In the European Union in 2007, caliciviruses (primarily NV) were responsible for 507 of 675 foodborne viral disease outbreaks (5).Multiple issues related to the quality of thermally processed foods, e.g., nutritional losses and adverse effects on organoleptic quality, have led to the emergence of so-called nonthermal technologies, which consist of preservation treatments that are effective at ambient o...

The question of how normal electrolysis (NE) at high voltages breaks down and transforms into contact glow discharge electrolysis (CGDE) was addressed with the anode as the preferred center for the phenomenon. Because close analogies in physical characteristics exist in the NE-to-CGDE transition and the natural convection-to-stable film boiling transition observed during pool boiling of liquids, the applicability of Helmholtz–Taylor’s boiling heat transfer theory to the breakdown of NE and the transition to CGDE was examined. The approach was justified by the proportionality relationships observed between the critical flux of heat dissipated by the Joule effect near the anode and the anolyte surface tension or the radius of the anode wire. The results led to a detailed mechanism of the transition of NE to CGDE at the anode consisting of the following sequences: local solvent vaporization, setting up of stable counterflows between the vapor bubbles and the liquid anolyte at the anode, collapse of this flow pattern and formation of an unstable vapor film with an overlying heavier liquid, stabilization of the vapor film, and incipience of glow discharges across the film.