Change in Process of Disinfecting Greens Could Reduce Illness Outbreaks

Cross contamination in commercial processing facilities that prepare spinach and other leafy greens for the market can make people sick. But researchers are reporting a new, easy-to-implement method that could eliminate or reduce such incidences. The scientists presented their work at the 250th National Meeting & Exposition of the American Chemical Society (ACS) in August.

Greens are washed by commercial processes before they head to the grocery store. But these methods, which can include water and bleach rinses or irradiation, are not completely effective, said Nichola Kinsinger, Ph.D. She says scientists have estimated that 99% of foodborne illnesses from leafy greens can be traced back to disinfection issues. As a result, they have searched for and developed a different approach to attacking the bacteria, most notably E. coli, which is the cause of many outbreaks.

Using a parallel-plate flow chamber system developed by Sharon Walker, Ph.D., at the University of California, Riverside, the researchers tested 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,” Walker said. “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 leaf, taking its bumps and grooves into account. The model revealed that the concentrations of bleach on leaves may not be consistent. “We found that, because of the topology of the spinach leaf, nearly 15% of the surface may ‘see’ a bleach concentration that is 1,000 times less than that of the rinse solution,” Kinsinger said. In some cases, that translated to a 90% bacterial survival in their tests – and a high risk for cross contamination.

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 TiO2absorbs light, it produces a strong oxidant that kills bacteria. The scientists plan to conduct more studies on the photocatalyst, and they will look at a broader range of foods, engineered surfaces and pathogens.

The researchers acknowledge funding from the USDA National Institute for Food and Agriculture under the Agriculture and Food Research Initiative.