Question

Why do oils and fats melt over a range of temperatures?

What do the melting temperatures of the fats and oils suggest about their fatty acid composition?

How could you use this information to make a reduced-fat chicken stock or beef stock?

Answer 1

Why do oils and fats melt over a range of temperatures?

Oils and fats are not polar.  They don’t have positive and negative parts that attract one another.  Instead, they are attracted by much weaker but similar forces that arise because the electrons in the molecules are always moving.  When electrons move to one side of a molecule, a temporary state exists where one side is more negative than the other.  Electrons in a nearby molecule are attracted to the more positive side, and for a very short time the two molecules are synchronized, with their electrons on the same side, so they behave as if they were polar.  But this attraction is very weak, and small amounts of heat energy break them, and they form and break continuously. The long chains in fats can line up together, so the attractions between the molecules are stronger than if they only touched at one or two points. This attraction raises the melting point. There are tryglyceride molecules where the long chains have kinks in them, so they don’t line up easily. These have lower melting points. Oils have more of these kinked molecules than fats do, so they are liquid at room temperature. Because the molecules are so big, it takes more energy to get them to leave the liquid state and become a gas. Oils and fats do not evaporate as easily as small molecules like water. Most fats are a mixture of many different types of tryglyceride molecules. In pure form, each molecule would make a liquid that has a distinct sharp melting point. But when many different types are all mixed together, the substance softens slowly over a range of temperatures, instead of melting at one temperature.

What do the melting temperatures of the fats and oils suggest about their fatty acid composition?

Fats are generally solids and oils are generally liquids at ordinary room temperatures. The characteristics of fats and oils are related to the properties of the fatty acids that they contain. The larger the number of carbon atoms, the higher the melting point ; the larger the number of double bonds, the lower the melting point.

How could you use this information to make a reduced-fat chicken stock or beef stock?

It is possible using fats or oils of low melting point , that is, more number of double bonds in the carbon chain , in effect , is healthier eating unsaturated fats.