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Effect of Separation and Grinding of Corn Dry-Milled Streams on Physical Properties of Single-Screw Low-Speed Extruded Products¹

¹Journal paper J-17303 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA, Project No. 3326. Contribution No. 99-2-J from the Kansas Agricultural Experiment Station, Manhattan, KS. ²Graduate research assistant, Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA 50011. ³Associate professor, Department of Grain Science and Industry, Kansas State University, Manhattan, KS 66506; formerly with the Departments of Agricultural and Biosystems Engineering and Food Science and Human Nutrition, Iowa State University, Ames, IA 50011. Corresponding author. E-mail raf@wheat.ksu.edu

Three streams of corn dry-milled products (corn grits, corn cones, and corn flour) were sieved and separated according to average diameter, and some segregated fractions were ground to produce nine streams. Corn grits were separated to produce grits with diameters of 1.19 and 0.841 mm, and selected fractions were ground into grits with average diameters of 0.297 and 0.210 mm. Corn cones were separated into average diameters of 0.595, 0.420, and 0.297 mm. Corn flour was separated into fractions with average diameters of 0.297 and 0.210 mm. The original and the additional streams were extruded at constant speed (50 rpm) and at three different processing extruder barrel temperature profiles: low (LTP, 100-110-120°C), medium (MTP, 110-120-130°C), and high (HTP, 120-130-140°C). The least significant difference (P < 0.01) test showed that additional grinding of corn grits affects the expansion ratio of extrudates processed at LTP and HTP. Additional separation of corn flour affects (P < 0.01) the bulk density and water solubility index of extrudates at HTP. At HTP, corn cones with diameters of 0.595 mm had significantly (P < 0.01) higher torque, specific mechanical energy, and die pressure than did the original corn cone extrudates without separation.