Formulation and stability of topical water in oil emulsion containing corn silk extract

Purpose: To formulate the water in oil (W/O) emulsion of corn silk (CS) extract and to evaluate its stability at various storage conditions.
Methods: Ethanol CS extract was prepared using maceration (cold) technique. A 4 % CS emulsion was prepared using varying concentrations of liquid paraffin, ABIL EM90 and water. The formulations were kept at 40 ^oC for 28 days and to screen out the less stable formulations. The remaining formulations were further stressed at 50 ^oC to choose the most stable formulation. The optimized formulation was evaluated for physical characteristics including phase separation, rheology and mean droplet size. The physical stability of the formulation was evaluated by monitoring these parameters over a period of 12 weeks at 8, 25, 40 and 40 ^oC, and 75 % RH.
Results: The chosen formulation showed good resistance to phase separation on centrifugation under all storage conditions. Rheological behavior followed non-Newtonian pseudoplastic pattern at various storage conditions. Mean droplet size of freshly prepared formulation was 2.98 ± 1.32 µm and did not show significant (p < 0.05) changes at normal storage conditions (8 and 25 ^oC).
Conclusion: The findings indicate that the developed CS extract W/O emulsion is stable and therefore may be suitable for topical use on skin as an antioxidant preparation.

Keywords
Corn silk; Emulsion; Nonionic surfactant; Rheology; Flow index; Droplet size; Newtonian pseudoplastic