A new project explores the addition of food-grade antimicrobials to the wax and fungicidal coatings applied to stone fruit to reduce contamination risks and extend shelf life.

While stone fruit, fleshy fruit with a hard pit, is generally considered safe, multi-state outbreaks and recalls prompted Dr. Qixin Zhong of the University of Tennessee to investigate ways to enhance safety. “So we need to enhance the safety of stone fruit,” he said. 

The current practice in packinghouses involves applying edible wax coatings to stone fruit to mitigate moisture loss during storage and extend shelf life. A regulatory-approved fungicide is added to control yeasts, molds, and fungi, but according to Dr. Zhong, this mixture falls short against Salmonella enterica and Listeria monocytogenes.

The researchers explored various food-grade antimicrobials, assessing their physical and chemical properties for compatibility with coatings. Next, they screened the antimicrobials individually and in combination for their efficacy in controlling Salmonella enterica and Listeria monocytogenes.

Adjusting pH levels further enhanced antimicrobial effectiveness. Identifying the most promising antimicrobials, the researchers initiated the second phase, testing antimicrobial-enhanced coatings on peaches during the summer of 2023.

Prima Wawona and the California Fresh Fruit Association provided freshly picked peaches for the study. The researchers simulated commercial packinghouse conditions, inoculated the peaches with pathogens, applied coatings, and monitored the fruit over a 20-day storage period.

Results from this phase will be validated during the 2024 California peach harvest. Dr. Zhong expressed optimism about the project’s potential impact on industry practices: “We hope this research will give the industry some great information to think about possibly different practices.”

The project has been funded with $324,925 from the Center for Produce Safety (CPS). 

Projects funded by CPS will have guidance from an Industry Advisory Council. A council is paired with each research group. As the name implies, the council will meet periodically with researchers to discuss their progress and provide guidance from an industry perspective. “It’s an excellent mechanism and provides much support to the project,” Zhong said.

about CPS
The Center for Produce Safety (CPS) is a 501(c)(3), U.S. tax-exempt, charitable organization focused exclusively on providing the produce industry and government with open access to the actionable information needed to enhance the safety of fresh produce continually.