Control of Morphological and Rheological Properties of Carrot Cell Wall Particle Dispersions through Processing

A range of thermal and mechanical processes were used to create dispersions with different particle morphologies, i.e., systems that contain primarily plant cell wall clusters with an average particle size (d(0.5)) of similar to 200 A mu m, single cells ((d(0.5) = similar to 70 A mu m) or cell fragments (d(0.5) = similar to 40 A mu m). The small and large deformation rheology (viscoelastic properties and flow properties) of these dispersions, with a range of total solid contents covering textures varying from a fluid to a paste, were determined. The particle dispersions showed weak gel-like behaviour. Their elastic modulus (G') as a function of total solid content exhibited three regions of different rheological behaviours. The particles formed particulate colloidal networks at relatively low solid content. The interaction of particles contributed to the sharp increase in the elastic modulus of the dispersion in the concentrated region. Further packing of particles beyond the critical packing volume fraction, caused the G' for the 'cluster-cell' and the 'single-cell' dispersions to reach a plateau value. This is due to particle deformation resulting in changes in their microstructure and their ability to pack closely. Plant particle dispersions displayed abrupt yielding at the critical stress with a 3-4 order decrease in viscosity and high yield stress at low solids due to the formation of particulate colloidal network.