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) × 105 M−1 and (1.04 ± 0.05) × 105 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.