The scratches that inevitably form on stainless steel may seem minuscule to us, but they provide a haven for microscopic bacteria. Scientists at the University of Toronto have developed a method of making those scratches less hospitable to the microbes, using a surprisingly simple substance – cooking oil.

The researchers have been investigating methods of treating the steel surfaces of food-processing machinery, in order to keep disease-causing bacteria from settling on them and forming into biofilms. They found that when such surfaces were chemically-treated with alkylphosphonic acid and then coated with a layer of food-grade oil, that oil filled in all the tiny nooks and crannies, making it very difficult for bacteria to access them.

When the treatment was tested on the interior surfaces of stainless steel food-processing machines, the result was a 1,000x reduction in Pseudomonas aeruginosa bacterial levels within those devices. Even when the bulk of the oil layer was eroded away using glass beads, the antibacterial effect persisted, suggesting that oil still remained within the scratches.

While disinfectants are commonly used to kill bacteria in such machines, non-toxic cooking oil is considerably safer to humans, plus bacteria can't build up a tolerance to it.

"Coating a stainless steel surface with an everyday cooking oil has proven remarkably effective in repelling bacteria," says Prof. Ben Hatton, who led the study along with Dr. Dalal Asker and Dr. Tarek Awad. "The oil fills in the cracks, creates a hydrophobic layer and acts as a barrier to contaminants on the surface."

A paper on the research was recently published in the journal ACS Applied Materials and Interfaces.