Microbial testing can be a helpful way to identify pathogen risks for fresh produce, but it’s not a guarantee of safety. That’s why this one option in the toolbox is used differently by Americans and Europeans.
Testing in the U.S. varies somewhat from company to company, but it follows similar procedures that were standardized in 2007 with the Leafy Green Marketing Agreement, says Trevor Suslow, food-safety specialist at the University of California, Davis. It involves sampling from a field before or after harvest to assess the risk of a lot.
“It’s submitted to a lab, the lab takes a random sub-sample from that tissue … they subject it to different types of enrichment, and then you use one of the rapid real-time PCR-type of test to ask the question, ‘Do we have detectable levels of pathogens in the sample or not?'” Suslow says. The result can then qualify a field for harvest or perhaps prompt further evaluation. Some companies go further and even uniformly test finished processed goods.
But the situation is different in Europe. While European labs do test for pathogens, it’s not their main concern, says Keith Warriner, a professor of food science at the University of Guelph and program director of the school’s food safety and quality assurance program.
“We just look for E. coli and Salmonella, whereas the Europeans are a bit more risk-based,” he says.
Mieke Uyttendaele, director of Belgium’s University of Gent Laboratory for Food Microbiology and Food Preservation, believes that less pathogen testing is done in Europe than the U.S.
“End-product testing is not assumed to be very effective in safeguarding the fresh produce supply chain,” she says. “So there is more effort put into a preventive approach – from farm to fork – which is also the basis of the EU General Food Law and EU food safety legislation, putting stress on ‘good agricultural practices.’”
Europe’s system focuses more on Hazard Analysis Critical Control Point (HACCP) principles, taking into account chemical and physical hazards as well as microbial ones and bringing in controls to address those risks.
North America doesn’t really have fully HACCP-based systems for produce, Warriner says, because the existing systems mainly address just microbial contamination and traceability.
“They believe that those production practices provide a high degree of protection and therefore also limit the value of pathogen testing as a way to qualify or disqualify a product for safety,” Suslow says.
There’s a low level of confidence in the statistics of sampling to detect pathogens, so testing is often targeted at hygiene indicators such as generic E. coli rather than pathogens themselves, Uyttendaele says. If the E. coli numbers are unacceptable, it’s probably followed up with pathogen testing or auditing of the farmer’s operations.
“The objective of testing is not the key issue for ‘safety assessment’ or ‘batch release’ but rather to pick up major breakages in good agricultural or good manufacturing practices,” Uyttendaele says.
Suslow and Warriner both say it’s very difficult to judge whether one system is better than the other since, after all, they are based on very different structures.
Europe’s agricultural system consists of a lot of smaller farms and, Suslow says, “The smaller the company, the harder it is economically to factor in the cost of pathogen-testing materials into your program.”
But in North America’s favor is “a much better surveillance system,” Warriner says. “And so when outbreaks happen, we’re really on to it.”© Food Safety News