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Abstract
The non-Newtonian behavior and dynamic viscoelasticity of Takanari and Reimei amylopectin solutions were measured with a rheogoniometer. The Takanari and Reimei amylopectin showed plastic behavior at a concentration above 2.0% at 25 °C. The viscosity of Takanari amylopectin decreased a little with increasing temperature at 2.0%. However, a little increase in the viscosity was observed with increasing temperature from 0 to 15 °C, then it stayed at a constant value with further increase in the temperature up to 80 °C at a concentration above 4.0%. An increase in the viscosity was also observed in Reimei amylopectin solution at various concentrations. The dynamic viscoelasticity of Takanari amylopectin increased with increasing concentration at low temperature (0 °C) and it stayed at a constant value with increasing temperature up to 80 °C. On the other hand, dynamic viscoelasticity for Reimei amylopectin showed a weak sigmoid curve. The tan δ of both amylopectins showed low values, 0.32-0.38, at low temperature range and kept constant with increasing temperature up to 80 °C. A little decrease of dynamic modulus of Takanari and Reimei amylopectin was observed upon addition of urea (4.0 M). The dynamic modulus of Takanari and Reimei amylopectin solution decreased rapidly when the temperature reached 45 and 60 °C, which was estimated to be a transition temperature, in 0.10 N NaOH solution. The molecular origin for the thermal stability of rice amylopectin (Takanari and Reimei) was essentially attributed to intramolecular associations in aqueous solution. Possible mode of intramolecular hydrogen bonding and van der Waals forces of attraction of amylopectin molecules are proposed.
1. Presented at the XVIIIth International Carbohydrate Symposium, Milan, Italy, July 2 1-26, 1996.
Notes
1. Presented at the XVIIIth International Carbohydrate Symposium, Milan, Italy, July 2 1-26, 1996.