Abstract
Three water-soluble dietary fibers (SDFs : polydextrose, non-digestible dextrin, and a partially decomposed guar gum) were examined for the behavior of bound water. The monolayer water content (g/100 g of dry matter) was found to be 3-6 g by the sorption isotherm method, whereas it was 1-3 g by the pulsed NMR method. The correlation time for the bound water in SDFs was in the range 2-5×10-9 sec. These values are 3 orders greater than that for free water, indicating that the bound water detected by the pulsed NMR method represents the monolayer sorption water in an aqueous solution, where the substrates are more motional than those in the solid state. In addition, the enthalpy change in the bound water formation from 10°C to 30°C was from-14 to-36 kJ/mol, suggesting that the formation of bound water was exothermic and associated with 1-2 hydrogen bonds/water molecule.
