The Reverse Phenomenon in Water Absorption Rate in Japonica Rice Grains Caused by Long-term Soaking in Water at Different Temperatures

Abstract

We investigated the influence of soaking temperature on the water absorption in three cultivars of Japonica rice, Kinuhikari, Sasanishiki, and Hatsushimo, based on the modified water absorption rate calculation method for rice. The grains of each cultivar were processed under different conditions, i.e., 70% polished and polished rice. We compared the water absorption curves of grains soaked in water at 5°C, 20°C, and 40°C for 10 min to 24 h to ensure that the absorption had reached equilibrium. The absorption curves of grains soaked at 5°C and 20°C intersected those of grains soaked at 40°C in all cultivars of both 70% polished rice and polished rice. This "reverse phenomenon" was specific to the granular shape of the rice grain. The findings for these three cultivars descended from the different rice lines contradict the established theories in the field of cookery science. It is suggested that this occurs for many cultivars of Japonica rice.