Correlation between Physico-Chemical Characteristics of Particulated β-Lactoglobulin and Its Behavior at Air/Water and Oil/Water Interfaces

Abstract

It is widely accepted that protein-based particles can efficiently stabilize foams and emulsions. However, it is not fully elucidated which particle properties are decisive for the stabilization of air/water and oil/water interfaces. To unravel this correlation, selected properties of nano-sized soluble β-lactoglobulin particles were changed one at a time. Therefore, particles of (1) variable size but similar zeta potential and degree of cross-linking and (2) similar size but different further properties were produced by heat treatment under a specific combination of pH value and NaCl concentration and then analyzed for their interfacial behavior as well as foaming and emulsifying properties. On the one hand, it was found that the initial phase of protein adsorption at both the air/water and the oil/water interface was mainly influenced by the zeta potential, independent of the particle size. On the other hand, foam stability as resolved from the time-dependent evolution of mean bubble area negatively correlated with disulfide cross-linking, whereas emulsion stability in terms of oil droplet flocculation showed a positive correlation with disulfide cross-linking. In addition, flocculation was more pronounced for larger particles. Concluding from this, foam and emulsion stability are not linked to the same particle properties and, thus, explanatory approaches cannot be used interchangeably.

Technofunctionality of β-Lg and β-Lg Nanosized Particles at Air/Water and Oil/Water Interfaces as a Function of Structural and Surface Characteristics

“…β-Lg Particle Generation, Purification, and Characterization. According to our previous study, 1 the thermal treatment of β-Lg as a function of pH and NaCl concentration in combination with a purification step allows for the formation of highly pure, soluble, nanosized particles with defined zeta potential and degree of disulfide crosslinking. With regard to particle purification aiming at removing the remaining native protein and NaCl, different options can be applied: isoelectric precipitation or membrane filtration.…”

“…Surface and Interfacial Tension. Determination of the surface (σ(t)) as well as interfacial tension (γ(t)) by the pendant drop method was performed with the Drop Shape Analyzer (DSA 100 R, Kruss GmbH, Hamburg, Germany) for a time period of 3600 s, as described by Kurz et al 1 For determination of the interfacial tension, a commercially available sunflower (SF) oil (THOMY, NestleD eutschland AG, Neuss, Germany) or medium-chain triglycerides (MCTs; 70% caprylic acid (C8) and 30% capric acid (C10), Primal State Performance GmbH, Berlin, Germany) were used. The densities of the protein dispersions and the oils were determined by DMA 4100 M (Anton Paar GmbH, Graz, Austria) at 20 °C and were considered for the calculation of the surface and interfacial tension.…”

“…Foam Formation and Stability. Investigation of the foam formation and decay was performed using the Dynamic Foam Analyzer DFA100 (Kruss GmbH, Hamburg, Germany), as described by Kurz et al 1 The evolution of the foam stability was recorded over a time period of 5400 s.…”

“…2,4,5 Thereby, the low diffusion rate resulting from an increased particle size was shown to be compensated by an increased surface hydrophobicity or lower zeta potential. 1,2,4 Overall, however, the specific role of certain protein characteristics such as surface hydrophobicity is still discussed controversially in the literature. While some authors 3,6−8 reported an increase in surface activity and improved foaming and emulsifying properties with increasing surface hydrophobicity, contradictory results were reported by other works.…”

“…Besides, different types of interfaces (i.e., a/w or o/w) require different protein properties to ensure high foam and emulsion stability, respectively. Kurz et al 1 reported that β-Lg particles of large size (120 nm) and high structural flexibility (i.e., a low content of intraparticle disulfide cross-links) were able to effectively stabilize foams, whereas emulsion stability was impaired. It is so far not clear whether, or how, surface hydrophobicity affects the interfacial behavior at different types of interfaces.…”