Abstract
Nuclear magnetic resonance measurements have been made on wheat starch pastes with contrasting rheological properties. Carbon-13 measurements indicate that about 60% of the polysaccharide in the pastes exists as mobile liquid-like polymer while the remaining 40% is in an immobile crystalline form. The ratio of mobile to crystalline polymer is the same for all pastes. Proton ( 1H) relaxation measurements show that in contrast to other gel systems the observed water relaxation times are not related to rheological properties and are governed by exchange between bulk and mobile polymer-associated water. Exchange at crystalline polymer sites is either nonexistent or too slow to be of significance on the NMR time scale. Measurements have also been made of water diffusion coefficients for pastes and for amylopectin-water systems. The modified Wang equation when fitted to the diffusion data gives shape factors that are consistent with an oblate ellipsoidal shape for the amylopectin molecule in solution.
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