THE FRACTURE-BEHAVIOR OF STARCH AND GLUTEN IN THE GLASSY STATE

Wheat starch and gluten have been gelatinized/heat-set in excess water and then dried to various extents to give materials with moisture contents in the range 2-15%. Fracture behaviour was examined by three-point bending, and glass transition behaviour was probed by dynamic mechanical thermal analysis. Wheat starch and gluten were also processed via a cooker extruder to give a model granular food covering the same moisture range noted above. Extruded granules were subjected to an instrumental compression test and the sounds produced (acoustic emission) during crushing were measured. The influence of extrusion conditions (amount of added water and die temperature) were evaluated. It was found that there were marked differences between starch and gluten in terms of the dependence of acoustic emission on moisture content. The degree of acoustic emission was also dependent on extrusion conditions. These differences are discussed in terms of: (i) the contrasting fracture behaviour observed in the bend test; and (ii) the different glass transition temperatures of starch and gluten. © 1992, Academic Press Limited. All rights reserved.