Physicochemical and stability profile of castor oil emulsions stabilized using natural and synthetic emulsifiers

Background: The quality and stability of castor oil emulsions may be influenced by the type and amount of its constituent emulsifiers. To our knowledge, the emulsifying potential of single, double, and triple-emulsifier systems comprising of Tween 20, acacia gum and methyl cellulose have never been compared. The aim of the work was to formulate castor oil emulsions stabilized using natural and/or synthetic emulsifying agents and evaluate their organoleptic, physicochemical, and stability profiles.

Methods: Six types of emulsions were prepared using the spontaneous emulsification method, and characterised in terms of their physical properties; centrifugation analysis, and real-time stability profile at 25 ℃ and 40 ℃ for 90 days.

Results: FT-IR analysis suggested that castor oil was compatible with all the studied emulsifiers. Tween 20-stabilised formulation (F2) and acacia gum/methyl cellulose-based samples (F5) exhibited unacceptable organoleptic attributes and/or physical properties. The physical properties of the remaining castor oil macroemulsions were satisfactory: pH (6.2 to 7.0); electrical conductivity (2253-4557 µS/cm); spreadability (0.7-2.1 cm); oil globule size (2.73-3.74 µm), and creaming index (9-18 %). The emulsions exhibited varying degree of instability over time and with elevated temperatures. The most promising emulsion was acacia gum/methyl cellulose/tween 20-stabilised sample F7: pH: 6.9, electrical conductivity: 4557 µS/cm, spreadability: 1.37 cm, oil globule size: 3.74 µm, creaming index: 9 %, and satisfactory stability profile at 25 °C and 40 °C.

Conclusion: Sample F7 may serve as cream base for dermal and transdermal delivery of active pharmaceutical ingredients intended to treat various local skin problems and systemic diseases.