Think a quick dunk in water is enough to clean your lettuce? Not so fast, warns a microbiologist from Toronto. Prompted by an outbreak of lettuce-borne E. cola 0157:H7 that sickened 21 people in a local hospital, Ross Davidson, Ph.D., set out to determine the best method for rinsing away pathogens.
Davidson sprayed heads of iceberg lettuce with E: cola and let them sit overnight in a refrigerator?enough time so the bacteria could move to the inner leaves, but not long enough to multiply appreciably. The next day, the lettuce was washed three different ways: (1) cored and washed in a sink of cold water: (2) cored and rinsed under running water; and (3) cored and leaves separated before swirling in a sink of water. Lettuce heads sprayed with E. coli, but not washed at all, served as controls.
The results? All three washing methods significantly reduced the amount of bacteria on the outer leaves compared to the unwashed lettuce heads. But only the separate-and-rinse method effectively cleaned the inner leaves, where pathogens had migrated. Even this won’t eliminate all risk, Davidson points out, since even small amounts of bacteria left behind can cause illness. But dunking separated lettuce leaves will reduce the risk. Rinsing under running water may be even more effective.
Separating lettuce leaves before washing, Davidson adds, is wise for all salad greens, even looser heads like Romaine and red-leaf lettuce, which are preferred nutritionally. Moreover, recent outbreaks of illness from E. coli, Shigella and Cyclospora underscore the importance of carefully washing all fruits and vegetables.
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