Abstract
Structures and mechanical properties of food hydrocolloids consisting of hydrated food macromolecules such as polysaccharide and protein have been reviewed. Food sols often exhibit a decrease in the viscosity with increasing flow rate (i.e., shear-thinning) due to flow-induced changes in the three-dimensional structure of food macromolecules. Relatively high viscosities at low flow rates are highly effective in slowing down the rate of floatation or sedimentation of insoluble particles. For transporting the bulk sol, the flow rate may be increased in order to decrease the viscosity to the same order of magnitude as that of water. A food sol may possess a true yield stress. If the yield stress value is sufficiently larger than the buoyancy or gravitational force, floatation or sedimentation of insoluble particles never occurs. Atomic force microscopy images of gellan gum bulk gels have revealed that the gel networks are composed of rigid rod-like strands that are crosslinked with other strands at the ends. It is unreasonable to assume that the elasticity of such a network is determined by entropic effects. A novel model for describing the concentration dependence of the elasticity has been proposed by considering the bending elasticity of rod-like network strands.
