Studies on the Relative Bacterial Cleanability of Milk-Contact Surfaces

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Abstract
Comparisons of the removal of Phosphorous32[long dash]labeled Escherichia coli A.T.C.C. no. 11229 and Micrococcus pyogenes var. aureus A.T.C.C. no. 6538, dried down in homogenized whole milk and 0.85% saline menstrums on a variety of metallic alloys, plastics and glasses, possessing diverse surface finishes, were made utilizing radiological (geiger-counting and X-ray autoradiography) and direct agar submersion plate techniques. Statistical analysis of the data at the 5% probability level indicated that bacterial removal was most readily effected from highly polished, non-porous surfaces, followed closely by finely ground and/or smoothly molded surfaces. Cold rolled, abraded, blasted and porous surface were most difficult to clean. Root Mean Square (R.M.S.) surface profile measurements alone were inadequate as guides in estimating the soil-retention capacity of a surface. Chemical inertness and good wettability were significant factors contributing to ease of removal of the test organisms. Multiple soiling resulted in a highly significant increase in bacterial retention. The radiological counting technique exhibited greater reliability and reproducibility than the direct agar submersion plate technique.

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