Described as a “purple blow torch” by food safety scientists, cold plasma treatment can kill 99.9 percent of norovirus on blueberries without damaging the delicate fruit, giving a food safety boost to the so-called superfood.

cold plasma blueberry researchBrendan Niemira, a microbiologist at the U.S. Department of Agriculture’s Eastern Regional Research Center in Wyndmoor, PA, and a team of scientists already demonstrated that cold plasma (CP) can kill pathogens such as Salmonella and E. coli on blueberries.

The researchers, led by Alison Lacombe, focused on blueberries with their latest project because of the increasing popularity of the fruit in recent years, attributed to its antioxidants and other nutritional benefits. They also considered the manner in which the blue fruit is grown, packed, shipped and consumed.

“… blueberries are susceptible to contamination by biological hazards from pre-harvest to post-harvest stages and are most commonly consumed raw,” according to the research results set for publication in the May 2017 edition of the journal Food Microbiology.

“Human norovirus is one of the most common etiological agents that contaminates food and causes foodborne illness.”

Another factor making blueberries prime for the research is the fragile nature of berries in general. They also have some of the shortest shelf lives in the produce aisle, adding pressure to move them through the harvest and packing process as quickly as possible.

With the cold plasma treatment tested by the USDA researchers, more than 99.9 percent of the two viruses being studied died after two minutes or less.

The process of creating plasma, which is considered the fourth state of matter after solids, liquids and gases, is created by breaking apart gas molecules and making a plume of charged electrons and ions, according to The problem with using it as a sanitizing step is that the creation process generates heat, which is even more damaging to delicate fruits such as blueberries.

Niemira and the other scientists found by simply injecting room-temperature air into the treatment chamber the heat problem was eliminated.

Brendan Niemira
Brendan Niemira

“These results demonstrate that CP viral inactivation does not rely on thermal inactivation, and is therefore nonthermal in nature,” Niemira wrote in the research report.

“Currently, the preventative measures for viral outbreaks in the food supply chain primarily rely on good agricultural practices, chemical washes and increased awareness on good hygienic practices in food handling areas. However, few optimized nonthermal intervention processes are available for fresh and fresh-cut produce…

“Cold plasma is an emerging nonthermal technology that offers the advantage of being chemical- and water-free, in addition to being able to operate openly and continuously at atmospheric pressure.”

Additional research is needed before the CP treatment will be available for commercial-sized operations, but the researchers reported the variety of benefits it provides should make it an affordable tool for the food industry.

The researchers say their purple blow torches require only one-fifth the power needed to run a hair dryer. Niemira told his team is already working to scale up the approach: “We’re making it bigger, we’re making it faster, we’re making it more efficient.”

There is also evidence that CP treatment can extend shelf life by slowing spoilage rates.

“CP treatment was recently shown to inactivate potential spoilage microorganisms on blueberries without effecting firmness, color, or anthocyanin concentration,” according to the research report.

“In addition to improving food safety, CP technologies are environmentally friendly and sustainable, as they do not require on-site storage of supply chemicals or large volumes of processing water, either for implementation or in post-treatment rinsing.”

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