New disinfection method could reduce illness outbreaks linked to leafy greens

Commercial processes used to wash spinach and other leafy salad greens are not always 100 percent effective in removing bacteria. But a new, easy-to-implement method could eliminate or reduce illnesses linked to these vegetables.

Research presented at a recent meeting of the American Chemical Society shows that an inexpensive titanium dioxide (TiO2) photocatalyst could be added to the rinse water or used 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 researchers explained.

Currently, greens are put through water or bleach rinses or irradiation. However, Nichola Kinsinger, Ph.D., said scientists have estimated that 99 percent of foodborne illnesses from leafy greens can be traced back to disinfection issues.

To address this problem, the research team at the University of California, Riverside, developed a different approach to attacking the bacteria, most notably E. coli, which is the cause of many outbreaks.

“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,” Kinsinger explained. “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.”

After modeling how a bleach rinse moves across the surface of a spinach leaf, the researchers found that the concentrations of bleach on leaves may not be consistent.

“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,” Kinsinger said. Tests showed that in some cases that meant 90 percent of adhered bacteria survived on the leaf surface.

To reduce that risk, the researchers are optimizing a TiO2 photocatalyst for potential use by food processing firms. They will also look at a broader range of foods, engineered surfaces and pathogens.