Fabrication and characterization of nanostructured lipid carriers (NLC) using a plant-based emulsifier: Quillaja saponin

Nanostructured lipid carriers (NLCs) are a type of colloidal delivery system that was developed in the pharmaceutical industry to combine the advantages and eliminate the shortcomings of oil-in-water (O/W) nanoemulsions and solid lipid nanoparticles (SLNs). The hydrophobic core of the particles within NLCs consists of a solidified fat phase with a partially disorganized structure, which inhibits morphological changes and bioactive expulsion. In the present study, we formulated NLCs using a hot-homogenization approach using fully hydrogenated soybean oil (HSO) as the lipid phase and quillaja saponins as a natural surfactant. The NLCs formed had a low viscosity and milky white appearance similar to that of O/W nanoemulsions. The fabrication conditions were optimized, including the number of passes through the microfluidizer, stirring conditions, cooling rate, and emulsifier level. Unlike bulk HSO, the emulsified form had to be supercooled substantially to promote crystallization of the lipid droplets, which was attributed to differences in nucleation behavior. The crystallization temperature decreased with increasing saponin concentration, which was probably because smaller droplets were formed at higher emulsifier levels. For instance, at 3, 6, 9, and 12 wt% saponin, the degree of supercooling was 10, 15, 18, and 18 °C, while the mean particle diameter was 0.82, 0.53, 0.41, and 0.44 μm, respectively. The melting and crystallization behavior of the NLCs was characterized using an optical microscope and differential scanning calorimetry (DSC), while the morphology of the NLCs was characterized using transmission electron microscopy (TEM). This analysis showed that the NLCs contained spherical particles with a crystallization temperature around 31 °C. This information may be useful for formulating NLC from natural ingredients for application in the food and beverage industry.