THE RATE OF STARCH GELATINIZATION AS OBSERVED BY PFG-NMR MEASUREMENT OF WATER DIFFUSIVITY IN RICE STARCH WATER MIXTURES/

The gelatinization rate of rice starch was studied by observing the wa ter diffusivity measured by a PFG (Pulsed-Field-Gradient)-NMR method. A rice starch/water mixture in glass capillary tubes was heated and co oled in a stepwise manner The water diffusivity in these samples decre ased as heating rime increased. This was recognized as the increase in the amount of carbohydrate polymer dissolved in the aqueous phase dur ing heating Consequently, the measured water diffusivity was converted into the moisture content in the dissolved polymer solution. The time course of changes in this moisture content was approximated as a firs t-order process, and a rate constant in the order of 10(-2) s(-1) was obtained for 66-80 degrees C. This value is comparable to that in the literature measured by a DSC isothermal method, while those measured b y other methods such as flow consistency and gravimetric methods were 100-fold smaller (C) 1998 Elsevier Science Limited All rights reserved .