Pathogen killing plasma method effective in ‘minutes’

By Joseph James Whitworth

- Last updated on GMT

Related tags Bacteria

Kevin Keener at work. Photo: Tom Purdue Agricultural Communication file photo/Tom Campbell)
Kevin Keener at work. Photo: Tom Purdue Agricultural Communication file photo/Tom Campbell)
The team behind a method that can kill foodborne pathogens “within minutes” using cold plasma in packaged liquids and foods is looking for industrial partners as they bid to commercialise the technology.

A Purdue University study found exposing the packaging liquids to the method, which uses electricity to generate a plasma from atmospheric gases inside the package, could extend shelf life by 20-30% depending on the product.  

The process involves applying a high voltage and using the packaging as a dialectic barrier, something that prevents electrical current flow but allows the movement of voltage.

It creates a wide variety of bacteria-killing molecules including ozone, nitrogen oxides, hydrogen peroxide and others.

Resistance is futile

Kevin Keener, a professor of food science at Purdue University, said they have seen no measureable resistance as yet in their experiments on a range of pathogens.

He said the novelty of the technique is its low energy and compared it to operating on the same principles as a 50-100 watt florescent light bulb.

The process has been demonstrated to work and the team is now looking for an industrial partner to gain specific data on specific applications and not just in the laboratory so they can tackle any regulatory review and work towards commercialization in the next few years.

The research builds on the process that we reported on in 2011​ that was focussed on the technology’s ability on fruits and vegetables.

Adapting the technology for liquids was a “natural progression​” and could allow development of portable devices to clean drinking water in areas with contamination or that lack other purification methods.

It could also allow food processors to bottle juices without first heating them, a process widely used to kill bacteria that can alter products.

Packaging types

Keener said the technology has been tested on a range of packaging with mostly positive results.

He said it works with common plastics such as polypropyelne (PP) and LDPE (low density polyethylene) and good results have been seen with cardboard, paperboard and glass.

Metal was an issue as it collected the charge but he added the team was evaluating their options in this area and said they had seen some capabilities in multi-laminate packages.

The process involves the passing of a dielectric discharge, two electrodes of high voltage electricity, through food in normal food packaging lined with plasma.

The atmospheric plasma creates an active species within the bag inactivating pathogenic bacteria in the packaging. These active species then convert back to their original atmospheric gas composition over a time varying from a few hours to 24 hours depending on a range of factors.

Keener and researchers at the Dublin Institute of Technology demonstrated that sealed-package atmospheric plasma kills bacteria in growth media with 20 seconds of treatment and 24 hours of exposure to the gases it creates.

He said that 45 seconds of treatment gave complete elimination of E.coli, as holes could be seen forming in the cell walls of the bacteria under a microscope.

Fruit and veg work

The fruit and vegetable work is still going on as Europe seeks new methods as alternatives to washing foods in chlorine baths.

Chlorine water works well on hard surfaces. But there can be issues if bacteria get inside organic matter on the produce, making chlorine ineffective, Keener said.

The use of ozone is a competition technology but has been shown to cause deterioration of some products quality and while it would be a competitive technology to high pressure processing (HPP), Keener said it was an off the shelf process which is likely to cost less.

The results are part of an EU project called SAFE-BAG which aims to reduce microbes on fresh produce while ensuring the technology does not affect the nutritional properties, texture or taste of the packaged fruit or vegetables.

Related topics Food Safety & Quality

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