Imagine a coating that prevents dirt and stains adhering to it, making surfaces easy to clean and also actively reducing the growth of bacteria and biofilm development – surely something of major value to the food and drink sectors. It would make cleaning much easier, and would contribute to improved hygiene and infection control strategies. But does something as good as this really exist?
Nano Hygiene Coatings believes it has something that achieves all of the above – and more – with its recently launched 4MED coating.
4MED is an innovative hygiene coating developed by Nano Hygiene Coatings Ltd, with hydrophobic and oleophobic properties. These properties make the surface non-stick and stain-resistant. The coating combines the benefits of the easy-to-clean properties derived from nano chemical technology with an antimicrobial additive, actively preventing the growth of bacteria such as Escherichia Coli and MRSA. The combination of a hydrophobic/oleophobic surface and active antimicrobial functionality has synergistic benefits, which contribute to improved hygiene and infection control strategies.
Acting as reservoirs for many types of organisms, soil can accumulate on surfaces creating the ideal conditions for many types of micro-organisms. While not all micro-organisms are of significance to human health, nor indeed to food production facilities, reducing their growth will significantly reduce the risks associated with any harmful effects. Having a surface that inhibits organisms adhering, such that they can be removed in a benign and environmentally friendly fashion, is beneficial.
Does the evidence support this?
At Nano Hygiene Coatings, we wanted to find out. We wanted to establish if soil built up on surfaces over time, despite the repeated cleaning effort, and whether having a hydrophobic/oleophobic surface affected the soil build-up. We also wanted to know if we could effectively reduce the bacteria in the soil. The reduction has to be quick and the antimicrobial effect long-lasting.
We set up a repeat-soiling and cleaning test. Stainless steel samples were soiled repeatedly by applying a solution containing bovine serum albumin (BSA) twice and then a mixed artificial organic soilant once. This soiling cycle was repeated three times and then followed by a final application of BSA. Between each soilant event, the samples were cleaned for 10 seconds using light manual abrasion under running mains tap water (ca 10-15ºC at 0.5 litres minute-1). Of the two stainless steel samples tested, one was uncoated, while the other was coated with an NHC hydrophobic coating.
The results revealed that the appearance of the uncoated surfaces deteriorated significantly when subjected to soiling. Repeated soiling and washing cycles caused further deterioration of the surface appearance. The appearance of the stainless steel became increasingly unattractive. The uncoated stainless steel sample retained significant organic deposits after the soiling/cleaning regime. In contrast, the coated samples maintained their appearance and retained very little soiling. They were both visually and microscopically cleaner than the uncoated surfaces.
To determine whether bacteria had been reduced, the above test was repeated but with some changes. The stainless steel was coated with 4MED – the hydrophobic, antimicrobial coating developed by Nano Hygiene Coatings. Antimicrobial activity was determined after the final soiling/cleaning event. A cell suspension of E Coli was held in intimate contact with each test piece for 24 hours at 35°C and tested according to the method described in ISO 22196.
The results revealed that biological-significant activity had occurred on the 4MED coated sample, with the bacterial population declining by four orders of magnitude in 24 hours: an effective kill rate of 99.99%. Over the same time period, bacterial populations had declined by 0.5 of a magnitude on the uncoated stainless steel.
Tests supporting the claims of any antimicrobial coating should be based on realistic exposure scenarios. That is to say, undertaken in the conditions that they will be used, or simulating those conditions. 4MED has been tested by an independent laboratory, simulating the effect of a surface being splashed by several contaminants: firstly by a splash of contaminated water, and secondly by a splash of contaminated animal/body fluid.
Both tests were undertaken with a sample coated with 4MED, and a sample coated with a hydrophobic coating but without antimicrobial functionality. For the contaminated water test, a suspension of E Coli was prepared using the method described in ISO 22196, standard but in sterile distilled water containing no nutrient broth. For the contaminated animal fluid test, an E Coli inoculum was prepared in a vegetable oil/bovine serum albumin (BSA) solution (oil/protein solution).
Results showed that 4MED achieves a fast rate of kill of the bacterial population, resulting in a reduction of ca 2.5 orders of magnitude in three hours and a reduction to below the limit of detection in six hours. The Oil/Protein test results showed that the bacterial population declined by ca 0.5 orders of magnitude within 12 hours and a statistically significant 2.5 orders of magnitude in 24 hours – a kill rate of over 99%. The presence of protein-rich soiling agents has slowed down the antimicrobial coating, yet not inhibited it.
These results are best seen graphically, so [please do see the gallery associated with this article]. The contaminated water tests have also been conducted on other metal substrates, including chrome plate and aluminium with similar results: kill rates of over 99% in 3-6 hours.
Longevity and durability
An antimicrobial coating that acts quickly and is effective against contaminated water and heavy soiling splashes has positive benefits, but what of its longevity and durability? To determine how 4MED performs under these circumstances, a 4MED-coated substrate was artificially aged and the antimicrobial efficacy subsequently tested.
Test samples were produced using sterile distilled water contaminated with E Coli. The samples were processed in a dishwasher at 40ºC with no detergent (13 litres per cycle). Sampling points were at 60 dishwash cycles and 120 dishwash cycles.
The results showed that the 60 and 120 dishwash cycles did not have any statistically significant impact on the performance of 4MED antimicrobial efficacy. The bacterial populations were reduced by four orders of magnitude following six hours’ contact to below the limit of detection in 24 hours. 4MED coated surfaces showed a statistically significant difference from the populations exposed to the hydrophobic, non-antimicrobial coating. The fastest kill rate is in the first three hours.
Dirt and organic deposits can build up on surfaces, severely impacting the appearance and making them visually unattractive and unappealing. Repeated washing and cleaning causes further deterioration of the surface appearance. Coated hydrophobic/oleophobic surfaces, however, have little or no build-up of soil, which makes them an easy-clean solution.
Combining the hydrophobic/oleophobic properties with the antimicrobial functionality of 4MED produces synergistic benefits. By testing under simulated real-life conditions, the claims should satisfy the increasing demand of the authorities for testing under realistic exposure scenarios. 4MED has shown that it’s robust and durable. It acts quickly and is effective even after artificial ageing.
The implications for improved cleaning and hygiene strategies are clear. 4MED makes the cleaning job easier. It can have a direct impact on the costs associated with the cleaning job, reducing the growth of bacteria and contributing to the lowering of the risks associated with their harmful effects.
Allen Chasteauneuf is Director of Nano Hygiene Coatings Ltd, a UK-based developer of high-performance coatings derived from nano chemical technology.
© FoodBev Media Ltd 2019
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