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

虽然已经有关于煮米粒的论文发表，但没有关于煮米粒中水分分布的测量的报告。在本研究中，一种非破坏性的核磁共振成像方法（NMR）应用于大米中的水分剖面。在第一次尝试中，将部分煮熟的米粒在选定的煮沸时间后淬火，在室温下使用二维核磁共振横向弛豫时间（T2）成像方法观察其中的水分分布。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。测量的水分分布清楚地表明淬火是成功的，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较长等待时间内，仍然存在水可能从外部高水分壳迁移到低水分芯的问题。这个问题是通过实时观察来探讨的。为了实现实时测量，我们需要大大缩短T2成像系列数据集的采集时间。我们开发了一种多回声应用程序，用于双切片梯度的三维成像。这种方法将收集数据的时间缩短到一分钟。这样就可以观察到沸腾过程中每分钟剖面的变化。利用水分通过淀粉筒扩散渗透的数学模型模拟了水分剖面的变化。计算的剖面与实验中观察到的相比，显示了相当大的水分吸收延迟。造成这种差异的一个可能原因是模拟中使用的糊化速率被低估了。

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.