Reduction of Escherichia coli O157:H7 and Salmonella spp. on Laboratory-Inoculated Mung Bean Seed by Chlorine Treatment†

Abstract

Three U.S. outbreaks of foodborne illness due to consumption of contaminated raw mung bean sprouts occurred in the past 2 years and were caused by Salmonella Enteritidis. The original source of the pathogens is thought to have been the seed. The aim of this study was to determine whether treatment with aqueous chlorine would eliminate the pathogens from mung bean seed inoculated in the laboratory with four-strain cocktails of Escherichia coli O157:H7 and Salmonella spp. Treatments (for 5, 10, or 15 min) with buffered (500 mM potassium phosphate, pH 6.8) or unbuffered solutions containing 0.3 or 3.0% (wt/vol) Ca(OCl)2 were tested. In order to mimic common commercial practice, seed was rinsed before and after treatment with sterile tap water. Treatment for 15 min with buffer (500 mM potassium phosphate, pH 6.8) or sterile water in combination with the seed rinses resulted in maximum reductions of approximately 3 log10 CFU/g. The largest reductions (4 to 5 log10 CFU/g) for the chlorine treatments in combination with the rinses were obtained after treatment with buffered 3.0% (wt/vol) Ca(OCl)2 for 15 min. Treatment of mung bean seed for 15 min with unbuffered or buffered 3.0% (wt/vol) Ca(OCl)2 did not adversely affect germination. Even though treatments with 3% (wt/vol) Ca(OCl)2 in combination with the water rinses were effective in greatly reducing the populations of both bacterial pathogens, these treatments did not result in the elimination of the pathogens from laboratory-inoculated seed.