Stabilization of Phase Inversion Temperature Nanoemulsions by Surfactant Displacement

Abstract

Nanoemulsions are finding increasing utilization in the food and beverage industry to encapsulate and protect lipophilic functional components. Low-intensity methods, such as the phase inversion temperature (PIT) approach, are of particular interest for forming food-grade nanoemulsions because of their ease of formation and relatively low energy costs. Nevertheless, this type of emulsion tends to be highly unstable to droplet coalescence after preparation. In this study, we develop a potential solution to this problem using model water/surfactant (Brij 30, C(12)E(4))/oil (tetradecane) systems. The PIT and system morphology were determined by monitoring the temperature dependence of the electrical conductivity, turbidity, and microstructure of the emulsions. Nanoemulsions were formed by holding water/surfactant/oil mixtures at their PIT and then rapidly cooling them. The influence of storage temperature on emulsion stability was investigated, which indicated that the optimum temperature (13 degrees C) was about 27 degrees C lower than the PIT (approximately 40 degrees C). Higher storage temperatures resulted in an increase in droplet growth rate due to coalescence, while lower temperatures led to gelation. Nanoemulsions that were relatively stable to coalescence could be formed at ambient temperatures by adding either Tween 80 (0.2 wt %) or SDS (0.1 wt %) to displace the Brij 30 from the droplet surfaces. We propose that these surfactants increase nanoemulsion stability by changing the optimum curvature of the interfacial layer, as well as by increasing the repulsive interactions (steric or electrostatic) between the droplets. This study may lead to a novel approach to create stable nanoemulsion-based delivery systems that are suitable for utilization within the food industry.