pH-modified insoluble soybean fibers tailor structural and rheological properties of emulsion gels for modulated lipid digestion

Structuring emulsion gels with dietary fibers offers a promising strategy for regulating lipid digestion. In this study, insoluble soybean fibers (ISFs) modified by acidic (pH 3, S₃-ISF) or alkaline (pH 11, S₁₁-ISF) steam-cooking were used to prepare emulsions/emulsion gels, and their effects on interfacial behavior, gel structure, rheology, and digestion properties were evaluated. S₃-ISF formed self-supporting weak emulsion gels at 1.0 wt%, whereas S₁₁-ISF required 2.0 wt%. Although both systems exhibited similar droplet sizes at these concentrations (25.89 and 25.14 μm, respectively), S₃-ISF produced a denser and more integrated droplet-fiber network. Consistent with its higher residual protein content, S₃-ISF reduced interfacial tension more rapidly and reached a lower value than S₁₁-ISF (8.56 vs. 11.24 mN/m), while forming a stronger and more elastic interfacial film. Accordingly, S₃-ISF emulsion gels exhibited higher viscosity, storage modulus (G' up to 405.3 Pa), and plateau modulus (G'_p up to 270.05 Pa). During simulated digestion, S₃-ISF emulsion gels maintained smaller gastric droplet/aggregate structures, whereas S₁₁-ISF systems showed weaker interfacial protection and greater aggregation. Final free fatty acid release ranged from 25.20% to 29.95%, with S₃-ISF systems generally showing slightly higher values than S₁₁-ISF systems. These findings demonstrate that pH-modified ISF can tailor interfacial and matrix-structuring roles, thereby moderately regulating emulsion-gel structure and lipid digestive.