Emulsifying Properties of Soybean β-Conglycinin and Glycinin: Evaluation by Turbidimetry

The emulsifying properties of soybean β-conglycinin (7S protein) and glycinin (11S protein) were investigated by turbidimetric measurements after their emulsification with oil by an ultrasonic instrument. The emulsifying properties were also evaluated by emulsion stability and microscopic observations. The turbidity of the 7S protein-stabilized emulsion showed a larger value than that of the 11S protein-stabilized emulsion with less protein quantity. The pH-turbidity curve of the 7S protein-stabilized emulsion decreased sharply at pH 5.0 and was closely related to its emulsion stability. However, the pH-turbidity curve of the 11S protein-stabilized emulsion had a broad concave curve near pH 6.0. The low turbidities at the isoelectric point were ascribed to large oil particles in the case of 11S protein and to the flocculation of small oil particles in the case of 7S protein. At ionic strengths between 0.1 and 0.4, the turbidity of the 11S protein-stabilized emulsion decreased considerably, while that of t...