Soy protein structures and performance properties

A realistic view is needed to understand soy performance properties when used as wood adhesives. Proteins definitely behave neither as elongated organic polymers with inter-chain interactions along their length, nor as standard colloidal adhesives with a surfactant surface layer. The soy adhesive literature is unfortunately filled with misconceptions that lead to incorrect models for explaining soy dispersions. Individual soy protein chains have their own primary, secondary and tertiary structures. Changes in the tertiary protein structure by interactions with the external environment influences the formation of quaternary structures. The flocculation of the proteins in solution to form higher order structures is clear from rheological experiments. Denaturation affects the secondary and tertiary structures, which alters the globular surface, but does not eliminate the proteins from forming higher order complexes. During denaturation processes proteins become molten globules that allow alteration of their refolding and interaction with other proteins, but does not exhibit the very high viscosity expected for an extended chain. Contrary to the often mentioned model in the literature, formation of an extended chain in solution is very energetically unfavored due the loss of internal hydrophobic and polar interactions and the loss of water-water bonds if the protein is to worm its chain into the water.