Construction and mechanism analysis of walnut protein-polysaccharide heterogeneous composite: Enhancing solubility...

This study investigated the effects of pH cycling-mediated heterogeneous conjugation with fucoidan on the functional properties of walnut protein isolate (WPI). Through systematic screening of five polysaccharides based on solubility and emulsifying characteristics, fucoidan was identified as the optimal conjugate partner, with the WPI:Fucoidan (F) ratio of 1:0.7 demonstrating significant functional enhancement. The combined pH cycling and polysaccharide conjugation treatment induced substantial structural modifications, as revealed by multi-spectroscopic analyses. While SDS-PAGE confirmed the preservation of primary structural integrity, circular dichroism spectroscopy indicated secondary structural reorganization characterized by decreased α-helix content (from 43.7 % to 31.5 %), increased β-sheet proportion (from 7.1 % to 22.3 %). Complementary fluorescence and UV-Vis spectral analyses revealed tertiary structural alterations, suggesting exposure of aromatic residues and conformational rearrangements. Physicochemical characterization demonstrated a 48.6 % increment in particle size (from 416 nm to 618 nm), decreased surface hydrophobicity (from 3562 to 2062 AU), and altered surface charge characteristics (zeta potential shift from -24.2 mV to -52.8 mV). These structural modifications collectively contributed to enhanced functional performance, particularly in emulsification capacity and interfacial stabilization. The findings establish pH cycling-assisted fucoidan conjugation as an effective strategy for modulating plant protein functionality through controlled structural reorganization.