Using the surface characterization techniques of quartz
crystal
microbalance with dissipation, atomic force microscopy, and scanning
electron microscopy, the structure of the salivary pellicle was investigated
before and after it was exposed to dairy proteins, including micellar
casein, skim milk, whey protein isolate (WPI), and a mixture of skim
milk and WPI. We have shown that the hydration, viscoelasticity, and
adsorbed proteinaceous mass of a preadsorbed salivary pellicle on
a PDMS surface are greatly affected by the type of dairy protein.
After interaction with whey protein, the preadsorbed saliva pellicle
becomes softer. However, exposure of the saliva pellicle to micellar
casein causes the pellicle to partially collapse, which results in
a thinner and more rigid surface layer. This structure change correlates
with the measured lubrication behavior when the saliva pellicle is
exposed to dairy proteins. While previous studies suggest that whey
protein is the main component in milk to interact with salivary proteins,
our study indicates interactions with casein are more important. The
knowledge gained here provides insights into the mechanisms by which
different components of dairy foods and beverages contribute to mouthfeel
and texture perception, as well as influence oral hygiene.