Fabrication of rhamnogalacturonan-I enriched pectin-based emulsion gels for protection and sustained release of curcumin

Rhamnogalacturonan-I (RG-I) was considered to be incompatible with gel formation. Due to its important health benefits, our previous study reported synergistic gelation of RG-I enriched pectin from citrus membranes with sequential acidic and alkaline treatment. In the present study, we further fabricated RG-I enriched pectin-based emulsion gels with the synergistic gelation for hydrophobic bioactive encapsulation. The effect of oil fraction and interfacial compositions including pectin itself and Tween 20 on the physical properties and delivery characteristics of emulsion gels was investigated. As to interfacial compositions, pectin reduced syneresis and swelling ratio and increased water holding capacity. Oil fraction had no marked influence on syneresis and swelling ratio, but significantly increased water holding capacity. Particularly, all the emulsion gels showed an elastic behavior and a full structure recovery after shearing. Increase in pectin instead of Tween 20 onto the surface of oil droplets and oil fraction markedly improved their gel strength. Curcumin was encapsulated within the oil phase of emulsion gels. Improvement in gel strength provided enhanced protection of curcumin against heat-induced degradation. In vitro digestion revealed that interfacial compositions decelerated curcumin release by increasing the proportion of pectin onto the surface, but didn't change its bioaccessibility eventually. Increase in oil fraction accelerated curcumin release, but reduced its bioaccessibility. Overall, fabrication of RG-I enriched pectin-based emulsion gel with pectin itself as interfacial composition and low oil fraction would contribute to improving curcumin bioavailability for its sustained release, which should be further validated in vivo.