Comparison of interaction mechanism between chlorogenic acid/luteolin and glutenin/gliadin by multi-spectroscopic and thermodynamic methods

This research aims to investigate and compare interaction mechanisms between glutenin (Glu)/gliadin (Gli) and chlorogenic acid (CA)/luteolin (LU) at pH7.0, as well as its impacts on the structure of Glu/Gli and antioxidant activity of CA/LU. CA/LU strongly quenched the fluorescence of Glu/Gli in a static mode, and fluorescence quenching of Glu/Gli by CA was stronger than that of LU. Binding constant (Ka) of CA and Glu was the largest among four mixed systems. The isothermal titration calorimetry also confirmed that Ka were declined in the order of Glu-CA, Gli-CA, Glu-LU and Gli-LU, and the main forces were hydrogen bonding and hydrophobic force. Synchronous fluorescence demonstrated the interaction sites of CA/LU with Glu/Gli were close to Tyr and Trp residues, respectively. Three-dimensional fluorescence spectra manifested CA had a greater impact on conformation of Glu/Gli. Meanwhile, secondary structure analysis displayed that CA made the structure of Glu/Gli disordered, whereas LU made the structure of Glu/Gli more compact. Furthermore, CA/LU reduced the surface hydrophobicity of Glu/Gli. This interaction displayed a synergistic antioxidant effect, and the synergistic effect was stronger in CA-Glu and CA-Gli. Therefore, these findings suggest that interaction mechanisms and the effect of CA/LU on structure of Glu/Gli are significant different.