Getting ahead of tainted lettuce

In this era of E. coli and Salmonella outbreaks, consumers are concerned about harmful bacteria and viruses hitching a ride on fresh fruits and vegetables. But few want their produce dipped in harsh disinfectants that will damage the environment or human health.

Joellen Feirtag, a university professor of food science and nutrition, is testing a way of purifying produce using only a dilute salt solution and an electric current. The technology, called ECT (electro-chemical activation), was developed by Russian scientists to get rid of bacterial films gumming up oil and gas pipelines. Feirtag, a microbiologist, is helping companies that handle fresh produce assess ECT''''s potential in the food arena.

According to estimates by the Centers for Disease Control and Prevention, foodborne agents cause approximately 76 million illnesses, 325,000 hospitalisations and 5000 deaths in the United States each year. The causes range from mild viral infections to fatal illnesses and include poisoning by metals as well as living pathogens.

In her studies of ECT, Feirtag performs experiments that recreate the situation in agricultural fields, where pathogens may be introduced by contaminated irrigation water sprayed on crops.

The process works by running a solution of table salt through the ECT module, where an electric current separates the chlorine and the sodium into adjacent chambers. In one chamber, chemical reactions form disinfectant compounds. In the other chamber, detergent compounds form. The disinfectant and the detergent flow out of the module in separate streams.

"You can use the detergent to remove organic matter, then dip the produce in the other to kill pathogens," Feirtag explains.

Early results with such items as lettuce, tomatoes and spinach have been encouraging. When Feirtag sprayed the produce with several strains of E. coli, the ECT treatment achieved kills of eight orders of magnitude that means that for every bacterial cell that survived the treatment, between 100 million and one billion were killed. The process also killed the intestinal pathogen, norovirus, plus a strain of avian flu and hepatitis A, and it removed Salmonella from plastic surfaces. A 30-second dip in the disinfectant stream was enough to kill the pathogens.

Feirtag and her colleagues are collecting a month''''s worth of data at a produce facility. While not revealing the identity of the facility, Feirtag did say that Dole Food Co was looking into the process for its fruit and vegetable plants in California. Feirtag has also been visiting other companies with produce processing plants, including ones that make sandwiches and salads, in an effort to introduce ECT technology more widely into US industry. She says the units can handle 280 L of the salt solution per day in a small plant and have potential for use in hospitals and cities. The two streams exiting the ECT modules can be remixed and reused this is done at plants in Europe and Russia, she says.

Feirtag is also gathering data on the efficacy of different salt solutions for publication in peer-reviewed journals.

Efficient though it may be, the ECT technology could never unilaterally eliminate infectious bacteria and viruses from food. ECT may, however, find a place in the fight against foodborne illnesses.