Abstract: The in vitro simulated digestion of soybean protein isolate (SPI)-anthocyanin complexes with pepsin was carried out to investigate the effect of anthocyanin on protein digestibility, structure, subunit composition and molecular mass distribution were investigated during the digestion process. The results demonstrated that SPI was significantly digested in 30 min, and the protein digestibility of the control finally reached 48.5%. Furthermore, the addition of anthocyanins inhibited protein digestion. Anthocyanins inhibited 11S globulin digestion but promoted the degradation of 7S globulin α-subunit, one of the major soybean allergens, thus likely reducing the allergenicity of SPI. Size exclusion chromatography showed that the protein macromolecule was hydrolyzed into small molecular peptides, and the addition of anthocyanin inhibited the formation of small molecular peptides. The molecular mass distribution of the final products was mainly concentrated in the range of 3–100 kDa. Circular dichroism spectrum showed that anthocyanins changed the conformation of SPI; α-helix content gradually decreased and the contents of β-sheet and random coil while β-turn content changed irregularly. Fluorescence spectroscopy showed that anthocyanin increased the λmax and had fluorescence quenching effect on SPI. This study has clarified the mechanism of SPI dissociation from SPI-anthocyanin complexes, which will provide theoretical guidance for the preparation of easily digestible, highly absorbable, low allergenic protein products and well balanced nutritious diet in the field of food processing.

Key words: soy protein, anthocyanin, in vitro simulated digestion, structure