Effects of Residual Milk Components on the Removability of Spores from Solid Surfaces

Abstract

Bacterial spores attached to the surfaces of food processing equipment may lead to contamination of food to be processed. In this study, spores of Geobacillus stearothermophilus and Bacillus subtilis were attached to stainless steel (SS) and polypropylene (PP) surfaces by drying with milk, and then subjected to rinsing in water with agitation to evaluate the residual fraction of spores as a measure of their removability. Three types of milk products with different fat contents were found to give low residual fractions of spores with no significant differences. However, dilution of milk with water increased the residual fraction of spores. To identify factors affecting the removability of spores, rinsing experiments were performed for spores attached by drying with whey or lactose solutions of different concentrations. The residual fraction of spores after rinsing decreased with increasing whey concentration. However, the increase in lactose concentration gave no significant effect; approximately 90% of spores remained on SS and PP surfaces after water rinsing irrespective of lactose concentration. These results indicate that whey protein is a factor reducing adhesive interaction between spores and solid surfaces.