Effects by the Hard Water Boiling of Chalky Rice in Terms of Texture Improvement and Ca Fortification

Global warming has led to the increase in chalky grains of rice, which has also caused the deteriorations of physicochemical and cooking qualities of rice grains. These chalky rice grains are characterized by high α-amylase activity, high protease activity, and low apparent amylose contents, low degree of hardness and stickiness of boiled rice than those of the whole rice grains. In the present paper, we evaluated 14 Japonica unpolished rice grains harvested in Japan in 2021, and these samples (original grains) were divided to two groups (whole grain group and chalky grain one). We found that the chalky rice grains showed higher values of xylanase activity than those of the whole rice grains, while cellulase activity were lower than that of whole rice grains. Using rice grains blended with 30 % of chalky grains as material, we compared sugar and mineral contents and textural properties of the boiled rice grains soaked and boiled in the ordinary water or in the hard water, such as Evian or Contrex. It was shown that the hard water is useful for the prevention of the texture deterioration of the boiled rice grains due to the inhibition of the reduction of endogenous hydrolytic enzymes, such as amylase, proteinase, and xylanase. Furthermore, we found that hard water is useful for the increase of calcium and magnesium intake through the meal with the boiled rice grains soaked and cooked using hard water.