Desenvolvimento de esferas de alginato de cálcio com óleo essencial de Lippia origanoides Kunth como possível larvicida contra Aedes aegypti

Abstract

Lippia origanoides Kunth, popularly known as “alecrim-pimenta”, has an essential oil (OELO) whose major constituent is thymol, which exhibits several biological activities, highlighting the larvicidal activity against Aedes aegypti. Thus, it may constitute an alternative to synthetic larvicides. However, it is necessary to overcome limitations presented by essential oils, such as their volatilization. Furthermore, a slow release is interesting, as it makes it possible to reduce the frequency of applications. The present study aimed to develop spheres/beads of calcium alginate containing OELO cross-linked with calcium chloride, slow release for possible application as a larvicide against Aedes aegypti. The OELO was obtained from PRONAT LTDA. and had its thymol content determined by UV-vis spectrometry at 275 nm. The spheres were produced by dripping emulsions composed of OELO, Tween 20 and Sodium Alginate (ALG) solutions at 1.5, 2 and 2.5% in Calcium Chloride 5%, to obtain three formulations, with drying in desiccator coupled to the vacuum pump. The spheres were characterized in terms of size, by processing images in the Image J software, data which were submitted to analysis of variance (ANOVA), in addition to their Encapsulation Efficiency (EE) by extracting thymol by grinding with absolute ethanol and reading spectrophotometric. A release test was carried out with the spheres in Tween 20 solution and aliquots were withdrawn at times of 30, 60, 90, 120, 150 and 180 minutes and subsequent spectrophotometric reading, with the results processed in DDSolver for analysis of release kinetics. For the analyzed OELO, the content of 79.17% of thymol was obtained. For beads with 1.5%, 2% and 2.5% ALG, proportionality was observed between ALG concentrations and size, in addition to obtaining the respective 49,41%, 44,98% and 62,88% of EE, with higher recovery for the formulation with higher concentration of ALG. In the release assay, it was verified that OELO was released more slowly by the 1.5% ALG formulation, but better linearity was observed for 2.5% ALG. Furthermore, the three formulations fit the Korsmeyer-Peppas model and release is governed by a diffusion mechanism. Therefore, the study demonstrated the possibility of formulating a possible larvicide against the vector of still prevalent diseases such as Dengue, Zika and Chikungunya, and that can protect and control the release of the chosen plant active.