* Project will provide industry with scientifically valid data to optimize spray-wash process control and practices during apple packing
* Lab results will be verified using a pilot-scale packing line
* Pilot line will be as close to real world as possible
* Results are likely transferable applied to other smooth-skinned fruits and vegetables washed under similar conditions
Although Pacific Coast apple packers have been applying antimicrobial sprays to fruit on the packing line, limited scientifically determined data are available to optimize the process parameters to reduce the risk of Listeria monocytogenescross-contamination and persistence potential.
Dr. Meijun Zhu, an associate professor in the School of Food Science at Washington State University, Pullman, hopes to change that with her research project, "Control of Listeria monocytogenes on apple through spray manifold-applied antimicrobial intervention. "The co-investigator is Dr. Trevor Suslow, a University of California, Davis, extension research specialist in postharvest quality and food safety.
The two laid the initial groundwork by working closely with the apple industry to ensure the project reflects real-world operations and practices. Throughout the project, the industry representatives' have been both open and cooperative --which Suslow and Zhu have praised.
"One of the key challenges, and one of the key expectations of the project that we're both trying to address, is the research results have to be as close to industry practices as reasonable," Suslow said. "And everything - the dose, the type of spray nozzles, all of those things - has to fit into a series of options relative to the different chemistries. It has to be almost turn-key. The industry is already doing many of these things, but standardized data under controlled conditions are limited. We're trying to optimize them and have the needed reference data. It's a real-world science project consistent with the mission of CPS." As part of that effort, the researchers surveyed 16 commercial apple packing lines in Washington about packing line spray-wash configurations and management. The research will reflect those consensus practices Suslow and Zhu affirmed. The survey also gave them information about water treatment process aides and application methods currently used on apples.
During the first year of the two-year project, Zhu conducted extensive lab tests with about a half dozen antimicrobial products either registered for use on food or very close to being registered. She also looked at dose, contact time, and application methods. "We're trying to compare different sanitizers to determine their efficacy, and we're trying to optimize treatment conditions," she said. In addition, Zhu's group is conducting lab experiments to determine whether Enterococcus faecium NRRL B-2354, a non-pathogenic microorganism already qualified as a surrogate in other food processing systems, would be a viable surrogate for Listeria monocytogenes in non-thermal inactivation applications. "Finding a non-pathogen substitute that adheres to apple surfaces and reacts to antimicrobials similarly to Listeria would eliminate researchers' inability to apply and handle an infectious pathogen during the project's second phase," said Zhu.
Drawing from the first year's laboratory results, Suslow will lead trials using a pilot-scale packing line running two apple varieties: Granny Smith and Fuji. The University of California has a pilot line at the Lindcove Field Station used for citrus and one at the Kearney Agricultural Research and Education Center used for primarily for stone fruit. Suslow said he believed either could be modified to handle apples. A dedicated spray-wash line at the UC Davis Field Research Facility, built from cooperators' "boneyards," is an option being pursued as well. "We want it to be as close as possible to a commercial line as we can make it," Suslow said. "We need to have a large enough volume of fruit to get a realistic idea of things like contact time, coverage, and preventing cross contamination."
After the pilot plant trial, Zhu will lead final validations in commercial apple packing lines in Washington using a potential surrogate strain. Once the project is complete, Zhu and Suslow plan to share the information with as many industry groups as possible. "I'm an extension specialist 100 percent, and this is what I do," said Suslow. "We'll translate it down to different levels, maybe two to three different styles and technical levels of outreach. In addition to dissemination of results within the CPS lines of communication, we'll make sure to talk at trade meetings, talk at the annual apple industry meetings and tree fruit meetings. We will certainly host and highlight the outcomes on the UC Postharvest Technology Center website. We want to make sure the information is shared in an understandable way."
Suslow said they anticipate their results could be applied to other smooth-skinned fruit and vegetables that are handled and packed in similar ways.