P3-87 Survival of Escherichia coli O157:H7 87:23 on Arugula, Kale, Lettuce and Mizuna Microgreens, and Comparison of Leaf Surface Morphology for Mature Greens and Microgreens

Wednesday, July 31, 2013
Exhibit Hall (Charlotte Convention Center)
Hee Kyung Park, University of Illinois at Urbana-Champaign, Urbana, IL
Mosbah Kushad, University of Illinois at Urbana-Champaign, Urbana, IL
Hao Feng, University of Illinois at Urbana-Champaign, Urbana, IL
Introduction: Microgreens are young edible greens that are used to enhance the color and flavor of salads, as well as being highly nutritious. Unlike sprouts, which lack true leaves, microgreens are allowed to grow and form the first true leaves.  Sprouts are legally defined, and have additional regulations due to their relatively high risk of microbial contamination. Microgreens, however, lack any legal definition or food safety regulations.

Purpose: The objectives of this study were to determine the survival characteristics of Escherichia coli O157:H7 on microgreen surfaces stored in a refrigerator and to examine the surface morphology of microgreens and mature greens.  

Methods: Arugula, kale, lettuce and mizuna seeds, obtained from Harris Seeds, Rochester, NY, were planted and grown in a container filled with general purpose soil mix in a greenhouse before harvesting.  The harvested microgreens were rinsed in tap water and dried for 1 h.  Samples (1 g each) were spot-inoculated with 150 µl  of E. coli cells (ranging from 7.45 to 7.76 log CFU/g), dried in a laminar flow hood for 1 h, packaged in plastic bags and stored at 83% RH in a refrigerator. Microbiological counting was performed at 0, 1, 4, and 7 days after inoculation. Scanning electron microscopy (SEM) was used to examine the surface morphologies of the produce.

Results: Most of the inoculated E. coli cells survived on the microgreen surfaces, showing only a slight decline (6.94 to 7.15 log CFU/g) at 7 days of storage. In the SEM images, all three types of microgreens leaves were more wrinkled than the mature leaves. The hills and valleys on the microgreens were deeper than for the mature produce.  The stomata of the microgreens were a little longer than those of the mature leaves. 

Significance: The ability of E. coli O157:H7 to survive on microgreens surfaces and the rougher microgreen surfaces compared to mature produce highlighted the importance of developing effective sanitation strategies for reducing the microbial safety risk associated with this produce product.