Formation and characterization of Listeria innocua biofilm on stainless steel pits

The aims of this research were to observe formations and to characterize biofilm of Listeria innocua on stainless steel 304 pitting holes artificially corroded by electrochemical methods. Pitting holes were classified as small (10-20nm), medium (21-30nm) and large (31-50nm). Cells of L. innocua cultured in liquid milk were grown on the stainless steel at 30 ℃ for 0, 3, 7 and 14 days. Analysis of biofilm formation was carried out with stereo-microscope and scanning electron microscopy (SEM). It was found that biofilm was formed in pitting holes and grains of the stainless steel. The thicker of biofilm formation was observed in the longer of incubation time. The control stainless steel contained indigenous Bacillus spp. cultured in BHI semi-solid media instead of L. innocua indicated Bacillus that survive pasteurization treatment of the milk could be seen in the pitting holes as well. The results of Scanning electron microscopy of this study indicated growth formation and biofilm build up in pitting holes. Therefore, this could be expected and problematic to clean and sanitize of stainless steel surfaces. This work attempts to indicate effective cleaning/sanitizing for removal of biofilm in pits on corroded stainless steel equipment of dairy plants which are important for quality and safety of dairy products.