Abstract: The aim of this study was to compare the effects of different concentrations of anthocyanins on the functional properties of proteins through non-covalent/covalent interactions. The complexes of anthocyanins and soybean protein isolate (SPI) were studied by three-dimensional fluorescence spectroscopy. The relationship between the structural changes of protein-anthocyanin complexes and protein functional properties with non-covalent/covalent interactions was analyzed by determination of emulsifying properties and foaming properties, light microscope observation and measurement of sulfhydryl content. The results showed that the fluorescence intensities of the characteristic peaks of the proteins decreased, accompanied by the occurrence of unfolded polypeptide chains, with the increase of anthocyanin concentration after treatment at pH 7.4 for 2 h or at pH 9.0 for 24 h, and the covalent binding was stronger than the non-covalent one. The emulsifying properties and foaming properties of the complexes were improved as compared with SPI, and the content of sulfhydryl group was decreased, especially for sample 6 (treatment with 2 mg/mL anthocyanins at pH 9.0 for 24 h). The droplet sizes of emulsion systems 5 (with 1 mg/mL anthocyanins at pH 9.0 for 24 h) and 6 were homogeneous, and the emulsions were stable.

Key words: soybean protein isolate (SPI), anthocyanins, emulsifying properties, foaming properties