Influence of interfacial structure on physical stability and antioxidant activity of curcumin multilayer emulsions

Curcumin is a strong natural antioxidant compound, but its use as a nutraceutical ingredient is limited due to its low water solubility and poor chemical stability. This study aims to elucidate the key colloidal aspects determining the physical stability and antioxidant activity of emulsified curcumin, specifically focusing on the effect of the interfacial structure of curcumin multilayer emulsions. Curcumin dissolved in coconut oil was encapsulated in multilayer emulsions prepared by layer-by-layer (LbL) deposition using gelatin (primary emulsion), gum arabic (secondary emulsion) and tannic acid (tertiary emulsion) as wall materials. The primary emulsion exhibited stability at higher gelatin concentrations (≥0.5% w/v) due to the droplets were completely coated by the biopolymer (mean diameter, 377 nm). The secondary emulsion was stable only at low gum arabic concentrations (01% w/v, mean diameter, 412 nm). The tertiary emulsion was more stable at an intermediate concentration of tannic acid (0.0004% w/v, mean diameter, 470 nm). The antioxidant activity of emulsified curcumin was well preserved during exposure to light for 6 days, while it significantly decreased in free curcumin beginning from day 0. In conclusion, the control and modulation of the interfacial layer properties seem to play a key role in regulating the physical stability and antioxidant activity of emulsified curcumin.