Complexation with Ionic Polysaccharides Mitigates pH-Dependent Degradation of Soy Protein Fibril Structure and Functionality

This study explored complexation of soy protein fibrils with gellan gum (anionic) and chitosan (cationic) to mitigate pH-induced degradation of fibril structure and function. Unfibrillated proteins combined with polysaccharides were studied as controls. Chitosan complexation preserved fibril integrity, with a moderate particle size increase (∼2.5x) and AFM imaging of fibrils alongside some aggregates when pH was increased from 2 to 4. FTIR analysis confirmed that chitosan best preserved the fibril β-sheet structure, primarily through electrostatic interactions. A Rapid Visco Analyzer study revealed that chitosan-modified fibrils retained their gelling ability at pH 4 (final viscosity ≈ 115 cP), comparable to fibrils at pH 2 (∼93 cP). Gellan gum complexation resulted in the formation of self-supporting gels at pH 7 (final viscosity ≈ 688 cP), likely due to electrostatic repulsion between like-charged components. Overall, this work provides valuable insights into mitigating pH-induced fibril degradation, thus expanding the potential applications of protein fibrils in food matrices.