Complexation of curcumin with whey protein isolate for enhancing its aqueous solubility through a solvent-free pH-driven approach

In this study, whey protein isolate (WPI) was employed to increase the water dispersibility of curcumin using a solvent-free pH shifting method (pH 12 to pH values of 7.0 and 3.0). The aqueous solubility of curcumin was significantly improved by this method compared to the method without pH shifting at pH values of 7.0 and 3.0. Fluorescence measurements and Fourier transform infra-red (FT-IR) spectroscopy revealed that the complexation occurs through the hydrogen bonding and hydrophobic interactions between curcumin and WPI. Circular dichroism (CD) spectroscopy and X-ray diffraction (XRD) analysis indicated that the secondary structures and crystallinity of WPI at pH values of 7.0 and 3.0 did not significantly change after binding to curcumin. The complexation with WPI greatly improved the heat- and photo-stability of curcumin with a higher stability at pH 3.0 than at pH 7.0. WPI-curcumin complexes also showed a high antioxidant activity and sustained-release profile under simulated intestinal condition. Practical applications In this research, a solvent-free pH shifting approach was used to produce curcumin-WPI complexes for improving the aqueous solubility, chemical stability, and antioxidant activity of curcumin. The resulting curcumin-WPI complexes could be used in the aqueous formulation of functional foods and beverages owing to their high water dispersibility, excellent antioxidant activity, and good chemical stability which can improve the health-promoting attributes of the food products.