Interaction of Curcumin with β-Lactoglobulin-Stability, Spectroscopic Analysis, and Molecular Modeling of the Complex

Curcumin (diferuloyl methane) is the physiologically and pharmacologically active component of
turmeric (Curcuma longa L.). Solubility and stability of curcumin are the limiting factors for realizing
its therapeutic potential. β-Lactoglobulin (βLG), the major whey protein, can solubilize and bind many
small hydrophobic molecules. The stability of curcumin bound to βLG in solution is enhanced
6.7 times, in comparison to curcumin alone (in aqueous solution). The complex formation of curcumin
with βLG has been investigated employing spectroscopic techniques. βLG interacts with curcumin at
pH 7.0 with an association constant of 1.04 ( 0.1 � 105 M-1 to form a 1:1 complex at 25 �C. Entropy
and free energy changes for the interaction derived from the van’t Hoff plot are 18.7 cal mol-1 K-1
and -6.8 kcal mol-1 at 25 �C, respectively; the interaction is hydrophobic in nature. The interaction of
βLG with curcumin does not affect either the conformation or the state of association of βLG.
Competitive ligand binding measurements, binding studies with denatured βLG, effect of pH on the
curcumin-βLG interaction, Fo¨rster energy transfer measurements, and molecular docking studies
suggest that curcumin binds to the central calyx of βLG. These binding studies have prompted the
preparation and encapsulation of curcumin in βLG nanoparticles. Nanoparticles of βLG prepared by
desolvation are found to encapsulate curcumin with >96% efficiency. The solubility of curcumin in βLG
nanoparticle is significantly enhanced to ∼625 μM in comparison with its aqueous solubility (30 nM).
Nanoparticles of βLG, by virtue of their ability to enhance solubility and stability of curcumin, may fit
the choice as a carrier molecule.