α-LACTALBUMIN-CURCUMIN COMPLEX: A THERMODYNAMIC APPROACH TO ENABLE CURCUMIN APPLICATION IN SEVERAL MATRICES

Curcumin (CUR) is a natural, liposoluble pigment that presents biological activities such as antioxidant, anti-inflammatory, antimicrobial, and neuroprotective. However, it exhibits higher hydrophobicity and is unstable to light, oxygen, pH, and high temperatures, which limits its application in low-fat food. The usage of carrier proteins has shown potential to enable CUR application in several matrices, although it is necessary to know its interactions with CUR to optimize the complex formation. The α-lactalbumin (ALA) is one of the main whey proteins, having 123 amino acids, four of which are tryptophan residues, allowing fluorescence spectroscopy (FS) to be utilized for monitoring its interaction with various molecules. Therefore, this study evaluated the thermodynamic parameters for complex formation between CUR ([CUR]= 6.10x10^-6 to 5.77x10^-5 mol.L-1) and ALA ([ALA]= 1.0x10^-5 mol.L-1) in pH 7.0, employing the FS technique at different temperatures (288.15 to 308.15 K). The stoichiometry (n) of the ALA-CUR complex was around 1.0 to all temperatures, showing that for each ALA there was only one CUR molecule. The binding constant (Kb) values fluctuated between 7.64x10^4 to 1.21x10^5 mol.L-1 as the temperature increased, indicating that the complex formation is an endothermic process. The values of standard Gibbs free energy change (ΔG°) were negative (-26.90 to -29.96 kJ.mol-1), showing that the thermodynamic equilibrium lies towards the complex formation. The complex formation occurred through an entropically driven process, as evidenced by the positive values of the standard enthalpy and entropy changes for complex formation (from 7.06 to 28.28 kJ.mol-1 and from 12.35 to 56.89 kJ.mol-1, respectively). Our results indicated the formation of a specific and stable complex between both molecules, which may contribute to allowing CUR to be more viable for usage in food and pharmaceutical applications.