Investigation of thermal and kinetic behavior of the Stryphnodendron adstringens dry extract with antimicrobial activity

Stryphnodendron adstringens Coville (Fabaceae), popularly known as "barbatimao," is a Brazilian Cerrado tree, rich in tannins. It is used as antinociceptive, in the treatment of vaginal inflammations and infections in general. The objective was to investigate the thermal, kinetic behavior and the antimicrobial activity of the dry extract of S. adstringens. The dry extract was obtained from the leaves of S. adstringens and submitted to the thermal characterization by thermogravimetry (TG), at different atmospheres and heating rates, and by kinetic degradation by Ozawa model. Furthermore, in order to evaluate the antimicrobial activity, the minimum inhibitory concentration of the dry extract against pathogenic microorganisms was obtained. The TG curves of the sample presented six stages of thermal decomposition in both atmospheres with the beginning of decomposition of compounds in the third stage, reaching up to 16.55% of mass loss, and the fourth step achieved a maximum decomposition of 45% mass loss under inert atmosphere. The DTA curve profile of the extract presented two exothermic events with a higher enthalpy in the first event. Thermal decomposition was shown to be a zero-order reaction by the Ozawa method. The extract was presented to be sensitive to all strains tested, thus showing potent antibacterial and antifungal action (minimum inhibitory concentration < 12.5 mg mL(-1)). Thus, it is concluded that the characterization was done by appropriate analytical techniques and the dry extract was shown to be an active agent against all microorganisms tested, prospecting a new herbal medicine with antimicrobial activity.