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The emulsifying properties of soy protein isolate were measured at various conditions, and the relationships between the emulsifying properties and solubility, viscosity, hydrophobicity, protein adsorption, the tension at water-oil interface were investigated. The emulsifying properties are minimum at the isoelectric point(pI), and the effect of pH parallels its effect on protein solubility. The emulsifying activity is increasing up to 50 and then is somewhat decreasing above that temperature, while the emulsion stability is continuously decreasing. Except for phosphates, the salts cause the decrease of the emulsifying properties. The hydrophobicity is increasing as the temperature increases and decreasing somewhat as pH gets lower. However, it is increasing substantially at pH below the pI. The maximum protein adsorption at the water-oil interface is 0.78, 0.47, and 0.33㎎/㎡ at pH 2, 7, and 4, respectively. The tension at water-oil interface is 19.76 dyne/㎝ in the absence of soy protein, whereas it is decreasing to 11.45-18.08 dyne/㎝ in the presence of the protein.
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