Food Safety from Farm to Fork

Dozens of cruise ship passengers felled by gastrointestinal illness. Hundreds across the U.S. sickened by E. coli in spinach and Salmonella in tomatoes and peppers. Scores killed in Kenya by a toxin in moldy corn. The headlines in recent years have repeatedly ratcheted up concerns about food safety among consumers, regulators, and farmers. NC State researchers are trying to calm those fears by attacking the problem on several fronts, such as building resistance in crops, detecting germs in advance, and tracking disease outbreaks.

An estimated 4.5 billion people worldwide are exposed each year to aflatoxin, a fungal compound known to suppress the human immune system and cause liver cancer. Exposure is most prevalent in developing countries in Africa and Asia, says Dr. Gary Payne, William Neal Reynolds Professor of Plant Pathology. A subtropical fungus, Aspergillus flavus, produces the toxin in the seeds of crops like corn and peanuts, which aren’t well adapted to the hot, dry growing conditions. “Many of these places are so poor,” he says, “the people don’t have any choice but to eat the crops, even if they know the aflatoxin is present.”

Payne has studied aflatoxin for about 30 years, starting in the realm of aspergillosis management. He has since moved to the world of genetics and bioinformatics to find ways to develop resistance to toxin accumulation and predict the presence of other potentially lethal compounds in the fungus. He helped sequence the Aspergillus genome and determine which genes are responsible for aflatoxin production. He’s now using assays to measure the expression of the genes under various conditions. “We need to figure out which genes are important to making the fungus a pathogen so we can find a way to block them,” he says. On the opposite side of the equation, Payne and other researchers are analyzing the genetics of corn to determine which of its genes might be vital to creating resistance to aflatoxin accumulation and how their expression can be increased in high-yield lines of the crop.

NC State researchers are attacking the food safety problem on several fronts, building resistance in crops, detecting germs in advance, and tracking disease outbreaks.

Across campus, building resistance to norovirus, a leading cause of food-borne illnesses, is an equally challenging proposition. Even recovering from a norovirus infection brings only temporary immunity, says Dr. Lee-Ann Jaykus, a professor in the Department of Food, Bioprocessing & Nutrition Sciences. Norovirus disease has gained notoriety in recent years for shutting down schools and curtailing Caribbean cruises by spreading rapidly among groups in close quarters. It is often spread by a lack of hand washing by food handlers or by fecal contamination of shellfish harvesting areas or water used to irrigate crops. Jaykus’ research has shown that the virus can last for weeks in foods and for months on surfaces, and only a concentrated dose of chlorine bleach can overpower the germ.

“With produce eaten fresh, anything the food comes in contact with can contaminate it.”

Jaykus is working on a sensor to detect noroviruses, both to test suspect food samples to determine the origin of an outbreak and for environmental monitoring of oyster beds and other potential contamination sites. She’s using a technique known as reverse transcription polymerase chain reaction that converts norovirus RNA into DNA, which is then copied repeatedly. Amplifying the virus’ genetic material makes it sufficiently concentrated to make detection possible in a food or water sample. For the sensor to work properly, it must also break down other components of the food without damaging the virus. “It only takes a few particles of norovirus, maybe 10, to make you sick,” she says. “We have to be able to detect minute amounts of the virus in a food sample of 25 grams or so.”

Meanwhile, for Dr. Benjamin Chapman and the rest of the NC Fresh Produce Safety Task Force, tracing the source of a food-borne pathogen is as important as knowing what—a norovirus, E. coli, or some other germ—caused the outbreak. Formed three years ago, the task force includes members from NC State and NC A&T State University, state and federal agriculture officials, industry representatives, and growers. It is dedicated to promoting practices “from farm to fork” that will limit the potential for contamination. “With produce eaten fresh, anything the food comes in contact with can contaminate it,” Chapman says, “and because you’re not cooking it, there is no kill step for bacteria.”

A food safety specialist and assistant professor in the Department of 4-H Youth Development and Family & Consumer Sciences, Chapman has studied how various types of produce move from the field to consumers to help improve “traceability,” which he says could benefit North Carolina farmers in the future. For example, when Salmonella-tainted tomatoes began sickening people in 2008, farmers in the state couldn’t prove that their tomatoes weren’t the source of the outbreak. Much of their crop then ended up in lower-margin processed foods. “A lot of product moves around, and tracking it isn’t always simple,” Chapman says. He found smaller produce like berries easier to track than melons and other large produce because berries are usually packed on the farm in labeled cartons instead of being put in bins that include produce from numerous fields.

Diane Ducharme, a Cooperative Extension Service horticulture and food safety specialist at the NC Research Campus in Kannapolis, is using Chapman’s findings to help large and small farmers improve their ability to track their produce as it moves to consumers. The procedures need to be scalable, she says, because small farmers often have limited finances. “Food safety is pretty much an all-or-nothing proposition,” Ducharme says. “You need to accommodate everyone, or it doesn’t work.”

 

Dr. Gary Payne has sequenced the genome of the fungus that produces aflatoxin to find ways to block it and to help crops develop resistance to toxin accumulation.

Dr. Lee-Ann Jaykus discusses ways to detect norovirus in food with Dr. Hari Dwivedi, a 2009 graduate in comparative biomedical sciences.

Tracing the origin of fresh produce at the State Farmers Market in Raleigh is easier for Dr. Benjamin Chapman than the task consumers face at the supermarket.

Microscopic views of Aspergillus and E. coli.