Intermolecular interactions and phase structures of plasticized wheat proteins materials

The intermolecular interactions and phase structures of thermally processed wheat proteins with glycerol and water as plasticizers were studied by dynamic mechanical analysis and solid-state high-resolution NMR spectroscopy. The results of phase structures at scales of molecular level to tens of nanometers were correlated with the mechanical properties of the materials. The strong hydrogen bonding intermolecular interactions between the components in wheat proteins and the plasticizers resulted in a significant change in molecular motions of wheat protein materials. The plasticized systems, however, still presented a wide distribution of chain mobility at a scale from the molecular level to 20-30 nm, and the plasticizing effect was different for each wheat protein system. High protein content systems tended to be plasticized relatively easily especially when lipid content is high, but the existence of residual starch would require more plasticizers to reach a similar level of chain mobility. On a scale of 20-30 nm, plasticized vital wheat gluten (WG) and the deamidated wheat proteins (WP-I) were heterogeneous with each component exhibiting its individual mobility, whereas the plasticized insoluble protein system (WP-II) with poor mechanical properties was homogeneous. Both WG and WP-I systems showed excellent mechanical polymeric properties in tensile strength and elasticity despite the heterogeneity. The strong intermolecular hydrogen bonding interactions and soluble protein components in the materials could provide an adhesion among different components and act as a continuous matrix in the systems. Therefore, these materials displayed excellent mechanical properties via coordination effects among different components.