Know your dirt

Tiny amounts of food soil stuck to surfaces can act as a reservoir for potentially pathogenic bacteria. This food may help bacteria to survive industrial cleaning regimes in food processing factories, scientists heard.

Researchers from Manchester Metropolitan University have discovered that standard ultraviolet (UV) light and detection techniques may not show up the minute quantities of food soil that are stuck to surfaces, making it difficult to decide on the best way to clean them.

Even stainless steel surfaces can have tiny quantities of soil of unknown composition stuck to them, leading to possible contamination of food with pathogenic bacteria. "Tiny amounts of soil are enough to provide nutrients and a reservoir for contaminating bacteria to survive the cleaning processes, leading to food spoilage later," says Dr Kathryn Whitehead from Manchester Metropolitan University, UK. "The soil should be identified to make sure effective cleaning regimes are used on food preparation surfaces."

The researchers compared different methods used for the detection of food residues to determine which one was the best for different industries, including chemical and physicochemical methods, microscopy and rapid industrial methods such as UV light. They found that using more complex analytical methods is the most effective way to identify the food soil and develop a suitable cleaning regime.

"Some methods are not as sensitive as others at detecting food residue and microorganisms in the food industries. A rapid industrial technique using UV light may be optimised to detect soil," says Dr Whitehead. "Our results also showed that different techniques may be better suited to different disciplines."

The researchers suggest that knowing the type of soil build-up on food surfaces can lead to recommendations for the best strengths and types of cleaning products to help shift the residues. In some cases this may mean using lower strength cleaners, rather than higher concentration products. This should lead to a greater level of hygiene in the food industry.

"By using more precise methods to detect food residue and microorganisms on surfaces, it may be possible that different cleaners could be used to target key fouling components," says Dr Whitehead. "We hope our work will lead to a greater level of hygiene in the food industry."