AN APPLICATION OF MAGNETIC RESONANCE IMAGING TO THE REAL TIME OBSERVATION OF THE CHANGE OF MOISTURE PROFILE IN A RICE GRAIN DURING BOILING AND ANALISIS OF GELATINAIZATION PROCESS

虽然有关于米饭蒸煮的文献报道，但是还没有关于米饭蒸煮过程中水分分布的测量的报道。本文首次尝试将非破坏性的核磁共振成像方法应用于大米水分分布的研究，即在室温下，用二维核磁共振横向弛豫时间（T2）成像方法，对一个部分煮熟的大米在经过一定时间的煮沸后进行淬火，观察其水分分布。为了获得清晰的图像，我们需要两个小时来拍摄一张水分图像。测得的水分分布清楚地表明，淬火成功地在一定程度上保留了水分分布。然而，在淬火和成像测量之间的长时间等待期间，仍然存在水可能从外部高水分壳迁移到低水分核的问题。通过实时观测探讨了这一问题。为了实现实时测量，我们需要大大缩短收集T2成像数据集的时间。我们开发了一种多回波应用程序，用于双切片梯度的一维成像。这种方法将数据收集时间缩短到一分钟。这使得有可能观察到在沸腾过程中每分钟的轮廓变化。水分分布的变化是用一个数学模型模拟的，在该模型中，水通过扩散通过淀粉圆柱。计算的配置文件显示了相当大的延迟与实验中观察到的水分吸收。这种差异的一个可能原因是在模拟中使用的糊化速率被低估。

Although there has been published paper on cooking rice grains, no report has dealt with the measurement of moisture profile in a grain of rice during cooking. In the present study, a non-destructive method of nuclear magnetic resonance (NMR) imaging was applied to the moisture profile in a grain of rice.In the firs attempt, a partly cooked rice grain was quenched after selected period of boiling the moisture distribution in this was observed at room temperature using the two dimensional NMR transverse relaxation time (T2) imaging method. To obtain clear images, we needed two hours to take one moisture image. The measured moisture profile clearly showed that the quenching was successful to reserve the moisture profile to some extent. However, there remained a question of possible water migration from outer high moisture shell into the low moisture core during the long waiting time between the quenching and imaging measurement. This quesiton was explored by a real-time observation. To achieve the realtime measurement, we needed to shorten greatly the time required to collect the series of data sets for T2 imaging. We developed a multi-echo application for on-dimensional imaging with double slicing gradient. This method reduced the time of collecting data so short as one minute. This made it possible to observe the change of profile in every minute during boiling. The change of moisture profile was simulated using a mathematical model in which water percolates through a starch cylinder by diffusion. The calculated profile showed a considerable delay in moisture uptake compared with that observed in the experiment. One of the possible cause of this discrepancy is that the gelatinization rate used in the simulation were underestimated.