June 24, 2022

Study Examines Treatments for Microbial Contamination in Sprouts

A study published int he April issue of the Journal of Food Science looked at seed disinfection treatments of sprouts. In the last few years, there have been several major foodborne illness outbreaks linked to raw sprouts, including an E. coli outbreak linked to clover sprouts served at Jimmy John’s restaurants that sickened 29 people in 11 states. And there were seven recalls of sprouts for pathogenic bacterial contamination.

Bean SproutsSprouts are problematic for several reasons. First, the bacteria can be encapsulated inside the seed, making it impervious to physical disinfection such as the application of calcium hypochlorite. And the seeds are sprouted in warm, moist conditions, which are ideal for bacterial growth.

The FDA released guidelines in 1999 designed to limit this problem, including growing seeds using good agricultural practices, conditioning and storing seed under sanitary conditions, following GMPs at sprouting facilities, applying a disinfection treatment just before sprouting, and in-process testing of spent sprout irrigation water for pathogens before the product enters commerce. While sproutbreaks declined after these guidelines were released, the treatments are variable and food poisoning cases continue.

The study examined chemical disinfection with 20000 ppm calcium hypochlorite, and found that it does reduce microbial load on seeds. But there is a high variability in efficacy. Increasing treatment time did not improve the microbial load, but reduced germination rate of seeds. Other chemicals have not been adequately tested.

Physical inactivation, using heat and high pressure treatments, may be promising. These treatments can reach more bacterial sheltered in the nooks and crannies of seed coatings, and are more environmentally friendly than chemical treatments. Irradiation is effective at reducing the microbial load, but it negatively affects the yield, nutrition, and appearance of sprouts, and sprout consumers are opposed to this method of decontamination.

Competition from normal microbial flora may work to a certain extent, working as effectively as the calcium hypochlorite treatment. But the treatment method is complicated and there may be adverse health effects with this method. Combined treatments could be more effective, but this method is challenging because it is more complex.

The study’s authors recommend that alternative intervention approaches should be considered and further investigated. They think that a microbial sampling and testing program (test and hold) should be implemented in the industry, as well as changing industrial practices based on science-based evidence. And the government continues to recommend that those in high risk groups avoid eating raw sprouts of any kind because of the risk of illness.

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