The sweet smell of safe grain: Can essential oils protect organic cereal grains during storage?

The loss of cereal grains to insect infestation and mold contamination during post-harvest storage is no small matter for farmers and grain processors, especially those working in extremely hot and humid climates.

Equally damaging can be the threat to food safety and security.

Jianmei Yu, Ph.D., a food and nutrition researcher at N.C. A&T, hopes to shed new light on a potentially safe alternative to the synthetic pesticides typically used to combat insect infestation, mold growth and the production of toxic compounds known as mycotoxins that can naturally occur in stored cereal grains. The use of synthetic pesticides is banned in organic grain storage due to their high level of toxicity.

Yu’s project investigates the effectiveness of five essential oils — cinnamon, clove, orange terpenes, oregano and thyme — all categorized as General, Recognized as Safe (GRAS) – against these industry problems.

“Mycotoxins, by name, are toxins that are poisonous to human beings and all kinds of animals. Oral exposure to high doses of mycotoxins can cause series diseases and even death,” Yu explains.  “Low doses of mycotoxins consumed over time will accumulate in the liver and kidneys, and can cause disease and cancer as well as reduce immunity.

“Mycotoxin contamination also causes a large economic loss. A lot of grains cannot be consumed by even animals because of regulations, and farmers lose that income.”

A native of China, Yu is no stranger to ground-breaking research. Her discovery of a relatively simple enzyme treatment that reduces key allergens in peanuts by up to 98 percent made international headlines. She earned bachelor’s and master’s degrees in sugar engineering from universities in her home country. After a chance encounter with a Louisiana State University researcher at a conference in China, she immigrated to America in 1993 and earned a doctorate in food science at LSU.

Yu’s research team at A&T first investigated the effectiveness of the five essential oils in destroying the maize weevil, an insect that develops as larvae within the corn kernel and can cause tremendous damage after harvest when stored in elevators or bins. The results proved promising, with cinnamon, clove and thyme oils being most effective in repelling infestation. All five oils showed similar or higher effectiveness when compared with the commonly used pesticide pirimiphos-methyl at its recommended concentration.

Yu’s current research focuses on mold growth.

“Many people have used essential oils as antimicrobials. Either they use micro-culture medians — they add them in the medium to see if mold is growing or not — or they dip a product like fruit in different concentrations of essential oils to see if the growth of molds is inhibited,” she said.

Jianmei Yu, Ph.D., a food and nutrition researcher, is working to combat insect infestation, mold growth and the production of mycotoxins that can naturally occur in cereal grains.

“You cannot do that with corn or other cereal grains because the oils have a very strong odor.”

To overcome this obstacle, Yu simulates fumigation by attaching a cotton ball to the lid of a small container of grains and adding the essential oil to the cotton ball, which releases the vapor. The containers are stored in a temperature-controlled environment.

“So far, we’ve found that all of these essential oils more or less inhibit the growth of molds. Cinnamon oil showed the highest inhibitory effect,” Yu said. “Our next step is to figure out first which mold is inhibited the most, and then, which essential oils inhibit the production of mycotoxins the most.”

Graduate student Esther Iwayemi works alongside Yu in the lab. A native of Nigeria, she earned a bachelor’s degree in food science and technology at Obafemi Awolowo University in Osun State. A friend from home who enrolled in A&T’s food and nutritional sciences program inspired Iwayemi to apply.

When Yu contacted Iwayemi to offer an assistantship, and she accepted immediately.

“It is a very, very important project. Corn is a staple food everywhere. Most is infected with mold right from the field. I come from a place where people can see the mold, but they just clean it off and still eat it,” explains Iwayemi, who began her second year in the master’s program this fall and hopes to continue work on a doctorate at A&T.

“This research has opened my eyes to see this is something we shouldn’t overlook. We have to eat safe food so that we can reduce the medical issues we have in the world.”

In the future, Yu hopes to perfect her method for use by large-scale farmers and grain processors seeking alternatives to synthetic pesticides.

“We have to find how to apply our lab setting to the farm storage setting, to see how we can scale up,” she says. “To do that I need to work with people in the food industry who are using grain elevators.”