Abstract: Microcapsules of star anise oil with β-cyclodextrin were prepared by an ultrasonic method in attempt to improve the stability of star anise oil. An orthogonal array design was used to optimize the preparation conditions for increased embedding rate. Thermal release characteristics of the microcapsules were also investigated. The optimized conditions were obtained as follows: mass ratio of star anise oil to β-cyclodextrin, 1:6 (g/g); ultrasonication time, 40 min; temperature, 50 ℃ and ultrasonic power, 198 W. Under these conditions, the embedding rate, drug loading and average diameter of microcapsules were 94.21%, 6.93%, and 2.53 μm, respectively. Temperature and ultrasonic power had significant effects on the embedding rate. The successful formation of microcapsules of star anise oil in β-cyclodextrin was confirmed by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Results of thermal release characteristics demonstrated that only 4.60% of free star anise oil was retained after being heated at 200 ℃ for 120 min, while at the same time and temperature the retention rate of star anise oil in microcapsules was 78.38%, which was 17.04 times higher than that of free star anise oil, indicating improvement of the thermal stability of star anise oil by encapsulation. There was no significant difference in drug loading of the microcapsules prepared by the ultrasonic and saturated aqueous solution methods, while microcapsules prepared by the ultrasonic method had higher embedding rate and recovery with 7.80% and 4.98% improvement as compared to those prepared by the saturated aqueous solution method, respectively. Meanwhile, the microcapsules prepared by the ultrasonic method exhibited higher embedding rate (by 14.68%) and recovery (by 1.88%), and had higher drug loading (by 1.85%) than the kneading method. The ultrasonic method is an easy and feasible method for preparing star anise oil-β-cyclodextrin microcapsules with high quality. Encapsulation with β-cyclodextrin can provide an efficient way to increase the stability of star anise oil, thereby making it valuable for food preservation applications.

Key words: star anise oil, β-cyclodextrin, microcapsule, ultrasonic preparation, characterization