A Basic Study on the Absorption and Migration of Water in Rice Kernels (Part 1)

Observation of Water Absorption Utilizing Ice Crystallization by Liquid Nitrogen Freezing Technique

Abstract

The study of water migration into the rice kernel in a short span of time is important for the development of the post-milling treatment technology such as washing of milled rice. It is conjectured that the water absorption rate of the rice kernel is significantly affected by its surface condition after drying and milling. However it is difficult to observe water migration at the level of the microscopic grain structure. Thus this research was conducted to provide a mode to visualize the water absorption phenomenon in milled rice, through observation of the microstructural changes of ice-crystallized water, utilizing the quick freezing effect of the liquid nitrogen. The results showed that, in the starchy endosperm (the starch storage tissue), the water penetrated primarily through the compound starch granules, and secondarily, through the single starch granules. Furthermore, it was confirmed that the aleurone layer on the surface of the milled rice inhibited water absorption by the kernel. Therefore, retaining the aleurone layer can be an effective means of preventing water absorption.