Polysaccharide charge and molecular architecture modulate whey protein isolate foams through colloidal association,...

Protein-polysaccharide interactions provide an effective strategy for regulating the multiscale structure and stability of food foams. In this study, whey protein isolate (WPI) was combined with sodium alginate (SA), pectin (PC), guar gum (GG), or chitosan (CS) to elucidate how polysaccharide charge characteristics and chain architecture influence WPI colloidal association, protein conformation, interfacial behaviour, rheology, and foam stability. At pH 4.0, SA and PC induced marked charge reversal, decreasing the zeta potential of WPI from +4.35 mV to -16.30 and - 16.13 mV, respectively. Circular dichroism analysis showed that PC caused the most pronounced secondary-structure redistribution, with the α-helix content decreasing from 20.67% to 12.60% and the β-sheet content increasing from 38.60% to 49.37%. Interfacial adsorption kinetics further differentiated the two anionic polysaccharides: WPI-SA exhibited the highest K_diff (3.04 mN·m^-1·s^-1/2), whereas WPI-PC showed the highest K_P (8.18 × 10^-4) and K_R (25.12 × 10^-4), together with the strongest elastic interfacial response. Consequently, WPI-PC achieved the highest foaming capacity (187.88%), the lowest equilibrium surface tension (37.86 mN/m), the smallest initial bubble diameter (10.93 μm), and the lowest TSI (17.05). In contrast, GG mainly enhanced viscous resistance and late-stage interfacial dissipation, whereas CS showed limited interfacial film reinforcement under pH 6.0. These results demonstrate that WPI foam stability is governed by the coordinated effects of colloidal association, protein conformational redistribution, interfacial adsorption and restructuring, and bulk/interfacial rheology. This study clarifies the distinct mechanisms by which different polysaccharides regulate WPI foam properties and provides a theoretical basis for designing protein-polysaccharide-stabilized food foams.