Changes in β-Lactoglobulin Conformation at the Oil/Water Interface of Emulsions Studied by Synchrotron Radiation Circular Dichroism Spectroscopy

Abstract

The structure of proteins at interfaces is a key factor determining the stability as well as organoleptic properties of food emulsions. While it is widely believed that proteins undergo conformational changes at interfaces, the measurement of these structural changes remains a significant challenge. In this study, the conformational changes of beta-lactoglobulin (beta-Lg) upon adsorption to the interface of hexadecane oil-in-water emulsions were investigated using synchrotron radiation circular dichroism (SRCD) spectroscopy. Far-UV SRCD spectra showed that adsorption of beta-Lg to the O/W interface caused a significant increase in non-native alpha-helix structure, accompanied by a concomitant loss of beta-sheet structure. Near-UV SRCD spectra revealed that a considerable disruption of beta-Lg tertiary structure occurred upon adsorption. Moreover, heat-induced changes to the non-native beta-Lg conformation at the oil/water interface were very small compared to the dramatic loss of beta-Lg secondary structure that occurred during heating in solution, suggesting that the interface has a stabilizing effect on the structure of non-native beta-Lg. Overall, our findings provide insight into the conformational behavior of proteins at oil/water interfaces and demonstrate the applicability of SRCD spectroscopy for measuring the conformation of adsorbed proteins in optically turbid emulsions.

Stability and bioavailability of lutein ester supplements from Tagetes flower prepared under food processing conditions

“…Other studies reported relatively lower values (0.4-0.5 lm) of D [3,2] (Onsaard, Vittayanont, Srigam, & McClements, 2005;Zhai et al, 2010). The concentration of b-lg in these two studies ranged from 0.1 to 0.3% (w/w), being considerably lower than that used in the present study.…”

Complex Molecules at Liquid Interfaces: Insights from Molecular Simulation

“…Recently the development of synchrotron radiation circular dichroism (SRCD) spectroscopy [78] has allowed the quantitative determine of protein secondary structure at oil-water interfaces. This has been applied to a number of proteins at oil-water interfaces, showing that, in general, there is a tendency for the -helical content of proteins to decrease upon interfacial adsorption [30,79], although this is, by no means, a universal phenomenon. In contrast to experimental studies simulation may allow the direct visualisation of protein structure at oil-water interfaces.…”

Effect of pectin adsorption on the hydrophobic binding sites of β-lactoglobulin in solution and in emulsion systems

“…The tertiary structure of bLG, including the inner calyx, collapses upon adsorption of the protein to the interface, as seen by synchrotron circular dichroism (Zhai et al, 2010). The higher retinol RFI observed above pH 6.0 for both systems suggest the signals were mostly related to the intact non-adsorbed bLG as seen in solution.…”

“…Recent studies have shown that upon adsorption of bLG at an O/W interface, substantial changes in the secondary structure occur (Sakuno, Matsumoto, Kawai, Taihei, & Matsumura, 2008;Zhai et al, 2010). The change in bLG can be described as a partial unfolding coupled with surface aggregation, and is expressed by loss of b-sheets and an increase in unordered a-helices.…”