May was a rough month for fresh produce. Alfalfa sprouts, bagged salads, and diced onions were recalled because of possible listeria contamination, while baby spinach and papayas were recalled because of possible salmonella contamination.

It’s enough to make one scout for something new in food safety systems.

And Brendan Niemira is working on something.

Untapped potential

Niemira, lead scientist at the USDA’s Food Safety and Intervention Technologies Eastern Regional Research Center in Wyndmoor, Pa., has been studying cold plasma for nearly a decade. The process uses electricity and a gas — such as oxygen — to deactivate contaminating microbes on meats, poultry, fruits, and vegetables.

Niemira and his colleague Joe Sites have treated a variety of foods — including almonds, apples, cantaloupe, lettuce and tomatoes — with cold plasma and produced multi-log reductions of E. coli O157:H7, salmonella and listeria.

While cold plasma already is used to clean electronics, bond plastics in manufacturing and bind dye to fibers in textile production, its potential remains untapped in the food industry.

“Anytime a technology is being developed, it’s only going to be used in the industry if it shows some significant advantages,” Niemira said. “Cold plasma is a waterless sanitizing process with no chemical inputs, so it’s got some attractive points. The big key right now is to develop the technology so that it gives a solid level of sanitizing antimicrobial effects without unwanted side effects. That’s the kind of thing that might lead an interested party to petition the FDA.”

Niemira said that in cold plasma trials with apples and almonds there were no changes in the product’s appearance. Another advantage, he said, is the level of efficacy. While most chlorine rinses will give one or two logs of surface sanitization, Niemira said cold plasma systems have been shown to give three or four logs in trials.

Unanswered questions

However, there are obstacles.

The FDA hasn’t issued any rules on the use of cold plasma on foods or food contact surfaces.

It’s also unclear how much it would cost to implement cold plasma on a full-scale, commercial packing line.

“One of the major determining factors will be the kind of gas you use to generate the plasma,” Niemira said. “It will be cheapest to use if the plasma is generated using air. If the system requires the use of a defined mix of oxygen and nitrogen, that would add costs. Other gases, such as helium or neon, would add still more to the costs.”

Although the research is ongoing, much depends on interest and demand for new solutions from industry.

“There would need to be a push-pull to do the engineering necessary to scale up cold plasma equipment from the lab scale to the pilot scale to the commercial scale,” Niemira said.

“The USDA is always interested in working with commercial partners to license existing technologies and to do collaborative R&D to solve problems in the real world. For this to move from the lab to the supply chain, it needs to achieve significant kill of pathogens in a reliable, consistent manner, and to do it in a way that preserves the color, aroma, texture, etc. of the foods.”

The USDA researchers also are developing cold plasma systems for food contact surfaces, such as conveyor belts.

“Since it’s more straightforward to treat plastics, metals and ceramics than it is to treat tomatoes, cantaloupes or lettuce, it may be that, in the short term at least, treatment of food contact surfaces could be where cold plasma finds its first applications for the food processing industry,” Niemira said.