Impact of delivery system type on curcumin stability: Comparison of curcumin degradation in aqueous solutions, emulsions, and hydrogel beads

The impact of molecular environment on the chemical stability of curcumin was determined. Equal amounts of curcumin were incorporated into different kinds of delivery system: aqueous dimethyl sulfoxide (DMSO) solutions; oil-in-water emulsions; or filled hydrogel beads. Two types of filled hydrogel beads were fabricated by injecting solutions containing curcumin-loaded lipid droplets and gelling polysaccharides (alginate or chitosan) into ionic gelling solutions (calcium or tripolyphosphate) using an extrusion device. The delivery systems were then incubated under acidic (pH 3) and neutral (pH 7) conditions at 55 °C for 14 days. The initial rate of curcumin degradation, determined by measuring the color change (b* value) over time, depended on storage pH and delivery system type. At pH 7, the curcumin degradation rate increased in the following order: chitosan beads < emulsion < aqueous solution < alginate beads, but at pH 3 it increased in a different order: emulsion < aqueous solutions < chitosan beads < alginate beads. Overall, our results showed that curcumin was more stable under acidic than neutral conditions. Interestingly, encapsulation of curcumin in alginate beads promoted its degradation at both acidic and neutral pH, but encapsulation in chitosan beads enhanced its stability at pH 7 by reduced it at pH 3. These effects may be related to the different charge status of the polysaccharides used to fabricate the hydrogel beads: alginate is anionic, whereas chitosan is cationic. Overall, our results provide valuable information for the design and development of emulsion-based delivery systems to encapsulate and protect curcumin for functional food applications.