Mechanical behaviour of corn flour and starch-zein based materials in the glassy state: A matrix-particle interpretation

Starch-zein systems were characterised by their dynamic mechanical behavior. Although the main relaxation temperatures were located in the same range of temperature for the various zein contents, significant differences were observed for the tan 6 peak amplitude. They were related to the morphology of the system, i.e., dispersed zein aggregates in starch matrix or dispersed amorphous starch in zein matrix, the phase inversion domain, determined by image analysis, being in the (17-34%) phase concentration interval. When testing processed corn flour under different thermomechanical conditions, at a moisture content of 12.0% (wb), higher values of tan b peak were found when starch transformation was increased. For the same trend, values of E' modulus in the rubbery state continuously decreased which was attributed to the reduction of remaining starch granules within the flour. The application of models of composites materials points out the matrix-particles behaviour of processed corn flour and starch-zein blends, whatever the particles composition. The quality of adhesion between starch and zein is inferred for the mechanical properties of their blends. (c) 2006 Elsevier Ltd. All rights reserved.