Protein adsorption at gas-liquid interfaces: Mechanism and applications

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The ability of proteins to interact with interfaces is their nature. This ability has been used in process technology from fermentation to product isolation and formulation throughout the years. Although the surface activity of proteins is known, this property cannot be used to design processes directly, due to the lack of the molecular understanding. The aim of the project is to forecast the performance of proteins under various operating conditions to design processes of the macroscopic world, namely production processes, by understanding the underlying molecular processes during protein adsorption. Foam fractionation, an easy and gentle separation process to concentrate and selectively separate proteins, uses the ability of proteins to adsorb at a gas-liquid-interface as the driving force for separation. To utilize this separation property effectively, the adsorption process needs to be understood on molecular level and should be describable in macroscopic terms. To achieve this, the estimation of protein properties like surface charge density, hydrophobicity, and flexibility of the tertiary structure, which influence the surface activity, needs to be standardized. Furthermore, proteins should be classified according to these protein properties. As a next step the evaluation of thermal, chemical and mechanical stress on the surface activity protein properties shall be investigated. Foam fractionation experiments follow to determine the surface activity of the previously defined protein classes as well as to investigate the influence of varying operating conditions on separation performance, foam and protein stability to describe the adsorption process on macroscopic level. To elucidate the molecular mechanism techniques like Infrared-Reflection-Absorption-Spectroscopy to observe the adsorption process in real time, surface pressure curves to estimate adsorption kinetics and X-ray reflectometry to analyze the adsorption layer will be used. In addition, circular dichroism and infrared spectroscopy are applied to determine reversible or irreversible structural changes. With the applied methods and techniques, it will be possible to interpret the influence of various chemical and thermal parameters, structural changes of the protein due to mechanical and thermal stress as well as the protein-interface interaction on molecular level. The quantification of these effects on macroscopic level enables the development of processes, in terms of operating conditions, equipment design or selective protein engineering, to get the desired foamability functions of the proteins.