Plasma technology may help extend fruit shelf life

Seeing fruit “turn bad and going to waste” inspired a team of researchers in China to explore using atmospheric pressure nonequilibrium plasma—already widely used for medical purposes—as a novel solution to extend the shelf life of fruit and other perishable foods.

When bacteria attaches to food surfaces, it can extract nutrients and continue to proliferate in the form of “biofilms.” Bacterial biofilms on food and food-processing surfaces diminish the food’s quality and safety. But plasma sources are capable of killing bacteria such as Salmonella and E. coli on apples, as well as other types of spoilage microorganisms on mangos and melons, and Listeria on meat.

A study published in Physics of Plasmas details the researchers’ computational study of how air plasma interacts with bacterial biofilms on an apple’s surface, showing that plasma technology could be used to decontaminate food in the future. The fundamental concept behind the team’s work is to harness the reactive species generated by plasma to kill bacterial biofilms, which are notoriously difficult to wipe out.

For this study, the researchers simulated how the structure of the biofilm affects the discharge dynamics and then zeroed in on how the reactive species generated by the plasma are distributed on the biofilm’s surface—because it can later kill the bacteria within the biofilm.

“Plasma is formed when enough energy is added to a gas to ‘free up’ electrons from a significant number of atoms or molecules,” said Xinpei Lu, a professor in the College of Electrical and Electronic Engineering at Huazhong University of Science and Technology. “This process, known as ‘ionization,’ creates a mixture of positively charged particles, negatively charged particles, and various uncharged particles.”

The researchers then explored how plasma interacts with biofilms and how the reactive species generated by the plasma are able to penetrate the cavity of the biofilm. They found that air plasma can be used to kill bacteria within biofilms, which could “significantly prolong the amount of time fruit remains edible,” said Lu. Such a technique could be on the market within a few years, once a low-cost plasma source is developed.

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