Food Irradiation and Chlorine Team Up to Kill Ecoli

FoodIrradiation and Chlorine Team Up to Kill E. coli O157:H7 and Salmonella

By Doris Stanley Lowe
June 1, 1999

Treatingalfalfa seeds and sprouts with a combination of irradiation and chlorineeffectively safeguards them against contamination by E. coli O157:H7 and Salmonella,Agricultural Research Service scientistsreport.

ARSscientists Donald W. Thayer, Kathleen T. Rajkowski and William F. Fett foundthat a treatment of irradiation and chlorine solution not only killed bothorganisms, but extended the shelf life of sprouts from aboutfive days to more than a week. They conducted the lab studies at the ARS EasternRegional Research Center’s Food Safety and PlantScience and Technology Research Units in Wyndmoor, Pennsylvania. Theresearch is part of the effort by a task force of representatives from severalFederal Government agencies and industry to find ways to control microbialcontamination of sprouts .

Thefinding is good news for sprout growers. Since 1995, raw alfalfa sprouts havebeen recognized as a source of foodborne illness in the United States, withseveral outbreaks of both E. coli O157:H7 and Salmonella. FDA andthe Centers for Disease Control and Preventionhave advised those at high risk-including children, the elderly, and personswith compromised immune systems-to avoid eating raw alfalfa sprouts. Sincesprouts can’t withstand abrasive physical washing because of their fragility,cleaning the seed has become the primary focus.

In thetests, the scientists used the irradiation dose approved for irradiating meat.The U.S. Food and Drug Administration (FDA) hasapproved ionizing radiation as a safe and effective food preservation tool.

Alongwith irradiation, they subjected alfalfa seeds to 2-percent, 2.5-percent, and3-percent weight-per-volume concentrations of calcium hypochlorite (a chlorinesource). A 3-percent concentration equals about 20,000 parts per million ofavailable chlorine. With a neutral pH of about 7, the 2.5 and 3-percentconcentrations reduced E. coli O157:H7 99.99 percent. The pH level isimportant because at a higher pH level, such as 10, the chlorine would change toa form that would not be as effective in killing bacteria.

Accordingto the scientists, the best way to eliminate pathogens would be a combination ofirradiation and sanitation treatments. This is because sprouts can becontaminated internally, which would prevent a surface disinfectant from workingeffectively.

ARS isUSDA’s chief scientific research agency. More information on this storyappears in the agency’s June AgriculturalResearch magazine, available at: