Some Rheological Properties of Starches from Glutinous Rice, Waxy Corn, and Cassava

Rheological properties of pastes of glutinous rice, waxy corn, and cassava starch were mea-sured with rheometers. The temperature at which viscosity increased was observed on viscogram to be highest for waxy corn starch, followed by cassava starch, and glutinous rice starch. Waxy corn starch showed the highest maximum viscosity, while cassava starch showed the largest setback upon cooling. Changes in degree of gelatinization of various starch samples, which had been stored at 5 and -20°C for 72 hr, were very small. This fact suggests that these materials would hard-ly suffer from retrogradation. The spinning distance of a starch paste increased with an increase in concentration. The increasing ratio of glutinous rice starch was the highest, followed by cassava starch and waxy corn starch. Cassava starch had the highest elastic modulus and viscosity. The apparent activation energy of glutinous rice, waxy corn, and cassava starch was 38. 60, 28. 30, and 76.35 kJ/mol, respectively. Though dynamic modulus and the dynamic loss of each starch paste increased with an in-crease in frequency, cassava showed significantly high values, compared with those of glutinous rice and waxy corn. The tanδ of waxy corn and cassava starch increased with an increase in frequency, while glutinous rice starch was scarcely changeable. Cassava starch showed the smallest tanδ.