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.

Preparation of nanoemulsions by phase inversion temperature (PIT)

“…In the fast cooling process, the mixture is rapid cooled either by immersing into an ice bath 44,[46][47][48][49] or by diluting with cold water 17,27,34,43,50 . The influences of the formation parameters (i.e., preparation temperature, electrolytes, temperature cycling process and cooling rate) and composition parameters (i.e., oil type and surfactant concentration) have been investigated and reported.…”

“…Since the stability of nanoemulsions is sensitive to the temperature near the PIT, the stability of nanoemulsions could be improved by displacing surfactant with co-surfactants. It was found that adding either Tween 80 or sodium dodecyl sulfate in the poly(oxyethylene)-4-lauryl ether (Brij 30)/ tetradecane nanoemulsions improved nanoemulsion stability by increasing the PIT of the system and increasing the repulsive interactions between the droplets 47 .…”

“…This effect can be attributed to the ability of oil molecule to penetrate between surfactant tails. Short chain hydrocarbon oils can penetrate more easily between the surfactant tails and thus favor a curvature that is closer to planer than long-chain hydrocarbon oil 47 .…”

Extending Emulsion Functionality: Post-Homogenization Modification of Droplet Properties

“…The stability of the emulsions can be improved after formation by displacing the original surfactant from the droplet surfaces using another surfactant. This approach was used to improve the thermal stability of phase inversion temperature (PIT) nanoemulsions [46]. The nanoemulsions were formed from hydrocarbon oil (tetradecane), non-ionic surfactant (Brij 30), and water using the phase inversion temperature method.…”

Tailorable nanocarrier emulsion for drug delivery

“…Particularly, nanoemulsions have been intensively studied for pharmaceutical and food applications (Beck-Broichsitter et al, 2010, Anton et al, 2010, Calderó et al, 2011, Morral-Ruíz et al, 2012, MacHado et al, 2012, Rao and McClements, 2010, Henry et al, 2010, Silva et al, 2012. The term nanoemulsion has been quite widely used, but not with a consistent definition.…”