Stable oil-in-water emulsions prepared from soy protein-dextran conjugates

The solubility of acid soluble soy protein (ASSP) is poor in the pH range of 4-7. ASSP-dextran conjugates were prepared through the Maillard reaction to increase the solubility and/or dispersibility of ASSP. By using the conjugates and ultrasonication emulsification, stable oil-in-water emulsions with submicrometer-sized droplets were obtained. The factors, such as ASSP conjugation degree, that influence the emulsion stability were investigated. The emulsions were characterized using dynamic light scattering, zeta-potential, and atomic force microscopy. In the ultrasonication process, the increases of surface activity and aggregation of protein result in the formation of stable oil-water interface films. The dextran molecules conjugated to the protein effectively enhance the hydrophilicity and steric repulsion of the oil droplets, and therefore the emulsions are stable against heat treatment, long-term storage, and changes of pH and ionic strength. It was further verified that using protein-polysaccharide conjugates and ultrasonication emulsification is a versatile method for preparing stable emulsions.