Binding of curcumin to barley protein Z improves its solubility, stability and bioavailability.

Although excessive pharmaceutical activities of curcumin have been reported, the poor solubility, low stability and low bioavailability greatly limited its application. In this study, the interaction between protein Z (PZ) and curcumin, and the effects of PZ on the stability and bioavailability of curcumin were investigated. Fluorescence quenching results indicated that curcumin molecule binds PZ with a stoichiometry of 4:1, and the binding affinity is stronger than other reported protein carriers. Molecular dynamics simulation results suggested that curcumin binds in the hydrophobic region of PZ, and the interaction was maintained mainly by hydrogen-bond (Pro-287, Asn-340 and Tyr-234). PZ-curcumin complex possessed better encapsulation efficiency (64.10 %) and loading capacity (5.49 μg/mg) for curcumin. In addition, binding with PZ not only improved the thermal, light and digestive stability of curcumin significantly, but lowered its toxic effect on Caco-2 cells and improved relative bioavailability (305 %) compared with that of curcumin only.