title: Influence of high voltage atmospheric cold plasma process parameters and role of relative humidity on inactivation of Bacillus atrophaeus spores inside a sealed package.
abstract: BACKGROUND
  Non-thermal plasma has received much attention for elimination of microbial contamination from a range of surfaces.
  
  
  OBJECTIVE
  This study aimed to determine the effect of a range of dielectric barrier discharge high voltage atmospheric cold plasma (HVACP) parameters for inactivation of Bacillus atrophaeus spores inside a sealed package.
  
  
  METHODS
  A sterile polystyrene Petri dish containing B. atrophaeus spore strip (spore population 2.3 × 10(6)/strip i.e. 6.36 log10/strip) was placed in a sealed polypropylene container and was subjected to HVACP treatment. The HVACP discharge was generated between two aluminium plate electrodes using a high voltage of 70kVRMS. The effects of process parameters, including treatment time, mode of exposure (direct/indirect), and working gas types, were evaluated. The influence of relative humidity on HVACP inactivation efficacy was also assessed. The inactivation efficacy was evaluated using colony counts. Optical absorption spectroscopy (OAS) was used to assess gas composition following HVACP exposure.
  
  
  RESULTS
  A strong effect of process parameters on inactivation was observed. Direct plasma exposure for 60s resulted in ≥6 log10 cycle reduction of spores in all gas types tested. However, indirect exposure for 60s resulted in either 2.1 or 6.3 log10 cycle reduction of spores depending on gas types used for HVACP generation. The relative humidity (RH) was a critical factor in bacterial spore inactivation by HVACP, where a major role of plasma-generated species other than ozone was noted. Direct and indirect HVACP exposure for 60s at 70% RH recorded 6.3 and 5.7 log10 cycle reduction of spores, respectively.
  
  
  CONCLUSIONS
  In summary, a strong influence of process parameters on spore inactivation was noted. Rapid in-package HVACP inactivation of bacterial spores within 30-60s demonstrates the promising potential application for reduction of spores on medical devices and heat-sensitive materials.
authors.affiliation: School of Food Science and Environmental Health, Dublin Institute of Technology, Dublin, Ireland.
authors.forename: S
authors.initials: S
authors.lastname: Patil
authors.affiliation: School of Physical Sciences and National Centre for Plasma Science and Technology, Dublin City University, Dublin, Ireland.
authors.forename: T
authors.initials: T
authors.lastname: Moiseev
authors.affiliation: School of Food Science and Environmental Health, Dublin Institute of Technology, Dublin, Ireland.
authors.forename: N N
authors.initials: NN
authors.lastname: Misra
authors.affiliation: School of Food Science and Environmental Health, Dublin Institute of Technology, Dublin, Ireland.
authors.forename: P J
authors.initials: PJ
authors.lastname: Cullen
authors.affiliation: School of Physical Sciences and National Centre for Plasma Science and Technology, Dublin City University, Dublin, Ireland.
authors.forename: J P
authors.initials: JP
authors.lastname: Mosnier
authors.affiliation: Purdue University, Nelson Hall of Food Science, West Lafayette, IN, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Keener
authors.affiliation: School of Food Science and Environmental Health, Dublin Institute of Technology, Dublin, Ireland. Electronic address: Paula.bourke@dit.ie.
authors.forename: P
authors.initials: P
authors.lastname: Bourke
mesh_terms: D001407:Bacillus / Q000254:growth & development / Q000502:physiology*; D003080:Cold Temperature; D006813:Humidity; D050296:Microbial Viability; D058626:Plasma Gases / Q000009:adverse effects; D013171:Spores, Bacterial
chemical_list: D058626:Plasma Gases
keywords: Bacillus atrophaeus; Gas types; High voltage atmospheric cold plasma; Inactivation; Optical absorption spectroscopy; Relative humidity