Study on the interaction of allura red food additive with pepsin using fluorescence technique

In this study, the interaction of pepsin with allura red food additive was investigated using a fluorescence spectroscopy method under quasi-physiological conditions. The experimental results indicated that allura red can quench the fluorescence of pepsin, the quenching rate constant (Kq), indicates that the quenching mechanism is static. The apparent binding constant (Ka) and binding site number (n) were evaluated at different temperatures. The results show that that the Ka for the association of SY with pepsin decreases with the rising temperature. Enthalpy (ΔH°) and entropy (ΔS°) were calculated as -45.584 (kJ mol-1) and -49.052 (J K-1 mol-1) respectively, which shows the importance of hydrogen bond formation and van der Waal’s interaction in binding of allura red to pepsin, the negative sign of free energy changes (ΔG°) indicates the affinity of color to protein. The results of synchronous fluorescence spectra showed that the microenvironment around Tyr and Trp residues is not significant changed binding between pepsin and allura red. According to experimental data, red allura can reducing the pepsin activity.