Structural dichotomy in soy protein isolate-chitosan oligosaccharide gels: unraveling the distinct roles of 7S and 11S globulins.

Soy protein isolate (SPI) is widely used in food applications, but the natural variation in its 7S/11S globulin ratio leads to inconsistent gel properties. In this study, we investigated how the 7S/11S ratio influences the structural and rheological properties of composite hydrogels formed with chitosan oligosaccharide (COS). Spectroscopic analyses revealed that 7S-rich systems maintain a more flexible conformation with higher α-helix content (12.7%), whereas 11S-rich systems adopt a rigid, β-sheet-rich structure with β-sheet content increasing to 49.6% (compared to 34.7% in 7S-rich systems). Rheological measurements showed that increasing the 11S fraction progressively enhances the storage modulus, which reaches approximately five times that of 7S-rich gels, transforming the gel network from physically entangled to covalently cross-linked. Microstructural and water mobility analyses confirmed that 11S-rich gels form dense, compact structures that restrict water mobility, with transverse relaxation time decreasing from 238 ms to 180 ms, whereas 7S-rich gels exhibit looser structures. These findings demonstrate that the 7S/11S ratio is a critical determinant of the macroscopic properties of SPI-COS composite gels, providing a practical strategy for tailoring plant protein gel textures.