Rheologische Eigenschaften von rehydratisierten Zellwandmaterialien und Ballast-stoffen

The knowledge of rheological properties of rehydrated cell wall materials and dietary fiber preparations plays an important role for their application as swelling and thickening agent and for their physiological effects. Model investigations are useful in order to study the connection between structure/physical state and the hydration properties of the preparations as well as the rheological properties of the rehydrated samples. It was found that the rheological properties of the cell wall material-water-suspensions, formed during rehydration, can be dependent multivariately on a variety of factors and their interactions. For instance, mechanical disintegration or demethoxylation and cation charging resulted in cell wall materials showing systematic correlations between structural changes and hydration properties or rheological parameters of the rehydrated samples, such as yield value τ 0 or storage modul G'. Especially, the deterioration of the hydration properties (swelling, water retention capacity, water uptake) was connected with a systematic decrease of the rheological parameters τ 0 and G'. In contrast, the Casson-viscosity η Ca and the damping factor tan δ did not correlate with the hydration properties, but preferentially with structural parameters, such as particle size and firmness as well as surface state and surface hydration properties. Furthermore, materials disintegrated step by step with extraction solvents or by enzymatic treatments did not show correlations between individual structural parameters, such as pectin or glucose content or porosity, and hydration properties or rheological parameters. In these cases, the hydration properties and the texturization effect could be explained, however, if the materials were subdivided to the structure types (i) tissue particles, (ii) single cell materials, (iii) partly disintegrated materials and (iv) completely destroyed materials (aggregated cell fragments). At the application of cell wall materials or fiber preparations for the manufacture of innovative food products has to be considered that the texturization effect individually depends on the concentration, the surrounding conditions and the external stress during processing for each material.