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Research seeks more efficient, accurate virus detection in berries and leafy greens

Researchers in Spain are investigating methods to improve the detection of human norovirus and hepatitis A virus on leafy greens and berries. Led by Susana Guix, Ph.D., at the University of Barcelona, the study aims to refine virus extraction, concentration, and detection processes to overcome challenges associated with low virus concentrations and false positives.

"It's very difficult to grow viruses in the laboratory as we do bacteria, so we have to rely on molecular methods to test," Guix said. "If viruses are on produce, they're usually in very low numbers and at very low concentrations, so we need to have very good extraction procedures."

"Another challenge is if we do get positive (test) results, it doesn't necessarily indicate there's a real risk — the virus may be inactivated."

The project is supported by the Center for Produce Safety (CPS) and involves collaboration with Gloria Sánchez Moragas, Ph.D., at IATA-CSIC in Valencia, Spain. While Sánchez specializes in molecular methods for detecting enteric viruses and monitoring inactivation, Guix focuses on cell culture procedures. "I think the two labs are complementary," Guix noted.

Initial steps involved developing two alternative virus extraction and concentration protocols, one commercial and one non-commercial. Both were tested against the Food and Drug Administration (FDA) and ISO industry-standard protocols. Viruses were extracted from leafy greens and berries purchased from grocery stores and spiked with known quantities of norovirus or hepatitis A virus.

Results showed the commercial method recovered more viruses from leafy greens, raspberries, and blueberries compared to the other methods. For strawberries, the commercial method performed similarly to the FDA protocol. "So far, it's given us better results for hepatitis A virus and norovirus on six different types of food, and the results are consistent," Guix said.

Once virus samples are prepared, testing often relies on RTqPCR, a molecular assay that detects and quantifies viral RNA. However, the presence of RNA does not confirm whether the virus is viable and infectious. The researchers addressed this by combining their new extraction method with modified RTqPCR, reducing non-viable virus detections compared to FDA and ISO protocols.

In the project's second phase, researchers will measure virus die-off on berries and leafy greens stored under simulated post-harvest conditions. Additionally, they will evaluate the efficacy of three disinfectant washes commonly used for leafy greens: chlorine, chlorine dioxide, and peracetic acid.

The findings are expected to provide tools for the produce industry to better assess virus risks, improve detection accuracy, and understand virus persistence during post-harvest storage and processing.

Source: www.centerforproducesafety.org

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