Protein adsorption at gas-liquid interfaces: Mechanism and applications

蛋白质与界面相互作用的能力是它们的本性。多年来，这种能力已经被用于从发酵到产品分离和配方的工艺技术。虽然蛋白质的表面活性是已知的，但由于缺乏对分子的了解，这种性质不能直接用于设计过程。该项目的目的是通过了解蛋白质吸附过程中的潜在分子过程，预测蛋白质在各种操作条件下的性能，以设计宏观世界的过程，即生产过程。泡沫分离是一种简单、温和的浓缩和选择性分离蛋白质的分离过程，它利用蛋白质在气液界面上的吸附能力作为分离的驱动力。为了有效地利用这种分离性能，吸附过程需要在分子水平上被理解，并且应该在宏观上被描述。为了实现这一点，需要标准化对蛋白质性质的估计，如表面电荷密度、疏水性和三级结构的灵活性，这些性质影响表面活性。此外，蛋白质应该根据这些蛋白质的性质进行分类。作为下一步，应研究热、化学和机械应力对表面活性蛋白质性质的影响。泡沫分离实验测定了上述蛋白质类的表面活性，考察了不同操作条件对分离性能、泡沫和蛋白质稳定性的影响，以便在宏观水平上描述吸附过程。为了阐明吸附的分子机理，采用红外反射吸收光谱等技术实时观察吸附过程，采用表面压力曲线估算吸附动力学，用X射线反射仪分析吸附层。此外，还利用圆二色谱和红外光谱确定了可逆或不可逆的结构变化。利用所采用的方法和技术，将有可能在分子水平上解释各种化学和热参数的影响、由于机械和热应力引起的蛋白质的结构变化以及蛋白质与界面的相互作用。这些影响在宏观水平上的量化能够使工艺的发展，无论是操作条件、设备设计还是选择性蛋白质工程，都能获得所需的蛋白质发泡功能。

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.