Lefèvre Thierry, Subirade Muriel
Institut de recherche sur les nutraceutiques et les aliments fonctionnels, Centre de recherches en Sciences et Technologie du Lait, Faculté des sciences de l'agriculture et de l'alimentation, Université Laval, Sainte-Foy, Québec, G1K 7P4 Canada.
J Colloid Interface Sci. 2003 Jul 1;263(1):59-67. doi: 10.1016/s0021-9797(03)00252-2.
Oil-in-water emulsions stabilized with beta-lactoglobulin (beta-lg) were made using a homogenizer or a high-speed blender. The protein was studied by Fourier transform infrared (FTIR) spectroscopy in the raw emulsion, in the bulk phase, and at the interface, as a function of pH, oil content, and homogenizing pressure. Results show that the amount of adsorbed protein varies with the available interfacial area. The protein that remains in the aqueous phase exhibit no spectral change, which suggests that homogenization causes no conformational modification or reversible ones. Strong and irreversible changes were observed in the adsorbed protein. Our findings reveal the formation of intermolecular antiparallel beta-sheets upon adsorption due to the protein self-aggregation. As deduced from transmission electronic microscopy, this surface aggregation leads to the formation of continuous and homogeneous membranes coating the globules. The structure of the adsorbed proteins is unaffected by the homogenizing pressures used in our study and slightly modified by the pH. FTIR spectroscopy allows to characterize the type of aggregates formed at the interface. An analysis of the spectra of beta-lg heat-induced gels shows that the aggregates at the interface are very close at a molecular scale to those that constitute particulate gels near the protein's isoelectric point. Since the type of aggregates is similar when the emulsion water phase is pure D(2)O and D(2)O at pD 4.4, the interface not only seems to induce aggregation, but seems to determine the type of aggregation as well. The mechanism that drives the formation of particulate aggregates (rather than fine-stranded ones) may reside in strong protein-protein interactions that are promoted by adverse oil-protein interactions.
使用均质器或高速搅拌机制备了用β-乳球蛋白（β-lg）稳定的水包油乳液。通过傅里叶变换红外（FTIR）光谱研究了该蛋白质在原始乳液、本体相和界面处随pH值、油含量和均质压力的变化情况。结果表明，吸附蛋白质的量随可用界面面积而变化。留在水相中的蛋白质没有光谱变化，这表明均质化不会引起构象修饰或可逆的构象变化。在吸附的蛋白质中观察到了强烈且不可逆的变化。我们的研究结果揭示了由于蛋白质自聚集，吸附时分子间反平行β-折叠的形成。从透射电子显微镜推断，这种表面聚集导致形成覆盖小球的连续且均匀的膜。吸附蛋白质的结构不受我们研究中使用的均质压力的影响，而受pH值的影响较小。FTIR光谱可以表征在界面处形成的聚集体类型。对β-lg热诱导凝胶光谱的分析表明，界面处的聚集体在分子尺度上与蛋白质等电点附近构成颗粒凝胶的聚集体非常接近。由于当乳液水相为纯D(2)O和pD 4.4的D(2)O时聚集体类型相似，界面不仅似乎诱导聚集，而且似乎也决定聚集类型。驱动颗粒聚集体（而非细链聚集体）形成的机制可能在于由不利的油-蛋白质相互作用促进的强蛋白质-蛋白质相互作用。
