Correlated XPS, AFM and bacterial adhesion studies on milk and milk proteins adherent to stainless steel

Adhesion of Staphylococcus aureus and Listeria mono‐cytogenes to a stainless steel surface increased as the amount of surface‐adsorbed milk proteins decreased, as indicated by the x‐ray photoelectron spectroscopy (XPS) N Is signal. The iron signal was inversely related to the nitrogen signal, a decrease indicating either thinner surface coverage with protein or increased exposure of the alloy surface. Stainless steel samples were further studied using Tapping Mode™ atomic force microscopy (TM‐AFM) following a number of protein treatments. Both skimmed milk and the individual milk‐protein k‐casein provided AFM images consistent with a high level of surface coverage, confirming the XPS and bacterial adhesion data. Conversely, α‐lactalbumin exhibited sparse coverage as determined by both AFM and XPS analysis. Consequently this protein was less effective at reducing bacterial adhesion to the stainless steel. This study has shown that correlated surface analytical techniques can be successfully applied to inve...