Researchers have reported a new and easy to implement method that can eliminate or at least reduce instances where people got sick from cross contamination in the processing of greens. Spinach or other leafy salad greens were responsible for 18 food poisoning outbreaks over the last decade according to the U.S. Centers for Disease Control. Forty-eight million Americans get sick from food poisoning each year, 128,000 are hospitalized and 3,000 die.
Typically, greens are washed by commercial processes before heading to market but the methods including water and bleach rinses or irradiation - are not completely effective. Scientists estimate that 99 percent of food-borne illnesses from leafy greens can be traced back to disinfection issues. Because of this they have developed a different approach for attacking the bacteria mainly E. Coli the cause of many outbreaks.
The researchers used a parallel-plate flow chamber system to test the real-time attachment and detachment of bacteria to the outer layer of spinach leaves. At low bleach concentrations, the bacteria fell off the leaves, but remained alive. At the higher concentrations used commercially, however, all of the bacteria were killed.
This result was perplexing, said Sharon Walker, Ph.D. and inventor of the flow chamber system. Our experiments were telling us that commercial bleach rinses should be much more effective than they are. But then we studied the leaf itself in more detail.
Because a spinach leaf is not perfectly smooth, the team modeled how the bleach would move across the surface of a spinach leaf, taking its bumps and grooves into account. Surprisingly, the model revealed that the concentrations of bleach on leaves may not be consistent. To reduce that risk, the researchers are optimizing an inexpensive titanium dioxide (TiO2) photocatalyst that companies could add to the rinse water or use to coat equipment surfaces that come into contact with the leaves as they are processed. When TiO2 absorbs light, it produces a strong oxidant that kills bacteria. The scientists also plan to conduct more studies on the photocatalyst, and they will look at a broader range of foods, engineered surfaces and pathogens.
Despite current disinfection rinsing, bacteria are surviving on the leaf and causing cross contamination, resulting in the numerous outbreaks we hear about in the media, says Nichola Kinsinger, Ph.D. and a postdoc in the lab of Walker at the University of California, Riverside. Pathogens can come from irrigation waters or from water used during processing, and they can adhere to spinach leaves. If these bacteria are not all killed in the disinfection process, they can continue to live, grow, spread and contaminate other surfaces within the facility and other leaves. We found that because of the topology of the spinach leaf, nearly 15 percent of the surface may see a bleach concentration that is 1,000 times less than that of the rinse solution. In some cases, that translated to a 90 percent bacterial survival in their tests and a high risk for cross contamination.
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