posted on 2021-02-12, 12:34authored byYaohui You, Liu Yang, Hong Chen, Linying Xiong, Fan Yang
In
the present study, soy protein isolate (SPI) was noncovalently
modified by (−)-epigallocatechin-3-gallate (EGCG), and its
foaming, emulsifying, and antioxidant properties were all significantly
increased. Fluorescence analysis revealed that the fluorescence quenching
of SPI by EGCG was static quenching. EGCG mainly changed the folding
state of SPI around Trp and Tyr residues, and the binding site was
closer to Trp. UV–vis spectra further proved that more hydrophobic
residues of SPI were exposed to a hydrophilic microenvironment. Circular
dichroism spectra indicated that the contents of ordered structures
were transforming into random coils with the reduce of α-helix,
β-sheet, and β-turns by 3.8%, 2.0%, and 1.2%, respectively.
Meanwhile, the binding stoichiometry of two molecules of EGCG per
one molecule of SPI was obtained from isothermal titration calorimetry,
and the interaction was a spontaneous endothermic process with a noncovalent
complex preferentially formed. According to thermodynamic parameters
and molecular docking model, hydrophobic force and hydrogen bonds
were considered to be the main interaction forces between SPI and
EGCG. Overall, after modification through the high affinity to EGCG,
the structure of SPI became looser and exposed more active groups,
thus resulting in an improvement of its foaming, emulsifying, and
antioxidant properties.