Nonthermal plasma treatment of Aspergillus spp. spores on hazelnuts in an atmospheric pressure fluidized bed plasma system: Impact of process parameters and surveillance of the residual viability of spores

In this study, the impact of fluidized bed reactor diameters and plasma forming gases on inactivation efficiency of the Atmospheric Pressure Fluidized Bed Plasma (APFBP) system for aflatoxigenic spores of Aspergillus flavus and Aspergillus parasiticus on hazelnuts were investigated. Hazelnuts were artificially contaminated with A. flavus and A. parasiticus and then treated with dry air or nitrogen plasma for up to 5 min in two different fluidizing bed reactors of APFBP system at various plasma parameters. The decontamination effect of APFBP on Aspergillus spp. spores increased with the applied reference voltage and the frequency. The killing effect of plasma on the spores decreased as the diameter of the fluidized bed reactor increased. The fungicidal effects on A. flavus (4.17 log) and A. parasiticus (4.09 log) were found for air plasma treatment after 5 min. Due to the formation of active plasma species in the presence of oxygen, the air plasma generated at APFBP system was more effective than nitrogen plasma on decontamination of Aspergillus spp. spores, as expected. The total inactivation of the natural background microbiota of hazelnuts was obtained within maximum 2 min APFBP treatment. The aflatoxigenic spores that remained on hazelnuts after plasma process were considered as damaged cells, because they could not continue growing during storage at 25 °C for 30 days. The damage caused by APFBP treatment on Aspergillus spp. spore cells was demonstrated by using scanning electron microscopy.