Small-angle x-ray scattering study of the effect of pH and salts on 11S soy glycinin in the freeze-dried powder and solution states.

The nanostructures from powders of native protein, glycinin, and corresponding solutions from which the powders have been formed, have been studied as a function of pH and 1 M salts using small-angle X-ray scattering. All powders showed Porod scattering with the exception of that prepared from the solution close to pl which displayed fractal behavior. Well-defined Bragg peaks in the powder scattering at pH 5, pH 7, and 1 M NaCl indicate the presence of long-range order. The scattering from solutions at pH 7, pH 9, and 1 M NaCl can be described well on the basis of particles derived from the known atomic structures of homohexameric glycinin. Extreme acidic (pH 2) and basic (pH 11) environments lead to the partial denaturation of glycinin. Decreasing the pH to 2 initiates dissociation of the hexameric structure, while increasing the pH to 11, as well as the presence of 1 M NaSCN, results in the formation of large unimodal particles. This is reflected by "featureless" SAXS patterns for both powders and solutions. © 2010, American Chemical Societ