Abstract
Plant and fruit cells encase themselves within a complex polysaccharide wall which are complex and highly sophisticated composite material made of cellulose, hemicellulose and pectin and which form a scaffold matrix with intertwined structure. In this work the viscoelastic properties of cell wall particles dispersions, which were extracted from fresh and aged apple flesh with selective solvents precipitation method, or alternatively with water as a solvent, were studied by means of steady and oscillatory measurements. The solid-like dispersions showed a shear thinning behaviour, and immediately recovered back into their original elastic character upon removal of the shear strain. This means that the cell wall particle dispersions have self-healing capabilities. They can be easily processed as low viscosity materials and subsequently form an elastic gel. Interestingly, the nonlinear mechanical response characterized by single step stress relaxation experiments, and re-plotted as isochrones of stress vs strain, revealed an early nonlinearity of the response and subsequent yield, as well as a clear time-dependent behavior. This behavior of the cell wall dispersions resembles closely that of colloidal gels, which also display shear-thinning rheological behavior and interesting aging response. We are therefore facing some structural properties, which can be of interest for new additives/ingredients to be used in food formulation technology. Cell wall materials, or some selected constitutive components, might hence play a key role as adaptable thickening agent in food formulations, due to their well-known ability to bind a large amount of water.
