Abstract
HypothesisMany traditional or emergent emulsion products contain mixtures of proteins, resulting in complex, non-equilibrated interfacial structures. It is expected that protein displacement at oil-water interfaces depends on the sequence in which proteins are introduced during emulsion preparation, and on its initial interfacial composition. ExperimentsWe produced emulsions with whey, pea or a whey-pea protein blend and added extra protein post-emulsification. The surface load was measured indirectly via the continuous phase, or directly via the creamed phase. The interfacial composition was monitored over a three-day period using SDS-PAGE densitometry. We compared these findings with results obtained using an automated drop tensiometer with bulk-phase exchange to highlight the effect of sequential protein adsorption on interfacial tension and dilatational rheology. FindingsAddition of a second protein increased the surface load; especially pea proteins adsorbed to pre-adsorbed whey proteins, leading to thick interfacial layers. The addition of whey proteins to a pea protein- or whey-pea protein blend-stabilized emulsion led to significant displacement of the pea proteins by β-lactoglobulin. We determined that protein-protein interactions were the driving force for this displacement, rather than a decrease in interfacial tension. These outcomes could be instrumental in defining new strategies for plant-animal protein hybrid products.
Highlights
Proteins are commonly used to stabilize food emulsions
The current study focused on whey-pea protein blend-stabilized emulsions
We found that the whey proteins, and b-lactoglobulin, were able to displace pre-adsorbed pea proteins from the oil-water interface
Summary
Proteins are commonly used to stabilize food emulsions. After adsorption at the oil-water interface, proteins provide steric and electrostatic repulsion that prevents droplets from approaching each other too closely [1]. Displacement of proteins adsorbed at an oil-water interface by surfactants has been studied extensively, for which the orogenic displacement theory has been suggested According to this theory, displacement of a pre-adsorbed protein film starts at a so-called nucleation site where surfactants can adsorb, and displacement proceeds from this site [7]. The predominant adsorption of ovalbumin was attributed to its higher surface activity, and the interaction of ovalbumin and lysozyme in the interfacial region led to the formation of additional layers. This interaction is fascinating, since the proteins did not interact in the bulk: it implies that the protein conformational changes induced by interfacial adsorption are a pre-requisite for the interaction
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