Molecular Mobility Characterization of Polymer and Solute Water States as Determined by Nuclear Magnetic Resonance, Rheology and Hydrodynamic Equilibrium (Nmr)
Richardson, Shelly Jane
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https://hdl.handle.net/2142/70090
Description
Title
Molecular Mobility Characterization of Polymer and Solute Water States as Determined by Nuclear Magnetic Resonance, Rheology and Hydrodynamic Equilibrium (Nmr)
Author(s)
Richardson, Shelly Jane
Issue Date
1986
Department of Study
Food Science
Discipline
Food Science
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Food Science and Technology
Abstract
The extreme importance of moisture content in the overall stability and acceptability of foods has been known for many years. The analytical determination of total moisture content and the measure of water activity (a(,w)) have both been shown to be imprecise indicators of stability. Therefore, both a theory and an analytical method which will fully elucidate the mobility and availability of water in food systems is still being sought; both are present in this work.
The theory of water states is relatively recent and was developed in this laboratory. According to this theory, water in foods exists in different states. The water associates differently with a polymer, such as starch or protein, than it does with a solute, such as sucrose. The objective of this work was to characterize the dynamic molecular mobility of polymer and solute water states and their interaction by three experimental techniques, Nuclear Magnetic Resonance (NMR) spectroscopy, rheology and hydrodynamic equilibria.
The major experimental focus of this work was to employ high field ('1)H, ('2)H and ('17)O NMR to study the mobility of water in polymers (corn starch, amylopectin and wheat flour), in a solute (sucrose) and in mixtures of a polymer and a solute (corn starch and sucrose). For the polymers and mixtures the concentration ranged from suspensions to pastes to powders and for the solute from undersaturated to supersaturated solutions. Data from the other two techniques, rheological and hydrodynamic equilibria, were correlated to the NMR results.
The major results were: (1) The best NMR methodology for the characterization of water mobility was provided by measuring the ('17)O NMR relaxation rates in deuterium oxide. (2) The isotropic two-state model with fast exchange was adequate to interpret these data by means of both a physical and a chemical activity model. (3) NMR showed one linear relation with water activity of starches in the monolayer region and another above this. (4) NMR was linear with both consistency coefficient and flow behavior in three water content regions, and (5) All the systems studied showed very high water mobility, with correlation times ranging between 10 and 100 picoseconds.
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