Foams pose an even greater challenge because they are
intrinsically much less stable than emulsions. The article of
Murray and Ettelaie (pp. 314–320) addresses the issue of the
involvement of adsorbed and non-adsorbed protein nanoparticles in the stabilization and destabilization of aerated
food systems. This topic is important because it has been
recently demonstrated that, whereas a viscoelastic protein
monolayer can retard but not entirely inhibit the shrinkage
of gas bubbles, a layer of irreversibly adsorbed particles can
stop bubble coarsening altogether and so can confer
excellent long-term foam stability. The degree to which
these adsorbed and aggregated particles contribute to the
unique whipping properties of egg white is an intriguing
question, albeit one that remains as yet unresolved. As well
as their stabilizing action, nanoparticles may cause destabilization of foams by bridging between bubble surfaces or
becoming excluded from thin films. Most fundamental
research at air–water interfaces is still concerned with
individual protein molecular adsorption to form monolayers.
There is clearly a need, however, for more work on wellcharacterized systems involving aggregated proteins, since it
is these latter entities that commonly occur in real food
products.