Two-step method for encapsulation of oregano essential oil in chitosan nanoparticles: Preparation, characterization and in vitro release study

► Oregano essential oil was encapsulated in chitosan nanoparticles. ► Oil presence in nanoparticles was corroborated by FTIR, TGA and XRD techniques. ► Particles had spherical shape and size range about 40–80nm. ► The release profile of the OEO showed burst effect followed by slow release. In this study, oregano essential oil (OEO) has been encapsulated in chitosan nanoparticles by a two-step method, i.e., oil-in-water emulsion and ionic gelation of chitosan with sodium tripolyphosphate (TPP). The success of OEO encapsulation was confirmed by Fourier transform infrared (FT-IR) spectroscopy, UV–vis spectrophotometry, thermogravimetric analysis (TGA) and X-ray diffraction (XRD) techniques. The obtained nanoparticles exhibited a regular distribution and spherical shape with size range of 40–80nm as observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). As determined by TGA technique, the encapsulation efficiency (EE) and loading capacity (LC) of OEO-loaded chitosan nanoparticles were about 21–47% and 3–8%, respectively, when the initial OEO content was 0.1–0.8g/g chitosan. In vitro release studies showed an initial burst effect and followed by a slow drug release.