Abstract
Plasma activated water (PAW) has rapidly emerged as a promising alternative to traditional sanitizers applied in the fresh produce industry. In the present study, PAW chemistry and storage stability were assessed as a function of plasma operating conditions. Increasing plasma exposure time (5, 12.5, 20 min) and power (16, 26, 36 W) led to a significant drop in pH (2.4) and higher nitrates and nitrites levels (320 and 7.2 mg/L, respectively) in the PAW. Non-detectable hydrogen peroxide concentration, irrespective of the treatment conditions, was attributed to its instability in acidic environments and the remote PAW generation mode. pH, nitrates and nitrites levels in the PAW remained unaffected after two weeks at 4 °C. The potential of PAW for microbial inactivation and quality retention was demonstrated on baby spinach leaves. Rinsing steps influenced colour development during chilled storage to a greater extent than PAW treatment itself. About 1 log reduction in total bacterial counts (5 log CFU/g) was achieved through PAW rinsing, with no variability after eight days at 4 °C (typical shelf-life at retailers). Moreover, microbial levels on PAW-treated samples after storage were significantly lower than those on control samples, thus contributing to extended product shelf-life and reduced food waste generation.
Highlights
IntroductionOtherwise referred to as the fourth state of matter, manmade plasma is typically sustained via an electric discharge in a gas subset (e.g., room air); the partially or fully ionised air assembles a bunch of subatomic/molecular entities (reactive oxygen and nitrogen species, RONS) besides quanta of electromagnetic radiation (UV-photons, visible light), all co-existing as thermal or non-thermal plasmas upon thermodynamic equilibrium [1,2]
Otherwise referred to as the fourth state of matter, manmade plasma is typically sustained via an electric discharge in a gas subset; the partially or fully ionised air assembles a bunch of subatomic/molecular entities besides quanta of electromagnetic radiation (UV-photons, visible light), all co-existing as thermal or non-thermal plasmas upon thermodynamic equilibrium [1,2]
As cold plasma (CP) treatment is limited to surface applications, which may negatively affect product colour, surface topography or bioactivity [10], a recent application of this technology to overcome such limitations relies on the activation of liquids through their exposure to CP discharges, resulting in a cocktail of reactive oxygen and nitrogen species (RONS) often affecting the pH of the media
Summary
Otherwise referred to as the fourth state of matter, manmade plasma is typically sustained via an electric discharge in a gas subset (e.g., room air); the partially or fully ionised air assembles a bunch of subatomic/molecular entities (reactive oxygen and nitrogen species, RONS) besides quanta of electromagnetic radiation (UV-photons, visible light), all co-existing as thermal or non-thermal plasmas upon thermodynamic equilibrium [1,2]. As CP treatment is limited to surface applications, which may negatively affect product colour, surface topography or bioactivity [10], a recent application of this technology to overcome such limitations relies on the activation of liquids (e.g., water) through their exposure to CP discharges (e.g., air plasmas), resulting in a cocktail of reactive oxygen and nitrogen species (RONS) often affecting the pH of the media (e.g., acidification). The chemical composition of PAW generated with a surface dielectric barrier discharge (SDBD) set-up was determined as a function of the CP power (voltage peak-to-peak) and exposure time, as well as its storage stability under relevant conditions for industrial settings (two weeks at 4 ◦ C). The potential of PAW for microbial disinfection, quality retention (colour) and shelf-life extension was assessed on baby spinach leaves after eight days of refrigerated storage
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