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

Abstract

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.