Food safety advice for home cooks has always included certain rules. Always wash your hands before preparing foods and after handling raw meats, poultry, and eggs; keep perishable foods refrigerated, and wash all utensils well after using them.
But a new study conducted at the University of Georgia has found that utensils should also be washed after each use and before they are used on another food. Scientists found that the bacteria will “latch on” to utensils such as knives and graters and then contaminate the next food prepared with that item.
But most consumers are not aware that this problem exists, according to the study’s lead author Marilyn Erickson, an associate professor in the College of Agricultural and Environmental Sciences’ department of food science and technology. She said, “just knowing that utensils may lead to cross-contamination is important. With that knowledge, consumers are then more likely to make sure they wash them in between uses.”
It’s also important to note that produce, items that are not associated with food poisoning in most consumers’ minds, can be, and often are, contaminated with pathogenic bacteria. Foods such as tomatoes, lettuce, berries, and sprouts have caused food poisoning outbreaks from contamination with everything from E. coli to Cryptosporidium.
Erickson was co-author on a study in 2013 that was looking at the transfer of norovirus and hepatitis A between produce and kitchen utensils. That research revealed that cutting and grating produce increases the number of contaminated items in the kitchen.
While researchers have known for decades that poor hygiene and improper food preparation practices in a consumers’ home can cause illness, considering how the consumer prepared food that may lead to contamination has not been studied. “The FDA was interested in getting more accurate numbers as to what level of cross-contamination could occur in the kitchen using standard practices,” Erickson said.
In the study, many types of fruits and vegetables were contaminated with Salmonella and E. coli bacteria. They were then cut up to see how easily the bacteria was spread when the knife was used continuously without being cleaned. The team did not wash the knives between cutting the different produce. They also grated produce. Researchers found that both knives and graters can cause “additional cross-contamination in the kitchen and that the pathogens were spread from produce to produce if they hadn’t washed the utensils.”
Ericsson said that “a lot of the broken up material and particles from the contaminated produce remained on the graters. Then if you were to shred another carrot or something else immediately after that, it gets contaminated, too.”
Erickson also found that different fruits and vegetables spread the pathogens to different degrees. “For items like tomatoes, we tended to have a higher contamination of the knives than when we cut strawberries. We don’t have a specific answer as to why there are differences between the different produce groups. But we do know that once a pathogen gets on the food, it is difficult to remove.”
The information about tomatoes is interesting since a Salmonella outbreak at Chipotle restaurants in Minnesota last summer were caused by contaminated tomatoes. That outbreak sickened at least 64 people in that state.
The researchers also looked at brushes and peelers. Those results found that scrubbing or peeling produce items such as melons, carrots, and celery didn’t eliminate contamination on the produce but caused contamination of the brush or peeler. Even rinsing under running water while scrubbing produce didn’t stop the cross-contamination.
Erickson also pointed out that while there is a small chance of buying produce that is contaminated with bacteria, buying store-bought produce that has been shipped for miles or something locally grown won’t make a difference in the contamination levels.
