THE STUDY OF CURCUMIN-α-LACTALBUMIN COMPLEX FORMATION FOR INDUSTRIAL APPLICATIONS: INFLUENCE OF THERMAL TREATMENT AND ULTRASOUND

The use of techniques for structural protein modification has been widely explored to enhance their technical-functional properties and compound carriage. Ultrasound (US) is an unconventional technology that interferes with the bonds and intramolecular interactions, modifying the conformational structure of proteins. Conformational alterations in proteins are also caused by technical treatment (TT) denaturation, in which the protein loses its tridimensional structure, exhibiting groups of interest. The treatment of globular protein, such as α-lactalbumin (ALA), with US or TT can improve its interaction with other molecules. Therefore, this study compared thermodynamic parameters of complex formation between curcumin (CUR) ([CUR]= 6.10x10^-6 to 5.77x10^-5 mol.L-1) and ALA ([ALA]= 1.0x10^-5 mol.L-1), with TT (65.2°C/15min) and US (20W/20min) in 7.0 pH, by fluorescence spectroscopy in 5 temperatures (288.15 to 308.15 K). The stoichiometry (n) of the ALA-CUR complex was around 1.0 to all treatments and temperatures, indicating that even with ALA denaturation, only 1 CUR molecule has bonded to protein. The binding constant values (Kb) varied between 6.47x10^4 to 1.06x10^5 L.mol-1 for TT and from 8.18x10^4 to 1.36x10^5 L.mol-1 for US. Hence, with the temperature increase, there was a rise in complex formation for both treatments. The standard Gibbs’ free energy change of complex formation (ΔG°) was negative in both (TT=-26.51 to -29.60 kJ.mol-1 and US=-27.10 to -30.28 kJ.mol-1), showing that the thermodynamic equilibrium happened towards ALA-CUR complex formation. The interaction process was entropically directed, as shown by the positive values for standard enthalpy change (TT= 18.77 and US= 19.12 kJ.mol-1) and standard entropy change (TT=45.27 a 48.37 kJ.mol-1 and US= 46.22 to 49.40 kJ.mol-1) of complex formation. Our results showed that the protein denaturation by TT or US promoted the formation of stable complexes between CUR and ALA. These treatments may be attractive for industrial applications.