The effects of emulsifier concentration, ionic strength, and heating on the emulsions formed by soy protein isolate (SPI) sodium caseinate (SC), and sucrose ester (SE) were investigated to evaluate their emulsifying properties. Results showed that fine and stable emulsions could be prepared at 20 g/L for SPI, 12 g/L for SC, and 2.0 g/L for SE, with the average diameter of (0.724±0.238), (0.451±0.003), and (0.541±0.003) μm for d4,3, respectively. When the emulsifier concentration was not enough to saturate the oil/water interface created during emulsification, the instability mechanisms of emulsions formed by different emulsifiers were different. Emulsions formed by SC and SE only showed droplet coalescence, however, emulsions formed by SPI showed bridging flocculation of droplets probably caused by the insoluble protein particles existed in SPI dispersion. The addition of NaCl into the emulsions formed by SPI, SC, and SE could cause emulsion creaming and droplet flocculation as observed using confocal laser scanning microscopy (CLSM). However, the sizes of droplet flocs could not be measured using Mastersizer 3000, because they were broken up by the sample preparation procedures required for Mastersizer 3000, suggesting that the droplet flocculation was caused by the electrostatic shielding effect of NaCl were rather delicate. The heat of the 90 ℃ at NaCl concentration of 0.15 mol/L resulted in a conformational change of the SPI and a slow unfolding of the globulin at the oil-water interface, exposing more hydrophobic groups to hydrophobic interactions and leading to increased flocculation, indicating that the SPI is stable against coalescence under environmental stresses.
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