Insights into the mechanism on Glucono-delta-lactone induced gelation of soybean protein at subunit level

To elucidate the gelation process and gel properties of coagulation in soybean protein at subunit level, the dispersions of subunits (αα′- and β-subunit) of β-conglycinin and polypeptides (acidic and basic polypeptides) of glycinin were coagulated by Glucono-delta-lactone (GDL), and the gelation processes were monitored with a dynamic rheometer. The rheological properties, microstructure, water distribution, and secondary structure of the gels were determined as well. The results showed that the β-subunit and basic polypeptide coagulated faster, while αα′-subunit and acidic polypeptide developed firmer and finer gels, who had stronger ability of water holding and contained higher content of β-sheet structure. The GDL-induced subunits/polypeptides gel network were dominated by hydrophobic interactions and disulfide bonds. It is proposed that the mechanism on gelation of soybean protein at subunit level as: with acidification of GDL, the basic polypeptide and β-subunit initially aggregate and form a proto-gel matrix. Subsequently, with the developing of gelation, α- and α′-subunits, especially acidic polypeptide, who is the last one to coagulate, complements to form finer and firmer network, and finally grows together to a mature gel. Besides the gelation rate, the higher content of β-sheet secondary structure and better water holding ability of acidic polypeptide and αα′-subunits would also contribute to the firmness of gel. The elucidation of the gelation mechanism at subunit level would support innovation of gelling technique and benefit the soybean industry.