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Effects of Hydrocolloids on Shear-thickening Behavior of Starch Dispersions and Its Impacts on Gastric Emptying Rate
F. FANG (1), O. Campanella (1), B. Hamaker (1) (1) Purdue University, West Lafayette, IN, U.S.A..

Gelatinized waxy corn and potato dispersions had shear-thickening behavior at a shear rate around 20 s-1, a phenomenon that is not observed in gelatinized waxy wheat and rice starch dispersions and normal starches. Shear thickening behavior may have some implications on delaying gastric emptying time. Thus, in order to improve shear-thickening behavior of starch for potential nutrition advantages the shear thickening was enhanced with the use of hydrocolloids. Starches were mixed with various hydrocolloids following gelatinization and their rheological properties were studied. Both gelatinized waxy corn and potato starch dispersions showed increased viscosity with time. With addition of agar and xanthan gum, the viscosity of gelatinized waxy corn and potato starch dispersions decreased with increased shear rate with no shear-thickening behavior. The addition of pectin, sodium alginate or guar gum had no effects on shear-thickening behavior but altered the overall viscosity of the dispersions. However, upon addition of gum arabic, shear-thickening behavior was more obvious and moved to higher shear rates. In simulated gastric juice, waxy potato starch dispersions showed continuously increased viscosity to around 1 Pa.s over the test; whereas the viscosity of corn starch dispersions firstly increased to 0.1 Pa.s followed by a decrease of viscosity up to 0.05 Pa.s over the test. These studies indicated that gelatinized waxy potato starch dispersion has a potential to delay the gastric emptying rate compared to waxy corn starch. Results of this research should help to understand how rheological properties of starchy foods affect the digestion process in terms of gastric emptying.