IFR researchers put plasma technology to the test

Researchers hope to find safer alternatives to chlorine-based decontamination, the current method of removing food poisoning bacteria from fresh fruits and vegetables. The challenge is also to find methods that would not affect the quality or flavour of foods.

One technique being investigated is cold atmospheric gas plasma technology. Plasmas, a mix of highly energetic particles created when gases are excited by an energy source, can be used to destroy bacteria in food. However, it may not totally wipe out micro-organisms present on the surface structures of different foods, says a research done by the Institute of Food Research. Plasmas can effectively inactivate microorganisms, and as they don’t involve extreme conditions such as high temperature they have been suggested for use in decontaminating food surfaces without affecting the structure. Dr Arthur Thompson has been investigating how well cold atmospheric plasmas (CAP) inactivate Salmonella under different conditions and on different fresh produce foods at the Institute of Food Research, which is strategically funded by the Biotechnology and Biological Sciences Research Council.

Publishing in the journal Food Microbiology, Dr Thompson found Salmonella could be effectively inactivated by plasmas, but the length of exposure varied greatly depending on the type of produce. Other variables, such as the ambient temperature of the produce or the growth phase of the Salmonella had no significant effect. Inactivation on food surfaces took longer than on an artificial membrane filter surface.

To understand why, the researchers looked at the food surfaces with an electron microscope. At this microscopic level of detail, it was possible to see how Salmonella could ‘hide’ from the effects of the plasmas. Different structures, such as the bumps on the strawberries, the pores in lettuce leaves or the cell walls of potatoes create shadowed zones that block plasma reaching bacteria.

“The results suggest scaled up devices or combinations with other mild treatments could provide a very effective solution for destroying bacteria with little or no effect on the produce itself,” said Dr Thompson. “What this study shows is that it will be important to take into account the type of food and its surface structure.”

Dr Arthur Thompson will give a talk on Insights into the inactivation of Salmonella by cold gas plasma treatment at Campden BRI, November 14 and 15. This conference, the 11th of its

kind, will look at some of the major new concerns:
? Microbial toxins – which can be present in foods, even if the producing organisms have been destroyed
? Salmonella – a pathogen that can be present in a wide range of foodstuffs, including chocolate and dry ingredients
? Seafood – Vibrio and Norovirus species are a specific worry, and detection and environmental occurrence are particular issues
? Dairy products – from concerns over the use of raw milk in pasteurised cheese to the microbiology of cream and butter