The potential of plasma-processed air (PPA) for industrial food safety in herbs and spices

Non-thermal plasma is gaining attention for food decontamination due to effective microbial inactivation, minimal quality deterioration, reduced energy consumption compared with thermal treatment. However, the lack of upscaled equipment suitable for industrial production has limited its transfer from lab to industry. The present study aims to validate the production efficiency of reactive species of an upscaled microwave plasma source – PLexc 2 . Fourier transformation infrared (FTIR) spectroscopy was applied for the chemical characterization and quantification of long-living reactive species in PPA. PLexc 2 could deliver 15,412, 13,263, and 11,522 ppm of NO x (sum of NO 2 and NO) at flow rates of 63, 73, and 83 L/min, respectively. Throughout a 60-min PLexc 2 operation, the temperature in the treatment chamber remained within the range of room temperature (20–25 °C). PPA treatment was then tested against Enterococcus faecium inoculated on crushed oregano leaves. For 1- and 30-min PPA treatments, 1.90 log 10 and 4.49 log 10 reductions were achieved, respectively. One hour of post-discharge sample incubation in the treatment chamber, in addition to a 1-min PPA treatment, increased the reduction from 1.90 log 10 to 3.21 log 10 . The economic feasibility was assessed by estimating conversion costs of PPA treatment, which ranged from 0.04 to 80.60 €/kg depending on treatment mode and scale. The return on capital investment of PLexc 2 equipment was estimated to be less than one year for a production quantity of 2000 t/yr. In conclusion, this study demonstrates the potential and the economic feasibility of applying an upscaled microwave plasma source in the food industry. • The up-scaled plasma source produces 63–93 L/min of PPA. • The maximum concentration of NO x in PPA achieved was 15,400 ppm. • 4.49 log reduction of E. faecium was achieved after 30 min of PPA treatment. • The treatment cost of dry oregano for 1 min is 0.04 €/kg for industrial scale. • Return of investment would be 1 year for a production quantity at 2000 t/yr.