Soy Protein Functionality: Emulsion and Gels

Soy proteins are a heterogeneous group of proteins that are often used as ingredients in foods because of their functionality. The most abundant storage proteins, glycinin and β-conglycinin, play a major role in imparting processing functionality to soy protein-based ingredients. Soy proteins readily adsorb at the interface of oil droplets, with surface loads varying between 2 and 4 mg m−2 and a layer thickness between 30 and 40 nm. Heating of emulsions increases the surface load at the interface, and the composition at the oil–water interface depends not only on the temperature of heating but also on the order of heating and homogenization. Heating is also a step necessary for the formation of soy protein gels, causing unfolding of soy proteins, formation of disulfide bridges, and an increase in gel stiffness. After heating, gels continue to stiffen with cooling. After heat denaturation, gelation can be induced with acid or ions. This chapter attempts to summarize our current understanding of the fundamentals of protein functionality in emulsions and gels, and it shows how with processing or genetic variability it will be possible to obtain a number of soy protein isolates with different protein subunit ratios, affecting the processing performance of the ingredients, and the quality of the final product.