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ARS Home » Research » Publications at this Location » Publication #116477
Title: ELIMINATION OF SALMONELLA MBANDAKA FROM NATURALLY CONTAMINATED ALFALFA SEEDBY TREATMENT WITH HEAT OR CALCIUM HYPOCHLORITE

Author
item SUSLOW, TREVOR - UNIVERSITY OF CALIF.DAVIS
item WU, JIANGCHUN - UNIVERSITY OF CALIF.DAVIS
item FETT, WILLIAM
item HARRIS, LINDA - UNIVERSITY OF CALIF.DAVIS

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2002
Publication Date: 9/1/2002
Citation: N/A

Interpretive Summary: Since 1995 there have been numerous outbreaks of foodborne illness in the US and other countries due to the consumption of alfalfa sprouts contaminated by Salmonella. It is generally believed that in almost all cases the original source of contamination was the seed. Current recommended industry practice for sprout growers included the treatment of seed with very high levels of chlorine (20,000 ppm). This recommendation i based on research utilizing seed inoculated in the laboratory with the human pathogen. However, it is not known if this treatment is effective in eliminating Salmonella from naturally contaminated seed. In this study we evaluated the efficacy of treating naturally contaminated seed with 2,000 and 20,000 ppm of chlorine provided by calcium hypochlorite and compared these treatments to hot water dips. A seed lot naturally contaminated with Salmonella that was involved in a 1999 US foodborne illness outbreak was used. Soaking the seed in the chlorine solutions at either concentration for 10 to 15 minutes was found to eliminate the natural contaminant from the seed. In contrast, hot water dips (up to 80 C for 1 minute in duration) were not effective in eliminating the pathogen. In summary, exposure of the naturally contaminated alfalfa seed to high levels of chlorine, but not hot water, led to the elimination of Salmonella from the naturally contaminated seed lot.

Technical Abstract: In 1999, consumption of alfalfa sprouts contaminated with Salmonella Mbandaka led to a multi-state outbreak of salmonellosis. In this study, the implicated alfalfa seed lot (number 8119) was confirmed as contaminated with Salmonella Mbandaka at a detection frequency of approximately 72% per replicated 100g of seed. The sensitivity of detection was improved by a combination of nonselective and selective enrichment of 5.0 ml of germination effluent followed by immunomagnetic separation. Detection of low levels of viable cells from nonselective enrichment, employed to enhance the recovery of stressed or injured cells, was facilitated by the application of Salmonella specific PCR. By PCR assays, Salmonella Mbandaka was detectable on seed stored at 5oC for at least 11 months, but at an increasingly diminishing frequency. Viable populations were detected in the seed germination effluent for up to 8 months with conventional techniques. Treatment of seed with buffered (to pH 7) or unbuffered solutions of calcium hypochlorite providing approximately 2,000 or 20,000 ppm of free chlorine solutions for 10 min were equally effective in eliminating viable populations of Salmonella. However, aqueous heat treatments at up to 85oC for 1 min did not eliminate the naturally occurring contaminant from the seed. Economically significant reductions in germination were observed, starting at 65oC for 4 min and 70oC for more than 2 min. Based on these results, aqueous heat treatments do not appear to be a viable alternative to hyperchlorination as an effective method to eliminate Salmonella from alfalfa seed.