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Partially crystalline fat globules in oil-in-water emulsions are susceptible to aggregation via partial coalescence. In this study, the role of solid fat content and interfacial composition on the aggregation behavior of a model food emulsion (35 wt% fat, 2 wt% sodium caseinate) was investigated. By displacing adsorbed sodium caseinate from the oil-water interface using Tween 20, we prepared partial coalescence sensitive emulsions with interfacial compositions of mixed sodium caseinate-Tween 20 (0.5 wt% Tween 20) and Tween 20 dominated (≥1.5 wt% Tween 20). Stability was monitored quiescently and under shear over 6 days of storage at 5 °C. Quiescently, the emulsions were stable with 0.5 wt% Tween 20 regardless of solid fat content. At 1.5 wt% or above, stability decreased with increasing solid fat content and Tween concentration. Under steady shear, the aggregation time of emulsions with Tween 20 dominated interfaces decreased with increasing solid fat content whereas for mixed sodium caseinate-Tween 20 emulsions it increased with increasing solid fat content. Cryo-TEM micrographs of the fat globules revealed a relatively smooth surface at low SFC but increasingly rough surface containing protuberances with increasing SFC. Notably, the protuberances were not jagged but rather round indicating that protruding fat crystals may not initiate partial coalescence especially in Tween 20 dominated emulsions. These findings have important implications on how the partial coalescence mechanism changes with solid fat content and interfacial film composition. |
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