2004 Volume 10 Issue 2 Pages 218-223
The behavior of water molecules in refrigerated cooked rice was examined by measuring spin-spin relaxation time T2 using a pulse NMR spectrometer. T2 decay curve was analyzed using two-component and non-linear regression analysis and the presence of three kinds of water components with different T2 were revealed. In the case of fresh cooked rice, the observed T2 and the relative population were 0.9 ms (short T2) and 13%, 26 ms (intermediate T2) and 76%, and 200 ms (long T2) and 11%, respectively. The short T2 component was ascribed to the water molecules hydrated directly on the starch molecules. Intermediate T2 component was dominant and ascribed to the water molecules accommodated in the starch matrix inside the rice grain. The mobility of water molecules was suppressed remarkably during the storage at 0°C while it was almost independent of the refrigerated storage below −18°C. The long T2 component was ascribed to those grains accommodated in the surface luster film that was formed in the initial stage of the cooking process and composed of low molecular weight polysaccharides. The relaxation property observed by NMR was well consistent with the physicochemical properties.
