Removal of Bacillus spores from stainless steel pipes by flow foam: Effect of the foam quality and velocity

Food industry cleaning operations must efficiently mitigate any risk of remaining unwanted contamination without consuming large amounts of water, chemicals and energy. This study's originality was in analysing the capacity of flowing foams to remove Bacillus spores from stainless steel surfaces. A set-up was designed to allow the formation of wet foams to flow under three differing regimes: bubble-size rearrangement was observed at the wall with increased velocity, thus reducing cleaning efficiency. Foam at 50% air/water and low velocities permitted a 2 log removal of B. amyloliquefaciens spores, which is comparable to similar CIP conditions. Removal kinetics were modelled showing potentially very high constant rates at the start of cleaning. Such efficient cleaning was related to the local high wall shear stress fluctuations and to the capillary forces (low velocities, favorable bubble-size repartition and to the hydrophilicity of bacteria spores).