43-5 |
Rheological and structural properties of foods thickened with different starches |
Y. MENG and M. A. Rao. Food Science & Technology, Cornell Univ., New York State Agricultural Experiment Station, 630 W. North St., Geneva, NY 14456-1371 The terminology used in dysphagia management is often qualitative and can create confusion. There is a need for a rheological approach in standardizing foods used in a dysphagia diet, such as starch-thickened apple juice. Our objective was to study the rheological and structural properties of cross-linked waxy maize (CLWM) and cold-water-swelling (CWS) waxy maize starch dispersions in apple juice and water. Granule size distribution was determined using a laser-diffraction particle size analyzer. The CLWM starch was heated above the gelatinization temperature determined by differential scanning calorimetry. The CWS starch was pasted at room temperature. Volume fraction was determined by the Blue Dextran exclusion method. Rheological tests were conducted at 37C using an AR1000-N rheometer with a cone and plate geometry. Frequency sweeps were conducted in the linear viscoelastic region from 0.628 to 125.7 rad/s. Flow behavior of the dispersions was studied by shearing continuously from 0-200 1/s and back for three consecutive cycles. CWS had a broader granule size distribution and higher mean granule diameters than CLWM. Volume fraction of both starch dispersions in water showed a weak dependence on concentration. Values of G’ and G” plotted against frequency were dependent on starch type and concentration, and whether heated in water or apple juice. Flow tests showed distinct time-dependent behavior for both starches, with shear stress values greatly dependent on starch concentration, starch type and continuous medium. Light microscopy, after staining with 0.05% Congo Red, showed that CLWM granules had more convoluted surfaces and larger intra-granular cavities than CWS granules. These results show that the rheological behavior of both CLWM and CWS dispersions was influenced by starch concentration, the liquid in which they were heated, and the structural characteristics: inherent and induced during processing.
Session 43, Food Engineering: Rheology and texture
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