36D-28 |
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L. N. Sadar, Y.-C. YEH, and Y. M. Lo. Dept. of Nutrition and Food Science, Univ. of Maryland, Food Bioprocess Engineering Lab., 3407 Marie Mount Hall, College Park, MD 20742 Curdlan, a microbial hydrocolloid composed of a three-dimensional structure stabilized by cross-links connecting junction zones between molecules, forms high viscosity aqueous suspensions with shear-thinning properties. The ability to form thermo-reversible gels by heating to 60º C, adding Ca2+ or Mg2+, or neutralizing an aqueous alkaline solution, as well as forming strong, irreversible gels when heated above 80º C has distinguished curdlan from other hydrocolloids. To date, however, limited information is available on the heat sensitivity of copolymerized solutions containing curdlan gum and other hydrocolloids. The objective was to characterize the heat sensitivity of the texture of copolymerized hydrocolloidal solutions containing curdlan gum. Hydrocolloidal mixtures containing curdlan were prepared respectively with xanthan gum, locust bean gum, carrageenan, and guar gum. The solution viscosity of various combinations of hydrocolloids in question was measured at a constant shear rate of 2 s-1 over a temperature range of 20º to 80º C using an AR 2000 Rheometer with a 40 mm parallel plate. Without combining with curdlan gum, carrageenan showed the most dramatic decrease in viscosity as temperature increased, with its steepest and quickest decrease starting around 40º C and reached below 0.02 Pa•s at 55º C. Xanthan gum, known for its stability over a wide temperature range, is the only gum to have an overall increase in viscosity as temperature increased. There is approximately a 4 Pa•s viscosity difference from 20º to 80º C. This increase is primarily due to the intermolecular entanglement during the breakdown of the native conformation of xanthan molecules. For the combinations that involved guar and locust bean gum, as curdlan concentration increased, viscosity values did as well. Characterizing the heat sensitivity of textural property, a crucial criteria during processing, storage, and distribution of food, will significantly improve the quality of food products while reducing their production costs.
Session 36D, Food Engineering: Rheology
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |