Cellular water and proton relaxation times of Thai rice kernels during grain development and storage

NMR relaxation and the water transport in Thai rice (rice kernels) during grain development and storage were investigated using time-domain NMR. During the early stages, 4-13 days after flowering (DAF), the T-1 value rapidly decreased, and then increased again when the grains became white and dry at 52 DAF and storage stages. It was also found that T-1 can be used to measure relative water content in the grains until 49 DAF. Three types of cellular water in the grains were presumed as being strongly-bound, moderately-bound and weakly-bound water. The 4 DAF grains contained the most weakly-bound water. Moderately-bound water reached its maximum value at 13 DAF. Strongly-bound water was lost in storage stages. The existence of water transport in the grains was revealed by changes in the proportion of these components. The highest water transport occurred during the early and dried-white grain stages. The long T-2 component changed over time, while the medium changed significantly in the early and dried-white grain stages. The short T-2 component was constant until 46 DAF. Moreover, the findings revealed an interesting relationship between the physical change of the seed-coat color and the medium component of T-2.