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

虽然已经发表了关于烹调米粒的论文，但还没有关于在烹饪过程中测量米粒中水分分布的报告。本文首次将核磁共振成像技术应用于大米水分分布的无损检测。首次尝试将部分煮熟的大米煮沸一段时间后进行淬火，利用二维核磁共振横向弛豫时间(T2)成像方法在室温下观察了其中的水分分布。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漫长的等待时间内，仍然存在一个问题，即水可能从外层高水分壳体迁移到低水分核心。通过实时观测对这一问题进行了探讨。为了实现实时测量，我们需要大大缩短采集T2成像所需的一系列数据集的时间。我们开发了一个多回波应用程序，用于具有双切片梯度的二维成像。这种方法将采集数据的时间缩短到了一分钟。这使得观察沸腾过程中每一分钟的轮廓变化成为可能。采用水分通过淀粉柱体扩散渗流的数学模型，模拟了水分分布的变化。计算的剖面显示，与实验中观察到的相比，吸湿量有相当大的延迟。造成这种差异的可能原因之一是，模拟中使用的糊化率被低估了。

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.