This study aimed to research the effects of β-sheet content and fibril length in three categories ((low, medium, and high β-sheet) and (short, medium, and long fibrils)) on soy protein isolate (SPI) emulsions. The highest surface hydrophobicity (H0) (27,600 ± 100) was detected in the sample with the highest β-sheet content and the longest fibril length. The interfacial tension presented that the sample with the highest β-sheet content and longest fibril length could adsorb quickly at the oil (O)/water (W) interface. The emulsion stabilized by high β-sheet content and long fibril length had a lower droplet size (202 ± 4.35 nm) with more homogenous distribution and higher viscosity (8.75 ± 0.13 cP) due to more entanglement. According to the environmental stresses results (i.e., various ionic strengths (0–400 mM), pH changes (2–9.5), thermal treatment, and 30 days of storage), the emulsion prepared by the sample with the highest β-sheet content and the longest fibril length was more stable than other emulsions. Moreover, all emulsions were unstable against freeze-thaw treatment. Finally, it could be concluded that higher content of β-sheet and longer fibril led to the stability of emulsion through higher initial absorption at the O/W interface, formation of a continuous and thicker membrane coating at the O/W interfaces, viscosity improvement, and H0 enhancement.

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