Emulsification performance and stabilization mechanism of okra polysaccharides with different structural properties

To systematically study the relationship between structural and emulsification properties of okra polysaccharide, OPW (okra polysaccharide extracted by water), OPH (okra polysaccharide extracted by hydrochloric acid), and OPA (okra polysaccharide extracted by alkali) were prepared, which were all Rhamnogalacturonan-I enriched polysaccharides. OPW and OPH showed the same glycosidic bonds, while the degree of methyl-esterification (DM) and protein content were significantly different. The molecular weight (Mw, 7304.39 kDa) and DM (6.54%) of OPA decreased significantly, while its (Gal + Ara)/Rha was the largest. OPW, OPH, and OPA were able to emulsify oil in water over a wide pH range (3–7) at low concentration, while OPA demonstrated the poorest emulsifying stability under thermal and storage conditions. The emulsifying properties of okra polysaccharides were regulated by multi-scale molecular structure. OPA, with the highest electrostatic repulsion and the longest side chain, formed the largest d4,3 (108.94 μm) and the thinnest interface layer (0.25 μm). OPW, with the highest acetyl content (6.33%) and protein content (14.04%), formed the thickest interfacial layer (0.97 μm) and a medium d4,3 (86.40 μm). OPH, with the highest DM (33.43%) and the largest Mw (8454.63 kDa), formed a medium interfacial thickness (0.83 μm) and the smallest d4,3 (72.30 μm), exhibiting the best emulsifying performance. The present results showed controlling factors for emulsifying properties of okra polysaccharide were hydrophobic groups and steric interactions, rather than electrostatic repulsion. Meanwhile, okra polysaccharides can be strong candidates for emulsification.