Abstract: Covalent binding of ferulic acid (FA) to soy protein isolate (SPI) by free radical method was used to prepare gluconolactone (gluconolactone, GDL)-induced emulsion gels. The effects of FA covalent binding on the SPI structure, emulsion properties and emulsion gel characteristics were investigated. The optimum concentration of FA binding was determined at 150 μmol/g protein by the analysis of intermolecular forces, textural properties and water holding capacity of the SFA emulsion gels. Under this conditions, spectral analysis showed that FA had a fluorescence quenching effect on SPI, and after covalent binding of FA a decrease in the β-folded content and an increase in the α-helical content, β-turned content and irregular curl content of SPI were appeared. The absolute value of ζ-potential and interfacial protein content of SFA emulsions increased, and the mean particle size and apparent viscosity of SFA emulsions decreased. Final storage modulus of SFA emulsion gels (G ') increased, and the changes in relaxation time and peak ratios in the low-field NMR measurements indicated that the SFA emulsion gels had better hydration properties; the SFA emulsion gels had a more uniform and dense porous network structure. The results show that the SPI covalently bound by the 150 μmol/g protein FA radical method is valuable for the preparation of emulsion gels.

Key words: ferulic acid, polyphenol covalently combined, soy protein, gel properties, emulsion gels