Solid Lipid Nanoparticles: Effect of Carrier Oil and Emulsifier Type on Phase Behavior and Physical Stability

The impact of surfactant type and carrier oil type on the phase behavior and physical stability of emulsified tripalmitin was investigated. Solid lipid nanoparticles (SLNs) were prepared by homogenizing lipid and aqueous phases at a temperature (≈80 °C) above the melting point of tripalmitin, and then cooling the resulting oil-in-water emulsion to induce lipid droplet crystallization. When stored at 37 °C, tripalmitin particles had good long-term stability (d < 150 nm) when coated with Tween 20, but were prone to aggregation and gelation when coated with modified starch (MS). Conversely, when stored at ≤20 °C tripalmitin particles coated by MS were more stable to aggregation/gelation than those coated by Tween 20. Blending tripalmitin with low melting point lipids (either medium chain triglycerides or orange oil) prior to homogenization led to a considerable alteration in the SLN phase behavior and stability. DSC measurements indicated that the presence of the carrier oils reduced the crystallization temperature, melting temperature, and melting enthalpy of tripalmitin. In addition, the carrier oils improved the stability of SLNs to particle aggregation and gelation, although some particle coalescence still occurred. These results have important implications for formulating colloidal delivery systems for utilization within the food and other industries.