Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia.
Langmuir. 2011 Aug 2;27(15):9227-36. doi: 10.1021/la201483y. Epub 2011 Jul 6.
Understanding the factors that control protein structure and stability at the oil-water interface continues to be a major focus to optimize the formulation of protein-stabilized emulsions. In this study, a combination of synchrotron radiation circular dichroism spectroscopy, front-face fluorescence spectroscopy, and dual polarization interferometry (DPI) was used to characterize the conformation and geometric structure of β-lactoglobulin (β-Lg) upon adsorption to two oil-water interfaces: a hexadecane-water interface and a tricaprylin-water interface. The results show that, upon adsorption to both oil-water interfaces, β-Lg went through a β-sheet to α-helix transition with a corresponding loss of its globular tertiary structure. The degree of conformational change was also a function of the oil phase polarity. The hexadecane oil induced a much higher degree of non-native α-helix compared to the tricaprylin oil. In contrast to the β-Lg conformation in solution, the non-native α-helical-rich conformation of β-Lg at the interface was resistant to further conformational change upon heating. DPI measurements suggest that β-Lg formed a thin dense layer at emulsion droplet surfaces. The effects of high temperature and the presence of salt on these β-Lg emulsions were then investigated by monitoring changes in the ζ-potential and particle size. In the absence of salt, high electrostatic repulsion meant β-Lg-stabilized emulsions were resistant to heating to 90 °C. Adding salt (120 mM NaCl) before or after heating led to emulsion flocculation due to the screening of the electrostatic repulsion between colloidal particles. This study has provided insight into the structural properties of proteins adsorbed at the oil-water interface and has implications in the formulation and production of emulsions stabilized by globular proteins.
了解控制蛋白质在油水界面结构和稳定性的因素仍然是优化蛋白质稳定乳液配方的主要关注点。在这项研究中，结合同步辐射圆二色光谱、正面荧光光谱和双偏振干涉（DPI）来表征β-乳球蛋白（β-Lg）在两种油水界面上的构象和几何结构：十六烷-水界面和三辛酸甘油酯-水界面。结果表明，β-Lg 在吸附到两个油水界面时，经历了β-折叠到α-螺旋的转变，伴随着其球状三级结构的相应损失。构象变化的程度也与油相的极性有关。与三辛酸甘油酯油相比，十六烷油诱导了更高程度的非天然α-螺旋。与溶液中的β-Lg 构象相反，界面处富含非天然α-螺旋的β-Lg 构象在加热时不易进一步发生构象变化。DPI 测量表明，β-Lg 在乳液液滴表面形成了一层薄而致密的层。然后通过监测 ζ-电位和粒径的变化来研究高温和盐对这些β-Lg 乳液的影响。在没有盐的情况下，高静电排斥意味着β-Lg 稳定的乳液能够抵抗加热至 90°C。在加热之前或之后添加盐（120 mM NaCl）会导致乳液絮凝，因为胶体颗粒之间的静电排斥被屏蔽。这项研究深入了解了吸附在油水界面上的蛋白质的结构特性，对球形蛋白质稳定乳液的配方和生产具有重要意义。
