Cereal Chem 67:427- 433   |  VIEW ARTICLE

Transformation of Wheat Flour by Extrusion Cooking: Influence of Screw Configuration and Operating Conditions.

C. Barres, B. Vergnes, J. Tayeb, and G. Della Valle. Copyright 1990 by the American Association of Cereal Chemists, Inc. 

An experimental study of wheat flour extrusion cooking was carried out on two different sizes of twin-screw extruders (Clextral BC 45 and BC 72). By stopping the machine and rapidly opening the barrel, the location of the material in the screws was observed, and samples were collected in order to analyze the macromolecular transformation of the product. This transformation was evaluated through starch solubility measurements. The influence of screw configuration and operating conditions on the level of transformation was examined. It appeared that reverse screw element played a major role and that varying the feed rate induced more effects in terms of product transformation than varying the screw speed. Theoretical investigations of the flow through the reverse screw element were developed in order to compute the specific energy given to the material. The level of transformation appeared to correlate well with energy input. This might provide an interesting basis to solve extruder scale-up problems in extrusion cooking.