Sesame oil is one of the herbal oil with high antioxidant content and medicinal applications. It has hydrophobic property which causes low absorbance as oral administration and skin intention. Changing the normal form of this compound to a hydrophilic structure with small particle size can enhance its effectiveness. Microemulsion system is a suitable form for this oil delivery. The aim of this study is preparation of a microemulsion containing sesame oil and investigation the effect of various co-surtfactants from alcoholic groups. Tween 80 was selected as surfactant. Ethanol, ethylene glycol, propylene glycol and glycerol were separately used as co-surfactant. Four various surfactant/co-surfactant ratios (1:1, 2:1, 4:1 and 6:1) were investigated for preparation of microemulsion. Pseudo-ternary phase diagram was used to determine the microemulsion area. Samples containing the higher oil content were selected for physical properties evaluations as the particle size, electrical conductivity and stability. The microemulsion areas in pseudo-ternary phase diagrams in the order of higher oil content were arranged as glycerol> ethylene glycol> propylene glycol> ethanol. The best surfactant to co-surfactant ratios was 4:1 for preparation of microemulsion. The particle size of the prepared samples are estimated around 12-65 nm. These results indicate that the microemulsion containing sesame oil, Tween 80 as surfactant and glycerol as co-surfactant produces more stable microemulsion which is appropriate for topical and oral delivery.

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