Influence of surface roughness and wettability of stainless steel on soil adhesion, cleanability and microbial inactivation

Stainless steel is a material commonly used in the food industry. Numerous papers therefore have been published dealing with the influence of its characteristics on fouling, cleaning and disinfection. In most cases the authors refer to qualitative and quantitative aspects of the contact surface, e.g., topography. Some of these researchers additionally looked at the qualitative role of surface wettability. However in none of these papers was the analysis extended to identify and quantify a possible combined or synergistic influence of roughness and wettability. To clarify this question the author analyses the data base and results of three existing papers with respect to such a combined influence on soil adhesion, cleanability and microbial inactivation. The analyses show that surface roughness and contact angle in fact are of particular importance: double linear regressions based on both (appropriately converted) independent variables improve the coefficients of correlation to about 0.99, compared to approaches regarding roughness only: 0.76 (adhesion, inactivation) and 0.89 (cleanability). The results also support previous findings that with respect to the interesting surface effects the roughness Rz seems to be a better indicator of the surface topography than the roughness Ra, usually preferred for these kinds of investigations. The new insight can now serve as a guideline for further research on the influence of 'topography and wettability' on hygienic features of stainless steel surfaces for the food industry.