Food-grade waxes are applied to many produce items before storage and distribution to control postharvest decay and extend shelf life. But relatively little is known about how different waxes and the waxing step impact microbial food safety.

In her project funded by the Center for Produce Safety (CPS), “Waxing of whole produce and its involvement in and impact on microbial food safety,” Luxin Wang, Ph.D. an associate professor with the University of California-Davis, is studying the microbial food safety of waxing produce.

Wang hopes to address the knowledge gaps related to waxing produce.

“We hope to provide the industry with information about how waxes contribute to the microbial safety of fresh produce by using lemons and oranges as model products,” she said.

In addition, Wang said, the results could be used by individual packinghouses to support the development of their food safety plans or risk assessments.

The studies objectives

  1. The team will artificially inoculate different storage and finishing waxes to determine the survivability of human pathogens in these waxes under simulated storage conditions.
  2. The team will evaluate the impact of the application of storage waxes on the behavior of pathogens on fruit surfaces. The evaluation will be conducted under both degreening and long-term storage conditions.
  3. The team will characterize the bactericidal efficacy of the application of finishing waxes and the following heated drying steps.

Early results
For objective one, the team obtained four storage waxes and 15 finishing waxes from industry collaborators. They evaluated the chemical and microbial characteristics of these waxes as well as their impact on pathogen survival.

“The waxes had a wide range of pH from 8-13 and varying compositions,” Wang said. “Among them, two storage waxes and one finishing wax had background populations of microorganisms.”

The team observed that the behavior of pathogens inoculated into the waxes depended upon the pathogen type, the type of wax and the storage temperature.

“In general, Listeria survived better than Salmonella, and both pathogens survived better at 4 degrees Celsius than 22 (degrees) Celsius and in diluted waxes than in undiluted waxes,” she said. “Since storage waxes are used in diluted form, information obtained from objective one will help the industry decide how to better store their unused or used storage and finishing waxes.”

For the second objective, storage waxes will be applied to lemons inoculated with pathogens and then stored at 4 degrees Celsius or 22 degrees Celsius for specific periods of time mimicking storage conditions at lemon packinghouses.

“For the first two objectives, we would like to mimic two scenarios. The first is to evaluate what happens if the fruit is exposed to contaminated waxes,” Wang said. “In the second scenario, the fruit arrives at the packinghouse already contaminated on the surface before the wax is applied.”

The team is just beginning objective two.

About CPS: The Center for Produce Safety is a 501(c)(3) nonprofit organization. CPS is a collaborative partnership that leverages the combined expertise of industry, government and the scientific and academic communities to focus on providing research needed to continually enhance food safety. This level of collaboration allows CPS to fill the knowledge gaps on produce food safety and address both research priorities and immediate industry needs.

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