Unraveling pH-shifting modulation of gluten-ionic polysaccharide interactions and network structure reconstruction: From physicochemical properties to microstructure

The S-G system maintained better structural integrity than other systems at pH 5. • The C-G system exhibited the maximum ordered structure content at pH 8. • The G-G system had higher water-holding capacity than other systems at pH 9. • The viscoelasticity and thermal stability of all systems were the lowest at pH 9. This study systematically investigated the effects of pH (5.0–9.0) on wheat gluten (G) and its composite systems with polysaccharides of different ionic characteristics: chitosan-gluten (C-G, cationic), guar gum-gluten (G-G, non-ionic), and sodium alginate-gluten (S-G, anionic). Results demonstrated that pH critically regulates intermolecular interactions and network formation by modulating the charge state of gluten and the ionization behavior of polysaccharides. Conformational rearrangements induced by pH significantly altered intermolecular forces—including hydrogen bonds, hydrophobic interactions, ionic bonds, and disulfide bonds—thereby influencing protein subunit stability and microstructure. Under neutral to weakly alkaline conditions (pH 7–8), all systems formed stable networks with uniform pore structures, primarily stabilized by ordered disulfide cross-linking, with synergistic contributions from electrostatic and hydrogen bonding interactions. In strongly alkaline environment (pH 9), thermal stability decreased significantly, with the lowest peak temperature (Tp) and enthalpy change (ΔH) observed across all groups, notably in G system (80.87 °C, 21.05 J/g). Under acidic conditions (pH 5), the S-G system exhibited superior structural integrity, showing higher storage modulus (G′ = 2350.53 Pa), disulfide bond content (18.2 μmol/L), and intensity of low-molecular-weight glutenin subunits (39.41 a.u.) than the G system (1753.43 Pa, 10.5 μmol/L, 31.5 a.u.), the C-G system (1943 Pa, 12.3 μmol/L, 33.87 a.u.), and the G-G system (1840 Pa, 11.8 μmol/L, 34.13 a.u.). These findings clarify how pH modulates the physicochemical and structural properties of gluten–polysaccharide composites, offering theoretical support for the rational design of gluten-based foods with tailored functionality and optimized process control.