Food grade microemulsion systems: Sunflower oil/castor oil derivative-ethanol/water. Rheological and physicochemical analysis

Microemulsions are thermodynamically stable systems that have attracted considerable attention in the food industry as delivery systems for many hydrophobic nutrients. These spontaneous systems are highly dependent on ingredients and composition. In this work phase diagrams were constructed using two surfactants (Kolliphor RH40 and ELP), water, sunflower oil, and ethanol as cosurfactant, evaluating their physicochemical properties. Stability of the systems was studied at 25 and 60 °C, monitoring turbidity at 550 nm for over a month to identify the microemulsion region. Conductivity was measured to classify between water-in-oil and oil-in-water microemulsions. The phase diagram constructed with Kolliphor RH40 exhibited a larger microemulsion area than that formulated with Kolliphor ELP. All formulations showed a monomodal droplet size distribution with low polydispersity index (<0.30) and a mean droplet size below 20 nm. Systems with higher water content presented a Newtonian behavior; increasing the dispersed phase content produced a weak gel-like structure with pseudoplastic behavior under flow conditions that was satisfactorily modeled to obtain structural parameters.