Bad news for fans of the so-called “five-second rule” that claims that food that falls on the floor is safe if picked up and eaten quickly: it’s completely false, as demonstrated by researchers from Rutgers University in a newly-published Applied and Environmental Microbiology study.
Proponents of the five-second rule claim that a piece of food that falls onto the floor is safe for consumption as long as it is retrieved quickly because bacteria requires a certain amount of time to transfer onto its surface. However, food scientist Donald Schaffner and his colleagues debunk that myth in their new study, showing that the transfer takes place almost immediately.
“The popular notion of the ‘five-second rule,’” Schaffner explained in a statement, “is that food dropped on the floor, but picked up quickly, is safe to eat because bacteria need time to transfer.” The truth, however, is that moisture, surface type and contact time all contribute to contamination levels and that in some cases, bacterial transfer can begin in less than one second, he noted.
“The five-second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food,” he said. “Bacteria can contaminate instantaneously.”
Floor surface and food type, not just time, play a key role in transfer
While the five-second rule has been previously tackled by the science-themed television show Mythbusters and has also been the topic of some small-scale studies, Schaffner pointed out that there had been a limited analysis of the subject published in peer-reviewed academic journals.
“We decided to look into this because the practice is so widespread,” he said. “The topic might appear ‘light’ but we wanted our results backed by solid science.” To that end, he teamed up with Robyn Miranda, a graduate student in his laboratory at the Rutgers School of Environmental and Biological Sciences, to put the five-second rule to the test.
The scientists tested four different surfaces (stainless steel, ceramic tile, wood, and carpet) as well as four different foods (watermelon, bread, bread and butter, and gummy candy) and four contact times (less than one second, five, 30 and 300 seconds). Furthermore, they used one of two media (tryptic soy broth or peptone buffer) to grow the bacteria Enterobacter aerogenes, a strain which occurs naturally in the human digestive system and is related to Salmonella.
They conducted a total of 128 different test scenarios, each of which were reproduced 20 times, and analyzed both the surface and the food samples for bacterial contamination. They found that watermelon was typically the most contaminated food and gummy candy the least, while transfer appeared to be most affected by moisture, which made it easier for the bacteria to move.
“Also, longer food contact times usually result in the transfer of more bacteria from each surface to food,” Schaffner said, adding that carpet had significantly lower transfer rates than either tile or stainless steel surfaces. While longer contact time did result in greater bacterial transfer, “the topography of the surface and food seem to play an important role in bacterial transfer.”
—–
Image credit: Thinkstock
Comments