Emulsions, Vegetable oils coalescence

Salad dressings are made by emulsifying vegetable oil in an aqueous mixture that contains vinegar. When made at home, this emulsion is rather unstable the droplets coalesce relatively quickly, so one has to shake it before use. Commercial variants are usually stabilized by other components. 

For inducing coalescence, o/w emulsions were prepared using the different emulsifiers Tween 20, Tween 80, and Tween 65. The emulsifiers were used at a concentration of 1% m/m (above the CMC). Vegetable oil (Floreal Haagen, Germany) was used as dispersed phase. The hydrophiUc-Upophilic balance (HLB) values of each emulsifier, as well as the characteristics of the emulsions, are shown in Table 1. 

The principles of colloid stability, particularly including DLVO theory and steric stabilization, can be applied to many food emulsions [80,81]. The applicability of DLVO theory is restricted, however, partly because the primary potential-energy minima are somewhat shallow and partly due to the tendency of adsorbed proteins extend outward from surfaces so far that steric stabilization becomes more important [34,126]. The presence of protein in an adsorption layer can also contribute a viscoelastic restriction to coalescence. Finally, the oils in food colloids are usually triglycerides (of either animal or vegetable origin). These oils may exist in liquid or crystalline states at room temperature frequently both simultaneously. The existence of the crystal form at interfaces contributes yet another stabilizing component [34]. 

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