Preparation methods and release kinetics of Litsea cubeba essential oil microcapsules

In this paper, using β-cyclodextrin (β-CD) as the shell material, LCEO (Litsea cubeba essential oil) microcapsules were prepared by various preparation methods, such as grinding, saturated solution, freeze-drying and spray-drying. The encapsulation yield, encapsulation efficiency, retention rate of the microcapsules and the citral content of the microcapsules were investigated. The surface morphologies of the microcapsules were observed using SEM (Scanning Electronic Microscopy); the entrapment efficiencies of the microcapsules were detected using IR (Infrared Spectrum) analysis; the citral contents of microcapsules were detected by GC (Gas Chromatography) analysis. The highest encapsulation efficiency for the microcapsules was obtained using spray-drying, followed by freeze-drying, saturated aqueous solution and grinding, while the encapsulation yield followed the opposite sequence to the encapsulation efficiency. At a specific storage temperature (15 °C) and humidity (60%), spray-drying had the most satisfactory protective effect on citral in LCEO, followed by freeze-drying and saturated aqueous solution, while the grinding method appeared to provide the worst protective effect. Avrami's model was used to simulate the release rates of the four kinds of microcapsules. The release mechanism parameters of microcapsules prepared by grinding, saturated aqueous solution, freeze-drying and spray-drying were 0.961, 1.096, 1.156 and 0.945, respectively. The release rate constants of microcapsules prepared by grinding, saturated aqueous solution, freeze-drying and spray-drying were 2.53 × 10^-2, 2.22 × 10^-2, 1.84 × 10^-2, and 7.27 × 10^-3 d^-1, respectively. It was concluded that the release reactions of the microcapsules prepared by grinding or spray-drying lay between the diffusion limiting kinetics and the first-order release kinetics, and the release reactions of the microcapsules prepared by saturated aqueous solution or freeze-drying were larger than the first-order release kinetics.