Enhancing the discharge uniformity of atmospheric pressure DBD cold plasma for food efficient microbial inactivation

Identification and optimization of the discharge uniformity is worldwide problems in the plasma industry. In this study, a simple, practical, and economical alternative for quantitatively identifying discharge uniformity of DBD plasma was proposed using the gray-level histogram, discharge area curve, and gray level transformation characteristics of discharge images. The influences of discharge peak voltage, excitation frequency, dielectric material, and dielectric thickness on discharge uniformity on the time scale of seconds were discussed, and the intrinsic relationship and mechanism between discharge uniformity and microbial inactivation efficiency were revealed. Within a certain range, with the gradual increase of discharge peak voltage (13–17 kV), excitation frequency (9–11 kHz), relative dielectric constant (3.6–9.6), and the gradual decrease of dielectric thickness (1–5 mm), the discharge image corresponded to the relative discharge uniformity and the average inactivation of L. monocytogenes and S. typhimurium (0.12–1.40 log-reduction and 0.26–2.34 log-reduction) increased as a whole. Overall, the findings revealed disruption or improvement of the discharge uniformity was the main factor contributing to the inactivation of bacteria by cold plasma, facilitating the scaling-up of DBD reactors on an industrial scale.