Recently, there have been reports on the biological influences of refined material, e.g., the antibacterial action, promotion of mammalian cell growth for medical equipment usage. We investigated the effect of the controlling grain size of austenitic stainless steel on microorganism adhesion, using familiar organisms, i.e., lactic acid bacteria in yogurt as gram positive bacteria and dry yeast used in bread making as a fungus. The results suggest that the adhesion of lactic acid bacteria is reduced and the adhesion of yeast is promoted when the grain size is of nanometer order. In contrast, the opposite outcome is obtained when the grain size is of micrometer order, particularly larger than 3 µm. Note that the optimal condition of the contact material grain size is different for each organism, then this phenomenon enables us select grain size in accordance with the desired purpose, e.g., fermentation.
