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