Controlling the yield behavior of fat-oil mixtures using cooling rate

The rheological behavior such as yielding of fat crystal networks are dictated by many variables. Among these variables, the shape of the constituent fat cluster is important yet relatively unexplored. In this work, we describe the rheological investigations of a fat-oil system which can be formulated to either contain bundles of needles or spherical clusters by controlling the cooling rate and fat concentration. Fat-oil mixtures containing high-fat concentrations exhibited weak frequency dependence of storage modulus (G′) and loss modulus (G″). The yielding behavior of the mixtures were investigated by large amplitude oscillatory shear (LAOS) rheology using strain and stress controlled modes. Lissajous-Bowditch plots and orthogonal set of Chebyshev polynomials were used to analyze the non-linearities associated with the yielded fat-oil mixtures. For a given fat concentration, the yield stress of fat networks obtained at low cooling rates (bundles of needles) were similar to that of networks obtained at high cooling rates (spherical clusters). However, after yielding, Lissajous-Bowditch plots suggested that the mixtures comprising of bundles of needles exhibited viscous-like behavior while the spherical clusters exhibited a plastic-like behavior. This was further supported by microscopy images of yielded fat-oil mixtures. Overall, for a given fat concentration, the two different shapes of fat clusters can give rise to networks of similar yield stress values but different behaviors after yielding.