Studies on the Emulsifying Properties of Soybean Proteins

Part IV. Emulsifying Behavior at High Protein Concentration

Abstract

Behavior of O/W emulsions which were formed by stirring 17.5% protein-water dispersion with soybean oil were studied, and the following results were obtained;
1. Any emulsions were not formed at isoelectric region of the proteins.
2. Native proteins showed much higher emulsifying capacity than that of heat-denatured proteins throughout pH range. Emulsifying capacity of the denatured proteins, however, increased 2-3 times by addition of NaCl or sucrose.
3. Effect of protein denaturation on emulsion stability appeared most remarkably when emulsions were frozen after being heated, and native proteins exhibited higher stability than that of heat-denatured proteins throughout pH range.
4. Emulsion stability was not generally affected by addition of NaCl or sucrose except the case of native proteins at neutral pH where emulsion stability for freezing was considerably improved by addition of sucrose.
5. Physical nature of emulsions generally showed sticky paste. After being heated at 90°C, however, these sticky pastes turned to weak or brittle gels in acidic and neutral pH range, and also turned to fairly tough gels in alkaline range.