An ‘accepted study’ in the Journal of Applied Microbiology claims that a prototype dielectric barrier discharge atmospheric cold plasma (DBD-ACP) generator inactivated E.coli ATCC 25922 in a sealed package.
An isolated colony of E.coli ATCC 25922 was inoculated into 10 ml tubes containing tryptic soy broth and incubated overnight at 37°C.The overnight culture (18 hours) was harvested by centrifugation at 8720 g for 10 minutes.
After samples were washed in sterile phosphate buffered solution (PBS), prepared and sample density was adjusted, a working concentration of samples was dispensed into the wells of a microtiter plate.
This was then placed in the centre of a rigid polypropylene plastic container directly between the electrodes within the plasma discharge for direct plasma treatment. A separate container was used for indirect plasma treatment.
Each container was then sealed with the high barrier polypropylene bag. Bacterial samples were then treated with plasma for 10, 20, 30, 45, 60, and 300 seconds at 40kV peak-to-peak voltage.
In order to assess the retention effect of plasma generated reactive species over time, samples were stored at room temperature for 0, 15, 30, and 60 minutes following 300 seconds of plasma treatment or 1 hour and 24 hours after 60 seconds of treatment.
Shorter time intervals
Samples treated with shorter treatment intervals (10, 20, 30, and 45 s) were stored at room temperature for 24 hours.
The effect of the plasma treatment on the microbial load was determined in terms of reduction in viable counts. Plasma treated samples were diluted in appropriate solutions and incubated for 37 degrees for 24 hours and further incubated for two to three days.
Results were presented as surviving bacterial population in Log10CFUml−1 units. All experiments were carried out in duplicate and replicated at least twice.
Direct plasma treatment
Best results were achieved for direct plasma treatment in PBS. But in all solutions and for all treatment times, after 24 hours bacteria were completely inactivated.
Effects of ozone, temperature and pH on results were also analysed.
Indirect plasma treatment by other scientists of ready to eat sliced meat demonstrated 1.6 log bacterial reductions, the study notes.
Indirect plasma treatment
Indirect plasma treatment could also have the widest possible uses in the food industry where a balance between maintaining quality characteristics of sensitive fruits and vegetables and microbial decontamination is required, it states.
“It was demonstrated that the novel DBD-ACP can inactivate high concentrations of E. coli suspended in liquids within sealed packages in seconds,” the scientists concluded.
“A key advantage of this in-package non-thermal novel disinfection approach is the elimination of post-processing contamination.”
Source: Journal of Applied Microbiology, 'Accepted Article', doi: 10.1111/jam.12087
Authors: D.Ziuzina1, S. Patil1, P.J. Cullen1, and K.M.Keener2 P. Bourke1
1. School of Food Science and Environmental Health, Dublin Institute of Technology, Ireland
2. Purdue University, Nelson Hall of Food Science, Rm 3215745 Agriculture Mall Drive West Lafayette, IN 47907-2009