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Effects of Extrusion Variables and Chemicals on the Properties of Starch-Based Binders and Processing Conditions¹

¹Journal Paper J-16699 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Project No. 3258. ²Department of Food Science and Human Nutrition, Iowa State University, Ames, IA 50011. ³Current address: Department of Biological and Agricultural Engineering, University of California, Davis, CA 95616. ⁴Corresponding author. E-mail: jjane@iastate.edu

The effects of extrusion variables (moisture, screw speed, and temperature) and chemicals (urea and sodium bicarbonate) on the properties of starch-based binders (water absorption, bulk density, binder yield, expansion ratio, solubility, pH) and processing conditions (die temperature and pressure, feed rate, and specific mechanical energy) were studied using a central composite design. All quadratic regression models, except the models for bulk density and pH, were significant at the P ≤ 0.06 level. These models can predict the binder properties and processing conditions when extrusion variables and the chemical concentrations are known. Optimum combinations of the chemical concentrations (g/100 g of starch) and extrusion variables to achieve high water absorption in the binders were 15–20 g of urea /100 g of starch, 0–4 g of sodium bicarbonate/100 g of starch, 35–40 g of moisture/100 g of starch, 100–120 rpm screw speed, and 185–215°C barrel temperature. The molecular degradation of the starch occurred during extrusion, especially when the moisture content of starch was <30 g/100 g of starch.