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United States Department of Agriculture

Agricultural Research Service

Title: Efficacy of Calcium Hypochlorite for Eliminating Escherichia Coli 0157:h7 and Salmonella from Laboratory-Inoculated Mung Bean Seed

Author
item Fett, William

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 20, 2001
Publication Date: N/A

Interpretive Summary: Since 1995 in the US there have been numerous outbreaks of foodborne illness due to consumption of raw alfalfa and other types of sprouts contaminated with the human bacterial pathogens Salmonella and Escherichia coli O157:H7. The first US outbreak due to consumption of contaminated mung bean sprouts occurred in California in April 2000. The sprouts were contaminated with Salmonella. The primary source of contamination for almost all sprout-related outbreaks is the seed used for sprouting. Thus, effective means of sanitizing mung bean and other sprouting seed before germination and growth are needed. In this study we determined the effectiveness of chlorine treatments with or without adjusting the sanitizer solutions to a neutral pH for eliminating Salmonella and E. coli O157:H7 from laboratory-inoculated seed. Results indicated that chlorine treatment drastically reduces, but does not eliminate, the pathogens from the seed. The most effective treatment was the use of very high levels of chlorine (16,000 ppm) employed at a neutral pH. This treatment reduced the bacterial population by approximately 99.99 to 99.999%. Treatment with a lower concentration (1,800 ppm) was almost as effective. Treating seed with the highest level of chlorine did not adversly affect the germination of the seed. In conclusion, treatment of mung bean seed with very high levels of chlorine before sprouting will help to ensure the microbial safety of the mung bean sprouts.

Technical Abstract: The first US outbreak of foodborne illness due to consumption of contaminated raw mung bean sprouts occurred in the spring of 2000 and was due to contamination with Salmonella enteritidis. In this study we wished to determine if treatment of laboratory-inoculated mung bean seed with chlorine provided by Ca(OCl)2 would eliminate the bacterial pathogens. Treatments (5, 10 and 15 min in duration) with buffered (to pH 6.8) or unbuffered (prepared in sterile tap water) solutions containing 1,800 to 18,000 ppm free chlorine were compared. In order to mimic common commercial practices, seed was rinsed before and after treatment using sterile tap water. For seed inoculated with a cocktail of strains of E. coli O157:H7, the presence of buffer and longer treatment times (10 to 15 min) resulted in greater log reductions with the maximum log reduction (3.8 log CFU/g) obtained by treating seed for 15 min with 3% (w/v) Ca(OCl)2 in buffer (16,000 ppm free chlorine) in combination with the rinses. A reduction of 3.2 log CFU/g occurred after a 15 min treatment with 0.3% (w/v) Ca(OCl)2 in buffer (1,800 ppm free chlorine). For seed inoculated with a Salmonella cocktail, the greatest reduction (5.02 log CFU/g) was also obtained with a 15 min treatment with 3% Ca(OCl)2 in buffer (16,000 ppm free chlorine) in combination with the rinses. Treatment for 15 min with unbuffered 3% or buffered 0.3% Ca(OCl)2 (18,000 ppm free chlorine and 1,800 ppm free chlorine) resulted in reductions of 4.23 and 3.80 log CFU/g, respectively. Even though the chlorine treatment in combination with the seed rinses appeared to be effective in significantly reducing the populations of the two human pathogens, none of the treatments led to their complete elimination from laboratory-inoculated seed.

Last Modified: 4/23/2014
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