Avaliação Térmica e Biológica de Óleos Essenciais de Origem Comercial

Abstract

Essential oils (EOs) are an alternative for the development of formulations that can combat the resistance of microorganisms to antimicrobial agents. However, aiming a better applicability of these products, studies involving chemical and biological characterization are necessary, mainly because they are volatile substances. Thus, this work aimed to evaluate the microbiological and cytotoxic potential, as well as the thermoanalytical characteristics of four essential EOs of commercial origin. The oils were purchased from a national cosmetics company, obtained from different species of plants: lavender, orange, lemon and mint. For the microbiological analysis, the broth microdilution tests were used to determine the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal/Fungicide Concentration (MBC/CFM), microbial susceptibility test by diffusion in agar and the death curve test (time-kill), using ATCC strains Staphylococcus aureus (ATCC 17193), Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853) and Candida albicans (ATCC 10231). The cytotoxicity of the oils was also evaluated in vitro by the hemolysis test. The evaluation of the thermal profile of the EOs was carried out using Thermogravimetric (TG) and Differential Thermal Analysis (DTA) techniques, in addition to determining the activation energy (Ea) by the kinetic model of thermal degradation using the Flynn-Wall-Ozawa methods (FWO) and Kissinger-Akahira-Sunose (KAS). As a result, it was observed that all EOs showed antimicrobial activity, being the orange EO the one that showed the best activity against the tested strains. C. albicans strain showed the greatest sensitivity to EOs (MIC = 0.25 mg/mL). In the death curve, different behaviors were observed in the EOs tested, which vary according to the concentration. In the thermogravimetric analysis, all EOs presented only one thermal event corresponding to volatilization, which was also observed by the DTA curves. This event occurs at different temperatures for each of the EOs and the orange EO showed the lowest initial temperature of degradation (58.43 ºC), as well as the lowest Ea determined by the FWO (29.07 ºC) and KAS (36 .01°C). In the cytotoxicity assay, the EOs showed low toxicity (< 40%), being considered little toxic. Thus, it is possible to infer that the results obtained provide complementary subsidies for scientific literature with regard to microbiological analysis and thermal characterization of EOs, aiming at carrying out further studies aimed at the application of these substances in pharmaceutical formulations.