Kinetics of microbial inactivation using in-package nonthermal plasma generated by dielectric barrier discharge

Abstract

Escherichia coli and Staphylococcus aureus inoculated on nutrient agar were packaged in polyethylene bags with ambient air or Ar/O₂ mixture and treated with in-packaged nonthermal plasma (NTP) generated by dielectric barrier discharge. Surviving cell colonies were directly counted to investigate microbial inactivation kinetics. The results showed that Weibull and biphasic models adequately described inactivation kinetics, which depended on power level, gas type, treatment time, bacteria species, and initial cell concentration. Approximately 5-log reduction of the targeted microbes was achieved within 5 min at 22.0 W with argon/oxygen mixture at 6-log initial cell/plate. Interestingly, each microorganism drastically gained heightened resistance at different initial cell concentrations being 6 and 5-log cell/plate, equivalent to 4.2 and 3.2-log CFU/cm², for E. coli and S. aureus, respectively. Although uneven microbial inactivation occurred in the results, likely due to limited plasma diffusion, in-package NTP treatment remains a promising, energy-efficient, nonthermal method for microbial control.

Industrial relevance

This study investigated the microbial inactivation kinetics of in-package nonthermal plasma treatment generated by dielectric barrier discharge which can be easily scaled into industry level. Understanding these kinetics helps determine appropriate processing parameters such as electrical input power and treatment time. Atmospheric modification by using argon/oxygen mixture reduced the energy required in the process and greatly improved the microbial inactivation effect. In addition, good hygiene practice would facilitate the treatment since microbial load affects the inactivation rate as demonstrated in this study.