The change of moisture distribution in a rice grain during boiling as observed by NMR imaging

The change of moisture distribution in a grain of rice during boiling was observed using the nuclear magnetic resonance (NMR) transverse relaxation time (T-2) imaging method and the factors which governed the cooking process were examined. Partly cooked samples were taken at various intervals and the moisture profile in a slice perpendicular to the long axis of the grain was obtained. Since the change of moisture profile during cooking in a cellulase-treated rice grain showed no remarkable difference from that of a nontreated one, it suggested that the non-cellulase-treated wall of endosperm cells had little effect on suppressing water migration. A one-dimensional moisture profile, which was constructed from an experimentally obtained two-dimensional moisture map, was simulated using a mathematical model in which water percolated through a starch cylinder by diffusion and was limited by gelatinization. Although the calculation successfully simulated the shape of the moisture profile, it showed a delay in the rise of the moisture. The cause of this delay is not yet known. (C) 1997 Elsevier Science Limited. All rights reserved.