Retrogradation Mechanism of Rice Starch

The non‐Newtonian behavior and dynamic viscoelasticity of rice starch (Akihikari, 18.8% amylose content) solutions after storage at 25 and 4°C for 24 hr were measured with a rheogoniometer. The flow curves, at 25°C, of Akihikari starch showed plastic behavior >3.0% (w/v) after heating at 100°C for 30 min. The dynamic viscoelasticity of the starch increased after storage at 25 and 4°C for 24 hr and stayed at a constant value with increasing temperature. A small dynamic modulus of rice starch was observed upon addition of urea (4.0 M ) at low temperature (0°C), but it produced a sigmoid curve when plotted against increasing temperature. A small dynamic modulus was also observed in 0.05 M NaOH solution. However, it increased rapidly after the temperature reached 70°C. Possible models of retrogradation mechanism of rice starch were proposed.