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United States Department of Agriculture

Agricultural Research Service

Title: Inactivation of Escherichia Coli O157:h7 and Salmonella by Gamma Irradiaton of Alfalfa Seed Intended for Production of Food Sprouts

item Thayer, Donald
item Rajkowski, Kathleen
item Boyd, Glenn
item Cooke, Peter
item Soroka, Douglas

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 13, 2002
Publication Date: N/A

Interpretive Summary: Eating alfalfa sprouts has caused outbreaks of disease due to the contamination of the seeds used for growing the sprouts with Salmonella or Escherichia coli O157:H7. We investigated the possibility of inactivating these foodborne pathogens by gamma irradiation of the seed. We discovered that both Salmonella and E. coli can be inactivated by irradiation, but that nutrients present in the alfalfa seed resulted in unusually high resistance to radiation by both foodborne pathogens. The results will be of value to the sprout seed supplier and the sprout producers to help them protect the public from foodborne pathogens.

Technical Abstract: Ionizing irradiation was determined to be a suitable method for the inactivation of Salmonella or Escherichia coli O157:H7 on alfalfa seed for use in producing food sprouts. The radiation D-values for the inactivation of either Salmonella or E. coli O157:H7 on the seed were higher than similar values for their inactivation on meat or poultry. The average D- value for the inactivation of Salmonella was 0.97 plus or minus 0.03 kGy; the D-values for cocktails of meat isolates or of vegetable-associated isolates were not significantly different. The D-values for non-outbreak and outbreak isolates of E. coli O157:H7 were 0.55 plus or minus 0.01 and 0.60 plus or minus 0.01 kGy, respectively. The relatively high D-values were determined not to be due to the low moisture content or water activity of the seed. Nor were there differences in the D-values for Salmonella on either of two seed sources, even though there were significant differences in seed size. The increased moisture of the seed, following artificial inoculation, did not significantly alter the D-value for the inactivation of Salmonella.

Last Modified: 5/5/2015