Preparation and sustained-release study of Litsea cubeba essential oil inclusion complex with γ-cyclodextrin-metal–organic frameworks

Abstract

Abstract Background Litsea cubeba essential oil (LCEO) is a food additive that requires encapsulation to delay its release due to its irritating nature. To identify an appropriate inclusion material, gamma (γ)-cyclodextrin (CD)-metal organic frameworks (MOF) were prepared, and the sustained release of the inclusion complex (IC) was studied. Results The γ-CD-MOF was formed using γ-CD, potassium hydroxide (KOH), cetyltrimethylammonium bromide (CTAB), and silane coupling agents through the vapor diffusion method. The highest encapsulated rate achieved was 26.02%, with a temperature of 50 °C, a stirring time of 2.5 h, and an LCEO to γ-CD dosage ratio of 1:8. During the adsorption test, the amount of LCEO gradually increased within the first 180 min. However, after this time, there was no significant change in the adsorption amount of LCEO, indicating that the γ-CD-MOF had reached adsorption equilibrium. The average release rate of the IC reached 9.76% at 11 h. By comparison, the average release rate of the IC with γ-CD was 9.30% at 10 min, resulting in a diffusion index of 0.349. Under ultraviolet (UV) scanning, the sustained-release solution of the IC exhibited a strong characteristic citral absorption peak at 238 nm. Moreover, under infrared spectroscopy scanning, the absorption peak intensity of the IC was 1.19 times higher than that of blank γ-CD-MOF at 1676 cm−1. The IC, as observed through a scanning electron microscope, exhibited round pellets with a diameter of 40–60 μm. Energy dispersive spectroscopy images showed uniform distribution of potassium and sulfur elements. In X-Ray diffraction, the diffraction peaks of the IC were found at 5.27°, 7.45°, 10.54°, 12.08°, 14.20°, 14.92°, 15.84°, 16.68°, 19.24°, 21.80°, and 23.69°, with no significant change in the adsorption amount of LCEO. The Brunauer–Emmett–Teller (BET) testing revealed that the surface area of γ-CD-MOF was 5.089 m2/g, and the pore diameter was 3.409 nm by the Barrett–Joyner–Halenda (BJH) method. Conclusion These data demonstrated that the sustained effect of the γ-CD-MOF was superior to that of γ-CD. The adsorption kinetics curve followed the Quasi-primary kinetics model, while the release curve adhered to the Ritger–Peppas model. Furthermore, the release behavior was primarily governed by the Fick diffusion mechanism, which was advantageous for achieving the sustained release of LCEO. The UV spectrum, infrared spectroscopy (IR), scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS), X-ray diffraction (XRD), and BET techniques confirmed the successful formation of the IC of LCEO with γ-CD-MOF. This study offers a promising technical solution for delaying the release and improving the sustained-release product of LCEO. Graphical Abstract