NC State researchers explore using herbal oils to kill pathogens on fruits, vegetables

CorrespondentMay 5, 2013 

When Penelope Perkins-Veazie picks up a cantaloupe, she is probably thinking something a little different from other shoppers, most of whom probably give the fruit a sniff to check for ripeness, then plunk it in the grocery cart.

Perkins-Veazie, on the other hand, peers down at the cantaloupe’s netted skin and mulls the perils of listeria, a bacteria that can cause sepsis, meningitis, or even death.

“Netting on cantaloupe is place for things to harbor,” said Perkins-Veazie, professor and post-harvest physiologist with the Plants for Human Health Institute at N.C. State’s N.C. Research campus in Kannapolis. “Last year, they were able to show listeria will hide under the net and will migrate into the fruit.”

Perkins-Veazie might see the dark side of fruits and vegetables, but she also sees a potential solution. She and other researchers at N.C. State and the University of Tennessee are experimenting with the use of oils extracted from herbs or spices to kill dangerous pathogens such as E. coli, listeria and salmonella on organically grown tomatoes, cantaloupe and other produce.

Cleaning with essential oils

While current packing-house practices involve the use of chlorine or hydrogen peroxide to wash produce, those don’t always work well after a lot of produce goes through the system. And organic growers have to dilute the spent chlorine heavily with water before it’s allowed to go into discharged wastewater, an expensive proposition. In addition, the idea of diluted bleach on produce may not square with the organic image, Perkins-Veazie said.

So she and other scientists want to learn whether bacteria-killing oils such as cinnamon, cloves and thyme can be dispersed into a liquid and sprayed on produce to clean it, all without leaving an aftertaste.

The project is funded with a $1.9 million grant through the National Institute of Food and Agriculture, Organic Agriculture Research and Extension Initiative. The institute is a division of the U.S. Department of Agriculture.

“There’s a lot of supporting scientific data to show this really works and works really well,” said Faith Critzer, assistant professor and food safety extension specialist with the University of Tennessee’s Department of Food Science and Technology.

“What we’re working on is trying to get some antimicrobial solutions that are acceptable to organic farmers and producers that can be used in produce washing. What we know is sometimes (standard produce washing) can actually lead to contamination,” Critzer said. “The water used is sometimes a dunk-tank method – kind of like a swimming pool for produce. If that water is contaminated, bacteria can travel to other produce washed afterward.”

Overhead spray bars can be better, but they are difficult to clean, she said.

Every year, one in six Americans gets sick from foodborne illness, 128,000 are hospitalized, and 3,000 people die, according to the Centers for Disease Control. Contamination can come from soil, sediment in irrigation ponds, animal feces or human handling.

For those who wonder why outbreaks of foodborne illness seem to be so much more frequent than in the past, Perkins-Veazie said part of the reason is that the CDC is better at tracking down sources of illness than it once was. Another part is that some pathogens are more dangerous than they once were.

“We know there’s a new variant of salmonella; it’s mutated. That’s one reason people didn’t encounter it growing up,” she said.

A help to farmers

Farmers are looking for new solutions to the bacteria that cause illness.

Randall Patterson, president of Rowan County-based Patterson Farms, said the chlorine his farm uses requires constant monitoring and corrodes the farm’s grading equipment.

“It’s real encouraging to know there’s a lot of research being done because (cleaning produce is) something that’s hard to do … with the products on the market right now,” said Patterson, whose third-generation farm produces tomatoes, strawberries, peppers and other crops. “We just need a better, safer, noncorrosive product that will disinfect our tomatoes.”

The germ-killing properties of cinnamon, clove and thyme oil have been known for ages.

“I first got involved when I found years ago that basil oil was used in preparing mummies,” said Perkins-Veazie. “Cinnamon oil was used pretty commonly up until World War II. Here’s the kicker: How do you get it to disperse and get even dispersal?”

That’s the focus of the Tennessee team’s work. Researchers are blending essential oils with food-safe surfactants that act as a carrier in water. They’re growing salmonella, listeria and E. coli in the lab and inoculating lettuce and tomatoes with the harmful bacteria.

“Then we’ll treat them with the mixes we are making,” Critzer said.

After the lab work, the scientists will move to the field.

“We’re going to be applying this to tomatoes and lettuce that have been growing organically and in packing houses where they wash produce,” Critzer said. “What we’re going to be looking for is general bacterial reduction (and) how well the product can be integrated into a wash system.”

N.C. State will look at how cost-effective the oils are – and if they’re pricier than chlorine, researchers will find out whether that increase is mitigated by adding to a fruit or vegetable’s shelf life. The N.C. State team also will test the consumer perception of produce cleaned with essential oils.

In 2015, university-owned farms in the mountains and Piedmont will try out the essential oil washes.

In 2016, the entire team will do a “traveling road show of sorts,” Critzer said, visiting farms and county extension offices with the results of the research.

“North Carolina is unique because it’s one of the few states that has a huge amount of specialty crops in fruits and vegetables,” said Perkins-Veazie. “We have a diverse collection of growers in the state small growers in the mountain and very large growers in the east.

“Our first audience is certainly organic farmers, but we’re hoping this will be adapted to conventional growers.”

Especially, she added, for growers of cantaloupe.

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