Slippery way to cleaner food processing equipment

The sheer scale of modern food processing vessels makes them difficult enough to clean even before the added complications of small scratches and grooves which inevitably appear through use, make cleaning even harder.

These surface imperfections provide bacteria and biofilms perfect places to hide and then emerge and contaminate product made in the equipment.

But it looks as if a simple answer may be on hand. Researchers from the University of Toronto’s Department of Materials Science & Engineering have come up with a new way to prevent bacteria from thriving inside food processing equipment. They have shown that a thin layer of cooking oil trapped on the stainless steel equipment surfaces can fill in microscopic scrapes, cracks and fissures and create a barrier to bacterial attachment.

Using this technique resulted in a thousand-fold reduction in bacterial levels inside the industrial machines tested.

This simple and cost-effective treatment is based on the Slippery Liquid-Infused Porous Surfaces (SLIPS) principle, initially developed at Harvard.

SLIPS technology which essentially traps lubricant layers into a surface microstructure and so creates slippery, non-wetting and non-adhesive properties, was bio-inspired by the lotus leaf. By locking in water and other fluids, SLIPS technology creates slick, exceptionally repellent and robust self-cleaning surfaces on metals, plastics, optics, textiles and ceramics. These slippery surfaces repel almost any fouling challenge a surface may face — whether from bacteria, ice, water, oil, dust, barnacles or other contaminants.

“Coating a stainless steel surface with an everyday cooking oil has proven remarkably effective in repelling bacteria,” said Professor Ben Hatton (MSE), who collaborated on the project with AGRI-NEO, an Ontario seed processing company looking for a solution to a common problem in its industry. “The oil fills in the cracks, creates a hydrophobic layer and acts as a barrier to contaminants on the surface.”

Cooking oils such as olive, corn or canola also provide a safer option for cleaning food-processing equipment than the harsh chemicals and disinfectants that are typically used. The sheer size of the machines makes it harder for cleaning materials to do a thorough job, and leftover bacteria can build up resistance to the cleaning agents. Hatton’s method of filling the scratches with oil prevents bacteria from settling and essentially cleans the surface without leaving chemical residues on the stainless steel surface.

“Contamination in food preparation equipment can impact individual health, cause costly product recalls and can still be present after chemical-based cleaning occurs,” Hatton said. “The research showed that using a surface treatment and a cooking oil barrier provides greater coverage and results in 1000-fold fewer bacteria roaming around.”

Hatton’s U of T research group is continuing to test new combinations of oils, foods and biofilm types to increase the efficiency of the bacteria barriers. They will also explore options of using this method in developing countries to minimise bacterial infection and improve mortality rates.

Their work has been published in the journal ACS Applied Materials & Interfaces.

Professor Ben Hatton (MSE), Dr Dalal Asker and Dr Tarek Awad research cheaper, safer and more effective ways. This minimises the risk of cross-contamination, which can lead to foodborne disease. Their team have proposed a simple new solution: trapping a thin layer of cooking oil at the metal surface to fill in microscopic scrapes, cracks and fissures and create a barrier to bacterial attachment.

Image: Food particles can accumulate on an untreated stainless steel surface, at left, increasing the risk of contamination in food production facilities. The oil-treated surface, at right, repels material. Image credit: Liz Do