wooden versus plastic cutting boards/OT

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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.

Publications to date from our work:

Ak, N. O., D. O. Cliver, and C. W. Kaspar. 1994. Cutting boards of

plastic and wood contaminated experimentally with bacteria. J. Food

Protect. 57: 16-22.

Ak, N. O., D. O. Cliver, and C. W. Kaspar. 1994. Decontamination of

plastic and wooden cutting boards for kitchen use. J. Food Protect.

57: 23-30,36.

Galluzzo, L., and D. O. Cliver. 1996. Cutting boards and bacteria--oak

vs. Salmonella. Dairy, Food Environ. Sanit. 16: 290-293.

Park, P. K., and D. O. Cliver. 1996. Disinfection of household cutting

boards with a microwave oven. J. Food. Protect. 59: 1049-1054.

Park, P. K., and D. O. Cliver. 1997. Cutting boards up close. Food

Quality 3(Issue 22, June-July): 57-59.

Others are in preparation.

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