The1H NMR relaxation of a series of carbohydrates (glucose, fructose, sucrose, corn syrups) and chemically modified waxy maize starch in solutions or suspensions reveals marked differences in hydration behaviors, determined primarily by compositional and structural differences. Our results suggest that the stereochemistry of the solute plays an important role in determining the extent of hydration. Extensive aggregation of Polar Gel-5 (modified) corn starch and amylopectin in concentrated suspensions is prevented by brief heat treatment at 60 °C, consistent with the involvement of hydrogen bonding in the aggregate formation. Such a preheating treatment results, strikingly, in a linear concentration dependence of1H NMR relaxation rates of water protons up to concentrations as high as 0.7 g of solids/g of H20, in agreement with a two-state, fast-exchange model for relaxation. On the other hand, the concentration dependences of viscosities and apparent viscosities of amylopectin and Polar Gel-5 remain nonlinear above ≃0.2 g of solids/g of H20, suggesting the presence of some residual hydrogen bonding between polysaccharides in the preheated samples, at high concentrations. Our1H NMR study of the molecular “mobility” of water, combined with viscosity measurements, indicates that the macroscopic, flow behavior of starch suspensions is not correlated with the molecular mobility of water in such systems.170 and13C NMR data are consistent with the results of our1H NMR relaxation measurements on corn carbohydrates and chemically modified waxy maize starch, concerning compositional and structural differences that determine hydration behavior. © 1989, American Chemical Society. All rights reserved.