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Chapter 12: Problem 121

Making mayonnaise involves beating oil into small droplets in water, in the presence of egg yolk. What is the purpose of the egg yolk? (Hint: Egg yolk contains lecithins, which are molecules with a polar head and a long nonpolar hydrocarbon tail.)

Short Answer

Expert verified
The egg yolk in mayonnaise serves as an emulsifier. The lecithins present in the egg yolk reduce the surface tension between oil and water, forming and stabilizing the emulsion. This results in the creation of a stable, homogenous blend of oil droplets in water, forming the mayonnaise.

Step by step solution

01

Understand the Problem

Mayonnaise is an emulsion which is formed when water and oil, which are immiscible liquids, are forced to mix. In this case, the hint provided helps understand what role the egg yolk plays, as it mentions that the egg yolk contains lecithins, which are amphipathic in nature, meaning they have both a polar and a nonpolar end.
02

Understanding Lecithins

Lecithin molecules have a polar head (attracted to water) and a nonpolar hydrocarbon tail (attracted to oil). When lecithin is added to a mixture of oil and water, the polar heads align towards the water due to their hydrophilic nature, while the nonpolar tails align towards the oil because of their hydrophobic nature.
03

Formation of an emulsion

The lecithin molecules form a sort of 'bridge' between the oil and water molecules, holding them together and stabilizing the mixture. The polar heads of the lecithin molecules attach themselves to the water droplets and the nonpolar tails integrate with the oil, thereby enabling an otherwise impossible mix between oil and water. This mechanism leads to the formation of small oil droplets in water, creating an emulsion.
04

Role of egg yolk in making mayonnaise

In the context of making mayonnaise, the lecithins in the egg yolk serves as an emulsifier. As discussed above, the emulsifier (lecithins) helps to stabilize the emulsion by reducing the surface tension between the oil and water, preventing the oil droplets from coalescing and separating from the water. This is a key step in making mayonnaise.

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