Water Mobility in Glassy and Rubbery Solids as Determined by Oxygen-17 Nuclear Magnetic Resonance: Impact on Chemical Stability |
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| Authors: | Leonard N. BellHarold M. Bell Thomas E. Glass |
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| Affiliation: | a Auburn University, Department of Nutrition and Food Science, Auburn, AL, 36849, U.S.A.b Virginia Polytechnic Institute and State University, Department of Chemistry, Blacksburg, VA, 24061, U.S.A. |
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| Abstract: | Although chemical reactivity in solid food systems has been studied as a function of water activity and glass transition, the possible effects of water mobility on chemical reactions have not been investigated. The effect of the glass transition on water mobility at constant temperature and water content was determined. The relationship between the experimentally determined water mobility in polyvinylpyrrolidone (PVP) systems and chemical reactivity data from the same PVP systems was evaluated. Water mobility, as determined via 17O-NMR, was not affected by the glass transition; PVP systems at constant water activities and water contents, but different physical states (glassy and rubbery), had the same water mobility. An evaluation of four chemical reactions showed no relation between water mobility and kinetic data. The effect of water on chemical reactions is multidimensional and cannot be reduced to a single physicochemical parameter. |
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| Keywords: | water mobility NMR glass transition water activity chemical stability |
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