Cereal Chem 48:360 - 368.  |  VIEW ARTICLE
Denaturation of Soybean Proteins by Isoelectric Precipitation.

A. M. Nash, W. F. Kwolek, and W. J. Wolf. Copyright 1971 by the American Association of Cereal Chemists, Inc. 

Water extracts of soybean meal were acidified with hydrochloric acid; neutralized; equilibrated with a buffer of pH 7.6, ionic strength 0.5, containing 0.01M mercaptoethanol; and analyzed in an ultracentrifuge. Loss of solubility in the buffer, as compared to a nonacidified control, served as a criterion of denaturation. Factors causing denaturation were time of acid treatment and extremes of acidity. Two-hour acidification of water extracts to pH 4.5 decreased solubility and total ultracentrifuge area of the globulin fraction about 12%, with decreases in 2S, 7S, 15S, and greater than 15S fractions. Alkylation of sulfhydryl groups did not prevent these losses. When whey was removed before neutralizing, protein solubility was reduced and all ultracentrifugal fractions decreased in area. Even though no loss of protein solubility occurred on pH 4.5 treatment of water extracts that were dialyzed to remove phytates, total ultracentrifuge areas decreased. The 7S and 11S fractions accounted for most of the area losses. Although stable on titration of a water extract to pH 4.5, the 11S protein showed marked sensitivity to lower pH values. The 7S and 11S fractions decreased in water extractability with aging of the meal.