318
Rheological behavior of waxy maize starch dispersions in water and dimethyl sulfoxide. M. A. Rao.
Department of Food Science and Technology, Cornell University-NYSAES Geneva, NY 14456-0462.
Heated starch dispersions exhibit rheological behavior including
shear-thinning, shear-thickening, thixotropic, and antithixotropic. Shear rate-shear stress data on heated (at 120°C
and 70°C) cross-linked waxy maize starch dispersions exhibited either time-dependent shear-thickening
(antithixotropic) or both antithixotropic and time-dependent shear-thinning (thixotropic) behavior. The
antithixotropic behavior appears to be due to shear-induced structure formation when the level of shear
stress imposed on a sample is less than 120-150 Pa. Rheological properties of polymers in solution are
sensitive to variations in molecular structure and they are useful in understanding structure-function
relationships. Therefore, intrinsic viscosities of acid-hydrolyzed Amioca starches in 90% dimethyl sulfoxide
/ 10% water were determined using the approach for polyelectrolytes. Double logarithmic plots of the
specific viscosity against the coil overlap parameter revealed that the trend in the dilute regime was similar
to that seen with other polysaccharides and in the concentrated regime was similar to that of hyperentangled
systems.
|
