Emulsifier

Generally, any ingredient used to bind together normally noncombinative substances, such as oil and water. Egg yolks contain a natural emulsifier (Lecithin) and are used to thicken and bind sauces (such as Hollandaise), as well to bind ingredients in baking. Xanthan gum is a commercial emulsifier used in numerous foods like salad dressings and dairy products. Some commercial emulsifiers also inhibit baked goods from going stale.