β-CAROTENE-LYSOZYME SUPRAMOLECULAR COMPLEX FORMATION: A KINETIC AND THERMODYNAMIC APPROACH

β-carotene (BC) is a powerful antioxidant; however, its low water solubility and high chemical instability limit its application in foods. The BC-lysozyme (LYS) complex formation can overcome such limitations, but the successful use of BC-LYS complex requires understanding the kinetics and thermodynamics of this complex formation. Here, we determined the kinetic and thermodynamic parameters of BC-LYS complex formation, at pH 7.4 and temperature range of 12-28 ºC, using the surface plasmon resonance technique. The kinetic association constant (ka) was 103 M-1s-1, and it increased 2.6-fold when temperature increased from 12 to 28 ºC (ka= 1.15 ˣ 103 to 3.00 ˣ 103 M-1s-1, respectively). These values were lower than those found for other bioactive molecules interacting with globular proteins, which is probably related to the rigid structure of BC. On the other hand, the kinetic dissociation constant (kd) showed a second-order polynomial behavior, with a minimal point at 20 ºC (kd=0.362 s-1). The ka/kd relationship yielded the thermodynamic binding constant (Kb), which ranged from 2.71 ˣ 103 to 7.26 ˣ 103 M-1, from 12 to 28 ºC, respectively. At equilibrium, the BC-LYS concentration predominated over the free LYS and BC molecules since the standard Gibbs free energy was negative (ΔG°≈ -20.63 kJ.mol-1). The standard enthalpy and entropy changes were positive (ΔH°= +43.72 and TΔS°≈ +64.34 kJ.mol 1, respectively), indicating that the process of BC-LYS complex formation was entropically driven. Considering that the complex formation is endothermic, more complexes will be formed, and they will be more stable during processing steps involving absorbing energy. This work showed that LYS and BC formed complexes, whose kinetics and thermodynamics depended on temperature. Additionally, LYS shows to be a potential carrier for BC in different matrices.