Manipulation of Adsorption Behaviour at Liquid Interfaces by Changing Protein–Polysaccharide Electrostatic Interactions - Food Colloids: Self-Assembly and Material Science - page 206

of the mixed layers seems to be at least qualitatively the same at air-water and
oil-water interfaces, with respect to both adsorption kinetics and surface dilatat-
ional rheology. Also the surface shear rheology at the oil-water interface would
be expected to depend strongly on mixing ratio and adsorption sequence.
13.5 Concluding Remarks
The carrier-mediated protein adsorption mechanism, as depicted in Figure 1,
provides an opportunity to control adsorption kinetics at air-water and oil-
water interfaces via protein-polysaccharide interactions in the bulk. This is a
new approach offering a variety of parameters to manipulate adsorption
kinetics to liquid interfaces, and presumably therefore to manipulate foam
and emulsion formation. Small changes in ionic strength or pH can change
protein adsorption kinetics by changing the relative amounts of complexed and
free protein or the binding strength. In addition to system properties like ionic
strength and pH, the mechanism can be controlled by molecular parameters
like the charge density of the protein or polysaccharide. The charge distribution
on the protein surface and along the polysaccharide chain is also expected to
play a role, but this needs to be further explored. Moreover, since diffusion of
the complexes plays such a dominant role, the hydrodynamic radius of the
polysaccharide molecules can also affect adsorption kinetics.
Besides adsorption kinetics, also the rheological behaviour of the adsorbed
layers is affected by the mixing ratio, by the protein-polysaccharide-binding
affinity, and consequently by the charge density on the protein and polysaccha-
ride, the pH, and the ionic strength. Furthermore, the sequence of adsorption
of the individual components influences the layer structure and surface rheo-
logical properties. Understanding the mechanism of mixed and sequential
protein + polysaccharide adsorption should be of great value in manipulating
surface rheological properties at both air-water and oil-water interfaces. This
could then help to improve understanding and control of foam and emulsion
stability.
Acknowledgements
The authors thank Jan Benjamins for many valuable discussions and Frouke
Duijzer for performing the surface tension and surface rheological measure-
ments at the oil-water interface.
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