Encapsulation of Cinnamon and Thyme Essential Oils in γ-Cyclodextrin: Studies on Tribology and Rheology of Diluted Emulsions and Morphologies of Encapsulates

Essential oils (EO) are extensively used in food and pharmaceutical formulations for their exotic flavor and antimicrobial properties. The objectives of this work were to develop a cinnamon essential oil (CEO) and thyme essential oil (TEO) inclusion complex using γ-cyclodextrin (GCD) as a wall material at a mass ratio of GCD to EO 80 to 20. The main focus of the work was to understand the flow and frictional behaviors of the individual EOs and their emulsions/solutions using the tribological and rheological behavior prior to transformation into dry encapsulates. EOs exhibited non-Newtonian shear-thickening behavior with yield stress. The Stribeck curves exhibited the lubricating effects of EOs during friction tests. The addition of GCD to the solution caused larger friction coefficients in mixed and hydrodynamic lubrication regions. The surface morphology of emulsions displayed larger wear in the balls and disks of the tribometer. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) analysis confirmed the formation of stable encapsulates between GCD and EOs, with the appearance of new peaks confirming an improvement in thermal stability. Surface morphology data indicated an increase in height parameters and a difference in roughness between two encapsulates. The obtained results can be helpful in food and drug formulation and their delivery systems.