Removal kinetics of Bacillus cereus spores from a stainless steel surface exposed to constant shear stress 2.: Removal kinetics mode influence of adhesion conditions

In the food industries, the efficiency of food-contact surface cleaning and disinfection procedures is of prime importance to ensure the bacteriological quality and safety of the products. Hydrodynamic removal kinetics of Bacillus cereus spores adhering to a stainless steel surface was studied as a function of attachment medium and surface hydrophobicity. The method was based on the use of a controlled shear rate viscometer. The well-known enhancing effect of hydrophobic surfaces on soil adhesion was clearly observed. Conversely, the presence of macromolecules in the attachment medium was found to favor spore detachment. Spore removal kinetics were modelled by a simple three-parameter hyperbolic tangent model. The influence of both the adhesion medium and surface hydrophobicity on the predicted values of spore spontaneous detachment, residual adhering spores and relaxation time, a parameter directly linked to the removal rate, were assessed by analysis of variance. Experimental spore removal kinetics were then predicted as functions of attachment medium and surface hydrophobicity, with a 15% relative error. In the conditions tested, lowering the adhesion forces between spores and surface was found to be necessary to remove more than 1 log within 1.5 h shearing at 28 Pa under a laminar flow regime. A clear definition of the "acceptable cleanliness level" concept appears to be necessary prior to any attempt at CIP procedure optimization.