Interactions of phenolic acid derivatives with interfacial proteins and their impact on emulsion stability

Abstract

Processed foods are often emulsions, which are thermodynamically unstable systems. Proteins such as β-lactoglobulin (β-Lg) can stabilize the oil-water interface in emulsions due to their amphiphilic, film-forming, and electrostatic properties. They initially adsorb at the interface and undergo conformational changes. At the molecular level of an emulsion, intermolecular interactions between interfacial proteins enable the formation of a viscoelastic interfacial film. This, along with electrostatic effects, stabilizes the emulsion at the technofunctional level, resulting in both physical and chemical emulsion stability.

In food-based emulsions, proteins also interact with other components such as phenolic compounds. These interactions can compete with the intermolecular protein interactions within the interfacial film and influence the protein conformation, leading to changes in emulsion stability. However, studies show that these interactions can either increase or decrease the physical and chemical stability of an emulsion. In fact, studies focusing on interactions between phenolic compounds and proteins in aqueous environments indicate that these interactions are significantly affected by intrinsic factors, and the ambient conditions which could explain these opposing findings. Intrinsic factors primarily include the structural properties of the phenolic compounds and proteins, while ambient conditions describe parameters such as the pH. For emulsion systems, it is not yet systematically understood how these factors affect the interactions between phenolic compounds and interfacial proteins at the molecular level and how the changes reflect at the technofunctional level.

This thesis aimed at investigating the effects of the factors interaction location, pH, and chemical structure of phenolic compounds on the interactions with β-Lg at the molecular level and to characterize their impact on the emulsion stability at the technofunctional level. The interaction location in the emulsion was varied because β-Lg exists in a globular conformation in the aqueous phase before adsorption and then partially unfolds at the interface, affecting protein conformation and sterically accessible binding sites. The pH influences the protonation degree of molecules and thus, the electrostatic effects, which in turn affect the interactions between phenolic compounds and β-Lg at the interface. The chemical structure of phenolic compounds influences their partitioning behavior between oil, interface, and water, whereby phenolic compounds can interact with the interfacial protein from either the oil phase or the aqueous phase.