Effect of cyclodextrins and Mexican oregano (Lippia graveolens Kunth) chemotypes on the microencapsulation of essential oil

Lippia graveolens (Kunth) essential oil (EO) contains the bioactive compounds carvacrol and thymol in different concentrations according to their chemotype. We evaluated the effect of the essential oil chemical composition, and different cyclodextrins (CD), beta- and gamma, on the microencapsulation process and its efficiency. Complex formation of L. graveolens EO with beta-CD and gamma-CD was determined by Scanning Electron Microscopy, X-Ray Diffraction, Thermogravimetric Analysis, and Fourier Transform Infrared Spectroscopy. Carvacrol and thymol concentrations in the gamma-CD complexes were higher than in the beta-CD complexes, as demonstrated by Gas Chromatography analysis. After 14 days of storage, carvacrol concentration in the beta-CD complex remained similar to the initial values; while in the gamma-CD complex the concentration was significantly reduced. In the case of thymol concentrations, no significant losses were observed after storage in the complexes obtained with beta-CD or gamma-CD. Our results confirmed that the microencapsulation of L. graveolens EO with CDs retained the bioactive compounds, carvacrol and thymol. Based on the amount of bioactive terpenes in these complexes and their relative stability, the best combinations to be used as delivery systems were the complexes formed between chemotypes thymol-gamma-cyclodextrin and carvacrol-beta-cyclodextrin.