Water relations of simple sugar solutions and skim milk powder as studied by nuclear magnetic resonance spectroscopy
The water mobility in simple sugar-water systems as a function of sugar concentration was monitored by $\sp1$H, $\sp2$H and $\sp1$H decoupled $\sp{17}$O NMR transverse relaxation rates (R$\sb2$). For all three nuclei, R$\sb2$ increased with increasing sugar concentration with different magnitude and different trends of increases. Comparison of $\sp1$H, $\sp2$H and $\sp{17}$O NMR R$\sb2$ relaxation rates, on a normalized basis ($\Delta$R$\sb2$/R$\sb{\rm 2F}$), suggested that only the $\sp{17}$O monitors directly the water in the sugar-water systems. The contribution of proton exchange broadening effect to the $\sp{17}$O NMR R$\sb2$ measurement in both water and sugar-water systems as a function of pH could be eliminated by applying the proton decoupling on the $\sp{17}$O NMR. The trend of the relaxation rates versus sugar concentration were the same for R$\sb1$ and R$\sb2$ measured by single-pulse and multipulse methods. Water mobility measured by $\sp1$H decoupled $\sp{17}$O NMR R$\sb2$ relaxation rate was used as a method of monitoring lactose crystallization in supersaturated solutions over time. $\sp2$H NMR R$\sb2$ relaxation rate was used to monitor the water mobility during the amorphous to crystalline state transition of lactose in skim milk powder. Changes in water mobility were found to be directly related to the observed moisture changes and the transition of lactose from the amorphous to crystalline state.
Agriculture, Food Science and Technology, Chemistry, Agricultural
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign