Studies on the Relative Bacterial Cleanability of Milk-Contact Surfaces

These studies are concerned with the removal of bacteria, deposited with various soils, on milk-contact surfaces. The bacteria were labeled with Phosphorus:"-', incorporated into test soils, dried down with the soils upon various milk-contact surfaces under highly reproducible conditions, removed by a standard cleaning procedure, and assayed by the agar-submersion, Oeiger-counting, and autoradiographic techniques. The data so derived were tested for significance by an Analysis of Variance, and grouped by the Duncan Multiple Range Test. The results show statistically significant differences i'n clean~lbility, between different surface finishes applied to a given material and between different materials having comparable finishes. Organisms suspended in a homogenized whole milk soil were much more easily removed from the surfaces studied than organisms suspended in an 0.85% saline solution. Multiple soiling and washing of a .~urface results in a general increase in the number of bacteria retained by a surface. Brushing was found to be effective in cleaning smooth polished, grouud, and molded surfaees, and relatively ineffective in removing bacteria entrapped in the surface features of cold rolled, abraded, blasted, and porous surfaces.