Gelation mechanism and rheological properties of rice starch.

Three rice starches were isolated from indica (KSS7), japonica (TNu67) and waxy (TCW70) varieties, respectively. Amylose contents of isolated starches were 25.6% for KSS7; 14.80% for TNu67; and 0.99% for TCW70. When heated from 55 to 95°C at 10° C intervals, starch with higher amylopectin content had higher swelling power. Both swelling power and water solubility index increased with increased temperature. The blue values of all samples were <0.08. As examined by scanning electron microscope and x-ray diffractometer, the typical A-type diffraction pattern of the peak became slightly flattened at the temperature below the gelatinization temperature (GT), and no peak was detected at the temperature higher than the GT. The change of starch during heating or cooling was also analyzed by mechanical spectrometry with an oscillatory rheometer. G' and G were dependent on amylose content and starch concentration.