Food-safety surveillance programs depend on research, education, and outreach to reduce risks from food-borne pathogens. A thorough evaluation of production and distribution processes can identify specific food hazards and help growers and distributors find ways to eliminate them from our food supply.
During the spring and early summer months of 2008, a Salmonella enterica outbreak associated with jalapeno and serrano peppers affected consumers in 35 states. Initially, the outbreak was incorrectly attributed to tomatoes, causing a great deal of concern among Virginia tomato growers who feared that regulators would order the destruction of their crops.
Such incidents encourage extensive research into the causes of contamination and the development of measures to prevent future outbreaks. Food scientists at Virginia Tech are working to inform produce growers and distributors about ways to minimize the risks of food-borne illness. Three new projects in Department of Food Science and Technology at the College of Agriculture and Life Sciences are helping to increase the safety of store-bought produce.
Assistant Professor Monica Ponder’s research is characterizing the microbial ecology of spinach plants to identify naturally occurring bacteria that could compete with pathogens on the surface of spinach leaves. Her research determined that 35 species of bacteria typically found on spinach leaves inhibit growth of the pathogens E. coli and Salmonella in laboratory conditions. “The ability to identify and quantify the antimicrobial effects of these bacteria on the safety of the spinach plant holds the promise of natural controls over food-borne pathogens in fresh spinach,” Ponder said.
In addition, Ponder is working with Greg Welbaum, professor of horticulture, to determine whether spinach seeds are carriers for food pathogens. They will determine whether the pathogen will be translated to the leaf of the plant by soaking seeds in a Salmonella solution prior to sprouting.
Assistant Professor Renee Boyer is studying the effect that modified-atmosphere packaging (MAP) has on the survival of the pathogen E. coli O157:H7 in lettuce and spinach. MAP is used in the bagged spinach and lettuce blends available in grocery stores.
In the study, samples of cut and whole-leaf lettuce and spinach were stored under normal and modified atmospheric conditions and held at 4 degrees C or 10 degrees C. Spoilage began to occur on the seventh day for the lettuce and on the ninth day for the spinach. Populations of E. coli O157:H7 survived at high levels during this time, indicating the pathogen’s ability to flourish under standard distribution conditions.
“The study shows that the modified atmosphere packaging will not control or reduce populations of E. coli once they are present,” Boyer said. “This stresses the importance of preventing contamination at the farm and packinghouse levels.”
Boyer is also collaborating with Associate Professor and Extension Food Safety Specialist Robert Williams to determine the effect of high-pressure processing on whole and diced red tomatoes contaminated with Salmonella. This initiative – funded in part by the Virginia Agricultural Council – involves inoculating store-bought tomatoes with Salmonella, exposing the tomatoes to three different pressures, and examining the tomatoes' microbial counts and quality after treatment.
“Although food safety is our primary objective, we aren’t really helping the fresh tomato industry unless we develop a process that can preserve the high quality and flavor of a fresh tomato.” Williams said. “A safe product that tastes bad is not a viable solution.”
The researchers are also studying the effects of high pressure on green, unripened tomatoes, and whether the pressure treatment will inactivate the enzymes that ripen the tomato. The results of this research will help determine ways for the food industry to make its products safer through the use of high-pressure processing.
According to Williams, it is critically important for growers to educate themselves about specific handling practices that minimize the risks to consumers, including field preparation, harvest, distribution, and worker hygiene. Interventions to remove contamination from fresh produce are limited in their effectiveness. Therefore, prevention is essential, he said.
Virginia Tech has collaborated with Cornell University and North Carolina State University to establish the Good Agricultural Practices program, which trains farmers in ways to prevent pathogenic contamination of their food crops. Read more.
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