Effect of annealing temperature on gelatinization of rice starch suspension as studied by rheological and thermal measurements

The effect of annealing temperature (T_a) on the rheological behavior of 10 wt % rice starch suspension was investigated by the dynamic viscoelasticity, the differential scanning calorimetry (DSC), and the amount of leached out amylose and the swelling ratio of starch suspension. The rheological behaviors of the annealed samples are classified into three types in terms of T_a: T_a1, 48 and 55°C, which are much lower than the gelatinization temperature, T_gel (=62°C); T_a2, 58, 60, and 62°C, which are almost the same as T_gel; and T_a3, 65, 68, 70, and 73°C, which are much higher than T_gel. For the samples annealed at T_a2, the onset temperature of the storage and the loss moduli, G′ and GPrime;, increased with increasing T_a, and G′ and G″ in the temperature range from 65 to 90°C gradually increased though smaller than those for the nonannealed sample, the control. This can be understood by the partial gelatinization; i.e., the leached out amylose prevents further amylose from leaching out. The rheological property of the samples annealed at T_a1 is not so different from that of the control, and the samples annealed at T_a3 are almost gelatinized. The rheological behavior of starch suspension can be controlled by T_a.