Application of Plasma-Activated Fog (PAF) in postharvest treatment to reduce spoilage by fungal pathogens and pesticide residues in fruits

During storage, fruits and vegetables are notably susceptible to significant pathogens responsible for postharvest decay and are affected by the presence of undesirable pesticide residues. Non-thermal plasma is currently proposed as a novel, promising technology against microbial and chemical contamination of produce. Atmospheric air plasma consists 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 in RONS and can be applied during postharvest stages. In this study, PAF was generated using a device developed at CNR-ISTP (Bari, Italy) 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 recorded, with A. alternata showing the lowest sensitivity to treatments. For most of the species, the complete spore inactivation was obtained after 3-5 min of exposure. The efficacy of PAF against fungal 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). PAF treatments also reduced pesticide residues on fruits contaminated by acetamiprid (-40%), abamectina (-90%), bifenazate, and spinetoram (-68%) and several fungicides with various results (up to 38% of reduction).