Role of β-Conglycinin and Glycinin Subunits in the pH-Shifting-Induced Structural and Physicochemical Changes of Soy Protein Isolate
Article first published online: 1 MAR 2011
© 2011 Institute of Food Technologists®
Journal of Food Science
Volume 76, Issue 2, pages C293–C302, March 2011
How to Cite
Jiang, J., Xiong, Y. L. and Chen, J. (2011), Role of β-Conglycinin and Glycinin Subunits in the pH-Shifting-Induced Structural and Physicochemical Changes of Soy Protein Isolate. Journal of Food Science, 76: C293–C302. doi: 10.1111/j.1750-3841.2010.02035.x
- Issue published online: 1 MAR 2011
- Article first published online: 1 MAR 2011
- MS 20101005 Submitted 9/6/2010, Accepted 12/8/2010.
- emulsifying property;
- soy protein
Abstract: Soy β-conglycinin (7S) and glycinin (11S) were incubated up to 4 h in acidic (pH 1.5 to 3.5) or alkaline (pH 10 to 12) solutions to induce protein structural unfolding followed by refolding 1 h at pH 7.0, a process known as pH-shifting. The pH-shifting markedly increased (P < 0.05) emulsifying activity of 11S and to a lesser extent 7S; the former also produced more uniform oil droplets. The emulsifying activity improvements were accompanied by a significant rise in protein surface hydrophobicity, slight loss of the secondary structure (circular dichroism), and substantial dissociation of disulfide-linked basic and acidic 11S subunits. The findings suggested that 11S globulins of soy protein isolate (SPI) were more responsive to pH-shifting treatments than were 7S globulins, and the resulting emulsifying activity enhancements of 11S, in parallel with that of SPI, were indicative of its determinant role in the overall emulsifying properties of pH-shifting-treated SPI.
Practical Application: Extreme alkaline (pH 12) and acidic (pH 1.5) medium treatments can significantly modify the structure and enhance the emulsifying properties of both β-conglycinin and glycinin components of SPI. The functionality improvement by the pH processes is more remarkable for the glycinin protein fraction. Therefore, SPI enriched with glycinin seems to be particularly suitable for extreme acidic or alkaline processes to produce surface-active functional ingredients for food applications.