pH-dependent interaction between Gallic acid and mung bean globulin amyloid fibrils: effects on interfacial behavior and emulsifying properties

Abstract

The structural properties of mung bean globulin amyloid fibrils (MBGF) regulated by pH and their influence on the binding behavior with gallic acid (GA) and interfacial functionality were systematically investigated. Zeta potential results showed that pH dominated the aggregation and dispersion behavior of MBGF by altering its net charge. At pH 4.0, electrostatic shielding induced MBGF aggregation, leading to the lowest ThT fluorescence intensity. FT-IR analysis revealed that increasing pH reduced the contents of α-helix and β-sheets. At the same time, the introduction of GA further modulated the β-sheets organization through hydrogen bonding and hydrophobic interactions. Fluorescence quenching analysis demonstrated that the interaction between MBGF and GA followed a static quenching mechanism. The thermodynamic parameters (ΔH > 0, ΔS > 0) suggested that the binding process was spontaneous under all pH conditions and primarily driven by hydrophobic interactions. Functionally, pH regulated the emulsifying performance of MBGF by controlling its aggregation state. At pH 2.0 and 7.0, the MBGF-GA complexes exhibited higher interfacial pressure, faster adsorption kinetics, and superior emulsifying activity and stability. These findings provide valuable insights into the rational design of MBGF-GA systems as efficient emulsion stabilizers under different pH conditions.