Effect of NaCl on physicochemical and rheological properties of hydroxypropyl cassava Starch–Xanthan gum mixture

As the primary electrolyte in salt-containing foods, NaCl governs interparticle repulsions and water partitioning across polymer networks. The mechanisms by which NaCl tunes electrostatic screening, hydration, and interpolymer association in HPCS–XG gels remain insufficiently defined. Here we integrate RVA, ζ-potential, LF-NMR, oscillatory/steady rheology, FTIR/XRD, and SEM to establish a salt-mediated mechanism that links ionic strength to gelatinization, network assembly, and water dynamics. NaCl decreases the absolute ζ-potential, contracts XG coils, and tightens HPCS–XG contacts while reducing effective water availability and perturbing hydrogen-bonding. These coupled effects suppress granule swelling and amylose leaching (19.92 → 12.02 g/g; 13.9 → 8.38 %), increase apparent solubility (18.0 → 63.5 %), and shorten the long-T₂ water population (1126 → 464 ms). At moderate ionic strength, reinforced interpolymer association yields a viscosity maximum (∼1246 cP at 0.5 M) and higher optical clarity; at 1.0 M, hydration limitation and restricted chain mobility outweigh associative gains, producing softer weak-gel networks (G′↓, tan δ↑) and reduced thixotropic recovery. Pasting temperature increases with salinity, and particle size shifts downward, consistent with suppressed swelling and screened interparticle repulsions. Microstructural evidence corroborates this pathway: lamellar matrices evolve into flocculated, particulate networks with increasing salinity; FTIR indicates no new covalent functionalities, and XRD reveals salt crystallites in dried gels. Collectively, the data converge on a unifying mechanism in which NaCl tunes electrostatic screening and hydrogen-bond architecture to control granule swelling, chain association, and water partitioning, defining a concentration-dependent optimum for viscosity and clarity and a predictable softening beyond 0.5 M. These rules provide actionable levers for designing salt-containing foods with targeted texture, stability, and processing robustness.