Effect of pH and ionic strength on rheological and textural properties of fava bean protein–pea starch composite gels

Understanding the structure formation of protein–starch composite gels is essential for tailoring texture and functionality in plant-based systems. This study systematically investigated fava bean protein–pea starch gels to determine how starch-to-protein ratio, pH (5 and 7), and ionic strength (0.0, 0.3, and 0.5 M NaCl) affect gel formation, texture, and rheological properties. Differential scanning calorimetry showed that increasing ionic strength shifted starch gelatinization to higher temperatures, while protein denaturation temperatures increased with NaCl and at elevated pH. Pasting behavior was strongly ratio-dependent, with starch-rich systems showing reduced viscosities at pH 7 and pronounced salt effects at pH 5. Texture profile analysis indicated that gel hardness depended on composition and formulation conditions: protein-rich gels were harder at pH 7 than pH 5, with NaCl increasing hardness at pH 5 but decreasing it at pH 7, while starch-rich gels softened at pH 5 with increasing NaCl. Oscillatory rheology showed that intermediate mixtures exhibited reduced storage modulus (G′), whereas protein-rich gels displayed maximum stiffness at pH 5 and improved elasticity at pH 7. Increasing the total solids content to 20% enhanced the complex modulus (G*), particularly at pH 5. ATR-FTIR analysis indicated primarily non-covalent protein–starch interactions, with no evidence of new covalent bond formation and spectral changes consistent with hydrogen bonding interactions. Overall, the starch-to-protein ratio governs pasting, gelation, and texture, with pH and ionic strength acting as modulators, yielding formulation-relevant insights that enable the targeted design of protein–starch-based foods with tailored textural, rheological, and stability properties.