Physical and light oxidative properties of eugenol encapsulated by molecular inclusion and emulsion–diffusion method

The aim of this research was to study the encapsulation of eugenol as a volatile active substance by inclusion with β-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD), and by an emulsion–diffusion method with polycaprolactone (PCL). After formulation of each type of complex, size, zeta-potential, and thermal properties were determined by using Nanosizer®, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Overall, the mean sizes of encapsulated eugenol were the same at 320 nm. However, the size distribution of the β-CD and 2-HP-β-CD inclusion complex was poly-disperse as compared with eugenol encapsulated with polycaprolactone (PCL). TGA analysis revealed the encapsulation efficiency of PCL, β-CD eugenol and 2-HP-β-CD eugenol inclusion complexes were 100%, 90.9% and 89.1%, respectively. The study of oxidation stability revealed the emulsion–diffusion method was more efficient than the molecular inclusion method resulting from high stability depending on storage time. On the other hand, β-CD was more effective than 2-HP-β-CD for eugenol encapsulation. It is supposed that the side chain of hydroxypropyl group of 2-HP-β-CD might interrupt eugenol inclusion within the cavity of 2-HP-β-CD molecule. From our experiments, we concluded that the emulsion–diffusion method was the most effective for eugenol encapsulation to protect from light oxidation during storage time due to their complete wrapping of eugenol by PCL layer from TEM analysis.