VISCOELASTICITY OF GELATINIZED STARCH DISPERSIONS

Data are presented for the elastic moduli of gelatinised dispersions of a range of starch types, including native and chemically modified starches, over a much wider concentration range than examined heretofore. As found previously, there is a threshold concentration for measurable elasticity, near the close-packing point, and a concentration region above this over which elasticity increases roughly linearly with concentration. A second, higher, "threshold" concentration at which a fairly sharp slope change occurred was also found. Three types of behaviour were found, apparently corresponding to the distinction between chemically modified starches, root and tuber starches, and cereal starches. At the second threshold concentration these, respectively, showed a significant fall in slope, little or no slope change and a marked slope increase. A recent study (Evans and Lips 1990) has provided a useful description of the elastic properties of concentrated dispersions of model deformable particles. Comparison between the behaviour of the "baseline" model dispersions with that of the starch dispersions examined here reveals significant similarities, especially when considering the behaviour of the chemically modified starches. There are some noteworthy differences which raise important questions about the structural origins of the rheological properties of starches and we briefly speculate about these.