U.S – In response to unexpected multistate outbreaks challenging the perception of stone fruits as low-risk for foodborne pathogens, Dr. Qixin Zhong of the University of Tennessee embarked on an investigation funded by the Center for Produce Safety (CPS).

Despite stone fruits growing off-ground and undergoing packing in dry conditions, recent events prompted a reevaluation of microbial risks.

Recently, the Food and Drugs Administration (FDA) reported an outbreak of Listeria monocytogenes infections associated with peaches, plums, and nectarines, leading to 10 hospitalizations and one tragic death.

The FDA and the Centers for Disease Control and Prevention (CDC) launched an investigation into the source of the contamination, urging consumers to exercise caution and take immediate action if they have purchased affected fruit.

The regulator revealed that the outbreak has been under investigation for several years, with cases emerging between August 22, 2018, and August 16, 2023.

Collaborating with UT microbiologist Dr. Thomas Denes, Dr. Zhong delved into food-grade antimicrobials, seeking to enhance the efficacy of the wax and fungicidal coatings routinely applied to stone fruit.

The goal was twofold: reduce contamination by pathogens like Salmonella enterica and Listeria monocytogenes and extend the shelf life of these delectable fruits.

While traditional wax coatings aim to combat moisture loss and extend shelf life, the regulatory-approved fungicides added fall short in addressing foodborne pathogens.

Dr. Zhong’s study explored the integration of selected food-grade antimicrobials to create a comprehensive defense against contamination during storage.

Through a meticulous review of literature, Dr. Zhong and Dr. Denes identified antimicrobial candidates based on their physical and chemical properties.

Testing these antimicrobials individually and in combinations, the researchers uncovered synergies that demonstrated greater efficacy against pathogens than the sum of their individual effects. pH adjustments were also explored to enhance antimicrobial performance.

Real-world trials

In a partnership with industry players, including Prima Wawona and the California Fresh Fruit Association (CFFA), the study transitioned to a real-world scenario.

Freshly picked peaches, supplied by industry collaborators, underwent simulated packinghouse treatment.

Antimicrobial coatings were applied, and the peaches were inoculated with pathogens before storage at 32 °F to mimic packinghouse conditions.

Initial results from this innovative trial are set to be validated during the 2024 California peach harvest. Dr. Zhong anticipates that the findings will not only enhance food safety practices but also provide the industry with valuable insights to navigate the intricate landscape of pathogen mitigation and shelf life extension in stone fruits.

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