PORTLAND - Alfalfa sprouts - the healthy, crunchy addition to salads and sandwiches - have been implicated in an increasing number of food poisoning cases over the last five years.
Now Oregon State University and Oregon Department of Agriculture researchers are initiating study of a heating technique used in the plywood industry they believe can combat the problem. Sprout-related illness is a public safety issue and a threat to Oregon agriculture, which supplies a significant portion of the nation's sprout seed supply.
Occasionally, E. coli O157:H7 and salmonella bacteria are found on alfalfa seeds used for sprouting. These bacteria can rapidly multiply while the seeds are in the warm, moist environment needed to produce sprouts.
OSU and ODA researchers think innovative packaging and "capacitive dielectric heating" - a process similar to microwave heating - might be a solution to the problem of foodborne illness associated with sprouted seeds.
Many other fruits and vegetables are eaten raw, but they are handled from farm to table as a food product, explains Norma Corristan, ODA administrator of lab services. Also, people generally wash these foods before they eat them.
Alfalfa seeds don't start as food products. The seeds are grown to be replanted for crops. A small percentage are set aside for sprouts. The seeds are sifted to remove weed seeds, but they are never really cleaned with food safety in mind.
Cleaning them after the fact is possible, Corristan says. However, methods such as bleaching, conventional heating or irradiation all either leave residues or adversely affect the germination properties of the seeds - yielding fewer sprouts.
A research project administered jointly by OSU and ODA as part of the Food Innovation Center in Portland will examine capacitive dielectric heating of seeds embedded in edible films as a way to greatly reduce the chance of spreading foodborne illness through sprouts.
Capacitive dielectric heating is similar to microwave heating but operates at much lower frequencies and results in more uniform heating, says John Henry Wells, an OSU food packaging engineer.
Seeds will be embedded in an edible film, resembling a thick sheet of plastic wrap, to keep them from coming in contact with any contaminants after they are heated, he adds.
"One of the challenges of the research project will be determining the precise heating frequency that will heat the seeds but not melt the film," Wells said.
To that end, he notes that knowledge of the specific dielectric properties of edible films and alfalfa seeds is essential in determining the optimum heating frequencies. This will be the early focus of the project.
Edible films are already used with food products such as hot dogs to enhance freshness and increase resistance to spoilage and bacteria, Wells says. The edible films, made from milk and milk byproducts, were developed by Hongda Chen at the University of Vermont.
Capacitive dielectric heating has been successfully used in the plywood industry to heat glue between layers of wood, he says. The University of Vermont and Flugsted Engineering, a technology development firm in Charleston, Ore., will collaborate on the project.