If produce is tainted with contaminated soil or water, pathogens such as E. coli and Salmonella may be present throughout the tissues of the plant, rendering ineffective traditional sanitation methods that focus on the outside of produce. That’s the conclusion of new research from Purdue University food scientists, recently published in papers in the Journal of Food Protection and Food Research International.
Determining whether pathogens originate on the inside or outside of produce has been difficult because slicing off pieces of the plant—a necessary step in testing—can move the bacteria from its original location. So food science researcher Amanda Deering, PhD, and Robert Pruitt, PhD, professor of botany and plant pathology, overcame this problem by freezing the bacteria in place, then using antibodies labeled with fluorescent dye to detect the pathogens.
Prior to planting, Drs. Deering and Pruitt contaminated mung bean seeds with E. coli 0157:H7 and peanut seeds with Salmonella. “We tried to come as close as we could in a lab setting to what could happen in a growing environment,” Dr. Deering said. When tested, the sprouts and seedlings had pathogens throughout every major tissue, including the tissue that transports nutrients. “The number of bacteria increased and persisted at a high level for at least 12 days, the length of the studies,” she noted.
“This underscores the importance of risk management in the fertilization and irrigation component of the process,” Dr. Deering added. “Growers need to make sure that fertilizer is properly sanitized in the autoclave and that contaminated irrigation water does not come in contact with the plant. Once a plant is contaminated internally in this way, external sanitation processes can’t eliminate the pathogen. The only way you can make sure that the pathogen is no longer there is to cook the produce.”