The effect of nanometer dimension topographical features on the hygienic status of stainless steel

Wear of food contact surfaces through abrasion may increase the surface rou ghness and introduce different topographical features. Both of these proper ties may enhance retention of soil and microorganisms and affect the surfac e cleanability. To test this hypothesis, stainless steel surfaces with topo graphical features and surface roughness (Ra) values simulating those of wo rn in-use surfaces were prepared. Surfaces were imaged and Ra values determ ined using atomic force microscopy (AFM). These ranged from 23 to 900 nm. S urfaces were sprayed with standardized cell suspensions of Pseudomonas aeru ginosa or Staphylococcus aureus and allowed to air dry and were then cleane d using a nonionic detergent delivered via a manual linear cleaning device. There was a 2-log reduction in numbers attached after cleaning, but there was no significant difference (P > 0.05) between the cleanability of the su rfaces in terms of the numbers of cells per unit area remaining after clean ing, although cells appeared to be retained within topographical features. Thus, the simulated effect of wear of a hygienic food contact surface did n ot affect its cleanability after a one-off microbiological soiling event, A FM provided hitherto unavailable information on the topography of worn stai nless steel surfaces. In future work, the surfaces will be repeatedly chall enged with an organic soil-microorganism mixture after cleaning events, to provide a more rigorous, realistic test.