EFFECTS of FEED MOISTURE and BARREL TEMPERATURE ON the RHEOLOGICAL PROPERTIES of EXTRUDED COWPEA MEAL1

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Abstract
Decorticated cowpea meal was adjusted to 20, 30, and 40% moisture and extruded in a Wayne pilot‐scale extruder at barrel temperatures of 150, 175 and 200°C. the resulting products were subjected to rheological evaluation using the Instron Universal Testing Machine equipped with standard tensile jaws, the Warner‐Bratzler shear device and the Kramer Shear Press. Regression equations relating rheological properties to feed moisture and barrel temperature were computed from the data, and response surfaces were generated from these models. Tensile strength of extrudates was greatest for the dense products produced in the low moisture‐low temperature region and declined at higher moistures and temperatures. Shear strength as determined by either the Warner‐Bratzler or Kramer devices exhibited a ridge of high values extending from 20%‐150°C to 30%‐200°C, and declined for brittle, expanded products made at low moisture and high temperature and for soft products made at high moisture.