Non-thermal atmospheric gas plasma for decontamination of sliced cheese and changes in quality

The atmospheric-pressure non-thermal dielectric barrier discharge (DBD) plasma has recently emerged as an efficient decontamination method for the food safety enhancement. Thus the objective of this study was to evaluate the effectiveness of a simple DBD plasma treatment, with a relatively low-frequency power supply operating at 60 Hz, for microbial inactivation. A parametric study of operating conditions for bacterial inactivation was conducted using nutrient agar inoculated with Escherichia coli (2.28--6.28 log CFU/ml). The microbial log reduction was enhanced with increasing input power (30, 50, 70 W) and plasma exposure time (0, 1, 3, 5, 7 min). The inactivation effect was increased by decreasing inter-electrode gap (2, 1.5, 1 cm) and by reducing the initial microorganism concentration. Accordingly, a DBD plasma treatment at 50 W for 10 min could lead to complete killing of E. coli and partial inactivation of Listeria innocua on cheese (mean log reduction: 4.75 ± 0.02 and 0.72 ± 0.01, respectively). The decontamination efficacy of DBD plasma was affected by the types of microorganisms. The changes in hardness and color of cheese were unnoticeable after 10 min treatment with a power of 50 W. Overall, the results suggested that the DBD plasma can be potentially exploited to improve the food safety.