Retrogradation mechanism of rice starch

The non-Newtonian behavior and dynamic viscoelasticity of rice starch (Akih ikari, 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 degr ees C, of Akihikari starch showed plastic behavior >3.0% (w/v) after heatin g at 100 degrees C for 30 min. The dynamic viscoelasticity of the starch in creased after storage at 25 and 4 degrees C for 24 hr and stayed at a const ant value with increasing temperature. A small dynamic modulus of rice star ch was observed upon addition of urea (4.0M) at low temperature (0 degrees C), but it produced a sigmoid curve when plotted against increasing tempera ture. A small dynamic modulus was also observed in 0.05M NaOH solution. How ever, it increased rapidly after the temperature reached 70 degrees C. Poss ible models of retrogradation mechanism of rice starch were proposed.