Cereal Chem 40:504 - 514.  |  VIEW ARTICLE

Physical Properties of Alcohol-Extracted Soybean Proteins.

W. J. Wolf, A. C. Eldridge, and G. E. Babcock. Copyright 1963 by the American Association of Cereal Chemists, Inc. 

Isolated soybean proteins contain phospholipid-like materials which are extractable with aqueous alcohols. Since alcohols are protein denaturants, their effects on the physical properties of soybean proteins were investigated. Solubility of freeze-dried, isoelectric-precipitated soybean proteins in pH 7.6, 0.5 ionic strength, phosphate buffer was 59%. In the presence of 0.01M mercaptoethanol, solubility in buffer increased to 80% as a result of depolymerization of disulfide polymers of the 7S and 11S ultracentrifuge components. Extraction of the proteins for 2 hr. at 25 C. with 94% methanol, 83% ethanol, or 77% isopropanol decreased solubility (in the presence of mercaptoethanol) to 66-71%. Water-saturated butanol decreased solubility to 25%. The 7S and 11S components accounted for most of the protein insolubility. Loss of protein solubility apparently is caused by denaturation rather than by extraction of phospholipids by the alcohols. Optical rotation, viscosity, and ultracentrifugal measurements indicate that the proteins which retain their solubility are undenatured. Purified 11S component, in which the sulfhydryl groups are blocked with N-ethylmaleimide, forms soluble aggregates upon extraction with 83% ethanol. Extent of aggregation was reduced at low extraction temperatures.