Influence of high voltage atmospheric cold plasma process parameters and role of relative humidity on inactivation of Bacillus atrophaeus spores inside a sealed package
Introduction
Non-thermal atmospheric plasma is gaining interest for a number of applications including decontamination of contaminated surfaces, improvement of food safety, material surface treatment, and sterilization of medical instruments.1, 2, 3
Plasma discharge results in generation of a number of antimicrobial agents including reactive oxygen species (ROS), reactive nitrogen species (RNS), ultraviolet (UV) radiation, energetic ions, and charged particles. Parameters such as applied voltage, mode of plasma exposure, gas type, treatment time, and relative humidity (RH) influence the generation of reactive species, thus affecting the overall process. The type of reactive species and their concentration depend on the type of gas used for plasma discharge, thereby dictating the microbial inactivation efficacy.4, 5 The role of various charged particles and reactive species generated in the mechanism of plasma inactivation is under investigation.
Plasma treatment for the inactivation of spores using low pressure, atmospheric pressure and surface micro-discharge-type plasma has been reported.6, 7, 8 The significant role played by relative humidity on the plasma inactivation of spores has also been investigated in previous works.5, 9 The influence of increasing RH level on ozone germicidal efficiency and the likely contribution of additional radicals such as hydroxyl ion and peroxides in the inactivation process have been reported.10, 11
In the current work, in-pack HVACP inactivation of B. atrophaeus spores using a high voltage level over short exposure times (30–120 s) in a sealed environment was evaluated for the first time. The effect of mode of exposure and process parameters including treatment time, gas type, and the interactive effect of RH on inactivation of spores were investigated. The inactivation of spores is explained and correlated to the plasma-induced gas chemistry and the generation of highly oxidizing species in a sealed package. System diagnostics included optical absorption measurements which were collected under identical experimental conditions.
Section snippets
HVACP system set-up
The HVACP device (Figure 1) is an atmospheric low temperature plasma generator. The HVACP system was operated at 70 kVRMS at a frequency of 50 Hz. The two 15 cm diameter aluminium disc electrodes were separated by a rigid polypropylene container (310 × 230 × 22 mm) which served as a sample holder and as a dielectric barrier with wall thickness of 1.2 mm. The distance between the two electrodes was 22 mm, equal to the height of the container. The top electrode served as a high voltage electrode and
Effect of HVACP process parameters on bacterial spore inactivation
Figure 2 represents HVACP reduction of B. atrophaeus spores as a function of mode of plasma exposure, gas types, and treatment time. There were significant interactive effects of gas types and mode of exposure. Direct plasma exposure for 60 s reduced spore population by 6 log10 cycles or more in all gas types studied. A strong influence of gas type on inactivation was noted when indirect plasma exposure was evaluated for spore reductions. Indirect exposure to plasma discharge generated in gas
Discussion
All of the process parameters studied showed a strong influence on the HVACP inactivation rate of bacterial spores. Direct HVACP exposure for only 60 s resulted in complete inactivation of spores irrespective of the gas types used for plasma generation. Previous studies also showed greater inactivation effects of plasma after direct exposure of bacterial cells. The important role of charged species in conjunction with the synergistic action of O3, OH radicals, excited molecular and atomic
Conflict of interest statement
None declared.
Funding source
This work has received funding from the European Community's Seventh Framework Program (FP7/2207-2013) under grant agreement number 285820.
References (35)
- et al.
Treatment of raw poultry with nonthermal dielectric barrier discharge plasma to reduce Campylobacter jejuni and Salmonella enterica
J Food Prot
(2012) - et al.
Ozone gas is an effective and practical antibacterial agent
Am J Infect Control
(2008) - et al.
Sterilizing Bacillus pumilus spores using supercritical carbon dioxide
J Microbiol Methods
(2006) - et al.
Evaluation of the roles of reactive species, heat, and UV radiation in the inactivation of bacterial cells by air plasmas at atmospheric pressure
Int J Mass Spectrom
(2004) - et al.
Cold plasma sterilization of open wounds: live rat model
J Plasma Med
(2011) - et al.
Low-temperature sterilization of wrapped materials using flexible sheet-type dielectric barrier discharge
Appl Phys Lett
(2008) - et al.
Effect of gas composition on spore mortality and etching during low-pressure plasma sterilization
J Biomed Mater Res
(2000) - et al.
Effect of feed gas composition of gas discharge plasmas on Bacillus pumilus spore mortality
Lett Appl Microbiol
(2003) - et al.
A parametric study of the destruction efficiency of Bacillus spores in low pressure oxygen based plasmas
Lett Appl Microbiol
(1998) - et al.
Sterilization of bacteria, yeast, and bacterial endospores by atmospheric-pressure cold plasma using helium and oxygen
J Microbiol
(2006)
Cold atmospheric air plasma sterilization against spores and other microorganisms of clinical interest
Appl Environ Microbiol
Influence of relative gas humidity on the inactivation efficiency of a low temperature gas plasma
J Appl Microbiol
Surface germicidal effects of ozone for microorganisms
Am Indust Hyg Assoc J
The electrical characteristics of the ozonator discharge
Trans Electrochem Soc
Microdischarge behaviour in the silent discharge of nitrogen–oxygen and water–air mixtures
J Phys D: Appl Phys
Atmospheric cold plasma inactivation of Escherichia coli in liquid media inside a sealed package
J Appl Microbiol
Cited by (142)
Resistance of Alicyclobacillus acidoterrestris spores to atmospheric cold plasma: Insights from sporulation temperature and mechanism analysis
2024, Innovative Food Science and Emerging TechnologiesPlasma treatment: An alternative and sustainable green approach for decontamination of mycotoxin in dried food products
2023, Journal of Agriculture and Food ResearchRecent advances in non-thermal processing technologies for enhancing shelf life and improving food safety
2023, Applied Food ResearchGrating-like DBD plasma for air disinfection: Dose and dose-response characteristics
2023, Journal of Hazardous Materials