In vitro digestion behavior of (W1/O/W2) double emulsions incorporated in alginate hydrogel beads: Microstructure, lipolysis, and release

The aim of the present study was to illuminate the digestion behavior of (W1/O/W2) double emulsions incorporated in alginate hydrogel beads using a simulated in vitro gastrointestinal tract model. Swelling study and fluorescence microscopy observation showed that compact beads gradually became swollen and heterogeneous during intestinal digestion, and the swelling extent was dependent on the alginate concentration. Laser diffractometry and flow cytometry were conducted to characterize the oil droplet population released from beads. The incorporated oil droplets were gradually released from the hydrogel matrix along with the swelling of beads, which might prevent the coalescence. The microstructure transformation from (W1/O/W2) double emulsion droplets to empty emulsion droplets could occur within beads without the requirement of the droplet release from beads, and oil droplets were mainly released from beads in the form of empty emulsion droplets at high alginate concentration. The release profiles of free fatty acids indicated that the lipolysis of incorporated double emulsions was gentler than that of double emulsions. Furthermore, the lipolysis was delayed at high alginate concentration. The incorporation had no influence on the cumulative release amount of encapsulated hydrophilic dye from double emulsions into digestive fluid. These results provided useful data for the design of (W1/O/W2) double emulsions-based delivery system with controlled lipolysis and adequate release of encapsulated hydrophilic active ingredients.