Microbiological and chemical analyses of stainless steel and ceramics subjected to repeated soiling and cleaning treatments

Verran, Joanna, Boyd, Robert D., Hall, Karen and West, Robin (2001) Microbiological and chemical analyses of stainless steel and ceramics subjected to repeated soiling and cleaning treatments. Journal of food protection, 64 (9). pp. 1377-1387. ISSN 0362-028X

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Abstract

Stainless steel and ceramic surfaces were subjected to repeated soiling and cleaning procedures, using a milk powder soil inoculated with Pseudomonas aeruginosa and Staphylococcus aureus, followed by spraying with water with or without 0.1% (vol/vol) nonionic detergent. Test surfaces were removed after 1, 5, 10, and 20 soiling-cleaning cycles and were analyzed for attached microorganisms (total viable count of bacteria removed by swabbing and percentage of coverage of cells plus soil stained with acridine orange). Surfaces were additionally examined using a range of analytical techniques: X-ray photoelectron spectroscopy (XPS), dynamic and imaging secondary ion mass spectroscopy (SIMS), and time-of-flight SIMS. Both microbiological and chemical analyses revealed an accumulation of material over the cycles to a maximum level. Surfaces were conditioned rapidly to saturation with organic material within one cycle (XPS), whereas fouling by microorganisms was less rapid (five cycles). Cleaning with detergent tended to retard the cumulative fouling process when compared with spray cleaning using water alone. The methods described provide a more realistic scenario for testing the cleanability of surfaces routinely found in food processing locations and for screening novel cleaning regimens and/or surface materials. The analytical techniques provide additional information on the kinetics of soiling, which complement the more familiar microbiological methods.