42-5 |
Rheology and relationship among rheological parameters of cross-linked waxy maize starch dispersions heated in fructose solutions |
K. S. Youn, Department of Food Science and Technology, Catholic University at Daegu, 330 kumrak 1-ri, Hyang-up, Kyungsan-City, Kyungpook, 712-702, South Korea and M. A. RAO, Department of Food Science and Technology, Cornell University-Geneva, P. O. Box 462, Geneva, NY 14456-0462. Granules of cross-linked waxy maize (CWM) starch remain intact when heated to high temperatures: 110-120 °C. Heated CWM starch dispersions (STDs) exhibit antithixotropic and viscoelastic behavior. The size and morphology of the granules in heated STDs, and the rheological behavior may be affected by addition of a sugar. Our objectives were to study trends in the flow and viscoelastic behavior of dispersions of 5% CWM starch heated in aqueous fructose solutions: 0 - 600 g/kg, and to compare experimental values of first normal stress coefficient and apparent viscosity with those predicted by the Goddard-Miller model. CWM STDs, 50 g/kg, were heated in fructose solutions: 0 to 600 g/kg of STD at 110 °C in sealed cans (#300) for 10 min under intermittent agitation. Shear rate vs. shear stress, normal force as a function of shear rate, and dynamic rheological data as a function of frequency were obtained on the STDs at 20 °C with a cone - plate geometry of an AR 1000N rheometer. Granule size distributions of the STDs did not change much with fructose concentration. At fructose concentrations 0 to 300 g/kg, the STDs exhibited antithixotropic behavior, but thixotropic behavior at 400, 500, and 600 g/kg. The experimental values of first normal stress coefficient and those predicted by the Goddard-Miller model from dynamic rheological and apparent viscosity data of STDs were in reasonable agreement with each other. Experimental values of the first normal stress coefficient were in good agreement with those predicted by the Goddard-Miller model; therefore, it should be useful in estimating values of first normal stress difference of foods. Also, experimental values of the apparent viscosity were close to those predicted by the Goddard-Miller model from dynamic data. Antithixotropic flow behavior was exhibited by the CWM STDs only at low fructose concentrations.
Session 42, Food Engineering: Rheology and texture
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