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 mum. Aliquots of the emulsions were temperature cycled (40 to -10 to 40 degreesC at 1.5 degreesC min(-1)) four times in a differential scanning calorimeter. The stable emulsion droplets crystallized at 0-6 degreesC (depending on the type of emulsifier) while the non-emulsified fat crystallized at similar to 15 degreesC. 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. (C) 2003 Elsevier Science B.V. All rights reserved.