Fabrication of double W1/O/W2 nano-emulsions loaded with oleuropein in the internal phase (W1) and evaluation of their release rate

Our main goal was to encapsulate oleuropein within double nano-emulsions stabilized by pectin-whey protein concentrate (WPC) complexes and prepared by sonication. Five independent variables including surfactant (Span) content, WPC and pectin content, ratio of inner to outer phase, and pH were considered along with size of emulsion droplets, zeta potential, and encapsulation efficiency as the dependent variables. Optimum conditions were determined as, 8% WPC, 1.97% pectin, 8.74% Span, 1:4 ratio of inner to outer phase and pH = 6.1. After 28 days storage, double emulsions loaded with oleuropein (260, 520, 780 and 1040 mu g/mL) released approximately 39.9, 40.2, 42.2 and 42.9% of their total content. The results of oleuropein release after 28 days determined by HPLC (40.4%) were consistent with those obtained spectrophotometrically (42.9%). To produce double emulsions with the highest load, samples with 1040 (mu g/mL) oleuropein were produced according to the optimum conditions and a droplet size of 191 nm, zeta potential of -26.8 mV, and encapsulation efficiency of 91% was achieved. SEM results showed particles with smooth, relatively spherical, somewhat asymmetrical surfaces with a size range of 100-200 nm compatible with dynamic light scattering results.