Mechanisms of in vitro controlled release of astaxanthin from starch-based double emulsion carriers

The aim of the present study was to illuminate the controlled release mechanism of Astaxanthin (AST) from the biocompatible double emulsions fabricated by inexpensive, renewable and biodegradable native starch (SDEs) using a novel two-step emulsification. The storage stability of the four types of AST-loaded SDEs was evaluated. The results indicated that SDEs prepared with a native corn starch concentration of 7 wt% (7% NCS DEs), and a droplet size of approximately 8 μm without stratification, exhibited excellent storage stability for 35 d. The chemical stability of AST remaining for 7% NCS DEs after 35 d was 90%. The AST-loaded SDEs displayed a high encapsulation efficiency (96%). The release of AST-loaded SDEs was <10% for 120 min in simulated gastric fluid. A sustained and slow release was achieved in simulated intestinal fluid. Moreover, several models have been tested to describe the kinetics of AST release, the most suitable being the diffusion-releasing mechanism. Furthermore, the interaction of SDEs and AST was investigated through steady-state fluorescence measurements and the complexing index. As a demonstration, AST was loaded in the SDEs by hydrophobic interaction and amylose-AST complex formation, enabling the regulation of diffusion and permeation phenomena. Thus, the SDEs are promising oral delivery carriers for lipophilic ingredients.