Structural characterization, function, and mechanism in enhancing WPI emulsion of blackcurrant polysaccharides: From...

In this study, the structures of blackcurrant polysaccharide (PNBP, M_w = 2.12 × 10⁶) and the high-pressure-assisted enzymatically degraded derivative (PDBP, M_w = 1.49 × 10⁵) were comprehensively characterized using high performance liquid chromatography, nuclear magnetic resonance, and methylation analyses. PNBP and PDBP featured a similar backbone composed of the repeating units →5)-α-L-Araf-(1→, →4)-α-D-GalAp-(1 → and →2,4)-α-L-Rhap-(1→, which provided additional potential sites for electrostatic attraction, hydrogen bonding and hydrophobic interactions. However, PDBP with relatively low molecular weight and high uronic acid content displayed better water-solubility, physical stability and rheological property than PNBP. Fluorescence microscopy and confocal laser scanning microscopy observations revealed that the PDBP-incorporated whey protein isolate (WPI-PDBP) emulsion exhibited smaller particle size (D_[4,3] = 2.89 ± 0.14 μm, D₅₀ = 2.14 ± 0.06 μm) than WPI-PNBP emulsion, reflecting superior dispersibility and stability. Rheology, interfacial tension and contact angle measurements demonstrated that the elevated viscosity of the continuous phase and reduced interfacial tension (13.05 mN/m) were key factors contributing to the improved performance of WPI-PDBP emulsions. Furthermore, ultraviolet spectroscopy, Fourier transform infrared spectroscopy and isothermal titration calorimetry analyses revealed strong intermolecular interactions between the polysaccharide and WPI, which induced conformational changes in WPI including the exposure of hydrophobic chromophores. Molecular docking and dynamics simulations confirmed the high stability of the PDBP-β-lactoglobulin (β-Lg) complex, with a binding free energy of -64.08 kcal/mol (vs. -56.29 kcal/mol for the PNBP-β-Lg complex). Therefore, this study provides critical insights into the molecular mechanisms through which natural polysaccharides improve the emulsifying properties of proteins.