(595c) Protein Adsorption At the Electrified Air-Water Interface: Effects On Foam Stability

Protein adsorption at the electrified air-water interface: Effects on foam stability

Kathrin Engelhardt, Wolfgang Peukert, Björn Braunschweig

Institute of Particle Technology

University Erlangen-Nuremberg,Germany

The surface chemistry of ions, water molecules and proteins as well as their ability to form stable networks in foams can influence and control macroscopic properties such as the stability of a macroscopic foam. Despite the great importance of protein adsorption at liquid interfaces, a molecular level understanding of proteins and their interactions at aqueous interfaces has been elusive.

Therefore, we have addressed the adsorption of the proteins bovine serum albumin (BSA) and β-lactoglobulin (bLG) at the air−water interface with vibrational sum-frequency generation (SFG) and ellipsometry. SFG provides specific information on the composition and average orientation of interfacial molecules, while complementary information on the adsorbate thickness can be obtained with ellipsometry.

Adsorption of charged proteins at the water surface leads to an electrified interface, pH depending charging and electric field-induced polar ordering of interfacial H₂O and proteins. Varying the bulk pH of protein dilutions changes the intensities of the protein vibrational bands substantially, while dramatic changes in OH stretching bands of interfacial H₂O are simultaneously observed.

These observations are related to the pH dependent charging of BSA and bLG and have allowed us to determine the isoelectric point of BSA and bLG directly at the air-water interface. At a pH near the isoelectric point proteins form an amorphous network of possibly agglomerated proteins, while highly charged proteins form monolayers with strong repulsions. Finally, we provide a direct correlation of the molecular structure of the investigated protein interfaces with foam stability and rheology¹.

[1] Engelhardt, K., Rumpel, A., Walter, J., Dombrowski, J., Kulozik, U., Braunschweig, B., Peukert, W., Protein adsorption at the electrified air–water interface: implications on foam stability, Langmuir 2012, 28, 7780–7787