The effect of photocatalytic coatings on microbial attachment in brewery field tests

Photocatalytic coatings have been reported to improve cleanability of surfaces and reduce bacterial attachment1,2,3. Only field tests, however, will eventually reveal their effect in industrial applications. Field tests cannot replace standardised laboratory tests due to uncontrolled variables and limited number of replicates, but they give valuable additional information. Here we report results from brewery field tests, where test coupons with photocatalytic coatings were mounted onto bottling machines for 18 months. In the brewery field tests, microbial attachment on photocatalytic and antibacterial TiO2+silver coatings was reduced compared to stainless steel for 6 months. The effect of TiO2 without silver was less clear. After 18 months the effect was lost, possibly due to the silica precipitates found on all test surfaces and to dissolving of silver ions. In spite of challenges connected to field tests in industrial environments, we conclude that functional coatings have potential in reducing the attachment of microorganisms at critical sites and facilitating their removal in cleaning operations. Long-term durability of the coatings and elimination of precipitates are questions still to be solved. The possible adverse effects of silver ions in the environment encourage the development of efficient photocatalytic coatings without antimicrobial additives. 1Kühn K P, Chaberny IF, Massholder K, Stickler M, Benz VW, Sonntag H-G & Erdinger L (2003) Disinfection of surfaces by photocatalytic oxidation with titanium dioxide and UVA light. Chemosphere 53: 71-77. 2Raulio M, Pore V, Areva S, Ritala M, Leskelä M, Lindén M, Rosenholm JB, Lounatmaa K & Salkinoja-Salonen MS (2006) Destruction of Deinococcus geothermalis biofilm by photocatalytic ALD and sol-gel TiO2 surfaces. J. Ind. Microbiol. Biotechnol. 33 :261-268. 3Allion A, Merlot M, Boulangé-Petermann L, Archambeau C, Choquet P & Damasse J-M (2007) Thin photocatalytic TiO2 coatings: impact on bioadhesion and cell viability. Plasma Processes Polym. 4: S374-S379.