Conformational Changes of 伪-Lactalbumin Adsorbed at Oil鈥揥ater Interfaces: Interplay between Protein Structure and Emulsion Stability

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• 作者：Jiali Zhai ; S酶ren V. Hoffmann ; Li Day ; Tzong-Hsien Lee ; Mary Ann Augustin ; Marie-Isabel Aguilar ; Tim J. Wooster
• 刊名：Langmuir
• 出版年：2012
• 出版时间：February 7, 2012
• 年：2012
• 卷：28
• 期：5
• 页码：2357-2367
• 全文大小：468K
• 年卷期：v.28,no.5(February 7, 2012)
• ISSN：1520-5827

文摘

The conformation and structural dimensions of 伪-lactalbumin (伪-La) both in solution and adsorbed at oil鈥搘ater interfaces of emulsions were investigated using synchrotron radiation circular dichroism (SRCD) spectroscopy, front-face tryptophan fluorescence (FFTF) spectroscopy, and dual polarization interferometry (DPI). The near-UV SRCD and the FFTF results demonstrated that the hydrophobic environment of the aromatic residues located in the hydrophobic core of native 伪-La was significantly altered upon adsorption, indicating the unfolding of the hydrophobic core of 伪-La upon adsorption. The far-UV SRCD results showed that adsorption of 伪-La at oil鈥搘ater interfaces created a new non-native secondary structure that was more stable to thermally induced conformational changes. Specifically, the 伪-helical conformation increased from 29.9% in solution to 45.8% at the tricaprylin鈥搘ater interface and to 58.5% at the hexadecane鈥搘ater interface. However, the 尾-sheet structure decreased from 18.0% in solution to less than 10% at both oil鈥搘ater interfaces. The DPI study showed that adsorption of 伪-La to a hydrophobic C18鈥搘ater surface caused a change in the dimensions of 伪-La from the native globule-like shape (2.5鈥?.7 nm) to a compact/dense layer approximately 1.1 nm thick. Analysis of the colloidal stability of 伪-La stabilized emulsions showed that these emulsions were physically stable against droplet flocculation at elevated temperatures both in the absence and in the presence of 120 mM NaCl. In the absence of salt, the thermal stability of emulsions was due to the strong electrostatic repulsion provided by the adsorbed 伪-La layer, which was formed after the adsorption and structural rearrangement. In the presence of salt, although the electrostatic repulsion was reduced via electrostatic screening, heating did not induce strong and permanent droplet flocculation. The thermal stability of 伪-La stabilized emulsions in the presence of salt is a combined effect of the electrostatic repulsion and the lack of covalent disulfide interchange reactions. This study reports new information on the secondary and tertiary structural changes of 伪-La upon adsorption to oil鈥搘ater interfaces. It also presents new results on the physical stability of 伪-La stabilized emulsions during heating and at moderate ionic strength (120 mM NaCl). The results broaden our understanding of the factors controlling protein structural change at emulsion interfaces and how this affects emulsion stability.