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Topology of spinach leaves responsible for inadequate disinfection rinsing
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Bleach used in commercial produce rinses may be unevenly distributed across the surface of spinach leaves, potentially leading to cross-contamination and foodborne illness, according to findings presented at the 250th National Meeting and Exposition of the American Chemical Society in Boston.
"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," researcher Nichola Kinsinger, PhD of the University of California, Riverside, said in a press release. "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."
Kinsinger and colleagues evaluated food-related bacterial contamination due to inadequate post-harvest rinses of produce, particularly within prepackaged salad and baby spinach. Citing recent outbreaks of Escherichia coli O157:H7 in leafy green produce, the researchers examined the attachment/detachment kinetics of E. coli from both whole baby spinach leaves and isolated epicuticle layers of spinach using a parallel plate flow chamber. They determined mass transfer rate coefficients for attachment/detachment as a function of range of relevant environmental parameters. They assessed the effects of water chemistry and commonly used disinfection rinses on the removal and inactivation of E. coli on spinach leaves. A COMSOL model was constructed for the spinach leaf texture to evaluate gradients of disinfectant concentration that may inhibit the efficacy of the rinse and potentially lead to dangerous foodborne outbreaks.
The researchers found that in commercial rinses with low bleach concentrations, the bacteria detached from the leaves, but remained alive. Rinses with higher bleach levels killed the bacteria. Analysis of the spinach leaf texture model revealed that, due to the uneven surface of a spinach leaf, bleach may not be evenly distributed across the surface of the leaf.
"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 the press release. “In some cases, that translated to a 90% bacterial survival in their tests — and a high risk for cross contamination.”
To address this concern, the researchers are currently investigating the addition of a titanium dioxide photocatalyst to the rinse water, according to the press release. This photocatalyst, which reacts to light to generate a strong, bacteria-killing oxidant, will also be assessed on a broader range of foods.
References:
Walker S. Presented at: 250th National Meeting & Exposition of the American Chemical Society, Aug. 16-20, Boston.
Disclosure: Infectious Disease News was unable to determine relevant financial disclosures at the time of publication.