(175e) Adsorption and Protein-Surfactant Interaction At the Air-Water Interface

Adsorption and protein-surfactant interaction at the air-water interface

Kathrin Engelhardt, Wolfgang Peukert, Björn Braunschweig

Institute of Particle Technology

University Erlangen-Nuremberg,Germany

Taste, texture and appearance of foamy dairy products such as mousse or cream are influenced and partially controlled by the interfacial properties of milk proteins and their tendency to form foam stabilizing networks. The stability of aqueous foams is dominated by the molecular composition of the ubiquitous air-water interfaces and the hierarchical structure - from the interface via the complex lamella structure to the macroscopic foam. The relation of adsorption kinetics and competitive behaviour of proteins and surfactants are yet not fully understood, which is caused mainly by the lack of interface sensitive methods.

In this contribution we introduce vibrational sum-frequency generation (SFG) as an inherently interfacial specific probe that that is shown to be a powerful technique to address experimental challenges associated with liquid interfaces. In order to obtain molecular level information with SFG, tunable infrared pulses are combined at the air-water interface with visible pulses of a fixed frequency. The resulting SFG spectra provide a vibrational fingerprint with information on composition and conformation of the interfacial molecular layer¹.

A combination of SFG spectroscopy, surface dilational rheology and foam stability measurements is used to study the adsorption kinetics and interfacial properties of β-Lactoglobulin and its mixtures with ionic and nonionic surfactants such as SDS and hexadecyllactate. The adsorption kinetics of competitive adsorption and displacement reactions of the two species are studied with SFG. The vibrational fingerprint combined with kinetic information on the interaction between β-Lactoglobulin and surfactants provides us with new insights in the adsorption of mixed protein-surfactant systems. The behavior at the interface is correlated with the macroscopic foam stability which changes with increasing surfactant concentration.

[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