U. ILLINOIS (US) —The secret to keeping radish, broccoli, alfalfa, and other sprouts free from food-borne bacteria lies in the cleanliness of their seeds.
“Once seeds have germinated, it’s too late. Sprouts are extremely complex structures with a forest-like root system that conceals microorganisms,” says Hao Feng, associate professor of food and bioprocess engineering at the University of Illinois. “Just a few E. coli cells can grow to a substantial population during germination and sprouting, and it’s very difficult to get rid of them all.”
For a new study published in the Journal of Food Science, Feng used both the FDA-recommended dose of chlorine to kill microorganisms and a new sanitizer that is a combination of surfactant and organic acid.
Using a laser-scanning confocal microscope, he looked at micro-slices of seeds, then employed computer software to get a three-dimensional view of their surface structure that allowed him to calculate each seed’s surface roughness.
Although E. coli can be eliminated on alfalfa seeds because of their relatively smooth surface, broccoli and radish seeds are rough—the texture makes them more susceptible to the attachment of pathogens and makes the microorganisms very difficult to remove, Feng says.
Low doses of irradiation can be successfully used on broccoli and radish seeds, but that treatment runs the risk of losing sprouts’ quality and exceptional nutritional value. Broccoli has been linked to cancer prevention and radishes are rich in vitamins A and C. Sanitizing broccoli in small batches achieves better results.
“In Asian cultures, sprouts are used in stir-fry recipes. Again, it’s a trade-off. Heat kills the pathogens, but you lose some of the sprouts’ nutritional punch,” Feng says. Asian cooks also use sprouts in dishes that use natural antimicrobials, such as vinegar, garlic, green onion, and spices, he says.
“These ingredients can inhibit the growth of E. coli, even kill pathogens, but there is still some risk involved.” The research demonstrates the importance of eliminating all pathogens on seeds before sprouting, he says.
“The food industry must maintain very strict control in the sprout production process, focusing on the cleanliness of seeds and expending money and effort on prevention. Then consumers can be assured that these nutritious food products are safe to eat.”
Funding was provided by the USDA and the Illinois Agricultural Research Station.
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