Abstract:

The interaction between tea polyphenol and soy protein isolate was studied by fluorescence, ultraviolet-visible
(UV-Vis) and Fourier transform infrared (FTIR) spectroscopies. The results suggested that tea polyphenol had a strong
ability to quench the fluorescence of soy protein isolate in a static mode. The binding constants (KA) and site numbers
(n) obtained at different temperatures were 4.571 × 105 L/mol, 1.316 (291 K); 2.955 × 105 L/mol, 1.299 (298 K); and
2.672 × 105 L/mol, 1.286 (310 K), respectively. According to the thermodynamic parameters, van der Waals force and
hydrogen bond played a dominant role in the interaction between tea polyphenol and soy protein isolate. The synchronous
fluorescence and UV-Vis spectra showed that tea polyphenol changed the microenvironment of the aromatic amino acid
residues in the space structure and the conformation of soy protein isolate. The synchronous fluorescence spectra also revealed
that tea polyphenol interacted with tryptophan residues in soy protein isolate, and the vicinity of tryptophan residues was less
hydrophobic. The FTIR spectra revealed that secondary structure of soy protein isolate was changed by tea polyphenol.

Key words: tea polyphenol, soy protein isolate, fluorescent spectroscopy, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy