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Twin-screw extrusion of rice flour
Twin-screw extrusion of rice flour - effects of extrusion processing conditions on extrudate characteristics
H. LEI1, R. G. Fulcher2, R. R. Ruan1, and B. van Lengerich3. (1) Dept. of Biosystems & Agricultural Engineering, Univ. of Minnesota, 1390 Eckles Ave., 310 Biosystems & Agricultural Engineering Bldg., Saint Paul, MN 55108-6005, (2) Dept. of Food Science & Nutrition, Univ. of Minnesota, 1334 Eckles Ave., 167 Food Science & Nutrition Bldg., Saint Paul, MN 55108-6099, (3) Bell Institute of Health & Nutrition, General Mills, Inc., 9000 Plymouth Ave. N., Minneapolis, MN 55427
Extrusion cooking is important and popular for processing starch-based products. Thermal and mechanical energies are usually present during extrusion cooking of starch. Reaction kinetics of starch extrusion is still not clear.
Our objective was to model rice extrusion process, more specifically the starch gelatinization and water solubility index as a function of extrusion system and process parameters.
Rice flour was processed using a DNDL-44/28D twin-screw extruder. Property changes of rice flour were characterized by measuring its water solubility index (WSI), water absorption index (WAI), expansion ratio, and bulk density of the extrudates. The pasting properties of extruded rice were studied using RVA.
The effects of screw shaft speed (350rpm-580 rpm), barrel temperature (70C-160C), and different screw configurations in this co-rotating twin-screw extruder with rice flour of different moisture content (16.5%-40%) on the extrusion system parameters (die pressure, product temperature, specific mechanical energy input (SME), and residence time distribution) and on extrudate characteristics (expansion ratio, density, WSI, WAI, pasting properties) were studied. Changes of WSI was monitored and used to understand the reaction kinetics during extrusion. WSI was correlated with the pasting properties. Reaction kinetics models were developed to predict WSI during extrusion. The rate constant was a function of both temperature and SME.
A new kinetic model was developed based on the Arrhenius equation with SME (R2>0.9). The new model can distinguish data from different screw configurations which provided different shear energies. The predictability of WSI was significantly improved by the new model.
