Synthesis of highly stable encapsulated astaxanthin/β-cyclodextrin microparticles using supercritical CO2 as an antisolvent

Although astaxanthin has promising physiological functions, its practical applications are limited by poor stability. Herein, astaxanthin was encapsulated in beta-cyclodextrin (beta CD) using CO2 as a supercritical antisolvent (SAS). The effects of process conditions, including temperature (313-333 K), pressure (12-18 MPa), solution concentration (3-5 wt%), solution flow rate (0.8-1.2 mL min-1), and astaxanthin-to-beta CD mole ratio (1:50, 1:25, or 1:10), on the encapsulation efficiency, particle morphology, and residual solvent content were investigated. Astaxanthin-beta CD complex spheres with an average diameter of 0.44 +/- 0.08 mu m were produced at 313 K and 15 MPa with a solution concentration and flow rate of 5 wt%, and 1.0 mL min-1, respectively. Under these optimal conditions, almost complete encapsulation (99.6% encapsulation efficiency) and residual organic solvent removal (0.22 ppm in the complex) were achieved. Density functional theory analysis of the configuration of the astaxanthin-beta CD complex indicate that the hydroxyl hydrogen atoms on an ionone ring of astaxanthin interact with the oxygen atoms of beta CD, but the ionone ring does not fit deeply within the beta CD cavity. Notably, the astaxanthin-beta CD complex exhibits higher thermal stability and antioxidant activity than free astaxanthin. The findings suggest that beta CD encapsulation via the SAS process can produce astaxanthin microparticles with potential utility for food and pharmaceutical applications.