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Extrusion of Cross-Linked Hydroxypropylated Corn Starches I. Pasting Properties¹

¹Journal paper no. J-18471 of the Iowa Agriculture and Home Economics, Experiment Station, Ames, IA, Project No. 3258. ²Graduate student and professor, respectively, Center for Crops Utilization, Research and Department of Food Science and Human Nutrition, Iowa State University. ³Professor, Department of Statistics, Iowa State University. ⁴Corresponding author. E-mail: jjane@iastate.edu

A series of cross-linked (0, 0.014, 0.018, 0.024, and 0.028% POCl₃, dry starch basis) hydroxypropylated (8%) corn starches were extruded using a Leistritz micro-18 co-rotating extruder. Process variables included moisture, barrel temperature, and screw design. Differential scanning calorimetry and X-ray diffraction studies showed the level of starch crystallinity decreased with increasing severity of extrusion conditions. Pasting properties of the extruded starches were examined using a Rapid Visco Analyser. Pasting profiles of starches extruded at different conditions displayed different hot paste viscosity and final viscosity. Increasing starch moisture content during extrusion and level of cross-linking increased starch viscosity (P < 0.0001), whereas increasing extrusion temperature and shear decreased starch viscosity (P < 0.0001). Interactions were found between level of cross-linking and screw design and between extrusion temperature and starch moisture content (P < 0.0001).