Plasma-Activated Fog (PAF) as a new alternative technology for fruit decontamination against postharvest fungal pathogens and pesticide residues

Fruits and vegetables play a crucial role in human nutrition. However, they are notably susceptible to pathogens causing postharvest decay and undesirable chemicals like residues of pesticides. Low temperature plasma (LTP) is currently proposed as novel promising technique against microbial contamination of produce. Atmospheric air LTP consists of a mixture of electrons, ions, radicals, stable and short living products, such as reactive oxygen and nitrogen species (RONS), and ultraviolet radiation. It can be applied either directly on product surfaces or indirectly through a plasma-activated medium, i.e. plasma-activated water (PAW) and plasma-activated mist (PAMi) or fog (PAF). These latter are rich of RONS and can be applied during postharvest stages. In this study, PAF was generated using a device developed at CNR-ISTP and applied to evaluate the effect on conidial germination of major fungal postharvest pathogens like Alternaria alternata, Aspergillus carbonarius, Botrytis cinerea, Cladosporium sp., Monilinia fructicola, Penicillium italicum and Penicillium expansum, Rhizopus sp. Differences in fungal sensitivity to PAF were observed, with A. alternata showing the lowest sensitivity to the treatments. For most of the species, the complete spore inactivation was obtained after 3-5 min of exposure. The efficacy of PAF against fruit rots was assessed on table grape and strawberry, revealing a significant reduction in the percentage of symptomatic fruits exposed to 10 min of treatment (up to 80% of efficacy). Furthermore, treatments of the same duration with PAF significantly reduced the pesticide residues in bunches of table grape artificially contaminated with acetamiprid (- 40%), abamectina (- 90%) and several fungicides with various results (up to 36% of reduction).