Effect of Heat-moisture Treatment of Glutinous Rice on Promotion of Hardness of Mochi-kiji

Abstract

() 2) 35) 1. () 90% 20% 15.2% 2 15.2% 91 88% 2. () 15.2% 750 g 1 L 80100 120 C 80 C 81632 100 C Abstract: Effect of the heat-moisture treatment of glutinous rice on the gelatinization temperature, the color tone of rice, and promotion of the hardness of mochi-kiji were studied. Heat-moisture treatment was carried out under both the limited moisture condition (the sealing system) and 100% relative humidity condition (the open system), using Hakuchomochi from Hokkaido, adjusting to 15.2 and 20.3% of moisture content of rice. By means of the heat-moisture treatment, the gelatinization temperature of glutinous rice shifted to the high temperature, and the hardness of mochi-kiji increased. The movement to the high temperature was affected by the method of the heat-moisture treatment, the heating temperature, the heating time, and the moisture content of rice before the treatment. It was recognized that a closed relationship existed between the effective accumulative temperature [[heating temperature − 80 C]×heating time (h)] and the gelatinization temperature. The gelatinization temperature of the heat-moisture treated rice showed an almost fixed value, when the total effective temperature was 120 (Ch) in the sealing system, and was 60 (Ch) in the open system. The whiteness of glutinous rice decreased with the heat-moisture treatment. However, the whiteness of the heat-moisture treated rice was improved by reducing to 88% the percentage milling.