WASHINGTON — Pick a tomato in the blazing sun and plunge it straight into cold water. If that happened on the way to market, it might be contaminated.
Too big of a temperature difference can make a tomato literally suck water inside the fruit through the scar where its stem used to be. If salmonella happens to be lurking on the skin, that’s one way it can penetrate and, if the tomato isn’t eaten right away, have time to multiply.
That doesn’t mean people shouldn’t wash their tomatoes — they should, just probably not in cold water.
But as the Food and Drug Administration investigates the nation’s outbreak of salmonella from tomatoes, the example shows the farm isn’t the only place contamination can occur, and checking aspects like water quality and temperature control in packing houses and other supply stops is one key to safety.
This newest salmonella outbreak is the 14th blamed on tomatoes since 1990.
There are some common themes when fresh produce sickens, either from salmonella — bacteria that live in the intestinal tracts of humans and numerous animals — or other microbes: Water sources, worker hygiene and wildlife or domestic animals near fields are frequent culprits because they involve points where safety systems can easily break down.
Washing fresh produce under running water is a commonsense consumer defense.
“We know you can wash off some salmonella,” said Virginia Tech food microbiologist Robert Williams, who accompanied FDA scientists to Virginia farms as part of the tomato initiative. But, “nobody’s ever shown it washes off all salmonella.”
Water is an automatic first suspect. Was clean water used to irrigate, mix pesticides sprayed on crops, wash down harvest and processing equipment, and wash field workers’ hands?
Then in packing houses, tomatoes often go straight into a dump tank, flumes of chlorinated water for a first wash. To guard against salmonella washed into the water in turn being sucked into the tomatoes, producers often keep wash-water 10 degrees warmer than the incoming crop, said food-safety scientist Keith Schneider of the University of Florida.
Beyond packing houses, the industry points to cases where suppliers were shipped unwashed, warm tomatoes and dunked them in ice-water baths to firm them for further processing.
Salmonella may be particularly hard to prevent in a variety of crops because birds, reptiles and amphibians carry the disease — the same reason children should wash their hands after handling a turtle, iguana or frog. The tomato industry’s guidelines already advise surrounding fields with bare soil “buffer zones” to discourage reptiles.
“You’re not going to stop a bird going through a field. You’re not going to stop a frog,” Schneider said.
U.S. Health and Human Services Secretary Michael Leavitt said Monday the United States wants to open an office in Latin America to monitor food safety.
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