Plasma technology can inactivate Salmonella in fresh produce: study

Cold atmospheric gas plasma technology in combination with other mild treatments can destroy bacteria in fresh produce, according to a new study conducted by researchers at the Institute of Food Research (IFR), UK.

While chlorine-based decontamination is usually used for eliminating bacteria, cold atmospheric gas plasma technology is a new method to eliminate bacteria on fresh fruits and vegetables, without affecting quality or flavour.

Plasmas are a combination of highly energetic particles formed when gases are stimulated by an energy source, and they can effectively destroy microorganisms on food surfaces without affecting their structure, as they do not involve extreme conditions such as high temperature.

For the study, researcher Dr Arthur Thompson evaluated how effectively cold atmospheric plasmas (CAP) can inactivate Salmonella under different conditions and on varied fresh produce foods.

The study revealed that Salmonella could be effectively destroyed by plasmas; however, the length of exposure for eliminating bacteria varied significantly based on the type of produce.

Factors such as the ambient temperature of the produce or the growth phase of the Salmonella had no significant impact, and the inactivation of Salmonella on food surfaces took longer than on an artificial membrane filter surface.

To understand the reason behind this, researchers studied the food surfaces with an electron microscope, and found that Salmonella could ‘hide’ in microscopic surface structures of different foods, and can be shielded from the effects of plasma.

The study found that different structures, such as the bumps on strawberries, the pores in lettuce leaves or the cell walls of potatoes, can form shadowed zones that can keep plasma from reaching bacteria.

Thompson said the study results indicate that scaled up devices or combinations with other mild treatments could provide an effective solution for eliminating bacteria with little or no effect on the produce itself.

"What this study shows is that it will be important to take into account the type of food and its surface structure," Thompson added.

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Image: Electron micrograph showing Salmonella in the pores of a lettuce leaf. Photo: courtesy of the Institute of Food Research.