Monitoring the dump tank

Apples from the 2015 harvest are washed and sanitized. (TJ Mullinax/Good Fruit Grower)

The increasing emphasis on food safety means changes are ahead for tree fruit packing houses. Among them: the requirement to demonstrate that their preventive practices are effectively controlling for microbial contamination.

It’s not just about producing high-quality, safe fruit anymore; it’s about proving that steps are being taken to prevent the pathogens that could lead to a food-borne illness and, ultimately, a recall.

Packing houses are still determining whether they will be required to meet standards of the Preventive Controls Rule or the Produce Safety Rule under the Food Safety Modernization Act. In the meantime, though, every step in the packing and storage system is under examination, including the dump tank, which was the subject of a two-year study funded by the Washington Tree Fruit Research Commission.

The study by Seattle-based iDecisionSciences collected and examined dump tank monitoring data from five Washington apple packing houses to determine whether dump tank water preventive controls are controlling microbial levels and meeting requirements of the companies’ food safety plans.

“We used microbial water testing data to establish how effective those preventive controls are during the course of normal packing operations,” said iDecisionSciences CEO Diane Wetherington. “Overall, we’re finding a mixed bag. Facilities would benefit from examining their individual operations in light of recently published industry research and determining how the science can best be applied to their individual operations.”

Studying the dump tank

iDecisionSciences, a scientific consultant for the specialty crop produce industry, began this study by asking the five participating packers to complete a 70-question survey about their food safety plans, equipment, dump tank cleaning and sanitation, dump tank operations and monitoring, and chemical usage, among other things. Researchers then gathered water samples and took measurements from those packers’ dump tanks during normal business.

The number of days the dump tank water was used prior to discharge varied by facility and was dependent on factors such as apple variety, appearance of the water and fruit inventory. The researchers evaluated each dump tank through two water cycles, meaning that if a packing house changed the water every three days, the researchers collected data for six days.

The first microbial samples were taken in clean water before fruit entered the dump tank and thereafter samples were taken at one-hour intervals throughout the day. Measurements for oxidation/reduction potential, sanitizer levels, pH, temperature, turbidity and conductivity were taken at 30-minute intervals until water was discharged from the tank.

Water samples were tested for total coliform, which measures biologic pollution in water that includes coliform species usually associated with fecal polluted water, and generic Escherichia coli. Generic E. coli tests are an indicator for contamination due to enteric pathogens, or those pathogens that live in an animal’s intestinal tract.

Are preventive controls effective?

All of the facilities had samples taken from dump tanks using either calcium hypochlorite (chlorine) or peracetic acid (PAA) to sanitize the water. The time between water cycles varied from one day to three days. The unwashed fruit came either from storage or directly from the orchard and, on one packing line, washed fruit came from storage to be rerun.

The researchers collected samples over 180 operational hours at the five facilities over the course of two years — 368 total coliform tests and 74 generic E. coli tests.

Among all those tests, 35 percent of the samples from PAA tanks were positive for total coliform, and 17 percent were positive for generic E. coli, the study showed.

In addition, 60 samples — or 18 percent — were measured at PAA levels greater than the U.S. Food and Drug Administration’s 80 parts per million limit for wash water, and 18 percent of these had levels greater than 100 parts per million. Overall, three of the four facilities that use PAA had positive total coliform samples.

PAA levels among the four facilities ranged between zero and 120 parts per million during the sampling periods.

For tanks with chlorine as the sanitizer, 19 percent of the samples were positive for total coliform, and 17 percent were positive for generic E. coli. Two of the four facilities that use chlorine had total coliform-positive samples.

Free chlorine levels ranged from 0.02 parts per million to 96 parts per million. Unlike PAA, the FDA has not set limits for chlorine.

Researchers also found that the oxidation/reduction potential (ORP), which is an indicator of how much active chlorine is in the system to control microbes, was the only predictor found to be significantly correlated to total coliform detection in tanks with chlorine. As ORP increased, total coliform concentration decreased. Chlorine concentration was not found to be a significant predictor for total coliform concentration.

However, ORP was not a good predictor of generic E. coli when using chlorine, Wetherington said. “You’ve got a number of things to consider when you’re looking at how effective your dump tank preventive controls are and measuring ORP when using chlorine is just one variable in the equation.

Since each facility is unique, establishing and monitoring sanitizer effectiveness requires companies to examine their individual operations and determine the appropriate preventive controls and monitoring program.”

The findings were reversed for PAA tanks: The concentration of PAA, ORP, pH, temperature and conductivity were collectively significant predictors for total coliform, the study showed. But only ORP was a good predictor of generic E. coli.

Keys to success

All five companies reported having food safety plans. However, in response to a question of whether the dump tank was considered a critical control point in their plans, one company responded yes, one company responded no, and the other three did not answer the question.

The research findings reflected some key areas of focus for packing houses going forward, iDecisionSciences researcher Susan Leaman said, including monitoring for debris levels in the tanks and training programs for employees.

“Companies need to establish some way to determine if their training is effective,” she said. “Have people in charge of certain preventive controls take those measurements and make sure they’re doing it right. Have employees explain what they’re doing — and why. Those kinds of checks are critical, and I’m not sure they’re happening.”

Leaman and Wetherington also noted the need for regular monitoring throughout the day, because workers in repetitive jobs can get bored by their work or perform it by rote, forgetting the importance of why they’re doing it.

“For those who are going to fall under the Preventive Controls Rule, this is a good example of what the FDA is looking for in terms of process validation studies,” Leaman said. •

– by Shannon Dininny