KEY TAKEAWAYS:
- Limited data is available about potential food safety risks tied to short- and intermediate-day onions.
- Research project will examine how varietal attributes, onion defects, and handling affect potential Salmonella and E. coil.
- The project also will look at the role of bulb rot in potential pathogen infection.
- Results should help growers, processors, and retailers pinpoint high-risk areas so they can refine risk-management plans.
Referenced CPS Research:
Since 2020, a handful of foodborne outbreaks linked to bulb onions have raised concerns about the bulbous vegetable’s potential food safety risks. But limited data is available about how handling and processing may affect pathogens.
Abby Snyder, Ph.D., with Cornell University, hopes to fill some of those gaps with a multi-faceted research project that examines how onion defects, varietal attributes and handling affect Salmonella. Based on industry feedback, she also plans to include E. coli. In addition, Snyder will look at both whole bulb and ready-to-eat chopped onions.
The results are intended to help growers, processors and retailers pinpoint potential pathogen risks in their operations and target those areas with mitigation plans.
CPS has funded past research that examined Salmonella contamination of onions. But Snyder said the current work will focus more heavily on production and handling of short- and intermediate-day varieties, which differ in composition, handling, and storage compared to long-day varieties. The day length refers to how onions are categorized based on the number of daylight hours needed to initiate bulb formation.
“Historically, a lot of food safety research has been based on storage onions, but there’s quite a bit of diversity to onions and how they’re handled. We hope to determine whether all of these situations are equal as far as risk,” Snyder said.
Key to Snyder’s project is industry cooperators in California, Texas, Georgia, and New York.
“It would be impossible without them, so I really appreciate CPS for facilitating those connections,” Snyder said. “It’s really important because we want to interact with different regions and varieties.”
In her first set of experiments, she and her team inoculated whole onions with a three-strain Salmonella cocktail along with the soft rot bacterium Pantoea. They then stored the onions at 54°F and 68°F.
Each day, they cut onions in half to examine for signs of spoilage. At the same time, they measured Salmonella growth or die-off.
The purpose of this study was to evaluate the impact of onion decay and mechanical damage on Salmonella in different onion varieties. At 68°F, spoilage significantly enhanced Salmonella growth in onions of both varieties. However, if the onion only had minimal surface damage, Salmonella concentrations were significantly higher in short-day onions than in long-day onions. At 54°F, no tissue decay was observed, and Salmonella levels declined on onions with damaged surfaces. However, the die-off rate was more rapid in long-day onions than in short-day onions.
In another experiment, Snyder and her team inoculated diced onions with Salmonella and stored them for 14 days at 42-50°F. They pulled samples daily to measure for pathogen growth or die-off as well as changes in physiochemical properties, such as pH and Brix. They have also conducted a similar experiment using E. coli.
In the future, Snyder will investigate the impacts of heading and tailing — a step where the roots and tops are clipped — on pathogen survival and growth under varying temperatures during harvest, processing, and retail handling of the day-length varieties. She also will determine how different curing and handling intervals affect Salmonella survival on the surfaces of short- and intermediate-day onions.
Because not all onion varieties and uses are created equal, Snyder said she hopes the project will help the industry evaluate risks.
“We’re still going to have GAPs (good agricultural practices), broadly speaking. But better knowledge about where the food safety concerns with onions truly lie leads to better food safety because we can better refine risk-management practices.”