Optimization of Extraction Process of Fennel Essential Oil by Response Surface Methodology and Its Microemulsion Characteristics and Shelf Life

In this study, the extraction process of fennel essential oil was optimized by response surface methodology. Fennel essential oil was used as oil phase, Tween 80+40 as surfactant and glycerol as cosurfactant to prepare fennel essential oil microemulsion system. The structure, particle size, total reducing power and storage property of fennel essential oil microemulsion were investigated by rheology, particle size analyzer and reduction reaction. The results showed that the yield of essential oil of fennel was as high as 15.99%±0.10% when the ratio of material to liquid was 1:8.40 g/mL, the extraction time was 4.09 h, the particle size was 80 mesh, and the extraction temperature 80 ℃. The diameter of fennel essential oil microemulsion was 30.92±0.13 nm, and when the moisture content was higher than 60%, it was a stable O/W microemulsion. The emulsification of fennel essential oil significantly improved the total reducing power of fennel essential oil. According to the principle of chemical reaction kinetics, the Arrhenius equation was established as k=2518.85·e^{−35583.09/RT}. The model predicted that the fennel essential oil microemulsion could store 1899.18, 932.03, 492.94 and 271.51 h at 20, 35, 50 and 65 ℃, the maximum relative error was 8.73%, and the error was small, which could accurately predict the shelf life of the microemulsion.