Wood vs Plastic

A common misconception is that plastic cutting boards are safer than wood cutting boards. It is thought (incorrectly) that plastic inhibits the growth of potentially harmful bacteria like salmonella and E-coli, while wood is a natural surface on which bacteria can grow. A scientific study found exactly the opposite to be true. In 1993, the Food Research Institute, Department of Food Microbiology and Toxicology, University of Wisconsin, conducted an experiment that intentionally contaminated different woods and different plastics with bacteria such as E-coli, salmonella and listeria to assess relative safety and cleanliness among the surfaces. Surprising even the researchers, the results showed that wood cutting boards are more resistant to food-borne bacteria and therefore safer than plastic boards, especially as they age. To summarize the findings, the University of Wisconsin, Madison issued the following article (emphasis added):

University of Wisconsin, Madison
University Communications
STUDY: WOOD CUTTING BOARDS, NOT PLASTIC, ARE SAFER FOR FOOD PREP
 
For decades now, cooks in homes and restaurants have been urged to use plastic rather than wood cutting boards in the name of food safety. The fear is that disease-causing bacteria (salmonella from raw chicken, for example) will soak into a cutting board and later contaminate other foods cut on the same surface and served uncooked, such as salad ingredients.
 
It's become an article of faith among "experts" that plastic cutting boards are safer than wood for food preparation because, as the thinking goes, plastic is less hospitable to bacteria.
 
It seems reasonable, but it just ain't so, according to two scientists at the University of Wisconsin-Madison's Food Research Institute.
 
Dean O. Cliver and Nese O. Ak, food microbiologists in the College of Agricultural and Life Sciences, have found that in some as yet unknown way wooden cutting boards kill bacteria that survive well on plastic boards.
 
"This flies in the face of the prevailing wisdom," says Cliver. "It isn't what I expected. Our original objectives were to learn about bacterial contamination of wood cutting boards and to find a way to decontaminate the wood so it would be almost as safe as plastic. That's not what happened."
 
Cliver is quick to point out that cooks should continue to be careful when they handle foods and wash off cutting surfaces after they cut meat or chicken that may be contaminated with bacteria.
 
"Wood may be preferable in that small lapses in sanitary practices are not as dangerous on wood as on plastic," he says. "This doesn't mean you can be sloppy about safety. It means you can use a wood cutting board if that is the kind you prefer. It certainly isn't less safe than plastic and appears to be more safe."
 
Cliver and Ak began by purposely contaminating wood and plastic boards with bacteria and then trying to recover those bacteria alive from the boards. They also tested boards made from seven different species of trees and four types of plastic. They incubated contaminated boards overnight at refrigerator and room temperatures and at high and typical humidity levels. They tested several bacteria (Salmonella, Listeria and enterohemorrhagic Escherichia coli) known to produce food poisoning. The results consistently favored the wooden boards, often by a large margin over plastic boards, according to Cliver.
 
The scientists found that three minutes after contaminating a board that 99.9 percent of the bacteria on wooden boards had died, while none of the bacteria died on plastic. Bacterial numbers actually increased on plastic cutting boards held overnight at room temperature, but the scientists could not recover any bacteria from wooden boards treated the same way.
 
So where did we get the idea that wood isn't safe? Cliver and Ak don't know. They did a literature search and have not found any studies that evaluated the food safety attributes of wood and plastic cutting boards.
 
Although Ak, a graduate student at the Food Research Institute, will soon return to Turkey, Cliver hopes to continue the studies. A major question now, he says, is why wood is so inhospitable to bacteria. He and Ak have tried unsuccessfully to recover a compound in wood that inhibits bacteria.
 
The first year of the study was funded by the Food Research Institute with unrestricted food industry gift funds; other funding sources are now being sought. Cliver and Ak will soon submit an article based on the research to a refereed scientific journal.
(End of article)

 

The University of California, Davis also published Dr. Cliver’s own summary as follows (emphasis added):

PLASTIC AND WOODEN CUTTING BOARDS
Dean O. Cliver, Ph.D.
 
We began our research comparing plastic and wooden cutting boards after the U.S. Department of Agriculture told us they had no scientific evidence to support their recommendation that plastic, rather than wooden cutting boards be used in home kitchens. Then and since, the U.S. Department of Agriculture's Meat and Poultry Inspection Manual (official regulations) and the U.S. Food and Drug Administration's 1999 Food Code (recommended regulations for restaurants and retail food sales in the various states of the U.S.) permit use of cutting boards made of maple or similar close-grained hardwood. They do not specifically authorize acceptable plastic materials, nor do they specify how plastic surfaces must be maintained.
 
Our research was first intended to develop means of disinfecting wooden cutting surfaces at home, so that they would be almost as safe as plastics. Our safety concern was that bacteria such as Escherichia coli O157:H7 and Salmonella, which might contaminate a work surface when raw meat was being prepared, ought not remain on the surface to contaminate other foods that might be eaten without further cooking. We soon found that disease bacteria such as these were not recoverable from wooden surfaces in a short time after they were applied, unless very large numbers were used. New plastic surfaces allowed the bacteria to persist, but were easily cleaned and disinfected. However, wooden boards that had been used and had many knife cuts acted almost the same as new wood, whereas plastic surfaces that were knife-scarred were impossible to clean and disinfect manually, especially when food residues such as chicken fat were present. Scanning electron micrographs revealed highly significant damage to plastic surfaces from knife cuts.
 
Although the bacteria that have disappeared from the wood surfaces are found alive inside the wood for some time after application, they evidently do not multiply, and they gradually die. They can be detected only by splitting or gouging the wood or by forcing water completely through from one surface to the other. If a sharp knife is used to cut into the work surfaces after used plastic or wood has been contaminated with bacteria and cleaned manually, more bacteria are recovered from a used plastic surface than from a used wood surface.
 
"Manual cleaning" in our experiments has been done with a sponge, hot tapwater, and liquid dishwashing detergent. Mechanical cleaning with a dishwashing machine can be done successfully with plastic surfaces (even if knife-scarred) and wooden boards especially made for this. Wooden boards, but not plastics, that are small enough to fit into a microwave oven can be disinfected rapidly, but care must be used to prevent overheating. Work surfaces that have been cleaned can be disinfected with bleach (sodium hypochlorite) solutions; this disinfection is reliable only if cleaning has been done successfully.
 
The experiments described have been conducted with more than 10 species of hardwoods and with 4 plastic polymers, as well as hard rubber. Because we found essentially no differences among the tested wood species, not all combinations of bacteria and wood were tested, nor were all combinations of bacteria and plastics or hard rubber. Bacteria tested, in addition to those named above, include Campylobacter jejuni, Listeria monocytogenes, and Staphylococcus aureus.
 
We believe that the experiments were designed to be properly representative of conditions in a home kitchen. They may or may not be applicable to other plastic and wooden food contact surfaces or to cutting boards in commercial food processing or food service operations, but we have no reason to believe that they are not relevant, except that not all plastic surfaces are subject to knife-scarring. Before our first studies had been published, they were criticized incorrectly for not having included used (knife-scarred) cutting surfaces. We had been careful to include used surfaces, and so were surprised that others who did later experiments and claimed to have refuted our findings often had used only new plastic and wood. Although some established scientific laboratories say their results differ from ours, we have received multiple communications from school children who have done science projects that have reached essentially the same conclusions that we did.
 
We have no commercial relationships to any company making cutting boards or other food preparation utensils. We have tested boards and cleaning and disinfection products, some of which were supplied to us gratis. We have not tested all of the products that have been sent to us, simply because there is not time. We are aware that there are other food preparation surfaces made of glass or of stainless steel; we have done very little with these because they are quite destructive of the sharp cutting edges of knives, and therefore introduce another class of hazard to the kitchen. We believe, on the basis of our published and to-be-published research, that food can be prepared safely on wooden cutting surfaces and that plastic cutting surfaces present some disadvantages that had been overlooked until we found them.
 
In addition to our laboratory research on this subject, we learned after arriving in California in June of 1995 that a case-control study of sporadic salmonellosis had been done in this region and included cutting boards among many risk factors assessed (Kass, P.H., et al., Disease determinants of sporadic salmonellosis in four northern California counties: a case control study of older children and adults. Ann. Epidemiol. 2:683-696, 1992.). The project had been conducted before our work began. It revealed that those using wooden cutting boards in their home kitchens were less than half as likely as average to contract salmonellosis (odds ratio 0.42, 95% confidence interval 0.22-0.81), those using synthetic (plastic or glass) cutting boards were about twice as likely as average to contract salmonellosis (O.R. 1.99, C.I. 1.03-3.85); and the effect of cleaning the board regularly after preparing meat on it was not statistically significant (O.R. 1.20, C.I. 0.54-2.68). We know of no similar research that has been done anywhere, so we regard it as the best epidemiological evidence available to date that wooden cutting boards are not a hazard to human health, but plastic cutting boards may be.

 

Sources:

http://news.wisc.edu/releases/1107.html

http://faculty.vetmed.ucdavis.edu/faculty/docliver/research/cuttingboard.htm

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