Thermodynamics of the interaction of the food additive tartrazine with serum albumins: A microcalorimetric investigation

The thermodynamics of the interaction of the food colourant tartrazine with two homologous serum proteins, HSA and BSA, were investigated, employing microcalorimetric techniques. At T = 298.15 K the equilibrium constants for the tartrazine-BSA and HSA complexation process were evaluated to be (1.92 +/- 0.05) x 10(5) M-1 and (1.04 +/- 0.05) x 10(5) M-1, respectively. The binding was driven by a large negative standard molar enthalpic contribution. The binding was dominated essentially by non-polyelectrolytic forces which remained largely invariant at all salt concentrations. The polyelectrolytic contribution was weak at all salt concentrations and accounted for only 6-18% of the total standard molar Gibbs energy change in the salt concentration range 10-50 mM. The negative standard molar heat capacity values, in conjunction with the enthalpy-entropy compensation phenomenon observed, established the involvement of dominant hydrophobic forces in the complexation process. Tartrazine enhanced the stability of both serum albumins against thermal denaturation. (C) 2014 Elsevier Ltd. All rights reserved.