Thermal characterization and microbiology assay of Annona muricata L. leaves

Abstract

Annona muricata L., Annonaceae, popularly known as soursop, has anticancer and antidiabetic pharmacological properties. This work aims the characterization by thermoanalytical technique and determination of antimicrobial activity of different A. muricata L. leaves particle sizes. The leaves were dried, knifed, and separated by particle size. Samples were characterized by scanning electron microscopy (SEM) and thermogravimetry (TG) using the Ozawa kinetics model in two atmospheres (nitrogen and synthetic air). The antimicrobial activity and minimum inhibitory concentration of infusions were performed by the broth microdilution method to Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumoniae. SEM analysis suggests heterogeneous distribution in the observed particle sizes. TG curves were able to differentiate the degradation events and the residue contents in the samples analyzed in the nitrogen and synthetic air atmospheres. In nitrogen atmosphere curves, the different particle sizes presented four mass loss events, and residue ranged from 20.90 to 26.80% at the end of the analysis. In synthetic air atmosphere, the different particle sizes presented three mass loss events, and residue ranged from 7.80 to 10.42%. Ozawa model showed reaction order equal to zero for all samples assayed, and the activation energy (Ea) ranged from 121.36 to 135.42 and 115.50 to 141.00 kJ mol−1 for the nitrogen and synthetic air atmospheres, respectively. Antibacterial activity was confirmed for all particle sizes, in special to AM4 with S. aureus, E. coli, and K. pneumoniae. These results indicate that leaves from A. muricata L. have great potential for a variety of medicinal applications.