<![CDATA[Vanilla fragrance oil has high lipophilicity and volatility, making it difficult to formulate in water-based cosmetic products without the use of alcohol solvents. This study aimed to determine the effect of stirring speed, stirring time, and solvent acidity (pH) on the characteristics of vanilla fragrance oil microemulsion, and to determine its optimal conditions using Response Surface Methodology (RSM) with a Box-Behnken Design (BBD). The microemulsion formulation used a mixture of nonionic surfactants consisting of Tween 20, Tween 80, and Span 80. The optimized factors included stirring speed (500-700 rpm), stirring time (3-5 minutes), and solvent pH (4.5-6.5). The results showed that solvent pH had the most dominant and highly significant effect (p < 0.01) on the transmittance percentage, followed by stirring time (p < 0.05). The optimal conditions for the microemulsion preparation were achieved at a stirring speed of 500 rpm, a stirring time of 3.35 minutes, and a pH of 5,01. Model validation demonstrated excellent accuracy with an error of 0.20%. Under these optimal conditions, the produced microemulsion had a transmittance value of 97.6 ± 0.058% after 24 hours of incubation and 97.6 ± 0.129% after centrifugation. The final product exhibited a particle size of 12.24±3.276 nm. Furthermore, the microemulsion formulation met the quality standards for eau de cologne (SNI 16-4949-1998), with a specific gravity of 1.05 ± 0.0005 g/mL and microbial contamination of 1.50 × 10³ ± 0.58 × 10³ colonies/mL.]]>
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