Abstract: In this study, four industrial modification methods including heat treatment, alkali treatment, glycosylation and oxidation were applied to modify soybean protein isolate (SPI) to investigate their effects on the structure of SPI. The texture and microstructure of the hybrid gels of the modified soybean protein and myofibrillar protein (MP) were further investigated. The results showed that the four industrial modifications did not have a significant effect on the subunit composition of SPI, but they reduced the contents of α-helix and random coil structures and increased the contents of β-sheet and β-turn. Industrial oxidation significantly reduced the disulfide bond content of SPI, while the other treatments significantly increased the disulfide bond content and reduced the free sulfhydryl group content of SPI (P < 0.05); all four treatments changed the disulfide bond configuration of SPI. Tyrosine residues of SPI modified by each method tended to be exposed outside, and tryptophan residues were buried inside after oxidation but were exposed outside after the other modifications. The texture characteristics of SPI-MP hybrid gel showed that the hardness, elasticity, adhesion, and chewiness of the hybrid gels with heat, alkali and glycosylation modification were significantly better than those of the control SPI (P < 0.05). All texture characteristics except cohesiveness of the hybrid gel with oxidized SPI were poorer than those of the control SPI. Under scanning electron microscopy, it was seen that the oxidized SPI-MP hybrid gel was rough and porous, while the hybrid gels with the other industrial modifications were more dense and uniform.

Key words: industrial modified soybean protein isolate, myofibrillar protein, structural properties, gel properties