Molecular Interactions of a Modified Soy Protein Isolate

Authors: CRAMP, GRACE - NC STATE UNIV; Kwanyuen, Prachuab; DAUBERT, CHRISTOPHER - NC STATE UNIV

Submitted to: Annual Meeting and Expo of the American Oil Chemists' Society
Publication Type: Abstract Only
Publication Acceptance Date: 4/5/2007
Publication Date: 5/13/2007
Citation: Cramp, G.L., Kwanyuen, P., Daubert, C.R. 2007. Molecular Interactions of a Modified Soy Protein Isolate. Annual Meeting and Expo of the American Oil Chemists' Society.

Interpretive Summary:

Technical Abstract: A thermally modified soy protein isolate (SPI), prepared at 8% protein (w/w) for three hours at 95°C, was readily reconstituted and demonstrated improved heat stability and cold-set gel functionality compared to an unheated isolate. Treatment of SPI with iodoacetamide prevented gelation, establishing the role of disulfide bonds in network formation. Addition of 8M urea to the SPI reduced the viscosity by two orders of magnitude, and when combined with 10mM DTT the viscosity was decreased by another order of magnitude. These results suggested that after disulfide bonds form, hydrophobic interactions or entanglements played a primary role in gel strength. The viscosity of 3% protein (w/w), prepared equivalently and reconstituted to 8% protein (w/w), was about three orders of magnitude less than the original sample. After both concentrations were reheated at 8% protein (w/w), the viscosity of SPI heated originally at 3% protein (w/w) was still nearly two orders of magnitude less. These results suggested that the protein is irreversibly denatured at low concentrations, limiting network formation even after an increase in protein concentration provides more interaction sites. The concentration dependence indicates that disulfide bonds are intermolecular. The combined protein interactions produced a powdered soy protein isolate ingredient with consistent cold-set and thermally-induced gelation properties.