Final answer:
Egg yolk is commonly used as an emulsifying agent in sauces and dressings, notably in making mayonnaise, due to the presence of lecithins which stabilize the mixture of oil and vinegar.
Step-by-step explanation:
The egg-isolate commonly used as an emulsifying agent in sauces and dressings is egg yolk. When creating an emulsion such as mayonnaise, which combines oil and vinegar, the addition of egg yolk helps stabilize the mixture. This is because egg yolk contains lecithins, which can interact with both polar and nonpolar substances, thus allowing the oil and vinegar to mix and remain mixed without separating.
Lecithins are phospholipids that possess both hydrophobic (water-repelling) and hydrophilic (water-attracting) regions in their molecular structure. This dual nature makes lecithins amphiphilic, allowing them to act as effective emulsifiers. In the context of mayonnaise, which is essentially an emulsion of oil and vinegar, the lecithins in the egg yolk play a crucial role in bringing about and maintaining the stability of the mixture.
When oil and vinegar are combined, they naturally tend to separate due to their differing polarities. Oil is a nonpolar substance, while vinegar is a polar substance composed of water and acetic acid. The lecithins in the egg yolk act as a bridge between these two dissimilar substances. The hydrophilic part of lecithins interacts with the water molecules in the vinegar, and the hydrophobic part interacts with the oil molecules. This interaction forms a stable, uniform mixture, preventing the oil and vinegar from separating over time.