Optimization of <i>Pickering</i> Emulsions Containing Andiroba Oil ( <i>Carapa guianensis</i> Aubl): Physicochemical Characterization, Experimental Approach, and Rheological Behavior for Topical Use

Amazonian vegetable oils, due to their medicinal properties, have become essential raw materials in the development of pharmaceutical and cosmetic products, with andiroba oil (<i>Carapa guianensis</i> Aubl.) standing out. Classical emulsions, which use conventional emulsifiers, often present stability limitations. In this context, <i>Pickering</i> emulsions stabilized by solid particles emerge as a promising alternative. This study aimed to characterize and optimize <i>Pickering</i> emulsions containing andiroba oil and magnesium aluminum silicate (Veegum). The physicochemical characterization of the oil was performed according to the guidelines of the <i>American Oil Chemists' Society</i>. X-ray diffraction (XRD), size, polydispersity index (PDI) and zeta potential (ZP) analyses of Veegum were performed. For optimization, a Rotational Central Composite Design (RCCD) was used, with analysis of variance (ANOVA) to evaluate the significance of the variables. The results showed that the oil had an acidity index of 8.90 ± 0.13 mequiv KOH·g^-1 and a saponification index of 194 mg KOH/g, indicating the presence of beneficial fatty acids. Fourier transform infrared (FT-IR) analyses confirmed characteristic functional groups. Regarding the XRD of Veegum, peaks characteristic of clay was found, with emphasis on 19.45; 21.68; 25.27°, suggestive of the interlamellar space of the material. For the particle size, a value equal to 1299 nm ± 0.04 was obtained with a PDI of 0.672 ± 0.3, suggestive of aggregation and with a ZP of -38 mV ± 0.02, consistent with the silanol groups of Veegum, which favors the formation of stable dispersions. Out of the 19 initial formulations, three were selected, with emulsion 22 standing out due to its ZP of -40.5 ± 0.8 mV, creaming index of 0%, and pH of 7.45 ± 0.72, suitable for topical use. Rheological analysis revealed pseudoplastic behavior, fitting the Herschel-Bulkley model. It was concluded that experimental design is a valuable tool for the development of stable emulsions, and formulation 22 proved to be promising for topical applications.