Alginate-based emulsion micro-gel particles produced by an external/internal O/W/O emulsion-gelation method: Formation, suspension rheology, digestion, and application to gel-in-gel beads

Alginate-based emulsion gels can be used as fat replacers and encapsulation materials, but studies on emulsion micro-gel particles and nano-gel particles have rarely been reported, compared to bulk emulsion gels and emulsion macro-gel beads. This study investigated external/internal O/W/O emulsion-gelation methods for preparation of alginate-based emulsion micro-gel particles. The size, micro-structure, rheological properties, and in-vitro digestion of emulsion micro-gels prepared by external/internal methods were compared. The external gelation could produce emulsion micro-gels with small size (<100 μm), while emulsion micro-gels prepared by the internal gelation had bigger size and a more narrow size distribution. The suspensions of emulsion micro-gels prepared by the external gelation had higher φ_rcp, φ_j, G′, and G″ values than those prepared by the internal gelation. Emulsion micro-gel particles swelled during intestinal digestion, but those prepared by the external method were collapsed faster than those prepared by the internal method. Structuring emulsion gel beads by introducing emulsion micro-gel particles was also investigated. The presence of emulsion micro-gel particles prepared by the external gelation improved the Young's modulus of gel beads, delayed their structural collapse and thus delayed release of encapsulated lycopene during intestinal digestion. The results of this study are critical for preparation and applications of alginate-based emulsion micro-gel particles prepared by external/internal O/W/O emulsion-gelation methods in the food industry.