Refrigerating Lettuce Reduces E. coli Risk, Study Shows

Written by Camilla Jessen

Mar.06 - 2024 9:27 AM CET

A new study reveals that storing lettuce in the refrigerator can significantly decrease the risk of E. coli contamination.

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Leafy greens, while nutritious, can sometimes carry unwelcome guests like E. coli bacteria. A University of Illinois Urbana-Champaign study sheds light on how to reduce contamination risks, especially in lettuce.

The research focused on the E. coli vulnerability of various leafy greens including romaine and green-leaf lettuce, spinach, kale, and collards.

"We are seeing a lot of outbreaks on lettuce, but not so much on kale and other brassica vegetables. We wanted to learn more about the susceptibility of different leafy greens," stated Mengyi Dong, the study's lead author.

Temperature's Role in Bacterial Growth

The study discovered that temperature and leaf surface characteristics greatly influence E. coli's ability to thrive.

While E. coli grows rapidly on lettuce at room temperature, refrigeration at 4°C (39°F) significantly reduces bacterial presence. Leafy greens with a natural wax coating like kale and collards showed resilience to E. coli at warmer temperatures but maintained bacterial presence under refrigeration.

The lessened susceptibility of kale and collards to E. coli, coupled with the common practice of cooking these vegetables, contrasts with the raw consumption of lettuce. Although rinsing lettuce can remove some bacteria, E. coli often remains due to its strong attachment to the leaf.

Impact of Cutting on Contamination

The researchers also compared E. coli growth on whole and cut leaves.

"Whole leaves and freshly cut leaves present different situations. When the leaf is cut, it releases vegetable juice, which contains nutrients that stimulate bacterial growth," Dong explained.

Interestingly, spinach, kale, and collard juices exhibited antimicrobial properties, suggesting potential as natural antimicrobial agents.

Recommendations for Consumers

"We can't completely avoid pathogens in food. Vegetables are grown in soil, not in a sterile environment, and they will be exposed to bacteria," stated Pratik Banerjee, co-author, associate professor in FSHN and Illinois Extension specialist.

"It's a complex problem to solve, but we can embrace best practices in the food industry and food supply chain. There's a lot of interest from the research community and federal agencies to address these issues, and the USDA imposes high standards for food production, so overall the U.S. food supply is quite safe."

The researchers advises against avoiding fresh fruits and vegetables due to these risks.

Instead, they suggest adhering to food safety protocols, such as thorough washing of lettuce, refrigeration, and staying informed on food recalls, to maintain a healthy diet.

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