In vitro studies of adsorption of milk proteins onto tooth enamel

The aim of this investigation was to study in vitro adsorption of milk proteins onto tooth enamel. In vitro “milk protein pellicles” were formed on enamel specimens incubated in fluid milk products: skimmed milk (pH 6.7), acidified skimmed milk (pH 4.2), yoghurt and neutralized yoghurt (pH 6.7). The enamel specimens were used as such or pre-incubated in saliva. The “milk pellicles” were desorbed from enamel surfaces, and proteins separated by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Proteins were identified by their pattern of migration in SDS-PAGE or by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) fingerprinting. Neutral “milk protein pellicles” (skimmed milk and neutralized yoghurt) mainly consisted of caseins. At pH values close to their isoelectric point, caseins remained unabsorbed, and lactoferrin and bovine serum albumin were the most abundant protein species in the acidified “skimmed milk pellicle”. Virtually no proteins in yoghurt were able to adsorb onto enamel. Pre-incubation of enamel specimens in saliva did not inhibit or affect “milk pellicle” formation indicating that in vivo adsorption of milk proteins may occur on tooth surfaces in the oral cavity and have implications in oral hygiene.