Plasma-activated aerosol for the decontamination of fresh strawberries: effects on natural microbiota and quality attributes

Plasma-activated aerosol (PAA) is an emerging non-thermal technology for the surface decontamination and shelf-life extension of fresh produce. Unlike conventional plasma-activated water treatments, the PAA system generates a plasma-activated aerosol by exposing liquid microdroplets to a gas plasma discharge, enabling the in-situ formation and delivery of reactive oxygen and nitrogen species (RONS) and potentially improving the transfer of short-lived reactive species to the product surface. Aim of the study was to investigate the effects of in situ generated PAA on microbial inactivation and quality attributes of fresh strawberries during refrigerated storage. Fresh strawberries were treated in a lab-scale PAA system operating at 10 kV and 4 Hz for four 5-min cycles. Three sample groups were produced and tested: non-treated control (NT), water aerosol without plasma activation (C-PAA), and plasma-activated aerosol (PAA). C-PAA and PAA samples were treated for 20 min and stored at 10°C for 5 days (t5). Specifically, natural microbiota (mesophilic and psychrophilic bacteria, lactic acid bacteria, Pseudomonadaceae, Enterobacteriaceae, yeasts, and molds) quality parameters (moisture content, firmness, total soluble solids, pH and CIE Lab* colour), enzymatic activity (phenylalanine ammonia-lyase and polyphenol oxidase activities, superoxide dismutase) and antioxidant capacity (TPC and ABTS assay) were evaluated after treatments (t0) and at the storage end point (t5). Microbiological analyses revealed significant (p < 0.05) inhibition of endogenous microbial growth, although reductions were moderate and not uniform across microbial groups. PAA application was particularly effective in the reduction of psychrophilic count, lactic acid bacteria, yeasts and molds, suggesting a positive impact on strawberries shelf-life. Enzymatic analyses showed no effects on phenylalanine ammonia-lyase and polyphenol oxidase activities, while superoxide dismutase was activated immediately after PAA treatment; however, after storage, no significant differences were observed among PAA and the control samples (NT and C-PAA). No significant changes were detected in antioxidant-related indices. In conclusion, in situ generated PAA contributed to preserving strawberry quality by limiting microbial growth and colour changes during refrigerated storage; however, process optimisation is required to enhance its efficacy on fresh fruit matrices.