Effect of surfactant type on the stability of oil-in-water emulsions to dispersed phase crystallization

Confectionery coating fat (CCF ) emulsions (40 wt.%) were prepared by mixing liquid fat with solutions (1–4 wt.%) of selected polymeric and small molecule surfactants, and homogenizing to a mean particle diameter of 0.71±0.05 μm. Aliquots of the emulsions were temperature cycled (40 to −10 to 40 °C at 1.5 °C min−1) four times in a differential scanning calorimeter. The stable emulsion droplets crystallized at 0–6 °C (depending on the type of emulsifier) while the non-emulsified fat crystallized at ∼15 °C. The ratio of the enthalpies at these temperatures was used to calculate the proportion of the emulsion that had destabilized after each thermal cycle. All of the small molecule-stabilized emulsions largely destabilized after one cycle. The caseinate-stabilized emulsions were relatively resistant to several thermal cycles unless ethanol (30 wt.%) was added or the pH lowered to 5, in both cases they destabilized during the first cycle. When a small molecule surfactant was added to displace the caseinate from the interface, there was a sharp reduction in stability at the surfactant to protein molar ratio R>25. Whey protein-stabilized emulsions were partly unstable to freeze–thaw even following a thermal pretreatment to denature the proteins. Cryo-SEM confirmed the destabilization of the emulsions was due to partial coalescence.