A new research project is taking a look at the efficacy of sanitizers used in apple processing dump tanks.
During processing, apples are soaked in dump tank and flume water systems. The water is commonly reused over several processing days. According to researchers, there is little data on the potential risks from apple packinghouse dump tanks. Meijun Zhu, Ph.D, of Washington State University, is leading a project that she hopes will fill knowledge gaps with science-based data that apple packers can use to enhance food safety plans or risk assessments.
The research project is titled, “Validation of sanitizer disinfection of wash water in dump tank operation of apple packing lines,” and is funded by the Center for Produce Safety (CPS).
“You’re never going to be able to totally eliminate or prevent cross-contamination, but we’re trying to look at additional options to see if we can improve (disinfectant) efficacy,” Zhu said.
The researchers focused on Listeria monocytogenes, which has been linked to previous outbreaks associated with apples.
The researchers have finished bench-scale research in the laboratory, where they examined the efficacy of three concentrations and three contact times of two standard disinfectants used in dump tanks — chlorine and peroxyacetic acid (PAA).
They inoculated water with three different concentrations of a three-strain Listeria cocktail and measured how many pathogens were recovered at three contact times.
To mimic conditions in packinghouse dump tanks, the researchers tested three types of water ranging from high-organic matter to plain water. The higher organic rate was designed to simulate a worst-case scenario and was created using a recipe that involved soil from a Yakima, WA, apple orchard and fluids from fresh-picked apples and decayed apples.
In lab testing, chlorine at 25 ppm had limited efficacy against Listeria in high-organic matter dump water. At 100 ppm, the efficacy of chlorine was not affected by low levels of organic matter but was reduced by high organic loads.
PAA efficacy, on the other hand, increased with concentration and contact time and was only minimally influenced by organic loads. PAA at 40 ppm had higher efficacy than 100 ppm chlorine.
“PAA and chlorine both can reduce Listeria when compared to no sanitizer,” Zhu said. “It definitely helps even though we couldn’t totally eliminate the pathogen, and it depends on the concentration.”
The next step
Next, the researchers will test disinfectant efficacy in a Washington State University pilot dump tank. The researchers will use the same recipe to simulate dump tank water.
“This testing will be essential before we move into commercial packinghouses,” Zhu said. “This [tank system] will be much smaller than a commercial operation but much bigger than our bench-scale testing. If the system is only water, it will be an easy assessment. Once you put fruit in, it becomes complicated.”
The researchers plan to validate their bench-scale and pilot-plant findings in three to four cooperating packinghouses before the end of 2022.
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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