On the stability of oil-in-water emulsions to freezing

Oil in water emulsions (40wt%) were prepared from a homologous series of n-alkanes (C10-C18). The samples were temperature cycled in a differential scanning calorimeter (two cycles of 40°C to -50°C to 40°C at 5°C min^-1) and in bulk (to -20°C). The emulsions destabilized and phase-separated after freeze-thaw if the droplets were solid at the same time as the continuous phase and were more unstable if a small molecule (SDS or polyoxyethylene sorbitan monolaurate) rather than a protein (whey protein isolate or sodium caseinate) emulsifier was used. The unstable emulsions formed a self-supporting cryo-gel that persisted between the melting of the water and the melting of the hydrocarbon phase. Microscopy provides further evidence of a hydrocarbon continuous network formed during freezing by a mechanism related to partial coalescence which collapses during lipid melting to allow phase separation.