Enhancing nutraceutical bioavailability using excipient emulsions: Influence of lipid droplet size on solubility and bioaccessibility of powdered curcumin

• Excipient emulsions were designed to increase curcumin bioavailability.
• Curcumin transfer into emulsions increased with incubation temperature.
• Curcumin bioaccessibility increased with decreasing lipid droplet size.
• Excipient emulsions may improve oral bioavailability of nutraceuticals.

The influence of lipid droplet size of excipient emulsions on the solubility and bioaccessibility of powdered curcumin was investigated. Corn oil-in-water emulsions with different initial mean droplet diameters were prepared: large (d32 ≈ 14 µm); medium (d32 ≈ 0.52 µm); small (d32 ≈ 0.18 µm). These excipient emulsions were mixed with powdered curcumin and the resulting mixtures were incubated at either 30 °C (to simulate a salad dressing) or 100 °C (to simulate a cooking sauce). The amount of curcumin transferred into the excipient emulsions after incubation was higher at 100 °C than at 30 °C, and increased with decreasing droplet size at the higher temperature. The curcumin concentration in the mixed micelle phase and total digesta depended on the droplet size of the original excipient emulsions: large > medium ≈ small. However, the bioaccessibility of curcumin did not depend strongly on size. These effects were attributed to the competing effects of the oil droplets on solubilization and chemical degradation of curcumin under simulated gastrointestinal conditions. This study shows the potential of designing excipient emulsions to increase the oral bioavailability of lipophilic nutraceuticals, which may be useful for incorporating curcumin into functional foods.