Dynamic emulsification and catastrophic phase inversion of lecithin-based emulsions

Abstract

In emulsification phase inversion is induced by several parameters like temperature, salt concentration, fraction of oil or water and energy input. In this work phase inversion of a sunflower oil–lecithin–water emulsion system was induced by the variation of water volume fraction ( f w ), called as catastrophic inversion, in a laboratory scale mixing tank. For this purpose two sets of dynamic emulsification were performed: (i) f w was decreased (0.5–0.1) and (ii) f w was increased (0.1–0.7). Hysteresis in phase inversion under dynamic condition was observed compared to direct emulsification and the degree of hysteresis seemed to depend on how the f w was varied, i.e. 0.5–0.1 or 0.1–0.7. However, inversion point depended on salt concentration which was used as one of the formulation parameters to place an emulsion on formulation-composition map (HLD versus f w ). Such map with the phase equilibrium behavior and colloidal interactions seems to be useful to explain the mechanism of catastrophic phase inversion under dynamic conditions. This study showed also that the dynamic emulsification lead to incorporate higher fraction of the dispersed phase (more than 82% volume) which is not possible with the direct emulsification. Moreover dynamic emulsification can be a useful protocol to prepare stable emulsions with smaller droplets.