46C-16 |
Effect of surfactant type on the stability of oil-in-water emulsions to temperature cycling |
J. PALANUWECH and J. N. Coupland. Food Science, The Pennsylvania State University, 126 Borland Lab, State College, PA 16801 When the dispersed oil in an emulsion is semi-crystalline, the system may destabilize by partial coalescence, initiated by a fat crystal penetrating the lamella separating two adjacent droplets. Emulsions vulnerable to partial coalescence may destabilize very rapidly during temperature cycling as the formation and subsequent melting of lipid crystals can cause partial followed by full coalescence. The goal of this work is to investigate the role of the interfacial membrane in controlling partial coalescence in oil-in-water emulsions during temperature cycling. Oil-in-water emulsions (40 wt%) were prepared by mixing liquid fat with solutions (0-4 wt%) of selected polymeric and small molecule surfactants and homogenizing to a mean particle diameter of 0.71±0.05 mm. Aliquots of the emulsions were temperature cycled (40°C to -10°C to 40°C at 1.5°C min-1) three times in a differential scanning calorimeter. The stable emulsion droplets crystallized at 1-5°C (depending on the type of emulsifier) while the destabilized 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 cycle. Electron microscopy (cryo-SEM) was used to visualize some of the structures formed. All of the small molecule-stabilized emulsions completely destabilized after one cycle. The caseinate-stabilized emulsions were relatively resistant to several thermal cycles unless ethanol (30 wt%) was added, in which case they destabilized during the first cycle. When a small molecule surfactant was added displace the caseinate from the interface, there was a progressive decrease in stability. Whey protein-stabilized emulsions were partly unstable to freeze-thaw even following a thermal pretreatment denature the proteins. Cryo-SEM confirmed the destabilization of the emulsions was due to partial coalescence. The interfacial structure is crucial to understanding the stability of emulsions to temperature fluctuations. Some real foods affected by these phenomena include ice cream mix and coffee creamers.
Session 46C, Food Chemistry: Lipids, antioxidants and emulsifiers
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