Insight into the effect of charge regulation on the binding mechanism of curcumin to myofibrillar protein.

Myofibrillar proteins (MPs), as a food-grade material, have the potential to improve the solubility and bioavailability of curcumin. However, the interaction mechanism between MPs and curcumin under charge regulation induced by alkaline pH and NaCl was unclear. In this study, the binding between curcumin and MPs at pH 12 was confirmed by the fluorescence quenching under different NaCl concentration (0, 0.3, 0.6 and 0.9 mol/L). Further kinetic experiments showed, MPs possessed a higher affinity to bind curcumin in the presence of NaCl, especially at 0.6 M NaCl. Followed pH shifting from 12 to 7 does not affect UV-Vis absorption spectra of protein-curcumin dispersions. The secondary structure of MPs was not affected by binding with curcumin. Formation of this stable complex can be explained by hydrophobic other than electrostatic interaction. Therefore, the presence of NaCl facilitated exposure of hydrophobic pocket to improve the binding affinity between curcumin and MPs due to the importance of hydrophobic interaction.