Spheroidal Fat Crystal Microstructures Formed with Confined Gap Shearing

Abstract

Confined gap shear-cooling was used to structure a model solid fat/liquid oil system consisting of fully hydrogenated canola oil (FHCO) and canola oil (CO). Samples were cooled at various cooling rates (0.2–5.0 °C/min) and shear rates (0, 500, 1000, and 2000 s–1) and characterized via polarized light microscopy and rheology. In the absence of shear (0 s–1), FHCO crystallized into an aggregated network of spherulites. Upon shearing, HCO crystallized into distinct spheroids whose size and structure were dependent on the cooling and shear rates used as well as crystallization duration and temperature. Lower shear rates resulted in larger, more irregularly shaped spheroids, whereas with higher shear rates these were more numerous and smaller. The simultaneous action of cooling and shear was required for spheroid formation, with shear having a greater impact. A mechanism was proposed to identify the multiple steps involved in the formation of the spheroids. Overall, these results demonstrated that it is possible to tailor the aggregation behavior of individual fat crystals toward novel morphologies that may be used to control fat crystal network microstructure and rheology.