Microencapsulation of citronella oil for mosquito repellent : Preparation and evaluation of release characteristics

The major aims of the current study were to prepare citronella oil microcapsules using the complex coacervation technique and evaluate the in vitro release properties of citronella oil from the prepared microcapsules. Gelatin and acacia, which are oppositely charged polymers, were chosen as the wall materials and the core substance was citronella oil produced by steam distillation of Cymbopogan winterianus. Formaldehyde was employed as a hardening agent. The core-to-wall ratio was fixed at 1:2, whereas the gelatin-to-acacia ratio, concentration of citronella oil, amount of hardening agent, and hardening time were varied. Among 18 formulations studied, three formulations produced satisfactory appearances of white microcapsules. Scanning electron microscopy revealed that the microcapsules were discrete and spherical in shape. Microcapsules with the smoothest surfaces were achieved in formulation F13 containing a 1:1 gelatin: acacia ratio. The percentages of oil content in formulations F13, F14, and F15 were 25.41±1.42%, 24.94±1.31%, and 19.89±1.31%, respectively. Simple diffusion cells with a synthetic membrane were used to study the in vitro release of citronella oil from the microcapsules. The release kinetics of citronella oil was also examined. The release data of citronella oil followed the Higuchi model with a high coefficient of determination values (r>0.97). Formulation F13 had the greatest release rate of citronella oil (P<0.05), while the release rate of formulation F14 was comparable to that of formulation F15. In conclusion, the potential microcapsule formulation for mosquito repellency was formulation F14, owing to its relatively high percentage of oil content and relatively slow release rate. The rapid volatility of citronella oil would be potentially reduced with the slow release properties.