The fat moleculeA fat molecule always consists of a carbon glycerol backbone that is connected to three fatty acids. Because all fat molecules are composed of three fatty acid units joined to glycerol, they are called triglycerides.
Fatty acids are chain-like molecules that are important components of several types of lipids. All naturally occurring oils and fats have a different fatty acid composition. Each fat consists of a combination of saturated (without double bonds) and unsaturated (with double bonds) fatty acids. The double bonds cause a kink in the fatty acid. Saturated fatty acids are called that way because of the lack of double bonds. This type of fatty acid can no longer absorb any more hydrogen; it is saturated. The unsaturated fatty acid is a form of fatty acid containing one or more double bonds and therefore can absorb additional hydrogen atoms. They may also be categorised into monounsaturated fatty acids and polyunsaturated fatty acids.
The molecular structure of a saturated fatty acid allows the molecules to be rather closely packed together. As a result, close intermolecular interactions result in relatively high melting points. The molecules in unsaturated fatty acids do not pack very well. The intermolecular interactions are much weaker than saturated molecules. As a result, the melting points are much lower for unsaturated fatty acids. The melting point indicate the temperature at which a fat becomes liquid.
Unsaturated fatty acids may occur in cis or trans configuration. In trans configuration, the carbon chain extends from opposite sides of the double bond, resulting in a straighter shape. These fatty acids are called trans fatty acids.
As explained, a glycerol can bond with a fatty acid three times. However, it can also react with one or two fatty acids, forming a monoglyceride and a diglyceride respectively.
Free Fatty Acids
If a fatty acid chain detaches from the glycerin molecule, we call that fatty acid chain a 'free fatty acid'. Free fatty acids (FFA) occur naturally in vegetable oils. They are created over time by a kind of aging process of the oil. The FFA content is a measure of the quality of the oil. This allows us to determine how fresh the oil is. For the end product quality, oxidation (a chemical process in which fat characteristics change due to the reaction with oxygen) of fats is undesirable because of odor and taste deviations. In principle, free fatty acids are more sensitive to oxidation. So the more free fatty acids, the faster the oil ages.