Physicochemical and Microstructural Stability of Food-Grade Olive Oil Nanoemulsions Prepared by Low-Energy Emulsification

Abstract

Olive oil attributes to innumerable health benefits due to presence of minor constituents including triterpenic acids and phenolics, as well as monounsaturated fatty acids (MUFA). Its utilization is limited due to poor aqueous solubility hence it requires an appropriate colloidal delivery system. The formation of oil-in-water nanoemulsion may improve its solubility by producing small size nano droplets with the help emulsion phase inversion approach (low energy emulsification technique). Electrical conductivity and rheological study confirmed phase inversion in the nanoemulsion preparation. A total of 18 nanoemulsion samples were prepared with olive oil at different concentrations (0.5, 1, and 2%), surfactant-oil-ratio (SOR) (1, 2) and mixing speed (500, 1000 and 1500 rpm). All the nanoemulsions were stable to phase separation. Formulation viz. olive oil (2%), SOR 2 and mixing speed of 1500 rpm were obtained as the best optimized condition to produce smallest droplet size and polydispersity index (PDI). The nanoemulsion developed with the optimized formulation was subjected to environmental stress conditions commonly used in food processing operations (heat treatment: 65, 95, 121°C; pH: 1, 3, 7; NaCl concentration: 0.1, 0.5, 1M). Olive oil nanoemulsion was found stable to in these stress environments. Transmission electron microscope (TEM) study observed less increase in the droplet growth during one month storage of nanoemulsion at 4°C indicating better stability of the emulsion during storage.