Encapsulation of essential oil obtained from schinus areira from Santiago del Estero. Characterization and antimicrobial activity against S. aureus

Abstract

Essential oil (EO) extracted by hydrodistillation from specimens of the species Schinus areira (Aguaribay) has been used in traditional medicine. Previously, we reported that EO obtained from S. areira leaves from Santiago del Estero (SDE) showed antibacterial action against Staphylococcus aureus. New studies were carried out with EO obtained in a second period, after its chemical characterization, the biological activity and liposomal encapsulation were assayed. The liposomes with EO encapsulated were obtained by the hydration of mixed lipid film generated from dipalmitoyl phosphatidylcholine (DPPC) and EO with a mass ratio of 1: 1, obtaining DPPC:EO multilamellar liposomes (MLV). Then they were characterized by physicochemical and microbiological methods. Size distribution and Zeta potential were determined by using dynamic light scattering (DLS Horiba, Nanosizer), DPPC MLVs were used as control. Formulations of MLVs with EO showed a significantly smaller size (p <0.05) in comparison with the control (1266.5 ± 255.7 nm and 299.8 ± 53.9 nm, respectively), this could be due to a higher cohesive Van der Waals forces that favor a higher packing and a reduction in curvature as reported for other EO. Regarding the zeta potential values of the liposomal formulations containing EO showed significantly more negative potential values (p <0.05) than the controls, showing zeta potential values of -14.0 ± 4.9 mV and -4.5 ± 2.5 mV, respectively. This difference in the first instance would be related to the presence of components of the EO at the lipid-water interface of the vesicles obtained. The encapsulation efficiency (EE) of formulations was determined by GC/MS spectrometry from the liposome pellet obtained by centrifugation of the suspensions and the chemical compounds were identified by a comparison of their retention times with those of EO leaf of S. areira. EE observed of liposome formulations was 90 ± 8%, with no changes in the chemical composition. Afterward, the antimicrobial activity of liposomal suspensions carrying the EO, as well as the pellet of its centrifuged liposomes showed to have antimicrobial action against a grass culture of S. aureus ATCC 25923, while the supernatant did not present antibacterial activity. This shows that the EO encapsulated in the MLVs obtained, has not lost its biological activity. However, the MIC values are a higher order with respect to methanolic solutions of pure EO. This may be due to the fact that the EO is encapsulated in a multilamellar system that has a strong interaction with PC phospholipids, which may be affecting the release kinetics, making the effective concentration lower. Finally, after 15 days of refrigerated storage, a decrease in the content of EO stored close to 16%. These data presented would indicate that the MLVs system with EO could be used as a controlled release system in an aqueous medium of EO. In order to corroborate this hypothesis, further experiments would be conducted.