Research on migration path and structuring role of water in rice grain during soaking

Abstract

Soaking is an important factor determining the final quality of cooked rice. Although the water content, distribution, and properties of cooked rice have been studied, the structuring role and migration path of water during soaking remain unresolved. In this study, the mobility and combinative state of molecular chains of starch and protein in soaked rice were investigated using proton nuclear magnetic resonance. The proton populations with different T2 reflected molecular mobility and interactions of water, starch, protein, and non-starch polysaccharides, which were affected by water content and hydration. The spaces between granules and cell walls and cracks were explored by scanning electron microscopy as these are the main channels to penetrate. However, the distribution and morphology of these channels showed significant differences at different temperatures, causing different penetrate paths. With the time and temperature increasing, water increasingly penetrated through inhomogeneous cell walls and then along different channels into the inner areas of grains, and the instrumental texture and rheological measurements showed significant structural changes and phase transition in the grains.