Published on 09/23/99

Washing Lettuce Reduces E. coli Risk, Doesn't Eliminate

University of Georgia researchers have found that consumers can reduce their risk of food-borne illness by washing lettuce before preparing homemade fresh salads.

Fresh salads, particularly those made with lettuce, have been linked to five outbreaks of E. coli over the past four years, according to the Centers for Disease Control and Prevention in Atlanta, Ga.

A Second Washing is a Good Habit

"Lettuce is washed before it's sold, but our research has shown the risks of food-borne illness can be greatly reduced by washing it again at home," said Joe Frank, a food microbiologist with the UGA Center for Food Safety and Quality Enhancement in Griffin, Ga.

Frank said lettuce is most likely contaminated in the field by polluted irrigation water, animal manures or improper handling by field workers.

To address the lettuce and E.coli problem, Frank studied how and where E. coli cells survive on lettuce leaves.

"Lettuce breathes through stomata or holes on the leaves," he said. "The E. coli cells attach to the surface around and inside these holes."

E. coli Likes Cut Edges and Bruises

He also found E. coli cells favor the cut edges of lettuce. "The edges of cut lettuce pieces had tremendous numbers of attached E. coli cells," he said. "The bruised areas did, too."

In the lab, washing the lettuce with a bleach solution was found effective for removing the E. coli cells on the lettuce surface.

"The solution removes or kills the cells on the surface of the lettuce, but those inside the holes still survive," Frank said.

UGA food scientists are working with the food industry to apply this chlorine method. But Frank warns consumers not to try it at home.

"Chlorine bleach is much too strong to be used at home for rinsing vegetables," he said. "Consumers shouldn't use chlorine to rinse vegetables at home."

Wash Well and Keep it Cold

For your home, the main recommendations are to wash lettuce and keep it cold.

"There is no way to totally eliminate your risk of food-borne illness," Frank said. "But taking these precautions can greatly reduce your risk."

(Lettuce image courtesy Scott Bauer, USDA. E. coli image courtesy UGA Center for Food Safety and Quality Enhancement.)

Sharon Omahen is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.