Astaxanthin encapsulation in ethyl cellulose carriers by continuous supercritical emulsions extraction: A study on particle size, encapsulation efficiency, release profile and antioxidant activity

Supercritical emulsions extraction (SEE) technology was used to encapsulate astaxanthin (AXT) in ethyl cellulose (EC). The operating parameters were 8 MPa and 311 K with an L/G ratio of 0.1 (CO2 flow rate of 1.4 kg/h). Several emulsion formulations were tested, fixing the oil-water ratio at 20:80 (ethyl acetate/water) and varying EC concentration in the oily phase from 1.0-2.5% mass and the surfactant amount in the water phase from 0.1 to 0.6% mass. Both parameters influenced carriers morphology, size and distribution; a correlation between the EC amount in oily phase and its dynamic viscosity was proposed to explain the droplets/carriers size variation observed. Carriers aggregation was monitored at surfactant concentration higher than 0.3% mass. The best emulsion formulation was obtained using 1.0% mass of EC in the oily phase and 0.1% mass of surfactant in the water phase; in these conditions spherical nanocarriers with unwrinkled and smooth surface were obtained with a size of 242 nm and Poly Dispersity Index of 0.16. EC mass recovery was of 90%. Higher carrier mean size of 363 nm (Poly Disperity Index of 0.31) was measured when AXT was encapsulated in the same conditions, achieving an encapsulation efficiency of 84%. The carriers were loaded with 21 mg/g of AXT and showed an excellent antioxidant capacity, measured as Trolox equivalent (Trolox equivalent per kg of pure AXT), and equivalent to 3900 M Trolox. In vitro release profiles obtained in a simulated intestinal fluid (SIF) at pH 7.2 and 310 K, showed a release of 70% of the total encapsulated AXT after 10 h. (C) 2019 Elsevier B.V. All rights reserved.