A Dynamic Light Scattering Study on the Complex Assembly of Glycinin Soy Globulin in Aqueous Solutions

In this work, the complex assembly of one of the major storage proteins in soybean, glycinin, was analyzed using dynamic light scattering, from the hydrodynamic diameter of assembled forms in solution. The protein concentration and temperature were maintained constant at 10⁻¹% w/w and 20 °C, respectively, and the pH was 7.6, 7.0 and 3.0. By analyzing the intensity and volume size distributions, a complex equilibrium between self-assembled forms could be determined. At pH 7.6 and an ionic strength of 0.5 M, where the self-assembly of glycinin has been widely reported in the literature, the DLS technique revealed an equilibrium between different assembled forms, that shifted towards the 11S form. At a lower ionic strength for pH 3.0 or 7.0, the 7S form predominated. The hydrodynamic diameter evolved differently upon heating, depending on pH and ionic strength. For pH 7 (I = 0.05) and 7.6 (I = 0.5) a significant increase in d_H was observed at a temperatures of 55 and 70 °C, respectively, which were significantly lower than the denaturation onset temperatures as determined by DSC. No changes in d_H nor a transition endotherm were observed at pH 3.