Partial coalescence in oil-in-water emulsions
1992
Boode, K.
The influence of crystals on the stability against partial coalescence at rest and during Couette flow was examined in emulsions of saturated triglycerides in SDS- or caseinate solutions and in natural cream. Partial coalescence was characterized by determining changes in globule size distribution and fat content. In the absence of crystals emulsions were stable at rest and in Couette flow. At rest partially crystallized emulsions remained stable unless numerous large fat crystals were present or a temperature cycle was applied (= rebodying process). A theory was developed to explain this temperature controled phenomenon. In Couette flow considerable partial coalescence was observed if the fat network inside the globules was continuous. Due to a lack of liquid oil crystals were sticking out of the globule further, thereby increasing aggregation. Aggregation could be nullified within a few hours after clumping by changing the wetting properties, so that the fat crystals became preferentially wetted by the aqueous phase. Deaggregation could occur also in a flow field if the solid fat fraction had exceeded the optimum, which depended mainly on the properties of the fat and on the velocity gradient applied. A theoretical model was developed that accurately describes the course of the partial coalescence process up to the point where most of the fat creamed out of the emulsion, when warming it. The model is based on Smoluchowski's frequency equation and distinguishes between singlets and clumps with and without crystals. From the model it was deduced that the kind of fat, the solid fat content and the number of globules that contains crystals are the main factors that determine the instability of the emulsion globules.
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