Structure and mechanical properties of brittle starch foams

Abstract

The mechanical properties of extrusion-cooked maize have been analysed according to the Gibson and Ashby models of closed cell foams. The data point to better agreement with the earlier model and indicate that the cell-face bending term is not negligible for foams with little draining into the cell edges. The shape of the cells in these maize foams changes with foaming conditions: non-equilibrium spherical cells with some anisotropy are formed at conditions of low moisture content or high temperature when the glass transition temperature, T _g, is elevated. Polyhedral cells which show some draining of material into the cell edges are formed under the converse conditions when the T _g is lower. The change from polyhedral to spherical cells is also accompanied by a change in amylose-lipid complex from the V to the metastable E type, as shown by X-ray diffraction.