Final answer:
An emulsifier is a substance that stabilizes mixtures of oil and water by allowing them to mix. The correct answer is D) Substance that stabilizes mixtures of oil and water. Lecithin in egg yolks acts as an emulsifier in mayonnaise by interacting with both oil and water to prevent separation.
Step-by-step explanation:
In the context of making mayonnaise, an emulsifier is a substance that stabilizes mixtures of oil and water, which normally do not mix well due to their different polarities. In mayonnaise, lecithin found in egg yolks acts as the emulsifying agent. This molecule has parts that are attracted to water (hydrophilic) and parts that are attracted to oil (hydrophobic), allowing it to bind with both and hold the emulsion of oil in vinegar or lemon juice together, preventing the ingredients from separating.
Examples of emulsions include butter, mayonnaise, and milk, where substances like lecithin in egg yolk and casein in milk serve as natural emulsifiers. In commercial food products, lecithins from sources like soybeans are commonly used as emulsifiers to maintain texture and consistency. Emulsifiers are also important in digestion, as seen with bile in the body, which breaks down fats into smaller globules to increase the surface area for more efficient digestion by enzymes like lipase.