Elastic reinforcement and yielding of starch-filled lipid gels

Many foods involve complex suspensions of assorted particles in a Newtonian liquid or viscoelastic medium. In this work, we study the case of suspensions of non-Brownian non-interacting rigid particles: starch, embedded in a soft solid: a colloidal lipid gel. We relate the macroscopic properties of the suspensions to the mechanics of the colloidal gel and the particle volume fraction. As particle volume fraction increases, the suspension gradually stiffens and becomes brittle as the system approaches its maximum packing fraction. The latter is independently determined from a geometric theory of random close packing for polydisperse hard spheres based on the log normal distribution of starch particles dispersed in oil. The elastic modulus, yield stress and yield strain are interrelated through simple scaling laws from a micromechanical homogenization analysis of hard spheres isotropically-distributed in yield stress fluids.