Stability of emulsions to dispersed phase crystallization: Effect of oil type, dispersed phase volume fraction, and cooling rate

Emulsified n-hexadecane or confectionery coating fat (CCF) were repeatedly thermally cycled (40 to -10-40°C at 1.5°C min^-1) in a differential scanning calorimeter. There is a single exotherm on cooling each emulsion (at 0.5 and 5°C, respectively) corresponding to lipid crystallization by homogeneous nucleation. However, on subsequent cooling cycles, an increasing proportion of the CCF crystallization enthalpy occurs at a higher temperature (15°C) corresponding to crystallization of non-emulsified fat. (The net enthalpy of crystallization is constant). The second peak is taken to be due to destabilized fat and increases with number of cycles and dispersed phase volume fraction. All n-hexadecane emulsions are stable to freeze-thaw. When the CCF emulsions are cooled more rapidly (5°C min^-1) there is no destabilization. Micrographs are presented and used to argue the destabilization is due to a collapse of partially coalesced structures on reheating.