91C-39 |
Examining the influence of screw paddles on the severity of extrusion of corn meal |
F. K. SAALIA and R. D. Phillips. Department of Food Science and Technology, University of Georgia, 1109 Experiment Street, Griffin, GA 30223 The desirable melt-in-the-mouth texture of extruded products is a result of physicochemical transformations of macromolecules caused largely by mechanical energy input and shear stresses. The magnitude of these forces is impacted by the screw configuration, in particular the mixing elements. The objective of this study was to determine the influence of reverse paddles and their position on the severity of screw configuration. Each of four screw configurations was examined on a 30mm (25:1 L/D) APV Baker twin-screw extruder. They were labeled CF6, 8, 9 and 10. The four screw configurations differed by the relative location of paddles along the length of the barrel. CF6 and 8 had two sets of 60° forwarding paddles in tandem with 60 reverse elements at 13.5D and 20D down the barrel. CF9 and 10 had forwarding and reverse elements interrupted by 1.5D, 2 lead screw elements. Yellow corn meal was extruded at 20% moisture and 10kg/H through a slit die. The severity of the screw configurations was measured by determining the specific mechanical energy consumption, and the mean residence time. Water absorption index and soluble solids of the extrudates were also determined as indicators of the severity of screw configuration. Screw configurations 6 and 8 had mean residence times of 141 and 147 seeconds respectively, while 9 and 10 showed reduced mean residence time. There was a greater spread of RTD with CF6 and 8 than with CF9 and 10. Configuration 8 and 6 showed comparable torque of 24 and 25% respectively, while 10 showed a torque of 35 %. Water absorption and solubility indices for configurations 6 and 8 were comparable. A good understanding of screw performance will facilitate the choice of screw configuration in new product development.
Session 91C, Food Engineering: Food process engineering
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