Leafy green vegetables are crucial for their dietary fibre and nutrient content, yet they can harbour harmful pathogens. Lettuce is often implicated in US foodborne illness outbreaks. A recent study by the University of Illinois Urbana-Champaign examined E. coli contamination factors across romaine lettuce, green-leaf lettuce, spinach, kale, and collards.
Lead author Mengyi Dong, now a postdoctoral researcher at Duke University, conducted the research at the Department of Food Science and Human Nutrition (FSHN), ACES, U. of I. The study infected whole leaves of these vegetables with E. coli O157:H7 and observed outcomes after storage at four °C, 20°C, and 37°C. Results showed temperature and leaf surface properties like roughness and natural wax significantly influenced susceptibility.
“E. coli thrives at room temperature or higher on lettuce, but refrigeration at four °C sharply reduces its population. Waxy greens like kale and collards, however, exhibit slower growth in warmth but survive longer when refrigerated,” Dong noted. Despite this, kale and collards are less susceptible overall than lettuce, which is often consumed raw.
The study also compared intact and cut leaves inoculated with E. coli, revealing that spinach, kale, and collard juices possess antimicrobial properties that hinder bacterial growth. The researchers isolated juices from kale and collards, finding potential applications as natural antimicrobial agents in controlling foodborne pathogens throughout the supply chain.
“Vegetables, grown in soil, are naturally exposed to bacteria,” explained co-author Pratik Banerjee, an associate professor in FSHN and Illinois Extension specialist. While acknowledging this complexity, Banerjee emphasised adherence to industry best practices and federal food safety standards to ensure a safe US food supply.
Banerjee and Dong underscore the importance of not discouraging fresh produce consumption but advocate for following food safety protocols: thorough washing, refrigerated storage, and awareness of food recalls. Their findings support ongoing efforts in the research community and federal agencies to address food safety challenges comprehensively.
More information: Mengyi Dong et al, Fates of attached E. coli o157:h7 on intact leaf surfaces revealed leafy green susceptibility, Food Microbiology. DOI: 10.1016/j.fm.2023.104432
Journal information: Food Microbiology Provided by University of Illinois College of Agricultural, Consumer and Environmental Sciences
