Nuclear magnetic resonance studies of corn zeins and other byproducts of corn wet milling: Dynamic and structural basis of functionality

Nuclear Magnetic Resonance (NMR) relaxation and spectroscopy techniques were used to evaluate the hydration properties and mobility of "bound" water in corn zein solutions and samples of corn gluten meal (CGM) and corn germ meal (CGRM). Multinuclear relaxation measurements using $\sp1$H, $\sp2$H and $\sp{17}$O nuclei indicated that $\sp{17}$O is the nucleus of choice for evaluating water mobility in protein solutions. Both $\sp1$H and $\sp2$H relaxation measurements were complicated by chemical exchange effects which were estimated to be as much as 50% of the observed relaxation rate for $\sp2$H NMR measurements of corn zein solutions. Subsequently, correlation times calculated from $\sp2$H NMR measurements were anomolously long. In addition, the binding of water to corn zeins could not be described using an isotropic binding model. An anisotropic binding model which contains two correlation times ($\tau\sb{\rm s}$ and $\tau\sb{\rm F}$) had to be invoked. Under conditions of 20 mM cation in the form of LiOD, NaOD or KOD required to solubilize the protein, specific cation effects were not observed in the $\sp{17}$O NMR relaxation rates due to cation saturation of the Stern Layer at the protein surface.The functionality of corn zeins, CGM and CGRM was evaluated under various conditions of thermal treatments and pH. A new approach which utilizes NMR relaxation measurements in conjunction with a chemical activity model for protein-protein interactions was used to calculate "protein activities" which were then used to evaluate water activity (a$\sb{\rm w}$) values. For corn zein solutions, a thermal treatment (80$\sp\circ$C/20 min. or 90$\sp\circ$C/20 min.) resulted in a hydrophobically driven aggregation process as indicated by the $\sp{\rm {13}}$C NMR spectra and the coefficients from the virial expansion of the protein activity coefficient. A comparison of NMR derived a$\sb{\rm w}$ values with a$\sb{\rm w}$'s obtained from relative vapor pressure (RVP) measurements showed significant differences above protein concentrations of 0.4 g/ml. This difference was attributed to "trapped" water which decreases the RVP measurements at higher protein concentrations whereas the NMR measurements monitor water "binding".The NMR relaxation rates of CGRM were larger than those of CGM suggesting an increased hydration. However, the functionality of CGM could be improved using either thermal treatments or increased pH (11.7) as measured by both $\sp{\rm 1}$H NMR relaxation measurements and water hydration capacities.U of I OnlyETDs are only available to UIUC Users without author permissio