Distribution of Encapsulated Materials in Colloidal Particles and Its Impact on Oxidative Stability of Encapsulated Materials

Abstract

The oxidative stability of encapsulated product is a critical parameter in many products from food to pharmaceutical to cosmetic industries. The overall objective of this study was to correlate differences in the distribution pattern of encapsulated material within solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) with the relative susceptibility of these materials to undergo oxidation. The distribution of an encapsulated lipid soluble dye (Nile Red) in SLNs and NLCs was quantitatively measured using fluorescence imaging. The relative susceptibility of the encapsulated material to react with free radicals generated in the aqueous phase and oxygen from the ambient environment was measured using peroxyl radical and oxygen sensitive fluorescent dyes encapsulated in the lipid phase of colloidal particles respectively. Imaging measurements demonstrate a significant exclusion of the encapsulated dye molecules from the lipid core of SLNs as compared to NLCs. Imaging results also showed significant differences in the intraparticle distribution of encapsulated dye between NLCs containing 1 and 10% liquid lipid. On the basis of these differences in distribution, we hypothesized that the relative susceptibility of encapsulated material to peroxyl radicals and oxygen would be in the order SLNs > 1% NLC > 10% NLC. Measurement of relative susceptibility of peroxyl radical sensitive dye encapsulated in SLNs and NLCs to peroxyl radicals generated in the aqueous phase validated the proposed hypotheses. However, the susceptibility of encapsulated oxygen sensitive dye to ambient oxygen was not significantly different between SLNs and NLCs. The results of this study demonstrate that difference in distribution pattern of encapsulated material within colloidal particles can significantly influence the susceptibility of encapsulated material to react with free radicals. Overall, this study demonstrates a comprehensive approach to characterize the susceptibility of encapsulated materials in colloidal particles to oxidation processes.