Abstract
Pretreatment of stainless steel (AISI 304 & AISI 316) surfaces with skimmed UHT milk significantly reduced the numbers of attaching Staphylococcus aureus and other Gram positive bacteria, although the same effect was not observed with the Gram negative Pseudomonas fragi and Escherichia coli. Milk constituents with molecular weights below 1000 Daltons did not show the observed effect. Droplet contact angle experiments showed that the stainless steel surface became only marginally more hydrophobic when milk was adsorbed. The attachment of S. aureus onto stainless steel was found to be dependent on the physico-chemical properties of the bacterial surface, the stainless steel surface and of the suspending solution. SDS-polyacrylamide gel electrophoresis showed that proteins are adsorbed onto the stainless steel surface in approximately the same proportions as those in the bulk milk. Of the milk proteins, the caseins were more effective at inhibiting attachment. This was found to be true even when the proteins were used at identical concentrations, rather than in the proportions found naturally in milk, k-Casein was the most effective at inhibiting attachment.