β-Carotene affects aggregation of lentil protein on oil-water interfaces

β-Carotene (BCT) is used as a colorant and a provitamin A source for vitamin A enrichment in food products to enhance product appearance and improve health benefits. It is sensitive to environmental factors such as oxygen and light. This compound can be protected from degradation through emulsion-based encapsulation. The incorporation of BCT in an emulsion-based system may impact the interfacial properties and emulsion stability. The aim was to gain a better understanding of the interfacial behavior of lentil protein (LPI) and investigate how the microstructure at the interface changes when BCT is incorporated in the oil phase.

The interfacial behavior of lentil protein with and without BCT in the oil phase was investigated using interfacial dilatational rheology in the nonlinear viscoelastic regime (NLVE). The nonlinear responses were quantified by using the general stress decomposition (GSD) method. In addition, interfacial shear rheology was studied to further explore the protein microstructure at the oil-water interfaces. The storage stability of emulsions was tested with different BCT concentrations to link with the interfacial rheological results.

The addition of BCT to the oil phase mostly affects the adsorption kinetics of LPI at oil-water interfaces in the later stages and indicates a higher accumulation of LPI at the interface. BCT weakens the stiffness of the interfacial layer formed by LPI in dilatational deformations, and increases the dissipated energy related to surface density changes. Based on these observations, we hypothesize that BCT accelerates the nucleation rate of protein clusters at the interface, while reducing the in-plane interactions between clusters. This process leads to the formation of smaller, yet more numerous, protein clusters. The incorporation of BCT leads to an increase in shear modulus and apparent negative Poisson ratio. While this could indicate auxetic behavior at the interface, we attribute this observation to the transition from an interconnected protein network to a particle glass of smaller protein clusters. In terms of emulsion storage stability, the emulsions enriched with 1000 ppm BCT exhibited larger droplet sizes after long-term storage than those without BCT, suggesting that the weakening of in-plane protein interactions induced by BCT interference may reduce resistance to coalescence.