Gelatinization Characteristics of Rice Starch (Yukihikari)

Abstract

The non-Newtonian behavior and dynamic viscoelasticity in an aqueous solution of rice starch (Yukihikari) were measured using a rheogoniometer. The gelatinization of Yukihikari starch oc-curred above 3.0% after heating at 105°C for 20 min. The flow curves, at 25°C, of Yukihikari starch showed shear-thinning behavior at 2.0, but plastic behavior above 3.0%. The viscosity of Yukihikari starch decreased gradually with an increase in temperature. The dynamic modulus of Yukihikari starch showed a large value during the increase in the temperature. The tan 6 was 0.23 in the low-temperature range and stayed at a low value with increasing temperature at a concentration of 4.0%. A slight decrease in dynamic modulus of Yukihikari starch was observed during the increase in temperature upon the addition of urea (4.0 M). The dynamic modulus, however, in-creased with increasing temperature up to 50°C, then it decreased rapidly with further increases in the temperature after storage at 20 and 4°C for 24 h in urea solution. The dynamic modulus of Yukihikari starch stayed in the low-values in 0.05 M NaOH solution even at low temperature range. The results supported a gelatinization mechanism of rice starch previously proposed.