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Mung bean seed safety optimized by heat.

Among different bacteria, researchers have linked S. typhimurium and E. coli O157:H7 to contaminated seed sprouts. Many outbreaks have been traced to seeds that have been contaminated with low levels of pathogens. Strains of E. coli O157:H7 can grow an average of 2.3 [logs.sub.10] over a two-day period during their germination.

Essentially, we must have an effective way to reduce E. coli populations on seeds before they sprout. Scientists at Cornell University have assessed the effectiveness of various heat treatments in reducing E. coli O157:H7 populations on mung bean seeds intended for sprout production. The mung bean, a small, green legume in the same plant family as peas and lentils, is a good source of protein, fiber, antioxidants and phytonutrients.

The Cornell scientists also learned how heat treatments can influence seed germination. They applied heat to significantly reduce the amount of pathogenic E. coli on mung bean seeds without affecting their germination rate.

Mung bean seeds were inoculated with five different strains of E. coli O157:H7, each harboring a green fluorescent protein gene. They were air-dried overnight. The scientists performed the heat treatments by incubating the seeds at 55 C for different periods of time. One-gram samples of the heated seeds were diluted in peptone water and macerated. Appropriate dilutions were plated onto tryptic soy agar and incubated at 37 C for 18 to 24 hours.

The scientists enumerated green fluorescent colonies. They soaked five grams of dried seeds in distilled water for six hours at ambient temperatures. The water was then poured off, and the seeds were transferred onto wet commercial filter paper and incubated at 22 C for two days to allow germination to occur. The researchers calculated the germination rates as the number of germinated seeds per total number of seeds after two days.

After inoculation and the drying process, about 5 logs per gram of E. coli were found on the seeds. However, after undergoing the heat treatments, the number of E. coli on the seeds was under detectable levels[??]less than 1 log per gram--while the germination rate was 100%.

Further information. Randy Worobo, Department of Food Science, Cornell University, 360 Stocking Hall, Ithaca, NY 14853; phone: 607-255-3614; email: rww8@cornell.edu.

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Publication:Emerging Food R&D Report
Date:Jun 1, 2018
Words:385
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