Abstract: Focuses on previous theories regarding which surfaces are safer for food preparation Study indicating that pathogens prefer plastic to wooden surfaces; Work of Dean O. Cliver and Nese O. Ak; Studies of Escberichia cali, Salmonella and Listeria; The Food and Drug Administration's (FDA) model codes for state agencies; More.


Science News, February 6, 1993, Vol. 143 Issue 6, p84
Section: SClENCE NEWS of the week


Chefs know that, any way you slice it, wooden surfaces are kinder to knife blades than either plastic or glass. But in recent years, everyone from kitchen suppers to the Department of Agriculture (USDA) has urged cooks to cut on nonporous materials, typically plastic. Supposedly plastic boards give bacteria, such as Salmonella in chicken, less chance of escaping rigorous cleaning, thus reducing the chance that such bugs will survive to contaminate Other foods.

If such arguments have frightened you away from slicing, dicing, or boning on wood, you may be able to bring your butcher block out of retirement New research indicates that the safety advocates were wrong: Pathogens prefer plastic.

No one was more surprised by this than Dean O. Cliver and Nese 0. Ak, two microbiolgists at the University of Wisconsin-Madison. They began studying cutting boards in hopes of identifying decontamination techniques that might render wood as safe as plastic.

But the pair quickly found that within three minutes of inoculating wooden boards with cultures of common food-poisoning agents - up to 10,000 cells of Salmonella, Listeria, or Escherichia cali – 99.9 percent of the bacteria were unrecoverablc and presumed dead. Under similar conditions, none of the bugs placed on plastic died.

Indeed, when the researchers maintained plastic boards overnight at high humidity and room temperature, microbe populations grew; the researchers recovered no live bacteria from wood the next morning.

The scientific literature suggests that the number of Salmonella cells that might wash off a chicken carcass probably will not exceed about 1,000, Cliver notes. "We can get less than 99.9 percent kills [on the wooden boards in three minutes] if we go to inordinately high levels of inoculation" -such as l million or more bacterial cells, he says. In those instances, he and Ak had to wait about two hours before achieving a 99 9 percent reduction in the bugs they recovered.

While the wooden boards appear to kill bacteria. "we've not recovered the little critters' dead bodies." Cliver acknowledges. "So all we know is that by the best available means, we can't get them back after they go onto a hoard." The big concern is whether bacteria hiding deep within the wood might subsequently surface to contaminate the foods an the chopping black "As best we can tell, that isn't going to happen," Cliver says.

The same is not true of knife-scored plastic cuning boards. The scientists found that bacteria lodged in the plastic's cut grooves not only survived a hot watcr-and-soap wash, but could later surface to contaminate foods. By contrast, Cliver says, with wood "a good wipe will do fine – and if you forget to wipe the board, you probably won't be too bad off."

At one point, the Wisconsin researchers inoculated wood and plastic on three successive days, maintatmng each board - without cleaning – at room temperatures and high humidity By that time, "the plastic boards were downright disgusting," Cliver says, "while the wood boards had about 99.9 percent fewer bacteria than [Ak] had put on them."

"Wood is more forgiving -and perhaps user-friendly - than plasttc is once it's been cut some," Cliver says.

Boards sold to homeowners typically come from the factory treated with mineral oil. "That treatment is intended to make the wood more impermeable – like plastic," Cliver says. "The bad news is that it does make wood more like plastic.... In every one of our tests, if the wood had been treated to retard the penetation moisture, the bacteria survived longer."

Wood's presumed bactericidal activity does not depend on whether it is new nor, apparently, an species. Cliver and Ak have already tested bonds from hard maple, birch, beech, black cherry, basswood, bunemut, and American black walnut. Tests on oak and ash are pending.

The microbiologists hope to submit their findings for publication within the next few months. One weakness, Cliver notes, is their inability to nail down a mechanism or agent responsible for wood's antibacterial properties.

Although no laws prohibit commercial establishments from using wooden cutting boards, the Food and Drug Administration's model code for state agencies call for using only "nonabsorbent" and easily cleaned materials for surfaces that food contacts, The USDA also recommends acrylic or other nonporous mxaterials to consumers asking about preferred cutting boards, according to Bessie Berry with its Ment and Poultry Hotline in Washington, D.C.

Cooks should never cut on glass, she says, because minute shards may chip off and become embedded in food.

Microbiologist Priscilla Levine of USDA's Food Safety and Inspection Service says she knows of no scientific studies demonstrating the advantages of one cutting-board material over another in inhibiting bacterial contamination. She told SCIENCE NEWS that her agency based its recommendations on "common sense.

Like state and local inspectors, these federal agencies have "bought the myth" that plaslic is safer than wood, says food scientist O. Peter Snyder, a St. Paul, Minn.based consultant to the retail-food industry For at least two decades, he says, "sanitarians [sanitation inspectors] out there have been telling us to use plastic cutting boards, even though they had no evidence that plastic was better."

Indeed, Snyder contends, the little research done on the subject has failed to demonstrate plastic's superiority He cited one study conducted about 25 years ago that showed wooden cutting boards were at least as good as plastic when it comes to cleaning off microbial contamination.

If others confirm the Wisconsin data, Snyder says, sanitarians may have to alter their advocacy in favor of wood. But, he adds, considering how slowly practices change in the food business, 10 years after such confirmatory data came in "sanitarians would probably still be requiring [retail establishments) to use plastic cutting boards."

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