Soy protein gelation

Abstract Heat‐induced protein gels are of importance for the structure and properties of many food products. Gel formation is a complex process which often involves several reactions such as denaturation, dissociation‐association, and aggregation. The kinetics of the reactions involved will determine the type of structure formed. Protein gels can be divided into two types: gels formed by random aggregation and gels formed by association of molecules into strands in a more ordered way. The two soy proteins glycinin and conglycinin both have the ability to form ordered structures consisting of strands 10–15 nm thick. The glycinin gel strands formed in distilled water are regular, and cross sections of strands showed a hollow cylindrical structure. In the presence of sodium chloride, glycinin forms an aggregated gel structure at 85 C, but at 95 C a regular structure similar to that found in distilled water was formed. The aggregated structure was interpreted as a transient state similar to the soluble aggregate formed on heating dilute solutions prior to dissociation into subunits. Conglycinin gels are more irregular and more cross‐linked than gels of glycinin. Also, the strands of conglycinin showed a complex mode of aggregation possibly in the form of double spirals. The addition of salt does not affect the microstructure of conglycinin gels as dramatically as in the case of glycinin gels. Commercially produced soy protein isolates may behave quite differently from native soy proteins, due to processing conditions causing denaturation and various states of aggregation.