Cereal Chem 51:220 - 227. | VIEW
Extraction of Soybean Proteins with Aqueous 2-Mercaptoethanol.
A. M. Nash, W. F. Kwolek, and W. J. Wolf. Copyright 1974 by the American Association of Cereal Chemists, Inc.
Water, 0.01M, and 0.1M 2-mercaptoethanol extracts of fresh and aged defatted soybean meals were equilibrated, either directly or after 10% sodium chloride solution-distilled water dialysis, with pH 7.6, ionic strength 0.5 buffer with and without 0.01M 2-mercaptoethanol. Kjeldahl and ultracentrifugal analyses of the extracts showed that reductant in the extraction medium increased protein extractability; mainly additional 7S and 11S proteins were solubilized. A portion of these proteins apparently exists in defatted meal as water-insoluble disulfide polymers that are depolymerized and solubilized by 2-mercaptoethanol. Ultracentrifugal analyses of the water extracts in buffer with and without 0.01M 2-mercaptoethanol also revealed significant amounts of water-soluble disulfide polymers of the 7S fraction. Similar analyses of the reductant extracts indicated that the 7S and 11S fractions repolymerized partially during dialysis against buffer to remove the reducing agent except when aged meals were extracted with 0.1M 2-mercaptoethanol. Exhaustive dialysis of the extracts against salt followed by distilled water failed to increase disulfide repolymerization over amounts obtained on shorter-term dialysis against buffer. Rather, losses of protein and changes in protein distribution occurred; generally, the 2S fraction increased and the 7S and 11S fractions decreased on exhaustive dialysis.