Inactivation of Escherichia coli on blueberries using cold plasma with chemical augmentation inside a partial vacuum

Authors: Hertrich, Sarah; Boyd, Glenn; Sites, Joseph; Niemira, Brendan

Submitted to: Annual Meeting of the Institute of Food Technologists
Publication Type: Abstract Only
Publication Acceptance Date: 3/10/2017
Publication Date: 6/26/2017
Citation: Hertrich, S.M., Boyd, G., Sites, J.E., Niemira, B.A. 2017. Inactivation of Escherichia coli on blueberries using cold plasma with chemical augmentation inside a partial vacuum.[Abstract]. Annual Meeting of the Institute of Food Technologists. Las Vegas, NV., Volume 1, Page 1.

Interpretive Summary:

Technical Abstract: Justification: The mechanism by which cold plasma inactivates pathogens is through the production of free reactive chemical species. Unfortunately, the most reactive chemical species have the shortest half-life. In a vacuum their half-life is believed to be prolonged. Additionally, these reactive species are able to fill the vacuum chamber allowing for indirect application of plasma and less damage to the product. Objective: The objective of this study was to determine if the effects of cold plasma could be enhanced when generated inside a partial vacuum with chemical augmentation using either H2O, EtOH or CO2. Methods: Blueberries (10g) were placed in a sterile Petri dish then inoculated by pipetting 100 ul of E. coli K12 into the calyx of each berry. After drying for two hours in a Biosafety cabinet samples were placed inside the vacuum chamber along with another Petri dish filled with either 20 ml H2O, 25% or 50% EtOH, or 55-60 of dry ice (CO2). Electrodes were positioned in the center of the chamber for plasma generation. Samples were treated with cold plasma in a vacuum of 25 inHg for 0, 1, 5 and 10 min. Bacteria were enumerated by plating stomached and serially diluted samples onto aerobic count Petrifilm and incubated for 18 h at 37 degrees C. Results: Cold plasma in partial vacuum treatment significantly reduced the amount of E. coli recovered from samples compared to non-treated controls (p<0.05). The greatest reduction of E. coli on blueberries was achieved with chemical augmentation using H2O after 10 min treatment (1.84±0.08 log CFU/g reduction; p=0.002). This may be linked to the high humidity (maximum 74% RH) that was produced in the chamber as water evaporated. Vacuum only, chemical augmentation with 25% EtOH, 50% EtOH, CO2 and CO2 + H2O, resulted in a 0.32, 0.41, 0.51, 0.28 and 0.68 log CFU/g reduction, respectively. Significance: In a partial vacuum, the maintenance of a high humidity environment with the addition of water may significantly enhance the effects of cold plasma through prolonged half-life of free radicals. Indirect application of plasma to fragile food products, such as fresh produce, will also allow for preservation of sensory qualities.