Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2006
Publication Date: 6/16/2006
Citation: Thayer, D.W., Boyd, G., Fett, W.F. 2006. Synergy between irradiation and chlorination in killing of salmonella, escherichia coli o157:h7, and listeria monocytogenes. Journal of Food Science. 71(6):R83-R87. Interpretive Summary: Several outbreaks of salmonellosis have been traced to the consumption of alfalfa sprouts that were grown from seeds that had been treated with chlorine. We evaluated the effectiveness of gamma irradiation followed by chlorination for the killing of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes. The two treatments killed more pathogens than would be predicted from the sum of the two individual treatments. The results suggest that significantly safer sprouts can be produced by the use of irradiated seeds and chlorination by the producer.
Technical Abstract: The objectives of the studies were to determine if radiation and chlorine acted in a simple additive process or if a non-additive increase in inactivation occurred when chlorination followed gamma irradiation both in vitro and in situ. Initially, a mixture of the following Salmonella enterica serovars: Anatum, Infantis, Newport, and Stanley; Escherichia coli O157:H7; and a mixture of Listeria monocytogenes ATCC 7644, 15313, 43256, and 49594 (Scott A) were treated by gamma irradiation (0.2 kGy at 20 deg C), chlorination (0.5 ppm for 10 min), or by irradiation followed by chlorination in vitro. In each case, greater inactivation was observed from irradiation followed by chlorination than would be predicted from the sum of the inactivation of the two treatments when applied separately. Inactivation of Salmonella cells was determined also with the pathogens adsorbed onto alfalfa seeds. Analysis of results of three sets of experiments with Salmonella adsorbed onto alfalfa seeds also led to the conclusion that the combination treatments were synergistic and produced a greater inactivation than would be expected from the sum of the treatments although experiments with larger number of seeds gave less evidence of synergy. The effectiveness of both interventions against Salmonella was significantly reduced when the pathogen was present on alfalfa seeds.