Effect of distribution of solid and liquid lipid domains on transport of free radicals in nanostructured lipid carriers

•Effect of solid and liquid lipid on distribution of encapsulant in NLC was studied.•In NLC with less liquid lipid, encapsulant was localized in liquid lipid regions.•Homogenous distribution of encapsulant was found in NLCs with more liquid lipid.•Uniform distribution of the encapsulant reduced peroxyl radical transport rate in NLC.•100% liquid emulsion may be better at protecting encapsulated material than NLC.

Peroxyl radical sensitive fluorescent dye (BODIPY 665/676) encapsulated nanostructured lipid carriers (NLCs) were prepared by blending solid (eicosane) and liquid (glyceryl trioctanoate) lipid in various proportions (10:90, 30:70, 50:50, 100:0 liquid: solid). Peroxyl radical transport rate was measured by adding 20 mmol/l 2,2′-azobis-2-methyl-propanimidamide, dihydrochloride in the aqueous phase. Fluorescence imaging of NLCs revealed that fluorescent dye was distributed in the liquid lipid regions of 10 and 30% NLCs. However, 50% NLC resembled NLCs with 100% liquid lipid in that, little or no solid domains were observed and the dye was more or less uniformly distributed. Peroxyl radical transport was in the order, 100% < 50% <30% < 10% NLCs. More uniform distribution of the encapsulant possibly reduced the effective peroxyl radical transport rate, particularly when solid domains were present in the core of NLCs. Thus, 100% liquid lipid emulsions may be better than NLCs in improving the oxidative stability of the encapsulant.