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SME-Arrhenius Model for WSI of Rice Flour in a Twin-Screw Extruder

¹Department of Biosystems and Agricultural Engineering, University of Minnesota, St. Paul, MN 55108. ²Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108. ³Department of Food Science, University of Manitoba, Winnipeg, MB R3T 2N2, Canada. ⁴Corresponding author. Also Yangtz Scholar Distinguished Guest Professor, Nanchang University. Phone: 612-625-1710. Fax: 612-624-3005. E-mail: ruanx001@umn.edu ⁵General Mills, Inc., 9000 Plymouth Ave. N., Golden Valley, MN 55427.

We have modeled a rice extrusion process focusing specifically on the starch gelatinization and water solubility index (WSI) as a function of extrusion system and process parameters. Using a twin-screw extruder, we examined in detail the effect of screw speed (350–580 rpm), barrel temperature, different screw configurations, and moisture content of rice flour on both extrusion system parameters (product temperature, specific mechanical energy [SME], and residence time distribution [RTD]) and extrudate characteristics (expansion, density, WSI, and water absorption index [WAI]). Changes in WSI were monitored to reveal a relationship between the reaction kinetics during extrusion and WSI. Reaction kinetics models were developed to predict WSI during extrusion. WSI followed a pseudo first-order reaction kinetics model. It became apparent that the rate constant is a function of both temperature and SME. We have developed an adaptation of the kinetic model based on the Arrhenius equation that shows better correlations with SME and distinguishes data from different screw configurations. This adaptation of the model improved predictability of WSI, thereby linking the extrusion conditions with the extruded product properties.