Quantitative NMR imaging study of the cooking of Japonica and Indica rice

NMR imaging was used to follow changes in the water content and distribution during the cooking of Nipponbare (Japonica), Khao Dawk Mali (Indica) and High Amylose (Indica) rice. Samples were cooked in closed glass vials for various times, quenched to stop cooking and then investigated using two-dimensional multi-echo 1H imaging experiments at 20 °C. Images calculated from the first-echo revealed changes in the water content of the rice grains. T2 images calculated using the first 16 echoes were converted into quantitatively reliable contour maps of the water concentration using an empirical T2 vs. water content calibration determined from a series of water/rice starch mixtures. Considerable differences in the rate of water uptake and diffusion, the average water contents and the proportions of under-, optimally- and over-cooked rice were observed for the three rice types studied.