Optimization of Solubilizers Combinations on the Transparent Liquid Soap with the Addition of Peppermint (Mentha piperita L.) and Lavender (Lavandula L.) Oil

Transparent soap usually produced using a synthetic substance. Therefore, the formula optimization of transparent soap must be conducted with natural substances. The essential oils can be used as alternative natural substances and a transparent agent such as peppermint and lavender oil. Furthermore, peppermint and lavender oil have an antibacterial activity which is beneficial for skin health. Therefore, this study aimed to determine the optimum formula mainly the solubilizer of essential oil to produce transparent soap using natural substances with antibacterial activity, especially S. aureus growth. The solubilizers used included ethanol, glycerin, and liquid sugar. The studied responses included transparency, viscosity, pH, and total fatty acids. A Simplex Lattice Design (SLD) method which consisted of 13 formulas was carried out to determine the optimum soap characteristics namely organoleptic, free alkali, specific gravity, foam power, and antibacterial activity. The results showed that the optimum solubilizer formula was 20% liquid sugar, 18% ethanol, and 18% glycerin. The average of transparency, viscosity, pH, and total fatty acids responses were 98,3%, 553,33 cP, 10,04 and 19,85%, respectively. The characteristics of soap were free alkali 0,12 +/- 0.015%, specific gravity 1,161 g/ml, foam power 1,05 +/- 0,050 cm, and growth inhibition zone of S. aureus 10,17 +/- 2,753 mm.