October 23, 2015

Passing Grades: A multiplicity of tests await companies that strive for food safety

If you don’t like tests, don’t get into the produce processing business. There are constant daily product safety tests, tests for government audits and other tests to comply with certification bodies. All these tests converge into one big Final Exam: that the produce products coming from a plant are safe.

With the health and safety of consumers at stake, this final exam isn’t graded on a curve. It’s pass/fail. Success is determined by knowing customer specifications, what is being tested for and who is doing the testing.

“There are as many ways to test for pathogens and pesticide residues as there are different pathogens and different residues,” said Don Schaffner, Extension specialist in food science at Rutgers University. “The most important thing for a processor to know is that they should be using an accredited lab and that the testing lab is using standard procedures.”

Of the many ways to test, three methods are the most common. PCR (polymerase chain reaction) is a DNA-based diagnostic method used to detect the presence of pathogens. Immunoassay tests (also known as lateral flow) are usually simpler tests designed to detect the presence of a target organism from a sample. Then there are simple culture tests, the oldest and simplest methods of detection, which allows microbes to multiply in enriched media under controlled lab conditions.

The most common pathogens tested for in the produce processing setting are Listeria monocytogenes, E. coli and salmonella. The tests are designed to answer one basic question: Is the target bacteria there or isn’t it?

“We’re reading a lot of data, but at the end of the day we want to simplify the answer,” said Tim Curran, CEO of Sample6, a company that provides food pathogen detection solutions.

Sample6 is offering another way to conduct tests that bypasses the enrichment step and performs direct detection, using a technology developed at MIT called bioillumination with bacteriophages, which are tiny organisms that are natural enemies of pathogens. The phages attach to the target pathogen and emit an enzyme that produces light that can be detected by test instruments.

Pathogen testing is almost never done at the site of the food processing facility, but by outside laboratories where there is often more expertise than in a food processing plant. Companies also want to avoid any possibility of conflict of interest in the testing and reporting of results.

There’s another good reason not to have pathogen testing take place at a food processing facility: the potential of cross-contamination from the lab into the processing facility.

“Most companies don’t want to have a lab at the site, especially for pathogens,” said Heena Patel, technical director of supply chain food safety and audit services for SCS Global Services, which supplies third-party certification and auditing. “It’s hard to control personnel, the drainage system and the ventilation system. The lab would have to be totally isolated if they really want to conduct testing at the site.”

Many of the food safety issues that tie into food safety, audits and certification apply to all kinds of produce industries, while others are unique to a particular type of processing. One of the unique environments is fresh-cut. Its products are highly perishable with a short shelf life. When the raw product is cut, plant cells are opened, which releases moisture and nutrients that can be a breeding ground for pathogens if the product is not held under the proper conditions.

Frozen products do not support the growth of pathogenic bacteria. However, if the pathogens are already present, they do pose a risk and need to be detected. Listeria has been found on frozen products, said Schaffner, and FDA has a zero tolerance for it there.

Canned and bottled products are unlikely to contain foodborne pathogens, but may contain spoilage organisms that don’t make people sick but cause undesirable flavors. Dried fruits and vegetables don’t promote the growth of pathogens, but as with frozen food, if a pathogen is already present it can pose a problem.

“It’s not so much that there are different kinds of tests for different kinds of products; it’s more a matter that certain products are more likely to have certain kinds of microorganisms present than other products,” Schaffner said.

The formal pathogen tests are only one form of evaluation that takes place in a produce processing plant. Other examinations involve the machinery and the physical plant that food passes through. Places in the plant to keep a close eye on include coolers, freezers, drains, spaces behind storage racks, other rooms beside the main processing room and outside grounds.

When self-audits are conducted, Patel advises doing them during all shifts to give a complete picture of a plant’s facilities and practices. Don’t stop with self-audits, which are advisable but shouldn’t be relied on exclusively due to the tendency to overlook certain features of a facility.

“The best advice is to start with a self-audit but then bring in an outside agency to help with identifying those blind spots,” Schaffner said.

The key to conducting good self-evaluations and being able to pass audits is to be in control of your plant, Curran said.

“You must be doing surveillance of the plant and all surfaces. Test all gutters, conveyor belts, storage bins and make sure that these surfaces don’t have a pathogen like listeria. Usually, when a contamination happens, listeria is introduced into the plant and grows into the corner of a machine or on the floor,” he said.

Curran said each facility can be divided into zones and sampling can be scheduled to be sure all the zones are properly tested. Food plants are often divided into four zones.  Zone 1 is for food contact surfaces, such as cutting blades and conveyor belts. The other zones are designed with boundaries farther away from the food.

“What is critical is that you take those four zones and put up walls between them so that something like listeria can’t get through. You conduct surveillance of Zone 4 so it doesn’t get into Zone 3, and surveillance of Zone 3 so that I doesn’t get into Zone 2 and so on,” Curran said. “You want to look at all the zones and cover them all very thoroughly.”

Any audit should be conducted as a systems audit, Patel said. It covers the food safety process from senior management commitment to customer complaints. These audits can takes two to three days and provide a complete assessment of every part of the plant and its processes.

“It takes a whole team to support the program,” Patel said. “It takes financial resources and employee resources to support it. It’s the responsibility of every department to understand the program requirements and to invest the time to train employees.”

Testing and evaluation can be conducted to meet the standards of a certification body. There are a number of these bodies, and selecting the proper one depends on the type of processing being done, government regulation and customer requirements.

In the end, the customer and the government are the ultimate constituent groups that testing must please. The upcoming changes in the Food Safety Modernization Act will have a profound effect on testing and food safety in general.

“We don’t know exactly what the future will hold, because FDA has not published a final rule. I think everyone would agree that no matter what happens, there will be an increased focus on the safety of fresh produce, and the testing and certification are now a way of life for everyone in the food industry, including those in fresh produce,” Schaffner said.

Lee Dean, editorial director



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