Characterisation of interaction between food colourant allura red AC and human serum albumin: Multispectroscopic analyses and docking simulations

• Allura red AC formed complexes with HSA showing high affinity binding.
• Structural changes of HSA were demonstrated by CD and Raman quantitative analysis.
• CDOCKER algorithm in Discovery Studio was applied to analyse the specific binding sites in subdomain IIA.

Binding interaction of human serum albumin (HSA) with allura red AC, a food colourant, was investigated at the molecular level through fluorescence, ultraviolet–visible, circular dichroism (CD) and Raman spectroscopies, as well as protein–ligand docking studies to better understand the chemical absorption, distribution and transportation of colourants. Results show that allura red AC has the ability to quench the intrinsic fluorescence of HSA through static quenching. The negative values of the thermodynamic parameters ΔG, ΔH, and ΔS indicated that hydrogen bond and van der Waals forces are dominant in the binding between the food colourant and HSA. The CD and Raman spectra showed that the binding of allura red AC to HSA induces the rearrangement of the carbonyl hydrogen-bonding network of polypeptides, which changes the HSA secondary structure. This colourant is bound to HSA in site I, and the binding mode was further analysed with the use of the CDOCKER algorithm in Discovery Studio.