Institute of Food, Nutrition and Health, ETH Zurich, Zurich, Switzerland.
Langmuir. 2012 Aug 28;28(34):12536-43. doi: 10.1021/la3026705. Epub 2012 Aug 15.
Proteins can aggregate as amyloid fibrils under denaturing and destabilizing conditions such as low pH (2) and high temperature (90 °C). Fibrils of β-lactoglobulin are surface active and form adsorption layers at fluid-fluid interfaces. In this study, β-lactoglobulin fibrils were adsorbed at the oil-water interface at pH 2. A shear rheometer with a bicone geometry set up was modified to allow subphase exchange without disrupting the interface, enabling the investigation of rheological properties after adsorption of the fibrils, as a function of time, different pH, and ionic strength conditions. It is shown that an increase in pH (2 to 6) leads to an increase of both the interfacial storage and loss moduli. At the isoelectric point (pH 5-6) of β-lactoglobulin fibrils, the maximum storage and loss moduli are reached. Beyond the isoelectric point, by further increasing the pH, a decrease in viscoelastic properties can be observed. Amplitude sweeps at different pH reveal a weak strain overshoot around the isoelectric point. With increasing ionic strength, the moduli increase without a strain overshoot. The method developed in this study allows in situ subphase exchange during interfacial rheological measurements and the investigation of interfacial ordering.
在变性和失稳条件下，如低 pH 值（2）和高温（90°C）下，蛋白质可以聚集形成淀粉样纤维。β-乳球蛋白的纤维具有表面活性，并在液-液界面形成吸附层。在这项研究中，β-乳球蛋白纤维在 pH 值为 2 时被吸附在油水界面上。一个带有双锥几何形状的剪切流变仪经过改装，允许在不破坏界面的情况下进行亚相交换，从而可以在吸附纤维后，根据时间、不同 pH 值和离子强度条件，研究流变性质。结果表明，pH 值从 2 增加到 6 会导致界面储存模量和损耗模量都增加。在β-乳球蛋白纤维的等电点（pH 5-6）处，达到了最大的储存和损耗模量。超过等电点后，进一步增加 pH 值，可以观察到粘弹性性质的下降。在不同 pH 值下进行的振幅扫描显示，在等电点周围存在弱应变过冲。随着离子强度的增加，模量增加而没有应变过冲。本研究中开发的方法允许在界面流变测量过程中进行原位亚相交换，并研究界面有序性。
