Molecular interaction of soybean glycinin and β-conglycinin with (-)-epigallocatechin gallate induced by pH changes

The effect of pH on interactions of soybean glycinin (11S) and beta-conglycinin (7S) with (-)-epigallocatechin- 3-gallate (EGCG) were determined by turbidity. Results confirmed that the protein structure and interactions of 11S and 7S with EGCG depended largely on the pH. The binding affinity between 11S, 7S proteins and EGCG was strongest at pH 7.0 among the three pH levels and 75 showed a greater affinity to EGCG compared to 11S. The interaction mechanisms and structures of 11S-EGCG and 7S-EGCG complexes were further determined by multiple spectroscopic technique and molecular docking. Results showed that EGCG induced changes in the microenvironment of tryptophan, tyrosine, and C-H bending vibration at different pH levels. Binding to EGCG altered the secondary structures of the 11S and 7S proteins, inducing an increase in p-sheet at the cost of alpha-helix at pH7.0 and alpha-helix at pH5.0, respectively. The 11S and 7S presented more compact microstructure with the addition of EGCG. Electrostatic interaction, hydrogen bonding and hydrophobic interaction were all involved in the formation of complexes, where the hydrogen bond was the dominant one. These results might be helpful for the development of 11S-EGCG and 7S-EGCG as a bioactive food additive in the food industry.