Cereal Chem 61:500 - 503. | VIEW
Yield Stresses in Dispersions of Swollen, Deformable Cornstarch Granules.
D. D. Christianson and E. B. Bagley. Copyright 1984 by the American Association of Cereal Chemists, Inc.
Dispersions of cornstarch granules were heated in excess water at a temperature of 67-80 C. In Couette flow at 23 C (shear-rate range of 3-500/sec), many of these dispersions showed a yield stress. Yield stresses in cornstarch dispersions are significantly lower than those reported earlier for wheat starch granule dispersions at the same volume fraction. Yield stress values depend on the extent of swelling of the granules and thereby increase with the temperature of the dispersion preparation. For example a 9% dispersion prepared at 75 C gave a yield point of 54 Pa (Pascal, Newton/m2), whereas a dispersion prepared at 80 C gave a yield point of 120 Pa. These results can be compared to the yield value of the 250 Pa reported earlier for cornstarch heated at 90 C and measured at 60 C. Yield points appear to occur only when the volume fraction of the swollen granules is greater than approximately 0.6-that is, at a volume fraction between cubical (loosest) packing of uniform spheres (0.524) and tetahedral (tightest) packing (0.74).