Podcast: Episode 2, mayonnaise and vinaigrette

1. What is an emulsion?

We see creams every day, some apply them every day on the face (which I also recommend for well-hydrated skin) but do you know what a cream is? So a cream is what we call an emulsion, it's a system made up of two liquids that don't mix naturally, like oil and water.

One of the two liquids is in the form of fine droplands dispersed in the second liquid which it is not miscible, in which it cannot mix.

2. Example based on mayonnaise

An everyday example of two liquids that don't mix is vinegar and oil. If you mix vinegar with olive oil only, you will not be able to obtain a homogeneous mixture, no matter how hard you insist on mixing.

But if you add an egg yolk then you will gand a mayonnaise can be stable. Mayonnaise can be broken down into two phases: the first composed of vinegar, mustard and egg yolk and the second phase composed of olive oil. The drops of olive oil will be dispersed in the first phase.

So how is this made possible?

3. Lipophile + hydrophile = amphiphile ?

Mayonnaise remains mayonnaise thanks to the egg yolk! Egg yolk contains lecithin. Lecithin is a group of molecules that has a part that is attracted to the water phase and a part that is attracted to the fatty phase. The part of the molecule that likes water is called hydrophilic - hydro referring to water and vial which refers to attraction among other things.

With that we could guess the adjective given to the part that loves oil, we say that it is lipophilic. And our lecithin which has a hydrophilic part which likes water and a lipophilic part which likes oil, it also has a small name. It is said to be amphiphilic, an amphiphilic molecule is a molecule having a hydrophilic part and a lipophilic part.

And that's good because being an amphiphile is a prerequisite for being a good emulsifier. That is to say, it is the molecule that is needed to stabilize a system composed of two liquids which do not mix naturally, two immiscible liquids.

4. Emulsifier

An emulsifier also called emulsifier, surfactant, surfactant or surfactant is the molecule that will allow an emulsion to be stable over time. It is the lecithin that will allow your mayonnaise to stay beautiful and shiny throughout the meal. And so you won't end up with your oil separated from the vinegar when you serve the fries.

The properties and quantity of this emulsifier will directly affect the stability of your emulsion, your sauce.

5. Example based on vinaigrandte

For example, take the case of a vinaigrette, unlike mayonnaise, it will have to be reacted before serving it. It is not as stable as mayonnaise.

The emulsifying properties of mustard are not enough to keep your sauce stable throughout the meal. In vinaigrandte, the vinegar is the hydrophilic phase, the oil is the lipophilic phase and the phospholipids in the mustard act as an emulsifier. But the properties of its phospholipids and the quantity of these do not allow a stable emulsion.

6. How does the emulsifier keep the oil separate from the water?

Surfactants are amphiphilic molecules, they have a part attracted by water and another part attracted by oil.

By swirling your sauce you create tiny droplets of oil. These oil droplets will be stabilized thanks to all the microscopic surfactant molecules. These surfactant molecules can be represented as a tadpole. They will position themselves all around the droplet of oil, at the interphase of the oil and the vinegar.

This is called an interfacial film. The head of your schematic tadpole is the part which is hydrophilic so which likes water and vinegar, it will position itself in the vinegar and the tail of the tadpole is the lipophilic part which likes oil, will position itself towards the inside the oil droplet.

You can see the diagram below.

Mayonnaise and vinaigrette are emulsions that are called oil in water because they are the oil droplets that are suspended in the hydrophilic phase that is called the external phase, the purple part of the table. At the same time, the oil is said to be the internal phase in this example.

7. Other examples of emulsions

There are other types of emulsions, such as water-in-oil emulsions. In this case it is the water droplets which are dispersed in the external phase which is the oil.

Generally, the external phase must be in greater quantity for the system to be stable. There are other more complex emulsions, such as emulsions involving silicone, Pickering emulsions, triple emulsions or even micro-emulsions.

Emulsions are generally what is called a cream, that is to say a more or less viscous, more or less opaque, more or less white liquid. The moisturizing face cream is an emulsion, the foundation and the mascara are pigmented emulsions, the face mask is often an emulsion.

On the contrary, a make-up remover oil and a lip balm are only composed of fatty substances. A micellar water has very few fat-soluble ingredients, generally only the perfume is completely fat-soluble and requires the addition of a solubilizer to obtain a homogeneous system.

8. Conclusion

To recap, a cream is an emulsion. An emulsion is a system composed of two phases that do not usually mix, such as oil and water. Ingredients that are in the fatty phase are said to be lipophilic and those in the aqueous phase are said to be hydrophilic. The two phases mix thanks to a surfactant which has a hydrophilic part and a lipophilic part.

A molecule that is both lipophilic and hydrophilic is said to be amphiphilic. Its molecules are schematized as microscopic tadpoles and are positioned at the interphase between the oil droplet and the water. A cream is therefore water with lots of microscopic droplets of oil in suspension.

Episode Notes

• The diagram of the vinaigrette:

• Emulsion : a system made up of two liquids that do not mix naturally, such as oil and water. One of the two liquids is in the form of fine droplets dispersed in the second liquid of which it is not miscible, in which it therefore cannot mix.
• Lipophile : is said of a molecule (or part of a molecule) which "likes" oil, which is soluble in oil
• Hydrophilic : is said of a molecule (or part of a molecule) which "likes" water, which is soluble in water
• Amphiphile : is said of a molecule that has a part that "likes" water and another part that "likes" oil
• Surfactant / surfactant / surfactant / emulsifier : amphiphilic molecule which stabilizes the emulsion - Note: an emulsifier is a surfactant. The term surfactant includes several amphiphilic molecules such as emulsifiers, solubilizers, cleaners, etc.
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