Designing Akebia trifoliata seed protein-polysaccharide complexes: An approach to improve emulsifying property

This study investigates noncovalent complexes of Akebia trifoliata seed protein (API) with chitosan (CS), guar gum (GG), sodium alginate (SA), and xanthan gum (XG) at pH 3.0 and 7.0. The zeta potential of API shifts from +33.90 mV at pH 2.0 to -32.55 mV at pH 7.0. At pH 3.0, positively charged API forms insoluble aggregates with anionic SA and XG via electrostatic attraction, while CS interacts with API to form soluble complexes; the particle size decreases from 1456.7 nm (API-3) to 1184.3 nm (API-CS-3), and the surface hydrophobicity declines by 6.2%. Neutral GG mainly interacts with API through hydrogen bonding. At pH 7.0, electrostatic repulsion between identically charged API and SA suppresses molecular aggregation, reducing particle size from 1632.6 nm (API-7) to 1580.6 nm (API-SA-7) and elevating API solubility by 57.57%, accompanied by a 24.56% reduction in surface hydrophobicity. Functionally, API-SA-7 exhibited the highest emulsifying activity (EAI = 27.86 m²/g), 55.7% higher than API-7 (17.90 m²/g). API-XG-7 showed superior emulsion stability (ESI = 93.49%), significantly exceeding API-3 (78.62%). These results demonstrate that pH-mediated charge matching and polysaccharide type synergistically modulate API functional properties, providing a clean-label strategy for valorizing this underutilized seed protein.