An emulsion, as defined by Food Technology, is a “temporarily stable mixture of immiscible fluids, such as oil and water, achieved by finely dividing one phase into very small droplets.”1 Nature designed multiple functions into the egg, including its ability to emulsify. While most commonly associated with mayonnaise,2the emulsifying capacity of whole eggs, egg yolks and even egg whites plays a role in baking and other applications. The absence of eggs in certain formulations such as mayonnaise can affect emulsion stability and final product appearance.2
Fresh liquid eggs, frozen eggs and spray-dried all have the capacity to emulsify, and according to Christine Alvarado, Ph.D., Texas A&M University, there is no essential difference found between them.3 The most popular forms however, include liquid, refrigerated whole eggs or frozen yolks. Frozen yolk has 10 percent added salt or sugar to promote a smooth, creamy, viscous yolk. Egg white emulsifies due to its albumin protein component, while for egg yolk it is its lecithoprotein content.4
Specifically the egg as emulsifier:
- Acts as a stabilizing agent by reducing surface tension
- Reduces the force required to create the droplets that comprise an emulsion
The reduction of surface tension is due to the lecithin or phosphatidylcholine contained within the egg yolk. This amphiphilic molecule has two ends, one hydrophobic and one hydrophilic, which minimizes the energy required to form an emulsion by reducing oil/water interfacial tension.5
There are multiple factors that can affect an emulsion’s stability such as temperature, mixing speed and time and more. Two critical pieces of the puzzle include viscosity and the size and uniformity of the droplet.
An emulsion is thicker or more viscous than its separate components, or the oil and water it contains. Egg yolks provide a viscous, continuous phase. This promotes stability in emulsions because it prevents the dispersed oil droplets from moving around and gathering, or coalescing. Adding egg yolk to whole eggs increases emulsion viscosity, lending it greater stability.
In addition, the smaller the droplet and more uniform in size, the better the emulsion and the better the mouthfeel and texture of the finished product. When mixed at the proper speed and adding ingredients in the proper order, formulators can control droplet size and dispersion. For example, oil must be added slowly to water so that the lecithin within the egg yolk can thoroughly coat the small droplets. This coating acts as a barrier to prevent the droplets from joining back together (flocculating or coalescing) to enhance emulsion stability and improve product appearance and texture.6
Some common applications for eggs as emulsifier beyond mayonnaise and sauces includes salad dressing, ice cream and baked goods such as muffins, bread, cinnamon rolls and cheesecake6 to name a few.
In ice cream, eggs added during the freezing process help promote a smoother texture and ensure the ice cream does not melt rapidly after serving. Emulsifiers also help improve freeze/thaw stability, an important quality for ice cream as well as sorbets, milkshakes, frozen mousse and frozen yogurt.7
Within the commercial baking industry, which relied upon eggs as the first emulsifier, a proper emulsion impacts both product and process. Eggs can help increase product volume, supply a tender crust and crumb, finer and more uniform cell structure, a bright crumb color and slow the crumb from firming, increasing product shelf life. In terms of process, emulsification activity enables proper blending of ingredients and protects the dough during mechanical handling.4