Chitosan nanoparticles encapsulating lemongrass (Cymbopogon commutatus) essential oil: Physicochemical, structural, antimicrobial and in-vitro release properties

This study was aimed to encapsulate lemongrass (Cymbopogon commutatus) essential oil (LGEO) into chitosan nanoparticles (CSNPs) and to investigate their physicochemical, morphological, structural, thermal, antimicrobial and in-vitro release properties. CSNPs exhibited spherical morphology with an average hydrodynamic size of 175-235 nm. Increasing EO loading increased the average size of CSNPs from 174 to 293 nm (at CS:EO ratio from 1:0 to 1:1.25). SEM and AFM confirmed the results obtained by hydrodynamic size indicating that EO loading led to formation of large aggregated NPs. The successful physical entrapment of EO within NPs was shown by fourier-transform infrared spectroscopy. X-ray diffractogram of loaded-CSNPs compared to non-loaded CSNPs exhibited a broad high intensity peak at 2θ = 19-25° implying the entrapment of LGEO within CSNPs. Thermogravimetric analysis (TGA) showed that encapsulated EO was decomposed at a temperature of 252 °C compared to a degradation temperature of 126 °C for pure LGEO, indicating a two-fold enhancement in thermal stability of encapsulated CSNPs. Differential scanning calorimetry also proved the physical entrapment of EO into polymeric matrix of chitosan. In-vitro release study showed a time- and pH-dependent release of EO into release media demonstrating a three-stage release behavior with a rapid initial release of EO, followed by a steady state migration of EO from its surrounding envelope at the later stages. Antimicrobial assay showed strong antimicrobial properties of free form of LGEO against the bacteria (both gram positive and gram negative) and fungi species tested. Moreover, loaded-CSNPs exhibited stronger antibacterial and anti-fungal activities than non-loaded CSNPs.