**3. Soy Proteins**

Soy proteins are mainly composed of 40% 7S (β-conglycinin) and 30% 11S (glycinin) fractions. The 7S globulin has been shown to have better emulsifying properties than the 11S globulin, which is due to the 11S globulin's more stable oligomeric form. Rivas and Sherman [6] found that 7S formed a stronger viscoelastic film at the oil–water interface than 11S at all the tested pH and NaCl concentrations. They concluded that the 7S globulin molecules have a higher degree of intra- and intermolecular cohesion, resulting in more organized films at the interface. Glycinin cannot adsorb quickly to the air–water interface due to its low surface hydrophobicity, large molecular size, and low molecular flexibility. Liu et al. [7] observed that the acidic subunits of glycinin adsorb more quickly to the air–water interface than raw glycinin. Soy protein acts as a macromolecular surfactant to stabilize oil-in-water emulsion systems in food products such as sausages, ice cream, yogurt, and coffee whitener [8]. It has been proposed that the surface hydrophobicity and solubility are the major factors determining emulsifying activity, while the molecular flexibility of the proteins is important for emulsion stability [9]. However, the solubility of soy proteins was limited in the food matrix due to the isoelectric point being around 5.0. Moreover, the globular structure of the soy proteins prevents the exposure of the hydrophobic residues and retards the conformational change of protein when adsorbing at the interface, preventing them from becoming more efficient at reducing interfacial tension [10]. In recent years, soy proteins are considered effective starting materials to produce functional emulsifiers with modified physico-chemical properties by using different enzymatic, physical, chemical, and biological methods [11].
