Relationship between Physical Properties and Water Absorption Characteristics of Milled Rice.

Abstract

It is important to soak milled rice grain in water before boiling in order to achieve cooked rice of the best quality. The quantity of absorbed water may be influenced by the characteristics of milled rice. In this paper, the relationship between such properties of milled rice, as water content, raw weight, dry weight, volume, specific gravity, hardness of grain, and water absorption characteristics during the soaking process were examined for five varieties, Chidori, Koshihikari, Nihonmasari, Nipponbare, and Kinki-33, which were harvested from two different areas. Temperature effect on water absorption in the soaking process was also analyzed. 1) The water absorption rate of milled rice during The soaking process sharply decreased at temperatures below 20°C, but the final water content slightly increased. 2) Hardness was the property of the milled grain that differed most by variety. 3) Water absorption characteristics of milled grain had a highly positive correlation with grain hardness with regard to the absorption rate and the final water content. 4) Both water absorption and grain hardness were increased with milled percentage, and the regression coefficient between water absorption and grain hardness varied with milled percentage. 5) The change of grain hardness with milled percentage suggested differences of histogenesis in grain filling among the varieties. These results indicated that the water absorption characteristics of milled grain during soaking in water were based on the grain characteristic that was apparently determined by grain hardness and milled percentage.